A method for heat-treating metallic workpieces, in which a flow of cooling gas is generated in a vacuum furnace by a fan in order to quench the workpieces, with the fan being driven by a rotary current motor that is operated with a predetermined supply voltage above a minimum pressure in the vacuum furnace...http://www.google.es/patents/US6428742?utm_source=gb-gplus-sharePatente US6428742 - Method for heat-treating metallic workpieces
