Question Set 30

Question No. 1

Define the term critical speed.

Answer:

The speed, at which the shaft runs so that the additional deflection of the shaft from the axis of rotation becomes infinite, is known as critical or whirling speed.

Question No. 2

Factors considered designing a shaft?

Answer:

Strength and Stiffness

Question No. 3

What is a key? What are the types of keys?

Answer:

A key is device, which is used for connecting two machine parts for preventing relative motion of rotation with respect to each other.

The different types of keys are

1.     Saddle key

2.     Tangent key

3.     Sunk key

4.     Round key and taper pins

Question No. 4

What is the main use of woodruff keys?

Answer:

A woodruff key is used to transmit small value of torque in automotive and machine tool industries. The key-way in the shaft is milled in a curved shape whereas the key way in the hub is usually straight.

Question No. 5

What are the various failures occurred in sunk keys?

Answer:

Shear failure and Crushing failure.

Question No.6

What is the function of a coupling between two shafts?

Answer:

Couplings are used to connect sections of long transmission shafts and to connect the shaft of a driving machine to the shaft of a driven machine.

Question No. 7

Under what circumstances flexible couplings are used?

Answer:

They are used to join the abutting ends of shafts when they are not in exact alignment.

They are used to permit an axial misalignment of the shafts without under absorption of the power, which the shafts are transmitting.

Question No. 8

What are the purposes in machinery for which couplings are used?

Answer:

Couplings are used

1.     To provide the connection of shafts of units those are manufactured separately such as motor and generator and to provide for disconnection for repairs or alterations.

2.     To provide misalignment of the shafts or to introduce mechanical flexibility.

3.     To reduce the transmission of shock from one shaft to another.

4.     To introduce protection against over load.

Question No. 9

What are the main functions of the knuckle joints?

Answer:

It is used to transmit axial load from one machine element to other.

Question No. 10

How is a bolt designated?

Answer:

A bolt is designated by a letter M followed by nominal diameter and pitch in mm.