Influence of Spring-Back on the Characteristics of the Spiral Spring

Abstract

In this paper, the method of manufacturing the spiral spring is examined to develop a theory for this type of spring giving a closer agreement with practical tests than does the conventional theory. The theory makes use of Gardiner's (1***)† equation for spring-back to develop the equation of the free spiral of the spring and then considers that, in operation, the process of winding up or running down can be considered as the difference between winding up from the free spiral to the run-down state and winding up from the free spiral to the wound-up state. In the conventional theory for this type of spring, the active length is considered to be constant and equal to the strip length and the moment versus the rotation of the arbor plot (torque characteristic) is apparently always linear. In the theory presented below, the variation in active length is taken into account and non-linearities in the torque characteristic become evident. The theory assumes that the forming of the spring takes place under the action of pure bending without anticlastic curvature and the strip is assumed to behave as an ideal elastic-perfectly plastic material.