Patent GB-407971-A (GB)
Title: An automatic resistance welding system
IPC: B23K11/24
Filed: 1932-07-25
Abstract: 407,971. Momentary contact switches. BUDD MANUFACTURING CO., E. G., 2500, Hunting Park Avenue, Philadelphia, U.S.A.- (Assignees of Ragsdale, E. J. W. ; Curren Terrace, Norristown, Pennsylvania, U.S.A.) July 25, 1932, No. 20913. Convention date, Aug. 20, 1931. [Class 38 (v).] A timing-device for an electric resistance welding system for effecting substantially instantaneous welds comprises a stationary contact and a contact adapted to be continuously rotated past the stationary contact at a high rate of speed being normally spaced a short distance therefrom and adapted to be moved into and out of a position in which it can engage the stationary contact during rotation upon actuation of an electric switch, electric means preventing repetition of the cycle however long the switch is closed. Fig. 4 and 6 shew a timing device for controlling the supply of currents to the primary of a transformer employed for spot welding. The stationary contact comprises a nonconducting block 24 on which are mounted contact segments 27 arranged on an arc of a circle, Fig. 9, electrically connected by means of individual flanges 61 to a binding post 70 on a distributer 62. The movable contact comprises a timing brush 28 carried by a rotary brush arm 29 of insulating material arranged to sweep over segments 27 but normally spaced therefrom. The brush holder is pivoted to the arm 29 at 32 and is biassed toward the fixed contact member by springs 33 but is held from forward movement by stops. The brush 28 is electrically connected to a rod 42, slidably mounted in an insulating bearing 43, by means of a conductor 38, a metal hub centre 39, a carbon or graphite plug 40 and a spring pressed cap 41. The other end of the rod 42 carries nuts 45 constituting a terminal for a lead in wire 117, Fig. 10. The brush arm 29 is carried by an axially shiftable shaft 30 driven through gears 46, 48 from a constant speed motor 47. A spring 44 normally serves to maintain the shaft 30 in the position shewn in Fig. 6. The shaft 30 carries a grooved cam member 50 in which works a pin 52 carried by a yoke member 53 pivoted at 54. Normally the member 53 merely vibrates with the rotation of the cam member but mav be held in one extreme position by actuation of a detent 55, Fig. 10, by an electromagnet 60, whereby continued rotation of the cam member causes the shaft 30 to move axially to move the brush 28 into contacting relation with contact segments 27. A locking relay 78 is also provided comprising an electromagnet 80, Fig. 4, and an armature 81 pivoted at 89 and arranged upon energization of the magnet to raise a bar 82 interrupting a circuit between contacts 84 and closing contacts 85. Energization of the magnet 80 is synchronized with shaft 30 by means of a commutator disc 71 on shaft 30 having a segment 72 arranged to bridge contacts 73 at a given point in the rotation of the shaft. The contacts 73 are normally clear of the disc 71 and are rendered operative by axial movement of the shaft 30. The armature 81 is spring biassed in the position shewn. The above-described apparatus is mounted on a shelf 4 in a transportable casing in the lower half of which is mounted the transformer. Externally of the casing are arranged the control knob 17, rheostat controls for varying the turns used in the primary of the transformer and switches for the main current supply lines. The welding transformer comprises a primary winding 94, Fig. 10, having tap terminals 95 arranged to be engaged by contact wiper arms 96, 97 for varying the number of effective primary turns. Secondary winding 100 terminates in lugs 8, 9 to which are connected flexible leads 102,103 for a welding tool 101. Power is supplied to the primary from an A.C. supply lines AB, line A being connected through the timing mechanism. Current for the motor 47 and switching mechanism is taken from lines CD which are at a lower voltage than AB. Conductors CD connect to binding posts 91, 92 through a switch 106, and are directly connected to the motor 47. A push button switch 107 which is held by the welding operator is connected by flexible leads to binding posts 91, 93. Operation. Closing the switch 106 starts the motor 47 which rotates the shaft 30 at a constant speed. The main power switch of lines AB is then closed. The rotation of the shaft 30 causes the yoke 53 to oscillate about its pivot. If now the button 107 is pressed by the operator the circuit energizing the magnet 60 is closed, this circuit passing through contacts 84. The magnet 60 causes the armature 55 to swing over and hold the yoke 53 as soon as it is in its extreme left position, and the shaft 30 is thereby traversed to the left causing brush 28 to engage with a tapered ramp 77, Fig. 9, and sweep over contacts 27 completing the circuit to the transformer. The conducting segment 72 on disc 71 which has now been moved laterally to the left is arranged to bridge contacts 73 when the brush 28 has swept off the last segment 27. A circuit is now completed through magnet 80 causing the armature 81 to rock about its pivot, breaking the circuit of the magnet 60, and closing contacts 85 to maintain the magnet 80 in an energized state so long as the operator maintains pressure on the button 107. De-energization of the magnet 60 causes unlocking of the yoke 53 so that the shaft 30 is moved to the right into its original position by the spring 44, Fig. 6. Release of the button 107 causes restoration of the original positions of the parts. Brush 28 thus passes once only over the contacts 27. The number of effective contacts may be varied by turning the knob 17, which as indicated in Fig. 4 varies the number of flanges 61 bridged by the distributer brush 62, whereby the time during which circuit AB is closed may be varied. The last two segments 27X, 27Y, Fig. 11, may be arranged permanently out of operative engagement with the distributer brush and be connected to the preceding segment through resistances R1, R2. in order to reduce the current and reducing the arc at breaking. Specification 389,460, [Group XXXV], is referred to.