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Originally Posted by [url=http://www.tribology-abc.com/abc/sinter.htm

this site[/url]]Porous bearings are manufactured by sintering, e.g. powder of the material components is pressed together at high temperature and high pressure. Despite of the powder is melted together capillary channels remain resulting in a porous material. By impregnation of the channels with liquid or solid lubricants, bearing materials acquires that are lubricated for life, they have not to be lubricated during lifetime. As a fact of the capillary channels porous materials are bros and sensitive for cracks.

Examples of sintered porous bearing materials are the ceramic materials, carbon brushes of electric drives, porous bronze bearing bushes, aluminum matrix composites consisting of a mixture of aluminum powder and ceramic granules and sintered polymers.

The most widely used type of porous bearing in consumer apparatus is a porous bronze consisting of 90% bronze, 10% tin and often some addition of graphite and lead to improve dry running properties. Furthermore a frequent use is made of porous iron bearings, which can take up a higher bearing load but have a lower permissible speed of the shaft in the bearing.

Lubrication regime: About 10 to 35% of the porous material consists of lubricant impregnated channels. As a consequence of the porous bearing surface a sufficient hydrodynamic pressure distribution to avoid mechanical contact between shaft and bush as in solid bearings cannot be created. The pressure build up forces the oil into to pores of the loaded part of the bearing. Then the oil flow to the unloaded section of the porous bearing and replenish the gab [Morgan, 1957]. The type of lubrication that occurs can be assessed by determining the so-called Stribeck curve, which gives the relation between the friction and the shaft speed. Depending on rotational speed and load porous bearings almost invariably operate in the region of mixed lubrication.

It could be a mix of bronze and PTFE or graphite powders