Abstract: This invention relates to a muffle furnace, for continuous heat treatment during passage of material therethrough, of products, the production cycle of which includes a treatment of predetermined duration at a temperature which may be about 1100.degree. to about 1150.degree. C., which furnace is heated by a flame producing burner without the combustion gases directly contacting the products to be treated. This furnace comprises: an inlet zone provided with a means for preheating, by circulating recycled combustion gases in a double casing provided around the muffle; a heating zone, provided inside a heat-insulated chamber provided with at least one means for circulating combustion gases around the heating zone of the muffle; and an outlet zone provided with at least one means for controlling the cooling rate of the treated product.

Abstract: A nippled joint utilizes a biconical threaded nipple, for joining the ends of graphite electrodes. This new joint involves a particular machining of the threads of each end of the nipple or of the two electrode seats into which the nipple is screwed, which allows a variable clearance to be produced along the threading, this clearance passing through a minimum value into a zone located between a tenth and a quarter of the height of the engaged threading, measured from the base of each seat. A stop system which is produced by shifting at least one thread of the nipple or of the corresponding electrode seat, allows the clearance to be distributed on both sides of the joining plane of the two electrodes. The joint finds great utility in the assembly of electrode columns in an arc furnace and allows them to endure extremely severe thermomechanical strains without breaking.