Midland-ross Corporation

Steven H Verhoff

Klaus H Hemsath

Arvind C Thekdi

Frank J Vereecke

James G Conybear

David A Krieger

An electrically heated vacuum furnace is described as having a fault detection system which has the ability to sense among other things, carbon arc buildup, a load touching a heating element, short circuits from broken heating elements, and short circuits in any heating element connection whether it be single phase, three phase delta or three phase wye connections. The system essentially comprises an electrically balanced wheatstone bridge which is in a main circuit in parallel with the electric heating element and the grounded casing of the furnace. A switching mechanism maintains the circuit in a normally open condition. A timer is provided to periodically disrupt the flow of electric current to the electric heating element in the furnace. The switching mechanism will be operated to close the circuit if the circuit is free of electric current. Should any of the aforementioned faults occur, the bridge will be thrown out of balance so that there will be a small leakage of current which is detected and utilized in the shutting down of the furnace in cases where the fault is severe and necessitates stopping the operation of the furnace.

Electrically heated vacuum furnace with a fault detection system

A radiant burndown tube for furnaces which have a chamber sealable from the ambient atmosphere and in which there is a combustible gas. The burndown tube is divided into three functional areas; the burner leg, the exhaust leg and a tube portion. The tube portion is located within the furnace chamber. There is an inlet where the combustible gas from the furnace chamber is drawn into the burndown tube. The combustible gas is mixed with air and ignited in the tube and the combustion products are exhausted via the exhaust leg. Thus, the heat energy normally lost in the burndown of combustible furnace exhaust gases outside of the furnace is captured and used to provide additional heat to the furnace.

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Toledo, OH, United States of America

Steven H Verhoff