Discussion: "Load-Deflection Behavior of Conical Spiral Compression Springs" (Wang, Han-Chung, and Worley, Will J., 1962, ASME J. Eng. Ind., 84, pp. 329–337)
Journal of Engineering for Industry
The equations represented in this paper are based on the assumption that the "large diameter end" of the conical spiral 2 Professor and Head, Engineering Mechanics, Virginia Polytechnic Institute, Blacksburg, Va. spring "is fixed," and that the load-deflection characteristics will change if the spring is also supported on a flat plate or on inactive coils. The writer would like to comment on the effect of these and other boundary conditions on the behavior of springs. Generally, the end coils
... r helical compression springs of constant radius are tapered and the seats ground. When the ends are closed the free or active coils are seated on tip contact points very near the tapered ends of the wire. The inactive turns tw r ist and bend and increase the deflection of the spring by adding about 0.4 equivalent active turns. The bending results from load eccentricity, even when the spring is compressed between parallel plane surfaces, and produces a sinusoidal variation 3 in the deflection unless the number of active coils is approximately n + 0.5 where n is an integer. 4 This effect is most noticeable in short springs where the stress augment can amount to as much as 30 per cent. It would appear that such sinusoidal variations would also develop in conical spirals for eccentric axial loads since the end seats would seldom be fixed. The dead or seated coils would increase the deflection as they do for helical springs and compensate for increased stiffness resulting from a decrease in the number of active coils with load. The writer would be interested in learning whether the authors know of ail}' tests on conical spirals similar to those noted above for helical springs in which stress augments and sinusoidal variations in deflection were measured. Such tests would confirm or invalidate the accuracy of the assumption regarding fixation of the ends.