Investigation of the application of nickel dispersion coatings for fluid-free lubrication systems in linear guides

Linear guides with roller bearings are of great importance in many applications. In the case of high loads, they usually have to be lubricated with fluids to ensure low friction and sufficient service life. However, in some applications fluids cannot be used. Therefore, fluid-free lubrication systems are sought that can withstand high loads and can be operated maintenance-free over a longer period of time. One approach is to use solid lubricants that are continuously released during operation, e.g. as part of the cage. The suitability of nickel-phosphorus composite layers with embedded PTFE and hBN particles, which shall be used for coating the cages, was investigated. A multi-stage test procedure was used, consisting of two-stage ball-on-disc tests, three-roller tribometer tests and application tests with linear bearings. In the tests with linear bearings, a setup decoupled by air bearings was used, to enable a sensitive friction force measurement. Different coating variants were investigated which included coating of the cage as well as the rolling elements. The effects on the friction and wear behaviour were evaluated. The evidence of transfer layer formation was provided. Friction and wear could be significantly reduced in comparison to the uncoated, unlubricated reference system.