The when and why of plastic springs is rarely a simple matter, made as they are from highly engineered composites and technically advanced new generation materials. Typical properties include operation at elevated temperatures, neutral magnetic characteristics, light weight, low thermal conductivity, electrically insulating and ability to recycle at end of life.
Lee Spring has worked very closely with Sabic Innovative Plastics to select the right material, adopting the Ultem resin, which is a very high-strength plastic, for compression springs ex-stock. Ultem polyetherimide performs in continuous use to 170°C and in the LeeP springs is designed to perform under load with minimum side thrust. This is achieved with a design that has a nearly rectangular cross section to maximise the amount of active material used as opposed to the more common round wire spring design. The exact cross section is a slight trapezoid to facilitate manufacturability. The design element that proved difficult yet critical is the configuration of the ends to provide for minimal side thrust and maximum flat load bearing surface without creating stress points or increasing the solid height while again accounting for manufacturability.
Plastic composite springs offer many advantages including stability of physical and mechanical properties (up to 170°C), high strength to weight ratios and excellent corrosion resistance. The Lee Spring patented design maximises spring rates and cycle life while minimising solid height. The high strength to weight ratio optimises performance while reducing mass. The material is resistant to a wide range of chemicals including acids, alkalis, bases, aromatics and ketones. And being non-magnetic, it does not interfere with imaging or ferro-sensitive technologies. As a dielectric insulating material, it is suitable for non-conductive applications, and being inert and non-contaminating, it protects product purity.
LeeP plastic composite springs are available in five colours, with the colour coding indicating the strength of the individual product, running through red, orange, yellow, green and violet in order from weakest to strongest.
Plastic springs have wide ranging applications in medical products and apparatus, imaging and X-ray equipment, food processing and packaging machinery as well as in the aerospace, marine, electronics, electrical, water purification, chemical, automotive, semiconductor, instrumentation and communications sectors.