Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 7th Sem 2171909 Machine Design Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?VII (NEW) EXAMINATION ? WINTER 2020
Subject Code:2171909 Date:28/01/2021
Subject Name:Machine Design
Time:10:30 AM TO 12:30 PM Total Marks: 47
Instructions:
1. Attempt any THREE questions from Q.1 to Q.6 .
2. Q.7 is compulsory.
3. Make suitable assumptions wherever necessary.
4. Figures to the right indicate full marks.
Q.1
(a) What is Lewis form factor? How does it vary with number of teeth on gear?
03
(b) Derive the expression for beam strength of a gear tooth.
04
(c) A pair of helical gears with pinions 26 teeth and gear 100 teeth supplies power 5KW 07
at 2000 rpm of pinion. Normal pressure angle is 20o and helix angle of teeth is 15o.
Both the gears are made of hardened steel with Sut = 660 N/mm2. Gears are finished
to accuracy of grade 8. Assume service factor =1.5, factor of safety = 1.8 and pitch
line velocity of gears as 10 m/s, determine normal module of gear teeth as per beam
strength. Specify the hardness of the surface of gears if Sw = Sb.b =12mn.Where b is
face width.
Q.2
(a) Why heat dissipation is an important consideration in worm gear drive?
03
(b) Derive and express the force analysis in worm gear drive with sketch.
04
(c) A pair of bevel gears is required to transmit 10 KW power at 500 rpm from motor 07
shaft to a machine shaft. The speed reduction is 3:1 and the shafts are inclined at 60
o. the pinion is to have 24 teeth with pressure angle 20o and is to be made of cast
steel having strength 75 N/ mm2. The gear is to be made of cast iron with static stress
of 55 N/ mm2. Design the gear pair.
Q.3
(a) Plot the typical relationship between coefficient of friction and bearing characteristic 03
number for a journal bearing. Elaborate the different regions of the plot.
(b) Explain the design parameters to be considered in the performance of a 04
hydrodynamic bearing.
(c) A 360o hydrodynamic bearing has 50 mm diameter and 50 mm length. The journal 07
is carrying a load of 15 KN and rotates at 1450 rpm. The eccentricity ratio is 0.8.
The radial clearance is 20 m. Calculate
a) Probable coefficient of friction. b) Viscosity of oil.
c) Minimum film thickness. d) Quantity of oil in circulation.
e) Oil leakages through sides.
If the oil is supplied at 28oc, find the oil temperature. The specific gravity of oil is
0.86 and the specific heat can be taken as 2.09 KJ/Kg oc.
Q.4
(a) What are the typical causes of failure in rolling contact bearings?
03
(b) Derive the expression for the equivalent load for a rolling contact bearing operating 04
under cyclic loads in usual notations.
(c) A ball bearing is subjected to purely radial force. The magnitude of radial force 07
acting on the bearing varies in a sinusoidal manner from 0 to 1500 N in first half
revolution and 1500 N to 0 in second half revolution. The cycle then repeats. The
direction force remains fixed. The speed of rotation is 720 rpm. Determine the
dynamic load carrying capacity of the bearing for a life of 8000 hours.
1
Q.5
(a) What is the flexibility of wire rope? How does the flexibility of the wire rope 03
influence in wire rope design?
(b) Explain different types of stresses in wire rope design.
04
(c) At the construction site, 1 tonne of steel is to be lifted up to a height of 20 m with 07
the help of 2 wire ropes of 6 x 19 size, nominal diameter 12 mm and tensile strength
designation 1770. Determine the factor of safety if the sheave diameter is 56d and if
the wire rope is suddenly stopped in 1 second when travelling at a speed of 1.2 m/s.
What is the factor of safety if bending load is neglected? Assume mass per m is
0.498 kg, breaking load =78 KN for given tensile strength designation and metal
cross section area is 0.39d2.
Q.6
(a) What is bulk load? Explain the typical character classifications of bulk materials.
03
(b) Explain different types of conveyors used in material handling systems.
04
(c) Design the crane hook of a hoisting block for a maximum load lifting capacity of 10 07
ton. The material for hook is forged for which permissible tensile stress may be taken
as 120 N/2. The modified triangular section is used for hook.
Q.7
(a) Explain different types of crankshafts used in IC Engine with their application.
05
OR
Q.7
(a) What are the functions of rib, cup, compression ring and oil scraper ring in piston? 05
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This post was last modified on 04 March 2021