US2951978A - Reverse pulse generator - Google Patents

Description

Sept. 6, 1960 D. T. DICKSON ETAL 2,951,978

REVERSE PULSE GENERATOR Filed May 29, 1957 2 Sheets-Sheet l FIG. l

+ ll INVENTORSJ DAVID T. DICKSON 8| JOHN W. VAN DYKE BY w/W ATTORNEY Sept. 6, 1960 D. T. DICKSON ETAL 2,951,978

REVERSE PULSE GENERATOR Filed May 29, 195'] 2 Sheets-Sheet 2 FORWARD VOLTAGE VOLTAGE O l REVERSE I VOLTAGE I I I I FORWARD REVERSE FIG. 2

INVENTOR DAVID T. DICKSON 8 JOHN W. VAN DYKE ATTORNEY Patented Sept. 6, 1960 2,951,978 REVERSE PULSE GENERATOR David Thomas Dickson, Burton, and John W. Van Dyke, Seattle, Wash., assignors, by mesne' assignments, to Thor P. Ulvestad and David T. Dickson Filed May 29, 1957, Ser. No. 662,474 21 Claims. (Cl. 322.6)

The present invention relates to the rapid reversal of electrical current direction with the substantial elimination of any off period between the diiferently directed unidirectional pulses of electrical current. The present invention is particularly directed to electrolytic processes and especially electroplating by a procedure in which the current direction is rapidly reversed and the off period substantially eliminated so that the ions in the area surrounding the cathode electrode can be more efficiently replenished and the electrolytic process enhanced as a result of the fact that the ions are more efiiciently replenished in the area of the cathode and the anode is more efliciently depolarized.

In accordance with the invention, an electrical current is supplied from a DO generator and the current direction is rapidly reversed with the substantial elimination of any off period between the forward and reverse current directions. It has been found that this rapid reversal of current direction aids in replenishing the ions in the area around the cathode and that the anodes are more efliciently depolarized. As a result, the invention enables a greater current density to be used in both directions and the electrolytic process proceeds more rapidly and more uniformly.

Referring more particularly to the process of electroplating, there are several important factors governing the value and usefulness of an electroplating process. These are (1) electrical efficiency, (2) speed, (3) quality of finish and (4) the amount of prior and subsequent treatment such as bufiing and polishing which are necessary in connection with the process. The factor of speed is of particular importance since if the time of treatment can be shortened by 50% to 75%, a decrease in electroplating efliciency can be tolerated. Further, if the strength and uniformity and also the quality of the finish (smoothness and brightness) can be enhanced, such improvement will justify a lowered electrical efficiency.

In the past, some advantage has been attained by the utilization of reverse current plating. In this method, a generator was used for a current source and the field was reversed periodically by means of a mechanical switch. Some small improvement in plating was obtained by reverse current plating. However, the time constant of the field made switching relatively slow. Attempts were made to improve the situation by the use of rectifier power supplies but it was still necessary to switch the primary circuit off, to reverse the output of the rectifier and to turn on the primary, all mechanically.

In accordance with the present invention, the direction of the electrical current is reversed electronically and at a much more rapid rate so that the off period between forward and reverse is substantially eliminated and the electrolytic process improved in themanner previously indicated.

In accordance with the present invention a general improvement has been made in electrolytic processes. Thus, in addition to improvement in the electroplating process, electrolytic cleaning or polishing and the anodizing of metals, e.g. aluminum and magnesium, are also improved. The invention is also applicable throughout the electrochemical industry, and may be utilized to advantage in electrolytic decompositions.

In accordance with the present invention, the reverse current produces a cleaning or etching effect and the deposit is free from impurities between the various layers of plate, whereas in the mechanical switching method, the deposit is subject to laminations and will break up in ductility tests.

The invention will now be more fully described in connection with the accompanying drawings in which:

Fig. 1 is a circuit diagram illustrating the applicability of the invention to an electrolytic process such as electroplating; and,

Fig. 2 is a graph comparing voltage with time for the purpose of illustrating a single cycle of output current.

Referring more particularly to the drawings, a direct current generator 10 is fitted with two identical sets of field coils 11 and 12 and with commutating interpoles 13 and 14. One terminal of one set of field coils 11 is connected to the anode of an arc-type gas valve or thyratron 15, the anode being identified by the numerals 16. In place of the thyratron 15, any other type of control such as an ignitron may be employed. The other end of the same set of coils 11 is connected to an adjustable resistor bank 17. The resistor bank 17 is in turn connected with the positive terminal of a suitable source of direct current.

The second set of field coils 12 is similarly connected to an arc-type gas valve 18 and particularly to the anode 19 thereof. Field coils 12 are also connected to an adjustable bank of resistors 20, said resistor bank 20 being in turn connected with the positive terminal of the direct current source.

