August 23, 2011

Some of the questions that were asked in this test include:

1. When boiler bursts, whom u would inform?
2. What does one mean by modular ratio?
3. What is ‘envelope of damped free vibration’?
4. A ball with a mass M is falling on to the ground with some velocity V1 and rising with velocity V2 . Find the impulse?
5. Contd.. for 5th problem. When time of contact is given then find force exerted on the ground.
6. Two masses are connecting with string on to pulley coefficient of friction of mass m1 is given and also m1 and m2 are given. Find the relation b/n m1 and m2 , to make m2 move downwards .
7. In a damped free excitation system maximum amplitude occurs
a. before resonance             b. after resonance
8. What are set screws?
9. A four bar link mechanism is given with moment m acting on crank and also a force given at crank end. Find the reaction at hinged end of crank.
10. Deflection due to self weight of a uniform rod of diameter D and unit density and length is given by____________.
11. Name the type of key used in wrist watch?
12. Bending stress is proportional to_____________
13. The hypoid gears are __________
14. Hollow cylinder of outer D0 is given. Find the diameter of solid cylinder for the same material and same torsional strength ?
15. What is the principle plane ?
16. Two masses are resting on a inclined plane with 30 degree angle and the two masses are welded with weightless rod and coefficients of friction is given. Find the common acceleration of a two masses.
17. Two masses are of different weights smaller one is placed on the bigger mass. If the force is acting on bigger mass (given),  find the acceleration of smaller mass.
18. Stress on minor diameter of bolt when bolt is subjected to longitudinal force.
19. no of independent elastic constants required for isotropic material?
20. pitch of the bolt of 30 mm metric thread dia meter is?
21. the ratio of natural frequency on earth to moon?
22. upper portion of set screw is given fig shown and asked which type of set screw is ?
23. Efficiency of screw jack formula?
24. which of the parts given is harder one? Ans a). inner case b)outer case like that?
25. Max efficiency of screw jack formula?
26. Given some c/s of diffirent types which is having more torsional strength ?
27. Max principle stress theory is valid for which material?
28. efficiency of reveted joints of different types has given which is having max efficiency ?
29. if the roots are real then which type of vibrations will occur in damped systems ?
30. problem on transmissibility ?
31. when the disc is rotating on which on man is standing at the edge then what is the possibility of increase in speed of the disc? A).man moves towards centre b)out ward? Like that
32. what is the principle behind the collisions of ball ?which is related to Q.7 ? ans constant linear momentum.
33. Find the elongation of the bar due to self weight
34. Problem on the cantilever deflection
35. Problem on the two blocks connected by string one is on table and on is hanging from the pulley…mechanics’ problem
36. Ratio of the tension of the band block breaks
37. max and normal efficiency of the power scew
38. what is monel metal
39. for which material max normal stress theory is used
40. efficiency of the riveted joints
41. coefficient of friction for the greased ball bearing
42. which key is used in wrist watch
43. bending stress is proportional to 1. directly/inversely proportional to section modulus
44. find the width of the strongest beam that can be cut of cylindrical log of wood whose dia is ‘d’
45. if the phi is friction angle then which of the following can not be the value of the tan(phi) a) 0 b) 1.5 mu etc. ans is 0
46. problem on the transmissibility …to calculate dynamic amplitude
47. what is the poison’s ratio?

12. Bending stress is proportional to  section modulus
13. The hypoid gears are non intersecting non parallel gears.

BELT DRIVES

August 23, 2011

Types and Selection of Drives:

• Single Unsnubbed Bare / Lagged pulley Drive
• Snubbed Bare / Lagged Pulley Drive
• Tandem Drive
• Special Drives

Single Unsnubbed Bare / Lagged Pulley Drive:

This is the simplest drive arrangement consisting of a steel pulley connected to a motor and the belt wrapped round it on an arc of 180°. This can be used for low capacity short center conveyors handling non-abrasive material. The pulley may be lagged to increase the coefficient of friction.

Snubbed Bare / Lagged Pulley Drive:

Here the angle of wrap is increased from 180° to 210° or even up to 230°, by providing a snub pulley to the driving pulley. In majority of medium to large capacity belt conveyors, handling mild abrasive to fairly abrasive materials, 210° snub pulley drive with load pulley lagged with hard rubber is adopted.

Tandem drive:

Here belt tension estimated to be high; the angle of wrap is increased by adopting tandem drives. Both of tandem pulleys are driven. The tandem drive with arc of contact from 300° to 480° or more can operate with one or two motors. The location of such drive is usually determined by the physical requirements of the plant and structural constraints.

Special Drive:

Special drives with snub pulleys and pressure belts used in heavy and long conveyors.

PULLEY

August 23, 2011

Pulley:

The diameters of standard pulleys are: 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1400 and 1600 mm. pulley may be straight faced or crowned. The crown serves to keep the belt centered. The height of the crown is usually 0.5% of the pulley width, but not less than 4 mm. The pulley diameter Dp depends on the number of plies of belt and may be also be determined from the formula:

Dp > K.i (mm)

Where

K = a factor depending on the number of plies (125 to 150)

i = no of plies

The compound value should be rounded off to the nearest standard size. While selecting the pulley diameter it should be ascertained that the diameter selected is larger than the minimum diameter of pulley for the particular belt selected.

The drive pulley may be lagged by rubber coating whenever necessary, to increase the coefficient of friction. The lagging thickness shall vary between 6 to 12 mm. The hardness of rubber lagging of the pulley shall be less than that of the cover rubber of the running belt.

Pulley types:

Pulleys are manufactured in a wide range of sizes, consisting of a continuous rim and two end discs fitted with hubs. In most of the conveyor pulleys intermediate stiffening discs are welded inside the rim. Other pulleys are self cleaning wing types which are used as the tail, take-up, or snub pulley where material tends to build up on the pulley face. Magnetic types of pulleys are used to remove tramp iron from the material being conveyed.

Typical welded steel pulley-Drum conveyor pulley

Spun end curve crown pulley

Spiral drum conveyor pulley

Welded steel pulley with diamond grooved lagging

Welded steel pulley with grooved Lagging

Spiral Wing Conveyor pulley

Power calculation for the drive unit:

The horse power required at the drive of a belt conveyor is derived from the following formula:

H.P = Te . V

Where

Te is the effective tension in the belt in N

V = velocity of the belt in m/s

The required effective tension Te on the driving pulley of a belt conveyor is obtained by adding up all the resistances.