US3023154A

US3023154A - Apparatus for electroplating

Info

Publication number: US3023154A
Application number: US736586A
Authority: US
Inventors: Fred O Hough; Donald R Scott
Original assignee: General Motors Corp
Current assignee: Motors Liquidation Co
Priority date: 1958-05-20
Filing date: 1958-05-20
Publication date: 1962-02-27
Anticipated expiration: 1979-02-27

Description

Feb. 27, 1962 F. o. HOUGH ETAL APPARATUS FOR ELECTROPLATING Filed May 20, 1958 LmALA 3 INVENTORS N i 6% Jada/w 42 N BY davflaflfl up I I g I '0 3 Sheets-Sheet 1 HTTOIQNEV 1962 F. o. HOUGH ETAL 3,023,154

APPARATUS FOR ELECTROPLATING 3 Sheets-Sheet 2 Filed May 20, 1958 (fa c592 'Feb- 1962 F. o. HOUGH ETAL 3,023,154

APPARATUS FOR ELECTROPLATING 3 Sheets-Sheet 3 Filed May 20, 1958 AHA! lhmllii.

i E N TORS 0520A I I ATTOPNEY deposited is used in the electroplating process.

United States r atent 3,023,154 APPARATUS FOR ELECTROPLATIN G Fred 0. Hough and Donald R. Scott, Indianapolis, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed May 20, B58, Ser. No. 736,586 4 Ciaims. (Cl. 204-242) This invention relates to a method and apparatus for coating metal articles and more particularly to a method and apparatus which is especially satisfactory for electrodepositing uniform silver layers on steel bearing shells.

requently the metal being deposited from an electroplating solution is simultaneously replaced therein by means of anodic dissolution. An anode of a composition generally similar to that of the metal being electro- Since the anode metal dissolves at generally the same rate at which dissolved metal is deposited, a continuous generally self-regulating replenishment of the electroplating solution is efiected. However, in electroplating systems of this type, wherein anodic dissolution is used to replenish the plating solution, it is quite difficult to attain coatings of uniform thickness, particularly on contoured surfaces.

Although it is commonly preferable to replenish silver in silver plating solutions by anodic dissolution, silver plating systems of this type tend to form coatings of a non-uniform thickness, especially when forming heavier steel backed bearings, it is essential to deposit a silver bearing layer having a uniform thickness. Heretofore, it has been diflicult to obtain uniform silver coatings on all areas of the backs of steel bearing shells. It is therefore a primary object of this invention to provide a method and apparatus which is especially satisfactory for producing highly uniform silver bearing layers on steel bearing shells.

Briefly, our invention comprehends a method and apparatus in which Work pieces, such as steel bearing shells, are immersed in a suitable electroplating solution in which the coating metal is replenished by anodic dissolution. The work pieces are suspended therein on a work support which will inhibit excessive treeing at points of high current density on the work piece. A substantially nonporous bafiie plate is placed in the electroplating tank between the work pieces and the anode. The bafiie plate is oriented in such a manner as to inhibit direct flow of dissolved anode metal to the work piece during electrolysis.

Other objects, features and advantages of this invention will appear more clearly from the following description of a preferred embodiment thereof and from the drawings, in which:

FIGURE 1 is a sectional view with parts broken away along the line 1 -1 of FIGURE 2 showing an electroplating apparatus comprehended by the present invention; FIGURE 2, is a similar view along the line 22 of FIGURE 1;

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FIGURE 3 is an enlarged elevational top view of a bearing shell support such as shown in FIGURE 1;

FIGURE 4 is a sectional view with parts in elevation along the line 44 of FIGURE 3; and

FIGURE 5 is a sectional view along the line 5-5 of FIGURE 4.

Referring now to the drawings, FIGURES 1 and 2 show electroplating apparatus such as comprehended by our invention, including a conventional rectangular plating tank which contains a suitable electroplating solution 12. Horizontal bus bars 14 and 15 supported-by suitably insulated brackets 16 extend along the opposite sides 18 and 20 on the upper edges of the tank. Interjacent these bus bars a third bus bar 22 extends across the open center of the plating tank. This latter bus bar 22 is supported on rollers 24 to facilitate axial movement thereof. Suitable means (not shown) are provided adjacent the tank 10 to axially move the central bus bar 22 providing agitation of the bearing shells 26 during electrodeposition. The bus bars 14, 15 and 22 are connected to a source of direct electrical current (not shown) in such a manner that a positive potential is induced in the outer bus bars 14 and 15 and a negative potential is induced in the central bus bar 22. The bus bars can be made of any suitable conductive material, such as copper or the like.

