US3103483A

US3103483A - Electroplating apparatus

Info

Publication number: US3103483A
Authority: US
Publication date: 1963-09-10
Anticipated expiration: 1980-09-10

Description

Sept. 10, 1963 F. E. BLUM ETAL ELECTROPLATING APPARATUS 3 Sheets-Sheet 1 Filed April 17, 1959 MILL I INVENTOR 1 7616 fill/777 BY ffiedfl/wz/ HTTOH/YZ Y F. E. BLUM ETAL ELECTROPLATING APPARATUS Sept. 10, 1963 Filed April 1'7, 1959 3 Sheets-Sheet 2 (a y 6 T! 0 v W W W W A M% A, 6%

United States Patent 3,103,483 ELECTRGPLATING APPARATUS Fred E. Blurn' and Fred 0. Hough, Indianapolis, Ind., assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Apr. 17, 1959, Ser. No. 8ii7,155 4 Claims. ((11. 294242) This invention relates to an apparatus for coating metal articles and more particularly to a method and apparatus which is especially satisfactory for electrodepositing a uniform silver layer on steel bearing shells.

Reinforced bearings formed of a steel bearing shell with an electrodeposited coating of silver thereon have been used in internal combustion aircraft engines for quite some time. Although the reinforced or steel backed silver bearing has properties which are superior to bearings made of other materials, it suffers from the inherent fault of being relatively costly compared to bearings made of other bearing materials. Thus it is mandatory that the commercial manufacturer produce a silver bearing at a sufficiently low price to be able to find a market for silver bearings. Moreover, the respective producers of silver bearings have made the field such a competitive business that it is essential to the commercial manufacturer that he produce quality silver bearings as cheaply as possible.

Since a major proportion of the relatively high cost of reinforced silver bearings is due to the use of expensive silver, the cost of a silver bearing can be materially reduced by using smaller amounts of silver. Silver bearings having complex surface contours, such as flanges and the like, are extremely difiicult to electroplate uniformly. Some areas of the complex surface have higher current densities than others. Consequently, the higher current density areas tend to build up thicker silver deposits than the other areas. However, a minimum satisfactory silver thickness must be applied. :Thus, an unnecessarily heavy thickness of silver results in the high current density areas in order that the thickness at the lower current density areas be built up to the minimum acceptable amount.

Frequently the metal being deposited from an electrov plating solution is simultaneously replaced therein by means of anodic dissolution. 'An anode of a composition generally similar to that of the metal being electrodeposited is used in the electroplating process. 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 effected. 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.

In addition, the complex contour of the flanged silver bearing requires that the inner (concave) surface and the outer (convex) surface be individually electroplated. It is generally preferred to apply the inner silver layer to the bearing shell prior to applying the outer silver surface. Accordingly, a suitable masking means must be employed when electroplating the outer surface. In commercial production it is essential that the method of masking be inexpensive and adaptable to rapid rates of production. Moreover, it is extremely desirable that the ends of the bearing shells be masked since these areas need not be electroplated. Leaving the ends unplated, of course, contributes to reducing the overall cost of the bearing.

It is therefore a primary object of this invention to provide an apparatus which is highly satisfactory for electrodepositing silver coatings on the outer surface of steel bearing shells. Briefly our invention comprehends immersing a workpiece, such as a cylindrical flanged bear- Patented Sept. 10, 1963 ice ing shell, in a suitable electroplating solution in which the coating metal .is replenished by anodic dissolution. The workpiece is suspended on a work support which will mask the inner surface ofsthe bearing shell and provide high concentrations of coating metal at low current density areas on the bearing shell. A substantially non-porous baffle plate is immersed in the electroplating solution between the workpiece and a primary soluble anode. The baffle plate is oriented in sucha manner as to inhibit direct flow of dissolved anode metal to the workpiece 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 along the line 11 of FIGURE 2 showing an electroplating apparatus comprehended by the present invention;

FIGURE 2 is a similar view along the line 2-2 of FIGURE 1;

