Method for electrical heating of furnaces for heat treatment of metallic workpieces
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United States of America Patent
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Sep 21, 2004
Grant Date -
May 29, 2003
app pub date -
Nov 13, 2002
filing date -
Nov 28, 2001
priority date (Note) -
Expired
status (Latency Note)
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Abstract
In order to refine a method for electric heating of furnaces for heat treating metallic workpieces, especially vacuum furnaces usable for plasma carburizing or nitriding, in which the heater elements of a furnace are supplied with a heating voltage that is generated in the secondary circuit of a three phase transformer connected to the three phase power network such that a comparatively small reactive power component can be obtained in a simple and economical manner, it is proposed that the primary coil windings of the three phase transformer be switched in the delta connection during a first heating phase and in the star connection during a second heating phase, whereby the switchover time from the delta connection to the star connection is determined as a function of operating parameters characteristic for the heating process.
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