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Innovative Plastic Compression Springs Are Introduced

A new suite of Plastic Compression Springs produced in a plastic composite by Lee Spring mark a breakthrough in spring technology. Called LeeP, the springs combine the strength of metal with the special attributes of high performance engineered thermoplastics. This is not something Lee Spring developed on a whim. Increasingly, the company was being challenged by design requirements that went far beyond just load bearing capability. Users wanted springs that were resistant to chemicals, non-magnetic, physically stable at high temperatures, lightweight, non-conductive and recyclable.

Metal alloys met some of these criteria, but not all, and at varying levels of success. But the specifications could be met by 'space age' inert non-metallic alloys. So Lee Spring looked at designs and materials that combined the strength of metal with the special characteristics of high performance plastics. The solution was to use plastic resins, strengthened with a suitable filler (such as fibreglass, carbon fibre or others) to form a high strength plastic composite.

Following years of engineering design and materials research by the company's technical team in the USA, Ultem resin was chosen, being used already in components meeting similarly challenging design requirements. Ultem resin is produced by SABIC Innovative Plastics, a leader in engineered thermoplastic material solutions.

The resulting springs are manufactured in Ultem PEI resin. Of the various manufacturing processes available, Lee Spring's research led it to injection moulding. From a manufacturing point of view, there are some interesting differences between making wire coiled springs and injection moulded springs. If you want to change the spring rate change of a wire coiled spring, then you change the wire size or change the outside diameter and/or free length. It is also easy to change the physical dimensions. With injection moulding, the corresponding process requires altering the amount or type of filler in the composite, or, if you want to change the physical dimensions, you need a new mould. But in terms of the manufacturing process itself, it turns out that it is easier to produce consistent springs, with greater precision and tighter tolerances, in plastic than it is in metal, although the tooling time and costs are significantly greater.

Performance advantages
Plastic composite springs offer many advantages including stability of physical and mechanical properties up to 170°C (340°F), high strength to weight ratios and excellent corrosion resistance. The 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. Low toxicity and flammability ensures environmental safety, and the material is fully recyclable, as well as RoHS and REACH compliant.

LeeP plastic composite springs are available in six colours, but that's not simply for aesthetically pleasing reasons. The colour coding indicates the strength of
the individual product, running through red, orange, yellow, green, blue and violet in order from weakest to strongest.

There are 48 designs to fit standard hole sizes. If your design requirements should change, instead of changing to a different size of spring, you can instead use different composites with the same physical dimensions to give you different spring rates. And different sizes can be stacked or nested to give varied lengths and spring rates, affording a high degree of flexibility. Custom design options to meet precise performance requirements will also be offered.

Applications are expected 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, semi-conductor, instrumentation and communications sectors.

Elsewhere in the Lee Spring portfolio, recognising that as components get smaller so do the size requirements for springs, the company has responded to the challenge of miniaturisation by introducing Bantam Mini compression springs and will soon announce the availability of smaller sized products within its stock spring range.

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