Subject :- Machine Design -I

Topic :- Spring

Difficulty :- Medium

Surge in spring: When the natural frequency of vibrations of the spring coincides with the frequency of external periodic force, which acts on it, resonance occurs. In this state, the spring is subjected to a wave of successive compressions of coils that travels from one end to the other and back. This type of vibratory motion is called ‘surge’ of spring.

Surge in springs is avoided by….:

• The spring is designed in such a way that the natural frequency of the spring is 15 to 20 times the frequency of excitation of the external force. This prevents the resonance condition to occur.
• The spring is provided with friction dampers on central coils. This prevents propagation of surge wave.
• A spring made of stranded wire reduces the surge. In this case, the wire of the spring is made of three strands. The direction of winding of strands is opposite to the direction of winding of the coils while forming the spring. In case of compression of the coils, the spring tends to wind the individual wires closer together, which introduces friction. This frictional damping reduces the possibility of surge.

Note: Surge is a serious problem in typical vibrations like valve springs and guns. It is not a problem in other applications where the external load is steady.