Case – Damage Analysis
Vibration measurements while driving showed increased friction in an engine with non - regreasable bearings. Therefore it was advisable to replace the bearings at the next opportunity. Considering the short service life of the bearings, a damage analysis was conducted.
Analysis of all tested bearings results in an identical type of damage. Only the degree of deterioration of the grease differs. These pictures show the two bearings:
What is striking is the strong discoloration of the grease. The cover shows more signs of burning near the outer rim.
Between the balls there is dark grease that is starting to form chunks.
The picture below is a magnification:
One can clearly see the grease has become brown to dark brown. In some places there are small globules of black grease. There the grease has lost all of its lubricating value.
The picture below shows a microscopic image of the grease on the closing lid:
Clearly, the grease in the non-regreasable bearings is not suited for this use (high ambient temperature). In the course of its limited time of use the grease has completely degraded.
A higher temperature speeds up the degradation of the grease. Bad lubrication in turn causes the temperatures to rise, thus creating a vicious circle.
After some deliberation we formulated the advice not to use closed ball bearings anymore and to install automatic grease containers on the engines.
The damage analysis has helped pinpoint the cause of the short service life. It also resulted in a solution to the problem. This case teaches us that analysis of ball bearing damage is a useful tool to clarify problems fast. The course of action we followed leads to a dramatic decrease in the cost of maintenance, because there will be a clear drop in the number of overhauls.