Patent GB-574957-A (GB)
Title: Improvements in process and apparatus for edge to edge welding
IPC: B23K11/00
Filed: 1944-01-18
Abstract: 574,957. Welding. DILLER, I. M. Jan. 18, 1944, No. 976. Convention date, Feb. 6, 1943. [Class 83 (iv)] In a process of butt-welding the edges of metal sheets, particularly thin sheets from 0.008 to 0.06" in thickness in making tin cans, the edges are aligned close to or touching each within a, closely confined space, are resistance heated locally and instantaneously to welding temperature and are pressed together while being heated and the current interrupted immediately thereafter. The edges may be initially separated by 20 to 30 thousandths of an inch or may be in slight contact, and they may be previously honed or may be roughened or provided with serrations up to one-hundredth of an inch in depth. The heating which is effected by the contact resistance between the edges is effected by spacing electrodes about #" from the welding line so as to prevent conduction of heat thereby from the joint and to avoid heating parts adjacent the joint so. as to prevent buckling when the welding pressure is applied and to prevent damage to the structure of the sheet or to any coating thereon. Alternating current may be used of either 60 or 300-500 cycles per second or short discharges of direct current, the duration of the current being less than 1/60 of a second. The can body 48 is placed on an insulating mandrel 13 provided with a gap 27 and containing a rotatable non-magnetic metallic core 12 with a non-conducting refractory support 28, the support and the mandrel co-operating respectively with the movable and fixed electrodes 32, 24 which are of length equal to the width of the blank and are connected to the terminals of the secondary of a transformer 40 connected to a supply including an electronic timer 47. The density of the current passing the joint is rendered as uniform as possible by spacing the centre further from the welding line than the ends so as to counteract the tendency of the current to concentrate at the centre thereof. The electrodes are pressed against the work by springs 34, 26 adjusted by screws 33, 25. The electrode 32 is carried by an arm 30 extending from the core 12 to which is hinged the core 36 of an electromagnet 35 hinged to the frame and connected in a parallel circuit with respect to the transformer. The mandrel 13 is provided with an insert 15 of electrically non-conducting refractory material of poor heat conductivity such as carborundum or zirconium silicate which may contain or be coated with graphite or of insoluble sodium silicate. This insert co-operates with a block 20 of similar material carried by spring- pressed supports 19 in a vertically adjustable member 18. The member may be raised or lowered by a cam or by a screw 21. The blocks prevent the edges of the work from sliding over each other, prevent radiation of heat from the joint, or oxidation thereof and also spattering or lateral extrusion at the joint. On placing the body on the mandrel, the electrodes and block 20 are lowered thereon and on starting the operation the parts by the action of the electromagnet are first brought into light contact, whereupon heating is effected almost instantaneously and the resulting increase of current causes the electromagnet to increase the pressure to complete the weld, whereupon the current is immediately cut off and the pressure relaxed.