US3109783A - Electrolytic plating - Google Patents

Description

Nov. 5, 1963 w. J. MANSON ELECTROLYTIC PLATING 3 Sheets-Sheet 1 Filed Nov. 20, 1958 INVENTOR. 1 41 767? 4744 10 W. J. MANSON ELECTROLYTIC PLATING Nov. 5, 1963 3 Sheets-Sheet 3 Filed Nov. 20, 1958 United States Patent aware Filed Nov. 20, 1958, Ser. No. 775,210 7 Claims. ((31. 204-28) This invention relates to an improved process and ap paratus for electroplating wire and similar strip material continuously and more particularly it relates to an improved process and apparatus for supplying electrolytic current to the wire.

In any process where wire or strip is continuously electroplated the necessary electroplating current must be supplied thereto either through sliding or rolling electrodes. Where sliding or frictional contacts or electrodes are employed the amount of current supplied depends on the degree or quality of frictional contact between the wire and the electrode and it is rarely possible to obtain uniformity of the electrolytic current in the wire. When the wire, in the form of a helix, is fed in and out of an electroplating bath a plurality of times (as in the apparatus of US. Patent No. 2,680,710) the filrn of bath liquid carried by the wire sometimes serves to separate the contact from the Wire thereby producing a miniature electrolytic cell between the wire and the contact electrode. Such miniature cells produce undesirable effects such as a rough deposit on the electrode, a small depression in the wire or an undesirable growth on the wire. The effect is especially undesirable where the electrode contact is caused to bounce due to small imperfections in the wire or due to some instability of the wire helix such as a swinging motion; in such cases the surface tension of the bath liquid prevents the latter from completely breaking away from the elements and instead the contact and wire are connected by a narrow tube of electrolyte. The roughness of the deposit caused by this effect is cumulative so that it has been found impossible to continuously plate very great thicknesses of metal onto the basis wire in a single plating operation with such electrodes.

Roller contacts are ordinarily mechanically more complicated than sliding contacts since some sliding contact is still required to feed the current to the roller contact and since it is difiicult to make the axis of rotation of a roller sufficiently adjustable to assure permanentcontact with a moving wire.

This application is a continuation-in-part of US. application Serial No. 700,801, filed December 5, 1957, now Patent, No. 3,073,773, issued January 15, 1963. In that application a process and apparatus for feeding electroplating current to a wire helix supported on one or more hori- Zontal supporting rollers by feeding the electric current to each of a series of coils of the wire (helix through the supporting roller, is disclosed. The current is fed to the supporting roller or rollers through a plurality of especially constructed and enlarged shoes positioned on said supporting roller which shoes, due to their larger diameter than the remainder of the supporting roller, are maintained substantially dry. Specially constructed carbon brushes are clamped to slide in close contact with the shoes and the brushes are connected to a bus bar or similar source of electroplating current.

Among the objects of this invention is to, provide an improved process and apparatus for feeding electroplating current to the coils of the helix by feeding the electric current through the supporting rollers.

One phase of this invention is based on the discovery that a better electrical current feed and a greater and more uniform amount of electroplating current can be fed to the supporting rollers and thence to the coils'of the helix through wet brush-roller contacts.

3,109,783 Patented Nov. 5, 1963 Among other objects of the invention is to provide a new improved bath structure, improved anode structures, an improved means and method of agitating the electrolyte of the plating bath and means for decreasing drag-out.

The objects of the invention are attained by supporting a plurality of successive coils of a continuously formed, rotating and progressing helix on at least one horizontal supporting roller; providing a series of baths beneath the supported helix into which the coils of the latter dip and pass in and out as the helix rotates and wherein. at least one of said baths is an electroplating bath containing anode structures; providing the portion of one of the supporting rollers which is over the electroplating bath or baths with a current conducting surface layer (if the roller itself is not a good electrical conductor); feeding electroplating current to the conducting portion of the supporting roller at a plurality of points so that the current passes from the conducting surface layer to the individual coils supported on said layer, and spraying all parts of the roller where sparking may occur or where a salt deposit may form with an aqueous solution adapted to Wet the roller and/ or remove salt deposits therefrom.

It has been found possible to feed greater amounts of electroplating current to the wire by the process and apparatus of the present invention. One method of obtaining the benefits of this increase is to move the wire through the baths at a faster rate provided better agitation of the electrolyte is obtained. An improved agitation means is therefore provided. Faster movement of the wire through the baths increases the drag-out and a counter current washing method for decreasing drag-out has been provided. ince the plating is rapid and cleanliness is essential improved anode containers have been provided to prevent the contamination of the electrolyte by small, remaining particles of almost completely dissolved soluble anodes. An improved flexible overflow bath structure making it easier to align essential parts of a long series of tanks has also been provided.

