BASIC MECHANICAL ENGINEERING: 1FY3-07/2FY3-07) Programme: B

A Course File of BASIC MECHANICAL ENGINEERING: 1FY3-07/2FY3-07) Programme: B. Tech. I YEAR Semester: I/II Session: 2020-2021

Mr. Sanjay Bairwa Assistant Professor Mechanical Engineering Department

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Contents

1. Institute Vision/Mission/Quality Policy 2. Departmental Vision/Mission 3. RTU Scheme & Syllabus 4. Prerequisite of Course 5. List of Text and Reference Books 6. Time Table 7. Syllabus Deployment: Course Plan & Coverage* 8. PO/PSO-Indicator-Competency 9. COs Competency Level 10. CO-PO-PSO Mapping Using Performance Indicators(PIs) 11. CO-PO-PSO Mapping: Formulation & Justification 12. Attainment Level (Internal Assessment) 13. Learning Levels of Students Through Marks Obtained in 1st Unit Test/Quiz 14. Planning for Remedial Classes for Average/Below Average Students 15. Teaching-Learning Methodology 16. RTU Papers (Previous Years) 17. Mid Term Papers (Mapping with Bloom’s Taxonomy & COs) 18. Tutorial Sheets (with EMD Analysis)** 19. Technical Quiz Papers 20. Assignments (As Per RTU QP Format) 21. Details of Efforts Made to Fill Gap Between COs and POs (Expert Lecture/Workshop/Seminar/Extra Coverage in Lab etc.) 22. Course Notes

Note:

1. *1st lecture of the course should cover prerequisite 2. **E: Easy, M: Moderate, D: Difficult 3. Format for Points 8-11 should be referred from AICTE’s Recommendations for Examination Reforms

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Institute Vision/Mission/Quality Policy

Institute Vision

"To promote higher learning in advanced technology and industrial research to make our country a global player."

Mission

"To promote quality education, training and research in the field of Engineering by establishing effective interface with industry and to encourage faculty to undertake industry sponsored projects for students. "

Quality Policy

We are committed to ‘achievement of quality’ as an integral part of our institutional policy by continuous self-evaluation and striving to improve ourselves.

Institute would pursue quality in

o All its endeavors like admissions, teaching- learning processes, examinations, extra and co-curricular activities, industry institution interaction, research & development, continuing education, and consultancy. o Functional areas like teaching departments, Training & Placement Cell, library, administrative office, accounts office, hostels, canteen, security services, transport, maintenance section and all other services.”

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Departmental Vision/Mission

Departmental Vision

Our Vision is to be a: "World-class department catering to the changing needs and aspirations of all our present and future stakeholders."

Departmental Mission

Our Mission is: "To create a conducive and supportive environment for all round growth of our students, faculty & staff."

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Prerequisite of Course

• Some principles and formulas of physics and mathematics are applicable. • Basic knowledge of combustion and chemistry.

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List of Text and Reference Books

Text Book

S.No. Title of Book Author(S) Publication Basic Mechanical Mathur, Mehta 1 Jain Brothers Engineering & Tiwari

Reference Books

S.No. Title of Book Author(s) Publication Basic Mechanical G. Shanmugan, S. TATA Mc 1 Engineering Ravindaran Graw Hill Elements of Mechanical Dhanpat Rai 2 M M Rathore Engineering Publishing

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Time Table

Sanjay Bairwa Time Table 8:30-9:15 9:30-10:15 10:30-12:00

Monday

F-All Groups CAEG LAb- Tuesday J-All Groups BME(Lecture)2F5 1F3

Wednesday J-All Groups BME(Lecture)2F5

H-All Groups CAEG LAb- Thursday 1F5 B-All Groups CAEG LAb- Friday 2F2

Saturday J-All Groups BME(Lecture)2F5

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Syllabus Deployment: Course Plan & Coverage*

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Chapters Applicable POs Applicable COs Lecture Lecture Actual Hours Fundamentals: Introduction to mechanical engineering, concepts of 1 1 thermal engineering, Chalk and 1 Concepts of mechanical machine Board

design, industrial engineering and 1 1

manufacturing technology. First Transmission of Power: Introduction to Belt Drives, Types 4 1 of belt

Types of belt drives, Velocity ratio, 4 1 Effect of slip on Velocity ratio

Length of Open and Cross belt, 4 1

Ratio of tensions in flat belt drive,

Power transmission by belt drives, , 4 1

Ratio of Tension for V belt drives Chalk and 1 Numerical on belt drives Board 4 2 Introductions to rope drives 4 1

Introduction of Gears, Types of 4 1 Gears

Advantage and Disadvantages of 4 1 gear drives

Type of Gear Train 4 1

Numerical on Gear drive 4 1 Second

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Introduction to material Science, 5 1 Properties of Metals.

Types Of Metal, Difference between Chalk Ferrous and nonferrous metal , Non 5 1 and 1 Ferrous Alloy Board Introduction to heat treatment of

steel, Steel Structure, Stages of Heat 5 1

Treatment and critical temperatures Third Classification of steam boilers , 2 1 Selection of Steam Boiler

Types Of Steam Boiler (Cochran, Lancashire, Locomotive, Babcock & 2 2 Wilcox, La-Mont, Benson)

Introduction of Steam turbines, Chalk Classification of Steam Turbine and 1 2 2 (Impulse / Reaction), Introduction Board of Axial/Radial /Tangential Flow

Introduction and Classification of power plants, Hydroelectric / Thermal / Nuclear / Gas / Diesel 2 3

Power Plant. Comparison of

Various Types of Power Plant. Forth Applications and working of Reciprocating and Centrifugal 2 2 pumps Chalk and 1 Introduction and Classification of IC Board

Engines, Main component of IC 2 3

Engine Fifth Introduction of Refrigeration and 3 1 Air Conditioning (RAC) Chalk and 1 Classification and types of Board refrigeration systems and air- 3 2

conditioning. Sixth

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Applications of refrigeration and 3 1 Air-conditioning.

Metal Casting Process: Introduction to Casting Process, Patterns, 5 3 Molding, Furnaces.

Metal Forming Processes: Introduction to Forging, Rolling, Chalk 5 2 Extrusion, Drawing. and 1 Board

Metal Joining Processes:

Introduction to various types of 5 2 Welding, Gas Cutting, Brazing, and

Soldering. Seventh

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PO/PSO-Indicator-Competency

PO 1: Engineering knowledge: Apply the knowledge of mathematics, science, engineering fundamentals, and an engineering specialisation for the solution of complex engineering problems. Competency Indicators

1.2 Demonstrate competence in 1.2.1 Apply laws of natural science to an engineering basic sciences problem 1.3 Demonstrate competence in 1.3.1 Apply fundamental engineering concepts to engineering fundamentals solve engineering problems 1.4 Demonstrate competence in 1.4.1 Apply Mechanical engineering concepts to specialized engineering solve engineering problems. knowledge to the program

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COs Competency Level

Explain the basic concepts of thermal engineering, machine design, industrial CO1 engineering and manufacturing technology. 1.1 Demonstrate competence in basic concepts of thermal engineering, machine Competency design, industrial engineering and manufacturing technology. Explain working of different type of steam turbines, boilers, IC engines, pumps and CO2 classify different power plants. 2.1 Demonstrate competence in explaining the working of different type of power Competency plant. 2.2 Demonstrate competence in explaining the working of IC Engines. Explain working of different type of refrigeration and air conditioning systems. CO3

3.1 Demonstrate competence in working of different type of refrigeration and air Competency conditioning systems.

CO4 Describe various modes of power transmission and their application

4.1 Demonstrate competence in explaining the various modes of power Competency transmission.

Explain various primary manufacturing processes, various engineering materials and CO5 heat treatment processes.

5.1 Demonstrate competence in explaining the various primary manufacturing processes. Competency 5.2 Demonstrate competence in explaining the various engineering materials. 5.3 Demonstrate competence in explaining the heat treatment processes.

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Attainment Level (Internal Assessment) Section –I Semester –J (2020-21)

First Mid Term Evaluation

PART → A Note→ Attempt All QUESTION NO. → Q1 Q2 Q3 Q4 Q5 COURSE OUTCOME(S) CO1 CO4 CO2 CO5 CO2 SATISFIED → MAXIMUM MARKS → 10 10 10 10 10 MINIMUM QUALIFYING 5 5 5 5 5 MARKS (50%) → NAME OF STUDENT ↓ Total No. of DEBARRED (DB) Total No. of ABSENT (AB) 1 Total Students Appreaed for Exam (A) 67 67 67 67 67 Total Students Attempted the Question (A) 67 64 67 61 60

No. of Students scored >=50% marks (B) 64 63 52 55 46

Percentage Attainment of Criterion (B/A) 0.96 0.98 0.78 0.90 0.77 CO Attainment Level 3 3 3 3 3 Attainment of CO-1 96% 3 Attainment of CO-2 98% 3 Attainment of CO-4 90% 3 Attainment of CO-5 Criterion of Percentage for CO Attainment Attainment

Level Level Percentage attainment Below 60% 1

Percentage attainment 60%-69.99% 2

Percentage attainment Above and equal to 3 70%

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Teaching-Learning Methodology ➢ Lectures ➢ Self Study ➢ Practical ➢ Power Point Presentation ➢ Demonstrations ➢ Concept Maps

Large Group Small Group Individual

-Lecture -Group Discussion -Self Study

-Power Point -Tutorial -Assignment Presentation

-Topic Video -Demonstration -Project Work

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RTU Papers (Previous Years)

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Mid Term Papers (Mapping with Bloom’s Taxonomy & COs)

Course with Code: BASIC MECHANICAL ENGINEERING (2FY3-07)

Maximum Marks : 20 ; Duration: 1½ Hours

C PI Q.No Questions Marks BL O

PART – A : Attempt All questions

1.3.1,1.4 1 Write names of four different types of manufacturing process. which type 2 CO5 L2 of process is suitable for manufacturing of large size components. .1

2 2 CO4 L1 1.3.1 Explain compound gear train with a neat sketch.

3 2 CO5 L1 1.3.1 Explain normalising heat treatment process. PART – B : Attempt Any Two questions

In Gupta’s workshop limited flat belt drive is being used to transmit the 1.3.1,1.4 4 4 CO4 L2 power. The manager has asked you to derive an expression for ratio of .1 tension on the tight and slack side of the belt. Derive the same. 1.3.1,1.4 In Choudhary’s foundry shop a machine component is being produced by .1 5 casting. As a production engineer what are the different allowances that 4 CO5 L2 you will take care of and why?

6 What is gas welding? Explain three different type of flames produced in 4 CO5 L2 1.3.1 oxy- acetylene gas welding. PART – C : Attempt Any One question

7 What is extrusion process? Explain different types of extrusion process with neat 6 CO5 L2 1.3.1 diagram. In a private limited a flat belt is used for transmission of power. Find the 1.3.1,1.4 power transmitted by the belt running over a pulley of 60 cm in diameter .1 8 6 CO4 L2 at 200 rpm. The coefficient of friction between belt and pulley is 0.25,angle of contact is 1600 and maximum tension in the belt is 2500 N.

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SWAMI KESHVANAND INSTITUTE OF TECHNOLOGY, MANAGEMENT AND GRAMOTHAN JAIPUR I -B.Tech I Semester Assignment-2 Sub: Basic Mechanical Engineering Max. Marks: 20 Instructions: a) Attempt all the parts of the Assignment. b) Each question of part A carries 2 marks each and attempt all three questions from this section. c) Each question of part B carries 4 marks each and attempts any 2 questions from this section. d) Each question of part C carries 6 marks each and attempts any 1 question from this section.

Part -A

1. Define: a. Pattern. b. Coefficient of Performance.

2. Write differences between petrol and diesel engines.

3. Draw a neat and labelled diagram of casting technique.

Part –B

4. What is gas welding? Explain three types of flames use in gas welding.

5. Explain different types of pattern allowances.

6. Explain construction and working of vapour compression refrigeration system with neat diagram.

Part –C

7. Explain construction and working of four stroke petrol engines with neat diagram.

8. Explain construction and working of vapour absorption refrigeration system with neat diagram.

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Details of Efforts Made to Fill Gap Between COs and POs (Expert Lecture/ Workshop/ Seminar /Extra Coverage in Lab etc.)

• We will plan Experts lectures • We will plan Workshop • We will plan Seminar • We will plan Extra Coverage in Lab

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Working Principle of a Boiler The boiler works on the same principle as the water is heated in a closed vessel and due to heating, the water changes into steam. This steam steam possesses high pressure kinetic energy. The boiler contains water. The water is heated to its boiling temperature by the use of heat from the furnace. Due to heating of water,it gets converted into high pressure steam. The steam generated is passed through the steam turbines. As the high pressure steam strikes the turbine, it rotates the turbine. A generator is attached to the turbine and the generator also starts to rotate with the turbine and produces electricity.

Different Types of Boiler Boilers can be classified in different basis but here I am discussing the only important basis of boiler classification. 1. According to the Contents in the Tubes According to the contents in the tubes, the boilers can be classified as fire tube boiler and water tube boiler. (i) Fire Tube Boiler: In fire tube boiler the fire or hot gas are present inside the tubes and water surrounds these fire tubes. Since fire is inside the tubes and hence it is named as fire tube boiler. The heat from the hot gases is conducted through the walls of the tube to the water. The examples of the fire tube boiler are: simple vertical boiler, Cochran boiler, Lancashire boiler, Cornish boiler, Locomotive boiler. (ii). Water Tube Boiler: In water tube boilers, the water is present inside the tubes and the fire or hot gases surrounds these water tubes. The examples of water tube boilers are: La-Mont boiler, Benson boiler, Babcock and Wilcox boiler.

2. According to the Number of Tubes According to the no of tubes, the boilers are classified as single tube boiler and multitubular boilers. (i). Single Tube Boilers: The boilers which contain one fire tube or water tube are called as single tube boiler. The examples of single tube boilers are Cornish boiler and simple vertical boiler. (ii). Multitubular Boiler: The boilers which has two or more water tube or fire tubes are called multi tubular boilers. Lancashire boiler, Locomotive boiler, Cochran boiler, Babcock and Wilcox boilers are multitubular boilers. 3. According to the Position of the Furnace According to the position of the furnace, the steam boilers are classified as internally fired boilers and externally fired boilers. (i). Internally Fired Boilers:

4. According to the Axis of the Shell According to the axis of the shell, the boilers are classified as vertical boilers and horizontal boilers. (i). Vertical Boilers: the in which the axis of the shell is vertical are called vertical boilers. Examples of vertical boilers are: simple vertical boiler and Cochran boiler. (ii). Horizontal Boilers: when the axis of the shell in a boiler is found horizontal than it is called as horizontal boiler. Lancashire boiler, Babcock and Wilcox boiler and locomotive boilers are examples of horizontal boilers.

5. According to the Methods of Circulation of Water and Steam According to the method of circulation of water and steam, the steam boilers are divided into natural circulation boilers and forced circulation boilers. (i). Natural Circulation Boilers: In natural circulation boilers, the circulation of water takes place naturally by the convection currents that set ups during the heating of water. In most of the boilers there is a natural circulation of water such as Lancashire boiler, Cochran boiler etc. (ii). Forced Circulation Boilers: In this type of steam boilers, the water circulation takes place with the help of a centrifugal pump driven by some external power. Here the circulation is forced by some external agency. Forced circulation is used in high pressure boilers such as La-Mont boiler, Loeffler boiler, Benson boiler etc.

6. According to the use According to the use, the boilers are classified as stationary boilers and mobile boilers (i) Stationary Boilers: These are the boilers which are stationary and cannot be moved from one place to another. Once they are installed, cannot be transported to other destination. These boilers are used in power plants and in industrial process works. (ii). Mobile Boilers: These are the steam boilers which can be moved from one place to another. Locomotive and marine boilers are mobile boilers.

7. According to Pressure of steam generated 1. Low-pressure boiler: A boiler which produces steam at a pressure of 15-20 bar is called a low-pressure boiler. This steam is used for process heating. 2. Medium-pressure boiler: It has a working pressure of steam from 20 bars to 80 bars and is used for power generation or combined use of power generation and process heating. 3. High-pressure boiler: It produces steam at a pressure of more than 80 bars.

These are the fittings, which are necessarily mounted on the boiler itself and mandatorily required for the safe and proper operation of boiler. Various boiler mountings are being discussed here one by one.

1. Water level indicator: Water level indicator is fitted outside the boiler shell to indicate the water level in the boiler through a glass tube. In any type of boiler, water should remain at the designed level. If the water falls below the level due to change of phase into steam and simultaneously fresh water does not fill in by some reason, the hot surface may expose to steam only and overheat. This is because the heat transfers co-efficient of steam is very less as compared to water. Due to overheat, damage of tube surface may occur. To avoid this situation, level of water in the boiler needs to be constantly monitored & maintained by boiler operator by keeping watch on water level indicator. 2. Pressure Gauge: A pressure gauge is used to indicate the pressure of steam in the boiler. It is generally mounted on the front top of the boiler. Pressure gauge is of two types as (i) Bourdon Tube Pressure Gauge (ii) Diaphragm type pressure gauge. Both these gauges have a dial in which a needle moves over a circular scale under the influence of pressure. At atmospheric pressure it gives zero reading. Some gauges indicate only the positive pressure but some are compound and indicate negative pressure or vacuum also. Looking at the gauge, boiler operator can check the safe working pressure of the boiler and can take necessary steps to keep the pressure within safe limits. If pressure increases and crosses the safe limit due to any reason, the boiler shell material may fail and it can burst causing damage to life and property. Thus it is very important to constantly monitor pressure in a boiler with the help of pressure gauge. 3. Spring loaded safety valve: Spring loaded safety valve is a safely mounting fitted on the boiler shell and is essentially required on the boiler shell to safeguard the boiler against high pressure. It is a vital part of boiler and always be in good working condition to protect the boiler from bursting under high pressure and so to save life and property. 4. Fusible plug: The function of fusible plug is to protect the boiler from damage due to overheating of boiler tubes by low water level. 5. Blow-off-cock: It is a controllable valve opening at the bottom of water space in the boiler and is used to blow off some water from the bottom which carries mud or other sediments settled during the operation of boiler. It is also used to completely empty the water when the boiler is shut off for cleaning purpose or for inspection and repair.

