Abstract: A burner is connected to a fuel line and to an air supply line. A countercurrent recuperator is attached to the burner for providing heat exchange between the supply air and the exhaust gases. The recuperator has a frictional flow resistance to the exhaust gases and the supply air resulting in a pressure differential between entrance and exit of supply air, which is highly temperature dependent. This pressure differential is employed for self-controlling the relative supply air flow to the burner at different operating temperatures.

Abstract: To permit random loading of workpieces for passage through a furnace, and removal of the workpieces for subsequent handling by presses and the like, the furnace is constructed as a roller hearth furnace in which the width of the roller hearth is a multiple of the diameter of the ring-shaped workpieces, and adjacent the outlet an aligning means is provided in the form of a funnel of which one side wall is movable, for example by longitudinal or transverse reciprocation to align the randomly positioned workpieces in single file. A roller conveyor, with progressively increasing conveyor speed, is located beneath the aligning funnel to remove the aligned workpieces in single file for subsequent handling and treatment.

Abstract: A gas carbon nitriding method to produce .epsilon.-carbon nitride layers on ferrous metal substrates. The gas atmosphere comprises partially dissociated ammonia and contains between about 2 and 20% (by volume) of carbon monoxide and carbon dioxide. The treatment temperature is between 500.degree. and 650.degree. C. The process is characterized in that the average nitriding potential, p.sub.NH.sbsb.3 /p.sub.H.sbsb.2.sup.1.5 , is between 0.5 and 5, and the partial pressure ratio, p.sub.CO /p.sub.CO.sbsb.2, is between about 1 and 10.The gas atmosphere is formed by introducing into the furnace chamber (a) an ammonia-containing gas, and (b) a combusted gas containing carbon dioxide.