US2455997A - Current regulating system - Google Patents

Description

Dec. 14, 1948. R. w. HOLMAN CURRENT REGULATING' SYSTEM Filed Jan. 24, 1944 Patented Dec. 14, 1948 CURRENT REGULATING SYSTEM Robert W. Holman, Gary,

negle-Illinois Steel Corp of New Jersey Ind., assignor to Caroration, a corporation Application January 24, 1944, Serial No. 519,517

3 Claims.

This invention relates to a current regulating system, and particularly to-an improved means for controlling the current supplied to the electrolyte of electroplating equipment as the metal strip or similar work continuously passes therethrough at a varying rate of speed.

It is now common practice to apply a coating, such as tin, to continuous length metallic strip material, such as iron or steel, by electrolytic means. A coil of the uncoated strip is positioned on the entry end of an electrotinning line and the strip as it is uncoiled passes through various pieces of apparatus and finally into and through the electroplating equipment. .Such an electrotinning line is usually operated from a variable voltage system, and is started by increasing the generator voltage until it overcomes the internal drop of the various motors so that the strip starts to move at a very low traveling speed. The plating current and the line are then simultaneously increased automatically by various electrical devices and circuits until the desired operating speed is obtained. Since the thickness of the tin or other coating deposited on the strip is a function of both time and speed, the plating current required is determined by the speed of the line at which any given coating weight is to be applied to the strip. After these two factors have been ascertained, the total plating current requlre-' ments can be determined, but this does not necessarily mean that heavier coatings cannot be applied or that the line cannot be run at a higher speed. Heavier coatings can be obtained at reduced line speeds while on the other hand, lighter coatings can be obtained at higher or increased speeds. It will be understood that it is essential only that a proper relationship between the total plating current and the speed be maintained for the desired coating weight, and it is to a, current control system for maintaining this relationship that the present invention relates.

Various means have been heretofore suggested and used for maintaining this balance between the plating current and the line speed, but most of them have been unsatisfactory in that either the equipment required was expensive and necessitated special designing and construction, or was not fast enough in its action, that is, such equipment was usually sluggish in its function. Such means as heretofore suggested and used usually included a tachometer generator driven directly by one of the strip contacted rolls of the line. Direct current output of the tachometer, which is in equal ratio to the speed of the line, was used in conjunction with controlling apparatus to regulate plating current to the anodes 01' the plating equipment. Since, as has been stated that the-speed of the strip versus plating current is extremely critical insofar as maintaining an [even coating weight is concerned, it naturally anisms, and other devices. It has been found that V such a control is entirely too sluggish in its action as the time required for operation of thevarious circuits and devices was a matter of minutes, whereas the time usually required'to slow down or speed up the line is a matter of seconds.

Accordingly, it is thegeneral object of the present invention to provide an improved current control system for a power supply which will compensate for relatively rapid variations of the load requirements, and, at the same time, a control system which is sensitive and, almost instantaneous in its action thereby eliminating the disadvantages of controls heretofore suggested and used.

It is a further object of this invention to provide an improved electrical system for controlling the current output of a generator or powering means of electroplating equipment whereby the current output of the generator is varied as the speed of the strip varies.

It is still another object of the present inven' tion to provide an improved electrical system for controlling the current output of a generator or powering means includin a specially designed saturable reactor which is simple and inexpensive in its construction and, 'at the same time, eflicient and effective in its use.

Various other objects and advantages of this invention will be more apparent in the course of the following specification and will be particularly pointed out in the appended claims.

The accompanying drawing illustrates schematically an example of apparatus embodying the principles of the present invention.

In this drawing, S indicates a continuous length of metallicstrip material or the work which is adapted to be passed continuously'through an electrolyte L in a plating tank T for electroplating or depositing a coating, such as tin,

pose of illustration and that usually a plurality of generators are used in such equipment. The negative armature lead of the generator 2 is connected to a conventional type cathode bus bar 4 which, in turn, is connected to a plurality of copper conductor rolls 5 arranged above the platmg tanlr '1' through suitable brush arrangements (not shown) at each individual roll. There is also arranged at the bottom of the tank T preferably non-conductor rolls 6, and it will be understood that the strip passes in a sinuous path over the conductor rolls 5 and the non-conductor rolls 8 whereby vertically extending strip portions are provided in the electrolyte and the tank, as the strip passes therethrough. Since the strip passes over the conductor rolls 5 which are connected to the cathode bus bar it of the plating generator, it will be obvious therefore that the strip is in effeet the cathode of the plating process.