Boiler Accessories

Boiler accessories are the components which are attached to the boiler (Not mounted on it) and are essentially for working of boiler and for increasing its efficiency. Various boiler accessories are discussed as below

1. Feed pump

Feed pump is placed nearby the boiler and is used to feed water to boiler working at a high pressure. The job of feed pump is not just put the water in the boiler but as boiler is working at high pressure, discharge pressure of feed pump must be sufficiently higher than this to push the water inside the boiler. centrifugal pump is used as a boiler feed pump.

2. Economizer

An economizer is a specially constructed heat exchanger for harnessing the heat energy of outgoing flue gases and utilizing it in preheating of boiler feed water. It saves the heat energy and so the fuel and decreases the operating cost of boiler by increasing its thermal efficiency.

3. Air Pre-heater

The function of air pre-heater is to further utilize the heat of flue gases after coming out of economizer to preheat the air used in furnace or oil burner.

4. Super heater

The function of super heater is to increase the temperature of steam beyond its saturation temperature. It is a type of heat exchanger. Hot flue gases coming out of burner are first directed through super heater before the boiler. The main advantage of superheating of steam comes in power plants, where steam is expanded through a turbine. But in a processing industry superheating is required only to avoid condensation in pipes. Thus super heater has less advantage or use in a processing industry and many times not used but not always.

1. Shell: It has a vertical axis cylindrical drum with a hemispherical dome-type shell at the top. 2. Grate: It is the platform on which the solid fuel is burnt. 3. Combustion Chamber: The burning of fuel takes place in the combustion chamber. 4. Fire Tubes: Cochran boiler has multi-tubular fire tubes. The hot flue gases from the combustion chamber travels to the smokebox through these fire tubes. The fire tubes helps in the exchange of heat from the hot flue gases to the water. 5. Fire Hole: It is the hole provided to fire the fuel inside the furnace. 6. Furnace: It lies at the bottom of the boiler. Furnace is the place where all the fuel is burnt. Without furnace, the working of this boiler is not possible. 7. Chimney: The chimney is attached to the smokebox. It transfer smoke to the environment. The size of the chimney is small as compared with other boiler. 8. Fire Brick Lining: The fire brick lining is present in the combustion chamber and helps in the combustion of the fuel. 9. Manhole: A manhole is provided for the cleaning and inspecting of the boiler from inside.

Working In Cochran boiler first the fuel is inserted into the firebox and placed on the grate. The fuel is ignited through the fire hole provided at the right bottom of the boiler. The fuel is burnt in the firebox, and due to the burning of the fuel, smoke and hot flue gases emerge out. The hot flue gases enter into the combustion chamber. From the combustion chamber, hot gases enter into the fire tubes. The fire tubes are surrounded by water. The hot flue gases inside the tubes exchange the heat from the hot gases to the water. Due to the exchange of heat, the temperature of the water starts increasing and it gets converted into steam. The steam produced rises upward and collected at top of the boiler in the hemispherical dome. An anti- priming pipe is installed at top of the boiler which separates the water from the steam and makes it dry steam. This dry steam is then transferred to the turbines through the steam stop valve. The hot flue gases and smoke after exchanging heat moves to the smoke box. From the smoke box, the burnt gases and smoke is discharged to the atmosphere through the chimney. Burnt fuel is transferred to the ash pit. Blow off Valve is preset at left bottom of the boiler and is used to blow off the impurities, mud, and sediment from the boiler water. A fusible plug is also provided at the top of the combustion chamber. When the temperature of the combustion chamber crosses the permissible level, the fusible plug melts and the water through the combustion chamber enters into the furnace of the boiler and stops the fire. In this way, a big fire accident can be prevented to take place and also protects the boiler from damage. Advantages 1. Low initial installation cost. 2. It requires less floor area. 3. Easy to operate and handle. 4. Transportation of Cochran boiler is easy. 5. It can use all types of fuel. Disadvantages 1. Low rate of steam generation. 2. Inspection and maintenance is difficult. 3. High room head is required for its installation due to the vertical design. 4. It has limited pressure range.

Locomotive Boiler Locomotive boiler is a horizontal drum axis, multi-tubular, natural circulation, artificial draft, forced circulation, mobile, medium pressure, solid fuel fired fire tube boiler with an internally fired furnace. It is used in railway locomotive engines and in marine. It is a mobile boiler and has a high steam generation rate. Construction

The construction or main parts of a locomotive boiler are: 1. Fire hole: It is a hole provided at the rear end of the boiler. The solid fuel is inserted and ignited into the furnace through this hole. 2. Fire box: It is a box in which the burning of the fuel takes place. 3. Grate: Grate is a platform on which the solid fuel is kept and burnt. 4. Fire brick arch: It is a brick arch placed inclined over the grate. It prevents the entry of the ash, dust and burnt fuel particles into the fire tubes. It provides a way to the hot flue gases to travel a definite path before entering into the fire tubes of the boiler. 5. Boiler tubes: They are the fire tubes through which the hot flue gases pass and exchange the heat with the surrounding water. 6. Smoke box: According to its name, it is a box in which the smoke of the burnt fuel after passing through the fire tubes gets collected. From there it is exhausted in the environment by the chimney. 7. Blast pipe: It is a pipe provided above the steam engine. The exhaust steam passes through this blast pipe. It is used to create an artificial draft that pushes the smoke out through the chimney and creates suction for the hot flue gases. The suction created allows the hot flue gases to move forward through the fire tubes. 8. Steam pipe: It is a pipe through which the steam passes. We have two steam pipes; one is the main steam pipe present in between the super-heater header and dome. And the second one is that which connects the super-heater exit end to the steam engine. 9. Superheater: It superheats the steam to the desired temperature before entering into the cylinder of the steam engine. 10. Super heater element pipes: These are the pipes of superheater through which the steam travels and gets superheated. 11. Dome: It is present at the top and contains the regulator for regulating the steam produced through the steam pipe.

Swami Keshvanand Institute of Technology, Management & Gramothan, Ramnagaria, Jagatpura, Jaipur-302017, INDIA Approved by AICTE, Ministry of HRD, Government of India Recognized by UGC under Section 2(f) of the UGC Act, 1956 Tel. : +91-0141- 5160400Fax: +91-0141-2759555 E-mail: [email protected] Web: www.skit.ac.in 12. Regulator valve: It is a valve that regulates the steam through the main steam pipe for superheating. 13. Safety valve: It is used to maintain the safe working steam pressure in the locomotive boiler. It blows off steam when the pressure of the steam increases above safety level and prevents blasting of the boiler. 14. Superheater header: It is the head of the superheater which accepts the steam from the steam pipe. 15. Chimney: It is used to throw out the exhaust smoke and gases to the environment. The length of the chimney is very small in this boiler. Working In the locomotive boiler, first, the solid fuel (coal) is inserted on the grate and is ignited from the fire hole. The burning of the fuel starts and it creates hot flue gases. A fire brick arch is provided that makes the flow of hot flue gases to a definite path before entering into the long tubes (fire tubes). It also prevents the entry of burnt solid fuel particles into the fire tubes. The hot flue gases pass through the long fire tubes and heat the water surrounding them. Due to the heating, the water gets converted into saturated steam and gets collected at the top. The saturated steam from the dome enters into the main steam pipe through the regulator valve. The steam travels in the main steam pipe and reaches to the super-heater header. Form header, the steam enters into super-heater element pipes. Here it is superheated and then the superheated steam enters into the steam pipe of the smoke box. The steam from the super-heater goes to the cylinder containing piston. The superheated steam made the piston moves within the cylinder. The piston is connected to the wheels of the steam engine and the wheels start rotating. The exhaust steam from the cylinder enters into the blast pipe. The burnt gases and smoke after passing through the fire tubes enter into the smoke box. The exhaust steam coming out from the blast pipe pushes the smoke out of the boiler through the chimney. Here the smoke cannot escape out from the boiler on its own, so artificial draft is created by exhaust steam coming out from the steam engine. This artificial draft created pushes the smoke out of the smoke box and creates suction for the hot flue gases. Advantages It is portable and can be easily transported. It is capable of meeting sudden and fluctuating demands of steam. It is a cost-effective boiler. It has a high steam generation rate. Disadvantages It faces the problems of corrosion and scale formation. Unable to work under heavy load conditions because of overheating problems. Some of its water spaces are difficult to clean. Application Locomotive boilers are mostly used in railways and marines. The efficiency of this boiler is very less. It cannot work in heavy-load conditions because this leads to the overheating of the boiler and finally gets damage. They are also used in traction engines, steam rollers, portable steam engines, and some other steam road vehicles.

The various main parts of Babcock and Wilcox Boiler are as follows 1. Drum: It is horizontal axis drum which contains water and steam. 2. Down Take Header: It is present at rear end of the boiler and connects the water tubes to the rear end of the drum. It receives water from the drum. 3. Up Take Header: it is present at front end of the boiler and connected to the front end of the drum. It transports the steam from the water tubes to the drum. 4. Water Tubes: They are the tubes in which water flows and gets converted into steam. It exchanges the heat from the hot flue gases to the water. It is inclined at angle of 10-15 degree with the horizontal direction. Due to its inclination the water tubes do not completely filled with water and the water and steam separated out easily. 5. Baffle Plates: Baffle plates are present in between water tubes and it allows the zigzag motion of hot flue gases from the furnace. 6. Fire Door: It is used to ignite the solid fuel in the furnace. 7. Grate: It is a base on which the burning of the solid fuel takes place. 8. Mud Collector: It is present at the bottom of down take header and used to collect the mud present in the water. 9. Feed Check Valve: it is used to fill water into the drum.10. Damper: It regulates the flow of air in the boiler. The various boiler mounting and accessories used in this type of boiler are:

Working First the water starts to come in the water tubes from drum through down take header. The water present in the inclined water tubes gets heated up by the hot flue gases. The coal burning on the grate produces hot flue gases and it is forced to move in zigzag way with the help of baffle plates. As the hot flue gases come in contact with water tubes, it exchanges the heat with water and converts it into steam. The steam generated is moved upward and through up take header it gets collected at upper side in the boiler drum. An anti-priming pipe is provided in the drum. This anti-priming pipe filters the water content from the steam and allows only dry steam to enter into super-heater. The super-heater receives the water free steam from the anti-priming pipe. It increases the temperature of steam to desired level and transfers it to the steam stop valve.The superheated steam from the steam stop valve is either collected in a steam drum or made to strike on the steam turbine for electricity generation. Advantages 1. Steam generation capacity is high. It is about 2000 to 40000 kg/hr. 2. It occupies less space. 3. Replacement of defective tubes is easy. 4. It is the only boiler that is used to generate large quantity of heat in power stations. 5. The draught loss is minimum. 6. Inspection of this types of boiler can be done anytime during its working. Disadvantages 1. High maintenance cost. 2. It is not much suitable for impure and sedimentary water. In case of impure and sedimentary water, scale may deposit in the tubes and this leads to overheating and bursting of tubes. That’s why water treatment is must before feeding into the boiler. 3. Continuously supply of feed water is required for the working. In the case if feed water is not continuously supplied even for a short period of time, the boiler gets overheated. Water level must be carefully watched during the operation of the Babcock and Wilcox boiler.

Lamont Boiler Lamont Boiler is the first forced convection boiler.It is a high pressure water tube, forced circulation externally fired. In lamont boiler, external water pump is used to circulate water within water tubes of the boiler. So, pressure of water in the tubes is more as compared with pressure of water in natural circulation boiler.

Construction: In lamont boiler, air blower is connected to the air preheater and supply air to this. This air preheater is connected to the furnace. The water feed pump is connected to the economizer which preheats the water in this economizer is connected to steam seperator drum.The Steam seperator drum is connected to the radiant evaporator which is located near combustion chamber and this radiant evaporator is connected to convective evaporator which is present above it. The steam seperator drum is also connected to the super heater which further heats the air to desired level and then transfer the steam to turine to produce electricity.

These are the main parts of Lamont Boiler: 1. Feed Pump: Feed Pump supply water into the boiler from hot well. 2. Economizer: Economizer is used to increase the temperature of feed water. 3. Centrifugal Pump: Centrifugal pump is used to circulate water inside the Lamont Boiler as it is a forced circulation boiler. The pump is driven by a steam turbine and the steam for this turbine is taken by the boiler. This boiler uses its own steam to drive its pump that circulate water in it. 4. Steam Seperating Drum: Role of this part of Lamont Boiler is indicated by its name. It seperates steam from water. 5. Super Heater: Steam generated from the evaporator is saturated steam and if used in steam turbine can cause corrosion on the turbine. So the saturated steam is sent to the super heater where it converts into superheated steam and this superheated steam is sent to turbine. 6. Radiant Evaporator: Radiant Evaporator heats the water with help of radiation. It is located near furnace. 7. Convective Evaporator: Convective Evaporator is located above the Radiant Evaporator. It heats the water by convection process. 8. Air preheater: Air preheater is present near the top of the Lamont Boiler. Its main function is to improve thermal efficiency of boiler by preheating the air from coming from the blower and this preheated air is sent to the furnace.

Working Of Lamont Boiler: At first, the air blower will blow air to the air preheater where air is preheated and sent to the furnace to increase the thermal efficiency of the boiler. On the otherside, the water feed pump circulates the water into the economizer of the boiler. The economizer heat the water to some extent and this water is sent to the steam seperator drum. After the steam seperator drum, this water is forced circulated through the radiant evaporator by the external centrifugal pump which is driven by steam turbine. Radiant evaporator heats the water and convert some portion of water into steam. Water and steam mixture from the radiant evaporator is sent to convective evaporator. In convective evaporator, water is further heated and most of the water converts into saturated steam. Water passes from these two evaporators 10 – 15 times until almost all water converts into saturated steam. The mixture of saturated steam and water is then sent to steam seperator drum to seperate the steam from water. In the steam seperator drum, the steam is collected at upeer portion of the drum and the remaining water settles down. This saturated steam present in steam seperator drum cannot be sent to the turbine directly as it will cause corrosion in the turbine. So, the saturated steam is passed through superheater where the temperature of steam is increased to desired level and saturated steam converts into superheated steam and finally the superheated steam is either transfer to the steam collecting drum or made to strike on the blades of the turbine. The working pressure, temperature and capacity of this boiler is 170 bar, 773 K and 50 tonnes/h. Advantages of Lamont Boiler: 1. Lamont Boiler has very flexible and simple design. 2. It has high heat transfer rate. 3. This boiler has high heat transfer rate. 4. It has very high steam generating capacity (about 50 tonnes per hour ). Disadvantages 1. There is a bubble formation at surfaces of the tubes in this boiler. This reduces the heat transfer rate to the steam. Benson Boiler Benson Boiler is a high pressure, drum less, supercritical, water tube steam boiler with forced circulation. This boiler is a super critical boiler in which the feed water is compressed to a supercritical pressure and this prevents the formation of bubbles in the water tube surface. The bubbles do not form because at supercritical pressure the density of water and steam becomes same. It was Mark Benson who first proposed the idea to compress the water at supercritical pressure before heating into boiler and due to this the latent heat of water reduces to zero. As the latent heat of water reduces to zero the water directly changes into steam without the formation of bubbles. Construction

The main parts of Benson boiler are: 1. Air Preheater: It preheats the air before entering into the furnace. The preheated air increases the burning efficiency of the fuel. 2. Economiser: It heats the water to a certain temperature. 3. Radiant Superheater: It is super heater which heats the water with radiation produced by the burnt fuel. It raises the temperature to supercritical temperature. 4. Convection Evaporator: It evaporates the superheated water and converts them into steam. It does so by the convection mode of heat transfer to the water from the hot flue gases. 5. Convection Superheater: It superheats the steam to the desired temperature (nearly 650 degree Celsius). 6. Furnace: It is the place where the fuel is burnt. 7. Feed Pump: It is used to supply the water inside the boiler at supercritical pressure of 225 bars.

Working Principle It works on the principle that the pressure of the water is increased to the supercritical pressure (i.e. above critical pressure of 225 bar). When the pressure of water is increased to the super critical level, the latent heat of water becomes Zero and due to this, it directly changes into steam without boiling. And this prevents the formation of bubbles at tube surface. Working In Benson Boiler, the feed pump increases the pressure of the water to the supercritical pressure and then it enters into the economiser. From economiser, the water the water passes to the radiant heater. Here the water receives the heat through radiation and partly gets converted into steam. The temperature raises almost to the supercritical temperature. After that mixture of steam and water enters into convective evaporator where it is completely converted into steam and may superheated to some degree. Finally it is passed through the superheater to obtained the desired superheated steam. This superheated steam is then used by turbines or engine to produce the electricity.

FIRE TUBE BOILER WATER TUBE BOILER Fire-tube boiler is the boiler in which the fire or Water-tube boiler is the boiler in which the hot gas is present inside the tubes and water water is present inside the tubes and fire or surrounds these fire tubes hot gases surrounds these fire tubes They are low or medium pressure boilers and They are high pressure boilers and usually usually operate at pressure of about 25 bar operate at pressure of about 165 bar Fire-tube boiler can only work on Water-tube boilers work on fluctuating fluctuating loads for a shorter time loads all the time.

Due to low pressure in fire-tube boiler the risk The risk of explosion is higher due to high of explosion is low. pressure.

These boilers are generaly internally fired. These boilers are generally externally fired. Furnace is placed at the one end of fire tube.

This boiler is difficult to construct. They are This is simple in construction. They are usually heavy in weight so difficult in usually lighter in weight so simple in transportation. transportation

This boiler occupies large floor area. It It occupies less floor area compare to occupies less floor area compare to fire fire tube boiler It required large shell diameter because the It required large shell diameter because fire tube situated inside the shell the fire tube situated inside the shell The overall efficiency of fire-tube boiler is The overall efficiency of water-tube boiler up to 75%. is up to 90% with the economizer.

Fire-tube boiler is simple in design, easy to A water-tube boiler is complex in design, install and has a low maintenance cost. difficult to install and has high maintenance Operating cost is low. cost. Operating cost is low

Example Lancashire boiler, Cornish Example Babcock and Wilcox boiler. boiler.

