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GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER-VII (NEW) EXAMINATION - WINTER 2018
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Subject Code: 2171909 Date: 03/12/2018Subject Name: Machine Design
Time: 10:30 AM TO 01:30 PM Total Marks: 70
Instructions:
1. Attempt all questions.
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2. Make suitable assumptions wherever necessary.3. Figures to the right indicate full marks.
4. Use of Design data book is allowed Bhandari/PSG.
MARKS
Q.1 (a) Why pressure angle is generally taken as 20°? What is its effect? 03
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(b) Explain desirable properties of bearing materials used for sliding 04contact bearings.
(c) Design a pair of CI spur gear to transmit 12 kW having pinion speed 07
of 200 rpm. The speed reduction required is 2:1. Assume face width
as 3 times circular pitch. The minimum number of teeth on pinion is
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24. Check your design in all failures considering the following data;Pressure angel 14.5° full depth involute, Factor of safety 1.5.
The modulus of elasticity for pair is 0.8 * 10° N/mm?,
Error in manufacturing is not to exceed 0.05 mm,
Allowable bending stress for CI as 45 N/mm?,
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Surface endurance stress as 280 N/mm?.Q.2 (a) What is the function of cylinder liners in IC Engines? List down the 03
reasons for liner distortion.
(b) Give the classification of wire ropes and explain its construction with 04
neat sketches.
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(c) Design a helical gear to transmit 30 kW from the following data; 07Helix angle =30°, Speed of pinion = 1500 rpm,
Pressure angle = 20° FDI,Velocity ratio = 4,
No of teeth on pinion =24 Static stress for CI = 55 N/mm?,
BHN for pinion and gear material = 350,
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Young’s modulus, of elasticity for pinion and gear material = 2.1 *103 N/ mm?.
OR
(c) Draw layout diagram of gear box, ray diagram and speed chart for a 07
multi-speed gear box of a radial drilling machine required to give
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eight steps. The power from motor to the input shaft of gear box istransmitted by a V-belt drive with a speed reduction of 1:6. The
minimum and maximum spindle speeds are 70 rpm and 1800 rpm
respectively.
Q.3 (a) Explain the rang ratio in gear box design. 03
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(b) Explain in brief about mountings of bearings. 04(c) Calculate the maximum radial load that the journal can carry and 07
operate at hydrodynamic condition for the following data of a full
journal bearing. Journal diameter = 60 mm, bearing length = 60 mm,
radial clearance = 0.06 mm, minimum film thickness = 0.006 mm,
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journal speed = 1440 rpm, viscosity of lubricant = 20 cP.For the above calculated load, find the power lost in friction.
OR
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(a) Differentiate between progressions in case of design of gear box. 03
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(b) A deep groove ball bearing has a rated static and dynamic load 04capacity of 4150 N and 4750 N respectively. The bearing has to take
an axial load of 2075 N and a radial load of 4000 N. Find the expected
life of the bearing.
(c) A worm and worm wheel gear drive is designated as 2 /41 / 10/ 8. 07
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The drive is used to obtain a speed reduction of 20.5 from an inputspeed of 1450 rpm. Material of the worm wheel is Sand Cast and
Chilled Phosphor Bronze, while the worm is made of Case-hardened
alloy steel. Determine the power transmitting capacity of the drive
based on beam strength.
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Q.4 (a) What are the two most usual causes of failures of the crank shafts? 03
(b) Explain the classification cranes using different standards. 04
(c) The cylinder of a four-stroke diesel engine has the following 07
specifications:
Break Power = 7.5 kW, Speed = 1400 rpm, Indicated mean effective
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pressure = 0.35 MPa, Mechanical efficiency = 80 %, Maximum gaspressure = 3.5 MPa.
The cylinder liner and head are made of grey cast iron FG 260 having
UTS 260 N/mm? and poisons ratio 0.25. The studs are made of plain-
carbon steel having yield stress 380 N/mm?. The factor of safety for
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all parts is 6. Calculate: (1) bore and length of the cylinder liner,(i1) thickness of the cylinder liner, (iii) thickness of cylinder head,
(iv) size, number and pitch of studs.
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Q.4 (a) Explain the aspect of heat generation in design of worm gears. 03
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(b) A bearing is subjected to the following work cycle: radial load of 044450 N, 6675 N and 2225 N at 150 rpm, 600.rpm, and 300 rpm for
30 % of time, 10 % of time, and for remaining time of the cycle
respectively. The inner ring rotates and the loads are steady. Find the
expected life of this bearing in hours, by considering the static and
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dynamic load carrying capacities-of the bearing as 10013 N and14952 N respectively.
(c) Design a cast iron piston fora single acting four stroke engine for the 07
following specifications.-Cylinder bore = 100mm, stroke = 120 mm,
maximum gas pressure = 0.65 MPa,
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Fuel consumption =0.227 kg/kW/hr, speed = 2200 rpm.Assume the following data;
Allowable stresses in CI = 37.5 N/mm?,
Allowable stresses for piston rings = 90 N/mm?,
Assume suitable data.
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Q.5 (a) Discuss the different types of piston rings and function of each one 03
of it.
(b) How the rolling contact bearings are designed having probability of 04
survival other than 90 percent?
(c) An elevator at the construction site is required to raise building 07
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materials weighing 5.5 KN. A maximum velocity of 1 m/s is attainedin one second while raising the materials. The lift of material is 25 m.
The drum diameter is 40 times the rope diameter. Find the number of
6 X 19 wire ropes required if 12 mm diameter ropes are used.
Assume: diameter of wire dy= 0.063 d, area of rope A= 0.38 d’, mass of
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rope = 0.0036 d” kg/m, E, = 84000 N/m?, breaking strength = 385 d2, factorof safety = 5. d is diameter of rope.
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Q.5 (a) What is material handling? What are the essentials of good material
handling system?
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(b) A 360° full journal bearing operates under the following 10specifications:
Journal Diameter = 70 mm, bearing length = 70 mm,
Journal speed = 960 rpm, steady radial load = 12 KN,
Viscosity of lubricant = 16 cP, Mass density of oil = 880 kg/m?,
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Specific heat = 1.76 kJ/kg °C, bearing clearance ratio (r/c) = 800,Average heat transfer coefficient = 20 W/m?2-°C.
Determine the required flow rate of oil. Also find the temperature of
oil film and the bearing surface area for the desired heat transfer, if
the ambient temperature is 30°C. Assume that all heat generated in
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the bearing is carried away by the oil.FirstRanker.com
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