Rewound/rebuilt motors 1

[bigbigmac]

I have read articles in trade magazines that when you bake out a motor( in order to get the windings out) that there is some degridation of the iron. Does anyone have any references on that?

 

[electricpete]

A good description including test data published by EASA available for free:

http://www.easa.com/indus/rwstdy1203.pdf

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[aolalde]

Oven to burn the winding insulations could result in out of control temperature. Such an over temperature could destroy the lamination coat insulation creating short circuits that increase eddy currents and finally core losses.
Note that the insulation and resins will become combustibles out of control.
To reduce that problem, use special designed ovens for winding burnout and cut out the winding coil heads. 700 F seems to be a safe temperature for most common coats of electric laminations. Be careful since there are some exceptions.

 

[Farkel]

Another way the wire is stripped from the stator, is by a dip tank of chemicals, which eat away the resin, and there by the shop cuts, and pulls out the windings. This is so there is no iron degradation, and is done in say aluminum frame motors, which would melt otherwise.

 

[starkopete]

When properly controlled, a burn off oven will have negliable affect on the core. As a matter of fact the intial burn off on a core can actually reduce your core losses by releiving stresses that were present in the laminations (this occurs with stamped laminations).
The shop I work at is certified by an independant test lab (Advanced Energy) for maintaining motor efficiency after repair/rewind. Part of this certification involved sending them 2 new motors that they tested to establish base lines. They then returned them to us for a complete burn off/rewind cycle and they then retested them. Part of maintaining our certification is to go through this process on an annual basis using one of the original motors (must be the same one). After three burn off rewind cycles the core loss is virtually unchanged from the new motor. When the new motor was tested it had a core loss of 0.25kW and after the last test it was 0.25kW. The motor is currently being tested for the fourth time but we do not have the results yet.