Steam Turbine

The steam turbine is one kind of heat engine machine in which steam's heat energy is converted into mechanical work. The construction of steam turbine is very simple. There is no piston rod, flywheel or slide valves attached to the turbine. So maintenance is quite easy. It consists of a rotor and a set of rotating blades which are attached to a shaft and the shaft is placed in the middle of the rotor. An electric generator known as steam turbine generator is connected to the rotor shaft. The turbine generator collects the mechanical energy from the shaft and converts it into electrical energy. Steam turbine generator also improves the turbineefficiency.

Working principle of steam turbine Working principle of steam turbine depends on the dynamic action of steam. A high-velocity steam is coming from the nozzles and it strikes the rotating blades which are fitted on a disc mounted on a shaft. This high-velocity steam produces dynamic pressure on the blades in which blades and shaft both start to rotate in the same direction. Basically, in a steam turbine pressure energy of steam extracts and then it converted into kinetic energy by allowing the steam to flow through the nozzles. The conversion of kinetic energy does mechanical work to the rotor blades and the rotor is connected to a steam turbine generator which acts as a mediator. Turbine generator collects mechanical energy from the rotor and converts into electrical energy. Since the construction of steam turbine is simple, its vibration is much less than the other engines for same rotating speed.

Types of steam turbine 1. According to the working principle steam turbines aremainly divided into two categories: a) Impulse Turbine b) Reaction Steam Turbine 2. According to the direction of steam flow, it may be classified into two categories:- a) Axial Flow Steam Turbine b) Radial Flow Steam Turbine 3. According to the exhaust condition of steam, it is further divided into two categories:- a) Back Pressure or Non-Condensing types Steam Turbine b) Condensing type Steam Turbine 4. According to pressure of steam, it may be divided following categories:- a) High-pressure or pass-out or Extraction steam turbine

b) Medium-pressure or back pressure steam turbine c) Low-pressure turbine 5. According to the number of stages, it may be divided following categories:- a) Single stage steamturbine b) Multi-stage steam turbine 6. According to the blade and wheels arrangement, it may be divided following categories:- a) Pressure Compounding Steam Turbine b) Velocity Compounding Steam Turbine c) Impulse-Reaction Combined Steam Turbine d) Pressure-Velocity Compounding Steam Turbine

Difference between Impulse and Reaction Turbine

S.no Impulse Turbine Reaction Turbine In impulse turbine the steam flows In the reaction turbine, first the steam flows through the nozzle and strike on the through the guide mechanism and then flows 1. moving blades. through the moving blades. Steam strikes on the buckets with The steam glides over the moving blades 2. kinetic energy. with both pressure and kinetic energy. During the flow of steam through moving blades, its pressure During the flow of steam through moving blades 3. remains constant. its pressure reduces. The steam may or may not be admitted to the whole The steam must be admitted over the whole 4. circumference. circumference. The blades of impulse turbine are The blades of reaction turbine are not 5. symmetrical. symmetrical. While gliding over the blades the In reaction turbine, while gliding over the blades relative velocity of steam remains the relative velocity of steam 6. constant. increases. For the same power developed, the For the same power developed, the number 7. number of stages required is less. of stages required ismore. The direction of steam flow is radial The direction of steam flow is radial and 8. to the direction of turbine wheel. axial to the turbine wheel. 9. It requires less maintenance work. It requires more maintenance work.

Power Plant

A power plant or a power generating station is basically an industrial location that is utilized for the generation and distribution of electric power in mass scale, usually in the order of several 1000 Watts. These are generally located at the sub-urban regions or several kilometres away from the cities or the load centres, because of its requisites like huge land and water demand, along with several operating constraints like the waste disposal etc.

Types of Power plants A power plant can be of several types depending mainly on the type of fuel used. Since for the purpose of bulk power generation, only thermal, nuclear and hydro power comes handy, therefore a power generating station can be broadly classified as follows. a) Thermal Power plant b) Nuclear Power plant c) Hydro-Electric Power plant d) Diesel power plant e) Gas turbine powerplant

Thermal Powerplant A thermal power station or a coal fired thermal power plant is by far, the most conventional method of generating electric power with reasonably high efficiency. It uses coal as the primary fuel to boil the water available to superheated steam for driving thesteamturbine. Thesteamturbineis then mechanically coupled to an alternator rotor, the rotation of which results in the generation of electric power. Generally in India, bituminous coal or brown coal are used as fuel of boiler which has volatile content ranging from 8 to 33% and ash content 5 to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its pulverized form.

Layout of steam power plant In coal fired thermal power plant, steam is obtained in very high pressure inside the steam boiler by burning the pulverized coal. This steam is then super heated in the super heater to extreme high temperature. This super heated steam is then allowed to enter into the turbine, as the turbine blades are rotated by the pressure of the steam. The turbine is mechanically coupledwith alternator in away that itsrotorwillrotatewith the rotation of turbine blades. After entering into the turbine, the steam pressure suddenly falls leading to corresponding increase in the steam volume. After having imparted energy into the turbine rotors, the steam is made to pass out of the turbine blades into the steam condenser of turbine. In the condenser, cold water at ambient temperature is circulated with the help of pump which leads to the condensation of the low pressure wet steam. Then this condensed water is further supplied to low pressure water heater where the low pressure steam

increases the temperature of this feed water, it is again heated in high pressure. This outlines the basic working methodology of a thermal power plant.

Advantages of Thermal Power Plants

• Fuel used i.e. coal is quite cheaper. • Initial cost is less as compared to other generating stations. • It requires less space as compared to hydro-electric power stations. Disadvantages of Thermal Power Plants • It pollutes atmosphere due to production of smoke and fumes. • Running cost of the power plant is more than hydro electric plant.

Nuclear Powerplant Nuclear power plants are similar to the thermal stations in more ways than one. However, the exception here is that, radioactive elements like uranium and thorium are used as the primary fuel in place of coal. Also in a nuclear station the furnace and the boiler are replaced by the nuclear reactor and the heat exchanger tubes. For the process of nuclear power generation, the radioactive fuels are made to undergo fission reaction within the nuclear reactors. The fission reaction propagates like a controlled chain reaction and is accompanied by unprecedented amount of energy produced, which is manifested in the form of heat. This heat is then transferred to the water present in the heat exchanger tubes. As a result, super heated steam at very high temperature is produced. Once the process of steam formation is accomplished, the remaining process is exactly similar to a thermal power plant, as this steam will further drive the turbine blades to generate electricity.

Layout of nuclear power plant

Hydro-Electric Power Station In Hydro-electricplantstheenergyofthefallingwaterisutilizedtodrivetheturbinewhichin turn runs the generator to produce electricity. Rain falling upon the earth’s surface has potential energy relative to the oceans towards which it flows. This energy is converted to shaft work where the water falls through an appreciable vertical distance. This power is utilized for rotating the alternator shaft, to convert it to equivalent electrical energy. An important point to be noted is that, the hydro-electric plants are of much lower capacity compared to their thermal or nuclear counterpart. For this reason hydro plants are generally used in scheduling with thermal stations, to serve the load during peak hours. They in a way assist the thermal or the nuclear plant to deliver power efficiently during periods of peak

Layout of nuclear power plant

Advantages of Hydro Electric Power Station • It requires no fuel, water is used for generation of electrical energy. • It is neat and clean energy generation. • Construction is simple, less maintenance is required. • It helps in irrigation and flood control also.

Disadvantages Hydro Electric Power Station • It involves high capital cost due to dam construction. • Availability of water depends upon weather conditions. • It requires high transmission cost as the plant is located in hilly areas.

Diesel Power Station In a diesel power station, diesel engine is used as the prime mover. The diesel burns inside the engine and the products of this combustion act as the working fluid to produce mechanical energy. The

diesel engine drives alternator which converts mechanical energy into electrical energy. As the generation cost is considerable due to high price of diesel, therefore, such power stations are only used to produce small power. Although steam power stations and hydro-electric plants are invariably used to generate bulk power at cheaper costs, yet diesel power stations are finding favour at places where demand of power is less, sufficient quantity of coal and water is not available and the transportation facilities are inadequate. This plants are also standby sets for continuity of supply to important points such as hospitals, radio stations, cinema houses and telephone exchanges.

Layout of diesel power plant

Advantages of diesel Power Station The advantages of diesel power plants are listed below: • Diesel power plant design is simple for installation. • The layout of the diesel power plant is quite simple. • The limited quantity of cooling water required. • Standby losses are very less as compared to other Power plants.

• Low fuel cost for operation. • Smaller storage is needed for the fuel. • There is no problem of ash handling. • Less time monitoring is sufficient required. • For small capacity power generation, diesel power plant is more efficient than the steam power plant. • Quickly started and put on load. • They can respond to varying loads without having any difficulty. Disadvantages: • The disadvantages of diesel power plants are listed below: • High Maintenance and operatingcost. • The plant cost per kW power is comparatively more. • The working life of diesel power plant is small due to high maintenance. • The plant produces too much noise. • Diesel power plants are tough to construct for large scale. Applications: Diesel Power Plant finds wide application in the following fields: • Diesel power plant is used for electrical power generation in capacities ranging from 100 to 5000 H.P. • They are commonly used for mobile power generation and are widely used in transportation systems consisting of railroads, ships, automobiles, and airplanes. • They can be used as standby power plants. • They can be utilized as peak load plants for some other types of power plants. • For Industries where power requirement is small in the order of 500 kW, diesel power plants become more economical due to higher overall efficiency.

Gas Turbine PowerPlant The gas turbine power plant obtains its power by utilizing the energy of burnt gases and air, which is at high temperature and pressure by expanding through several rings of fixed and moving blades. It thus resembles a steam turbine. To get a high pressure (of the order of 4 to 10 bar) of the working fluid, which is essential for expansion a compressor, is required.

Layout of gas turbine power plant

The quantity of the working fluid and speed required are more, so, generally, a centrifugal or an axial compressor is employed. The turbine drives the compressor and so it is coupled to the turbine shaft. If after compression the working fluid were to be expanded in a turbine, then assuming that there were no losses in either component the power developed by the turbine would be just equal to that absorbed by the compressor and the work done would be zero. But increasing the volume of the working fluid at constant pressure, or alternatively increasing the pressure at constant volume can increase the power developed by the turbine. Adding heat so that the temperature of the working fluid is increased after the compression may do either of these. To get a higher temperature of the working fluid a combustion chamber is required where the combustion of air and fuel takes place giving temperature rise to the working fluid. Thus, a simple gas turbine cycle consists of a) a compressor, b) a combustion chamberand c) a turbine. d) Since the compressor is coupled with the turbine shaft, it absorbs some of the power produced by the turbine and hence lowers the efficiency. The network is, therefore, the difference between the turbine work and work required by the compressor to drive it. Gas turbines have been constructed to

work on the following: oil, natural gas, coal gas, producer gas, blast furnace, and pulverized coal.

Advantages of Gas Turbine Power Plant a) They are small in size, weigh less and have low initial cost per unit output. b) Theyareeasytoinstallwithinshortperiods. c) Theyarequick-startingandsmoothrunning. d) They offer flexibility by supplying electricity for power generation as well as by supplying compressed air for process needs. e) They are capable of using a range of liquid and gaseous fuels including synthetic fuels. f) They are subjected (put) to fewer environmental restrictions than other prime movers. g) Water consumption is less compared to steam power plant.

Disadvantages

a) An electric motor or an I.C. engine is necessary for starting the plant. The starting motor must bring the compressor well towards the operating speed. So, starting is not simple as in the case of other power plants. b) Gas turbine plants have fewer vibrations when compared with reciprocating engines of the same speed. However the high frequency noise from the compressor is objectionable. c) High temperatures impose severe restriction on the servicing conditions of the plant. d) Overall efficiency is low since two-thirds of the total power output is used for driving the compressor. e) The blades of the turbine require special cooling methods due to the severity of operating temperatures and pressures. In practice, the temperatures at the entry of the turbine are as high as 1100°C - 1260°C. Hence they should be made of special metals and alloys.

Reciprocating Pump Reciprocating pump is a positive displacement pump where certain volume of liquid is collected in enclosed volume and is discharged using pressure to the required application. Reciprocating pumps are more suitable for low volumes of flow at high pressures.

Components of Reciprocating Pump The main components of reciprocating pump are as follows: a) Suction Pipe

b) Suction Valve

c) Delivery Pipe

d) Delivery Valve

e) Cylinder

f) Piston and Piston Rod

g) Crank and Connecting Rod

h) Strainer

i) Air Vessel

Components of Reciprocating pump

1. Suction Pipe Suction pipe connects the source of liquid to the cylinder of the reciprocating pump. The liquid is suck by this pipe from the source to the cylinder. 2. Suction Valve Suction valve is non-return valve which means only one directional flow is possible in this typeofvalve. Thisisplacedbetweensuctionpipeinletandcylinder. Duringsuctionofliquid it is opened and during discharge it is closed.

3. Delivery Pipe Deliverypipeconnects cylinderofpumptotheoutlet source. Theliquidisdeliveredto desired outlet location through this pipe. 4. Delivery Valve Deliveryvalvealsonon-returnvalveplacedbetweencylinderanddeliverypipeoutlet.Itisin closed position during suction and in opened position during discharging of liquid. 5. Cylinder A hollow cylinder made of steel alloy or cast iron. Arrangement of piston and piston rod is inside this cylinder. Suction and release of liquid is takes place in this so, both suction and delivery pipes along with valves are connected to this cylinder. 6. Piston and PistonRod Piston is a solid type cylinder part which moves backward and forward inside the hollow cylinderto performsuctionanddeliveranceof liquid. Pistonrodhelpsthepistontoitslinear motion. 7. Crank and ConnectingRod Crank is a solid circular disc which is connected to power source like motor, engine etc. for its rotation. Connecting rod connects the crank to the piston as a result the rotational motion of crank gets converted into linear motion of the piston. 8. Strainer Straineris provided at the endof suction pipe toprevent the entranceof solids from water source into the cylinder.

9. Air Vessel Airvessels are connectedto both suctionand deliverypipes to eliminate the frictional head and to give uniform discharge rate.

Working of ReciprocatingPump The working of reciprocating pump is as follows: o When the power source is connected to crank, the crank will start rotating and connecting rod also displaced along with crank.

o The piston connected to the connecting rod will move in linear direction. If crank moves outwards then the piston moves towards its right and create vacuum in the cylinder.

o This vacuum causes suction valve to open and liquid from the source is forcibly o sucked by the suction pipe into the cylinder.

o When the crank moves inwards or towards the cylinder, the piston will move towards its left and compresses the liquid in the cylinder.

o Now, the pressure makes the delivery valve to open and liquid will discharge through delivery pipe.

o Whenpistonreachesitsextremeleftpositionwholeliquidpresentinthecylinderis delivered through deliveryvalve.

o Then again the crank rotate outwards and piston moves right to create suction and the whole process isrepeated.

o Generally the above process can be observed in a single acting reciprocating pump where there is only one delivery stroke per one revolution of crank. But when it comes to double acting reciprocating pump, there will be two delivery strokes per one revolution ofcrank.

Uses of Reciprocating Pump Reciprocating pump is mainly used for o Oil drilling operations

o Pneumatic pressure systems

Centrifugal Pump

The centrifugal pump is, a pump which can be used for handling huge amount of liquids to provide extremely high flow rates, and they have the capability to regulate their flow of liquid rates over a wide range. Generally, these pumps are designed for liquids which have a comparatively low viscosity that transfers like light oil otherwise water. Centrifugal pump components mainly include three parts such as an impeller, a casing, suction pipe by a foot valve & strainer delivery pipe. A centrifugal pump utilizes rotation to pass on velocity in the direction of the fluid. Each centrifugal pump uses a hydraulic component like an impeller that turns to pass on velocity toward the pumped fluid. This pump mainly used to change the velocity into liquid flow.

Each pump uses a hydraulic component like a casing that captures the velocity which is informed by the impeller & directs the pushed fluid toward the pump expulsion end.

Centrifugal Pump WorkingPrinciple

The centrifugal pump working principle mainly depends on the flow of forced vortex which means whenever a certain accumulation of liquid or fluid is permitted to turn with an exterior torque than there will be an increase within rotating liquid pressure head takes place. The increase in pressure head can be used to carry water from one site to another site. It is the force performing on the liquid that makes to supply in the casing.

Priming of CentrifugalPump

The pump priming is the most important step while starting a centrifugal pump. Because these pumps are not capable of pumping vapours otherwise air. It is the one type of method where the impeller of a pump will obtain totally submerged within fluid exclusive of some air trap inside. This is particularly needed as there is a primary start-up. The priming methods are classified into four types namely manually, with a vacuum pump, with a jet pump, and withseparator.

Advantages of CentrifugalPumps The centrifugal pumps advantages include the following. • These pumps do not include drive seals that reduce leakage risk. • These pumps are used to pump out harmful and risky fluids. • These pumps have magnetic coupling that can be damaged simply in overload situations as well as protects the pump from external forces. • The motor and pump are separated from each other so heat transfer is impossible from the

motor topump.

Disadvantages of CentrifugalPumps

The centrifugal pumps disadvantages include the following.

• The energy loss can be occurred due to the coupling that generates some magnetic resistance. • Once the intense load occurs, possibilities are there for the coupling fall. • If fluids with ferrous particles are pumped out, then rust occurs & over the time pumps stops working. • When the flow of liquid is less through the pump, then the overheating can occur.

Applications of CentrifugalPumps

The centrifugal pumps applications include the following. • These pumps are used in the oil and energy industries for pumping oil, mud, slurry, and power generationplants. • These pumps are used in industrial and fire protection for ventilation & heating, boiler feed, pressure boosting, fire security sprinkler systems, and air conditioning. • These pumps are used in waste management, agriculture, and manufacturing for wastewater processing plants, gas processing, irrigation, drainage, municipal industry, and overflow security. • These pumps are used in food, chemical, pharmaceutical industries for hydrocarbons, paints, cellulose, petrochemical, beverage production, sugar refining, and food.

INTERNAL COMBUSTION ENGINE INTRODUCTION Heat engine: A heat engine is a device which transforms the chemical energy of a fuel into thermal energy and uses this energy to produce mechanical work. It is classified into two types- (a) External combustion engine (b) Internal combustion engine

External combustion engine:

In this engine, the products of combustion of air and fuel transfer heat to a second fluid which is the working fluid of the cycle.

