When the temperature of the teeth of a plastic gear used for motive power transmission increases, for example due to frictional heating, the ability of the gear to resist bending decreases and wear increases. Gears are normally lubricated with grease to suppress this effect, but it is necessary for the lubrication effectiveness to be maintained over long periods. In the present study, we experimentally investigated the effect on lubrication performance and durability of providing oil grooves in gears made of four different materials as well as the effect of making the tooth flank rougher to form oil reservoirs. The results are summarized as follows: 1) In grease lubrication of plastic gears, since the base materials of the two gears are in contact over a fairly large proportion of the total gear area, the temperature increase of the gears depends on the material properties. 2) The durability of a polyacetal gear with oil grooves, lubricated with urea grease of high kinematic viscosity, is approximately 68% higher than that of an ordinary gear. Increasing the surface roughness had practically no effect. 3) The increase of durability due to oil grooves and increased surface roughness of a gear made of a hardened material consisting of nylon 66 rilled with fiberglass, is less than that of a polyacetal gear.
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