Preferably two or more internal, horizontally parallel, supporting rollers are employed because the stability of the helix is thereby increased. When two such rollers are employed only one need be provided with the current conducting means over the plating bath as sufilcient current can be conducted to the coils through one such roller. The roller which is not required to carry electrical current may be constructed of stainless steel or similar strong and corrosion resistant material. Where the supporting roller is a relatively poor conductor of electricity it may be wrapped with copper strip or a copper alloy of relatively good conductivity. Brass is an exceptionally good wrapping material in thatjt is not easily corroded by the solutions involved, is readily applied, and provides suflicient conductivity. With a machine which runs continuously it may be necessary to rewrap the supporting rollers with the conductivity tape about every 2-4 weeks. The rewrapping time required for the rollers of the present invention, i.e., without brush-contacting shoes is considerably less than required for the rollers of said application i 1 remaining portions of the rollers.

Elecrtocleaning baths may be employed prior to the electroplating and electrocleaning current may be fed to the helix through the supporting roller in the same way as for the electroplating baths.

Wherever the supporting roller carries an electric current or wherever it is likely to accumulate salt deposits,

etc., the roller is kept wet and clean by an applied aqueous solution. Above the electroplating bath the supporting roller is sprayed with electroplating solution to remove precipitates, etc., from the solution deposited thereon by the wire coils. Over the electrocleaning bath the roller is sprayed'with water to prevent arcing and to remove any deposits which may precipitate on this portion of the roller. Above or below the region where the current supplying brushes make contact with the rollers a small amount of water is provided to wet the contacting area between the brushes and the roller thereby preventing arcing and increasing the uniformity of the contact.

In the drawing:

FIG. 1 is a side vview partly in cross section of the apparatus which includes the improvements of the present invention.

FIG. 2 is a top plan view of the plating portion of the apparatus of FIG. 1.

FIG. 3 is a cross sectional view through the plating section of the apparatus.

FIG. 4 is a detail cross sectional view of the supporting rollers and spray means in the cleaning section.

FIG. 5 is a detail cross sectional view of a supporting roller and brush in the electroplating section.

FIG. 6 is a detail view similar to FIG. 5 but taken from the side.

FIG. 7 is a detail view showing how the wire contacts the supporting rollers.

In the specification and claims the term wire is used in the generic sense for all continuous material having relatively minor cross sectional dimensions with respect to its length. The term is understood to include ordinary wire of round, fiat, triangular or polygonal cross sectional shape as well as. strip materials. All of such materials can be plated by the process and apparatus of the present invention.

The wire which is to be plated may be formed into a helix in any desired manner but a very satisfactory apparatus for forming the helix is similar to that of US). Patent No. 2,680,710; The wire 10 is drawn axially 0E of a coil '(not shown) by a capstan device. Between the capstan device and the coil, the wire is drawn through a imperfections in the end wall structure of the baths, a flexible washing bath 25 has been provided. This bath may be made of chemical resistant material such as the polymeric resins, for example, resins made by polymerizing tetratluorethylene, chloroprene, or dichlordifluorethylcne or the bath may be made of any one of the natural or synthetic elastomers or rubbers since it is simply a washing bath adapted to contain water or a dilute aqueous solution. The bath section 25 is made with a concave wall 25-1 so that it can expand or contract at any portion without being pulled apart.

Wetting Supporting Rollers Over Pretreatment Baths The particular electrode contact structures for feeding current to the wire which are described below provide exceptionally uniform and high current to the wire being plated so that very thick platings may be applied to the wire. In the manufacture of conductivity wire with a steel core it is common to plate 20% or more of copper onto the steel basis wire. This wire is drawn down to size and Wound on what is known in the industry as 600 lb. reels. Occasionally where such reels were being produced the wire would break during drawing before a 600 lb. reel had been filled. Since there is no demand for fractional portions of such reels, the breakage caused a loss even though the wire appeared to be perfect on both sides of the break.

Close observation of the wire during the treating and plating process disclosed that occasionally arcing occurred die (not shown) which has an opening somewhat smaller than the cross section of the wire so as to draw the wire and thereby remove scale, kinks and also the twist in the wire. Thence, the wire 10 passes to pushing and forwarding roller pairs, which push the wire through a horizontal set and a vertical set of straightener roll 13 and then over the curving device (see FIGS. 1 and 2).

