Given the choice, most of us would prefer something new over something rebuilt, or re-manufactured. It just makes sense. New is always better. Right? Maybe not with electric motors.
75% of the rotors we rebuild here at New Core are cast aluminum rotors. That is, the rotors have aluminum bars and end rings. Virtually all of those rotors are factory rotors. Some have been in service for years, others not so long. When we rebuild these rotors, we rebuild every part of the rotor, including laminations, bars, and end rings.
Yes, we could save money if we reused the part of the old rotor. But, this is a case where, what came from the factory is not better.
The attached photos are a week’s worth of cast aluminum end rings on their way to the scrap yard. Enlarge the photos and look closely at the cavities and voids. If these were teeth they would be a dentist dream. But, these cavities did not come from decay. This is the way they were made. These rotors were cast at the factory that way. In the one photo, we turned both sides of the end ring down to get to the fins. Notice the cavities in the fin. These are the fins where many repair shops bolt on balance weights. It is a wonder that more fins do not collapse or fly off.
If you ever wonder why some new rotors have so many balance weights on them, the voids are part of the reasons. There is simply more mass in one part of the rotor than the other, because of cavities.
If you want to think of something that will keep you up all night, think about the aluminum cast bars. Unable to remove factory bars, we have no way of knowing what cavities lurch beneath the surface. But, be assured the cavities are there.
Why are the cavities there? It is simply a manufacturing flaw. Spin casting is not a perfect art. The aluminum does not heat, flow, and cool perfectly. Cavities result. To mass manufacture an aluminum rotor in a cost productive way results in voids and cavities.
Here at New Core, years ago, we experimented with a lot of things, including spin casting. We could do no better than the factory. We gave it up, for something better.
You may ask, “But, do the voids really hurt anything?” After all, some of the motors have been in service for years, cavities and all. This is true. You can also continue eating with cavities in your mouth. However, one day it will catch up with you. So it is with some of these rotors. Depending a number of factors including load, application, and the volume of cavities, some performance and efficiency is certainly compromised in rotors with casting cavities. Often failure is the ultimate result.
We eliminate that possibility at New Core with rotor bars that we custom extrude on site. The connecting rings are welded and not cast. The process is not nearly as fast or inexpensive as the factory’s process. However, it virtually guarantees there will be no voids or cavities, instead producing a solid bar cage. Not factory new, but certainly better.
Mark S. Ross