Surging in spring

Surging in the spring is define as the wave of successive compression of coils that travel from one end to another end and back is known as surging of spring.When there are impact loads on the springs, the stress propagates along the spring wire. The end coil of the spring in contact with the applied load takes up whole of the deflection and then it transmits a large part of its deflection to the adjacent coils.This wave of compression travels along the spring indefinitely. Resonance will occur depending upon time traveled. This results in very large deflections and correspondingly very high stresses. under these conditions ,it is just possible that the spring may fail. This phenomenon is called surge.

when helical springs are used in applications requiring in rapid reciprocating motion, the designer must be certain that the physical dimension of the springs is not such as to create natural vibratory frequency close to the frequency of the applied force.

Methods to avoid

1. Natural frequency of spring must be 15 to 20 times than expected frequency of applied load.
2. Frictional damper at the centre of coil can be used.
3. Pitch of the coil near extreme ends can be varied compare to other location.

Critical Frequency

The final equation for the natural frequency, derived from the governing equation of the wave motion, for a spring placed between two flat parallel plates is given by:

f=(d√G.g÷32ρ)/πD∧2Na

For steel, this can be simplified as:

f=38.5×10ʌ4(d/NaDʌ2)