The field coils 11 and 12 are oppositely wound so that, when direct current is flowing through coil 11, the armature polarity will be such that the terminal connected to the anode 21 of the electroplating bath 22 will be positive while the terminal connected to the cathode 23 of the electroplating bath 22 will be negative.

When the field coil 12 is energized, the above set forth polarity will be reversed, and the anode 21 will be negative while the cathode 23 will be positive.

A capacitor 24 is connected between the anodes 16 and 19 of the arc-type gas valves 15 and 18. The anode 25 of a third arc-type gas valve 26 is similarly connected through capacitors 27 and 28 to the anodes 16 and 19 respectively of the valves 15 and 18.

The anode 25 of the valve 26 is connected to the positive terminal of the direct current supply through resistors 29 and the inductor 30 (the inductor 30 being not essential).

The cathode returns of the valves 15, 18 and 26 are common and connect to the negative terminal of the direct current supply. The grids of the valves 15, 18 and 26 are suitably biased and controlled by a separate con troller 31 which provides spaced trigger pulses for the valves or thyratrons 15, 18 and 26.

The sequence of operation is as follows: A trigger pulse from the controller 31 causes the valve 15 to conduct, and current builds up in field coil 11 which produces a magnetic field in the armature or interpole 14. Current is therefore induced in the armature winding and its associated circuit causing metal from the plating bath 22 to be deposited on the cathode 23. After a short interval, determined by the control element 32 of control 31, a second pulse is applied, this second pulse being directed to the grid of valve 18 causing the valve 18 to conduct. The drop in voltage at the anode of valve 18 lowers the potential of the anode 16 of valve 15 and extinguishes the arc therein. The current is thus cut off in the field coil 11 and is built up in the field coil 12. The polarity of the armature is thus rapidly reversed and the anode 16 becomes temporarily cathodic while the cathode 33 of the valve 15 becomes temporarily anodic. The time and voltage relations which can be employed in accordance with the invention are discussed hereinafter.

After an interval determined by the control element 34 of the controller 31, a pulse fires valve 26 which extinguishes the arc in valve 18 thus causing the current and voltage of the generator to drop to zero. After an interval determined by control element 35 of the controller 31, a pulse fires valve 15 and the cycle repeats.

As will be understood, the time intervals for each pulse are separately adjustable and the voltage and amperage of the forward pulse are adjustable by means of the resistor 17 while'the voltage and amperage of the reverse pulse are controlled by the resistor 20. In this manner, the strength and timing of each pulse can be individually determined.

For example, the pulse interval may be set to 0.7 second with a forward interval of 0.4 second and a reverse interval of 0.1 second. The forward voltage may be 30 volts and the reverse voltage 45 volts. At these settings, a 2-2.5 mil coating of nickel may be plated from a Watts-type nickel bath in 10 minutes. The finish achieved is superior to that produced by standard methods both in grain and brightness and the speed-of-deposition is far in excess of that which is normally achieved. These superior results are due to the rapid reversal, the short cycle, and the rest period which permit a much greater current density than any previous method. The short high-current reverse pulse produces superior depolarization in certain cases which permits the achievement of heavier deposits of the metal which is plated.

The cycle of output current in accordance with the invention is graphically represented in Fig. 2 where voltageis correlated with time. Fig. 2 is self-explanatory and shows a complete cycle including the forward pulse, the reverse pulse and the ofi period. The rapid reversal of current direction between the forward and reverse pulses and the use of a rest period provides superior depolarization and permits the replenishment of ions around the cathode and enables greater current densities to be effectively employed. As a result, the electrolytic process is speeded and the electrolytic action is more uniform. More adherent and bright platings which may be thicker than conventional and which are obtained in shorter periods of time are illustrative of the improved electrolytic action achieved.

Example I Nickel sulfate (NiSO .6H O) 50.6 oz./gal. Nickel chloride (NiCl .6H O) 7.96 oz./ gal. Boric acid (H BO 6.5 z./gal. Wetting agent 0.5% by volume.

This solution contained the equivalent to 12.85 02/ gal. of nickel (Ni++). and 2.38 oz./ gal. of chloride (Cl).

The bath was adjusted to a pH of 3.3 (electrometric) and purified by potassium permanganate and activated carbon to remove organic impurities from the bath. This bath was then used to plate panels of polished high carbon steel in a 1000 ml. Hullcell. The panels were preliminarily degreased with a volatile solvent such as ether, air dried, and stored in dilute sodium cyanide solution. Before plating the panels were rinsed in water, dilute hydrochloric acid, and then again with water.

