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Technical Report · March 2017 DOI: 10.13140/RG.2.2.28195.45606


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A. Balasubramanian University of Mysore



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The user has requested enhancement of the downloaded file. SIZE REDUCTION BY CRUSHING METHODS By Prof. A. Balasubramanian Centre for Advanced Studies in Earth Science, University of Mysore, Mysore


In the field of extractive , dressing is the process of separating commercially valuable from their . There are two major categories of processing. One is and the other one is separation. The process "Comminution" involves size reduction and size-wise classification called as screening or separation. The objective of this lesson is to provide the details of size reduction methods involved in using crushing equipments. Crushing is the first step of mineral processing where the /rocks from the mine site is fed into the mechanical equipment in order to reduce the size of masses for subsequent usage by liberating the valuable mineral from the .

1.0 Introduction:

Mineral processing can involve four general types of unit operations. They are: 1) comminution – the process of particle size reduction; 2) sizing – separation of particle sizes by screening or classification; 3) concentration by taking advantage of physical and surface chemical properties; and 4) dewatering – solid/liquid separation.

Size Reduction is mainly done through and mills. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on the "run-of-mine" ore. The grinding process which is normally carried out after crushing, may be conducted on dry or slurried material.

2.0 The size reduction process:

Minerals being crystals have a tendency to break into endless numbers of sizes and shapes every time they are introduced to energy. The difficulty in size reduction lays in the art of limiting the number of over and under sizes produced during the reduction. If this is not controlled, the mineral will follow its natural crystal behaviour, normally ending up in over-representation of fines.

3.0 Comminution

Comminution is particle size reduction of materials. Comminution may be carried out on either dry materials or slurries. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on "run-of-mine" ore, while grinding (normally carried out after crushing) may be conducted on dry or slurried material. In comminution, the size reduction of particles is done by three types of forces: compression, impact and attrition.

3.1 Compression and impact forces are extensively used in crushing operations while attrition is the dominant force in grinding. The primarily used equipment in crushing are-jaw crushers, gyratory crushers and cone crushers whereas rod mills and ball mills, closed circuited with a classifier unit, are generally employed for grinding purposes in a mineral processing plant. Crushing is a dry process whereas grinding is generally performed wet and hence is more energy intensive.

Crushing is done using mechanical crushers. There are several types of crushers available in processing.


All crushers have a limited reduction ratio meaning that size reduction will take place in stages.

3.2 Operation stages:

The operating stages in minerals processing have remained the same for several years. In this, the hard, abrasive and inhomogeneous mineral crystals are o be treated in special ways in order to extract maximum value out of each size fraction. The following diagram shows the stages in operation of size reduction from crushing to upgrading.

3.3 Crushing of and minerals:

Crushing is the largest process operation in minerals processing. The goal of this process is to produce rock or (more seldom) mineral fractions to be used as for other industrial production. The quality parameters are normally strength, size and shape. There are two kinds of equipments used for crushing works. one is by using crushers and other one is by using impactors. This diagram illustrates the stages of size reduction from 1000mm to 4 mm.


Size reduction of ores is normally done in order to liberate the value minerals from the host rock. This means that we must reach the liberation size, normally in the interval 100 – 10 micron, see value curve 1 above.

3.4 Feed material:

All operations in size reduction, both crushing and grinding are of course determined by the feed characteristics of the minerals (rock/ore) moving into the circuit. The key parameters we need are the “crushability or grindability”, also called work index and the “wear profile”, called abrasion index.

4.0 Crushing of rock and minerals:

Crushing is the largest process operation in minerals processing. The goal is to produce rock or (more seldom) mineral fractions to be used as rock fill or ballast material for concrete and asphalt production. Quality parameters are normally strength, size and shape. The kinds of materials processed are Limestone, Granite, Gabbro, Basalt, River Stone, Coal Gangue, Quartz, Diabase, , Copper Ore, Ore and Manganese Ore.

4.1 The art of crushing:

Crushing means different things for different operations and the production goals are not always equal. In Mineral dressing, these two approaches are adopted: 1. Crushing of rock and gravel 2. Crushing of ore and minerals. There are three stages in crushing as stage 1, 2 and 3. In each stage the reduction in size ranges as referred to as R1,R2 and R3. This diagram illustrates the stages with equipments and reduction ratios. From 1000mm to 100 micron levels the mass is crushed.


4.2 Size control:

Neither crushers nor grinding mills are very precise when it comes to the correct sizing of the end products. The reason is to find partly in the variation of the mineral crystals compounds (hard-soft, abrasive – non abrasive), partly in the design and performance of the equipment. Size control is the for improvement of the size fractions in the process stages and in the final products. For the coarser part of the process, screens are used (in practise above 1-2 mm). In the finer part we have to use classification with spiral classifiers.

