Design of Machine Elements 2 - Dec 2013

Mechanical Engg. (Semester 6)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) A curved linked mechanism made from a round steel bar is shown in Fig Q1(a). the material for links is plain carbon steel 30C8 with an allowable yield strength of 400 Mpa. Determine the factor of safety. (10 marks) 1 (b) A high pressure cylinder consists of steel tube with inner and outer diameter of 20 mm and 40 mm respectively. It is jacked by an outer steel tube with an outer diameter of 60 mm. The tubes are assembled by shrinking process in such way that maximum principle stress induced in any tube is limited to 100MPa. Calculate the shrinkage pressure and original dimensions of the tubes. Take the Young's modules as 207 Gpa.(10 marks) 2 (a) Write a note on construction of flat and 'V' belt.(5 marks) 2 (b) It is required to design a 'V' belt drive to connect a 7.5 kW, 1440r/min induction motor to a fan, running at approximately 480 r/min for a service of 24 hr/day. Space is available for a centre distance of about 1m. Determine the pitch length of the belt and number of belts required.(15 marks) 3 (a) Enumerate the applications of springs. Also derive an expression for the deflection of a close coiled helical spring.(6 marks) 3 (b) A spring is subjected to load varying from 500N and 1200N. It is to be made of oil tempered cold drawn wire. Design factor based on Wahil's line is 1.25. the spring index is to be 6. The compression in the spring for the maximum load is 30 mm. Determine the wire diameter, mean coil diameter and free length of the spring. Take the yield stress in shear as 700 Mpa and endurance stress in shear as 350 Mpa for the material of the wire.(14 marks) 4 (a) Write a note on design of gear based on dynamics loading and wear.(6 marks) 4 (b) A cast steel 24 teeth spur pinion operating at 1150 R/min transmit 3 kW to a cast steel 56 teeth spur gear. The gear have the following specifications:
Module:3mm Allowable stress:100MPa
Face width : 35 mm Tooth from : 14 1/2° full depth profile.
Factor of dynamic loading, C=350N/mm Wear load factor, K=0.28 Mpa.
Determine the induced stress in the weaker gear. Also determine the dynamics load wear load. Comment on the results.(14 marks) 5 (a) Write a note on formative number of teeth in bevel gear.(4 marks) 5 (b) Hardened steel worm rotates at 1250 R/min and transmits power to phosphor bronze gear with a transmission ratio of 15:1. The centre distance is to be 225mm. Design the gear drive and give estimated power input ratings from the stand point of strength, endurance and heat dissipation. The teeth are of 14% full depth involute.(16 marks) 6 (a) A cone clutch has a semi cone angle of 12°. It is to transmit 10 kW power at 750 R/min, the width of the face is one fourth of the mean diameter of friction lining. If the normal intensity of pressure between contacting surface is not to exceed 0.085 N/mm² and the coefficient of friction is 0.2 assuming uniform wear conditions, calculate the dimensions of the clutch.(10 marks) 6 (b) A band break arrangement is shown in FigQ6(b). It is used to generate a maximum braking torque of 200N-m. Determine the actuating force 'P', if coefficient of friction is 0.25. the angle of wrap of the band is 270°. Determine the maximum intensity of pressure, if the band width is 30mm. (10 marks) 7 (a) Explain the following types of lubrication
i) Hydrodyanamic lubrication ii)Hydrostatic lubrication
iii) Boundary lubrication iv) Elasto hydro dynamic lubrication.(8 marks) 7 (b) The following data are given for a 360° hydro-dynamic bearing:
Bearing diameter:50.02mm Journal diameter:49.93 mm
Bearing length:50mm Jornoul speed:1140 r/min
Radial load=8 kN Viscosity of lubricant :12cp.
The bearing is machined on a lathe from bronze casting, while the steel journal is hardened and ground. The surfaces roughness values for turning and grading are 0.8 and 0.4 microns respectively. For thick film lubrication the minimum film thickness should be five times the sum of surface roughness values for the journal and the bearing. Calculate:
i) The permissible minimum film thickness
ii) The actual film thickness under the operating conditions
iii) Power loss in friction
iv) Flow requirement.(12 marks) 8 (a) Explain the considerations given in the design of pistons for IC engine.(5 marks) 8 (b) Design a trunk piston for an IC engine. The piston is made of cast iron with an allowable stress of 38.5 Mpa. The bore of the cylinder is 200mm and the maximum explosion pressure is 0.4 Mpa. The permissible bending stress of the material of the gudgeon pin is 100 Mpa . The bearing pressure in the gudgeon pin bearing of the connecting rod is to be taken as 200 Mpa.(15 marks)