Anode carriers 28 and 30 are suspended in the plating tank 10 and bolted to the positively charged bus bars 14 and 15 extending along the upper edges of the tank. The lower end 32 of each of the anode carriers 28 and 30 are curved toconform to' the outer diameter of a cylindrical silver anode 34 which is horizontally supported thereon. It has been found that especially uniform coatings are obtained when using a cylindrical anode which is horizontally disposed on the carrier adjacent the bottom of the plating tank. The anode carriers 28 and 30 can be formed of any suitable conductive metal which is relatively inert to electrolysis of the plating solution, for example steel.

The specific structure of the anode carrier can be varied considerably as well as the type of the metal stock 'used to form it. We have found that a welded framework of the structure shown in FIGURES 1 and 2 made of a small diameter rod stock is generally satisfactory. In general it is preferred to mask those portions of the anode carrier in the solution which are not in contact with the anode. The masking can be accomplished in any suitable manner, such as by the known and accepted methods of masking plating racks.

Suspended from the central or negative bus bar 22 is a work support or hearing carrier 36 which is generally of a U-shaped construction. The carrier has a horizontal base member 38 on which a plurality of semicylindrical, semi-annular bearing shells 26 are axially aligned to form a row. Secured to the base member 38 are vertical members 40 and 42 which'are mutually connected at their upper ends by means of a horizontal rod 44. Suitable metal hooks 46 attached to this rod are used to suspend the work support in the electroplating solution from the central bus bar 22.

A plurality of spring-type electrical contactsdS are provided on the base 38 of the bearing carrier 36. Each of these contacts is connected to a copper bar 56 which lies in a longitudinally extending recess or groove 52 in the underside of the base member 38. A cover plate (not shown) can also lie in the recess 52 over the copper bar 56 substantially masking it from contact with the plating solution 12. The copper bar 50 is in turn connected by means of an insulated wire 54 extending therefrom up to a projection 56 on one of the hooks 46 suspended from the negative bus bar 22. An electrical spring clip 58 on the opposite end of the wire 54 is attached to the projection 56 on the hook 46. In this manner the negative potential of the bus bar is thereby transmitted to each of the spring-type electrical contacts on the base of the work support and correspondingly to each of the bearing shells in engagement therewith.

A baffle plate 60 formed of a suitable non-porous material is positioned between the work support 36 and the anode 34 in such a manner that direct flow of silver from the anode 34 to the bearing shells is inhibited. The dimensions of the bafiie plate 60' can be varied to some extent depending on the size of the plating tank and preferably should be substantially larger than the greatest dimension of the anode. Preferably the bafile plate should be large enough to relatively isolate the anode from the cathode in the tank. Highly satisfactory results have been obtained using a bafile plate which rests on the bottom of the plating tank and has its upper edge slightly in the solution above the level of the bearings which are suspended in the plating solution. The lateral dimensions of the baffle preferably are such that it transversely extends almost completely across the tank, its ends being spaced a proportionately small distance from the adjacent walls of the tank.

The baffle plate 60 can be formed of any substantially non-porous material which the anode metal cannot pass through. Materials such as glass, plastic, wood, etc.', can be used. Uniform silver coatings on steel bearing shells can be obtained when using a baffile plate made of heavy plate glass, for example.

The work support or bearing carrier 36', such as shown in FIGURES 1 and 2, is more clearly shown in FIGURES 3, 4 and 5. The work support, as previously described, is generally of a U-shaped structure having a base member 38' with vertical members 40' and 42' at each end. Apertures 62 in the vertical members 40' and 42' are provided to facilitate movement of the solution through the work support and over the bearing shells which are to be plated.

The base member 38' and upright or vertical members 40' and 42' of the bearing carrier or work support 36' are made of any suitable non-conductive material, such as wood, glass, plastic, etc., provided that such material is not deleteriously elfected by the electroplating solution. A bearing carrier has been used in which the base member and upright members were composed of a phenol formaldehyde impregnated cloth lamina which was compressed under heat. Similar materials are commercially available under the name Micarta. The base member can be secured to the upright members in any suitable manner. When using the above-described lamina, for example, these members may be secured satisfactorily 'by means of threaded members 64, such as shown in the drawing.