'FIGURE 3 is an enlarged sectional view along the line 33 of FIGURE 1; and

FIGURE 4 is a sectional view along FIGURE 3. g

Referring now to the drawings, FIGURES 1 and 2 show electroplating apparatus such as comprehended by our invention, including a conventional rectangular plating tank 10 which contains a suitable electroplating solution 12. Horizontal bus bars 14 and 16 supported by suitably insulated brackets 18 extend along the opposite sides 20 and 22 on the upper edges of the tank. Interjacent these bus bars a third bus bar 24 extends across the open center of the plating tank. This latter bus bar 24 is supported on rollers 26 tofacilitate axial reciprocation of the bus bar. Suitable means (not shown) are provided adjacent the tank 10 to axially reciprocate the the line 4 4 of central bus bar 24 so as to move a work support 28 suspended from the bus bar 24 during electrodeposition. The bus bars 14, 16 and 24 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 16 and a negative potential is induced in the central bus bar 24. The bus bars can be made of any suitable conductive material, such as copper or the like.

Anode carriers 30 and 32 are suspended in the plating tank 10 and secured, such as by bolts or the like, to the positively charged bus bars 14 and 16 extending along the upper edges of the tank. The lower ends 34 of each of the anode carriers 30 and 32 are curved to conform to the outer diameter of a cylindrical silver anode 36 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 30 and 32 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 centralor negative bus bar24 is a work support or bearing carrier 28 which is generally of a U-shaped construction. The carrier has a horizontal base member 38 on which a plurality of cylindrical, flanged bearing shells 40 are linearly, radially aligned.

Secured to the base member 38 are vertical members 42 and 44 which are mutually connected at their upper ends by means of a horizontal rod or tie bolt 46. The vertical members 42 and 44 have apertures therein to facilitate movement of the electroplating solution through the work support and around the bearing shells thereon. Suitable metal hooks 48 attached to this rod are used to suspend the work support in the electroplating solution from the central bus bar 24.

The base member 38 and upright or vertical members 42 and 44 of the bearing carrier or work support 28 are made of any suitable non-conductive material such as wood, glass, plastic, etc., provided that such material is not deleteriously affected 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. 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.

The tie ibolt 46 between the vertical members 40 and 42 at the upper end thereof is used to stabilize the bearing carrier. The metal books 48 used in suspending the bearing carrier from the negative bus bar 24 are secured to this rod. The hooks 48, made of a suitably conductive material, such as copper, can be fastened to the rod in any suitable manner, preferably by welding, brazing or the like.

A baflle plate 50 formed of a suitable non-porous mate- "rial is positioned between the work support 28 and each anode 36 in such a manner that direct flow of silver from the anode 36 to the bearing shells is inhibited. The dimensions of the baffle plate 50 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 battle plate should be large enough to relatively isolate the anode 36 from the cathode or bearing shells 10 in the tank. Highly satisfactory results have been obtained using a baflle plate which rests on the bottom of the plating tank and has its upper edge 52 slightly below the surface of the solution. The upper edge 52 of the bafile plate 50, however, is preferably above the level of the bearings which are suspended in the plating solution. The lateral dimensions of the baflle plate 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 baflle plate 50 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 bafile plate made of heavy plate glass, for example.

As shown more clearly in connection with FIGURES 3 and 4, a plurality of individual bearing shell mounts 54 are provided on the base member 3 8. Each of the bearing shell mounts includes a cylindrical rubber core 56 which has its axis vertically disposed. The lower end of the rubber core has a lateral flange 58 thereon of a contour corresponding to that of the bearing shell 40 which is fitted over the core 56. An upwardly extending circumferential projection 60 on the periphery of the flange 58 seals or masks the end surface 62 of the bearing shell 40 from the electroplating solution 12.

The lower surface 64 of the core 56 has a central recess 66 therein. A central passage 68 extends axially "from the recess 66 to the upper surface 70 of the core 56. v A rod 72 of a metal, such as copper, extends upwardly through the passage 68 to a circular metal disk 74 on the upper surface 70 of the core.

The circular disk 74 is circumferentially relieved on its lower periphery at 76 to facilitate seating the disk ing shell.

on the upper end surface 76 0f the bearing shell 40. A cover plate 78 is used over the relieved disk to absorb any twisting movement caused by the internally threaded member or knob 80. The knob 80 is in threaded engage ment with the upper end 82 of the rod 72 and compresses the disk 74 and rubber core '56 against the bearing shell 40 to effectively seal :or mask the inner surface 84 and end surfaces 62 and 76 of the bearing shell from the electroplating solution -12.

