Lubrication and Life of Polymer Rolling Bearings

Dr Adam Beke, University of Sheffield
Prof Rob Dwyer-Joyce, University of Sheffield
Mr Kevin Smith, BNL Ltd.

Until recently the only bearing option available to machine engineers and designers was that of traditional steel bearings. These bearings although being low friction devices and cheap to manufacture are a commodity product limited by weight, the need for lubrication, and the possibility of corrosion.

The onset and use of plastics, particularly thermoplastics, as a bearing material offers new possibilities in versatility. Polymer bearings are lighter, corrosion resistant, lubricant free, cheaper to manufacture and can be formed as part of the product itself rather than being installed as a separate part. However, due to polymer material characteristics, the bearings cannot run at speeds and loads as high as those endured by its steel counterparts.

 

Some research into wear of polymers has previously been carried out, but there is limited information on the use of thermoplastic in raceways of ball bearings. Although lubrication is not a necessity for polymer bearings a small amount of research has been carried out with regards to this as a means of noise reduction due to bearing rattle.

Polymer bearings generally fail as a result of wear within the raceways or due to pitting when a lubricant is present, this is particularly common within the inner raceway. The bearings are considered to have failed when the play, or diametrical clearance, found between the contacts of the ball and raceway exceeds a specified amount.

 

This project aims to study the way in which polymer bearings fail, with particular focus on the rolling contact between the ball and the raceways. Experiments have been carried out to determine the most appropriate lubricants for maximising capacity and life of polymer bearings, and to define operating limits for lubricated bearings (i.e. the maximum load and speed ratings) for a variety of environments.

 

A thermal model of the bearing has been constructed. This is used to determine the surface temperature for the rolling bearing operation. The results of the model have been verified using thermal imaging studies of operating bearings. Once this temperature exceeds a critical value excessive wear will occur. The critical temperature criterion is used to construct load and speed limits for different bearing sizes.

Publications:

  1. Beke, A.F., Dwyer-Joyce, R.S., Jones, F.R., Gregory, J., Wear Testing of Acetal for the Prediction of Polymer Rolling Bearing Durability", presented at the 29th Leeds-Lyon Symposium on Tribology, 3rd-6th September, 2002