US2080506A - Process of and apparatus for electroplating articles - Google Patents

Description

F. B. RINCK ET A1.

PROCESS oP AND APPARATUS PoR ELECTROPLATANG ARTICLES Filed April 14, y.w55

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May 18, 1937.

Patented May 1.8, 1937 UNITED STATES PROCESS F AND APPARATUS FOR ELEO- TROPLATING ARTICLES Franklin B. Binck, La. Grange, and Bay C. Kivley, Oak Park, Ill., assignors to Western Electric Company,

Incorporated, New York,

N. Y., a

corporation of New York Application April 14,

Claims.

This invention relates to aprccess of and apparatus for electroplating articles and more particularly to a method oi' and apparatus for electrogalvanizing wire.

In the usual process of electrogalvaniz'ing in-` prohibitive rate, and it is possible to use soluble' zinc anodes for replenishing the zinc content Without building up the zinc in solution at a rate higher than that at which it is deposited out of the bath. In certain kinds of galvanizing,` such as continuously galvanizing Wire, there are decided advantages in being able to use a high cur= rent density because the rate of deposition in such a bath is high and also the eiiiciencyo-f the bath is high.

The continuous electrogalvanizing of wire presents many problems which are'peculiar to this art due to the fact that the wire must move continuously, which requires that'all factors relating to the rate .of electrodeposition, such as the cleaning oi' the wire and the regeneration of the .electrolyte to maintain its uniformity, must be under complete control.

Objects of the present invention are to provide an effective and eilicient method of electroplating articles.

In accordance with one embodiment of the invention, an iron or steel wire is passed at a con- 35 stant speed through a series oi cleaning baths designed to properly cleanse the Wire, after which it is passed through an electroplating bath of high purity and high acid concentration. In the bath an electric current of high density is 40 passed through the wire from insoluble anodes and the electrolyte of the bath is uniformly maintained by continuously withdrawing electrolyte therefrom and continuously adding regenerated electrolyte. In the regeneration of the electro- 45 lyte, substantially all of the impurities which are below zinc in the electromotive series are removed to decrease the solubility of the electrodeposited zinc in the electrolyte.

A complete understanding of the invention may 59, be had by reference to the following description taken in conjunction with the accompanying drawing, in'whlch Fig, 1 is an elevational view, partially schematic, of an apparatus embodying the invention f5 and by means of which the method of the invention may be practiced;

Fig. 2 is a fragmentary sectional view taken on line 2-2 of one of the containers for a cleaning '60 solution;

1933, Serial No. 866.080

(Cl. 20d- 18) Fig. 3 is a sectional view taken on line 3 3 of Fig. 1 showing the electrode structure of the plating bath; and f Fig. 4 is a sectional view similar to Fig. 3 showing a modified form of electrode structure.

The wire to be electrogalvanized is wound on a plurality oi supply reels 0 and passes through a caustic soda solution in container I. The container l may be made of metal, such assteel, and serves as a cathode by making electrical contact therewith,` and the wire itself serves as an anode by making contact therewith by means of a brush 9. Current is supplied to the electrodes by a direct current generator II or any other suitable source. The caustic soda removes grease and saponiable materials and the action of the electric current forms gas bubbles which give a mechanical action to increase the speed of the cleaning process. Fromthe container 'I the wire passes into a container I2, in which the wire is given a cold water rinse and from the container I 2 the wire passes into a container I3 having a 10% solution of hydrochloric acid therein. In this container an alternating current from any suitable source, such as a generator M, is passed through the wires by connecting one terminal of the generator It to one wire or set of wires and connecting the other terminal to another or alternate wire or set of wires. By thus connecting one wire to one terminal and another wire to another terminal of an alternating current source, the necessity of providing electrodes in the bath is obviated and a more direct contact with the wires is provided. In this container, scale, rust, and other materials, such as the coat of ferrie hydroxide, known as the Sull coat, from the drawing operation are removed. From the container I 3, the wire passes through a container I5 in which the wire is given a cold water rinse and from vthe container I 5 the wire passes through a container I6 having a 50% solution of sulfuric acid therein. In this solution, the' current is passed through the wire by connecting the negative terminal of a source of direct current, such as the generator I'l, to a cathode plate I8, preferably of lead, in the container and connecting the positive terminal oi' the source to a brush I 9 contacting with the wire. This tank is preferably lined with rubber or other material capable of resisting the action of sulfuric acid, although a lead lining may be used, which would then form the cathode I8. In this bath finely divided iron is removed from the wire and occluded hydrogen is liberated, leaving the wire bright as it leaves the bath. The removal of the finely divided iron is important due to the fact that iron is below zinc in the electromotive series and if the loose particles of iron were permltted to enter the plating bath, they would contaminate the bath and cause a redissolution of the zinc plated on the wire. 'I'he wires then pass through a cold water rinse and into a container 22 containing a plating bath. The wire passes from the plating bath through a container 32 containing a cold water rinse to take-up reels 2li@v Each ofthe containers 1, i2, I3, I5, I6, 2|, 22, and f 32 are provided with double end walls provided with slots through which the wires pass. The inner end walls 33 have wiers for restraining the uid inthe containers from passing. Each wier consists of a pair of flexible sheets of material clamped over the slot in the wall by a U-shaped support 36. The fluid passing through the wiers is collected in the space between the end walls and is drawn off through pipes 31. A pump 38 connected to these pipes returns the fluid to the containers through a pipe 39.

