GB1169882A - Improvements in or relating to Resistance Welding - Google Patents

Abstract

1,169,882. Welding by pressure. BRITISH ROPES Ltd. 18 Nov., 1966 [20 Aug., 1965], No. 35935/65. Heading B3R. In resistance butt welding wire workpieces the ends of the workpieces are butted, contact pressure is applied between the ends, a welding current is passed through the workpieces to heat the ends to forging temperature and after the forging temperature is reached a first forging pressure, higher than the contact pressure, is applied between the ends followed by a second and higher forging pressure. A stationary electrode jaw 1 and a movable electrode jaw 2 are connected to the secondary of a transformer 3 whose primary is energized via a contactor 4 controlled by a manual button 5 and a normally closed microswitch MS2. The movable jaw 2 is connected to a piston 6 in cylinder 7 having chambers 7a, 7b to which air is admitted via reducing valves 8a, 8b producing pressures P1 and P2 with P1 greater than P2. Solenoidoperated valves 9a, 9b connect the chambers to pressure or exhaust and the four control solenoids 11, 12,13, 14 are energized respectively via a contact S1/1 of a switch S1; a contact S2/1 of a switch S2; a contact S1/2 of switch S1 and S2/2 of switch S2; and normally open microswitch MS1. Depression of either switch S1 or S2 releases the other. In operation switch S1 and button 5 are pressed to admit air to both chambers 7a, 7b and close the contactor 4. The pressure differential supplies contact pressure while welding current is passed and as the wire workpieces soften the jaw 2 moves to operate switch MS2 which cuts off the current and operates switch MS 1 which exhausts chamber 7b through a throttle valve (not shown) to increase the pressure for forging. This throttle is opened or by-passed to produce a second forging pressure higher than the first. When the metal collapses the pressure falls and part of the forging takes place at low pressure. The instant at which pressure is exhausted from chamber 7b may be selected by means, e.g. photoelectric means measuring the temperature of the interface or by means measuring the pressure between the faces. With large workpieces the lower forging pressure squeezes out oxides and decarburized material in carbon steels, and the second faster movement completes forging. A timer may be used to control the duration of the welding current.