Patent GB-647704-A (GB)
Title: Improvements in and relating to electro-plating control systems
IPC: C25D21/12
Filed: 1944-12-15
Abstract: 647,704. Automatic control systems; inductive control. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 15, 1944, No. 25214. Convention date, Dec. 16, 1943. [Class 38 (iv)] [Also in Groups XXXVIII and XXXIX] In an apparatus for controlling the electroplating of a length of material in a tank containing an electrolyte and a plurality of electrodes, voltages are produced which are proportional to the speed of the material through the tank and to the sum of the electrode currents, the difference between these voltages being used to maintain a predetermined relationship between the sum of the electrode currents and the speed of the material. In Fig. 1, material 10 is passed from reel 11 into tank 12 through electrolyte 13 and wound on to reel 17 by rollers 17a, 17b driven by motor 18 which also drives tachometer generator 28 to produce a control voltage proportional to the material speed. The current through each electrode is controlled by a circuit identical with that shown in detail for electrode 14. In this, high current, low voltage generator 19 supplies current through bus-bars 22 and 23, contact rollers 21 and 21a, electrolyte 13, anode 14 and strip 10. Bus-bar 23 passes through saturable reactor unit 29, the reactance of which varies inversely as the current through 14. Reactor 29 and full-wave rectifier 32a are in series with alternating current source 37 and a change of electrode current produces a proportionate alteration of the D.C. output of 32a applied to resistor 38. Totalizing reactor 35 is provided with a direct-current and saturating winding for each electrode, that for electrode 14, winding 35a, is connected across resistor 38, and increases in electrode currents cause corresponding increases in the currents in saturating windings 35a, 35b and 35c with a consequent fall of the reactance of 35. This in turn leads to a rise of the D.C. output of full-wave rectifier 36 which is in series with 35 and A.C. source 37. Resistor 42 absorbs the power output of 36 and is connected in voltage opposition to tachometer 28 in series with control field winding 46a, the current through which is proportional to the difference between the voltage produced by 28 which is a function of material speed, and the voltage across 42 which is proportional to the sum of the electrode currents. Dynamoelectric machine 46, under the influence of 46a, produces a current in field winding 47d proportional to this difference voltage which causes exciter 47 to exercise control over the generators 19, 24 and 25 through their associated fields 19a, 24a and. 25a. The total plating current supplied by 19, 24 and 25 for any given speed of the material strip is adjusted by varying the position of the moving contact on the potentiometer 45. A sudden drop in the speed of the strip would tend to cause a reversal of the current through the control winding 46a, due to the excess of the voltage across 42 over that across 45, and this would produce a reversal of the plating currents. This condition is prevented by the rectifier 48 connected in series with winding 46a. For economy in the amount of iron used in the core of the reactor 29, a feed-back winding 29b is wound over the reactance winding 29a. Winding 29b is connected across the output circuit of rectifier 32a, and in a direction such that its ampere turns oppose those of the electrode current. To prevent cumulative self-excitation of 29 a small bias voltage is supplied by full-wave rectifier 40 from A.C. source 37 through transformer 41. The D.C. output of 40 is applied to resistor 39, connected in series with 38 and feedback winding 29b. The voltages across resistors 38 and 39 are in opposition and with zero electrode current the voltage across the feedback winding 29b is zero.' To neutralize the effect of the magnetizing current of reactor 35 in the output voltage of 36, the full-wave rectifier 44 fed from source 37 supplies a D.C. voltage to resistor 43 connected in series opposition to resistor 42. In a modification, Fig. 2 (not shown), the speed of the material strip through the electroplating tank is controlled as a function of the sum of the electrode currents flowing in the separate electrode circuits. This is accomplished by the control of the speed of the take-up reel by the totalizing apparatus.