Springs

Springs

The design and manufacture of all types of springs is a highly specialized process that includes substantial lore. Notwithstanding the well documented specification or drawing, dimensional variations will abound. For example, for a coil spring, variations in pitch, diameter, and total height (unless height is ground to size) may be independent of the speed at which the coil is formed. The ratio of wire size to the spring’s diameter may also result in final variations. These anomalies confirm that springs are manufactured with considerable lore. Therefore, the experience of the supplier will greatly influence the quality, reliability, and cost of springs.

An effective way to ensure that the required spring is produced as economically as possible commensurate with the stated documentation requirement is to provide liberal tolerances for the spring application. Also, if carbon steel can be used, stainless steel or derivative materials should not be used. Spring design depends on many factors generally not addressed on the drawing or in the specification. Some of these factors are the environment in which the spring will operate, i.e., extremes of hot or cold temperatures, chemical environment, frequency and velocity of load applications, requirement for a specific load deflection or range, etc.

Springs - Mechanical Properties

There are many different corrosion-resistant steels and various non-ferrous steel compositions used in spring applications. The material selection is based on the end result to be achieved in the design. The preferred spring wire should be round in cross-section because it is more readily available, less costly, easier to fabricate, and generally has better mechanical properties. Steel wire has the longest fatigue life and can withstand the highest stresses. Copper-base alloys have the best electrical conductivity combined with good corrosion resistance. Corrosion-resisting steels have good resistance to moderately elevated temperatures and to corrosion. Nickel-base alloys have the best resistance to elevated temperatures combined with excellent corrosion resistance. More specific data on these materials are included in this section. The SAE and AISI references and the specifications of bar stock in the following paragraphs represent typical compositions of metal from which springs with the specified mechanical properties can be produced.