Self-lubrication Solutions for Critical Applications - Polymer Bearings

About Polymer Bearings

In an already crowded bearing space, polymer bearings have made their mark for a host of different reasons. As a result, an area that was once dominated by steel and phosphor bronze is increasingly giving way to high performance polymers such as PTFE, PEEK, POM, and Nylons, where the sheer breadth of grades and fillers allows for a whole range of properties tailored to match the end-application and offer a solution that far exceeds what metal bearings were able to hitherto provide.

The advantages and disadvantages of polymer bearings against metals can be shown on the chart below:

Polymer Bearing
Advantages	Disadvantages
Lightweight	Limited load capability
Fully customisable	Can be expensive
Self-lubricating	Limiter temperature range
Easy to replace

 

As shown above, metallic bearings are typically preferred where the loads and possibly the temperatures are much higher. Here too, however, certain polymers such as PEEK and Polyimide (Kapton), can bear enormous loads and remain functional in temperatures of 300°C+. However, such polymers come at a price and are therefore limited in applications such as aerospace and medical, where cost may not be a key criterion.

However, for many applications, polymer bearings find that their advantages are highly sought after. Key among this is the ability to self-lubricate. Self-lubricating polymers such as PTFE, POM, and UHMWPE - to name just a few – offer dry-running capabilities which greatly reduce the need for external lubrication. This is especially valuable in consumer goods, where the structure of the device or appliance is such that the user will not have access to the moving parts. Similarly, in certain industrial applications, self-lubrication ensures minimal down time and greatly reduces the wear and load due to the build-up of friction.

Types of Polymer Bearings

Polymer bearings come in various shapes and sizes and can be either machined from a drawing or reverse-engineered from an existing part. Some of the typical bearings offered by Poly Fluoro Ltd. include:

1. Flange bearings
Flange bearings are designed to handle both axial and radial loads. In some designs the flange is also used as a locating mechanism to hold the sleeve in place.

Flange bearings can be machined either from stock rods or moulded. Polymer grades used would include PTFE (usually with a glass or bronze filling), PEEK (virgin or carbon filled), PPS (usually with a glass filling), and POM.

Flange bearings require a little more machining to the housing but can solve the unique load conditions of a shaft and some type of thrust surface.
 

2. Mounted bearings
Mounted bearings are machined with a double flange in order to sit within a pillow block. These bearings can be fabricated using several different plastic bearing materials to improve wear and reduce or eliminate lubrication.
 

3. Thrust bearings
Put simply, thrust bearings are washers made from any number of materials such as PTFE, PEEK, PPS, POM, Nylons, or Polyimides. They are generally thin, easy to install and prevent metal on metal contact in any thrust load conditions. They are easy to use and do not require lubrication of any kind in most conditions.

Although the design is simple, there is a need to machine the part so that the surfaces are perfectly parallel. This is where Poly Fluoro excels.
 

4. Sleeve bearings
These are the most common bearings, with a simple ID, OD, and length. However, as with the washers, care needs to be taken to ensure the tolerances are tight. Where most manufacturers would only offer a 100 Micron tolerance on linear dimensions, Poly Fluoro is able to go down to as low as 10 Microns in some cases.

The bearings are designed to carry linear, oscillating, or rotating shafts. The key to successfully designing a plastic sleeve bearing is paying attention to temperature, P, V and PV ratings for the material and match it with your application.
 

5. Spherical bearings
Spherical bearings are designed to allow for shaft misalignment, as they can rotate in two directions. Spherical bearings typically support a rotating shaft in the bore that calls for both rotational and angular movement.

Using self-lubricating polymers with very low static coefficients of friction, Poly Fluoro is able to ensure that even minor variations in alignment are immediately accommodated by the bearing to allow for non-stop performance.

While the above bearings are most common, application engineers are constantly finding new areas in which to apply the bearing properties of polymers. Ultimately, any application with repeated motion will benefit from a polymer bearing as it offers an unmatched ability to reduce wear and friction over a very long period of running time.

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