Design of Machine Elements | Gate Mechanical Basic Concepts
1.In majority of machine members, the damping capacity of the material should be zero.
2. At quite low temperatures (say -75°c) the notched bar impact value of steel decreases significantly.
3. The crest diameter of a screw thread is same as major diameter.
4. If d is the diameter of bolt hole then for a flanged pipe joint to be leak proof, the circumferential pitch of the bolts should be 20√d – 30√d.
5. Muntz metal contains copper-zinc.
6. A Babbitt is antimony bearing lead or tin alloy.
7. Steel balls for ball bearing are manufactured by cold heading.
8. The blow off pressure of a safety value is 106% of boiler working pressure.
9. A foundation bolt with a circular end is secured to the floor by means of a steel cotter. If the pull on the bolt is 14000 kg, the diameter of the bolt should be 60 mm.
10. In case knuckle joint the pin is most likely to fail in double shear.
11. The key is cut is both shaft and hub is case of sunk key.
12. Splines are used when axial relative motion between shaft and hub is necessary.
13. Splined shafts are generally used in automobiles.
14. Universal coupling/Hook’s joint is used for non-collinear shafts.
15. In flange coupling the weakest element should be key.
16. Turn buckle has left hand threads on one end and right hand threads on other end.
17. Elastic nut is a locking device that has hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip.
18. Treating the weld as a line, the moment of inertia about center of gravity of a circular weld of diameter d, would be πd3/4.
19. A single ply leather belt running at a belt velocity of 300 ft/min is likely to transmit per inch of width 4.0 HP.
20. For butt welding of two plates each of which is 25 mm thick, the best process would be electro slag welding.
21. The compression members tend to buckle in the direction of least radius of gyration
22. The diameter of a washer is generally slightly more than the diameter of the bolt.
23. A reinforced concrete beam is considered to be made up of heterogeneous material.
24. According to Euler’s theory the critical length of a column is given by Pc = π 2EI/L2 .
25. Rankine formula is valid up to slenderness ratio of 120.
26. Slenderness ratio of a column is length of strut/least radius of gyration.
27. In hydrodynamics bearing the oil film pressure is generated only by the rotation of the journal.
28. If P = bearing pressure on projected bearing area, z = absolve viscosity of lubricant, and N = speed of journal, then the characteristic number is given by ZN/p.
29. The rated life of bearing changes inversely as cube of load.
30. The oiliness bearing does not need external supply of lubricant.
31. In cross or regular lay ropes direction of twist of in stands is opposite to the direction of twist of stands.
32. Gears for wrist watches are generally manufactured by helix angle.
33. The type of cam used for low and moderate speed engines is generally harmonic
34. The form coefficient of a spring is capability to store energy.
35. Coriolis component of acceleration is found in wit worth-quick return motion
36. Cold working of material increase the fatigue strength.
37. A Babbitt is antimony bearing lead or tin alloy
38. Addendum of a cycloidal gear tooth is epicycloids
39. Spiral gears are suitable for transmitting small powers
40. As pump speed increases its NPSH (Net Positive Suction Head) requirement increases
41. If pump NPSH requirements are not satisfied, it will be cavitated
42. Bush roller chain is used in motor cycle.
43. The working load for a chain for crane application is expressed in terms of diameter of link in cm and given by 500 multiplied by square of diameter.
44. If a square key and shaft are to be of the same material and or of equal strength, the length of key would be 1.23d, d=diameter of shaft
45. In a standard coarse thread bolt the stress concentration is maximum at root.
46. Fatigue strength of a surface may be increased by polishing the surface
47. The maximum deflection allowed in gantry girders is L/1000
48. The maximum size of the fillet weld that can be used at 3 mm
49. The maximum size of fillet weld that can be made in single pass in 6 mm
50. A rolled steel flat designated as 50 ISF 8 means the flat is 50 mm wide and 8 mm thick.
51. The column splice is used for increasing length of column
52. The minimum thickness steel member exposed to weather and accessible for painting is 10 mm
53. For determination of allowable stress in axial compression, IS: 800-1962 has adopted secant formula
54. For accurately, cut gears operating at velocities upto 20 m/sec, the velocity factor v, is given by 6/6+v
55. Zero axial thrust is experienced in herinnghbone gears
56. In order to realize the advantage of fluid friction, it is essential to have parallel oil film in bearing
57. A Shaft rotating in anti-clockwise direction at slow speed inside a bearing will be towards left side of bearing and making metal to metal contact
58. Bearing characteristics number relating Z-absolute viscosity of lubricant, N-speed of journal and p-bearing pressure on projected bearing area is ZN/p
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