From the curving device the wire passes upwardly in helical form to the pair of longitudinal horizontal supporting rollers 20 and 21. These supporting rollers are themselves supported in half bearings positioned at spaced points along the frame of the apparatus and the supporting rollers 20 and 21. These supporting rollers are rotated at the same peripheral speed through an adjustable speed change device. Prior to being plated the suspended portion of the wire helix 10 dips into a series of pretreatment baths 22,. 23, 24, 25, 26, 27. The number and composition of such baths will depend on the wire being treated and on the nature of the plating or final treating solution. In a typical bath sequence, bath 22 is an anode cleaning bath, 23 a water rinse, bath 24 contains detergent for cleaning, bath 25 is another water rinse, bath 26 contains dilute sulfuric acid, bath 27 is another water rinse. The baths which follow are for electroplating.

Since the series of baths must be closely spaced and are preferably united to each other, difficulty is often encountered in aligning the baths of a long series. It is necessary to align the electroplating baths with the supporting rollers 20, 21 so that the anode baskets 72 inside the helical coil are substantially concentric therewith. To facilitate the aligning of the series of attached baths, which can be made diflicult by slight warping or by small between the wire to one of supporting rollers in the onplating sections. The arcing apparently produces melting which is followed by rapid cooling and it is the rapid cooling of the molten or high temperature spots which produces the martensiter It was found that this arcing could be prevented by keeping the rollers wet. However, if the rollers were wetted with the treating solutions the solutions would soon carry over and contaminate into the aqueous rinsing whereas if water were fed to the rollers the treating solutions would be diluted. The areing is actually prevented by spraying the rollers 20 and 21 with water from tubes 30 or 31 (see FIG. 4) and catch Supporting Rollers Over Plating Sections With respect to the supporting rollers over the plating baths a somewhat different problem results from the feed of the electrolytic current therethrough. As shown in FIG. 7 the wire 10 only makes a point or short-line contact with rollers 20,21 and as the combined result of this type of contact and the surface tension of the bath liquid, the regions '37 and 38 and 92 contain the bath liquid or plating solution between two metal electrodes with a difference in electrical potential. Deposition therefore takes place on the rollers 20 and 21. This eiiect is particularly pronounced with copper plating baths. In order to nullify this elfect, the rollers 20 and 21 are sprayed with plating solution by means of pipe spray devices 39, 40 which extend the length of the plating section and which may be held between the electrode structures 60 as illustrated in FIG. 3. These pipes comp-rise openings which extend toward rollers 20' and 21 but do not include any openings which spray onto the area of the brush contacts. The plating solution dissolves the plated metal from the roller and returns it to the bath.

porting rollers 20, 21 which may contain a conducting metal tape 120 thereon by a plurality of brush contact electrodes shown in detail in FIG. 5. At least one bus bar 44 extends lengthwise over that portion of the apparatus which includes baths that are to be electrolyzed. Extending down from the frame 36 is a support bar 45 along which are attached pairs of arms 46, 47 which may be of metal having some springiness. These arms 46, 47 diverge at the lower portions 48, 49 so as to straddle the roller 20 (or 21) at its horizontal diameter. Attached to the ends 48, 49 are carbon brushes 50, 51. The tension between the ends 48, 49 of arms 46, 47 can be adjusted by the wing nut 53 on bolt 52, the nut 53 compressing spring 54. The arms 46, 47 may be attached directly to a bus bar and may then be of sufficient size and of conducting material so as to transmit the power from bus bar to brushes 50, 51 but the separate support 45 with conductor cable connections 55, 56 between the bus bar 44 and the brushes 48, 49, as shown in FIG. 5, are more satisfactory.

In the electroplating section shown in FIG. 2 provision is made for electroplating approximately 80 turns of the helix simultaneously and 12 such brush contact electrodes 60 are provided, 6 on each supporting roller 20 or 21. Relatively large amounts of current may be fed through said brush contacts 50, 51; for example, it is common to feed 200 amps. at the voltage required through each of said brushes 50 or 51.

The area of slippage, between the brushes 50, 51 and the conducting portions of the rollers 20 or 21 or the tape '120 on such rollers is maintained wet but free from bath precipitates by dropping water from the pipe 1 onto the roller at the area where it contacts the brushes 50. Whereas all other parts of the roller 20 or 21 are continuously sprayed with the bath solution, from perforated tube 39, this spray is not directed against the areas of the brush contacts but instead pure water is fed to the rollers at these areas.

