Patent GB-554475-A (GB)
Title: Improvements in or relating to the control of electrical energy for resistance welding machines
IPC: B23K11/25
Filed: 1942-01-02
Abstract: 554,475. Electric welding. REYROLLE & CO., Ltd., A., and BAYLES, J. W. Jan. 2, 1942, Nos. 63 and 16062. [ Class 83 (iv)] Resistance welding machines are controlled by means operated by movement of the welding-electrodes pressing upon the work, such operation occurring when the electrode has moved back as the result of expansion of the work and from this position has moved forward a predetermined amount as the work under the electrode softens. Such means may be arranged when the electrode sinks into the work after it has become plastic automatically to interrupt the welding current, or relieve the pressure of the electrodes on the work or merely to indicate to the operator the progress of the weld. The electrodes U<SP>2</SP>, U<SP>1</SP> are operated by hydraulic cylinders V, T, respectively carried by the framing and by an hydraulic ram R<SP>3</SP> for operating the work clamps as described in Specifications 424,627 and 453,009. The electrodes are connected to the terminals of the secondary W4 of a transformer arranged as described in Specification 540,722. Arranged in a casing D3 connected to the ram R<SP>3</SP> or cylinder T is a switch mechanism comprising levers A, B pivoted at C, the lever B being normally pressed down by springs D<SP>1</SP> and being provided with an adjustable stop G, and the lever A being provided with spring washers D<SP>2</SP> so that it remains in any position to which it is moved. The levers A, B carry contacts H, J, the contact J being carried by a spring blade J<SP>1</SP> pressed by a spring J4 against the under side of the lever B. The lever A carries an adjustable screw stop K engaging the lever B and is connected by a spring P to a resetting knob Q. In operation the knob is first depressed to lower the lever A. The pressure between the contacts H, J, causes the blade J<SP>1</SP> to yield until the stop K engages the lever B. When the current is first applied the work parts heat up and expand and the electrodes are forced apart a small extent. Consequently the levers A, B are moved as a unit about their pivot C by a push rod F carried by a flange on the electrode U<SP>1</SP>. As heating proceeds the plate under such electrodes softens and the motion of the electrodes reverses. The lever B moves downwards alone by the action of the springs D<SP>1</SP> and after a predetermined downward movement the blade J<SP>1</SP> engages the lever B at the point J<SP>2</SP> and the contacts H, J then separate. The extent of the movement required to separate the contacts is varied by adjusting the stop K, which adjustment is indicated by a pointer K<SP>1</SP>and scale K<SP>2</SP>. The levers A, B are connected by conductors N<SP>1</SP> in a circuit which may contain a current indicator Z, coil W<SP>1</SP> of relay W for closing the primary circuit of the welding transformer, and a coil X<SP>1</SP> for operating a valve X which contacts the pressure supply to the electrode cylinders. This circuit forms the secondary of a transformer Y connected to the mains W2. The motion of the electrode may control either the cutting off of the welding current or relieving the electrode pressure instead of both as shown or may merely operate the indicator Z. The welding current or pressure may also be controlled directly by mechanical means responsive to the electrode movement. In another form the relative movement of the parts may control the passage of a beam of light to a photo-electric cell which in turn may effect the required control or indication.