Patent GB-545063-A (GB)
Title: Improvements in and relating to electric welding apparatus
IPC: B23K11/31
Filed: 1941-01-29
Abstract: 545,063. Welding ; steam &c. presses. BRIGGS MANUFACTURING CO. Jan: 29, 1941, No. 1192. Convention date, Jan. 29, 1940. [Class 83 (iv)] [Also in Group XXVI] In an electric welding apparatus having a pair of relatively movable fluid-operated electrodes arranged in an electric circuit containing a switch, means are provided for controlling the pressure applied to the electrodes to increase it gradually from a predetermined minimum to a predetermined maximum, the switch being controlled by the fluid pressure applied to the movable electrode so as successively to close and open the circuit during the rise in pressure from the minimum to the maximum. Articles of low melting point metals, such as aluminium or its alloys may thus be welded quickly at low pressure so as not to displace the plastic metal between the electrodes and heavy forging pressure being then only applied after the weld has become sufficiently cool to withstand such pressure. A portable welding apparatus is provided with water cooled electrodes 20, 21 of which the electrode 21 is universally adjustably mounted and connected to the contact arm 23 by a bar 25. The movable electrode 20 is secured to an arm 26 carried by a shouldered plunger 27 held by a spring 43 in contact with a shoulder 281 on a sleeve 28 which carries a piston 40 and flexible seal 41 and is screwed into a cap 42. The piston assembly is pushed down against the action of a spring 45 by fluid pressure passing into the cylinder through a trigger-operated valve 104, passage 56 and ports 55 in a fixed sleeve 50 the effective area of the bore of which is controlled by a valve 57 pivoted at 58 to the piston cap 42. The valve is provided with five pressure control portions 57a-57e. When a forward movement is started the portion 57a. is between the ports 55 and the cylinder 35 so that the initial movement of the electrode is relatively slow to overcome inertia of the parts. The portion 57a tapers to the smaller diameter portion 57b so as then to accelerate the motion until the electrode is in close proximity to the work, whereupon it is slowed down to prevent shock when the electrode contacts with the work by the tapered portion 57c the rate of flow being restricted for an interval determined by the portion 57d. After the electrode engages the work the tapered portion 57e controls the flow until the maximum line pressure is obtained in the cylinder. As the piston moves down it compresses the spring 45 and when the electrode engages the work the sleeve 28 moves relatively to the plunger and compresses the spring 43. During the return movement of the piston the fluid passes into the exhaust through a spring-pressed relief valve A. Any fluid trapped beneath the piston is exhausted through openings 48 and the cylinder 35 and liner 37. In order to control the switch 61 there is also pivoted to the cap 42 a tube 76 slidable in a sleeve 72 and having an annular shoulder 81 to engage the head 80 of a plunger 79 to which it is secured, the plunger having an adjustable stop 82 for engaging a spring closed valve 87 so as to open the valve to' connect the chamber 84 which is in direct connection with the passage 56, through passage 95 to a passage 91 through ports 89 and annular chamber 90 so as to supply pressure to operate the switch. The stops 82 may be adjusted so as to vary the time of opening of the valve 87 and thus the time of operation of the switch. The passage 91 communicates with the switch chamber 68 through an adjustable needle valve 123 and passage 122. The switch plunger 67 which has a head in the chamber 68 of smaller area than that in the chamber 63 and is normally held open by a spring 70, is now closed by pressure through the passage 122 to start the weld. The passage 91 also communicates through an adjustable needle valve 126 with an accumulating chamber 125 from which eventually fluid passes into the chamber 63 to open the switch. The chamber 125 also communicates via a needle valve 118 with a passage 115 so as to force forward the valve 104 and connect the cylinder and switch chambers with exhaust port 119 through an elongated passage 120 in the valve casing. The valve 104, which is normally pressed 'forward by a spring 108 into closed position is opened to supply by a trigger 100 which forces a plunger 106 against a partition in the valve, fluid passing from passage 97 to a passage 56 through annular groove 105 in the valve. After the valve is opened to pressure the plunger is retained against any pressure that may be exerted by the operator by fluid pressure passing through ports in the casing through annular groove in the plunger which communicates by a port with the rear of the plunger.