The reason for the superiority of the wet contacts is that the chemical gases and vapors around which both oxidize or otherwise alter the dry contact surface of the rollers of said application No. 700,801 after a time so that eventually a highly resistant contact surface is built up thereon whereas the wet contact surfaces do not develop this electrically resistant surface layer. It is believed that the film of water over the portion of the contact surface of said rollers (or the conducting tape thereon) shields the surface from deteriorating vapors and gases and possibly helps remove any electrically resistant film that may develop in spite of the water film. In any event the surface of a brass conducting wrapping which contacts the brushes is always somewhat brighter than the remaining portion thereof when water is continuously applied between the contacting surfaces and as stated above it continues to conduct large uniform amounts of plating current throughout the life of the wrapping.

Agitation System In order to obtain the full effect of the ,high current density (5000-7000 amps. per cell) it is necessary to provide for rapid movement of the fresh plating solution into contact with the cathodic wire being plated. The wire itself by its movement into and out of the bath assures a certain amount of circulation of the electrolyte but tor the high current densities possible, the rotation of the wire helix by itself is not sufiicient. An agitation is therefore added. As shown in FIG. 3 air line 73 passes lengthwise of the plating cell, and from this line arcua-te branches 74, 75 extend on either side thereof. The branches 74, 75 contain minute orifices about ,5 in diameter, for example, and air is forced through these orifices toward the helix 10-1.

The line 73 is fed by an air line 77 from a source controlled by valve 78 (shown only diagrammatically). Since the orifices of branches 74 are small eventually a number of them become partially clogged with precipitates from the electrolyte. Therefore, a steam line 79 controlled by a valve 80 is connected to line 77 so that salt precipitates can be removed therefrom.

Losses due to drag-out at high speeds of the helix 10-1 are prevented by the provision of an extra tank at the end of the plating cell (or at the end of each plating cell where there is more than one). One turn of the helix 10-1 passes through this cell and as this turn is coming up from the cell to leave the bath structure it is sprayed with a thin stream of pure water from pipe 86 which runs counter current to the movement of the coil and back into the cell 85. The solution from cell 85 can be used as the aqueous component for making new solution or the valuable salts may be recovered therefrom.

Anode backet overflow weirs or troughs 76 shown in FIG. 3 are provided to obtain faster replenishment of the anolyte. These overflow troughs 76 are below the level of the catholyte and cause the anolyte to flow out into the next compartment which may be between or at the end of plating cells. The liquid fromthe overflow compartment is filtered and returned to the catholyte. Thus, the anolyte which is rich in copper and low in free cyanide is continuously replaced.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.

I claim:

1. In a process of continuously electroplating wire by continuously forming said wire into the shape of a rotating helix with a horizontal axis so that the rotation of the helix moves the same in a horizontal direction and supporting said helix on at least two rotating parallel, horizontal, metal rollers of substantially equal and uniform diameters, while dipping the lower portions of a multiplicity of adjacent coils of said helix into an electrolytic bath containing a plurality of electrodes spaced from said coils, the steps comprising electrolyzing said bath to electrodcposit metal from said bath onto the wire by feeding an electric current to at least one of said metal supporting rollers through sliding contacts at a plurality of spaced points separated a distance sufficient to provide for the support of at least several coils of said helix therebetween.

providing the surface portion of said metal supporting roller through which current is fed with a layer of metal having an electrical conductivity at least as high as copper alloys,

whereby the surface of said metal supporting roller transmits the electrolyzing current to said coils held in non-swaying position on said roller by said second supporting roller,

said electrolyzing current of said wire coils connecting electrically to the electrodes of said bath through the electrolytic liquid of said bath,

continuously supplying water to that portion of the roller contacting said sliding contacts,

continuously spraying said supporting roller between the sliding contacts with the electrolyte solution of the electrolytic bath.

2. In an apparatus for continuously electroplating wire, of the type wherein the wire is continuously formed into the shape of a horizontal helix, fed over two parallel hori zontal supporting rollers of substantially equal and uniform diameters positioned above at least one bath including an electroplating vessel containing electrode structures connected to one side of a source of electroplating current, the improved apparatus for supplying the wire with current from the opposite side of said source of electroplating current comprising,

a layer of metal having a conductivity at least equal to that of copper alloys on that surface of at least one of said supporting rollers which overhangs the electroplating vessel,

a plurality of brush means connected to said opposite side of said source of electroplating current,

said brush means being in sliding contact with said roller and being spaced along said roller at distances sufficient to provide for the support of a plurality of the coils of said helix therebetween,

each of said brush means having a relatively large surface area facing said rollers and being curved to make surfiace contact therewith,

means for pressing said brush means into surface contact with said roller,

means for continuously supplying Water to the regions of said roller which contacts said brushes,

and means to maintain the surface of the remainder of said roller over the electroplating bath wet with aqueous liquid from the electroplating bath.

