Practical Problems in Spring Design *

Abstract

The author draws attention to the difficulties facing the engineer to whom spring design is merely incidental. These difficulties are mainly due to the complicated formulæ concerned, to lack of information regarding the materials, and to incorrect appreciation of the real functions of the spring. Standard formulæ require corrections for the effect of curvature; without these adjustments very dangerous results can be obtained. Corrections due to Wahl and Woods are incorporated in the formulæ, and finally two nomograms, for stress and deflexion calculations respectively, are produced to enable these involved formulæ to be handled easily and rapidly.

Consideration is given to physical properties, and it is pointed out that except for special conditions of service, the torsional elastic limit of the material is the most important physical property of the material in most helical tension and compression springs. Data are given for this property for patented carbon spring steel and for chromium-vanadium spring steel. Tolerances and limiting conditions are considered, and an arbitrary figure of 70 per cent of the torsional elastic limit is adopted as the maximum safe stress. Curves of load-carrying capacity are given for all standard gauges from 0·020 to 0·50 inch diameter-Special service conditions are finally considered, and suggestions made for dealing with them. In an Appendix are given various examples illustrating the use of the curves and nomograms, and the derivation of some special formulæ.