5.0 Types of Crushers:

A is a designed to reduce large rocks into smaller rocks, gravel, or rock dust. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated.

Crushing is the process of transferring a force amplified by mechanical advantage through a material made of molecules that bond together more strongly, and resist deformation more, than those in the material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, and apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so that its molecules separate from (fracturing), or change alignment in relation to (deformation), each other.

5.1 Jaw crusher

A jaw crusher is generally used as a primary crusher in a crushing circuit. Product is fed into the top of the jaw crusher by an vibrating grizzly feeder. The eccentric rotating drive shaft causes the movable jaw to oscillate crushing the aggregate against a fixed jaw. Jaw crushers are run on belt drives driven by an electric motor or diesel engine. Jaw crushers are used extensively throughout the aggregate and mineral processing . This diagram illustrates the structure of a jaw crusher.

Operating principle:

Jaw crushers operate according to the principle of pressure crushing. The crushing material is crushed in the wedge-shaped pit between the fixed crusher jaw and the crusher jaw articulated on an eccentric shaft.

The material is crushed by the elliptic course of movement and transported downwards. This occurs until the material is smaller than the set crushing size. The feed cavity of the Jaw Crusher consist of moveable jaw and fixed jaw, which imitate the movement of the animal’s two jaws to complete the materials’ crushing .

Jaw Crushers have found their extensive application for the mid crushing of the various ores and large-size materials block in the field of , , building material, highway, railway, water conservancy and , etc


5.2 Gyratory crusher :

A gyratory crusher is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head; both surfaces are typically lined with manganese surfaces. The inner cone has a slight circular movement, but does not rotate; the movement is generated by an eccentric arrangement. As with the jaw crusher, material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces.

The gyratory crushers are robust crushers with modern features. They are designed to give optimal capacity in primary crushing, increasing the total capacity in the mining crushing process. These crushers have a large feed opening and a grooved mantle, making them suitable for crushing large boulders.

This diagram shows the setup of a gyratory crusher.


5.3 Cone crusher :

With the rapid development of mining technology, the cone crusher can be divided into four types: compound cone crusher, spring cone crusher, hydraulic cone crusher and gyratory crusher. According to different models, the cone crusher is divided into VSC series cone crusher(compound cone crusher), Symons cone crusher, PY cone crusher, single cylinder hydraulic cone crusher, multi- cylinder hydraulic cone crusher, gyratory crusher, etc. A cone crusher is similar in operation to a

6 gyratory crusher, with less steepness in the crushing chamber and more of a parallel zone between crushing zones. This diagram illustrates the anatomy of a cone crusher.

Operating principle

With these crushers the crushing is effected by pressure crushing in an opening and closing crushing gap between the bowl liner and mantle. The opening and closing are effected simultaneously on the opposite sides of the crushing chamber. A cone crusher breaks rock by squeezing the rock between an eccentrically gyrating spindle, which is covered by a wear resistant mantle, and the enclosing concave hopper, covered by a manganese concave or a bowl liner. As rock enters the top of the cone crusher, it becomes wedged and squeezed between the mantle and the bowl liner or concave. Large pieces of ore are broken once, and then fall to a lower position (because they are now smaller) where they are broken again. This process continues until the pieces are small enough to fall through the narrow opening at the bottom of the crusher. A cone crusher is suitable for crushing a variety of mid- hard and above mid-hard ores and rocks.

5.4 Impact crusher:

Impact crushers involve the use of impact rather than pressure to crush material. The material is contained within a cage, with openings on the bottom, end, or side of the desired size to allow pulverized material to escape. There are two types of impact crushers: horizontal shaft impactor and vertical shaft impactor.

Operating principle In comparison to pressure crushing, the principle used here is impact crushing. In this process, the crushed material is picked up by a fast moving rotor, greatly accelerated and smashed against an impact plate ("impact toggle"). From there, it falls back within range of the rotor. The crushed material is broken again and again until it can pass through the gap between the rotor and impact toggle. The impact crushers are called as secondary impact crushers and are mainly used in the second crushing stage. They are suitable for medium-hard to hard stone and gravel for feed sizes up to 250 mm.


Main use of impact stone crusher :

This kind of impact stone crusher is a kind of high-efficient strong coarse and mid crushing equipment we company produced .And the anti-pressure is less than 150Mpa and it can replace the jaw crusher and become the primary cruhsing equipemnt .When the anti-pressure is over the 150Mpa ,it can be used as secondary mid crushing work .We can change the gap between the impact plate and rotor to change the discharging size and also can be used as the fine crushing work.The most feature of this series of Impact crusher lies :the final particle size with the cubic shape ,no crack ,fine shape .And now impact stone crusher has been applied in the field of mines, high-speed railway, highway, cement, chemicals, construction,etc.

