Grease Relubrication of Roller Bearings at Highest Speeds

The suitability for high speeds and the disproportionately decreasing grease operating life with increasing speed limit the number of possible applications for grease-lubricated hybrid spindle bearings in machine tool main spindles. Grease relubrication systems can solve the problem of limited grease operating life, but greases with the best speed suitability are only conditionally suitable for use in such systems. This project therefore has two main objectives: On the one hand, based on a grease with very good speed suitability, its suitability for use in grease relubrication systems is to be improved. On the other hand, strategies are to be developed using an existing grease relubrication system in order to reliably lubricate the bearing. In the end, a complete system consisting of a grease and a relubrication strategy will be developed, that will make it possible to operate grease-lubricated spindle bearings at speeds significantly higher than those normally used today.

The fat development should take place in several steps: First, comparative values for the further developed fats are to be determined on a reference fat. Then, optimized fats are to be produced by varying the composition and, if necessary, the production process. The basic suitability for speed must first be tested on these greases before investigating how the longer loading of the grease in the relubrication system affects its lubricating properties. When developing a suitable relubrication strategy, it must be investigated at which point (axial or radial) fresh grease should be supplied to the bearing and at what frequency and in what quantity this supply should take place. The aim here is, on the one hand, to ensure a reliable supply of lubricant to the rolling contacts in the bearing and, on the other hand, to avoid overlubrication, which can lead to spontaneous bearing failure.

The results of the project were published in DGMK Research Report 775.