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Helical Springs: Effect of Temperature of Environment
Effect of Temperature of Environment Low Temperatures Helical springs, even at temperatures down to -300oF made from high carbon spring steel show no sharp loss of toughness. In contrast, low carbon steels become brittle at sub-zero temperatures. Since a spring is basically a resilient structure which yields readily to impact loading, there appears to be little danger of failure attributable to low temperature lack of ductility in steel springs. The chart below shows how a change of elastic modulus is experienced with all spring materials, except the constant modulus alloys, as the temperature drops. If the spring rate is critical at lower temperatures then this must be allowed for in the spring design. 
Elevated Temperatures Increase in temperature will affect the elastic modulus and the elastic limit of most spring materials. The decreasing elastic modulus of spring alloys as temperature is increased is shown in the chart above. This change is completely reversible. Also, the rate of the spring will be changed in proportion to the modulus. 
The change in yield strength for several spring materials is shown in this chart to the right. The decrease in strength is not reversible. To avoid this, the designer needs to use a design with lower stresses when the spring is to work in and elevated temperature environment. Keep this in mind for compression spring design or torsion spring design.
When working out the preliminary helical spring design that is to work in an elevated temperature environment what must be considered are:
Time dependent changes in springs occur when a sustained stress is applied at an elevated temperature. Keep in mind, these changes will occur at room temperature if the stress is high enough. Increasing the temperature merely increases the rate of change. Normally the change occurs as a reduction in helical spring length under load or a reduction in spring load at a fixed length. This relaxation occurs rapidly at first and then at a decreasing rate over time. There is no apparent end point.
The primary factors that affect rate and total extent of stress relaxation in a helical spring are:
The degree of residual stress in the material affects total relaxation. Large amounts of cold work in the wire have been found to increase relaxation. The charts on this page: Spring Relaxation Data for Various Wires , are extremely useful in designing for load loss. This data should be used as reference data as it is impossible to cover all variables.
When springs are to be used in elevated temperatures the optimum design can be very complex. Special manufacturing techniques can reduce the total stress relaxation of the helical spring. This is why it is important to discuss these designs with the spring maker. His experience can provide great insight as to what can be accomplished and at what cost. Stay tuned for updated information related to Helical Springs: Effect of Temperature of Environment. Our team and visitors to spring-makers-resource.net will be contributing.
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