US2232019A - Apparatus for electrolytically treating metallic articles - Google Patents

Description

Feb. 18, 1941. G. J. BECKWITH 2,232,019

I APPARATUS FOR ELECTROLYTICALLY TREATING METALLIC ARTICLES Filed July 21, 1957 2 Sheets-Sheet 1 .fii... 1H v1.

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Feb. 18, 1941. G J BECKWIITH 2,232,019

APPARATUS FOR ELECTROLYTICALLY TREATING METALLIC ARTICLES Filed July 21. 1937 v 2 Sheets-Sheet. 2

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Patented Feb. 18, 1941 UNITED STATES APPARATUS FOR ELECTROLYTICALLY TREATING METALLIC ARTICLES Glenwood J. Beckwith, Brecksville, Ohio, assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey Application July 21, 1937, Serial No. 154,913

3 Claims.

This invention relates generally to the electroly-tic treatment of metallic articles, and is particularly concerned with devices, and methods of operating the same, for electrolytically coating a such articles in an improved manner.

There are two major problems encountered in coating metals by electrolytic process in accordance with current practices. The first of these relates to the uneven distribution of the coating upon the superficial areas of the work-piece. The second relates to the disfiguration of the coating during the plating operation. Each of these problems will be discussed briefly to afford better understanding of the present invention.

" It'is generally known that the amount of metal which is electrodeposited on a given surface is proportional to the amount of current flowing. It is also known that when current is passed through a single metallic conductor that flux 20 lines are set up around the conductor. These lines of force are generally known to encircle the conductor amuming the shape of the latter. In any electrolytic unitwhere direct current is em ployed it is commonly known that the current in passing from the anode to the cathode tends to seek the shortest distance and the sharpest edges.

The former tendency, however, is greatly diminished by the latter as in most cases current will be attracted to a sharp point or a series of points;

0 namely, a square edge rather than to afiat surface, even though the former may be at a greater distance than the latter, Where flat strip is being electrolytically treated and electrodes of the parallel type are being used, the greater current 35 density, therefore, tends to exist at the square edges of the metallic strip being treated. Hence, other factors being constant, metallic articles; such as, steel strips or sheets, which are electroplated in a continuous manner, inherently have 40 heavier deposits near or on their edges than at their centers.

Many ideas have been tried in seeking to overcome this uneven distribution of the coating, among which will be found the provision of ellip- 45 tic'al anodes to increase the current density adjacent the central portions of the articles to be coated. Shielding for anodes on, or adjacent, their outer portions has been suggested, including the use of rubber bands, or other non-conductive 50 baffles, to diminish the current density at the edges of the articles being coated. Any and all of the above means for correcting the uneven distribution of the coating have been found to be cumbersome and unreliable.

55 In connection with the second problem, the

troubles may be confined, generally speaking, to the contacts whereby the negative or cathodic side of the circuit is introduced to the articles to be coated. Such contacts may be divided into two groups: (1) those arranged to contact the work-piece beneath the surface of the electrolyte, hereinafter referred to as internal contacts, and (2) those arranged to contact the work exteriorly of the electrolyte, hereinafter referred to as external contacts.

In the case of internal contacts, these, being the cathodes in plating operations, are given to coating in the same manner as the work-pieces are coated. The accumulation of such coating necessitates frequently shutting down the apparatus to permit the cleansing or replacement of the cathodes.

Chain contacts, which are frequently employed internally of the electrolytic bath, due to the fact that they present such a small surface for plating current of relatively high density, quickly acquire dendritic deposits of granular metal, which ultimately tend to drop upon the articles being coated and become welded thereto and plated over, Undesirable surface imperfections on the finished articles are thus created. Furthermore, chain contacts are inclined to become stiff, due to the metal deposited on them, and thereafter tend to scratch and mar the surface of the articles, resulting in surface imperfections on the final product that are highly objectionable.

Where rolls are employed as internal contacts, excessive deposits form quickly thereon and, particularly, on that portion of the rolls that falls between the paths of the articles being coated; such, for instance, as in the case of strip, where annular deposits collect between strips. Such formations tend to bend the edges of the strips passing thereby, and to lump, and otherwise disfigure, the coaJtings acquired thereon. Chrome plated rolls take on loose deposits which unravel and weld to the articles being coated. Contact bars scratch and spall small metal globules and require replacement, or not infrequent cleaning, of the cathode itself.

