US3014851A - Process for plating a selective surface within a groove - Google Patents

Description

Dec. 26, 1961 c. H. BOMMERSCHEIM 3,014,851

PROCESS FOR PLATING A SELECTIVE SURFACE WITHIN A GROOVE Filed June 5, 1959 2 Sheets-Sheet 1 v INVENTOR. CAM/P15 HW/P) BO/VME/PSCHHM 1961 c. H. BOMMERSCHEIM 3,014,851

PROCESS FOR PLATING A SELECTIVE SURFACE WITHIN A GROOVE Filed June 5, 1959 2 Sheets-Sheet 2 Ilirlliii w E5. v f fi IN V EN TOR "in! lidrlr z. iillvi hmu-lruun- ATTOf/VFY United States Patent 3,614,851 PROCESS FGR PLATING A SELEGHVE SURFAGE WITHIN A GRUQVE Charles Henry Bomrnerscheini, Kalamazoo, Mich, assignor to Savage Plating & Anodizing Co., lino, Kalamazoo, Mich a corporation of Michigan Filed June 5, 1959, Ser. No. 818,287 6 Claims. (Cl. 264-) This invention relates to a process and apparatus for the metal plating of a selective surface within a groove which is normally subject to wear and/or corrosion.

Theprimary object of the invention is to provide an efiicient and practical method of plating a selective surface of a dimensionally deep and/or narrow groove in such a manner that the plating is of controlled and uniform thickness across the entire selected surface without requiring regrinding or resurfacing after plating.

It is well known that the horizontal land surfaces of cast iron diesel engine and other pistons are subject to wear and/or corrosion. Hence, these land surfaces should be plated with a corrosion and wear resistant metal, such as hard chromium, in thicknesses to meet tolerances.

Heretofore, conventional methods of plating the lands of the ring grooves of pistons have been unsuccessful. For example, when the piston is held in a vertical position and made cathodic and a parallel vertical anode is positioned one to twelve inches therefrom, metal will not deposit on the selected land surface of the ring groove with sufficiently uniform distribution as to coatihg thickness. Because the groove is dimensionally deep and/or narrow, the deposited metal will build up preferentially at the edge of the surface closest to the anode while the portion at the bottom of the groove which is at the greatest distance from the anode will receive little or no deposit.

If an attempt is madeto plate the surfaces within the grooves normally subject to wear and/or corrosion by anodes positioned within the narrow ring grooves, dif- I Patented Dec. 26,1961

FIGURE 1 is an elevational view of apparatus illustrating the present method of plating'a selected surface of the ring groove of a piston;

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is an enlarged vertical sectional view through a piston illustrating the manner of affixing the insoluble anode to the piston in positionto plate a se-. lected surface of the ring groove;

FIGURE 4 is a view similar to FIGURE 3 showing a modified form of the invention; and

FIGURE Sis a fragmentary diagrammatic View of an alternative method of applying the anode to the piston.

Specific reference is now made to the drawings wherein similar reference characters are used for corresponding elements throughout. the invention will be described with reference to a cast iron diesel engine piston, the principles thereof are applicable to anymetallic grooved member where it is necessary or desirable to plate one or more selected surfaces of the groove.

Indicated at 10 is a diesel engine piston Which, as is well known, is a cylindrical cast iron'member having a plurality of axially spaced ring grooves 12 which are relatively narrow and deep, the depth being approximately 0.25" and the average width approximately 0.253 to 0.255", the overall length of the piston approximating 9.781". When the piston is operated in the engine, the rings in the grooves subject the land surfaces 14 thereof to wear'and corrosion which, if not corrected, eventually causes cracking of the rings. Hence, itis desirable that these land surfaces of the new pistons be protected ficulties arise. Thus, if the anodes are lead foil or wire,

a short circuit will occur with arcing and injury to the surface and deposit. Moreover, lead wire of sufficient size tocarry current would inhibit the entrance of fresh electrolyte and might lead to localized overheating of the electrolyte plus. depletion. These considerations also preclude the possibility of supporting and accurately positioning a delicate anode structural shape Within a narrow ring groove around the circumference of a piston by means of an outside structure and maintaining accurate spacing between the anode and the surface to be plated.

