US2382018A - Apparatus for electroplating - Google Patents

Description

' Aug. 14, 1945. E. D. MARTIN 2,382,018"

APPARATUS FOR ELECTRCPLATING Filed Feb. 19, 1941 2 Sheets- Sheet 1 I Jew/2x041 I ($20102 Wig/22272 az/ s.

E. D. MARTIN Y APPARATUS FOR ELECTROPLATING 2 Sheets- -Sheet 2 Filed Feb; 19. i941 Patented Aug. 14, 1945 APPARATUS FOR ELECTROPLATING Edwin D. Martin, Chicago, Ill., assignor to Inland Steel Company, Chicago, 111., a corporation of Delaware Application February 19, 1941, Serial No. 379,611

7 Claims.

My invention relates to a new and novel process and apparatus for electrolytically depositing a coating of one metal on another.

This application is a continuation-in-part of my copending application Serial No. 313,537, filed January 12, 1940.

In prior practice 'in electroplating one metal on another from soluble anodes the current density, and therefore the rate of plating, have been limited by a number of troublesome factors. The comparative low rate of plating heretofore enforced by such factors, has been, in particular, a very serious commercial handicap in continuous processes for electroplating metal strips, such as cold rolled steel strip, fonexample, as the rate of production of the finished product has been greatly restricted, with attendant increase in cost. Important among these factors are the rate of release of the coating metal ions from the anode, and the rate of migration of those ions in the solution from the anode to the strip to be coated, the strip acting as the cathode. Concentration of the released coating metal ions about the anode naturally slows the rate of release of such ions. aifected by the rate at which the released metal ions migrate from the anode and this, in turn, is also influenced by the congregation of negatively charged ions about the anode. Similarly, concentration of positively charged ions, other than the coating metal, ions, about the cathode adversely influence the rate of depwition of the coating metal ions on the strip. a

The principal object of my invention is to provide a process and apparatus enabling the use of a much higher current density in a given solution and thereby greatly increasing the rate of plating. To this end I force some of the solution at high velocity against and along the faces of the anodes and in the direction of the metal cathode and transpose a lattice structure of insulating material which not only acts as an insulator between the anode and the cathode but which also assists in creating turbulence and thus distributes the coating metal ions more uniformly in the solution as it is rapidly propelled toward and against the cathode.

Other objects and advantages will become apparent as this description progresses and with This concentration is also reference to the accompanying drawings, where- Fig. 1 is a longitudinal section taken on the line 'Of Fig.2 and showing part of one form of apparatus for carrying out my invention;

Fig. 2 is a cross-sectional view taken through the apparatus and on the line 2-2 of Fig. 1, with the metal strip and part of the lattice structure broken away;

, Fig. 3 is a fragmentary sectional view taken on the line 3-3 of Fig. 2; and v Fig. 4 is a detail fragmentary view, illustrating the anodes in a modified position.

The plating tank or vat is indicated generally by the reference numeral 5. Suitably mounted near the bottom of the tank is the desired number of insulated rolls 6. Fixed to the top of the tank are standards I in which are journaled the shaft extensions of rolls 8 which are in staggered relation with respect to the rolls 6. The metal strip 9, which is to be plated, alternately passes over or about the rolls 8 and '6, the strip thus providing loops with vertical sides H which are moved vertically through a suitable plating solution 1'2 :as the strip is continuously advanced through the apparatus. The strip may be continuously pulled through the apparatus at substantially constant speed by a winding reel (not shown) :or other suitable means such as suitable driving :means (not shown) connected to the shafts 12' of athezrolls 0.

A skeleton frame work of insulating material, designated generally by the reference :numeral I3, is mounted within the tank 5 in any desired manner. Suitably mounted in the Iframe are pairs of adjacent and vertically disposed insulating devices l5, each in the form of :a ladder lat=- tice comprising round vertical rods ILB :and round horizontal rods l'l formed of insulating material, such as hard rubber or glass. It will be observed 40 that the lattices of each pair are on opposite sides and adjacent to the vertical portions H of the metal strip 9 to be plated. The horizontal bars ll are in contact with but behind the vertical bars I, the vertical bars being next to the vertical strip so that they aid in guiding the strip. Other functions of the insulating'lattices will be explained later.

