RO6503 Mechanical Design, Third year, Department of Robotics and Automation Engineering, Model Exam Questions

PART –A (10 ×02 = 20 Marks)
1.      Define form factor?
2.      What is meant by spur-gear?
3.      What is key?

4.      Define the term critical speed.
5.      What factors should be considered during the selection of a belt drive?
6.      Explain creep in belts.
7.      What is a journal bearing?
8.      What are the required properties of bearing materials?
9.      What is the function of a clutch?
10.  What are the properties required of the material used as a friction surface?
PART –B (5 ×16= 80 Marks)
11.(a) Design a helical gear to transmit 7.5 kw at 1400 rpm to the following specification; speed reduction 3. Pressure angle 200. Helix angle 100. Design surface compressive stress 900 N/mm2. Design bending stress 210 N/mm2.Modules of elasticity of materials 2.02×105N/mm2.                                                                                                              (16)
(OR)
(b). A pair of helical gears with 230 helix angle is to transmit 2.5 kw at 1000 rpmof the pinion. The velocity ratio is 4:1. The pinion is to be forged steel and the driven gear is to be cast steel. The gears are of 200 full depth involute form and the pinion is to have 24 teeth. Design the gear drive.                                                                                           (16)
12. (a). a hollow steel shaft of 800mm outside diameter and 500mm inside diameter is used to drive a propeller of a marine vessel. The shaft is mounted on a bearing 6m apart, and it transmits 6000kw at 200rpm. The maximum axial trust is 750kn and shaft weights 75kn. Determine
                  (i) Maximum shear stress induced.
                  (ii) Angular twist of shaft between bearings                                                  (16)
(OR)
(b). (b)A shaft carries a pulley A at the left end and a spur gear B at middle of bearing supports C and D. the pulley is 1000mm in diameter and gear pitch diameter is 600mm. the pulley is keyed to the shaft at 400mm to the left of the left hand bearing and the distance between bearings C&D is 1250mm. the shaft transmits 20KW and runs at 750rpm. The shaft receives power from a motor placed vertically below the pulley through a flat belt with ratio of tensions 2.5. the shaft delivers power to a gear placed horizontally in front. The shaft rotates in anticlockwise direction looking from left. Pressure angle of gear is20 degrees. Design the shaft if the weight of A and B are 300N and 250N respectively and the allowable shear stress of the shaft material is 70N/mm2 , shock and fatigue  factor in bending and torsion are 2.0 & 1.5 respectively.                           (16)







13.(a) A 30kw, 1440rpm. Motor is to drive a compressor by means of V-belts. The diameters of pulley are 220mm and 750mm. the centre distance between the compressor and motor is 1400mm. design a suitable drive.                                                                              (16)
(OR)
(b) Design a chain drive to actuate a compressor from 15kw electrical motor at 1000rpm. The compressor running at 550 rpm. Minimum centre distance is 550mm. the chain tension may be adjusted by shifting the motor on rails. The compressor is to work 8 hours/day.(16)
14. (a) (i) A 70mm machine shaft is to be supported at the ends. It operates continuously for 8 hrs per day, 320 days per year of 8 years. The load and speed cycle for one of the bearing are given below.
Sl.No
Fraction of cycle
Radial load ,N
Trust load, N
Speed, rpm
Factors
X
Y
Z
1
2
3
0.25
0.25
0.5
3500
3000
4000
1000
1000
2000
600
800
900
0.56
0.56
0.56
1.2
1.2
1.4
1.5
1.5
1.5
                                                                                                                                                (8)
 (ii) Select a bearing of a 40mm diameter shaft rotates at 400rpm. Due to a bevel gear mounted on the shaft, the bearing will have to withstand a 5000N radial load and a 3000N trust load. The life of the bearing expected to be at least 1000hrs.                                                                  (8)
(OR)
(b) (i) select a suitable Conrad type deep groove ball bearing for the following data, the radial load is 7500N, the shaft speed is 2000rpm, the L10 life required is 4.9×108 revolutions; the inner ring of the bearing rotates                                                                                     (8)
    (ii) A 30BC03 deep groove ball bearing is to operate at 1600rpm and carries 8KN radial load and 6KN trust load. The bearing is subjected to a light shock load. Determine the rating life of the bearing.                                                                                                                         (8)
15 . (a) A multiplate clutch has six plates each of outer and inner diameters of 150mm and 100mm respectively. Assuming µ=0.3 and uniform intensity of pressure of 30×104 N/m2, determine power transmitted at 1200rpm.                                                                                                  (16)
(OR)
(b).A multiple disc clutch has 5 plates having four active frictional surfaces. Determine the axial intensity of pressure between the discs transmitting 37.3kw at 500rpm. The inner and outer radii of friction surface are 75mm and 125mm respectively. Assume uniform wear and µ=0.3      (16)