Plastics have a relatively low friction factor even with insufficient lubrication, high toughness or low modulus of elasticity, low density and easy machinability. Bad thermal conductivity and sometimes absorbency or swelling capacity are a disadvantage. Most plastics can only operate at relatively low temperatures.
Hardened fabrics
Hardened fabrics are produced by winding or laminating fabrics, which are impregnated with phenol hardenable resin. The uppermost glassy resin layer has bad sliding properties, that is why it must always be removed. Before final machining, the bushings must be inserted into an oil bath for dimension stabilization. High compression strength allows using hardened fabric for stressed bearings when they do not have a high operating temperature. Bushings or segments must be in contact along the whole bearing face in order that they do not bend under heavy loads. Wall thickness should be the least possible, considering the low thermal conductivity, and considerable thermal expansion. Thin-walled bushings are glued onto steel support bushings; thick-walled bushings are pressed into bearing bodies or hubs.
The functional shaft surface should be ground fine to at least 0.2 microns, shaft surface must be hardened at HRC = 50 - 55. For pressure circulation lubrication, the maximum load capacity is said to be up to 16 MPa for the circumferential speed of 1 m/sec for winded and pressed hardened fabric. The maximum load capacity of 7 MPa is applied for laminated and pressed hardened fabric. The hardened fabrics are used for excavator bushings, shells of rolling mill stands, bearings for electric traction motors, and so on.
Polyamides
Polyamides are produced in several ways. With hydrolytic and alkaline polyamide, the thinnest bushings are produced, because of small thermal conductivity. They are from 1.5 mm to 2 mm thick for a journal thickness up to 30 mm. Before the final machining, the bushings are tempered in an oil bath for 24 hours and shrinkage occurs from 0.5 % to 1 %.
Polyamide has good resistance against wear, even when operating without lubrication, but the load capacity must be small and a sliding speed 1 m/sec maximum. The maximum load capacity for hydrolytic polyamide is said to be 8 MPa for the circumferential speed 1 m/sec, for alkaline polyamide it is 5 MPa.