With straight direct current of 3 amperes at 6 volts, for 10 minutes, and with a bath temperature of 140 F. and agitation, a maximum of plate thickness of .001" was obtained. The deposit was ductile and possessed a matte finish; With higher voltages and amperages, the quality of the plating decreased.

With high-speed periodic reverse current electroplating of the invention using a pulse interval of 0.3 second (forward 0.2 second, reverse 0.1 second) and an energy ratio of 4 forward to 1 reverse (the average forward voltage times the average forward current times forward time interval equals 4 times the average reverse voltage times average reverse current times reverse time interval), a current of 8.5 amperes at 14 volts, greatly improved results were achieved. The temperature of the bath was started at 140 F. and rose to 165 F. and agitation was used- In ten minutes the maximum deposit was over .002 in thickness. Optimum thickness was between .0018 and .002", and a bright ductile finish was attained. This finish was good enough for chromium plating without bufling.

In the above example and the following examples, all parts are by weight unless otherwise specified.

Example II The following is an example of the application of the invent-ion to rhodium plating, using as the plating bath 7.5 g./ gal. of rhodium metal dissolved in 2 A 11. oz./gal. of sulfuric acid:

Anodes Platinum.

Temperature F.

Current density amps/sq. it, forward and reverse.

F o r w a r d time/reverse time 4:1. Pulse interval 0.3 sec. Voltage 3 volts forward, .1 volt This deposited 0.2 mil bright rhodium plate over bright nickel in 2.5 rnins.

Example 111 This is an example of the application of the invention to plating nickel-tin alloy:

Plating solution:

Stannous chloride 5.8 oz./ga1. Nickel chloride 40.0 oz./gal. Sodium fluoride 3.75 oz./gal. Ammonium bifiuoride 4.67 oz./gal. Anodes 1 tin:2 nickel. Temperature F. Forward time/reverse time 4:1. Pulse interval 0.3 sec. Curent density 200 amps./sq. ft. forward and reverse. Voltage 14 volts.

This deposited 1 mil bright alloy plate in 5 min.

In each of Example IIll, no off period was used. The off period is not necessary in all plating methods but is particularly applicable to some solutions. Where there is no 01f period, the curve of Fig. 2, of course, would show no off period. In such a method, the tubes 15 and 13 are successively energized by the controller 31, the tube 26 not being utilized.

By way of example, the various values of the essential components shown in Fig. 1 may be as follows:

Component:

15, 18 06A. .26 CSB. r 17, 20 0-60 ohms, 500 w., plus a fixed resistor of 10 7 ohms, 500 w. 24 40 mfd. 28 10 mfd. 27 4 mfd. 29 5.0 ohms, 500 w. 10 Generator-40 v., 40 a.,.

2 pole battery charging generator, rewound 2 coils/pole, 4. ohm/coil.

-The controller 31 is a conventional controller well known in the prior art and forms no part of the present invention.

The method of the invention may be utilized, for example, in plating nickel-tin alloy from a nickelous chloride, stannous chloride, sodium and ammonium fluoride bath; plating copper from a cyanide bath; plating nickel from nickel sulfate baths; and plating copper from copper fiuoborate baths. Acid tin baths may also be used.

The ratio of forward time to reverse time and off period, if any, is variable depending upon the metal being plated, the base metal, and the degree of leveling required.

Generally, the current density which may be utilized in practicing the invention ranges from 2-10 times that of conventional practice. For example, there may be used in nickel plating, 100-800 amps. per square foot; in nickel-tin alloy, 800 amps. per square foot; or in rhodium, 100 amps. per square foot.

We claim:

1. Apparatus .for providing difierently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a D.C. generator having a pair of commutating interpoles and two oppositely wound field coils, the first of said field coils being connected on the one hand to the anode of a first arctype gas valve having an anode, a grid and a cathode, and on the other hand through a resistor to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, said anodes being connected together through a capacitor so that the firing of one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

2. Apparatus as recited in claim 1 in which said resistors are adjustable. V v

3. Apparatus for providing differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a first resistor to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, a third arc-type gas valve having an anode, a grid and a cathode, said third valve having its anode connected through a third resistor to said positive terminal, said anodes being connected together through capacitors so that the firing of any one of said valves Will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

4. Apparatus as recited in claim 3 in which said first and second resistors are adjustable.

5. Apparatus for conducting an electrolytic process using difierently directed unidirectional pulses of electrical current with a rapid'reversal of current direction comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, each of said interpoles being connected to an electrode, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode,

a grid and a cathode, and on the other hand through a resistor to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arctype gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, said anodes being connected together through a capacitor so that the firing of one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