The dimensions of the rubber core 56 are such as to provide an extremely close fit within the bearing shell 40. The diameter of the core generally should be only slightly smaller than the inner diameter 84 of the bear- The core is preferably only sufiiciently smaller in diameter than the inner diameter 84 of the bearing shell as will permit fairly easy positioning within the bearing shell. In order to facilitate fitting the bearing shell over the core '56, the core is preferably made in two parts 86 and 88. However, a unitary core structure may be preferred in some instances.

The length of the core from its flange area '58 to its upper surface 70 is preferably somewhat greater than the overall length of the bearing shell. Such length will permit a portion of the core to project above the upper end surface 76 of the bearing shell. Since the rubber core 56 projects above the bearing shell somewhat, turning the knob '80 forces the relieved disk 74 against the core, compressing it. Under compression the core spreads laterally against the inner surface 84 of the bearing shell to effectively seal the inner surface of the shell from the electroplating solution. Simultaneously the disk 74 is brought into engagement with the upper end surface 76 of the shell to seal the end surface from the electroplating solution.

The lower end of the rod 72 extends downwardly through the core 56 to a longitudinal recess 90 in the underside of the base member 38. A copper wire 92 lying in the recess or groove 90 passes through a transverse aperture 94 in the lower end of the rod 72. A cover plate 96 lies over the recess 90 sealing it from contact with the plating solution.

The wire 92 extends from the recess 90 to the tie bolt 46 where it is suitably secured, as by the nut 98. The wire has a suitable insulation 100 thereon in its length between the base member 3 8 and the tie bolt 46 to inhibit interaction with the electroplating solution. The tie bolt 46 and attached hooks 48, being suspended on the negatively charged bus bar 24, provide means for supplying a negative potential to the wire 92. The rods 72 within .the cores 56 are in electrical communication with the disks 74 and the disks in turn are in electrical contact with the upper end surfaces 76 of the bearing shells. Thus, electrons flow through the bus bar, hooks, tie bolt, wire, rod and disk to the bearing shell.

The base member also supports a plurality of supplemental insoluble anodes 102 which are positioned between the bearing mounts 54. Suitable support members '104 on the non-conductive base 38 hold solid, steel, cylindrical rods upright interjacent the bearing shells. A tightly fitting rubber tubing .106 insulates part of the rod from the electroplating solution. The lower part of the rod 108 is exposed adjacent the flange area 110 of the bearing shell. A loop 112 of copper wire 114 is fitted over the upper end of the rod which is exposed at 116 above the surface of the electroplating solution. The copper wire 114 extends to the anode bus bar 14 to which it is suitably connected, as by bolts, soldering or the like. Electrical current passing through the supplemental anodes =102 increases the current density on the bearing shell 40 at the flange area 110 to promote electrodeposition at the radius of the flange.

With the bearing shells positioned in the apparatus as hereinbefore described, silver is electrodeposited onto the bearing shells substantially as disclosed in United States Patent No. 2,440,672 which is in the name of Harry I.

t1 3 Green and which is also assigned to the vassignee of the inst-ant invention.

The anode 36 used in the electroplating solution 12 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 affects electrodeposition of silver on the bearing shell 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 suflicient duration to deposit the desired thickness of silver. After a suflicient duration of electrodeposition the parts are removed from the plating solution, Washed and dried.

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 electrodeposi-tion of the silver alloy containing 0.3% to 0.7% lead, by weight, and the balance being silver, an anode of similar composition 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 etals is 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. An electroplating apparatus for silver plating a flanged tubular bearing shell, said apparatus comprising an electroplating tank, a source of negative potential, a source of positive potential, a soluble anode immersed in said tank in communication with said source of positive potential, a support in said tank for said bearing shell, elastomeric means on said support coacting with nonelastomeric means on said support to mask the inner surface and ends of the bearing shell and induce a negative potentialthereon, means on said support for varying the current density on selected areas of the bearing shell, conductive means providing electrical communication between said non-elastomeric means and said source of negative potential and a generally impermeable baffle plate in said tank between said anode and said work support as so to inhibit substantially any direct flow of dissolved coating metal from said anode to said bearing shell.