A longitudinally extending metal rod 44 between the vertical members 40' and 42"at the upper end thereof is used to stabilize the bearing carrier. The metal hooks 46' used in suspending the bearing carrier from the negative bus bar 22 are secured to this rod. The hooks 46', made of a suitably conductive material, such as copper,

can be fastened to the rod in any suitable manner, prefposition on the base member 38' by means of suitable transverse contoured members 66. These members preferably are of a resilient material, such as rubber, but can be formed of the same material as the base member. They can be secured in any convenient manner, such as by threaded members 68. The axial ends of the bearing shells frictionally en age the transverse members and are thereby retained in proper position on the base member and in good electrical communication with the spring contacts 48' thereon.

A wire thief 70 on the base member surrounds the row of bearing shells following the general contour thereof. A semi-annular metal plate or thief plate 72 is vertically positioned at each end of the row of hearings to addi tionally serve in inhibiting excessive electrodeposition on the exposed ends of the outer bearing shells. The thief wire 70, the thief plate 72 and the spring contacts 48 are mutually connected to the copper bar 50 under the base member by means of threaded members 74. The copper bar is suitably connected, such as by silver soldering, to one end of an insulated wire 54. The opposite end of the wire is secured to an electrical spring clip 58' which, as shown in FIGURES l and 2, is attached to a projection 56 on one of the hooks 46, of the bearing carrier.

A description of the method of our invention will serve to illustrate the operation of the hereinbefore described apparatus. When silver plating ferrous metal parts, such as hearing shells for example, the ferrous metal parts or hearing shells are cleaned in a conventional manner as by degreasing in a suitable solvent, such as trichloro ethylene, acetone or the like. The parts can also be preferably cleaned of oxides and other surface impurities in the known and accepted manner for such cleaning, as by alkaline or acidic cleaning. Satisfactory results are obtainable when anodica-lly cleaning in a dilute aqueous solution of sodium hydroxide, 10% sodium hydroxide by weight, under a full current from a six volt source for about one minute. Subsequently, the cleaned part is rinsed thoroughly with water to remove the last traces of the cleaning solution and cathodically etched in a solution containing 4.0 grams per liter of nickel chloride (NiCl .6H O) in an 18 Baume to 20 Ban-me hydro chloric acid.

Using carbon anodes the bearing shell is cathodically etched under full current from a six volt source for about one minute. After the cathodic etch, the part is thoroughly rinsed with water to remove the last traces of the above solution and immersed as a cathode in a nickel strike solution for about one minute under a current density of about 15 amperes per square foot to 30 amperes per square foot of cathodic surface area. One such nickel strike solution which can be used is as follows:

Nickel (metal) 70-85 grams per liter. Nickel Fluoborate (Ni(BF 280340 grams per liter. Boric Acid (H BO 25-35 grams per liter. pH 3.0-4.0.

Temperature 7Sl 10 F.

Anodes Nickel.

The bearing shell is then rinsed thoroughly again and immersed as a cathode in a silver strike solution for about one minute under a current desity of about 20 amperes per square foot to 25 amperes per square foot of cathode surface area. The following is an example of a silver strike solution which can be used:

Silver Cyanide (A CN) -165 grams per liter. Potassium Cyanide (free) 2-4 grams per liter. Anodes Stainless steel.

Directly from the silver strike solution the bearing shells are introduced into a suitable silver plating solution. They are placed on the hercinbefore-described bearing carrier 36 in an axially aligned row and the insulated wire 54 from the bottom of the carrier attached to the projection 56 on the carrier supporting hook 46. The

bearing carrier is then suspended from the negative bus bar 22 with the bearing shells 26 immersed in the electroplating solution. Direct electric current is then passed through the solution in such a manner as to induce a negative potential on the steel bearing shells.