Examples:

*In the steam engine or a steam turbine plant, the heat of combustion is employed to generate steam which is used in a piston engine (reciprocating type engine) or a turbine (rotary type engine) for useful work.

*In a closed cycle gas turbine, the heat of combustion in an external furnace is transferred to gas, usually air which the working fluid of the cycle.

Internal combustion engine:

In this engine, the combustion of air and fuels take place inside the cylinder and are used as the direct motive force. It can be classified into the following types:

1. According to the basic engine design- (a) Reciprocating engine (Use of cylinder piston arrangement), (b) Rotary engine (Use of turbine)

2. According to the type of fuel used- (a) Petrol engine, (b) diesel engine, (c) gas engine (CNG, LPG), (d) Alcohol engine (ethanol, methanol etc)

3. According to the number of strokes per cycle- (a) Four stroke and (b) Two stroke engine

4. According to the method of igniting the fuel- (a) Spark ignition engine, (b) compression ignition engine and (c) hot spot ignition engine

5. According to the working cycle- (a) Otto cycle (constant volume cycle) engine, (b) diesel cycle (constant pressure cycle) engine, (c) dual combustion cycle (semi diesel cycle) engine. 6. According to the fuel supply and mixture preparation- (a) Carburetted type (fuel supplied through the carburettor), (b) Injection type (fuel injected into inlet ports or inlet manifold, fuel injected into the cylinder just before ignition).

7. According to the number of cylinder- (a) Single cylinder and (b) multi-cylinder engine

8. Method of cooling- water cooled or air cooled

9. Speed of the engine- Slow speed, medium speed and high speed engine.

10. Cylinder arrangement-Vertical, horizontal, inline, V-type, radial, opposed cylinder or piston engines.

11. Valve or port design and location- Overhead (I head), side valve (L head); in two stroke engines: cross scavenging, loop scavenging, uniflow scavenging.

12. Method governing- Hit and miss governed engines, quantitatively governed engines and qualitatively governed engine

14. Application- Automotive engines for land transport, marine engines for propulsion of ships, aircraft engines for aircraft propulsion, industrial engines, prime movers for electrical generators.

Comparison between external combustion engine and internal combustion engine:

External combustion engine Internal combustion engine *Combustion of air-fuel is outside the engine * Combustion of air-fuel is inside the engine cylinder (in a boiler) cylinder (in a boiler) *The engines are running smoothly and * Very noisy operated engine silently due to outside combustion *Higher ratio of weight and bulk to output * It is light and compact due to lower ratio of due to presence of auxiliary apparatus like weight and bulk to output. boiler and condenser. Hence it is heavy.

*Working pressure and temperature inside * Working pressure and temperature inside the engine cylinder is low; hence ordinary the engine cylinder is very much high; hence alloys are used for the manufacture of engine special alloys are used cylinder and its parts. *It can use cheaper fuels including solid fuels *High grade fuels are used with proper filtration *Lower efficiency about 15-20% *Higher efficiency about 35-40% * Higher requirement of water for dissipation *Lesser requirement of water of energy through cooling system *High starting torque *IC engines are not self-starting

Main components of reciprocating IC engines:

Cylinder: It is the main part of the engine inside which piston reciprocates to and fro. It should have high strength to withstand high pressure above 50 bar and temperature above 2000 oC. The ordinary engine is made of cast iron and heavy duty engines are made of steel alloys or aluminum alloys. In the multi-cylinder engine, the cylinders are cast in one block known as cylinder block.

Cylinder head: The top end of the cylinder is covered by cylinder head over which inlet and exhaust valve, spark plug or injectors are mounted. A copper or asbestos gasket is provided between the engine cylinder and cylinder head to make an air tight joint.

Piston: Transmit the force exerted by the burning of charge to the connecting rod. Usually made of aluminium alloy which has good heat conducting property and greater strength at higher temperature.

Fig. Different parts of IC engine

Piston rings: These are housed in the circumferential grooves provided on the outer surface of the piston and made of steel alloys which retain elastic properties even at high temperature. 2 types of rings- compression and oil rings. Compression ring is upper ring of the piston which provides air tight seal to prevent leakage of the burnt gases into the lower portion. Oil ring is lower ring which provides effective seal to prevent leakage of the oil into the engine cylinder.

Connecting rod: It converts reciprocating motion of the piston into circular motion of the crank shaft, in the working stroke. The smaller end of the connecting rod is

connected with the piston by gudgeon pin and bigger end of the connecting rod is connected with the crank with crank pin. The special steel alloys or aluminium alloys are used for the manufacture of connecting rod.

Crankshaft: It converts the reciprocating motion of the piston into the rotary motion with the help of connecting rod. The special steel alloys are used for the manufacturing of the crankshaft. It consists of eccentric portion called crank.

Crank case: It houses cylinder and crankshaft of the IC engine and also serves as sump for the lubricating oil.

Flywheel: It is big wheel mounted on the crankshaft, whose function is to maintain its speed constant. It is done by storing excess energy during the power stroke, which is returned during other stroke.

Terminology used in IC engine:

1. Cylinder bore (D): The nominal inner diameter of the working cylinder.

2. Piston area (A): The area of circle of diameter equal to the cylinder bore.

3. Stroke (L): The nominal distance through which a working piston moves between two successive reversals of its direction of motion.

4. Dead centre: The position of the working piston and the moving parts which are mechanically connected to it at the moment when the direction of the piston motion is reversed (at either end point of the stroke).

(a) Bottom dead centre (BDC): Dead centre when the piston is nearest to the crankshaft.

(b) Top dead centre (TDC): Dead centre when the position is farthest from the crankshaft.

5. Displacement volume or swept volume (Vs): The nominal volume generated by the working piston when travelling from the one dead centre to next one and given as,

Vs=A × L

6. Clearance volume (Vc): the nominal volume of the space on the combustion side of the piston at the top dead centre.

7. Cylinder volume (V): Total volume of the cylinder.

V= Vs + Vc

8. Compression ratio (r): V/ Vc

Four stroke engine:

- Cycle of operation completed in four strokes of the piston or two revolution of the piston. (i) Suction stroke (suction valve open, exhaust valve closed)-charge consisting of fresh air mixed with the fuel is drawn into the cylinder due to the vacuum pressure created by the movement of the piston from TDC to BDC. (ii) Compression stroke (both valves closed)-fresh charge is compressed into clearance volume by the return stroke of the piston and ignited by the spark for combustion. Hence pressure and temperature is increased due to the combustion of fuel (iii) Expansion stroke (both valves closed)-high pressure of the burnt gases force the piston towards BDC and hence power is obtained at the crankshaft. (iv) Exhaust stroke (exhaust valve open, suction valve closed)- burned gases expel out due to the movement of piston from BDC to TDC.

Figure show the cycle of operation of four stroke engine.

Fig. Cycle of operation in four stroke engine

Two stroke engine:

-No piston stroke for suction and exhaust operations

-Suction is accomplished by air compressed in crankcase or by a blower

-Induction of compressed air removes the products of combustion through exhaust ports

-Transfer port is there to supply the fresh charge into combustion chamber Figure represents operation of two stroke engine

Fig. Cycle of operation in two stroke engine

Comparison of Four-stroke and two-stroke engine:

Four-stroke engine Two-stroke engine 1. Four stroke of the piston and two revolution Two stroke of the piston and one of crankshaft revolution of crankshaft 2. One power stroke in every two revolution of One power stroke in each revolution of crankshaft crankshaft 3. Heavier flywheel due to non-uniform Lighter flywheel due to more uniform turning movement turning movement 4. Power produce is less Theoretically power produce is twice than the four stroke engine for same size 5. Heavy and bulky Light and compact 6. Lesser cooling and lubrication requirements Greater cooling and lubrication requirements 7. Lesser rate of wear and tear Higher rate of wear and tear 8. Contains valve and valve mechanism Contains ports arrangement 9. Higher initial cost Cheaper initial cost 10. Volumetric efficiency is more due to greater Volumetric efficiency less due to lesser time of induction time of induction 11. Thermal efficiency is high and also part load Thermal efficiency is low, part load efficiency better efficiency lesser 12. It is used where efficiency is important. It is used where low cost, compactness and light weight are important. Ex-cars, buses, trucks, tractors, industrial Ex-lawn mowers, scooters, motor cycles, engines, aero planes, power generation etc. mopeds, propulsion ship etc.

Comparison of SI and CI engine:

SI engine CI engine Working cycle is Otto cycle. Working cycle is diesel cycle. Petrol or gasoline or high octane fuel is Diesel or high cetane fuel is used. used. High self-ignition temperature. Low self-ignition temperature. Fuel and air introduced as a gaseous mixture Fuel is injected directly into the combustion in the suction stroke. chamber at high pressure at the end of compression stroke. Carburetor used to provide the mixture. Injector and high pressure pump used to Throttle controls the quantity of mixture supply of fuel. Quantity of fuel regulated in introduced. pump. Use of spark plug for ignition system Self-ignition by the compression of air which increased the temperature required for combustion Compression ratio is 6 to 10.5 Compression ratio is 14 to 22 Higher maximum RPM due to lower weight Lower maximum RPM Maximum efficiency lower due to lower Higher maximum efficiency due to higher compression ratio compression ratio Lighter Heavier due to higher pressures

Refrigeration and Air conditioning

Introduction to Refrigeration and Air conditioning:

Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, as the lower temperature is to maintain continuously the system must operate on cycle the aim being to cool some product or space to the required temperature.

One of the most important applications of refrigeration has been the preservation of perishable food products by storing them at low temperatures. Refrigeration systems are also used extensively for providing thermal comfort to human beings utilizing air conditioning.

Unit of Refrigeration:

The practical unit of refrigeration is expressed in terms of ‘tonne of refrigeration’. A tonne of refrigeration is defined as the amount of refrigeration effect produced by uniform melting of one tonne of ice at 0° to water at 0° in 24 hours

1TR=3.5 kW

Air conditioning:

Air Conditioning refers to the simultaneously control of four parameters of air as temperature, moisture content, cleanliness, odor, and circulation, as required by occupants, a process, or products in the space.

Types of Refrigeration System:

1. Natural Cooling:

Art of Ice making by Nocturnal Cooling

Evaporative Cooling

Cooling by Salt Solutions

2. Artificial Refrigeration

Vapour Compression Refrigeration Systems

Vapour Absorption Refrigeration Systems

Solar energy based refrigeration systems

Gas Cycle Refrigeration

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Steam Jet Refrigeration System

Thermoelectric Refrigeration Systems

Vortex tube systems

Electrolux Refrigeration System

Classification of Refrigeration system

Mainly refrigeration system are classified in two category

1 vapour compression refrigeration system

2 vapour absorption refrigeration system

Vapour compression refrigeration system:

• Vapour compression cycle is an improved type of air refrigeration cycle in which a suitable working substance, termed as refrigerant, is used.

• The refrigerants generally used for this purpose are ammonia (NH3), R11, R12, R134a, carbon dioxide (CO2), and sulfur-dioxide (SO2).

• The refrigerant used does not leave the system but is circulated throughout the system alternately condensing and evaporating. In evaporating, the refrigerant absorbs its latent heat from the solution which is used for circulating it around the cold chamber and in condensing; it gives out its latent heat to the circulating water of the cooler.

• The vapor compression cycle which is used in the vapor compression refrigeration system is nowadays used for all-purpose refrigeration. It is used for all industrial purposes from a small domestic refrigerator to a big air conditioning plant.

Components of Vapour compression refrigeration system:

1. Compressor

2. Condenser

3. expansion device

4. evaporator

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Schematic diagram of vapour compressor cycle.

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2. vapour absorption refrigeration system:

The vapor absorption refrigeration is a heat operated system. It is quite similar to the vapor compression system. In both systems, there are evaporators and condensers.

• The process of evaporation and condensation of the refrigerant takes place at two different pressure levels to achieve refrigeration in both cases. The method employed to create the two pressure levels in the system for evaporation and condensation of the refrigeration makes the two processes different. Circulation of refrigerant in both the cases is also different. • In the absorption system the compressor of the vapor compression system is replaced by the combination of absorber and generator. • A solution known as the absorbent, which has an affinity for the refrigerant used, is circulated between the absorber and the generator by a pump (solution pump). • The absorbent in the absorber draws (or sucks) the refrigerant vapor formed in the evaporator thus maintaining a low pressure in the evaporator to enable the refrigerant to evaporate at low temperatures. • In the generator the absorbent is heated. Thereby releasing the refrigerant vapor (absorbed in the absorber) as high-pressure vapor, to be condensed in the condenser. Thus the suction function is performed by absorbent in the absorber and the generator performs the function of the compression and discharge. • The absorbent solution carries the refrigerant vapor from the low side (evaporator–absorber) to the high side (generator-condenser). The liquefied refrigerant flows from the condenser to the evaporator due to the pressure difference between the two vessels; thus establishing the circulation of the refrigerant through the system.

Components of Vapour absorption refrigeration system:

1. Generator

2. Condenser

3. Expansion device

4. Absorber

5. Pump

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Simple Schematic diagram of vapour absorption cycle.

3. Electrolux Refrigeration System:

Construction of Electrolux Refrigeration System

Electrolux Refrigeration System is consist of the following parts.

Heat exchanger

Absorber

Evaporator

Condenser

Water separator

Boiler & Burner (Generator)

Heat exchanger

The heat exchanger is used to transferring heat to NH3. Page | 5

Absorber

It is used to remove the hydrogen from ammonia.

Evaporator

It is used to evaporate the NH3 with the help of H2.

Condenser

It is used to condense the NH3 into liquid.

Water separator

The water separator is used to separate the water particle from the vapor Ammonia.

Boiler and Burner (Generator)

It is used to generate the Amonnia vapor and supply only the strong solution of ammonia.

Working of Electrolux Refrigeration System:

Schematic diagram of Electrolux refrigeration system

In Electrolux refrigeration system NH3 gas coming out from the boiler is passed through the rectifier or water separator and then to the condenser. Page | 6

The liquid of refrigerant gravitates to u-shape trap filled with liquid NH3 to prevent the entry of H2 to the condenser and then enters the evaporator.

The whole plant is charged to a pressure of about 14 kgf/cm2 and the evaporator contains hydrogen at a pressure of 12 kgf/cm2. Therefore as soon as NH3 enters the evaporator, its pressure falls to 2kgf/cm2 and its temperature being about 18-degree centigrade.

Due to this low temperature, NH3 evaporator taking its latent heat from the refrigerated space and produces a cooling effect.

The dense mixture of NH3 vapor and H2 then passes into the absorber where it meets with H2O coming from boiler and NH3 is absorbed in H2O, while H2 rises and returns to evaporator.

The strong solution of NH3 then passed through the heat exchanger and burner and supplied to the boiler at pressure head h.

Classification of air conditioning system:

1. Central Air Conditioning System

The ideal cooling solution for most homes and businesses is a central air conditioning system. Central air will be the lowest maintenance, easiest to use, and most cost effective in the long run. However, a central air conditioning system is the most expensive to set up. Make sure the HVAC Company you’ve hired is reputable and highly experienced to install a central air conditioning system.

Working of central air conditioning: a central air conditioning system cools air in a cooling compressor, a unit that’s outside of the house. A fan blows the cool air through ducts to deliver it to all of the rooms in your house. Warm air is pulled out of the house through a return system and pushed outside through the exhaust. You control the temperature using the thermostat on the wall in your home.

Central air conditioning is standard in newly built homes, but older homes are not always set up for HVAC. However, most houses at least have the ductwork established so it’s easier to install central air conditioning.

2. Portable Air Conditioner

Portable air conditioners are convenient and affordable options for cooling down small spaces quickly. Comparable to a floor fan, you can take a portable air conditioner room to room, plug it in, and use it to cool your space down. Some models have wheels on the bottom making it easy to move. The bothersome thing about using these types of air conditioning systems is when the

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condensation catch gets filled up, or when you need to run a drainage tube out a window or into a bucket.

If you are conservative with the use of air conditioning, a portable AC unit may be the right choice for you. Instead of running your central air all day, use a portable air conditioner as needed, for shorts periods of time. Here are some other energy efficient air conditioning tips.

3. Ductless Split System

Even though central air conditioning is often the way to go, certain situations call for an alternative like ductless air conditioning

Example, although central air is set up in your house maybe there’s a room or a floor that needs its own independent cooling system. Such is the case for a new addition, a guest room or area that you rent out, a sunroom or a mancave, especially if its a designated smoking area. A ductless split system allows a room to have its own controls, and avoid circulating the same air throughout the rest of the house.

Using a ductless split system as needed in place of central air is more energy efficient. If your upstairs level is only utilized when you have guests, for example, it’s more cost effective to keep that floor shut off from central air and cool it down with the ductless system when needed.

4. Mini Split System

When you want to skip the ductwork, mini split systems are worth consideration. Similar to the ductless split system mentioned above, a mini split can also be installed without much fuss. A mini split is a smaller and more affordable system and it serves the same purpose. Put a mini split air conditioning system in a sunroom or a small addition. This simple and efficient type of air conditioner is easy to install and very affordable. The biggest perk to using these types of air conditioning units is that your energy bill will be so much lower compared to using central air.

5. Packaged Units

A packaged unit is a compact air conditioning system that works best for a home without a basement. If your home was built on a crawl space, there’s no indoor furnace or air handler. A packaged air conditioning unit is installed outside, so this is a great solution! Choose a model that has a compact footprint and is designed to blend with the outdoor environment. Packaged units can also be installed on a rooftop. Ductwork runs through a secure hole in the wall or roof to deliver cool, filtered air or heat to the home. You can buy packaged units with different fuel hookups: gas/electric, electric/electric, heat pump, and dual-fuel models.

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6. Swamp Coolers (Evaporative Air Conditioners)

Swamp coolers, also known as evaporative air conditioners, are a great choice for dry climates like Missoula, India, Montana. These types of air conditioning systems do not work well in the humid regions, but it’s a popular solution for Midwestern states. Swamp coolers use HVAC technology to mimic the natural process of evaporation. Choosing the right size for your space is key to cooling your spaces in a cost effective way.

7. Geothermal Air Conditioning

If you’re looking to save money on the most eco-friendly types of air conditioning systems, familiarize yourself with geothermal air conditioning. This relatively new HVAC solution has been around for 60 years in the US. It’s a method so promising that National Geographic published an article praising geothermal AC.