There is arranged in the tank T and disposed in the electrolyte L therein between the vertical portions or the strip S, a plurality of vertically extending cast tin anodes l or anodes consisting of the metal which is adapted to be applied to the strip. The anodes l are supported preferably by horizontal anode bridges ll arranged between the vertical pass-es of the strip and are connected to an anode bus bar 9 which, in turn, is connected to the positive lead of the armature 2. It will be seen that the armature 2 of the plating generator establishes an electric current between the electrolyte L and the work or strip S through a circuit which includes the conductor rolls d and anodes l immersed in the electrolyte, in a well known manner. It will be understood that the output of the armature 2 of the plating generator is directly proportional to the strength of its field 8 which is powered through a circuit i0 by an exciting generator having an armature l2 and a field IS with a rheostat It included in the circuit for controlling the strength of the field 3 01, the plating generator. The field E3 of the exciting generator is connected to a suitable regulator to, such as an electronic control, by the lines or circuit l6.

According to the present invention, there is provided a second or control circuit having an especially constructed saturable reactor it which performs the function of delivering a reference voltage from the cathode bus bar 4 to the regulator IS in a manner now to be described. One side of the saturable reactor ll consists of a rectangular-shaped extension bar-like member l8 which is attached to the cathode bus bar 4, preferably by means of two leg portions l9. This arrangement provides in the member i8, a direct current exactly proportioned to that existing in the cathode bus bar 4. The other side of the saturable reactor ll consists of alternating current windings 2i and 22 arranged on the cores 2d and which are connected to a suitable source of alternating current supply by means of lines 33 and 26. The alternating current windings 2i and 22 are connected in parallel with each other and with such polarity relationship that they oppose each other so that no alternating current will be generated or communicated to the member it between the points X and Y, and consequently to the cathode bus bar 4. There is con nected in series with the windings 2| and 22, a variable resistor 25 which is utilized to regulate voltage to the primary of a transformer 26 which is also arranged in the second or control circuit with the saturable reactor l1. When the electroplating line is in operation, it will be seen that direct current in proportion to the plating bus current will flow in the member i8, and as a result the reactance of alternating current windings 2| and 22 will be reduced thus allowing alternating current to flow into the second -circuit. The amount of alternating current passing into the second circuit when no direct current is present in member I8 is extremely small and of a negligible value and is only of an amount required for magnetizing the cores 20. As alternating current passes through the second circuit, the voltage drop occurring across the resistor at points A and B is multiplied or lncreased to a higher value by means of the transformer 26. 'It will be obvious that the increased voltage supplied by the transformer 26 to the second circuit, at points C and D bears a dennite relationship to the input voltage at points Al. and B because of the ratio of the transformer 25.

There is also arranged in this second or control circuit and connected to the secondary side oi the transformer 26, preferably a rectifier 2? for rectifying the alternating current supplied by this transformer so that direct current is sup plied at points E and F in the lines 23 and 23, respectively, of the circuit. If desirable, the voltage issuing from the rectifier 2t may be fil tered by use of a choke coil so. a condenser 36 and a loading resistor 32 arranged in the circuit.

It will be seen that the voltage occurring bctween the points E and or between points and G is approximately proportional to the cur rent in the member l8 and consequently the cathode bus bar l. In order to obtain substana tially straight line characteristics of the direct current in the member it) versus the direct current voltage between points E and F or E and in the secondary circuit. the cores ml of the saturable reactor ll necessarily must have. a sharp knee in their saturation curve. Also the cores 20, as well as alternating current windings 2| and 22, must be designed to operate at a magnetic saturation to provide the characteristics desired. By operating these cores within certain ranges of saturation, the output between points E and-G is independent of normal power source fluctuations of the alternating current as supplied to the saturable reactor I! by the lines 23 and 24.

