BBA Iind SEMESTER EXAMINATION 2008-09 s24

B.Tech V SEMESTER EXAMINATION 2011-12

Course Code: EME504 Paper ID: 0965123

Design of Machine Elements

Time: 3 Hours Max. Marks: 70

Max Marks: 75

Note: Attempt six questions in all. Q. No. 1 is compulsory. 1. Answer any five of the following (limit your answer in 50 words). (4x5=20) a) What are the different stages in the design of machine element, explain? b) Explain Soderberg method for combination of stresses. c) Explain surge in spring. d) State any two disadvantages of gear drive over other types of drives. e) Why is taper given to key? Why is taper given only on one side? f) Briefly discuss the BIS criteria for specification of carbon steels and alloy steels. g) What do you mean by technology based development? h) What is design by evolution? Discuss the example of an appropriate product.

2. Explain the criteria of failure for brittle materials subjected to static loading. Determine the maximum stress produced in a stepped shaft, stepped down from 40 mm to 30 mm with a fillet radius of 6 mm. It is subjected to a couple of 100 Nm. Take stress concentration factor kt = 1.23. (10)

3. What do you mean by stress concentration? A machine shaft transmits 7.5 kW power at 360 rpm from the pulley 1 to component is subjected to bending stress which fluctuates the pulley 2. The diameters of pulley 1 and 2 are 250 mm and between 300 N/mm2 tensile and 150 N/mm2 compressive in 500 mm respectively. The masses of pulleys 1 and 2 are 10 cyclic manner. Using Goodman formula, calculate the kg and 30 kg respectively. The belt tension act vertically minimum required ultimate strength of the material. Take downward and the ratio of belt tensions on the tight and slack factor of safety 1.5 and endurance limit in reversed bending side for each pulley is 2.5:1. The shaft is made of plain 2 as 50% of ultimate strength. (10) carbon steel 40C8 (Syt = 380 N/ mm ) and the factot of safety is 3. Estimate suitable diameter of the shaft. 4. Design a muff coupling to connect two steel shafts If the permissible angle of twist is 0.5o per meter length, transmitting 25 kW power at 360 rpm. The shaft and key are calculate the shaft diameter on the basis of torsional rigidity. made of plain carbon steel 30C8 (Syt = Syc = 400 N/mm2). Assume G = 79300 N/mm2. (10) The sleeve is made of grey cast iron FG200. The factor of safety for the shaft and key is 4. For the sleeve, the factor of safety is 6 based on ultimate strength. (10)

5. A safety valve, 60 mm in diameter, is to blow off at a pressure of 3.2 MPa. It is held on its seat by means of a helical compression spring, with initial compression of 40 mm. The maximum lift of the valve is 12 mm. The spring index is 6. The spring is made of cold-drawn steel wire with 8. What are the preferred numbers? Explain their application in ultimate tensile strength of 1400 N/mm2. The permissible the standardization. A manufacture is interested in shear stress can be taken as 25% of this strength. (G=81370 manufacturing 4 different models of generating sets ranging N/mm2). Calculate: from 5kW 50kW capacities. Using R5 series specify the a) Wire diameter b) Mean Coil diameter capacities of the models. If the manufacturer further wishes c) Number of active coils. to expand to 8 models within the same range what will be the (10) capacities of additional models. (10)

6. A screw jack is to lift a load of 80 kN through a height of 400 mm. The elastic strength of screw material in tension and compression is 200 MPa and in shear 120 MPa. The material for nut is phosphor-bronze for which the elastic limit may be taken as 100 MPa in tension, 90 MPa in compression and 80 MPa in shear. The bearing pressure between the nut and the screw is not to exceed 18 N/mm2. Design and draw screw jack. The design should include the design of screw, nut, cup and body. (10)

7. The layout of a shaft carrying two pulleys 1 and 2, and supported on two bearings A and B as shown in figure. The