The electrodeposition of the silver plate can be effected substantially as disclosed in United States Patent No. 2,440,672 in the name of Harry J. Green which is also assigned to the assignee of the instant invention. During passage of the current through the electroplating solution excessive electrodeposition on the bearing shells at areas of high current density is inhibited by using suitable thieves. The thief members hereinbefore described have been particularly successful in eliminating treeing in the high current density areas of bearing shells. Direct electric current is passed through the conductive members on the bearing carrier into the bearing shells and the thief members to effect a uniform electrodeposition on the bearing shells.

The anode 34 used in the electroplating solution preferably has a generally similar composition to that of the metal being plated and when plating silver, for example, a substantially silver electrode is preferred. Accordingly, during electrolysis of the silver plating solution referred to above, the direct electric current simultaneously effects electrodeposition of silver on the bearing shells and an anodic dissolution of silver from the anode. The direct electric current is passed through the solution to provide a cathode current density of about 20 amperes per square foot to 60 amperes per square foot for a sufiicient duration to deposit the desired thickness of silver.

After a sufficient duration of electrodeposition the parts are removed from the plating solution, washed and dried.

Especially uniform deposits of silver plating on the bearing shells by means of the present invention are obtained by inhibiting the direct fiow of anodically dissolved silver to the cathode or bearing shells. A baifie arrangement 60, such as hereinbefore described, can be used to inhibit this direct flow or migration and thus more uniformly diffuse silver throughout the electroplating solution. Thus, the above-mentioned method of plating on bearing shells is accomplished more successfully by inhibiting a non-uniform concentration build up in areas adjacent the cathode during electrodeposition by means of a baflling arrangement. The baffle 60 serves to functionally isolate the anode from the cathode area, extending the distance of the cathode from the anode and insuring more uniform diffusion of the dissolved silver from the anode throughout the electroplating solution.

Although our invention has been especially described in connection with silver plating, our invention contemplates the electrodeposition of other metals or alloys. By the term silver as used herein, we intend to encompass silver base alloys as well and by the term metal as used herein, we mean it to include mixtures of metals or alloys. The specific composition of the anode which is to be used, of course, is dependent upon the specific electroplating solution used and the composition of the metal being deposited. For example, in the electro-deposition of the silver alloy containing 0.3% to 0.7% lead by weight and the balance being silver, an anode of similar compsition can be used. Our invention, for example, is also useful when one is employing anodic dissolution to replenish the electroplating solution with only its major metal constituent. In such instance the balance of the metals are added directly to the particular solution, usually in the salt form.

It is to be understood that although our invention has been described in connection with certain specific embodiments thereof no limitation is intended thereby except as defined in the appended claims.

We claim:

1. A plating apparatus for the electrodeposition of a smooth, uniform, adherent silver plate on semicylindrical, semiannular steel bearing shells comprising a tank, a substantially nonconductive work support in said tank, said work support having a generally flat horizontal base portion for supporting at least one bearing shell on its longitudinal edges, a spring-type electrical contact means on said base of said work' support for contacting the inner diameter of the bearing shell, a thief ring on said base of said Work support for encircling the bearing shell to inhibit excessive undesirable electrodeposition on the longitudinal edges thereof, a pair of generally parallel semiannular conductive metal bearing shell end plates on said base between which said contact means is disposed, said electrical contacts, said thief ring and said semiannular metal plates in electrical communication with a source of negative potential to induce uniform current distribution on said bearing shell, and an anode in said tank in electrical communication with said source of positive potential.

2. A plating apparatus for the electrodeposition of a smooth, uniform, adherent silver plate on semicylindrical, semiannular steel bearing shells comprising a tank, a substantially nonconductive work support in said tank, said work support having a generally flat horizontal base portion for supporting at least one bearing shell on its longitudinal edges, a spring-type electrical contact means on said base of said work support for contacting the inner diameter of the bearing shell, a thief ring on said base of said work support for encircling the bearing shell to inhibit excessive undesirable electrodeposition on the longitudinal edges thereof, a pair of generally parallel semiannular conductive metal bearing shell end plates on said base between which said contact means is disposed, said electrical contacts, said thief ring and said semiannular metal plates in electrical communication with a source of negative potential to induce uniform current distribution on said bearing shell, an anode in said tank in electrical communication with said source of positive potential and a substantially imperforate nonconductive baffle interposed between said work support and said anode in the tank to inhibit any direct flow of silver from said anode to said work support.

