Patent GB-637581-A (GB)
Title: An electric control for the plating current of electro-plating apparatus
IPC: C25D21/12
Filed: 1946-09-13
Abstract: 637,581. Automatic current control systems. CARNEGIE-ILLINOIS STEEL CORPORATION. Sept. 13, 1946, No. 27580. Convention date, Sept. 26, 1945. [Class 38 (iv)] In an automatic system for controlling direct current for plating strip metal passing through - an electrolyte, the output of the source of plating current is controlled by an amplifying exciter having two opposed field windings, one energized through a rectifier in proportion to plating current and the other energized in proportion to strip speed. In an electrotinning system, Fig. 1, steel strip S to be tinned is drawn from an uncoiler 4 through a plating tank 2 by driven puller rolls 12. Anodes 14a, 14b for plating each side of the strip are respectively connected to the positive terminals of generators 20, 22, the negative terminals of which are commoned and connected to the strip through conductor 28. The generator field windings 34, 36 are energized by an exciter 38, the field winding 44 of which is, in turn, energized by an amplifying exciter 50. To cause the plating current to increase or decrease with increase or decrease of strip speed for uniform coating, a tachometer generator 60 driven from rolls 12 energizes one field winding 54 of exciter 50. To maintain the plating current at a value corresponding to the strip speed the energization of a field winding 56, opposing field winding 54, is made dependent on plating current by supplying-it from rectifier 70, the A.C. supply 68 to which is in series with the A.C. winding 76 of a saturable reactor 30 influenced by the total plating current in conductor 28. The plating current/strip speed characteristic is influenced by condenser 78 and " Thyrite " (Registered Trade Mark) resistor 82. To smooth out transients a field winding 86, opposing field winding 54, is supplied from the secondary winding of a transformer 88, the energization of the primary winding of which is dependent on the D.C. output voltage of exciter 50. Field winding 94 assisting field winding 54, energized by the D.C. output of a potentiometer 96 prevents reversal of generator polarities when the strip speed is zero. Overall coating thickness is controllable by rheostat 62 and relative thickness on the two sides is controlled by rheostats 40 and 42. In a modification a shunt 32 in conductor 28 is utilised instead of saturable reactor 30. The output of this shunt is, in Fig. 2, introduced in series with a circuit supplying the upper portion of a potential divider 108 with pulses from a full-wave rectifier 104 supplied from an A.C. source through a transformer 102. The lower portion of potential divider 108 is supplied in reverse polarity with pulses from rectifier 104 unaffected by shunt 32. The arrangement is such that when the plating current is zero the total voltage across potential divider 108 is zero. When plating current flows, the voltage across potential divider 108 is applied through a transformer 116 to an A.C. electronic amplifier 98, the output of which is applied to a rectifier 118 supplying field winding 56 as in Fig. 1. Typical waveforms and voltage values are given.