For an all-metallic ball bearing, cleaning in solvent in an ultrasonic cleaner can be a good option. Once I tried this for a bearing assembly that had some plastic components. The solvent dissolved the plastic and made a mess. Finding a solvent that will dissolve bearing grease is also quite challenging. I’ve had to use acetone, naptha, alcohol and still ended up having to clean the balls, races and cages tediously by hand with a cloth and cotton swabs and clean, compressed air. Filtering out the metallic or abrasive debris can be equally challenging when there are big blobs of mineral-filled grease. I’m sure that people who do bearing failure analysis every week for years have “tricks up their sleeves” to make this less tedious than it is for me. And all this happens before you can perform the necessary examination with the optical and scanning electron microscopes.

As with other types of damage, the wear analysis starts with a visual examination and document review. As just noted, there’s often quite a bit of work involved in preparing the subject components for the visual examination of both the components and the debris, when available. When there is a lubricant involved, a decision must be made regarding whether that will also be analyzed. If it is determined that this is not necessary, we must realize that we are not performing a true failure analysis. We are simply doing some lab work to gather data. We may get lucky. Sometimes it is fairly obvious that the grease wasn’t the problem. But if we haven’t taken steps to conserve the lubricant and if there are questions at the end of the component evaluation, we’ll have no way to double-check our original assumptions.

The visual examination may tell the inexperienced failure analyst something about the way the wear is occurring, but it’s more likely to simply reveal the severity of the wear so that individual components or test locations can be selected for more detailed evaluation with a microscope. We don’t want to skip the optical microscope evaluation because it’s a lot easier to view a component from different angles with an optical microscope than when it’s inside the sealed chamber of a scanning electron microscope. But, in many cases, the reflections may make it difficult to see the details of the damage that may be revealed with a scanning electron microscope. Even more difficult than viewing the damage details with an optical microscope is the task of photo documenting the relevant features on bearing assembly components. The reflections are difficult-to-impossible to entirely eliminate, and (depending on the viewing audience) a lot of arrows and the like are going to be required to highlight the features of interest.

More next time.