In order to provide a voltage in the second or control circuit proportional to the load or the traveling speed of the strip S, there is provided a tachometer generator 33 which is driven preferably by the main drive bridle R. of the line or any other roll contacted by the strip as it passes through the line. The negative terminal or side 29 of the rectifier 21 is connected to the negative terminal'or side of the tachometer generator 33 by means of the line 34 thus forming in asense one side of a loop in the control or secondary circuit. The positive side or line 28 leading from the rectifier 27 is connected to the regulator l5 and also the positive side of the tachometer generator I: is connected to the regulator by means of the line through the rheostat 38 and a resistor 31. Inother words, the line 28 together with the line 35, the rheostat 38 and the resistor 31 constitute the other or positive side of the loop in the control circuit.

As has been hereinbefore stated, the tachometer generator 33 supplies an electric voltage to the secondary circuit in proportion to the speed of the strip 8 through the line. It will be seen that this voltage is in opposition to the voltage supplied to the second or control circuit by the saturable react/or i1 together with the transformer 26 and the rectifier 21 from the cathode bus bar 4. When the voltage in the secondary circuit becomes unbalanced due to these opposed voltages, it is the purpose of the control or reg-- ulator I! to function so as to increase or decrease the strength of the exciter field i3 of the exciting generator which, in turn, controls the held 3 of the plating generator so as to increase or decrease the amount of current supplied to the load or the primary circuit for plating in a manner which will now be described.

When the line is in operation and the strip is passing over the conductor rolls 5 and through the electrolyte L, current is supplied to the anodes I from which it flows or is conducted through the electrolyte to the strip S and passes through the conductor rolls 6 and returns to the plating generator by way of the cathode bus bar 4. The saturable reactor ll transmits into the secondary circuit by means of the associated equipment, a voltage indication to the regulator it at terminal E which indication is in direct proportion to the plating current in the cathode bus bar 4. As the strip is passing through the line, it will be seen that the tachometer generator is simultaneously rotated by the drive bridle rolls R and transmits a voltage indication to the regulator or control l5 whici'i voltage is in direct relation to the speed of travel of the strip. Under normal operating conditions, i. e., where the speed of the line is constantly maintained, all portions of the control or secondary circuit will be in balance and the current therein will be flowing in an orderly and undisturbedmanner.

However, should the speed of the line be suddenly increased, the tachometer generator 33 will immediately transmit additional voltage to the secondary or control circuit in opposition to the reference voltage supplied thereto by the saturable reactor l'l thereby disturbing the balance of the control circuit at regulator l5. This unbalance of the circuit indicates to the regulator I! a need for an immediate increase of plating current to compensate for the increased rate of travel of the strip in order to apply the proper weight of coating thereon. The regulator responds to this unbalanced voltage in the secondary circuit by increasing the strength of the held I: of the exciting generator. When the strength of the field i3 is increased, the exciter armature i2 will automatically deliver more current to the shunt field 3 of the plating generator. As a result, it will be'seen that the plating generator will deliver more current to the plating circuit bus bars 4 and 8.

It will be understood that the plating current must be limited to the amount required for emcient coating and this is accomplished by the saturable reactor I! in the following manner. When the plating current is increased in the bus bar 4, it will also be increased proportionately in the crosspiece or member l8 of the saturable reactor ll. This increase of the current in the member l8 will cause an increase in the amount of alternating current flowing through the windings 2i and 22 of the saturable .reactor in a manner hereinbefore explained.

This increased flow of the alternating current through the windings 2| and 22 is reflected by a corresponding increase in the output of the transformer 26 and the rectifier 21 at points E and F and since the line 28 in which E is located is connected to the regulator i5, the voltage delivered at E and to the regulator will not match the voltage supplied to the regulator by the line 35 connected to the tachometer generator. As

long as this condition prevails, the regulator I5 will continue to increase the plating current in the bus bars 4 and 9 due to the predominating voltage in lines 34 and 35 or until the voltage between points E and G which is proportional to the plating current in bus bar t exactly equals the voltage generated by the tachometer generator 33 in the lines 34 and 35. When the reference voltage as supplied by the saturable reactor i'l. equals or matches the voltage supplied by the tachometer generator 33 and the voltage in the secondary or control circuit is again balanced, the regulator i5 will automatically cease increasing the plating current in the bus bars 4 and 9 by means of the exciting generator which controls the field of.the plating generator in a manner hereinbefqre described and stable conditions will prevail as long as the line speed continues at its increased rate of travel.