Behind each lattice ii, that is, on the side of each lattice away from the strip, is a row of vertical soluble anodes I! which are formed of the engage their shaft extensions l2.

. streaks as shown in Fig. 4. As-best 'shown in Fig. 3, the anodes are preferably triangular in cross-section with one of the sides parallel to the latticeand metal .strip. Metal-ions pass from the anodes through the lattices and are electrodeposited on the metal strip to coat the same [withthe metal of the ion as it is pulledthrough the plating apparatus.

trically connected to the positive pole of a source of power and the metal strip 9 is connected to the negative pole in any suitable manner, so that the strip serves as the cathode. For example, one or more of the rolls 8 may be of conducting material and brushes 2 I connected to the negative terminal ofa suitable source of direct current power 22, shown diagrammatically in Fig. 1, may The positive terminal of the source'of power 22 may be connected to the cross bars 20 supporting thefanodes l9 andthis is one way by which the strip may be negatively charged with respect' to the anodes.

The bottom of the plating tank is connected by any suitable conduits'23 with a tank 24 (Fig. 2)

which may be adjacent to, or in any other suitable position with respect to the tank 5. A pump 25 at the top of the tank 24 circulates the plating solution fromthe tank through a system of pipes (now to be described) into the tank 5, and

thence through the conduits 23 to the bottonr of the tank 24. The outlet of the pump is con-' I nected to two large pipes 26 and 26 extending The anodes are elec-' plating operation. Thestrip steel is to be plated with tin and therefore the anodes are formed of cast tin. The plating solution may have, for

example, the following composition:

- Grams Tin sulphate (SnSO4) 54.3 Ortho-cresol (CsH4 CH3OH) 33.0 Sulphuric acid of 60 B. (H2804) introduced with the cresol 67.0 Sulphuric" acid of 60 B. (H2804) additional 30.0-100.0 Sodium sulphate (NazSO4) 20.00 Beta naphthol (C1oH7-OH) 1.0 Glue (animal lue) perliter of water; 1.0

@In preparing the above solution, the tin sulphate may firstv be dissolved in water. The orthocresol and 67 grams of sulphuric acid are treated together at a temperature of around 115 C. for approximately two hours and then added to the tin sulphate solution. Thebet'a-naphthol may be dissolved in just suflicient ethyl alcohol to form a solution and then added to the plating solution. The additional sulphuric acid is added and the water with the gluelis'also added in such amounts as to adjust the pH of the plating solution to, approximately 3.5. During the plating operationthere' is a loss of the glue and smalllongitudinally outside the tank adjacent the roll supporting bracketsl. Extending downwardly from the pipes 26 and 26 and into the tank are vertical headers 21 and 21, each pair of headers- 21 and 21 bein positioned in the vertical plane through the axis of one of the rollers 6 or 8. Projecting inwardly from each header 2'! is a series of horizontal pipes 28 and like pipes 28' project in the opposite direction from the opposite header 2! and between the pipes 28. Directly behind the anodes the horizontal'pipes 28 and 28* are provided with orifices 30. The pipes, above described, are of insulating material, such as hard rubber.

amounts are added from time to time, otherwise thesolution is stable,'the necessary tin ions being supplied from the tin anodes.

The temperature of the solution during plating may beapproximately'fio to 70 F. The current density may. be from 60 to .200 amperes per square foot during circulation of the solution as compare'dwith the 23 amperes per squarefoot recommended in still solutions, although current densities lower than 60. can be employed. The strip may .be pulled through the apparatus at a speed of approximately 200 to 400 feet per minute or even as great as 600 to 800 feet per minute, depending upon the number of times the strip is passed through the solution and the length of strip in each pass. The pump is in continuous operation while'the apparatus is being operated.

