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Burning the insulation from motor has attacked the copper bars

My name is Lynn Wiltse. I am an electric motor rewinder. We are rewinding a large DC motor which was at one time a submarine propulsion motor during WWII. There is evidence of verdigris,(green copper), under the insulation on the copper bus bar. Some of these bars we cold cleaned and they appear to be fine. Some of them we burned the insulation off in a temperature controlled burn oven that we use to burn the insulation and resins from electric motor stator windings. The bars that we burned seem to have caused some kind of chemical reaction which has eaten away at the bars. They were burned at 730 degrees F. The integrity of the copper appears to have been negatively impacted also. I am assuming that the heat caused this. Can you tell me why? I live and work in Spokane, Wa.

Lynn Wiltse
industrial motor rewinder - Spokane, Washington, USA
November 25, 2009