Question Set 36

Question No. 1

Define pitch.

Answer:

Pitch of the spring is defined as the axial distance between the adjacent coils in uncompressed state. Mathematically Pitch=free length/n-1

Question No. 2

What are the points to be taken into consideration while selecting the pitch of the spring?

Answer:

The points taken into consideration of selecting the pitch of the springs are

1.     The pitch of the coil should be such that if the spring is accidentally compressed the stress does not increase the yield point stress in torsion.

1.     The spring should not be close up before the maximum service load is reached.

Question No. 3

Define active turns.

Answer:

Active turns of the spring are defined as the number of turns, which impart spring action while loaded. As load increases the no of active coils decreases.

Question No. 4

Define inactive turns.

Answer:

Inactive turns of the spring are defined as the number of turns which does not contribute to the spring action while loaded. As load increases number of inactive coils increases from 0.5 to 1 turn.

Question No. 5

What are the different kinds of end connections for compression helical springs?

Answer:

The different kinds of end connection for compression helical springs are

1.     Plain ends

2.     Ground ends

3.     Squared ends

4.     Ground & square ends

Question No. 6

Write about the eccentric loading of springs?

Answer:

If the load acting on the spring does not coincide with the axis of the spring, then spring is said to be have eccentric load. In eccentric loading the safe load of the spring decreases and the stiffness of the spring is also affected.

Question No. 7

Explain about surge in springs?

Answer:

When one end of the spring is resting on a rigid support and the other end is loaded suddenly, all the coils of spring does not deflect equally, because some time is required for the propagation of stress along the wire. Thus a wave of compression propagates to the fixed end from where it is reflected back to the deflected end this wave passes through the spring indefinitely. If the time interval between the load application and that of the wave to propagate are equal, then resonance will occur. This will result in very high stresses and cause failure. This phenomenon is called surge.

Question No. 8

What are the methods used for eliminating surge in springs?

Answer:

The methods used for eliminating surge are

1.     By using dampers on the centre coil so that the wave propagation dies out

2.     By using springs having high natural frequency.

Question No. 9

What are the disadvantages of using helical spring of non-circular wires?

Answer:

1.     The quality of the spring is not good

2.     The shape of the wire does not remain constant while forming the helix. It reduces the energy absorbing capacity of the spring.

3.     The stress distribution is not favorable as in circular wires. But this effect is negligible where loading is of static nature.

Question No. 10

Why concentric springs are used?

Answer:

1.     To get greater spring force within a given space

2.     To insure the operation of a mechanism in the event of failure of one of the spring