Rob Dumayne reviews the latest developments in plastic bearings, and how industrial manufacturers can use them to produce cost savings while increasing their environmental credentials.
The history of the plastic plain bearing goes back a long way, spurred on by the discovery of the lower friction properties of nylon in around 1860. But in the past few decades, the composition of plastic materials has been refined considerably; in the past 30 years igus has developed 35 different tribologically-optimised materials, which offer a lower coefficient of friction than conventional metals or composite materials – from the economical iglidur G all-rounder to the FDA-conforming iglidur A180 material.
In addition to being lubricant-free, plastic bearings are maintenance-free, impervious to dirt, water, chemicals, heat and shock loads; and because they have essentially the same dimensional structure as conventional bearings they are relatively straightforward replacements.
The base of each polymer bearing is, depending on specific requirements, a carefully selected and blended thermoplastic matrix material. To increase the compressive strength of the bearing, reinforcing fibres are embedded within the material during the moulding process, as well as solid lubricants that optimise resistance to wear and reduction of friction. The solid lubricants are very important for the dry-running performance of bearings between the running surface, usually a shaft and the bearing, where they sufficiently lubricate the immediate area.
The great advantage of this type of homogeneous construction is its lack of layers; during the transition to the next layer, there is a distinct change in material properties which can cause wear with traditional composite bearings, this usually means the end of the bearing, since the huge increase in rates of friction and wear lead to catastrophic failure. With an injection-moulded iglidur plain bearing however, this does not occur, and the friction and wear rates are constant over the entire wall thickness and therefore life of the bearing.
Replacing metal bushings
igus self-lubricating and maintenance-free plastic plain bearings are today replacing millions of metal bushings that require oiling or greasing. They increase the safety of the machinery, reduce costs and protect the environment; and because igus rigorously tests it plastics continuously – over 8,000 tests per year for durability, friction and wear – their lifespan can be reliably predicted.
The igus ‘Product Finder’ tool helps engineers find the most appropriate iglidur polymer material that matches specific requirements (highest service life in dry run operation, dirt-resistant, vibration-dampening, resistance to chemicals, good for edge pressure, etc) and state the allowed static surface pressure, as well as upper and lower temperature information.
Rob Dumayne is Director at igus.