Patent GB-519526-A (GB)
Title: Improvements in and relating to metal articles provided with metal veneers
IPC: B23K11/00
Filed: 1938-08-20
Abstract: 519,526. Making compound metal plates for pressure vessels &c. BABCOCK & WILCOX, Ltd. (Babcock & Wilcox Co.). Aug. 20, 1938, No. 24522. [Classes 83 (ii) and 83 (iv)] Welding. - A ferrous article is provided with a metal veneer comprising two or more superposed metal sheets by simultaneously resistance welding the sheets together and to the article by a multiplicity of welds, each weld being formed by pressing the veneers on to the article over a restricted area. A base metal plate may thus be veneered with sheets of corrosionresisting metal, such as chromium steel, chromium-molybdenum steel, nickel, with alloy sold under the Registered Trade Mark " Monel " for use in forming lined pressure vessels for pro- .cessing oil and other chemicals. A cleaned mild steel base plate 11, e.g., 3/4 inch thick, may be submerged in a water trough 12 on a table 1 of a planing machine which is reciprocated at constant speed and on it are placed two superposed cleaned chromium steel sheets each 1/32 inch thick, and the table is reciprocated within a pair of copper-alloy roller electrodes 10, e.g., of 14 inch diameter and 5/8 inch width, carried by slides 4, 5 on the vertically adjustable carriage 3, the electrodes being inserted to the opposite terminals of the secondary of a welding transformer 14. The electrodes are controlled by double-acting air cylinders and press the veneers on to the base plate with a force, e.g. of 2,700 1bs. The electrodes are first adjusted with respect to each other and to the work so as to effect a pair of spaced rows of spot welds, the first row being near the edge of the plate. They are then adjusted successively to obtain further spaced rows and subsequently are successively adjusted to effect intervening rows of spot-welds which overlap the previous rows. The electrodes first preheat and then weld each spot. Due to the parts being immersed in water the preheating facilitates the production of each spot weld without producing excessive temperatures at the outer 'surface of the veneer, or damaging the electrodes. The welding current is preferably controlled by electric-discharge valves 16 connected in series with the primary of the welding transformer 14 across the secondary of a step down transformer 15 supplied from A.C. high voltage mains. The ignition of the discharge valves 16 is under control of further discharge valves 17 the control grids of which are supplied with potentials from a phase shifting device 20 connected to the mains and also with potentials induced by magnetic pins on a disc 18 which is rotated by a synchronous motor 19. The disposition of the pins on the disc controls the ratio of welding time to welding process while the setting of the device 20 controls its phase and therefore the strength of the welding current and thus the heating effect. With' a traverse at the rate of 33 inches per minute forming two welds per electrode per second, for each weld the current is off during 13 consecutive cycles and preheating is accomplished with a sequence of 3 cycles on, 1 off, 1 on, 1 off, 1 on, 1 off and the weld produced with a sequence of 9 successive cycles during which the current is on. A thin sheet of metal such as a sheet of steel containing copper nickel or molybdenum or a sheet of nickel or copper nickel alloy may be placed between the base metal and the veneer sheets to prevent the migration of carbon from the base metal to the veneer. For use with two veneer sheets of 11 to 13 per cent. chromium-steel 0.035 inch thick, a banner sheet may consist of nickel 0.01 inch thick. Instead of using a water bath streams of liquid may be directed on the work. The process may be carried out by electrodes other than with electrodes in which there is no relative movement between the work and electrodes during current flow. According to the Provisional Specification single veneer sheets may be welded to the article or two sheets of different thickness. Further the veneer sheet may consist of austenitic-nickel-chromium steel.