Design and manufacture of long-life PM bearings

Abstract

The life of self-lubricating powder metallurgy (PM) bearings is generally determined by the amount of lubricant trapped in the pores. However, as the porosity of a bearing is increased to improve the lubricant retention capacity, its strength decreases correspondingly. New methods of designing PM bearings having high porosity without a significant loss in strength are thus of interest to the bearing manufacturing industry. This paper describes the design and manufacture of PM double-layer iron bearings comprising a denser core for strength and a more porous case for improved lubricant-retention capability. Bearings of different core-case combinations were manufactured, their radial crushing strengths measured and the failure mechanisms determined. The results obtained suggest that it is possible to make such bearings with increased lubricant-retention capacity with no significant loss in strength. Taking into consideration the various processing parameters used in manufacturing these bearings, it is further suggested that an even greater improvement may be achieved if special dies are used to make the core and case sections of the bearings.