Every plastic material has a set of attributes. Density, strength, or dimensional stability for example. For plastic bearing design to be effective a certain profile of these attributes will be needed. Specific applications require different sets of material attributes: low density, high strength, ability to work at certain temperatures or when exposed to certain chemicals. At BNL, we have a suite of frequently used plastic bearing materials we match to our customer’s application or product requirements.
Plastic Bearing Material Selection
We work closely with our customers in the design of custom bearing products – and material selection is an important part of this process. By examining their design requirements, we can identify the constraints they could impose upon the material. We then use this information to identify the most suitable materials for the bearing.
We injection mould the majority of our products. Where there are injection moulding limitations for a polymer material, we can machine bearings from bar stock.
We are often required to combine different materials in one product. We design and manufacture non-bearing, mating parts for our bearings, such as shafts, brackets and housings. Frequently, these need to be made of different plastic materials, not necessarily the same material as the bearing.
The material we most commonly use is Acetal (POM). It is an excellent engineering polymer and gives outstanding wear performance for both moulded and machined rolling element bearings and other components.
Click here for more information about our moulded plastic bearings: Why do we mould our plastic bearings at BNL?
Materials + Design
We research and select suitable materials for an operational environment or to achieve a specific function, using them in conjunction with design and moulding techniques to push the boundaries of plastic bearing capabilities. Using materials + design we have been able to increase load capabilities and replace more components.
Plastic bearing design and material selection was key to meeting high extraction and radial forces necessary to pass anti-theft and load tests for the steering column market, where we were able to strengthen our plastic part to reach nearly 11Kn, whilst the alternative all steel solution failed at 8Kn. Roller bearings that have been designed for a photocopier and made in a material that removes static build-up from the system, eliminated the need for an expensive grounding strap, in addition to replacing 6 other components with our single, integrated assembly.
Frequently Used Materials
Chemical Name: Polyoxymethylene (POM)
Types: Homopolymer & Copolymer
Acetal copolymer is a general-purpose engineering material, used for complex or highly durable components or bearings. It combines high stiffness and strength with outstanding resilience and excellent dimensional stability, even under the effect of mechanical forces, when in contact with a wide variety of chemicals, or over a range of temperatures.
For demanding applications, Acetal homopolymer has further benefits in mechanical properties, strength and toughness.
Applications: We use acetal for the majority of our moulded bearings; from poultry wheels and conveyor products, all the way to integrated, complex designs for automotive steering columns and instrument control knobs.
Chemical Name: Polyamide (PA)
There are many types of commercially-available nylons. Nylon is one of the most widely used engineering thermoplastics because of its versatility. PA66 is commonly used as a bearing material because of its excellent balance of strength, ductility and heat resistance.
Applications: Nylons are used in bearings that require a higher flammability rating or operate in higher temperature environments than Acetal can withstand. The addition of glass fiber strengthens the Nylon material, making it suitable for metal replacement parts, such as brackets and shafts. We use Nylons in many of our integrated bearing and shaft products for photocopiers, printers and ATMs.
Chemical Name: Polypropylene (PP)
Types: Homopolymer & Copolymer
Polypropylenes offer a good balance of mechanical properties and high chemical resistance. They can be a lower cost alternative to Acetal for applications operating at lower speeds with lighter loads. They are not suitable for use with common fuels and oils, such as petrol, diesel and kerosene, or in the higher or lower temperature range.
Applications: Polypropylene bearings offer a higher chemical resistance, especially acids and alkalis, so are used for bearings that may be exposed to chemicals. Applications include the processing of chemical products, systems that need sterilizing or frequent washdowns, the food and beverage industries, pharmaceutical or chemical industries. BNL design and manufacture a variety of PP bearings for these applications, including radial bearings, end cap bearings, conveyor bearings, rollers and thrust races.
Chemical Name: Ultra High Molecular Weight Polyethylene (UHMWPE)
UHMWPE is an extremely tough plastic with high abrasion and wear resistance, plus high biocompatibility. Its versatility has made it a popular plastic for countless industrial applications that require durability, low friction and chemical resistance, and for medical/biological applications. This material is not ideally suited to injection moulding manufacture, so bearings are usually manufactured by machining from bar stock. As it is relatively more expensive compared to other plastics and also more expensive to manufacture by machining versus injection moulding, it is not necessarily feasible for high volume production parts.
Applications: BNL’s UHMWPE bearings are used in the conveyors processing glass through chemical baths for LCD screen etching and manufacturing lines where they can be exposed to harsh chemicals. UHMWPE bearings are also used in joint arthroplasty – the restoration of the function of a joint, such as in hip replacements.
Chemical Name: Polybutylene Terephthalate (PBT)
PBT is a strong and stiff, semi crystalline, engineering thermoplastic with excellent, chemical resistance and bearing wear properties. With its low moisture absorption, resistance to staining and resistance to cleaning chemicals it is suitable for many applications.
Applications: PBT bearings are often used in the food and beverage industry because of their low moisture absorption, resistance to staining by the food and liquids being processed, and because frequent washdowns with harsh cleaning solutions are required. We use PBT in our bearings for swimming pool cleaners and spa-jet nozzles.
Chemical Name: Polyetheretherketone (PEEK)
PEEK (Polyetheretherketone), is a high-performance engineering polymer with excellent resistance to harsh chemicals, mechanical properties and dimensional stability. PEEK maintains its mechanical properties even when exposed to high temperatures over extended durations. This engineering plastic has a proven track record in challenging environments. We produce our PEEK bearings from bar stock using CNC machine manufacture.
Applications: LCD screen processing, electrical components, ovens, applications that operate in harsh environments. BNL make a range of products for these industries including PEEK radial bearings, shaft support rollers and crowned rollers.