In short, geothermal HVAC avoids using fossil fuels and uses electricity minimally; just to power the fan, compressor, and pump. A geothermal system offers heat and air conditioning using an underground loop set up. Most of these systems use water instead of refrigerant.

8. Variable Capacity Air Conditioners

Variable capacity is a feature that allows you to adjust cooling output like a dimmer switch to perfectly match your comfort needs to your energy use. Variable capacity air conditioners are the best way to control moisture in uncomfortably humid environments.

Lennox carries the best variable capacity types of air conditioning units. The XC25 and XP25 have Precise Comfort® technology. The XC20 model was named Most Efficient Energy Star Product in 2019, saving homeowners 50% on their cooling energy bills.

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Application of refrigeration and air conditioning:

Applications of Refrigeration

The applications of refrigeration can be grouped into following four major equally important areas:

• Food processing, preservation and distribution. • Chemical and process industries • Special applications • Comfort air conditioning

Refrigeration in Food processing, preservation and distribution:

Food preservation is one of the most important application of refrigeration. It is well known that food products can be preserved for a longer time, if stored them at lower temperatures. Both the live and dead products can be preserved for longer time using refrigeration.

Live products stands for the products like fruits, vegetables and dead products for the products like fist, meat etc.

Refrigeration in Chemical and Process Industries:

• For separation and liquefaction of gases in petrochemical industries. • For removal of heat of reaction in various chemical industries. • For dehumidification of process air in pharmaceutical industries. • For recovery of solvents, storage of low boiling point liquids.

Special Applications of refrigeration:

Cold treatment of metals in the manufacture of precision parts, cutting tools to improve dimensional accuracy, hardness, wear resistance and tool life.

• For storage of blood plasma, tissues, etc. • For manufacture and storage of drugs. • In surgery for local anesthesia. • In construction for setting of concrete and for freezing wet soil to facilitate excavation. • Desalination of water by freezing. • Manufacture of ice, ice cubes, flakes, etc. • For storage of vaccines, medicines in remote and rural areas.

Applications of Air Conditioning

Air conditioning is required for

1. Providing thermal comfort to humans and other living beings - Comfort air conditioning. Page | 10

2. Providing conditions required for various products and processes in industries - Industrial air conditioning.

Comfort Air Conditioning -

The objective of this is to provide thermal comfort to the occupants. Thermal comfort may be defined as the state of mind that expresses satisfaction with its surroundings. The requirement of thermal comfort is that human body core temperature to be maintained about 37 degrees. Classification of comfort air conditioning systems :

• Air conditioning systems for residences. • Commercial air conditioning system. • Air conditioning system for hospitals. • Laptop, mobile air conditioning systems.

Industrial Air Conditioning:

The objective of this is to provide favorable surrounding conditions so that the required processes can be carried out and required products can be produced.

Industrial air conditioning examples :

• Textile industries • Printing industries • Manufacturing of precision parts • Semi-conductor industries • Pharmaceutics • Photographic materials • Computer rooms • Mines, power plants, etc

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POWER TRANSMISSION DEVICES

INTRODUCTION The power is transmitted from one shaft to the other by means of belts, chains and gears. The belts and ropes are flexible members which are used where distance between the two shafts is large. The chains also have flexibility but they are preferred for intermediate distances. The gears are used when the shafts are very close with each other. This type of drive is also called positive drive because there is no slip. If the distance is slightly larger, chain drive can be used for making it a positive drive. Belts and ropes transmit power due to the friction between the belt or rope and the pulley. There is a possibility of slip and creep and that is why, this drive is not a positive drive. A gear train is a combination of gears which are used for transmitting motion from one shaft to another shaft.

Objectives

After studying this unit, you should be able to • understand power transmission derives, • understand law of belting, • determine power transmitted by belt drive and gear, • determine dimensions of belt for given power to be transmitted, • determine gear ratio for different type of gear trains, • classify gears, and • Understand gear terminology.

POWER TRANSMISSION DEVICES Power transmission devices are very commonly used to transmit power from one shaft to another. Belts, chains and gears are used for this purpose. When the distance between the shafts is large, belts or ropes are used and for intermediate distance chains can be used. For belt drive distance can be maximum but this should not be more than ten metres for good results. Gear drive is used for short distances.

Belts

In case of belts, friction between the belt and pulley is used to transmit power. In practice,

(a) Flat Belt and Pulley (b) V-belt and Pulley (c) Circular Belt or Rope Figure: Types of Belt and Pulley The flat belt is rectangular in cross-section as shown in Figure (a). The pulley for this belt is slightly crowned to prevent slip of the belt to one side. It utilizes the friction between the flat surface of the belt and pulley.

The V-belt is trapezoidal in section as shown in figure (b). It utilizes the force of friction between the inclined sides of the belt and pulley. They are preferred when distance is comparative shorter. Several V-belts can also be used together if power transmitted is more.

The circular belt or rope is circular in section as shown in figure (c). Several ropes also can be used together to transmit more power.

The belt drives are of the following types :

1. open belt drive, and

2. cross belt drive.

Open Belt Drive

Open belt drive is used when sense of rotation of both the pulleys is same. It is desirable to keep the tight side of the belt on the lower side and slack side at the top to increase the angle of contact on the pulleys. This type of drive is shown in figure.

Figure 3.2 : Open Belt Derive

Cross Belt Drive

In case of cross belt drive, the pulleys rotate in the opposite direction. The angle of contact of belt on both the pulleys is equal. As shown in the figure, the belt has to bend in two different planes. As a result of this, belt wears very fast and therefore, this type of drive is not preferred for power transmission. This can be used for transmission of speed at low power.

If the thickness of belt is also to be considered

The belt moves from the tight side to the slack side and vice-versa, there is some loss of power

Gears are also used for power transmission. This is accomplished by the successive engagement of teeth. The two gears transmit motion by the direct contact like chain drive. Gears also provide positive drive.

The drive between the two gears can be represented by using plain cylinders or discs 1 and 2 having diameters equal to their pitch circles as shown in Figure 3.5. The point of contact of the two pitch surfaces shell have velocity along the common tangent. Because there is no slip, definite motion of gear 1 can be transmitted to gear 2 or vice-versa.

The tangential velocity (Vt) = 1 r1 = 2 r2 where r1 and r2 are pitch circle radii of gears 1 and 2, respectively.

2 N1 1

Figure : Gear Drive

POWER TRANSMISSION BY BELTS

In this section, we shall discuss how power is transmitted by a belt drive. The belts are used to transmit very small power to the high amount of power. In some cases magnitude of the

The angle of lap may be defined as the angle of contact between the belt and the pulley. With the increase in angle of lap, the belt drive can transmit more power. Along with the increase in angle of lap, the idler pulley also does not allow reduction in the initial tension in the belt. The use of idler pulley is shown in figure.

Idler Pulley

Figure: Use of Idler in Belt Drive Law of Belting The law of belting states that the centre line of the belt as it approaches the pulley must lie in plane perpendicular to the axis of the pulley in the mid plane of the pulley otherwise the belt will run off the pulley. However, the point at which the belt leaves the other pulley must lie in the plane of a pulley.

The figure below shows the belt drive in which two pulleys are at right angle to each other. It can be seen that the centre line of the belt approaching larger or smaller pulley lies in its plane. The point at which the belt leaves is contained in the plane of the other pulley.

Figure : Law of Belting

If motion of the belt is reversed, the law of the belting will be violated. Therefore, motion is

possible in one direction in case of non-parallel shafts as shown in figure.

LENGTH OF THE BELT

For any type of the belt drive it is always desirable to know the length of belt required. It will be required in the selection of the belt. The length can be determined by the geometric considerations. However, actual length is slightly shorter than the theoretically determined value.

Open Belt Drive

The open belt drive is shown in figure. Let O1 and O2 be the pulley centers and AB and CD be the common tangents on the circles representing the two pulleys. The total length of the belt ‘L’ is given by

L = AB + Arc BHD + DC + Arc CGA

Let r be the radius of the smaller pulley, R be the radius of the larger pulley, C be the centre distance between the pulleys, and

be the angle subtended by the tangents AB and CD with O1 O2.

D K

C J β

β β N G = O1 O2 H r R

B C

Figure : Open Belt Drive

(푅 − 푟)2 = 휋(푅 + 푟) + + 2퐶 퐶

This provides approximate length because of the approximation taken earlier.

Crossed-Belt Drive

The crossed-belt drive is shown in Figure 3.10. Draw O1 N parallel to the line CD which meets extended O2 D at N. By geometry

Cone Pulleys Sometimes the driving shaft is driven by the motor which rotates at constant speed but the driven shaft is designed to be driven at different speeds. This can be easily done by using stepped or cone pulleys as shown in figure. The cone pulley has different sets of radii and they are selected such that the same belt can be used at different sets of the Cone Pulleys.

3 4 1 2 5 r3

Figure: Cone Pulleys

Let Nd be the speed of the driving shaft which is constant.

Nn be the speed of the driven shaft when the belt is on nth step.

rn be the radius of the nth step of driving pulley.

Rn be the radius of the nth step of the driven pulley. where n is an integer, 1, 2, . . . The speed ratio is inversely proportional to the pulley radii

Thus, two equations are available – one provided by the speed ratio and other provided by the length relation and for selected speed ratio, the two radii can be calculated. Also it has to be kept in mind that the two pulleys are same. It is desirable that the speed ratios should be in geometric progression. Let k be the ratio of progression of speed.

Since, both the pulleys are made similar

If radii R1 and r1 have been chosen, the above equation provides value of k or vice- versa.

RATIO OF TENSIONS The belt drive is used to transmit power from one shaft to the another. Due to the friction between the pulley and the belt one side of the belt becomes tight side and other becomes slack side. We have to first determine ratio of tensions. Flat Belt

Let tension on the tight side be ‘T1’ and the tension on the slack side be ‘T2’. Let ‘θ’ be the angle of lap and let ‘µ’ be the coefficient of friction between the belt and the pulley. Consider an infinitesimal length of the belt PQ which subtend an angle δθ at the centre of the pulley. Let ‘R’ be the reaction between the element and the pulley. Let ‘T’ be tension on the slack side of the element, i.e. at point P and let ‘(T + δT)’ be the tension on the tight side of the element. The tensions T and (T + δT) shall be acting tangential to the pulley and thereby normal to the radii OP and OQ. The friction force shall be equal to ‘µR’ and its action will be to prevent slipping of the belt. The friction force will act tangentially to the pulley at the point S. Considering equilibrium of the element at S and equating it to zero. Resolving all the forces in the tangential direction

R S Q δ θ δ θ 2 P 2

T δ θ T +

O θ

T2 T1

Figure: Ratio of Tensions in Flat Belt

or 푻 ퟏ = 풆흁휽 푻ퟐ

V-belt or Rope The V-belt or rope makes contact on the two sides of the groove as shown in figure.

POWER TRANSMITTED BY BELT DRIVE

The power transmitted by the belt depends on the tension on the two sides and the belt speed.

Let T1 be the tension on the tight side in ‘N’

T2 be the tension on the slack side in ‘N’, and V be the speed of the belt in m/sec.

Then power transmitted by the belt is given by Power P = (T1− T2 ) V Watt (푇1 − 푇2)푉 푘푊 1000

The maximum tension T1 depends on the capacity of the belt to withstand force. If allowable 2 stress in the belt is ‘t’ in ‘Pa’, i.e. N/m , then T1 = (t  t  b) N

where t is thickness of the belt in ‘m’ and b is width of the belt also in m. The above equations can also be used to determine ‘b’ for given power and speed. Tension due to Centrifugal Forces The belt has mass and as it rotates along with the pulley it is subjected to centrifugal forces. If we assume that no power is being transmitted and pulleys are rotating, the centrifugal force will tend to pull the belt as shown in figure (b) and, thereby, a tension in the belt called centrifugal tension will be introduced.

Let ‘TC’ be the centrifugal tension due to centrifugal force. Let us consider a small element which subtends an angle at the centre of the pulley. Let ‘m’ be the mass of the belt per unit length of the belt in ‘kg/m’.

Tension of tight side Tt = T1 + TC and tension on the slack side Ts = T2 + TC .

The centrifugal tension has an effect on the power transmitted because maximum tension can be only Tt which is

Tt = t  t  b

2  T1 = t  t  b − m V

Initial Tension

When a belt is mounted on the pulley some amount of initial tension say ‘T0’ is provided in the belt, otherwise power transmission is not possible because a loose belt cannot sustain difference in the tension and no power can be transmitted.

When the drive is stationary the total tension on both sides will be ‘2 T0’.

When belt drive is transmitting power the total tension on both sides will be (T1 + T2), where T1 is tension on tight side, and T2 is tension on the slack side. If effect of centrifugal tension is neglected. 2T0 = T1 + T2

Maximum Power Transmitted

The power transmitted depends on the tension ‘T1’, angle of lap , coefficient of friction ‘ ’ and belt speed ‘V’. For a given belt drive, the maximum tension (Tt), angle of lap and coefficient of friction shall remain constant provided that (a) the tension on tight side, i.e. maximum tension should be equal to the maximum permissible value for the belt, and (b) the belt should be on the point of slipping.

At the belt speed given by the Eq. the power transmitted by the belt drive shall be maximum.

CLASSIFICATION OF GEARS There are different types of arrangement of shafts which are used in practice. According to the relative positions of shaft axes, different types of gears are used. Parallel Shafts In this arrangement, the shaft axes lie in parallel planes and remain parallel to one another. The following type of gears are used on these shafts: Spur Gears

These gears have straight teeth with their alignment parallel to the axes. These gears are shown in mesh in figures (a) and (b). The contact between the two meshing teeth is along a line whose length is equal to entire length of teeth. It may be observed that in external meshing, the two shafts rotate opposite to each other whereas in internal meshing the shafts rotate in the same sense.

Line

(a) External Meshing (b) Internal Meshing

Figure : Spur Gears If the gears mesh externally and diameter of one gear becomes infinite, the arrangement becomes ‘Spur Rack and Pinion’. This is shown in figure. It converts rotary motion into translatory motion, or vice-versa.

Figure: Spur Rack and Pinion

Helical Gears or Helical Spur Gears In helical gears, the teeth make an angle with the axes of the gears which is called helix angle. The two meshing gears have same helix angle but its layout is in opposite sense as shown in figure. The contact between two teeth occurs at a point of the leading edge. The point moves along a diagonal line across the teeth. This results in gradual transfer of load and reduction in impact load and thereby reduction in noise. Unlike spur gears the helical gears introduce thrust

Thr Driver

Thru

Double-Helical or Herringbone Gears

A double-helical gear is equivalent to a pair of helical gears having equal helix angle secured together, one having a right-hand helix and the other a left-hand helix. The teeth of two rows are separated by a groove which is required for tool run out. The axial thrust which occurs in case of single-helical gears is eliminated in double helical gears. If the left and right inclinations of a double helical gear meet at a common apex and groove is eliminated in it, the gear is known as herringbone gear as shown in figure .

Figure : Herringbone Gears

Intersecting Shafts

The motion between two intersecting shafts is equivalent to rolling of two conical frustums from kinematical point of view. Straight Bevel Gears These gears have straight teeth which are radial to the point of intersection of the shaft axes. Their teeth vary in cross section through out their length. Generally, they are used to connect shafts at right angles. These gears are shown in figure. The teeth make line contact like spur gears.

Figure : Straight Bevel Gears As a special case, gears of the same size and connecting two shafts at right angle to each other are known as mitre gears. Spiral Bevel Gears When the teeth of a bevel gear are inclined at an angle to the face of the bevel, these gears are known as spiral bevel gears or helical bevel gears. A gear of this type is shown in figure (a). They run quiter in action and have point contact. If spiral bevel gear has curved teeth but with zero degree spiral angle, it is known as zerol bevel gear.

(a) Spiral Bevel Gear (b) Zerol Bevel Gear Figure : Spiral Bevel Gears Crossed-Helical Gears or Spiral Gears They can be used for any two shafts at any angle as shown in figure by a suitable choice of helix angle. These gears are used to drive feed mechanisms on machine tool.

Figure : Spiral Gears in Contact

GEAR TERMINOLOGY

Before considering kinematics of gears we shall define the terms used for describing the shape, size and geometry of a gear tooth. The definitions given here are with respect to a straight spur gear. Pitch Circle or Pitch Curve

It is the theoretical curve along which the gear rolls without slipping on the corresponding pitch curve of other gear for transmitting equivalent motion. Pitch Point It is the point of contact of two pitch circles. Pinion It is the smaller of the two mating gears. It is usually the driving gear. Rack It is type of the gear which has infinite pitch circle diameter. Circular Pitch

It is the distance along the pitch circle circumference between the corresponding points on the consecutive teeth. It is shown in figure.

Figure: Gear Terminology

If d is diameter of the pitch circle and ‘T’ be number of teeth, the circular pitch (pc) is given by 휋푑 푝푐 = 푇

Diamental Pitch

It is defined as the number of teeth per unit pitch circle diameter. Therefore, diametral pitch (pd) can be expressed as 푇 푝 = 푑 푑

pc pd = 

Module

It is the ratio of the pitch circle diameter to the number of teeth. Therefore, the module (m) can be expressed as

Addendum Circle and Addendum

It is the circle passing through the tips of gear teeth and addendum is the radial distance between pitch circle and the addendum circle.

Dedendum Circle and Dedendum

It is the circle passing through the roots of the teeth and the dedendum is the radial distance between root circle and pitch circle.

Full Depth of Teeth and Working Depth

Full depth is sum of addendum and dedendum and working depth is sum of addendums of the two gears which are in mesh.

Tooth Thickness and Space Width

Tooth thickness is the thickness of tooth measured along the pitch circle and space width is the space between two consecutive teeth measured along the pitch circle. They are equal to each other and measure half of circular pitch.

Top Land and Bottom Land

Top land is the top surface of the tooth and the bottom land is the bottom surface between the adjacent fillets.

Face and Flank

Tooth surface between the pitch surface and the top land is called face whereas flank is tooth surface between pitch surface and the bottom land.

GEAR TRAIN

A gear train is combination of gears that is used for transmitting motion from one shaft to another.

There are several types of gear trains. In some cases, the axes of rotation of the gears are fixed in space. In one case, gears revolve about axes which are not fixed in space.