6. Apparatus as recited in claim 5 in which said resistors are adjustable.

7. Apparatus for conducting an electrolytic process using differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, each of said interpoles being connected to an electrode, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a first resistor to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arctype gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, a third arc-type gas valve having an anode, a grid and a cathode, said third valve having its anode connected through a third resistor to said positive terminal, said anodes being connected together through capacitors so that the firing of any one of said valves Will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

8. Apparatus as recited in claim 7 in which said first and second resistors are adjustable.

9. Electroplating apparatus comprising, a DC generator having a pair of commutating interpoles and two oppositely wound field coils, each of said interpoles being connected to an electrode, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a resistor to the posi tive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, said anodes being connected together through a capacitor so that the firing of one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

10. Electroplating apparatus comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, each of said interpoles being connected to an electrode, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a first resistor to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand through a second resistor to said positive terminal, a third arc-type gas valve having an anode, a grid and a cathode, said third valve having its anode connected through a third resistor to said positive terminal, said anodes being connected together through capacitors so that the firing of any one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

11. Apparatus for providing differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, the first of said field coils being con nected on the one hand to the anode of a first ,arctype gas valve having an anode, a grid and a cathode, and on the other hand to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand to said positive terminal, said anodes being connected together through a capacitor so that the firing of one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

12. Apparatus as recited in claim 11 wherein each field coil circuit includes a variable resistor.

13. Apparatus for providing difierently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of commutating interpoles and two oppositely wound field coils, the first of said field coils being connected on the one hand to the anode of a first arc-type gas valve having an anode, a grid and a cathode, and on the other hand to the positive terminal of a source of direct electrical current, the second of said field coils being connected on the one hand to the anode of a second arc-type gas valve having an anode, a grid and a cathode, and on the other hand to said positive terminal, a third arc-type gas valve having an anode, a grid and a cathode, said third valve having its anode connected to said positive terminal, said anodes being connected together through capacitors so that the firing of any one of said valves will extinguish the other of said valves, said cathodes being connected to the negative terminal of said source of direct electrical current, and controlling means connected with said grids for supplying said grids with trigger pulses in timed sequence.

14. Apparatus as recited in claim 13 wherein each field coil circuit includes a variable resistor.

15. Apparatus for providing difierently directed unidirectional pulses of electrical current With a rapid reversal of current direction comprising, a DC. generator having a pair of output terminals, field coil means, a first electronic valve for directing current through said field coil means in one direction, a second electronic valve for directing current through said field coil means in the opposite direction, and means to alternately actuate said valves to alternately excite said field coil means with differently directed unidirectional pulses.

16. Apparatus for providing diiferently directed uni: directional pulses of electrical current With a rapid reversal of current direction comprising, a DC. generator having a pair of output terminals, a first. field coil and a second oppositely wound field coil, a first electronic valve for directing current through said first field coil, a second electronic valve for directing current through said second field coil, and means to alternately actuate said valves to alternately excite the field coils with difierently directed unidirectional pulses.

17. Apparatus for providing differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of output terminals, field coil means, a first arc-type valve for directing current through said field coil means in one direction, a second arc-type valve for directing current through said field coil means in the opposite direction, and control means to alternately fire said valves in timed sequence to alternately excite said field coil means with differently directed unidirectional pulses.

18. Apparatus for providing differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of output terminals, a first field coil, a second oppositely wound field coil, a first arc-type valve for directing current through said field coils, a second arctype valve for directing current through said second field coil, and control means to alternately fire said valves in timed sequence to alternately excite the field coils with dififerently directed unidirectional pulses.

19. Apparatus as recited in claim 18 includingmeans interconnecting said valves so that firing of one valve automatically extinguishes the other valve.

20. Apparatus as recited in claim 18 including a third arc-type valve for directing current through a load other than said field coils, means interconnecting all of said valves so that the firing of one of said valves automatically extinguishes the other valves, the firing of said third valve preventing excitation of the field coils of said D.C. generator.

, 21. Apparatus for providing differently directed unidirectional pulses of electrical current with a rapid reversal of current direction comprising, a DC. generator having a pair of output terminals, oppositely wound field coils, and means to alternately excite said coils with unidirectional pulses of electrical current to reverse the field of the generator.

References Cited in the file of this patent UNITED STATES PATENTS 2,451,341 Jernstedt Oct. 12, 1948 2,508,727 Shottenfeld et a1 May 23, 1950 2,565,540 Williams Aug. 28, 1951 2,575,712 Jernstedt Nov. 20, 1951 2,634,393 Wu et a1. Apr. 7, 1953 2,678,909 Jernstedt et al May 18, 1954 2,696,582 Willard Dec. 7, 1954

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