In the case of external cathodes, where rolls are employed for continuous plating operations, due to the fact that a certain amount of the electrolyte is entrained on the articles moving from the electrolyte to pass to the point of con- 0 tact with the cathode roll, such cathodes are also given to plating, which, for the reasons already enumerated, is regarded as highly objectionable. Such roll contacts, particularly wherein continu-- ous lengths of metal are being coated, are inclined to slip and scratch, or otherwise disflsure, the articles in contact therewith.

In order to obviate such slipping. it has here-' tofore been proposed to employ anti-frictional bearings for such cathode rolls, but ball or roller bearings, which are usually employed for this purpose, are so ineiiiclent from the standpoint of electrical conduction, that it is customary to attention from time to time.

Where rolls are employed as internal contacts, the links are given to slight corrosion, whereby they become more resistant to the passage of current and, in some cases, become redhot and melt streaks in the coating. Furthermore, the use of chain contacts greatly limits the extent of current density that can be used, and on high current density output, the chains are of no use at all due to these overheating effects.

The present invention has for its principal object the provision of a novel method and apparatus for electrolytically coating metal wherein all of the objections and difficulties outlined above will be obviated.

More specifically, the invention has for its ob- Ject the provision of means for electrolytically coating metallic articles, whereby a relatively uniform thickness of coating can be obtained on all coated areas thereof. Another object is the provision of improved means for preserving the finish and integrity of such coatings. Still another object is the provision of improved methods for the electrolytic treatment of metallic articles, whereby the desired ends may be obtained and the objectionable features of present day practices overcome. a

Otherobjects and advantagm will become apparent hereinafter by reference to the following specification when read in conjunction with the accompanying drawings, in which:

Figure 1 is a diagrammatic plan view of an electroplating apparatus embodying the invention.

Figure 2 is a longitudinal mid-sectional view of the layout shown in Figure 1.

Figure 3 is an enlarged fragmentary mid-sectional view showing a typical arrangement of parts in the preferred embodiment of the invention shown in Figure 1.

Figure 4 is a sectional view taken along the line IV-IV in Figure 3.

Figure 5 is a fragmentary sectional elevational view illustrating certain details of the invention.

Figure 6 is an end view of the construction shown in Figure 5.

These bus bars are supported and maintained in spaced relation by wooden insulators 8. arranged in any desired manner.

Secured transversely of the vat I, and suitably mounted in anti-friction bearings I arranged in spaced relation along the peripheral flange 3 thereof, are pairs of rollers'l, each roller in each pair being constructed with ,a yieldable peripheral portion: such, for example. as a rubber covering and are pressed into engagement with each other bybearing springs I3. Mounted adconductors I2, and anodic bus bars I in spaced relation. The cathode rolls are preferably chrome-plated copper, journaled in a plain bearing member II at each of their ends. The bearing members II are preferably bronze, and of suflicient depth so as to engage the ends of the cathode rolls for a substantial distance along their length, to afford good electrical contacts ofl'ering minimum resistance to the passage of current.

Carried at one or both ends of each of the cathode rolls I 0 is a belt I4, which extends to one of the adjacent pair of rubber covered rollers 8. This belt may advantageously be made of rubber, and, when positioned as described, be under slight tension so as to insure that any rotational movement of the pair of rubber covered rollers will be transmitted to the cathode rolls to rotate the same at a peripheral speed corresponding to that of the rubber covered rollers.

Anodes I5 are disposed upon the bottom of the vat I intermediate the groups of rubber covered rollers and cathode rolls, and are connected to the positive bus bars 4 in any desired manner. It will be understood that for plating, the anodes carry the metal to be deposited. In this connection, it is customary in coating strip or sheet material to provide another series of anodes substantially parallel to, but vertically spaced from those disposed on the bottom of the vat, so as to effect simultaneous plating upon both sides of such strip or sheet material, when it is passed therebetween.

In Figures 1, 2, 3 and 4, it is represented that a plurality of strips S are being coated in accordance with the present invention and, though the phases of the invention discussed hereinbefore are equally applicable .to the continuous plating of one or more strips or sheets of any desired width, a plurality of strips has been adopted in order that other phases of the invention (to be brought out hereinafter) may also be illustrated.

After passing through the necessary degreasers, scrubbers, and washers (not shown) the strips are introduced through the first pair of rubber covered rolls 8; over the first cathode roll III, and downwardly into the electrolyte solution I6, which is maintained at a level necessary to cover all anodes and articles to be coated in the coating process.

