GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER- VIII (New) EXAMINATION — WINTER 2019
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Subject Code: 2182004 Date: 02/12/2019Subject Name: Design of Mechanisms - II
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
- Attempt all questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.
- Use of PSG design data book is permitted
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Q:1 (a) Answer the following questions 03
- Which of the following stresses are associated with the design of pins in bushed pin type flexible coupling
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(a) Torsional shear and (b) Crushing and bending stress
bending stress
(c) Bending, bearing stress (d) Shear and crushing stress
and transverse shear - The design calculations for members subjected to fluctuate loading with the same factor of safety yield the most conservative estimate when using
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(a) Gerber relation (b) Soderberg relation
(c) Goodman relation (d) Modified Goodman relation - A wire rope is designated as 6 x 19 standard hoisting. The number 6 x 19 represent
(a) Number of strands X (b) Diameter in millimeter %
number of wires in each length in meter--- Content provided by FirstRanker.com ---
strands
(c) Number of wires in each (d) Wire diameter X sheave
strands X number , ‘of diameter
strands
(b) Answer the following questions 04
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- For safe design of spur gear
(a) Wear strength' < Dynamic (b) Wear strength > Dynamic
load load
(c) Beam strength > (d) Both (b) and (c)
Dynamic load - In the assembly design of shaft, pulley and key, the weakest member is:
(a) Shaft (b) Pulley
(c) Key (d) None - The bearing characteristic number in hydrodynamic bearing depends on
(a) Length, width and load (b) Length, width and speed--- Content provided by FirstRanker.com ---
(c) Viscosity, speed and load (d) Viscosity, speed and bearing
pressure - The life of a ball bearing is inversely proportional to
(a) (Load)"? (b) (Load)?
(c) (Load)"? (d) None of the above
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(c) Design a rigid flange coupling to transmit a torque of 250 N-m between two coaxial shafts. The shaft is made of alloy steel, flanges out of cast iron and bolts out of steel. Four bolts are used to couple the flanges. The shafts are keyed to the flange hub. The permissible stresses are given below:
Bearing or crushing stress on shaft =250 MPa
Shear stress on keys =100 MPa
Crushing stress on keys =250 MPa
Shearing stress on cast iron =15 MPa
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Shear stress on bolts =100 MPaAfter designing the various elements, make a neat sketch of the assembly indicating the important dimensions. 07
Q2 (a) What do you understand by self locking of brake? Explain self locking condition of block brake with suitable diagrams. 03
(b) How do you determine life of mechanical component which is subjected to different stress levels for different parts of work cycle? 04
(c) A double shoe brake is shown in following figure. The brake drum rotates in anticlockwise sense at 720 rpm, when the actuating force of 2.4 kN is applied. The coefficient of friction between the blocks and drum is 0.25. Determine the braking torque and the amount of heat generated. 07
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OR
A differential band brake is shown in following figure. The angle of contact is 280 deg. The brake is sustain a torque of 400 Nm. The band has compressed woven lining and presses against cast iron drum of 0.375 m diameter. Assuming coefficient of friction as 0.3:
1. Determine the necessary operating force P.
2. Find the'width of steel band for thickness of 2 mm, assuming safe stress in tension as 55 N/mm?.
3. Find the section of the brake lever. 07
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