Simple Gear Train

In this gear train, there are series of gears which are capable of receiving and transmitting motion from one gear to another. They may mesh externally or internally. Each gear rotates about separate axis fixed to the frame. figure shows two gears in external meshing and internal meshing.

Let t1, t2 be number of teeth on gears 1 and 2.

+ + P

(a) External Meshing (b) Internal Meshing Let N1, N2 be speed in rpm for gears 1 and 2. The velocity of P,

Referring figure, the two meshing gears in external meshing rotate in opposite sense whereas in internal meshing they rotate in same sense. In simple gear train, there can be more than two gears also as shown in figure.

Figure : Gear Train

Let N1, N2, N3, . . . be speed in rpm of gears 1, 2, 3, . . . etc., and t1, t2, t3, . . . be number of teeth of respective gears 1, 2, 3, . . . , etc. In this gear train, gear 1 is input gear, gear 4 is output gear and gears 2, 3 are intermediate gears. The gear ratio of the gear train is give by

This expression indicates that the intermediate gears have no effect on gear ratio. These intermediate gears fill the space between input and output gears and have effect on the sense of rotation of output gear.

Compound Gear Train In this type of gear train, at least two gears are mounted on the same shaft and they rotate at the same speed. This gear train is shown in figure where gears 2 and 3 are mounted on same shaft and they rotate at the same speed, i.e.

N2 = N3

4 1 3

Figure : Compound Gear Train

Let N1, N2, N3, . . . be speed in rpm of gears 1, 2, 3, . . . , etc. and t1, t2, t3, . . . , etc. be number of teeth of respective gears 1, 2, 3, . . . , etc.

Therefore, unlike simple gear train the gear ratio is contributed by all the gears. This gear train is used in conventional automobile gear box

Casting Terms

1. Flask or molding box: A frame made of metal or wood or plastic, in which the mold is formed. Lower molding flask is known as drag, upper molding flask as cope and intermediate molding flask, used in three piece molding, is known as cheek.

2. Pattern: The replica of the object to be cast is known as pattern. The cavity in the mould is created with the help of the pattern.

3. Parting line: The dividing line between the two molding boxes that makes up the mold.

4. Molding sand: Sand, which is sued for making the mould is called as molding sand. It is a mixture of silica sand, clay, and moisture in appropriate proportions. The molding sand must possess various properties such as permeability, flow ability, cohesive strength, etc.

5. Facing sand: In order to give a better surface finish to the casting, a small amount of fine carbonaceous material, known as facing sand, is usually sprinkled on the paring surfaces of the molding boxes.

6. Core: The part of mold, made of sand, used to create openings and various shaped cavities in the castings.

7. Pouring basin: A funnel shaped cavity at the top of the mold into which the molten metal is poured.

8. Sprue: The passage through which the molten metal flows from the pouring basin, and reaches the mold cavity. It controls the flow of metal into the mold.

9. Runner: The channel through which the molten metal is carried from the sprue to the gate.

10. Gate: A passageway through which the molten metal enters the mold cavity.

11. Chaplets: Chaplets are used to support the cores inside the mold cavity. The chaplets are used to prevent the core against buckling or metallostatic pressure.

12. Riser: The shapes of the Risers are like a sprue, which are placed at that part of the casting which is solidified in the last. the risers takes care of the shrinkage of the solidifying metal.

13. Vent: Small opening in the mold to facilitate escape of air and gases.

14. Drag: The bottom half of a horizontally parted mold.

15. Cope: The top half of a horizontally parted mold.

Fig: Mold Section showing some casting terms

Steps in Making Sand Castings

There are five basic steps in producing a sand castings:

1. Pattern making

2. Core making

3. Mold preparation

4. Melting of metal and its pouring

5. Finishing of casting

Flow diagram to produce a sand casting g is shown in following Figure

Fig: The Flow diagram to produce a casting

Pattern: In casting process, pattern is a replica of the object to be cast. It is used to prepare the cavity into the mould and to which molten material will be poured. Patterns used in sand casting may be made of wood, metal, plastics or other materials. Types of patterns: Following re the important type of patterns.

• Single Piece or solid pattern • Loose-piece Pattern • Match plate pattern • Gated Pattern • Sweep Pattern 1. Single-piece or solid pattern- Solid pattern is made of single piece without joints, partings lines or loose pieces. It is the simplest form of the pattern.

Fig: Single piece pattern

Fig: Loose piece pattern

3. Match plate pattern- This pattern is made in two halves and is on mounted on the opposite sides of a wooden or metallic plate, known as match plate. The gates and runners are also attached to the plate. This pattern is used in machine molding.

Fig: Match plate pattern

4. Gated Pattern: A gated pattern consists of casting patterns, pattern and stripping plates, core boxes, patterns of parts of the gating, molding and control patterns, jigs, and drying plates. Specialized flasks are also included in gated patterns.

Fig: Gated pattern

Fig: Sweep pattern

Pattern allowances: Following are important allowances that is given to patterns • Shrinkage allowance • Draft or Taper allowance • Machining Allowance • Distortion or Camber allowance • Raping or shaking allowance 1. Shrinkage Allowance: It is defined in DIN EN 12890 and specifies the difference in length of cast parts between casting mold and casting. Only linear shrinkage is taken into account. It depends on the type of casting material, construction as well as the stability of the mold during solidification and shrinkage. 2. Draft or Taper allowance: In engineering, draft is the amount of taper for molded or cast parts perpendicular to the parting line. It can be measured in degrees or mm/mm (in/in) ...... By tapering the sides of the mold by an appropriate "draft angle", for instance 2° (two degrees), the mold will be easier to remove.

Fig: Draft or Taper allowances

3. Machining Allowance: This refers to those allowances required on surfaces to be machined in order to remove casting-related inclusions in the casting skin or due to the effects of surface roughness and geometrical inaccuracies and to correct production-related dimensional variations 4. Distortion or Camber allowance: distortion or Camber Allowance Points : Distortion or Camber Allowance, Metal Casting, Foundry, Moulding Sometimes castings obtain unclear, through solidification, due to their usual shape

Fig: Distortion or camber allowances

5. Raping or shaking allowance hake allowance: A patter is shaken or rapped by striking the same with a wooden piece from side to side. This is done so that the pattern a little is loosened in the mold cavity and can be easily removed. In turnherefore, rapping enlarges the mould cavity which results in a bigger sized casting

Casting Defects: It is an unwanted irregularity that appears in the casting during metal casting process. There is various reason or sources which is responsible for the defects in the cast metal. Here in this blog we will discuss all the major types of casting defects. Some of the defects produced may

1. Gas Porosity: Blowholes, open holes, pinholes 2. Shrinkage defects: shrinkage cavity 3. Mold material defects: Cut and washes, swell, drops, metal penetration, rat tail 4. Pouring metal defects: Cold shut, misrun, slag inclusion 5. Metallurgical defects: Hot tears, hot spot.

1. Shift or Mismatch: The defect caused due to misalignment of upper and lower part of the casting and misplacement of the core at parting line. Cause : (1) Improper alignment of upper and lower part during mold preparation. (2) Misalignment of flask (a flask is type of tool which is used to contain a mold in metal casting. it may be square, round, rectangular or of any convenient shape.) Remedies (i) Proper alignment of the pattern or die part, molding boxes. (ii) Correct mountings of pattern on pattern plates. (iii) Check the alignment of flask.

2. Swell : It is the enlargement of the mold cavity because of the molten metal pressure, which results in localised or overall enlargement of the casting. Causes (i) Defective or improper ramming of the mold. Remedies (i) The sand should be rammed properly and evenly.

3. Blowholes: When gases entrapped on the surface of the casting due to solidifying metal, a rounded or oval cavity is formed called as blowholes. These defects are always present in the cope part of the mold. Causes : (i) Excessive moisture in the sand. (ii) Low Permeability of the sand. (iii) Sand grains are too fine. (iv) Too hard rammed sand. (v) Insufficient venting is provided. Remedies : (i) The moisture content in the sand must be controlled and kept at desired level. (ii) High permeability sand should be used. (iii) Sand of appropriate grain size should be used.

4. Drop: Drop defect occurs when there is cracking on the upper surface of the sand and sand pieces fall into the molten metal. Causes : (i) Soft ramming and low strength of sand. (ii) Insufficient fluxing of molten metal. Fluxing means addition of a substance in molten metal to remove impurities. After fluxing the impurities from the molten metal can be easily removed. (iii) Insufficient reinforcement of sand projections in the cope. Remedies : (i) Sand of high strength should be used with proper ramming (neither too hard nor soft). (ii) There should be proper fluxing of molten metal, so the impurities present in molten metal is removed easily before pouring it into the mold. (iii) Sufficient reinforcement of the sand projections in the cope.

5. Metal Penetration These casting defects appear as an uneven and rough surface of the casting. When the size of sand grains is larges, the molten fuses into the sand and solidifies giving us metal penetration defect. Causes : (i) It is caused due to low strength, large grain size, high permeability and soft ramming of sand. Because of this the molten metal penetrates in the molding sand and we get rough or uneven casting surface. Remedies : (ii) This defect can be eliminated by using high strength, small grain size, low permeability and soft ramming of sand.

6. Pinholes: They are very small holes of about 2 mm in size which appears on the surface of the casting. This defect happens because of the dissolution of the hydrogen gases in the molten metal. When the molten metal is poured in the mold cavity and as it starts to solidify, the solubility of the hydrogen gas decreases and it starts escaping out the molten metal leaves behind small number of holes called as pinholes. Causes : (i) Use of high moisture content sand. (ii) Absorption of hydrogen or carbon monoxide gas by molten metal. (iii) Pouring of steel from wet ladles or not sufficiently gasified. Remedies : (i) By reducing the moisture content of the molding sand. (ii) Good fluxing and melting practices should be used. (iii) Increasing permeability of the sand. (iv) By doing rapid rate of solidification.

8. Cold Shut It is a type of surface defects and a line on the surface can be seen. When the molten metal enters into the mold from two gates and when these two streams of molten metal meet at a junction with low temperatures than they do not fuse with each other and solidifies creating a cold shut (appear as line on the casting). It looks like a crack with round edge. Causes: (i) Poor gating system (ii) Low melting temperature (iii) Lack of fluidity Remedies: (i) Improved gating system. (ii) Proper pouring temperature.

9. Misrun When the molten metal solidifies before completely filling the mold cavity and leaves a space in the mold called as misrun. Causes: (i) Low fluidity of the molten metal. (ii) Low temperature of the molten metal which decreases its fluidity. (iii) Too thin section and improper gating system. Remedies (i) Increasing the pouring temperature of the molten metal increases the fluidity. (ii) Proper gating system (iii) Too thin section is avoided.

10. Slag Inclusion This defect is caused when the molten metal containing slag particles is poured in the mold cavity and it gets solidifies. Causes : (i) The presence of slag in the molten metal

• Natural molding sand: This is ready for use as it is dug from the ground. Good natural molding sand is obtained from Albany, New York etc. The following average compositions are seen in natural molding sand: 65.5% silica grains, 21.7% clay content, 12.8% undesirable impurities. Too much clay content and other impurities fill up the gaps between the sand grains. This will hinder the necessary passage of steam and other gases during pouring of the mold.

• Synthetic molding sand: Synthetic molding sand is made by mixing together specially selected high quality clay free silica, with about 5% of clay. They are tailor made to give most desirable results. Some of the advantages of synthetic molding sand are: 1. Refractory grain sizes are more uniform, 2. Higher refractoriness (= 3000oF), 3. less bonding agent is required (about 1/3rd of the clay percentage found in natural molding sand), 4. More suitable for use with mechanical equipment Advantages of natural molding sand: 1. moisture content range is wide, 2. molds can be repaired easily

Casting Furnaces 1. Induction Furnaces As the name implies, these furnaces use induction technology with alternating electric currents to achieve the required melting temperature of the metal.

Induction furnaces are widely used in foundries because they are high quality, easy to operate and energy efficient. A further advantage of this type of furnace is that it can melt both small quantities of less than 1 kg up as well as larger volumes of up to 100 tons. An inductor, i.e. a cooled coil, transfers the energy into the molten material. These coils are specially adapted and manufactured to suit the respective furnace shape or individual work pieces. The water- cooled inductor is located outside the electrically non-conductive crucible.

The crucible is placed above a heat source to melt the metal and additives it contains. The sizes of the crucibles vary greatly. There are also differences in the design and heating system of the furnaces. Apart from movable and fixed crucible furnaces, there are tillable and fixed crucible furnaces. A distinction must also be made between resistance-heated and fuel-heated furnaces.

3. Cupola Furnace: Cupola furnaces have been used in foundries for a long time. Characteristic of these furnaces is the high, cylindrically shaped chimney, which in turn is lined with clay, bricks and blocks to protect the interior of the furnace from the enormous heat, abrasion and oxidation. For the melting process, several layers of ferroalloys, coke and limestone are placed in the furnace before the metal is added. This results in a chemical reaction in which the impurities in the furnace float on the surface of the metal.

In practice, only a few foundries still use cupola furnaces, as the more energy-efficient induction furnaces have prevailed over the classic cupola furnaces.

4. Electric Arc Furnaces The electric arc furnace is an electric furnace in which an electric arc generates the heat required to melt the metal. To this end, carbon electrodes are used. In practice, electric arc furnaces are primarily used for melting steel scrap that is used to manufacture new produces.

WHAT IS FORGING?

Forging is a manufacturing process involving the shaping of a metal through hammering, pressing, or rolling. These compressive forces are delivered with a hammer or die. Forging is often categorized according to the temperature at which it is performed—cold, warm, or hot forging.

A wide range of metals can be forged. Typical metals used in forging include carbon steel, alloy steel, and stainless steel. Very soft metals such as aluminum, brass, and copper can also be forged. The forging process can produce parts with superb mechanical properties with minimum waste. The basic concept is that the original metal is plastically deformed to the desired geometric shape—giving it higher fatigue resistance and strength. The process is economically sound with the ability to mass produce parts, and achieve specific mechanical properties in the finished product.

HISTORY OF FORGING

Forging has been practiced by smiths for thousands of years. At first, bronze and copper were the most common forged metals, in the Bronze Age: later, as the ability to control temperature and the process of smelting iron was discovered, iron became the primary forged metal. Traditional products include kitchenware, hardware, hand tools, and edged weapons. The Industrial Revolution allowed forging to become a more efficient, mass-production process. Since then, forging has evolved along with advances in equipment, robotics, electronic controls, and automation. Forging is now a worldwide industry with modern forging facilities producing high-quality metal parts in a vast array of sizes, shapes, materials, and finishes.

FORGING METHODS

There are several forging methods with different capabilities and benefits. The more commonly used forging methods include the drop forging methods, as well as roll forging.

Drop forging

Drop forging derives its name from the process of dropping a hammer onto the metal to mold it into the shape of the die. The die refers to the surfaces that come into contact with the metal. There are two types of drop forging—open-die and closed-die forging. Dies are typically flat in shape with some having distinctively shaped surfaces for specialized operations.

Open-die forging (smith forging)

Open-die forging is also known as smith forging. A hammer strikes and deforms a metal on a stationary anvil. In this type of forging, the metal is never completely confined in the dies—allowing it to flow except for the areas where it is in contact with the dies. It is the operator’s responsibility to orient and position the metal to achieve the desired final shape. Flat dies are used, with some having specially shaped surfaces for specialized operations. Open-die forging is suitable for simple and large parts, as well as customized metal components.

Advantages of open-die forging:

• Better fatigue resistance and strength

• Reduces chance of error and/or holes

• Improves microstructure

• Continuous grain flow

• Finer grain size

Closed-die forging (impression-die)

Closed-die forging is also known as impression-die forging. The metal is placed in a die and attached to an anvil. The hammer is dropped onto the metal, causing it to flow and fill the die cavities. The hammer is timed to come into contact with the metal in quick succession on a scale of milliseconds. Excess metal is pushed out from the die cavities, resulting in flash. The flash cools faster than the rest of the material, making it stronger than the metal in the die. After forging, the flash is removed.

In order for the metal to reach the final stage, it is moved through a series of cavities in a die:

1. Edging impression (also known as fulleringor bending) The first impression used to mold the metal into a rough shape.

2. Blocking cavities Themetal is worked into a shape that more closely resembles the final product. The metal is shaped with generous bends and fillets.

3. Final impression cavity Final stage of finishing and detailing the metal into the desired shape.

Advantages of closed-die forging:

• Produces parts up to 25 tons • Produces near net shapes that require only a small amount of finishing • Economic for heavy production

Roll forging

Roll forging consists of two cylindrical or semi-cylindrical horizontal rolls that deform a round or flat bar stock. This works to reduce its thickness and increase its length. This heated bar is inserted and passed between the two rolls—each containing one or more shaped grooves—and is progressively shaped as it is rolled through the machine. This process continues until the desired shape and size is achieved.

Advantages of automatic roll forging:

• Produces little to no material waste • Creates a favorable grain structure in the metal

Press forging

Press forging uses a slow, continuous pressure or force, instead of the impact used in drop-hammer forging. The slower ram travel means that the deformation reaches deeper, so that the entire volume of the metal is uniformly affected. Contrastingly, in drop-hammer forging, the deformation is often only at the surface level while the metal’s interior stays somewhat undeformed. By controlling the compression rate in press forging, the internal strain can also be controlled.

Advantages of press forging:

• Economic for heavy production • Greater accuracy in tolerances within 0.01–0.02 inch • Dies have less draft allowing for better dimensional accuracy • Speed, pressure, and travel of the die are automatically controlled • Process automation is possible • Capacity of presses range from 500–9000 tons

UPSET FORGING

Upset forging is a manufacturing process that increases the diameter of the metal by compressing its length. Crank presses, a special high-speed machine, are used in upset forging processes. Crank presses are typically set on a horizontal plane to improve efficiency and the quick exchange of metal from one station to the next. Vertical crank presses or a hydraulic press are also options.

Advantages of upset forging:

• High production rate of up to 4500 parts per hour • Full automation is possible • Elimination of the forging draft and flash • Produces little to no waste

In automatic hot forging, mill-length steel bars are inserted into one end of the forging machine at room temperature, and hot forged products emerge from the other end. The bar is heated with high-power induction coils to a temperature ranging from 2190–2370°F in under 60 seconds. The bar is descaled with rollers and shared into blanks. At this point, the metal is transferred through several forming stages that can be coupled with high-speed cold-forming operations. Typically, the cold-forming operation is left for the finishing stage. By doing so, the benefits of cold-working can be reaped while also maintaining the high speed of automatic hot forging.