Working Principle of Impact Stone Crusher

This kind of impact stone crusher adopts the impact and centrifugal force to complete the crushing process .And during the operation ,driven by the motor ,the rotor will proceed a high speed and the materials will bump into the hammer plate installed on the rotors when the materials enter the impact cavity ,which will form the first cruhsing .And then the materials will be thrown out to the impact plate and form the second bump and crushing .Along with the materials’falling down ,they will be repeatedly thrown out to the first ,second,and third impact plate ,which will form several bumps and crushing in the impact cavity ,thus achieving the required size and be discharged from the discharge opening .So that’s the complete crushing process.

Features of Impact Stone Crusher:

1) Large feesing size ,high crushing cavity,wide range of the high-hardness of the materials ,large sizes and small ratio of the stone powder products. 2) Convenient adjustment to the gap between the impact plate and hammer ,high-efficient control to the dischaging degree and fine particle size. 3) Compact structure,high rigid and bigger rotating inertia mass of the totor. 4) High chrome of the hammer plate ,anti-shock ,anti-wearing. 5) No key-connection and convenient maintenance ,reliable economy. 6) Comprehensive crushing performance ,high production efficiency .low wearing consumption,comprehensive benefits.

5.5 Horizontal shaft impactor (HSI) / Hammer

The HSI crushers break rock by impacting the rock with hammers that are fixed upon the outer edge of a spinning rotor. HSI are sold in Stationary, trailer mounted and crawler mounted configurations. HSI's are used in recycling, hard rock and soft materials. In earlier years the practical use of HSI crushers is limited to soft materials and non abrasive materials, such as limestone, phosphate, gypsum, weathered shales, however improvements in metallurgy has changed the application of these machines.

5.6 Vertical shaft impactor (VSI) =VSI crusher:

VSI crushers use a different approach involving a high speed rotor with wear resistant tips and a crushing chamber designed to 'throw' the rock against. The VSI crushers utilize velocity rather than surface force as the predominant force to break rock. In its natural state, rock has a jagged and uneven surface.

6.0 Typical uses of commonly used crushers:

The following table describes typical uses of commonly used crushers:


Abrasion Moisture Reduction Type Hardness Main use limit content ratio Heavy mining, Soft to very Dry to slightly Quarried Jaw crushers No limit 3/1 to 5/1 hard wet, not sticky materials, sand & gravel, recycling Heavy mining, Gyratory Soft to very Dry to slightly Abrasive 4/1 to 7/1 Quarried crushers hard wet, not sticky materials Quarried Medium hard Dry or wet, not Cone crushers Abrasive 3/1 to 5/1 materials, Sand to very hard sticky & gravel Compound Medium hard Dry or wet, not Mine, Building Abrasive 3/1 to 5/1 crusher to very hard sticky Materials Quarried Horizontal shaft Soft to Slightly Dry or wet, not 10/1 to 25/1 materials, sand & impactors medium hard abrasive sticky gravel, recycling Vertical shaft Medium hard Slightly Dry or wet, not Sand & gravel, impactors (shoe 6/1 to 8/1 to very hard abrasive sticky recycling and anvil) Vertical shaft Quarried Soft to very Dry or wet, not impactors No limit 2/1 to 5/1 materials, sand & hard sticky (autogenous) gravel Dry or wet and Mineral sizers Hard to soft Abrasive 2/1 to 5/1 Heavy mining sticky

7.0 Key benefits of size reduction:

The key benefits of size reduction in mineral dressing are the following:

1. increased dissolution rate 2. improved drug delivery 3. cleaning product health & safety 4. controlling the rate of reaction 5. greater density 6. separating Grain Components 7. consistent Product Appearance 8. consistent Texture. 8.0 Conclusion:

When extracting and processing raw materials, the key element is proper preparation – no matter whether this takes place directly inside the mine complex or at the site where further processing is carried out. Particle size reduction is carried out in a number of industries, such as chemical, cosmetic, food and beverage, biotech, pharmaceutical and many others, in order to control the number and extent of chemical reactions that occur when the end product is used. Crushers are used for the crushing or medium-hard rock as well as for sticky and soft materials, i.e. lignite and mineral coal, clay, marl, limestone and similar raw materials as well as for overburden and ores. Sticky and soft materials are reliably crushed in 2 or 3 stages down to the required product size.


Gyratories and jaw type gyratory crushers as an integral part of semi-mobile and stationary processing plants are used for primary crushing of bulk materials mainly in ore mines and in the natural rock industry. Today, stationary, semi-mobile and mobile crushing plants with capacities ranging from 500 to more than 10,000 t/h are used proving for crushing and processing hard rock, limestone, coal, ore, overburden and other minerals in open pit pines and quarries.


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