It will be understood that the above described performance of the control circuit and the devices occurs almost instantaneously to balance the plating current against the speed oi the line. While the cycle of operation as above described relates to an increase in the line speed, it will be understood that the control circuit will function in identically the same manner when the speed of the line decreases, in fact, any deviation in the line speed including both acceleration and deceleration will be reflected by unbalanced. voltages at the regulator i5 and corrected by the regulator in the manner as hereinbeiore described.

While the improved current regulating system of my invention is shown for controlling the current supplied to the electrolyte of an electrotinning line, it will be understood that such a regulating system can be used to regulate and maintain constant the direct current flow in the direct current tie between any two alternating current systems connected for power interchange through an electronic mercury arc frequency changer or to maintain constant current input to a motor for driving tension reels or rolls. It will be seen that by use of the current regulating system of the present invention that a high voltage proportional to the current is obtained while in other control systems heretofore suggested and-used, millivolts are obtained.

While I have shown and described one specific embodiment of my invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms and uses may be devised within the scope of my invention, as defined in the appended claims. i

Iclaim:

1. A system for regulating the current output of a generator connected to a load including, in combination, a first circuit including a bus bar connected to the generator for conveying the dlrect current generated thereby to the load, a second electric circuit including a, saturable reactor wherein the bus bar constitutes one side thereof with alternotlng current windings constituting the other side of the same, a. source of alternating current supply for said windings, said windings being connected so that no alternoting current will be generated in the direct current bus bar when alternating current is supplied to said windings whereby a. voltage will be obtained in said second circuit proportional to the current in said first circuit and said bus bur, e. resistor connected in series with said windings, means for multiplying the voltage drop occurring across sold resistor, means for rectifying said multiplied voltage, means for obtaining a voltage in said second circuit proportional to that required by the load and in opposition to said multiplied voltage, and means responsive to the direction of current *fiow'in said second circuit for varying the output of said generator.

2. in a, current control system having a bus bur for supplying direct current to the load from a generator, a. secondary circuit including o satureble reactor wherein the bus bar constitutes one side of the suturoble reactor with ulternat ingcurrent windings constituting the other side of the some, soicl windings being connected so that no alternating current will be generated in the direct current bus bar when alternating current is supplied to said windings whereby a voltage will be obtained in sold secondary circult proportional to the current in the bus bar, means for multiplying the output voltage of said soturoble reactor, means for rectifying said. multiplied voltage, means for obtaining a voltage in said secondary circuit proportional to that required by the load and in opposition to said multiplied voltage, rind means responsive to the direction of current flow in said circuit for varying the amount of direct current supplied to said bus bar.

3. A system for regulating the current output of a generator including, in combination, a. first circuit including a. bus bar connected to the genorator for conveying the direct current generated thereby to the load, a second electric circuit including a saturable reactor with one side thereof connected to the bus bar so that a direct current proportional to that existing in the bus bar is provided therein with alternating current windings constituting the other side thereof, a source of alternatingcurrent supply for said windings, saicl windings being connected so that no alternating current will be generated in the direct current side of the suturable reactor when alternating current is supplied to said windings whereby a, voltage will be obtained in said second circuit proportional to the current in said first circuit and said bus bar, a resistor connected in series with said windings, means for rectifying the voltage drop across said resistor, means for obtaining a. voltage in said second circuit proportional to that required by the load and in opposition to said rectified voltage, and means responsive to the direction of current flow in said second circuit for varying the output of said generator.

. ROBERT W. HOLMAN.

REFERENCES QL'TED The following, references are of record in the file of this potent:

UNITED STATES PATENTS Number Name Date 1,680,806 Schmidt Aug. 14, 1928 1,710,755 West Apr. 30, 1929 1,776,151 Hall Sept. 16, 1930 1,921,703 Schmidt Aug. 8, 1933 1,994,324 Suits Mar. 12, 1935 2,137,043 Dawson Nov. 15, 1938 2,325,401 Hurlston July 27, 1943 2,332,042 Shobert Oct. 26, 1943 2,404,948 Croce July 31), 1946

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