As operating conditions in industries such as aerospace, automotive and rail become increasingly harsh, designers are reviewing components used. Bearings, for example, need to be able to withstand these hostile environments.

In transport such as the underground, trains, aerospace and automotive, safety is paramount, and being able to operate safely at high temperatures is a key quality for bearings; exceptional thermal properties and a resistance to high temperatures are critical for the prevention of fire. 

Linear bearings are used extensively throughout transportation, for example on the seating systems in aircraft, and on escalators and advertising boards on the underground.  

Metal, ceramic and some plastic bearings can withstand temperatures in excess of 315°C, and have been used successfully in these applications. However, they are high cost. To withstand fire, plastic bearings should be classified to UL94 – V0. This is the recognised standard for safety of flammability of plastic materials for parts in devices and appliances testing.

igus has developed a triboplastic material with enhanced flame retardance which meets the UL94 V0 flame test requirements. The company believes iglidur G V0 material represents a breakthrough in both flammability performance and affordability.

The base of each iglidur polymer bearing is, depending on requirements, a carefully selected thermoplastic matrix material with exceptional properties. There are usually reinforcing fibres embedded in it to increase the compressive strength, and solid lubricants that optimise resistance to wear and friction.

Iglidur G V0 has an upper long-term application temperature of 130ºC and an upper short-term application temperature of 210ºC.  It has a density of 1.53g/cm3 and is lightweight, with high abrasion resistance to provide a long service life.

There is increased demand to replace metal bearings with plastic bearings in transportation, especially aerospace applications, for their weight advantage.  They are lighter, and therefore afford cost savings.

Designers have trusted the reliable and robust qualities of metals, such as stainless steel, and bronze to meet their bearing needs for many years.  Ceramics have also been popular for their ability to withstand rapid accelerations and high speeds. However, periodic maintenance to prevent premature failure is essential for many bearings and this is especially true for bearings used in high cycle operations, where periodic lubrication and cleaning, and the occasional adjustment are needed to minimise the effects of wear.

The main reasons given as the causes of bearing failure are lubrication issues. Bearing failure can be catastrophic, leading to hot spots and potential sources of fire.  

Plastic bearings have been around for some time and in many applications. They are resistant to dirt, dust and chemicals, are self-lubricating and can endure high temperatures, heavy loads and high speeds. However, some engineers hesitate to use plastic bearings because of the extensive know-how they have with more conventional materials. 

Plastic bearings are reliable and maintenance-free, making them a fit-and-forget solution. iglidur plain bearings contain solid lubricants which are important for the dry-operating performance. They are integrated into the plastic matrix and so perform at the contact surface between shaft and bearing. With microscopic particles embedded in millions of tiny chambers in the matrix material, the plain bearings release tiny quantities of solid lubricants, which are sufficient to lubricate the immediate area.  

The advantage of this type of design is its homogeneity and lack of layers. Layering means that during the transition into the next layer – for example, by putting wear on the actual gliding layer – a more or less distinct change in properties occurs. With traditional composite bearings, this usually means the end of the bearing, since the rates of friction and wear lead to a dramatic increase in ‘seizing up’. With an injection-moulded iglidur plain bearing this does not occur; friction and wear are almost constant over the entire wall thickness.

Designers can accurately calculate the life of an iglidur plastic plain bearing according to wear rates, actual testing results and specific application parameters. igus’ iglidur high-performance plastics are tested continuously – with over 8000 tests per year for durability, friction and wear. igus provides an Expert System – a complimentary online tool where users enter the maximum loads, speeds, temperatures, and shaft and housing materials. Software calculates the appropriate plastic bearing and its expected lifetime.

Customers have driven igus’ materials development; based on their good experience with iglidur bearings, they want to see new bearing solutions that are increasingly challenging. Now a reliable and affordable solution for high temperature resistant bearings in transport applications is a reality.