Vacuum impregnation

One of the special properties of sintered materials is their porosity. 

We specifically exploit this property when manufacturing sintered filters and self-lubricating bearings.

In the case of self-lubricating bearings the pore system is filled with oil or a grease in a vacuum process usually referred to as oil impregnation.

The lubricating effects stem from the oil stored in the pore system having a higher thermal expansion coefficient than the base material, and therefore upon the slightest warming (caused by friction between the bearing and the shaft) extra lubricant flows onto the bearing surface. After use when the bearing cools down the oil is sucked back into the pores as a result of capillary effects.

This can also be exploited in other structures where self-lubrication is required.

It must be stressed that not only filters and self-lubricating bearings are able to absorb oil. All conventional powder compacted components are porous unless the pores have been sealed through after treatment. 

If such components are placed in a little oil they are able to fill themselves with oil just like a lump of sugar dipped in coffee.