Sintered metal, self-lubricating bearings are made from powdered metal alloys pressed and baked with heat to form various dimensions.
Upon exiting their moulds, the newly formed surfaces are formed with open pores. These pores channel lubricants between the bearing itself and the shaft.
The pores are then vacuum impregnated with an oil to improve the material's load bearing ability.
The bearing material holds approximately 20% oil by volume and acts as a "sponge like" resevoir.
The most common lubricant impregnated at the factory is straight SAE 30 oil.
Sintered metal is mostly made of copper with approximately 10% tin and up to 1% iron.
Sintered metals reduced coefficient of friction makes it useful for many applications.
Uniform oil coating of the mating shaft during operation ensures good lubricant distribution.
Due to the porous structure of sintered materials, machining them poses issues. A sharp cutting tool such as tungsten carbide is stipulated as it does not "smear" the surface of the sintered metal and block the pores lubrication ability such as a reamer will do.