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17/01/2012
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Bearing manufacturers are increasingly looking to develop and use alternative materials for a variety of different applications. It is being driven by both the demand from engineers for better solutions as well as the result of a concerted effort by industry to open up and engage with new market sectors.
 Plastic plain bearings have long been making inroads into the mindset of the design engineer, and while headway has been made in many applications, certain sectors remain largely untapped. Northampton based igus has long been identifying applications where its range of polymer bearings can be used with comparative performance to metallic bearings. The most recent is the development of a bearing for the food and drink industry.
The bearing can be recognised by metal detectors, despite being manufactured from plastic. The US Food and Drug Administration approved material allows the part to be in direct contact with food, where other bearings, such as nylon bushes, cannot. Furthermore the material can touch food and even be ingested, without causing harm.
Matt Aldridge, director of igus UK, says: "We have found that a lot of machine designers and builders are moving to blue components, as this has become the de facto standard, and it is not a sector that we have traditionally been strong in. So we decided to develop a plastic that would enable us to provide a better solution.
"Blue coloured items, ranging from plasters to hair nets, are now widely used in food preparation areas and large scale mass produced food lines, which is why we've developed a blue range of bearings specifically for this industry."
A dye is added to the bearing which slightly reduces mechanical properties, but enables the plastic to still be more than capable of operating in most food manufacture and processing machines. The bearing has high wear resistance, can handle long term exposure up to 180°C and is resistant to a variety of chemicals and other liquids. The plain bearing has a low coefficient of friction, is corrosion resistant and, lubrication and maintenance free.
Bearing specialist Schaeffler has been more traditional in that it is largely known for its metallic bearing products. But, it too, is using alternative materials to develop bearings for new applications and has identified renewable energy systems such as solar, wind, wave and tidal power as being ideal for composite plain bearings. In solar energy systems plain bearings are particularly suited to the operating conditions, which often involve slow swivelling movements at high loads.
Additionally, its metal polymer composite bearings are particularly effective in oscillating applications. The metal polymer is used to provide low wear sliding characteristics, as well as high load-carrying capacities - up to 250N/mm2 - and high thermal conductivity.
Composite materials can also be used in water or other media due to its high moisture resistance. These products are available as bushes, flanged bushes and thrust washers, and are ideal for applications where there are very small radial or axial design envelopes.
The materials available in the metal polymer composite bearings range include a porous bronze sintered structure applied to a steel or bronze backing, which is impregnated with a special plastic compound. The solid lubricant produces a film between the sliding surfaces, which provides low noise with a low friction coefficient throughout the bearings entire service life.
Schaeffler recently launched its Elgotex range of plain bushes to provide a variety of technical advantages. The products unique, entwined double layer design means each bush comprises of two layers of wound material. The inner, sliding layer is made from synthetic fibres and PTFE fibres in epoxy resin, whilst the outer layer comprises continuous glass fibres in epoxy resin.
Elgotex plain bushes are lighter than their bronze equivalents and highly resistant to corrosive media. They also perform well in applications where swivel or axial movement is required and have good vibration damping properties.
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Author
Justin Cunningham
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