Lubricant guidance in machine elements
Insufficient lubrication in loaded tribological contacts such as bearings and gears is a problem that causes severe damage. Due to frictional heating within the contact zone, a temperature gradient develops between the loaded contact (higher temperature) and the unloaded regions (lower temperature). This typically leads to a surface tension gradient within the lubricant and consequently migration from hotter to cooler regions by Marangoni-forces, finally yielding in a lack of lubricant in the zones where it is most urgently needed. In contrast to that, there are stabilizing factors, such as capillary forces and the viscosity of the lubricant, which hold the liquid in the zone of higher temperature. All these factors are highly depending on temperature. The possibly resulting inadequate lubrication conditions may produce changes in the lubrication regime leading to increased contact between the sliding surfaces, increased wear and component failure. To counter this, identifying and controlling the governing forces involved in promoting or impeding lubricant migration becomes decisive. Temperature gradients, surface chemistry and topography effects play an important role in this context.
There are numerous techniques to create well-defined topographies and thereby manipulate wetting and lubricant spreading. Introducing channel-like structures in material surfaces have the benefit of using capillary forces by guiding the lubricant to the tribologically stressed areas. Major drawbacks of most of the abovementioned methods include their multiple processing steps and their limitations in geometry and feature sizes. In this context, laser-patterning techniques are very efficient because they allow for fast and precise surface treatment of various materials.