The strips are held beneath the electrolyte by suitable small rubber covered sinker rolls ll, be-

tween which they extend in substantially flat coplanar relation, parallel to the faces of the anodes I5. They are then passed upwardly out of the electrolyte to the next pair of rubber covered rolls 8, as is shown more in detail in Figure 3, where any electrolyte entrained on the strips by the movement thereof is wiped off by the squeegee action of the rollers, which are set to squeeze the material passing therethrough. The strip thus wiped is passed on to the adjacent cathode roll, from whence it again is introduced into the electrolyte, in the manner already described. Thereafter, the cycle is repeated until the strip finally emerges through the last pair of rubber covered rolls 8, over the final cathode roll Ill, and passes on to a take-up device (not shown) which advances all strips at the same rate of speed.

In the arrangement of the parts described above, it will be seen that the rubber covered rolls bear the tension and weight of the strips passing through them, whereby the cathode rolls ID are held free of this strain, thereby permitting them to turn freely in the plain bearings I i without the aid of any anti-friction means. The rubber covered rollers 8 are rendered adaptable for supporting the moving strips by their respective anti-friction bearings 1 whereby, notwithstanding the stress and strains to which they are subjected, they may rotate freely, and forward the stock by rolling it along without any slippage on the surface thereof that causes disfigurement. In addition to this, the soft yieidable surface of these rollers precludes any damage being doneto the coating acquired by the strips.

The belts l4, transmitting the free motion of the pairs of rollers 8 to their respective cathode rolls I0, insure that the latter will havepositive rotation, and a peripheral speed corresponding to that of the stock, even though the cathode rolls are Journaled in plain bearings for the purpose of afiording the best possible electrical connection with the cathodic bus bars. The rotation of the cathode rolls in their plain bearings H maintains the surface between the moving and stationary parts clean and bright, thus assuring ample flow of the electric current. The squeegee, or wiping action, of the rubber covered rollers insures that any electrolyte entrained on the strips does not reach the cathode rolls, whereby the latter are maintained wholly free of any metallic deposits, and the attendant disadvantages thereof are accordingly obviated.

One of the greatest advantages to be derived from the relation of parts afforded by the construction of the present invention as shown herein, is that the cathode rolls III, in being adapted for the plating of a plurality of lengths of strip, or other flexible material, may be provided with a series of annular fins l8, as are shown in Figure 4, which serve to space adjacent strips from each other, but which are sufficiently thin as to bring such strips into close edge-wise proximity. This is desirable, since the field of magnetic fiux, which sets up incident to the application of the electrolyzing current, and which is represented schematically in Figure '7 by arrows F, extends completely around the entire gang of strips, when arranged in this manner, as though it were one piece; as is otherwise the case when each strip, having its own field of magnetic fiux independent of that of its neighbor, (see Figure 8) is in substantially spaced or isolated relationship.

In the latter case, with the strips spaced apart, the action of the fiux indicates that the current flows adjacent, or upon, the edges of each strip, thereby causing the greatest current density at these points, and a resultingly heavier local coating. However, when the strips are spaced closely together so as to give a fiux field surrounding the entire body as a unit, as is shown in Figure 7, it is indicative that the greatat current density occurs only at the exposed edges of the outermost strips, where it tends to coat more heavily, but otherwise leaving all portions of the intermediate strips (including the edge portions) substantially uniformly coated. It will be understood that the fins I! are adjustably movable longitudinally of the cathode rolls to accommodate any number of strips of any given width. In order that the outermost strips may receive a uniform coating as well as those disposed intermediately thereof, it is proposed that an attractor wire I! be disposed adjacent the exposed edge of each of the outermost strips (as is diagrammatically shown in Figure 1, and more clearly seen in Figure 4) The attractor wires are to divert most of the current, inherently attracted to such exposed edges, away therefrom, so as to materially diminish the current density at these points, and thus to render the resulting coating of the same magnitude as that acquired on other areas of the outermost strips, and adjacent strips. The attractor wires I! may be round, or any other shape, but preferably are flat (as shown) so as to provide corners or points to attract the current.

These wires may be run through the plating bath coextensively with, and parallel to, the strips, whereby they contact the cathode rolls and carry the cathodic current in a manner similar to the latter, and receive heavy deposits that would normally go to the exposed edges thereof. These wires may be run through the apparatus in endless fashion, or a new wire may be introduced by welding onto the receding end of one then in the system. If the wires are re-used, they may, from time to time, be immersed in a molten bath of the plating metal in order that the accretion of coating can be recovered. It will also be apparent that the outermost strips themselves may be utilized for attracting the denser current, so that the intermediate strips will be uniformly coated. It will also be apparent that bars parallel, and closely adjacent, the path of the stock through the electrolyte, may be rigidly set up and electrically connected with the cathodic circuit, whereby they will serve to attract the denser currents, and thus hold the adjacent strips free from excessive deposits. Any suitable attractor arrangement is within the contemplation of the present invention.

