Don’t Ignore Your Motors’ Lubrication

Sometimes, just looking at the outside of an electric motor will tell you a lot about what you are likely to see inside and the reason for it. The 185kW AC electric motor pictured was next to one of our engineers' benches, ready to be stripped down recently. What stood out to me immediately was the discolouration – the whitening where the bearing is surrounding the shaft extension.

It has been seen for many years in the electric motor repair industry. And it shouts out, "Something got extremely hot there”.

The whitening and discolouration are caused by paint that has been burnt due to the immense amount of heat generated by the bearing. If you've ever used a heat gun to strip paint, the paint usually goes white before peeling off. That is essentially what has happened here.

With the motor stripped down, it's exactly as I'd expect it to be at the drive end: a truly ruined bearing. Even the rolling elements have decided to turn 90 degrees!

So, what is the reason for this? Well, it's easy to point to a lack of lubrication; this is the most likely and most common cause. By mentioning a lack of lubrication, I'm saying here that I suspect nobody had added grease to this bearing since it was filled by the original manufacturer.

Without proper lubrication, friction increases, heat increases, and noise increases, until the bearing gives up completely. Once the bearing has failed, the rotor can drag on the stator laminations, causing the windings to blow. The shaft can bend at this point, and then you have a scrap motor on your hands.

There are other possibilities, too. Incompatible lubricants may have been mixed. If that happens, then that, too, is a lubrication failure.

When in service, this electric motor drove a fan and had a belt drive on its shaft. The belt may have been too tight for the application, and the same outcome is possible.

Two very simple yet important things that can increase the life of your electric motors are getting an expert to install and align them and having a suitable lubrication plan in place.

I suggest that if this had happened for this electric motor, then it would still be spinning away, not in our workshops for a rewind and repair.