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Helical Extension Springs Engineering and Design

Engineering Applications and Design
Engineering Materials
Spring Engineering and Design

Helical Extension Springs Engineering and Design
Design and Calculation for Springs Made From Circular Section Wire and Bar

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The object of this document is to provide an accurate and rapid method of determining the dimensions of helical extension springs made fkom circular section wire and bar. It can be used both for calculating the specification from available data and also for checking purposes. Worked examples have been included to promote understanding of the calculation methods.

The main requirements to be satisfied in the design of helical springs are maximum possible dependability and life combined with lowest possible weight and cost. At the same time the expenditure of time and effort involved in the calculation procedure needs to be reduced as much as possible. Two nomograms have been incorporated in the standard which can be used as a rapid method of arriving at provisional figures.

In spring calculations a distinction is made between springs subjected to a static or infrequently varying load and springs subjected to alternating load.

The cross-section of the wire or bar of which a helical spring is made is stressed mainly in torsion. In the calculations, therefore, the shear stresses likely to occur under load are compared with the permissible shear stresses. The stressing imposed on the spring, consisting in fact of an overwhelmingly torsional element and a negligibly small bending element, is more severe on the inside of the coil than on the outside. This stress maximum is taken into account in the calculation by introducing stress correction factor, k. Tests have shown, however, that stress correction factor k can be omitted in calculations concerned with springs subjected to a static or infrequently varying load.