During the plating operation, the pump forces.

. solution out through the orifices in the pipes 28 26% through the headers 21 and 21 into the horizontal pipes 28 and 28*, each of which is closed at one end; The pump thus forces the plating solution out through the holes or ports 30. This createshigh velocity streams or. currents in the plating solution, the streams being directed against and around the anodes, and.

through the lattices l5 and against the moving strip 9 which is to be plated. Valves 32, one for each pipe 21 and 21, may be adjusted to obtain the desired or uniform pressure in the pipes 28 and 28 In order to illustrate further the principle and operation of my invention, I will give now a specific example of one practice of my invention which may be considered as fairly typical. The metal to be plated is cold rolled strip steel which has been-properly prepared and cleaned for the 'and 28 at high velocity, thus creating strong streams or currents in the solution which are directed against and around the anodes, through the insulating lattices andtoward and against the metal cathode. The movement of the solution over the faces of the anodes lowers the concentration of the ions congregating about the anodes thus permitting a more rapid transfer of tin from the anodes to the solution. Large quantities of positively charged tin ions are thereby produced adjacent the anode. In still plating solutions, these ions are dependent upon slow migration through the solution toward the cathode. .An important factor tending to decrease the rate of this migration in still solutions is the tendency of the field between the electrodes to cause the negative ions such as the sulfate or other negative ions present to concentrate in the portion of the solution nearer the anode and the positive ions, such as, the tin or other positive ions, to concentrate in the portion of the solution nearer the cathode. This action effectively neutralizes the potentials upon the electrodes so. that the potential causing ions to move in the solution midway between the electrodes is small; That is to say, the potential gradient is large immediately adjacent the electrodes, but small in a relatively large region midway thereposit metallic tin.

between. The ions, therefore, move very slowly in the region midway between the electrodes. In the present invention, the tin ions are physically transported from the anode to the oathode, so that large numbers of these ions are continuously brought into contact with the cathode where they give up their positive charge to dethe solution which has been slightly impoverished in tin through having given up some of its tin to form the coating on the cathode is the solution which is directed over the surface of the anodes to have its tin content replenished. It is this enriched solution which is directed over the surface of the cathode to again deposit some of its tin. A cycle is thus created in which the impoverished solution, which is in the best condition to take up tin, is directed over the anodes and the enriched solution, which is in the best' condition to give up some of its tin, is directed against the cathode. This method of taking the solution from the vicinity of the cathode and pumping it back over the anode surfaces permits an external circuit in which the solution may be conditioned as to its chemical composition, its temperature and its cleanliness by the' addition of chemicals, by the use of a heat exchange in the circuit, and by filtering. Furthermore, the streams of solution impinging upon the anode structure and the lattice insulating structure adjacent the cathode, create turbulence and eddies in all directions as the solution passes through the same. This prevents the concentrations of ions above referred to and produces a more uniform potential gradient, while at the same time insuring an even distribution of the deposited tin upon the oathode. It has been found that a given potential difference between the anode and cathode, with a given electrode spacing will produce a much greater current density than in still solutions, thus effecting a substantial saving in electric power. Also, it has been. found that uniform adherent coatings may be produced with much greater current densitiesthan in still solutions.

It is now apparent that my invention enables the use of a high density current and results in a greatly increased rate of plating, while at the same time the plating itself is very satisfactory.

I have illustrated and described one form of embodiment of my invention, but it will be understood that changes in detail and arrangement of parts may be resorted to without departing from my invention as defined by the claims that follow. While I have given as a typical example the electroplating of a steel strip with tin, it is to be understood that I do not intend to so limit my invention. For instance the Object to be coated may be of other metals than steel, such as copper, and the plating metal may be' other than tin, such as copper, zinc, cadmium or nickel. The composition of the plating solution depends largely on the kinds of metals used. The anodes may be formed of the pure coating metal or any suitable alloy of such metal and the term anode, as used in the claims, has the broader meaning.