The plating bath in container 22 comprises from 15% to '20% of sulfuric acid and 8% of zinc. In some cases the sulfuric acid content may range from 10% Ato 25% and the zinc content from to 10%, although the eiiiciency near the limits of the latter ranges drops off materially. The zinc and sulfuric acid are combined prior to being supplied to the container and form an electrolytic bath from which the zinc is electrolytically deposited on the wire. This bath must be maintained practically free from impurities and particularly of such impurities as iron, nickel, copper, cobalt or arsenic, which are below zinc in the electro-motive series and would cause the sulfuric acid to redissolve the zinc plated on the wire.

One of the outstanding. advantages of electrogalvanizing wire is that a much heavier coating can be applied to the wire by this method than by such methods as the hot dip method. vHowever, it is evident that in order to realize the advantages of the present invention, it is necessary to provide a uniform coating so that all portions oi the wire will be equally protected. For this reason the wire must travel at a. uniform rateV and the electrolytic bath must be maintained uniform so that not only the rate 0f deposition will be uniform but the rate of dissolution of the deposit from the wire must be reduced to a minimum. 'I'he high current density employed in the plating bath and the high acidity of the vsolution give the bath a relatively low throwing power; however, on account of the uniform cross-section of the wire, a high throwing power of the electrolyte is not essential and the low throwing power of the bath substantially prevents electrodeposits on the electrodes contacting with the wire.

The electroplating of the wire is accomplished by making the wire the cathode. Contact is made with the wire by means ofthe electrode structure shown in Fig. 3. The wire 25 is engaged by a rod 26 of copper or other good conducting material, the lower end of which is provided with a cap 30 of Monel metal or other acid resistant material and the portion contacting with the Wire is made to conform to the shape of the wire. The upper portion of the rod 26 extending into the electrolyte is encased in an insulating sleeve 21 of rubber, porcelain or other suitable insulating material. The cap 30 of the rod 26 extends slightly through the sleeve 21 and an insulating member 28 extending longitudinally of the wire loosely supports the sleeve 21 and substantially encloses the wire to prevent a large amount of electrolyte from coming in contact with the rod 26 so as to avoid eiectrodepo'sition on the rod.

- The upper end of the rod 28 is connected to the negative side oi a source ot direct current, such as a generator 29. the positive side of which is connected toa pair of insoluble lead anode plates 3i which extend longitudinally of the wire for substantially the entire length of the bath. A current density of from 500 to 2000 amperes per square foot of the cathode surface' is used.

Fig. 4 illustrates a modified form of electrode structure in which a split tube 8| having a slot 62 throughout its length serves as an anode. At spaced points' the slot is enlarged as shown at 63 for receiving sleeves 64 of insulating material. Each of these sleeves fits into an aperture in a guide member 65 in-the tube. This guide member has a V-shaped cutout portion '66 through which the wire to be electro'plated passes and contact is made with the wire by means of a rod 61 extending through the sleeve. The guide member 65 extends longitudinally of the tube only a short distance from each side of the sleeve so that the wire is exposed to the tube or anode through a large portion of the length of the tube.

The uniformity of the electrolyte in the bath is maintained 'by performing all of the purifying and regenerating steps of the process outside of the bath and continuously draining electrolyte from the bath and adding regenerated electrolyte to the bath. A portion of the electrolyte in the container 22 continuously passes through the wiers 34 in the' inner end walls of this container and collects in the space between the double end walls of the container.v Aportion of the electrolyte thus withdrawn from the bath is alternately drained into tanks 4| and 42 and the balance is returned directly to the bath by a pump 40. The tanks 4l and 42 are connected to the container by pipes 43 and 44, respectively, which are provided with valves 45 and 46 so that the electrolyte may be drained into either tank. When the tank 4| is full,'valve 45 is closed and valve 48 is opened to drain the electrolyte into tank 42.

The purpose of the two containers 4l and 42 is to permit the electrolyte to be regenerated in batches. In these containers commercial zinc is added to the electrolyte to neutralize the acid therein. The action of the zinc with the sulfuric acid causes the impurities in the electrolyte to be reduced to their lowest valences. For instance, any iron in the electroplating bath is in the state of ferric sulfate and the addition ofzinc in the containers 4I and 42 reduces the iron to ferrous sulfate, in which state it is soluble in the neutral solution and cannot be removed by nltering. In the case where oxides or carbonates of zinc are added to neutralize the solution in regenerating a plating solution oi' the type referred to above, the ferric sulfate is not reduced and may, therefore, be removed by precipitation in this stage. The addition of commercial zinc, therefore, requires the addition of an oxidizing agent in a later stage to oxidize the impurities whose 'valences are reduced by the addition of the zinc.