From the foregoing it will be seen that the invention, as herein disclosed, has overcome all of the disadvantages of conventional apparatus enumerated in the forepart of this specification, in that a non-coating cathode is provided which cannot slip or stick, and yet, which is adapted to function efiiciently with currents of any density without overheating. Also, the articles to be plated receive substantially uniform coatings, the finish and integrity of which are preserved through the process.

Obviously, many changes may be made in the present construction which, though departing from the letter of this specification, will not be without the spirit of the invention: for instance, the spacer fins l8 may be omitted where the stock to be coated is of sufilcient thickness as to afford edgewise bearing for its several lengths upon themselves, or where the stock is otherwise susceptible of being controlled so as to maintain the proximate relationship. The spacer fins are preferable, but. there are a number of ways of accomplishing this end, and any suitable means is contemplated. Also, it will be understood that means independent of the squeegee rollers may that need driving to preclude damage upon the surface of the stock, are within the contemplation of the invention.

Therefore, while these modifications, and others too numerous to specify, are not to be found specifically illustrated herein, it will be understood that they, nevertheless, fall within the purview of the present invention, as is more comprehensively set forth, and in accordancewith, the appended claims.

I claim:

1. Apparatus for electrolytically metal strip or wire, including the combination of a container for a liquid electrolyte, an electrical contactor outside of the electrolyte containing portion of said container and means for tautly guiding strip or wire into and from said container and into engagement with said contactor, said means including a roll over which said strip or wire passes and anti-friction bearings journaling the same, and said contactor comprising a metallic roller and plain bearings journaling the same, said means further including guide elements spaced on either side of said roll with at least one of said elements at a lower level than said roll and said elements forming taut spans of strip or wire extending from said elements to said roll with one of said spans across said roller and the latter being positioned respecting said roll and the one of said elements forming said span across said roller to effect deflection of strip or wire engaged by the latter sufficiently to provide electrical contact with said strip or wire but insufllciently to cause the transmission to said roller of major portions oi the strip or wire guiding stresses.

2. Apparatus for electrolytically treating metal strip or wire, including the combination of a container for a liquid electrolyte, an electrical contactor outside of the electrolyte containing portion of said container and means for tautly guiding strip or wire into and from said portion of said'container and into engagement with said contactor, said means including pinch rolls between which the strip or wire passes and antifriction bearings journaling said pinch rolls, and said contactor comprising a metallic roller and plain bearings journaling the same, said means treating further including a guide element forming a taut span oi strip or wire extending from said pinch rolls to said element across said roller and the latter being positioned respecting said pinch rolls and said element to eflect deflection of strip or wire forming said span sumciently to provide electrical contact with said strip or wire but insufliciently to cause the transmission to said roller of major portions of the strip or wire guiding stresses, said pinch rolls being positioned between said container and said contactor to engage strip or wire leaving said container and having rubber covered surfaces for engaging the strip or wire, the rubber covered surfaces of said pinch rolls acting to remove liquid electrolyte from said strip or wire prior to its engaging said contactor.

3. Apparatus for electrolytically treating metal strip or wire,- including the combination of a container for a liquid electrolyte, an electrical contactor outside of the electrolyte containing portion of said container and means for tautly guiding strip or wire into and from said portion of said container and into engagement with said contactor, said means including pinch rolls between which the strip or wire passes and antifriction bearings journaling said pinch rolls, and said contactor comprising a metallic roller and plain bearings journaling the same, said means v further including a guide element forming a taut .span of strip or wire extending from said pinch rolls to said element across said roller and the latter being positioned respecting said pinch rolls and said element to effect deflection of strip or wire forming said span sumciently to provide electrical contact with said strip or wire but insuificiently to cause the transmission to said roller of major portions of the strip or wire guiding stresses, said pinch rolls being positioned between said container and said contactor to engage strip or wire leaving said container and having rubber covered surfaces for engaging the strip or wire, said combination including means for rotatively interconnecting said pinch rolls and roller so that the latter rotates with the former at synchronized peripheral speeds, the rubber covered surfaces of said pinch rolls acting to remove liquid electrolyte from said strip or wire prior to its engaging said contactor.

GLENWOOD J-. BECKWITH.

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