2. An electroplating apparatus for depositing silver coatings on the outer diameter of flanged tubular steel bearing shells comprising an electroplating tank, .a source of negative potential, a source of position potential, a soluble silver anode in said tank in electrical communication with said source of positive potential, a support in said tank for said bearing shells, elastomeric means on said support for masking the inner surface of a hollow steel bearing shell, an auxiliary anode on said support for varying the current density on selected areas of said workpiece, contact means on said support for biasing the shell against said elastomeric means, said contact means in electrical communication with said source of negative potential for inducing a negative potential on the bearing shell, and a generally impermeable baflie plate in said tank between said anode and said support so as to inhibit substantially any direct flow of dissolved silver from said anode to said bearing shell.

3. An electroplating apparatus for depositing silver coatings on the outer diameter of flanged tubular steel bearing shells comprising an electroplating tank, a source of negative potential, a source of positive potential, a soluble silver anode in said tank in electrical communication with said source of positive potential, at substantially non-conductive work support in said tank, elastomeric and non-elastomeric means on said support coacting to mask the inner and end surfaces of at least one of said bearing shells and induce .a negative potential thereon, an auxiliary anode on said support for increasing the current density on said flange on said bearing shell, conductive means providing electrical communication for said non-elastomeric means with said source of negative potential, and a generally impermeable baffle plate in said tank between said anode and said work support so as to inhibit direct flow of dissolved silver from said anode to said bearing shell. I

4. An electroplating apparatus for depositing silver coatings on the outer diameter of flanged tubularsteel bearing shells comprising an electroplating tank, a source I of negative potential, a source of positive potential, a soluble silver anode in said tank in electrical communication with said source of positive potential, a substantially non-conductive work support in said tank, said work support having a generally horizontal base portion for supporting a plurality of said bearing shells :with their axes vertically disposed, a plurality of generally cylindrical rubber cores having a flange at one end on said base, the axes of said cores vertically disposed on said base, a metal masking member on the end of said core opposite said rubber flange, means for compressing a bearing shell between said rubber flange and said metal member to concurrently mask the interior of the shell and apply a negative potential thereto, a supplemental anode interjacent said core members near said flange on said bearing shells, and a generally impermeable baflie plate in said tank between said anode and said work support so as to inhibit substantially any direct flow of dissolved silver from said anode-to the said bearing shell.

References Cited in the file of this patent UNITED STATES PATENTS 773,617 Wurth Nov. 1, 1904 950,777 Winslow Mar. 1, 1910 2,072,170 Herzog Mar. 2, 1937 2,181,256 Arbogast Nov. 28, 1939 2,316,917 Wallace et .al. Apr. 20, 1943 2,613,178 Grant Oct. 7, 1952 2,749,295 Svanstrom et a1. June 5, 1956 2,871,178 Dilling Jan. 27, 1959 2,960,455 Frankenthal Nov. 15, 1960 3,023,154 Hough et al. Feb. 27, 1962

Claims

1. AN ELECTROPLATING APPARATUS FOR SILVER PLATING A FLANGED TUBULAR BEARING SHELL, SAID APPARATUS COMPRISING AN ELECTROPLATING TANK, A SOURCE OF NEGATIVE POTENTIAL, A SOURCE OF POSITIVE POTENTIAL, A SOLUBLE ANODE IMMERSED IN SAID TANK IN COMMUNICATION WITH SAID SOURCE OF POSITIVE POTENTIAL, A SUPPORT IN SAID TANK FOR SAID BEARING SHELL, ELASTOMERIC MEANS ON SAID SUPPORT COACTING WITH NONELASTOMERIC MEANS ON SAID SUPPORT TO MASK THE INNER SURFACE AND ENDS OF THE BEARING SHELL AND INDUCE A NEGATIVE POTENTIAL THEREON, MEANS ON SAID SUPPORT FOR VARYING THE CURRENT DENSITY OF SELECTED AREAS OF THE BEARING SHELL, CONDUCTIVE MEANS PROVIDING ELECTRICAL COMMUNICATION BETWEEN SAID NON-ELASTOMERIC MEANS AND SAID SOURCE OF NEGATIVE POTENTIAL AND A GENERALLY IMPERMEABL BAFFLE PLATE IN SAID TANK BETWEEN SAID ANODE AND SAID WORK SUPPORT AS SO TO INHIBIT SUBSTANTIALLY ANY DIRECT FLOW OF DISSOLVED COATING METAL FROM SAID ANODE TO SAID BEARING SHELL.