Springs

Any device that can undergo repeated deflection and then return to its original shape with a predetermined force can be considered a spring.  When designing springs, Ticona’s engineering resins can offer weight savings, the ability to easily form complex shapes and a reduction in the number of manufacturing steps.  They can be used to make coil, leaf, and washer-shaped springs, as well as snap-fit buckles, twist-open chain links, and pop-open safety latches.

Material characteristics to consider when choosing a plastic material for a spring application include load-bearing properties, creep resistance and fatigue characteristics, as well as environmentally determined attributes like moisture absorption and temperature resistance.  Excellent long-lasting springs have been made from Celcon® and Hostaform® acetal copolymers (polyacetal is often referred to as the spring steel of thermoplastics).  Fortron® linear polyphenylene sulfide has excellent creep resistance and retains its toughness at higher temperatures, even when exposed to aggressive chemicals.  Unfilled resins such as these tend to be better candidates for small springs, since glass fibers and inert fillers limit deflection capability.  The use of impact modifiers may decrease creep resistance.

The most effective way to use plastic springs is not simply to attempt a simple one-to-one replacement of a metal spring, but rather to modify the part design to incorporate spring-like characteristics.  To get started you should first define the:

• Load on the spring element
• Shape of the spring element
• Expected duty cycle
• Operating environment (spring performance varies with temperature)
• Life requirements
• Cost of molds versus the price of common metal springs