3. A plating apparatus for the electrodeposition of a smooth, uniform, adherent silver plate on semicylindrical, semiannular steel bearing shells comprising a tank, a substantially nonconductive Work support in said tank, said work support having a generally flat horizontal base portion for supporting a plurality of said bearing shells in axial alignment on their longitudinal edges, a plurality of aligned spring-type electrical contact means on said base of said work support for contacting the inner diameter of each of said aligned, bearing shells, a thief ring on said base of said work support for encircling the bearing shells so as to inhibit undesirable electrodeposition on the edges thereof, a pair of generally parallel semiannular conductive metal bearing shell end plates on said base between which said contact means is disposed, said electrical contacts, said thief ring and said semiannular metal plates in electrical communication with a source of negative po tential, and an anode in said tank in electrical communication with a source of positive potential.

4. A plating apparatus for the electrodeposition of a smooth, uniform, adherent silver plate on semicylindrical, semiannular steel bearing shells comprising a tank, a substantially nonconductive work support in said tank, said work support having a generally flat horizontal base portion for supporting a plurality of said bearing shells in axial alignment on their longitudinal edges, a plurality of aligned spring-type electrical contact means on said base of said work support for contacting the inner diameter of each of said aligned bearing shells, a thief ring on said base of said work support for encircling the bearing shells so as to inhibit undesirable electrodeposition on the edges thereof, a pair of generally parallel semiannular conductive metal bearing shell end plates on said base between which said contact means is disposed, said electrical contacts, said thief ring and said semiannular metal plates in 7 electrical communication with a source of negative potential, an anode in said tank in electrical communication with a ource of poitive potential and :a substantially im perforate nonconductive bafile interposed between said work support and said anode to inhibit any direct flow of 5 silver from said anode to said work support.

References Cited in the file of this patent UNITED STATES PATENTS 680,408 Cdwper-Coles Aug. 13, 1901 10 8 Merritt Oct. 22, 1918 Wolf -9 Dec. 16, 1924 Hewitt Feb. 24, 1931 McBride Mar. 3, 1931 Cowper-Gales May 23, 1933 Martz Dec. 2, 1947 Kiefer Oct. 24, 1950 Zapponi Nov. 25, 1952 Boguski Aug. 28, 1956 Grigger Nov. 4, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 O23,154 February 27 1962 Fred 0. Hough et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 66 and 67 should appear as shown below instead of as in the patent:

Potassium Cyanide (free) 150-165 grams per liter. Silver Cyanide (A CN) 2-4 grams per liter.

Signed and sealed this 19th day of June 1962..

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer

Claims

1. A PLATING APPARATUS FOR THE ELECTRODEPOSITION OF A SMOOTH, UNIFORM, ADHERENT SILVER PLATE ON SEMICYLINDRICAL, SEMIANNULAR STEEL BEARING SHELLS COMPRISING A TANK, A SUBSTANTIALLY NONCONDUCTIVE WORK SUPPORT IN SAID TANK, SAID WORK SUPPORT HAVING A GENERALLY FLAT HORIZONTAL BASE PORTION FOR SUPPORTING AT LEAST ONE BEARING SHELL ON ITS LONGITUDINAL EDGES, A SPRING-TYPE ELECTRICAL CONTACT MEANS ON SAID BASE OF SAID WORK SUPPORT FOR CONTACTING THE INNER DIAMETER OF THE BEARING SHELL, A THIEF RING ON SAID BASE OF SAID WORK SUPPORT FOR ENCIRCLING THE BEARING SHELL TO INHIBIT EXCESSIVE UNDESIRABLE ELECTRODEPOSITION ON THE LONGITUDINAL EDGES THEREOF, A PAIR OF GENERALLY PARALLEL SEMIANNULAR CONDUCTIVE METAL BEARING SHELL END PLATES ON SAID BASE BETWEEN WHICH SAID CONTACT MEANS IS DISPOSED, SAID ELECTRICAL CONTACTS, SAID THIEF RING AND SAID SEMIANNULAR METAL PLATES IN ELECTRICAL COMMUNICATION WITH A SOURCE OF NEGATIVE POTENTIAL TO INDUCE UNIFORM CURRENT DISTRIBUTION ON SAID BEARING SHELL, AND AN ANODE IN SAID TANK IN ELECTRICAL COMMUNICATION WITH SAID SOURCE OF POSITIVE POTENTIAL.