Coefficient of Friction
The coefficient of friction of a composite material is not a constant. It is dictated by the materials of the mating contact surfaces and by the roughness of the harder one. With combinations that have very different strength values (such as polymer with steel), the coefficient of friction also depends on the load. In addition, due to the polymer's strong tendency to change all mechanical properties under temperature, the coefficient of friction is also affected by speed and ambient temperature. The coefficient of friction drops as load increases and as speed decreases. It also changes as the bearings wear.
During the wear-in period, NORGLIDE® bearings are shortly exposed to higher wear. A polymer transfer layer forms on the metal contact surface. After wear-in, a relatively constant performance range is found, which is controlled by the pure PTFE compound layer.
With bronze reinforced NORGLIDE® bearing types, the coefficient of friction increases slightly after prolonged service due to the exposure of bronze to the mating surface. The bronze may then have contact with the shaft. This factor should be taken into account when selecting materials for applications with higher admissible wear or high pressure.
The coefficient of friction of NORGLIDE® T bearings stays constant over the whole service life. With NORGLIDE® PRO XL bearings, the bronze layer can be reached after a short period, and the coefficient of friction grows gradually.
Generally speaking, the coefficient of friction of NORGLIDE® bearing materials is outstandingly low in comparison with other polymer bearings due to the use of PTFE as the main component in the bearing surface.
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