Advantages of automatic hot forging:

• High output rate • Acceptance of low-cost materials • Minimal labor required to operate machinery • Produces little to no material waste (material savings between 20–30% over conventional forging)

Precision forging (net-shape or near-net-shape forging)

Precision forging requires little to no final machining. It is a forging method developed to minimize the cost and waste associated to post-forging operations. Cost savings are achieved from the reduction of material and energy, as well as the reduction of machining.

Isothermal forging

Isothermal forging is a forging process where the metal and die are heated to the same temperature. Adiabatic heating is used—there is no net transfer of mass or thermal exchange between the system and the external environment. The changes are all due to internal changes resulting in highly controlled strain rates. Due to the lower heat loss, smaller machines may be used for this forging process.

What is Extrusion:

Extrusion is a metal forming process in which metal or work piece is forced to flow through a die to reduce its cross section or convert it into desire shape. This process is extensively used in pipes and steel rods manufacturing. The force used to extrude the work piece is compressive in nature. This process is similar to drawing process except drawing process uses tensile stress to extend the metal work piece. The compressive force allows large deformation compare to drawing in single pass. The most common material extruded are plastic and aluminum. Working Principle: Extrusion is a simple compressive metal forming process. In this process, piston or plunger is used to apply compressive force at work piece. These process can be summarized as follow.

• First billet or ingot (metal work piece of standard size) is produced. • This billet is heated in hot extrusion or remains at room temperature and placed into a extrusion press (Extrusion press is like a piston cylinder device in which metal is placed in cylinder and pushed by a piston. The upper portion of cylinder is fitted with die). • Now a compressive force is applied to this part by a plunger fitted into the press which pushes the billet towards die. • The die is small opening of required cross section. This high compressive force allow the work metal to flow through die and convert into desire shape. • Now the extruded part remove from press and is heat treated for better mechanical properties. This is basic working of extrusion process.

Types of Extrusion:

Extrusion process can be classified into following types.

According to the direction of flow of metal Direct Extrusion: In this type of extrusion process, metal is forced to flow in the direction of feed of punch. The punch moves toward die during extrusion. This process required higher force due to higher friction between billet and container.

Indirect Extrusion: In this process, metal is flow toward opposite direction of plunger movement. The die is fitted at opposite side of punch movement. In this process, the metal is allowed to flow through annular space between punch and container.

Hydrostatic Extrusion: This process uses fluid to apply pressure on billet. In this process, the friction is eliminated because the billet is neither contact with cylinder wall or plunger. There is a fluid between the billet and plunger. The plunger applies force on fluid which further applied on billet. Normally vegetable oils are used as fluid.This process accomplished by leakage problem and uncontrolled speed of extrusion.

According to the working temperature Hot Extrusion: If the extrusion process takes place above recrystallization temperature which is about 50-60% of its melting temperature, the process is known as hot extrusion.

Advantages:

• Low force required compare to cold working. • Easy to work in hot form. • The product is free from stain hardening. Disadvantages:

• Low surface finish due to scale formation on extruded part. • Increase die wear. • High maintenance required. Cold Extrusion: If the extrusion process takes place below crystallization temperature or room temperature, the process is known as cold extrusion. Aluminum cans, cylinder, collapsible tubes etc. are example of this process.

Advantages:

• High mechanical properties. • High surface finish • No oxidation at metal surface. Disadvantages:

Introduction: Metal Joining

The manufacturing technology primarily involves sizing, shaping and imparting desired combination of the properties to the material so that the component or engineering system being produced to perform indented function in design life. A wide range of manufacturing processes have been developed in order to produce the engineering components of very simple to complex geometries using materials of different physical, chemical, mechanical and dimensional properties. There are four chief manufacturing processes i.e. casting, forming, machining and welding. Selection of suitable manufacturing process is dictated by complexity of geometry of the component and number of units to be produced, properties of the materials (physical, chemical, mechanical and dimensional properties) to be processed. Based on the approach used for obtaining desired size and shape by different manufacturing processes these can be termed as positive, negative and or zero processes.

• Casting: zero process • Forming: zero process • Machining: negative process • Joining (welding): positive process

Casting and forming are categorized as zero processes as they involve only shifting of metal in controlled (using heat and pressure singly or in combination) way to get the required size and shape of product from one region to another. Machining is considered as a negative process because unwanted material from the stock is removed in the form of small chips during machining for the shaping purpose. During manufacturing it is frequently required to join the simple shape components to get desired product. Since simple shape components are brought together by joining in order to obtain desired shape of end useable product therefore joining is categorized as a positive process.

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Schematic diagrams of few typical manufacturing processes.

Selection of welding process

A wide range of welding processes are available in the market (Table 1). These were developed over a long period of time. Each process differs in respect of their ability to apply heat for fusion, protection of the weld metal and so their effect on performance of the weld joint. However, selection of a particular process for producing a weld joint is dictated by the size and shape of the component to be manufactured, the metal system to be welded, availability of consumables and machines, precision required and economy. Whatever process is selected for developing weld joint it must be able to perform the intended function for designed life. Welding processes with their field of applications are given below:

• Resistance welding: Automobile • Thermite welding: Rail joints in railways

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• Tungsten inert gas welding: Aerospace and nuclear reactors • Submerged arc welding: Heavy engineering, ship work • Gas metal arc welding: Joining of metals (stainless steel, aluminium and magnesium) sensitive to atmospheric gases

Advantages and Limitation of Welding as a Fabrication Technique

Welding is mainly used for the production of comparatively simple shape components. It is the process of joining the metallic components with or without application of heat, pressure and filler metal. Application of welding in fabrication offers many advantages, however; it suffers with few limitations also. Some of the advantage and limitations are given below.

Advantages of welding are enlisted below:

• Permanent joint is produced, which becomes an integral part of work piece. • Joints can be stronger than the base metal if good quality filler metal is used. • Economical method of joining. • It is not restricted to the factory environment.

Disadvantages of welding are enlisted also below:

• Labour cost is high as only skilled welder can produce sound and quality weld joint. • It produces the permanent joint so creates the problem in dissembling if required. • Hazardous fumes and vapors are generated so proper ventilation of welding area becomes mandatory. • Weld joint itself is considered as a discontinuity owing to variation in structure, composition and mechanical properties; therefore welding is not commonly used for critical application where there is danger of life.

Applications of welding

General applications

• Presently welding is being widely used in fabrication of pressure vessels, bridges, building structures, aircraft and space crafts, railway coaches and general applications

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besides shipbuilding, automobile, electrical, electronic and defense industries, laying of pipe lines and railway tracks and nuclear installations. • Specific components need welding for fabrication includes • Transport tankers for transporting oil, water, milk and • Welded tubes and pipes, chains, LPG cylinders and other items. • Steel furniture, gates, doors and door frames, andbody • White goods items such as refrigerators, washing machines, microwave ovens and many other items of generalapplications

The requirement of the welding for specific area of the industry is given in following section.

• Welding is also used for joining of pipes, during laying of crude oil and gas pipelines, construction of tankers for their storage and transportation. Offshore structures, dockyards, loading and unloading cranes are also produced by welding. • Nuclear Industry • Spheres for nuclear reactor, pipe line bends joining two pipes carrying heavy water require welding for safe and reliableoperations. • Defense industry • Defense industry requires welding for joining of many components of war equipment. Tank body fabrication, joining of turret mounting to main body of tanks are typical examples of applications of welding. • Electronic industry • Electronic industry uses welding to limited extent such as for joining leads of special transistors but other joining processes such as brazing and soldering are widely being used. • Soldering is used for joining electronic components to printed circuit boards (PCBs). • Robotic soldering is very common for joining of parts to printed circuit boards of computers, television, communication equipment and other control equipment etc. • Electrical Industry • Starting from generation to distribution and utilization of electrical energy, welding plays important role. • Components of both hydro and steam power generation system, such as penstocks, water control gates, condensers, electrical transmission towers and distribution system equipment are fabricated by welding. Turbine blades and cooling fins are also joined by welding.

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• Surface transport • Railways: Railways use welding extensively for fabrication of coaches and wagons, repair of wheel, laying of new railway tracks by mobile flash butt welding machines and repair of cracked/damaged tracks by thermite welding. • Automobiles: Production of automobile components like chassis, body and its structure, fuel tanks and joining of door hinges require welding. • Aerospace Industry • Aircraft and Spacecraft: Similar to ships, aircrafts were produced by riveting in early days but with the introduction of jet engines welding is widely used for aircraft structure and for joining of skin sheet tobody. • Space vehicles which have to encounter frictional heat as well as low temperatures require outer skin and other parts of special materials. These materials are welded with full success for achieving safety and reliability. • Ship Industry • Ships were produced earlier by riveting. Welding found its place in ship building around 1920 and presently all welded ships are widely used. Similarly submarines are also produced by welding. • Construction industry • Arc welding is used for construction of steel building leading to considerable savings in steel and money. • In addition to building, huge structures such as steel towers also require welding for fabrication.

Classification of Welding Processes I

Welding is a process of joining metallic components with or without application of heat, with or without pressure and with or without filler metal. Various welding processes have been developed so far. Welding processes can be classified on the basis of following criteria: • Welding with or without filler material • Source of energy for welding • Arc and non-arc welding • Fusion and pressure welding 1. Welding with or without filler material

A weld joint can be developed just by melting of edges (faying surfaces) of plates or sheets to be welded especially in case of thin sheet usually of less than 5 mm thickness. This type of weld is termed as “autogenous weld”. The composition of the autogenous weld metal corresponds to

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the base metal only. However, autogenous weld can be crack sensitive when solidification temperature range of the base metal to be welded is significantly high. Following are typical processes in which filler metal is generally not used to produce a weld joint. • Laser beam welding • Electron beam welding • Resistance welding, • Friction stir welding

However, for welding thicker plates/sheets using any of the following processes filler metal can be used as per needs which is primarily dictated by thickness of plates. Application of autogenous weld under such conditions may result in concave weld or under fill like discontinuity in weld joint. The composition of the filler metal can be similar to that of base metal or different one accordingly weld joints are categorized as homogeneous or heterogeneous weld.

In case of autogenous and homogeneous welds, solidification occurs directly by growth mechanism without nucleation stage. This type of solidification is called epitaxial solidification. The autogenous and homogeneous welds are considered to be lesser prone to the development of weld discontinuities than heterogeneous weld because of uniformity in composition and if solidification occurs largely at a constant temperature. Metal systems having wider solidification temperature range show issues related with solidification cracking and partial melting tendency. The solidification in heterogeneous welds takes place in two stages i.e. nucleation and growth. Following are few fusion welding processes where filler may or may not be used for developing weld joints:

• Plasma arc welding • Gas tungsten arc welding • Gas welding

Some of the welding processes are inherently designed produce a weld joint by applying heat for melting and filler metal both. These processes are mostly used for welding of thick plates (usually > 5mm) with high deposition rate.

• Metal inert gas welding: (with filler) • Submerged arc welding: (with filler) • Flux cored arc welding: (with filler) • Electro gas/slag welding: (with filler)

Comments on classification of welding processes based on with/without filler

The gas welding process was the only fusion welding process earlier in which joining could be achieved with or without filler material. The gas welding performed without filler material was

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termed as autogenous welding. However, with the development of tungsten inert gas welding, electron beam, laser beam and many other welding processes such classification created confusion as many processes were falling in both the categories.

Source of energy of welding

Almost all weld joints are produced by applying energy in one or other form to develop atomic/metallic bond between plates being joined and the same is achieved either by melting the faying surfaces using heat or applying pressure either at room temperature or high temperature. Based on the type of energy being used for creating metallic bonds between the components to be welded, welding processes can be grouped as under:

• Chemical energy: gas welding, explosive welding, thermite welding • Mechanical energy: Friction welding, ultrasonic welding • Electrical energy: Arc welding, resistance welding • Radiation energy: Laser beam welding, electron beam welding

Comments on classification of welding processes based on form of energy Energy in various forms such as chemical, electrical, light, sound, mechanical energies etc. are used for developing weld joints. However, except chemical energy all other forms of energies are generated from electrical energy for welding. Hence, categorization of the welding processes based on the form of energy criterion also does not justify classification properly.

1. Arc or Non-arc welding

Metallic bond between the plates to be welded can be developed either by using heat for complete melting of the faying surfaces then allowing it to solidify or by apply pressure on the components to be joined for mechanical interlocking. All those welding processes in which heat for melting the faying surfaces is provided after establishing an arc between the base plate and an electrode are grouped under arc welding processes. Another set of welding processes in which metallic bond is produced using pressure or heat generated from sources other than arc namely chemical reactions or frictional effect etc., are grouped as non-arc based welding processes. Welding processes corresponding to each group are given below.

• Arc based welding processes • Shielded Metal Arc Welding: Arc between base metal and covered • electrode • Gas Tungsten Arc Welding: Arc between base metal and tungsten electrode • Plasma Arc Welding: Arc between base metal and tungsten electrode • Gas Metal Arc Welding: Arc between base metal and consumable electrode • Flux Cored Arc Welding: Arc between base metal and consumable electrode

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• Submerged Arc Welding: Arc between base metal and consumable electrode

Non-arc based welding processes

• Resistance welding processes: uses electric resistance heating • Gas welding: uses heat from exothermic chemical reactions • Thermit welding: uses heat from exothermic chemical reactions • Ultrasonic welding: uses both pressure and frictional heat • Diffusion welding: uses electric resistance/induction heating to facilitate diffusion • Explosive welding: involves pressure • Comments on classification of welding processes based on arc or non arc based process

Arc and non-arc welding processes classification leads to grouping of all the arc welding processes in one class and all other processes in non-arc welding processes. However, welding processes such as electro slag welding (ESW) and flash butt welding were found difficult to classify to either of the two classes as in ESW process starts with arcing and subsequently on melting of sufficient amount flux the arc extinguishes and heat for melting of base metal is generated by electrical resistive heating by flow of current through molten flux. In flash butt welding, tiny arcs i.e. sparks are established during the welding followed by pressing of components against each other. Therefore, such classification is also found not perfect.

2 Pressure or Fusion welding

Welding processes in which heat is primarily applied for melting of the faying surfaces are called fusion welding processes while other processes in which pressure is primarily applied with little or no application of heat for softening of metal up to plastic state for developing metallic bonds are termed as solid state welding processes.

• Pressure welding • Resistance welding processes (spot, seam, projection, flash butt, arc stud welding) • Ultrasonic welding • Diffusion welding • Explosive welding • Fusion welding process • Gas Welding • Shielded Metal Arc Welding • Gas Metal Arc Welding • Gas Tungsten Arc Welding • Submerged Arc Welding • Electro Slag/Electro Gas Welding

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Comments on classification of welding processes based on Fusion and pressure welding

Fusion welding and pressure welding is most widely used classification as it covers all processes in both the categories irrespective of heat source and welding with or without filler material. In fusion welding, all those processes are included in which molten metal solidifies freely while in pressure welding, molten metal if any is retained in confined space (as in resistance spot welding or arc stud welding) and solidifies under pressure or semisolid metal cools under pressure. This type of classification poses no problems and therefore it is considered as the best criterion.

Classification of Welding Processes II

There is another way of classifying welding and allied processes which has been commonly reported in literature. Various positive processes involving addition or deposition of metal are first broadly grouped as welding process and allied welding processes as under:

• Welding processes • Cast weld processes • Fusion weld processes • Resistance weld processes • Solid state weld processes • Allied welding processes • Metal depositing processes • Soldering • Brazing • Adhesive bonding • Weld surfacing • Metal spraying

This approach of classifying the welding process is primarily based on the way metallic pieces are united together during welding such as

Availability and solidification of molten metal weld between components being joined are similar to that of casting, Fusion of faying surfaces for developing a weld, Heating of metal only to plasticize then applying pressure to forge them together Use pressure to produce a weld joint in solid state only.

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Cast welding process

Those welding processes in which either molten weld metal is supplied from external source or melted and solidified metal very slow during solidification like castings. Following are two common welding processes that are grouped under casting welding processes:

• Cast weld processes • Thermite welding • Electroslag welding

In case of thermite welding, weld metal is melted externally using exothermic heat generated by chemical reactions and supplied between the components to be joined while in electroslag welding weld metal is melted by electrical resistance heating and then allowed to cool very slowly for solidification similar to that of casting conditions.

Comments on classification based on cast weld processes

This classification is true for thermite welding where like casting melt is supplied from external source but in case of electroslag welding, weld metal obtained by melting of both electrode and base metal and is not supplied from the external source. Therefore, this classification is not perfect.

Fusion Weld Processes

Those welding processes in which faying surfaces of plates to be welded are brought to the molten state by applying heat and cooling rate experienced by weld metal in these processes are much higher than that of casting. The heat required for melting can be produced using electric arc, plasma, laser and electron beam and combustion of fuel gases. Probably this is un-disputed way of classifying few welding processes. Common fusion welding processes are given below:

• Fusion Weld Processes • Carbon arc welding • Shielded metal arc welding • Submerged arc welding • Gas metal arc welding • Gas tungsten arc welding • Plasma arc welding • Electrogas welding • Laser beam welding • Electron beam welding • Oxy-fuel gas welding

Resistance welding processes

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Welding processes in which heat required for softening or partial melting of base metal is generated by electrical resistance heating followed by application of pressure for developing weld joint. However, flash butt welding begins with sparks between components during welding instead of heat generation by resistance heating.

• Resistance welding processes • Spot welding • Projection welding • Seam welding • High frequency resistance welding • High frequency induction welding • Resistance butt welding • Flash butt welding • Stud welding

Solid state welding process

Welding processes in which weld joint is developed mainly by application of pressure and heat through various mechanism such as mechanical interacting, large scale interfacial plastic deformation and diffusion etc.. Depending up on the amount of heat generated during welding these are further categorized as under:

• Solid state welding process • Low heat input processes • Ultrasonic welding • Cold pressure welding • Explosion welding • High heat input processes • Friction welding • Forge welding • Diffusion welding

There are many ways to classify the welding processes however, fusion welding and pressure welding criterion is the best and most accepted way to classify all the welding processes.

