Patent GB-501546-A (GB)
Title: Improvements in electric welding machines of the spot type
IPC: B23K11/31
Filed: 1937-09-01
Abstract: 501,546. Electric welding. SOUDURE ELECTRIQUE. Sept. 1, 1937, No. 23914. Convention date, Sept. 5, 1936. [Class 83 (iv)] An electric spot welding machine includes n frame without fixed side walls and comprising n base plate to which arc secured two vertical uprights supporting on one side the welding arms and on the other side substantially all the other detail of the machine. Two channelshaped uprights 3, 4 are welded to the base 1, being reinforced by welded angles 5, 6. secured between the uprights is the upper arm 10 carrying the movable electrode 76 and operating device therefor, and to the uprights is also fixed a guide 17 for the adjustable lower arm 18 carrying the fixed electrode 77. The transformer II is bolted to the uprights and the base 15 of the welding contactor 16 is welded thereto. On the upright 3 is also secured by removable clamps 22 an insulating plate 21 to which terminals have been previously secured. The water circulating pipes 19, 20 for cooling the electrodes and transformer are connected to the angle 6 by junctions carrying rubber pipes. A top plate 7 welded to the top of the uprights supports the automatic-cut-out switch 9 or relay provided with an adjustable dial train. The frame is surrounded by a removable sheet metal casing consisting of hinged sheets 24, 25 secured by clamps 28 to the uprights at one end and connected at the other end by a hood fastening 33. The base 1 and top plate 7 are provided with angle irons 34-37<1> for seating the sheets. The leads from the transformer are connected to a commutator plate to which is secured by clamps a plate of transparent material such as glass 13 which may be graduated and through which the axle of the adjusting mechanism is passed and which is operated by an external handle 83. The sheet metal casing is provided with a framed aperture in front of the glass plate. The upper electrode is carried by the piston of a double-acting pneumatic-cylinder 38 which is vertically movable in the ann 10. The head 37 of the cylinder carries the controlling mechanism for the piston and the combined on-off switch and pressure contacts 71, 85 are secured to an angle iron 68 attached to or cast integrally with the side of the cylinder. Compressed air is supplied from a single pipe to the head at high pressure through a small pipe to a chamber 57 and at reduced pressure through a reducing device 40 to a chamber 39 provided with a manometer 49. The flexible contact 71 may be kept out of contact with the contact 85 by a cam 78 operated by a lever 80. On lowering the cam and admitting compressed air, high pressure air passes from chamber 57 through pipe 58 and a valve 54 to the lower end of the cylinder to retain the piston 47 in raised position. The valve consists of balls and an intermediate member the balls being under the control of springs and a plunger normally pressed inwards by a lever 50 and spring 52 to hold the valve open to pressure. When a pedal 99 is pressed an electromagnet 64 mounted on the angle iron 68, is energized to attract the armature 65 and so push in a second valve 63 similar to the valve 54 to open the upper end of the cylinder to reduced pressure from the chamber 39 through passages 51 and 66. Pressure at the same time passes by passage 82 into a pneumatic-relay valve 42. When the pressure builds up the valve 42 is forced out to push back the lever 50 so that the valve 54 moves to position for exhausting air from the lower end of the cylinder. The piston 47 is thus forced down to bring the electrodes, into contact with the work. The pressure is controlled by a spring 86. In order to cushion the piston to prevent damage to the electrodes a one-way spring-pressed ball valve 93, Fig. 5, is mounted in the passage 60, the opening of the valve being varied by a screw 96. Further supply of air then raises the cylinder and the parts carried thereby so that the contacts 71, 85 are connected to apply the welding current when a desired pressure of the electrodes on the work is reached. The contacts are normally held open by a fixed plunger 72 resting on an adjustable stop 74 on the arm 10. When welding is completed the switch 9 opens to cut off the welding current and de-energize the electromagnet thus causing the valve 63 to open to exhaust from the top of the cylinder. This causes the spring 52 to press back the valves 42, 54 and thus open the lower end of the cylinder to pressure to raise the piston. The Specification as open to inspection under Sect. 91 states that the commutator cover may be of translucent material and that the stop 74 may be supported on a movable part of the machine instead of the contact 71. This subject-matter does not appear in the Specification as accepted.