Grease relubrication of rolling bearings at highest speeds

 

The speed suitability and the disproportionately decreasing grease operating life with increasing speed limit the number of possible applications of grease-lubricated hybrid spindle bearings in machine tool main spindles. Although grease relubrication systems can solve the problem of limited grease operating life, greases with optimum speed suitability are only conditionally suitable for use in such systems. The grease in the feed lines is permanently stressed by waste heat from the bearings and the feed pressure of the relubrication system, which can lead to separation and hardening of the grease.

Two main objectives are therefore pursued in this project: 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 to reliably lubricate the bearing. In the end, a complete system consisting of a grease and a relubrication strategy will be developed, which makes it possible to operate grease-lubricated spindle bearings permanently well above the speeds usual today.

Grease development is to take place in several steps: First, comparative values for the further developed greases are to be determined using a reference grease. Then optimized greases are to be produced by varying the composition and, if necessary, the manufacturing process. The basic speed suitability must first be checked on these greases before the effect of the longer load on the grease in the relubrication system on its lubricating properties can be investigated. When developing a suitable relubrication strategy, it must be examined at what frequency and in what quantity fresh grease should be supplied to the bearing. The aim 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.