Method of gas welding Gas Welding

It is a fusion welding in which strong gas flame is used to generate heat and raise temperature of metal pieces localized at the place where joint is to be made. In this welding metal pieces to be joined are heated. The metal thus melted starts flowing along the edges where joint is to be made. A

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filler metal may also be added to the flowing molten metal to fill up the cavity at the edges. The cavity filed with molten metal is allowed to solidify to get the strong joint. Different combinations of gases can be used to obtain a heating flame. The popular gas combinations are oxy-hydrogen mixture, oxygen-acetylene, etc. different mixing proportion of two gases in a mixture can generate different types of flames with different characteristics.

Oxy-Acetylene Welding

Oxy-acetylene welding can used for welding of wide range of metals and alloys. Acetylene mixed with oxygen when burnt under a controlled environment produces large amount of heat giving higher temperature rise. This burning also produces carbon dioxide which helps in preventing oxidation of metals being welded. Highest temperature that can be produced by this welding is 3200oC. The chemical reaction involved in burning of acetylene is

2C2H2 + 5O2 = 4CO2 + 2H2O + Heat on the basis of supply pressure of gases oxy-acetylene welding is categorized as high pressure welding in this system both gases oxygen and acetylene supplied to welding zone are high pressure from their respective high pressure cylinders. The other one is low pressure welding in which oxygen is supplied from high pressure cylinder but acetylene is generated by the action of water on calcium carbide and supplied at low pressure. In this case high pressure supply of oxygen pulls acetylene at the welding zone.A comparison can be drawn between low pressure and high pressure welding. High pressure welding equipment is handy, supplies pure acetylene at constant pressure, with better control and low expenses as compared to low pressure welding.

FLAME FORMATION AND ITS DIFFERENT TYPES

Flame is established by burning (controlled) of the two gases mixture at the outlet of blow pipe or torch. The proportion of gasses in the mixture is controlled by controlling the flow rate of each of the two gasses. Here, it should be clear that burning of acetylene generates heat and oxygen only supports acetylene in burning. Insufficient supply of oxygen leaves acetylene unburnt in atmosphere creating pollution and adding cost of waste acetylene. A general nomenclature of the flame established in oxy-acetylene welding is given in Figure 5.1. The flame can be divided in to three zones. Zone ‘1’ is very near to the outlet of torch, where oxygen reacts with acetylene and burning of two gases takes place. Zone ‘2’ produces carbon monoxide and hydrogen in ratio 2 : 1 by volume. This zone gives the highest temperature of the flame. This zone is suppose to consume the oxygen available here and contribute reducing properly to the flame.

Zone ‘3’ is the outermost zone of the flame. Temperature of this zone is comparatively low. This zone converts CO to CO2 and H2O vapours. On the basis of supply proportion of acetylene and

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oxygen, flames can be divided into three categories, neutral flame, carburizing flame and oxidizing flame. These are described here.

Neutral Flame

A neutral flame is obtained when equal amount of O2 and C2H2 are mixed and burnt at the outlet of welding torch. The flame consists of two sharply defined zones inner white flame cone outer envelope of blue colour as shown in Figure 5.2. In this flame none of two gasses is supplied in excess. This flame is of white cone and has the maximum use for successful welding of many metals.

Carburizing Flame

This flame is obtained when excess of acetylene is supplied than which is theoretically required. This flame is identified by three zones the inner cone which is not sharply defined, an outer envelope as same in case of neutral flamed and middle zone surrounds inner one extended to outer envelope. It is white in colour due to excess acetylene.

Larger the excess of acetylene larger will be its length. To get a neutral flame a systematic procedure is to make carburizing flame first and then increase oxygen supply gradually till the excess acetylene zone disappears. The resulting flame will a carburizing flame. Its temperature generation range is 3100oC to 3300oC. It is used for the welding of metals where risk of oxidation at elevated temperature is more like aluminium, its alloys and lead and its alloys. The metals which have tendency to absorb carbon should not be welded by carburizing flame as they become brittle localized.

Oxidizing Flame

This flame as an excess of oxygen over that required for a neutral flame. The ratio O2 : C2H2 = 1.15 to 1.50. To have this flame set carburizing flame first convert it to neutral flame and than reduce the supply of acetylene to get oxidizing flame. Its inner cone is relatively shorter and excess oxygen turns the flame to light blue colour. It burns with a harsh sound. It is used for metals which are not oxidized readily like brasses and bronzes.

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GAS WELDING TOOLS AND EQUIPMENTS

Tools and Equipment

Gas cylinders (two)

Hose pipes and valves

Cylinder pressure gauge

Outlet pressure gauge

Pressure regulators

Blow pipe or torch and spark lights

Welding screens

Goggles, screens, gloves and apron

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Wire brush, trolley, chipping hammer.

Consumables

Oxygen gas

Acetylene gas

Filler metal (rod or wire)

Fluxes.

Arc Welding

Electric arc welding is one of the fusion welding processes in which coalescence of the metal is achieved by the heat from an electric arc between an electrode and workpiece. Electric arc is generated when electrode is brought into contact with the work and is then quickly separated by a short distance approximately 2 mm. The circuit operates at low voltage and high current so arc is established in the gap due to thermoionic emission from electrode (Cathode) to workpiece (Anode). The arc is sustained due to continuous presence of a thermally ionized column of gas. This arc produces at temperature of the order of 5500oC or higher. In this way a pool of molten metal consisting of workpiece metal and filler metal is formed in the welding zone. The electrode is moved along the joint with perpendicular zig-zag motion. The solidified molten weld pool makes the strong welded joint.

Movement of the electrode relative to workpiece is accomplished by either manually or by mechanical means in case of automatic welding machines. Better uniformity and good quality weldments are possible in case of automatic welding process.

ARC WELDING EQUIPMENT

Facilitator Equipment

Power source (welding machine)

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Electrode holder

Work table

Cables (for connection)

Finishing devices like chipping, hammer, wire brush, etc.

Consumable Equipment

Electrode

Flux

Workpiece

Filler metal

Protecting Equipment

Welding shields

Goggles

Screens

Gloves

Apron

Soldering and Brazing Process

Soldering is very much similar to brazing and its principle is same as that of brazing. The major difference lies with the filler metal, the filler metal used in case of soldering should have the melting temperature lower than 450oC. The surfaces to be soldered must be pre-cleaned so that these are faces of oxides, oils, etc. An appropriate flux must be applied to the faying surfaces and then surfaces are heated. Filler metal called solder is added to the joint, which distributes between the closely fitted surfaces. Strength of soldered joint is much lesser than welded joint and les than a brazed joint.

SOLDERING METHODS

Hand Soldering Hand soldering is done manually using solder iron. Small joints are made by this way in very short duration approximately in one second. Wave Soldering Wave soldering is a mechanical and technique that allows multiple lead wires to be soldered to a Printed Circuit Board (PCB) as it passes over a wave of molten solder. In this process a PCB on which electronic components have been placed with their lead wires extending through the through the holes in the

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board, is loaded onto a conveyor for transport through the wave soldering equipment. The conveyor supports the PCB on its sides, so its underside is exposed to the processing steps, which consists of the following :(a)flux is applied through foaming, spraying, brushing, and (b)wave soldering is used pump liquid solder from a molten both on to the bottom of board to make soldering connections between lead wire and metal circuit on the board. Reflow Soldering This process is also widely used in electronics to assemble surface mount components to print circuit boards. In this process a solder paste consisting of solder powders in a flux binder is applied to spots on the board where electrical contacts are to be made between surface mount components and the copper circuit. The components are placed on the paste spots, and the board is heated to melt the solder, forming mechanical and electrical bonds between the component leads and the copper on the circuit board.

BRAZING PROCESSES orch Brazing In case of torch brazing, flux is applied to the part surfaces and a torch is used to focus flame against the work at the joint. A reducing flame is used to prevent the oxidation. Filler metal wire or rod is added to the joint. Torch uses mixture of two gases, oxygen and acetylene, as a fuel like gas welding. Furnace Brazing In this case, furnace is used to heat the workpieces to be joined by brazing operation. In medium production, usually in batches, the component parts and brazing metal are loaded into a furnace, heated to brazing temperature, and then cooled and removed. If high production rate is required all the parts and brazing material are loaded on a conveyer to pass through then into a furnace. A neutral or reducing atmosphere is desired to make a good quality joint. Induction Brazing Induction brazing uses electrical resistance of workpiece and high frequency current induced into the same as a source of heat generation. The parts are pre- loaded with filler metal and placed in a high frequency AC field. Frequencies ranging from 5 to 5000 kHz is used. High frequency power source provides surface heating, however, low frequency causes deeper heating into the workpieces. Low frequency current is recommended for heavier and big sections (workpieces). Any production rate, low to high, can be achieved by this process. Resistance Brazing In case of resistance welding the workpieces are directly connected to electrical ---- rather than induction of electric current line induction brazing. Heat to melt the filler metal is obtained by resistance to flow of electric current through the joint to be made. Equipment for resistance brazing is same that is used for resistance welding, only lower power ratings are used in this case. Filler metal into the joint is placed between the electrode before passing current through them. Rapid heating cycles can be achieved in resistance welding. It is recommended to make smaller joints. Dip Brazing In this case heating of the joint is done by immersing it into the molten soft bath or molten metal bath. In case of salt bath method, filler metal is pre-loaded to the joint and flux is contained in to the hot salt bath. The filler metal melts into the joint when it is submerged into the hot bath. Its solidification and formation of the joint takes place after taking out the workpiece from the bath. In case of metal bath method, the bath contains molten filler metal. The joint is applied with flux and dipped to the bath. Molten filler metal, fills the joint through capillary action. The joint forms after its solidification after taking it out from molten

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metal bath. Fast heating is possible in this case. It is recommended for making multiple joints in a single workpiece or joining multiple pairs of workpieces simultaneously. Infrared Brazing It uses infrared lamps. These lamps are capable of focused heating of very thin sections. They can generate upto 5000 watts of radiant heat energy. The generated heat is focused at the joint for brazing which are pre-loaded with filler metal and flux. The process is recommended and limited to join very thin sections. Braze Welding This process also resembles with welding so it is categorize as one of the welding process too. There is no capillary action between the faying surfaces of metal parts to fill the joint. The joint to be made is prepared as ‘V’ groove. a greater quantity of filler metal is deposited into the same as compared to other brazing processes. In this case entire ‘V’ groove is filled with filler metal, no base material melts. Major application of braze welding is in repair works.

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Heat Treatment:-

• Heat treating is a group of industrial and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. • The most common application is metallurgical.Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material.

STAGES of HEAT TREATMENT :-

Heat treatment in three major stages:

• Stage l — Heat the metal slowly to ensure a uniform temperature.

• Stage 2 — Soak (hold) the metal at a given temperature for a given time.

• Stage 3 — Cool the metal to room temp

Classification of Heat Treatment Processes

Various heat treatment processes can be classified as follows:

1. Annealing.

2. Normalizing.

3. Hardening.

4. Tempering.

5. Case hardening.

Annealing:-

Annealing involves heating the material to a predetermined temperature and hold the material at the temperature and cool the material to the room temperature slowly.

The process involves:

1) Heating of the material at the elevated or predetermined temperature

2) Holding the material (Soaking) at the temperature for longer time.

3) Very slowly cooling the material to the room temperature.

Purpose of Annealing:

The various purpose of these heat treatments is to:

1)Relieve Internal stresses developed during solidification, machining, forging, rolling or welding,

2 )Improve or restore ductility and toughness,

3) Enhance Machinability,

4) Eliminate chemical non-uniformity,

5) Refrain grain size

6) Reduce the gaseous contents in steel.

Process Annealing:-

• In this treatment, steal (or any material) is heated to a temperature below the lower critical temperature, and is held at this temperature for sufficient time and then cooled. • Cooling rate is of little importance as the process is being done at sub critical temperatures. • The purpose of this treatment is to reduce hardness and to increase ductility of cold- worked steel so that further working may be carried easily • This process is extensively used in the treatment of sheets and wires. • Parts which are fabricated by cold forming such as stamping, extrusion, upsetting and drawing are frequently given this treatment as an intermediate step.

Recyrstallisation annealing:-

Recyrstallisation annealing is an annealing process applied to cold-worked metal to obtain nucleation and growth of new grains without phase change. This heat treatment removes the results of the heavy plastic deformation of highly shaped cold formed parts. The annealing is effective when applied to hardened or cold-worked steels, which recrystallise the structure to form new ferrite grains.

Benefits

• allows recovery process by reduction or removal of work-hardening effects (stresses)

• increases equiaxed ferrite grains formed from the elongated grains

• decreases the strength and hardness level

• increases ductility

Spheroidise annealing

The main purpose of spheroidise annealing is to produce a structure of steel which consists of globules or well dispersed spheroids of cementite in ferrite matrix. Following are the main methods through which the above objective can be obtained:

1. High carbon steels: Heating the steel to a temperature slightly above the lower critical point (say between 730oC to 770oC,depending upon the carbon percentage), holding it at that temperature for sufficient time and than cooling it in the furnace to a temperature 600oCto 550oC, followed by slowly cooling it down to room temperature instill air.

2. Tool steels and high-alloy steels: Heating to a temperature of 750oC to 800oC, or even higher, holding at that temperature for several hours and then cooling slowly.

Normalising

Normalising aims to give the steel a uniform and fine-grained structure. The process is used to obtain a predictable microstructure and an assurance of the steel’s mechanical properties

Benefits

After forging, hot rolling or casting a steel’s microstructure is often unhomogeneous consisting of large grains, and unwanted structural components such as bainite and carbides. Such a microstructure has a negative impact on the steel’s mechanical properties as well as on the machinability. Through normalising, the steel can obtain a more fine-grained homogeneous structure with predictable properties and machinability.

Application & materials

Normalisation is mainly used on carbon and low alloyed steels to normalise the structure after forging, hot rolling or casting. The hardness obtained after normalising depends on the steel dimension analysis and the cooling speed used (approximately 100-250 HB).

Process details

During normalising, the material is heated to a temperature approximately equivalent to the hardening temperature (800-920°C). At this temperature new austenitic grains are formed. The austenitic grains are much smaller than the previous ferritic grains. After heating and a short soaking time the components are cooled freely in air (gas). During cooling, new ferritic grains are formed with a further refined grain size. In some cases, both heating and cooling take place under protective gas to avoid oxidation and decarburisation.

Hardening

This process is widely applied to all cutting tools, all machine parts made from alloy steels, dies and some selected machine parts subjected to heavy duty work. In hardening process steel is heated to a temperature within the hardening range, which is 30oC to 50oC above the higher critical point for hypoeutectoid steels and by the same amount above the lower critical point for hypoeutectoid steels, holding it at that temperature for sufficient time to allow it to attain austenitic structure and cooled rapidly by quenching in a suitable medium like water, oil or salt both.

In the process of hardening the steel is developed in such controlled conditions,by rapid quenching, that the transformation is disallowed at the lower critical point and by doing so we force the change to take place at a much lower temperature. By rapid cooling the time allowed to the metal is too short and hence transformation is not able to occur at the lower critical temperature.

Tempering:

• Hardened steels are so brittle that even a small impact will cause fracture. Toughness of such a steel can be improved by tempering. However there is small reduction in strength and hardness • Tempering is a sub-critical heat treatment process used to improve the toughness of hardened steel. • Tempering consists of reheating of hardened steel to a temperature below Lower critical temperature and is held for a period of time, and then slowly cooled in air to room temperature.

Depending on temperatures, tempering processes can be classified as:

1) Low- temperature tempering (150 – 250 oC),

2) Medium – temperature tempering (350 – 450 oC)

3) High – temperature tempering (500 – 650 oC).

Surface Hardening:

In many situations hard and wear resistance surface is required with the tough core. Because of tough core the components can withstand impact load. The typical applications requiring these conditions include gear teeth, cams shafts, bearings, crank pins, clutch plate, tools and dies.

The combination of the these properties can be achieved by the following methods:

1. Hardening and tempering the surface layers (surface hardening)

(i) Flame Hardening

(ii) Induction Hardening

2. Changing the composition at surface layers (chemical heat treatment or case hardening)

(i) Carburising

(ii) Nitriding

(iii) Cyaniding

Carburising:-

Carburising is carried out on a steels containing carbon less than 0.2%. It involves increasing the carbon contents on the surface layers upto 0.7 to 0.8%.

In this process, the steel is heated in contact with carbonaceous material from which it absorbs carbon. This method is mostly used for securing hard and wear resistance surface with tough core carburising is used for gears, cams, bearings and clutch plates.

The Following methods are used to diffuse carbon into surface layers:

1) Pack (solid) Carburising,

2) Gas Carburising,

3) Liquid Carburising.

Nitriding:-

1. Nitriding involves diffusion of nitrogen into the product to form nitrides. The resulting nitride case can be harder than the carburized steel. This process is used for alloy steels containing alloying elements (Aluminum, Chromium and Molybdenum) which form stable nitrides. 2. Nitriding consists if heating a component in a retort to a temperature of about 500 to 600 oC. Through the retort the ammonia gas is allowed to circulate. 3. The atomic nitrogen diffuses into steel surface, and combines with the alloying elements (Cr, Mo, W, V etc) to form hard nitrides. The depth to which nitrides are formed in the steel depends on the temperature and the time allowed for the reaction. After the nitriding the job is allowed to cool slowly. Since there is no quenching involved, chances of cracking and distortion of the component are less. 4. The depth of nitrided case ranges from 0.2 to 0.4 mm and no machining is done after nitriding

Cyaniding

1. Similar to carbonitriding, cyaniding also involves the diffusion of carbon and nitrogen into the surface of steel. It is also called liquid carbonitriding. The components are heated to the temperature of about 800 – 900 oC in a molten cyanide bath consisting of sodium cyanide, sodium carbonate and sodium chloride. 2. After allowing the components in the bath for about 15 – 20 minutes, they are quenched in oil or water. Cyaniding is normally used for low-carbon steels, and case depths are usually less than 0.25 mm. 3. It produces hard and wear resistance surface on the steels. Because of shorter time cycles, the process is widely used for the machine components subjected to moderate wear and service loads. The process is particularly suitable for screws, small gears, nuts and bolts.