Patent GB-1237912-A (GB)
IPC: B23K9/29
Filed: 1968-06-26
Abstract: 1,237,912. Welding by fusion; making electrode contact tubes; forging. BERNARD WELDING EQUIPMENT CO. 26 June, 1968 [29 June, 1967], No. 30560/68. Headings B3A, B3H and B3R. [Also in Division H1] The handle 22 of a MIG welding gun comprises an open-ended tube of electrical and heat insulating material, preferably vulcanized paper base fibre, connected to a straight portion of a partly curved welding current conducting and electrode wire conveying trunk 21 by tangentially disposed elements 48 which radially space the tube and trunk so as to allow cooling air flow through the handle. The elements 48 comprise brass tubes 49 silver soldered in a transverse recess of a main trunk copper casing 35 and enclosing electrical and heat insulating bushings 51, e.g. of resin bonded fibre, accommodating self-threading handle attachment screws 52. The trunk casing 35 encloses respectively in its straight and curved portions a steel liner tube 36 and a series of hardened steel or tungsten carbide bushings 39. A cable connecting assembly 23 comprises an adaptor 32, one end of which is threaded on the casing 35 and the other end of which is spigoted to receive a helical cable core and electrode conduit 27 and cable conductor elements 29 respectively threaded into, and bound by wire 34 on to, the spigot. The curved portion of the casing 35 is enclosed in a jacket 43 of electrical insulating material, e.g. briaded or laminated glass fibre or neoprene. A gun head assembly 24 comprises a brass body 86 threaded on to the casing 35, an insulating and ion shield 89, a copper or brass gas nozzle 91, an adjustable shield and nozzle clamping clip 97, and a copper contact tube 37. The shield 89 prevents ion-promoted arcing and comprises a seamless tube, e.g. of silicone resin bonded laminated glass cloth, or silicone resin filled braided asbestos. The contact tube is secured in the body by a bayonet and rotary cam means which, as shown, comprises a radially adjustable screw 104 engaging a peripheral cam surface 101 of the contact tube. In Fig. 6 (not shown), the contact tube has two diametrically opposed cam surfaces 101 to provide two 180 degrees separated mounting positions, thereby increasing useful life. In Fig. 7 (not shown), the cam surface is provided in the body 86. The contact tube has wrench flats 106. Due to one-sided cam action the contact tube is flexed in its assembled position to enable it to remain firmly clamped, at three points, during expansion and contraction due to welding. Shielding gas is conducted through a hose 46, a tube 45 within the handle, the wall of the casing 35, the trunk bore 44, a chamber 87 of the body 86, and forwardly inclined ports 95 in said body, the gas impinging on the shield 89 and flowing along the walls of the shield and the nozzle. A switch assembly 25 comprises a switch housing 53 secured by screws 55 to the handle, a normally open snap action switch 58 connected by wires 81, 82 to a relay for ON/OFF welding current and electrode feed control, and a trigger 54 slotted at 65 for rectilinear and pivotal movement with respect to a bushing 67 by which a stepped leaf spring 66 is secured to the housing. For short period welding, the switch is closed by trigger depression, against leaf spring bias and away from the Fig. 1 position, to press the leaf spring against a switch button 63. To lock the switch " ON," the trigger is moved rectilinearly forwardly to the Fig. 9 position so that a trigger projection 72 rides up the step of the leaf spring to depress the latter. A housing projection 78 and a trigger cut-out 79 accommodate normal short period welding switch action, but together with the step of the leaf spring prevent the trigger being moved to the locked " ON " position whilst it is depressed. Further, in addition to its release by rectilinear rearward movement, the trigger may be released from its locked " ON " position by downward pressure thereon, the projection 78 coacting with the downwardly inclined trigger end which acts as a cam. Contact tube manufacture.-The contact tube 37 is produced from seamless commercial electrolytic copper tubing by a process whereby the copper is increased in density and refined in grain to provide greater hardness. The process comprises the following steps: (1) A piece of tubing is reduced in length and bore by its insertion in one of a pair of identical bores 114 of a die block 119 and its compression by a piston 116 having a bore-sizing mandrel 118. (2) Using a hairpin-shaped tool, the block 119 is rotated 180 degrees and the reduced piece is ejected from the bore 114 by a piston 122, the arrangement being such that during this ejection a further piece is being compressed in the other of the pair of bores. (3) The reduced piece is extruded back to its original length, and both its outside diameter and bore are reduced, by its insertion in one of a pair of identical stepped bores (128) of a further die block (136, Fig. 17, not shown) and its being forced into a reduced diameter section of said bore by a piston (129) having a bore sizing mandrel (135). (4) The block (136) is rotated 180 degrees and the extruded piece is ejected by a piston (137) during extrusion of a further piece in the other of the pair of bores. For a contact tube of finished diameter equal to that of the commercial tubing, steps (3), (4) are omitted. The mandrels 118, (135) may be dispensed with.