I claim:

1. In an electroplating apparatus for plating metal upon a major surface of a cathode, the combination of, a container for holding a bath of plating solution, means for supporting said cathode in said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in said bath directed toward said cathode, means for supporting a grid It will also be noted that of anodes of the plating metal in said bath in plating relation with said cathode and adjacent said cathode between said stream producing means and said cathode, said'anodes being triangular in cross section, each anode having one of its sides facing and substantially parallel to the major surface of the cathode to be plated, the stream producing means being positioned to direct said stream from said orifices against the other two sides of the anodes and then in a direction generally normal of and against said major surface of said cathode.

2. In an electroplating apparatus for plating metal upon a major surface of cathode, the combination of, a container for holding a bath of plating solution, means for supporting said cathode in said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in said bath directed toward said cathode, means for supporting a grid of anodes of the plating metal in said bath in plating relation with saidcathode and adjacent said cathode between said stream producing means and said cathode, said anodes being triangular in cross section, each anode having one of its sides facing and substantially parallel with the surface of the cathode to be plated, said stream producing means comprising a series of pipes in said bath having orifices directed toward said anodes, and a pump for drawing solution y from said container and forcing it through said of plating solution, means for drawing said strip through said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in said bath directed toward said strip, means for supporting a grid of anodes in said bath in plating relation with said strip and adjacent said strip between said stream producing means and said strip, said anodesbeing triangular in cross section, each anode having one of its sides facing and substantially parallel with the surface of the strip to be plated, said stream producing means [being positioned to direct the streams from said orifices against the other two sides of the anodes and then in a direction generally normal of and against a face of said strip.

4. In a continuous electroplating apparatus for plating a metal strip connected as a cathode, the combination of, a container for holding a bath of plating solution, means for drawing said strip through said bath, means for forming at least on loop in said strip as it is drawn through said bath and providing straight portions of said strip in said bath, means for producing streams. of substantial velocity in said bath directed toward said straight portions of said strip, means for supporting a plurality -of anodes forming a grid structure in said bath in plating relation with said strip, said anodes being supported in substantial parallel relation with said straight portions of said strip and between said stream producing means and said strip, said anodes being triangular in cross section, each anode having stream producing means comprising a series of pipes in said bath having a plurality of orifices directed toward said anodes, and a pump for drawing solution from saidcontainer and forcing it through said pipes and out of said orifices to create said streams in said solution directed from said orifices against the other two sides of said anodes and then in the direction of and against said strip, said stream producing means and said anodes being positioned to direct said streams generally normal of and against the faces of said straight portions of said strip.

5. In an'electrop'lating apparatus for plating metal upon a cathode, the combinationv of, a container for holding a bath of plating solution, means for supporting said cathode in said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in said bath directed toward said cathode, means for supporting a grid of anodes of the plating metal in said bath in plating relation with said cathode and adjacent said cathode between said stream producing means and said cathode, turbulence tainer for holding a bath of plating solution, means for supporting said cathode in said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in saidvbath directed toward said cathode, means for supporting anodes of the plating metal in said bath in plating-relation with said cathode and adjacent said cathode between said stream producing means and said cathode, a lattice of insulating material positioned between said anodes and said cathode, said stream producing means being positioned to direct the streams from said orifices against and around said anodes and then in the direction of said cathode through said lattice and against said cathode.

7. In a continuous electroplating apparatus fOr plating a metal strip, the combination of a container for holding a bath of plating solution, means for drawingsaid strip through said bath, means having orifices in said bath for producing a plurality of streams of substantial velocity in said bath directed toward said strip, means for supporting anodes in said bath in plating relation with said strip and adjacent said strip between said stream producing means and said strip, a

lattice of insulating material positioned between said anodes and said strip, said stream producing means Ibeing positioned to direct the streams from said orifices against and around said anodes and then in the direction of said strip through said lattice and against said strip.

EDWIN D. MARTIN.

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