Controlled atmos. for heat treatment furnaces - using mixt. of nitrogen and natural gas, suitable for annealing cold rolled steel sheet

摘要

Protective gas is prepd. for use as a controlled atmos. in heat treatment furnaces. The gas is a mixt. of N2 with 3-25% natural gas, where both gases have the same dew point of ca. -40 degrees C. The two gases are mixed in a cylindrical expansion chamber, fitted at one end with a side inlet for N2, and a perforated inlet pipe extending along the axis of the chamber and supplying the natural gas. The other end of the chamber has an axial outlet for the gas mixt. Used esp. during the annealing of coils of thin cold-rolled sheet made of extra-mild steel, using, e.g. a bell-type furnace. Avoids use of coke oven gas, which has a variable compsn.; shortens total cycle time; and improves the surface as compared with when coke oven gas is used.