GB812345A - Improvements in or relating to the annealing of ferrous metal sheets, strip, wire ortubing - Google Patents

Abstract

812,345. Annealing. KELLER, J. D. April 9, 1957, No. 11517/57. Class 72 A method of annealing steel strip comprises passing the strip through a bath of molten alkali metal having zones increasing in temperature from just above the melting point of the metal to a desired maximum at or above the annealing temperature, the steel strip entering the zone of lowest temperature, passing through progressively hotter zones and then through progressively cooler zones. As shown, a strip 4 is passed into a container 3 for liquid sodium having a series of partitions 14 dividing it into a series of zones, the temperature of each zone being maintained at a predetermined temperature graduated from the lowest temperature at the top of the container to the highest at the bottom, the strip entering the uppermost zone through sealing rollers 7, 8, pasing round a roller 10 in the hottest zone and leaving through the coolest zone by way of sealing rollers 11. In this manner the strip is heated to the required temperature and then gives up its heat to the cooler zones, thereby conserving heat. Paddles 22 in each zone aid in maintaining a constant temperature throughout the zone. The top of the container may be supplied with nitrogen under pressure to prevent escape of sodium vapour. In a modification Fig. 1 (not shown) a series of chambers may be provided and the molten sodium circulated from zone to zone in counter-current to the direction of movement of the strip. In a further modification, Fig. 3 (not shown), the strip, after leaving the hottest zone, may pass through a space maintained at the temperature of the hottest zone, again entering the hottest zone and passing through the series of cooler zones. The molten metal may be sodium, potassium, or lithium or alloys of these metals with one another, and "strip" is intended to include sheet, strip, wire, or tubing. Specification 812,346 is referred to.