On Tuesday, February 9, 2010, we had AGR in at Dreisilker to perform training on the Aegis Grounding Brush line. This is designed to eliminate shaft currents from damaging bearings in variable frequency drive applications (and high harmonic applications) and a solution we have available and one I have used in a variety of applications, including implementing them as best practice within several organizations and some pretty harsh duty environments.
The day before we had received a call concerning a motor that had been rebuilt in December for a customer. The bearing was noisy and a technician checked it out on site. The motor was brought in, disassembled, and the bearings inspected as a result of what was discussed in the class.
The following picture is at 40x power with an inspection microscope of a bearing worn after 60,000 hours of operation (from another RCFA project – yeah, you should see what we can do to investigate motor failures and provide solutions!):
You can see a smooth-ish pattern and some definite wear (there is actually a specification). This bearing was audibly noisy and was considered failed.
Following are the pictures from the motor that had been repaired and was making noise. Microscope power of 40x +:
Inner race - hazing is due to many many pits discharged into the race. Basically numerous craters that have high edges that make noise:
The following two pictures are of the outer race. The wear pattern is known as fluting and is definitively from electrical discharges. These also contribute to the noise. The patterns on both the inner and outer race were visible to the naked eye:
Shaft brushes are becoming more convenient to install with a smaller profile. Following is the motor and shaft ring.
The inspection microscope is also a new technology we have available at Dreisilker. (I have more toys!)
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