Electric Motor Failures

With out visual inspection it's a guess on my part. That the fluid is either a combination of bearing grease from bearing at the commutator end of the armature. Or the motor housing was never cleaned of machining fluids. One or the other mixed with the fine black carbon dust the brushes give off during wear. If it's on the commutator more likely from the bearing. They may have changed the grease they use and it's running do to heat it was never designed to endure. Or your use or the application has the grease to hot. Have seen this problem on many electromotive equipment where the improper grease was used to lubricate the bearings.

It could also be a number of other things. I have seen valves misapplied to steam that were not rated for that kind of temperature duty, I have also seen CIP (Clean In Place) systems in the food industry that use steam for sterilizng and nobody thought through the effects of the heat on things like valves etc. So just because you have 250° (assuming F) rated grease does not mean it will survive in a steam environment

Also, you mention that your controller is current limiting at 5 amps, but you don't mention if you ALSO included a time limit on that, often referred to as a "stall condition trip". If for example your end-of-travel detection was faulty and the motor never turns off against a completed travel, that 5A current limit will turn your motor into a heater and cook the grease.

The point is, there are a number of things this could be. Start by eliminating the obvious (if you haven't already) such as misuse, then work towards the less likely conditions. Assume nothing.

Good luck.

I think you have do a "failure modes and effects analysis (FMEA)"

You have had some suggestions as to the origin of this fluid.

I think that you need to examine and analyse, even modestly, the consistency etc of this fluid in a way that will help determine it's origin and composition. This way you will be able to know if it is the grease (not good for the environment or defective...) or some other contamination.

motor windings are normally insulated with a lacquer as an insulator. it sounds like the motors are running hot.

If the insulating lacquer is melting with the heat, then on examining the motor at cold temp, the lacquer will re-solidify... therefore, the consistency of the liquid should tell a lot about its origin and type.

Grease in motor bearing could become a fluid and gets sparyed.How is the unit? is it a monoblock?

Our evaluations are showing that it is possible to load the amature and commutator area of the motor with grease and create a failure. We did find that the substance on the inside of the motor looked dark due to the breaking down of the motor brushes and we found a more clear fluid behind the magnets in the motor. What is becoming a top cause may be due to a failure in the valve the motor is driving that leads to excessive heat build-up causing the grease to liquify much quicker than normal and then it would making wicking a possibility.