From the containers 4l and 42 the neutralized zinc sulfate solution is passed through a filter 5I for the purpose of removing lead and other-insoluble substances which may be introduced into the solution as an impurity in the zinc or from the anodes of the plating bath. 'I'he electrolyte is passed from the filter 5I into a container 52 where a quantity of potassium permanganate is added thereto. The addition of the potassium permanganate oxidizes the impurities'. For instance, the ferrous sulfate will be oxidized to ferric sulfate and the ferric sulfate will react with the water in the solution to hydrolyze the ferric sulfate and form ferric hydroxide which is insoluble in the solution. Other impurities, such as cobalt, arsenic, together with the potassium sulfate and manganese sulfate, will also be precipitated in this stage. The amount of potassium permanganate to be added may be determined' from the change in color of the electrolyte. When suincient potassium permanganate has been added to oxidize the impurities, the addition of a small additional amount will give the electrolyte a characteristic permanganate color. From the container 52 the solution is passed 'into a second filter 53, in which the insoluble iron and manganese compounds are ltered from the solution. 'I'he solution passes from the filter 53 into a container 54, in which zinc dust is added to the electrolyte to precipitate antimony, copper and small amounts of lead. The solution is then again passed through a lter 55 to remove these insoluble impurities and from this filter the solution is transferred to a storage ytank 56. 'I'he storage tank is connected to the container 22 by means of a pipe 51 which returns the electrolyte tothe container substantially midway between its ends and a pump 58 is provided in this pipe to continuously return the regenerated electrolyte to the container 22 at the rate at which it is withdrawn therefrom. 'Ihus by continuously replenishing the electrolyte in the container 22, the electrolyte in the container may be maintained at a substantially uniform acidity and purity so that the wire passing therethrough at a denite rate will have a denite thicknessof coating applied thereto.

` VInstead of using potassium permanganate for oxidizing the impurities in the neutralized electrolyte, other permangaiates, such as zinc permanganate, may be used or an oxidizing agent such as ozone may be passed through the electrolyte. The latter may be accomplished by passing air between electrical spark discharges to convert a portion of the oxygen in the air into ozone and then bubbling the resulting product through the electrolyte.

It will be understood that the embodiments of the invention herein disclosed are merely illustrative and that many changes andmodications may be made therein without departing from the spirit and scope of the invention.

We claim:

1. A method of electrogalvanizing wire, which comprises utilizing a sulfuric acid bath of high acidity having zinc in solution therein, moving a wire through the bath, passing an electric current of high density from the bath to the wire to form a zinc deposit thereon, withdrawing electrolyte from the bath, adding metallic zinc to the withdrawn electrolyte, filtering the withdrawn electrolyte, adding potassium permanganate thereto, filtering the withdrawn electrolyte, adding zinc dust thereto, and again ltering the electrolyte and returning the regenerated electrolyte to the bath.

2. A method of electrogalvanlzing wire, which comprises utilizing a sulfuric acid bath of high acidity having zinc in solution therein, moving a wire. through the bath, passing an electric current of high density from the bath to the wire to form a zinc deposit thereon, continuously withdrawing electrolyte from the bath, adding metallic zinc and again filtering the electrolyte and continuously returning the regenerated electrolyte to the bath.

3. A method of electrogalvanizing an article, which comprises immersing the article in a bath of high acid concentration zinc sulphate electrolyte, passing a high density electric current from the electrolyte to the article, continuously withdrawing electrolyte from the bath and collecting it in batches, neutralizing a batch of withdrawn electrolyte by the addition of metallic zinc, filtering the neutralized electrolyte to remove lead and other impurities, adding an oxidizing agent to the filtered electrolyte to precipitate iron and other impurities, filtering the electrolyte to remove the precipitated impurities, adding zinc dust to the filtered electrolyte to precipitate antimony and other impurities, again filtering the electrolyte, and continuously returning puried electrolyte to the electrogalvanizing bath. I

4; A continuous method of electrogalvanizing iron and steel wire, which comprises advancing the Wire through successive cleaning baths, one of which contains a solution of sulphuric acid, passing a direct current to the wire as an anode in said sulphuric acid containing cleaning bath to dissolve iron containing particles therefrom, .advancing the Wire through a plating solution containing between 10% and 25% of free sulphuric acid and between 5% and 10% -of zinc in the form .therein of -zinc to acid to Water substantially constant and maintaining a speed of travel of the vWire which under the conditions will cause the deposition of a uniform coating of at least one ounce of zinc per square foot of wire surface.

5. A method of electrogalvanizing iron or steel wire which comprises continuously passing the wire seriatim through a grease removing cleaning bath, a scale and rust removing bath, a sulphuric acid solution for dissolvingY iron containing particles, passing a current-to the wire as an-anode in said sulphuric acid solution, and then through a plating electrolyte containing about 8% of. zinc in the form of zinc sulphate and about 15% to'20% of free sulphuric acid, passing a current of between 500 and 2000 amperes per square foot of wire surface through said electrolyte to the wire as a cathode, maintaining the ratio of zinc to sulphuric acid substantially constant and substantially completely removing impurities which are detrimental to plating with a current of high density in an electrolyte of high acidity.

rRANmm B. Rnvcx.

RAY c. KIVLEY.

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