3. In an apparatus for continuously electroplating wire, of the type wherein the wire is continuously formed into the shapewofa horizontal helix, fed over two parallel horizontal supporting rollers of substantially equal and uniform diameters positioned above a series of at least three baths including a first relatively long vessel adapted to accommodate a plurality of individual coils of the supported helix and containing electrode structures therein connected to one side of a source of electroplating current, and a second relatively long vessel adapted to accommodate a plurality of individual coils of said supported helix, the improvement comprising a relatively short third vessel connecting the first vessel to the second vessel,

said third vessel being formed of elastomeric material.

4. The apparatus as claimed in claim 3 comprising a relatively short fourth vessel connected to the end of the electroplating vessel,

means above said fourth vessel to spray water onto at least one helical coil as it passes upwardly out of said fourth vessel to wash electroplating chemicals back into said fourth vessel.

5. The apparatus as claimed in claim 2 wherein said layer of conducting material is brass.

6. The apparatus as claimed in claim 2 wherein the means for maintaining the remainder of said roller over the electroplating vessel wet with aqueous liquid from said electroplating bath comprises spray means.

7. The apparatus as claimed in claim 2 comprising a plurality of liquid holding vessels positioned below said horizontal helix including said electroplating vessel, at least one of said vessels in the intermediate portion thereof being formed of elastomeric material.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES I The Electrochemical Society, Special Volume, Modern Electroplat-ing, 1942, p. 17.

Claims (1)

1. IN A PROCESS OF CONTINUOUSLY ELECTROPLATING WIRE BY CONTINUOUSLY FORMING SAID WIRE INTO THE SHAPE OF A ROTATING HELIX WITH A HORIZONTAL AXIS SO THAT THE ROTATION OF THE HELIX MOVES THE SAME IN A HORIZONTAL DIRECTION AND SUPPORTING SAID HELIX ON AT LEAST TWO ROTATING PARALLEL, HORIZONTAL, METAL ROLLERS OF SUBSTANTIALLY EQUAL AND UNIFORM DIAMETERS, WHILE DIPPING THE LOWER PORTIONS OF A MULTIPLICITY OF ADJACENT COILS OF SAID HELIX INTO AN ELECTROLYTIC BATH CONTAINING A PLURALITY OF ELECTRODES SPACED FROM SAID COILS, THE STEPS COMPRISING ELECTROLYZING SAID BATH TO ELECTRODEPOSIT METAL FROM SAID BATH ONTO THE WIRE BY FEEDING AN ELECTRIC CURRENT TO AT LEAST ONE OF SAID METAL SUPPORTING ROLLERS THROUGH SLIDING CONTACTS AT A PLURALITY OF SPACED POINTS SEPARATED A DISTANCE SUFFICIENT TO PROVIDE FOR THE SUPPORT OF AT LEAST SEVERAL COILS OF SAID HELIX THEREBETWEEN. PROVIDING THE SURFACE PORTION OF SAID METAL SUPPORTING ROLLER THROUGH WHICH CURRENT IS FED WITH A LAYER OF METAL HAVING AN ELECTRICAL CONDUCTIVITY AT LEAST AS HIGH AS COPPER ALLOYS, WHEREBY THE SURFACE OF SAID METAL SUPPORTING ROLLER TRANSMITS THE ELECTROLYZING CURRENT TO SAID COILS HELD IN NON-SWAYING POSITION ON SAID ROLLER BY SAID SECOND SUPPORTING ROLLER, SAID ELECTROLYZING CURRENT OF SAID WIRE COILS CONNECTING ELECTRICALLY TO THE ELECTRODES OF SAID BATH THROUGH THE ELECTROLYTIC LIQUID OF SAID BATH, CONTINUOUSLY SUPPLYING WATER TO THAT PORTION OF THE ROLLER CONTACTING SAID SLIDING CONTACTS, CONTINUOUSLY SPRAYING SAID SUPPORTING ROLLER BETWEEN THE SLIDING CONTACTS WITH THE ELECTROLYTE SOLUTION OF THE ELECTROLYTIC BATH.

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