GB801653A - Improvements in the thermal treatment of solid metallic articles or material by passage of current therethrough - Google Patents

Abstract

801,653. Heating by passage of current. REINECKEN, W. April 1, 1955 [April 20, 1954; July 22, 1954; Jan. 3, 1955; Feb. 8, 1955], No. 9650/55. Class 39(3) [Also in Group XXXVI] In heating elongated metallic material such as wires, strips, rods or tubes by passing current therethrough, two spaced contact devices for current supply to the material, are provided, the one, at which the material enters being a tank 2 containing heaped-up conductive balls 9 or the like through which the material passes, and other contact device at which the material leaves comprising a tank in which the surface of a conductive liquid is raised at one point e.g. by a pump or induction coil so as to contact the material. The balls 9 may be covered by a conductive liquid, which may be continuously circulated through the tank by a pump raising the liquid from a lower tank collecting overflow. The balls may be copper, bronze, brass or iron and may be plated with nickel or chromium or may be carbon or graphite. Good contact between the balls and the material is ensured by weights which may be periodically lifted pressing on the balls, or if the latter are of steel by permanent or electro-magnets on the tank, which may be vibrated or rotated. The tanks are wholly or partly of conductive material and may be heated or cooled e.g. by heat exchangers. When the elongated material is rigid, it is passed through openings or slots in the end walls of the tanks which are sealed by slides or diaphragms which are weight-loaded or resilient to reduce escape of liquid and to allow passage of materials with bulges or enlarged portions. The liquid may be a salt solution or a dilute acid or alkali. Escape of liquid through the openings is further reduced by gas jets 20 from apertures in annular gas pipes 18 exterior to the tank adjacent the openings, said jets being directed towards the openings at 20, or directed at 22 on to the material in order to disperse liquid adhering to the material leaving the tank. The gas may be air with added oxygen 'for scaling any decarbonized layer on the material from a previous operation or may be a protective gas, which may be recirculated. When the material is flexible e.g. metal strip, it is passed over several ceramic pulleys and a central pulley is mounted on an arm so that it may be lowered to bend the material into the mass of balls. Strippers are mounted where the material leaves the liquid to remove entrained liquid. The pulleys may be formed with V-shaped grooves and the immersed pulley has a strip mounted adjacent thereto to prevent balls from jamming between the strip and the pulley. Where the tanks are partly of insulating material the end walls, especially the outer opposed walls may form the electrode; or the central parts of the bottom walls of the tanks form the electrodes. When the tanks are wholly of insulating material. the electrodes are tubular and surround the material passing through the tank. The electrodes may be conical and widen in the direction of travel of the material which may be introduced through a slot at the top, and may be built as an open cage allowing free movement of the balls. The contact at the outlet for the material may comprise a ball of fused salt or metal or alloy, and its surface is raised by a pump to contact the material. The pump may comprise a submerged propeller raising the liquid preferably through a vertical tube immersed in the liquid, which may be a molten salt or metal. Horizontal partitions with tapering openings for passage of material may be arranged at the surface of the liquid, which may be heated by a resistance around the tank. The resistance may be tubular and alternatively serve for cooling. The liquid may be raised by a submerged pump which may (Fig. 17) direct the liquid from opposite sides 47 on to the material at an angle to its direction of movement. The liquid surface may be raised by a convection current. In Fig. 18 A.C. current is fed through a coil 51 surrounding the bath to raise its surface by induction and one end of the coil is connected at 12 to the tank for completion of the circuit through the material 1 being treated. D.C. or A.C. of another frequency may be used to heat the material. The material may be annealed and may be further heated by further contacts beyond the bath, or the material may be cooled.