Operational behavior and wear of PVD-coated and dry lubricated gears

The use of liquid lubricants in gear drives is limited due to the lubricant properties, for example by hygiene guidelines or high temperature fluctuations. Solid lubricants are an alternative to liquid lubricants in gear drives. However, the requirements placed on the lubricant in the tooth flank contact are not met to the same extent by a solid lubricant as by a liquid lubricant. The state of research shows that the application behavior is not stationary in terms of the frictional force and test piece temperature. For the knowledge of the application and wear behavior in tooth flank contact, test gears are coated with a MoS2:Ti-TiCN solid lubricant system and analyzed in running tests. The comparison of the load cycle numbers at two different load levels shows that the service life of the solid lubricated gear set decreases with increasing torque. When analyzing the tooth flanks after the running tests different wear phenomena can be found. A distinction can be made between wear of the solid lubricant layer, local layer failure and complete layer failure. Microscopic wear analysis show that the wear on the pinion and wheel varies in intensity. Greater wear tends to be observed in the areas with high sliding speeds in combination with negative slip. For future running tests with dry and solid-lubricated gears, the early detection of layer failure has to be investigated. Furthermore, the transferability of wear from the Disk-on-Disk analog contact to the tooth flank contact has to be investigated.