Abstract: 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.

Abstract: 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.