New spring materials for 2012

Paul Boughton
What is new for spring manufacturers next year? Responding to the needs of design engineers and manufacturers for eco-friendly, lighter, easier to manipulate fastener materials will be one of the challenges. Kay Stott reports.

Over the past couple of years some innovative spring materials were brought into use in well known catalogue products. Plastic composite springs, chosen for their strength, non toxicity and anti corrosion properties, are used in medical applications and have even been considered for food and drink machinery, and aviation seats. Egiloy, a lightweight malleable material is found in applications such as smart phone production or medical instruments.

So what's next? Saving the planet is a recurring theme for everyone so recyclable or ecologically friendly materials being put into new products is good news. For many industries, especially automotive or aerospace, robustness, lightness, and resistance to corrosion and flammability are also critically important.

Carbon fibre springs

Carbon fibre is something of a 'buzz' word right now. Why is carbon fibre so special? Aside from looking both aesthetically elegant and sporty, carbon fibre is an extremely strong and lightweight material. These characteristics make it desirable for a variety of applications and industries such as aerospace, military, motorsports, competitive sports, energy and civil engineering. A carbon fibre strand diameter is measured in micrometres, the lowest being around 5 micrometres - this is much, much less than the width of a human hair.

However, the material properties also have some disadvantages. Although the material has a very long life, recycling has been a problem. The University of Nottingham is the lead UK partner in developing new ways to extract long carbon strands from the polymer that can be reused.

Another concern is that the material is very brittle. So can carbon fibre be used to make a spring?

More flexible material at the core

A spring made purely from carbon fibre would have very limited elasticity. However, when used as a resin to reinforce a plastic composite spring, it can perform exceptionally well under load with minimum side thrust, giving a superb strength to weight ratio.

Carbon fibre reinforced resin comes only in black colour, as to introduce other colour pigment would make the material more brittle. This means spring manufacturers could not use their traditional method of colour coding to indicate the spring rate.

There is undoubtedly a need for an economical helical compression spring that doesn't compromise on performance, made of a material that is completely recyclable and meets some or all of the secondary requirements that have proved a challenge to traditional steel springs: including high corrosion resistance, light weight, high strength to weight ration, low electrical and thermal conductivity and non magnetism.

Carbon fibre reinforced springs could meet most of the above criteria and, if they could be efficiently manufactured at low and high quantities by means of injection moulding, that would be a breakthrough.

Despite the complexity of this process, leading spring manufacturers are already trialling carbon fibre polymer technology with a view to launch within the next year. The high strength to weight ratio of carbon fibre material makes it an irresistible product for all automotive and aerospace applications. Even down to the springs.

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Kay Stott is European Marketing Manager, Lee Spring, Wokingham Berkshire, UK.

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