The present invention overcomes the aforementioned difficulties' by using an insoluble anode whichis con formable to the contour of the grooved member and which is fixed to but insulated from the grooved member in such a mannerthat the anode covers the surfaces of the groove not to be plated but opposes the selected surfaces to be plated, the grooved member itself serving to-support the anode. By making the grooved member a'cathode and immersing the same in a suitable electrolyte. a uniform controlled thickness of such metals as chromium, nickel, copper, tin, zinc, silver, gold or cadmium can be deposited on the selected surfaces of the grooves.

The principles of the invention will best be understood with reference to the accompanying drawings, wherein:

against wear and corrosion by a metal plating, preferably hard. chromium. However, the deposited metal must be of controlled and uniform thickness coextensive with the land surface, generally in the order of magnitude of 1 to 2 mils and the present invention accurately and efficiently accomplishes this without the necessity of regrinding or resurfacing of the deposited metal.

A suitable vessel or tank lfi is provided in which is supported a steel rack 18, preferably U-shaped, the rack in turn supporting the piston 10 in a vertical position, the rack including vertically extending insulating mem bers 20. The steel members 22 passing through the insulation include horizontal portions which engage the lower end of the piston 19. Mounted upon a flange or other support on the upper end of the tank are insulators 24 whch in turn mount two copper buses 26, the upper ends of the vertical portions of the steel rack members 22 hooking around and contacting the copper buses, the latter being operatively connected to a current source (not shown) which is negative when plating takes place thereby rendering the piston cathodic.

The insoluble anode employed in the process is such as to be-conformable to the configuration of the piston and readily affixable but insulated from those portions'of the piston which are not to be plated so that the anode is automatically retained by the piston in a desired position adjacent to but opposite the surface or surfaces to backedinsoluble lead tape is preferred, the same being also satisfactory for nickel plating from a chloride-free nickel-sulfate bath or copper plating from a conventional acid copper-sulfate bath. A low carbon steel or alloy steel adhesive backed tape may alsob'eiused for plating copper, tin, zinc, silver, gold or cadmium from convenl Patent Re. 23,843. f

lt'should 'be understood that while ofthe type disclosed in U.S,

In practice, the land surface 14 to be plated should be given a satisfactory surface finish. In the case of new pistons, the surface finish should be 32 micro inch R.M .S. or better. In the case of worn pistons, the surface finish ,should be 16 micro inch R.M.S. or better because of the greater thickness of metal deposit which is normally required. The piston is then vapor degreased and an insulating strip 28, such as pressure sensitive tape for electroplating which is disclosed in US. Patent Re. 23,843, v

is applied around the piston to all of those surfaces which are not to be plated, the lower free edge 30 of one strip portion thereof terminating immediately above the land surface 14 to be plated.

The adhesive backed lead tape 32 is then applied to the insulating strip 23 in parallel strips with respect to the piston axis which overlap (shown exaggerated in FIGURE 3) starting approximately half way up the vertical surface 34 of the groove with the land 14 to be plated, as "at 36, then across the horizontal surface 38 ofthe groove opposite the land 14, then up the outside surface 40 of the piston where it terminates at or below the upper transverse surface 42 of the piston as at 44. lfnecessary, the overlapped strips of lead tape 32 are ultimately smoothed out. A lead wire 46 is then wrappedaround the, upper portion of the tape 32 gripping the outside of the piston firmly to make positive electrical contact. One or more lead wires 48, see FIGURES 1 and 2, are then carried a sufficient distance above the piston for operative connection to an outside current: source whereby the. tape is rendered positive, during the plating operation.

It is to be understood that the lead tape 32 may be applied to the piston in a series of vertically extending, overlapping strips whose longitudinal axes extend axially ot the piston as shown. in FIGURE instead of in a series of horizontally extending strips whose axes extend circumferentially aroundthe piston as. shown in FIGURE 3. The adhesive backing of the tape may be. conductive or insulating. If the. adhesive backing is conductive, the tape may be applied in overlapped horizontal layers and have adequate, conductivity both vertically and horizontally. If, the adhesive backing is. insulating, the tape may be applied in overlapped vertical layers and. have adequate vertical conductivity.

In the modification shown in; FIGURE 4', the lead wires 46 may be, stopped off with. an insulating masking tape 50 which terminates at the corner 52. representing the juncture of the. horizontal surface. 38 of the groove opposite the land 14. and the. vertical outer surface 40. ot the piston as a further means of confining current flow to the lead tape surface within. the, ring groove itself. This more closely controls the distribution of metal to be deposited upon, the bottom horizontal or land surface 14.

In the process of plating the land surface 14 with chromium, the. vapor degreasedpiston is supported, as

described hereinabove, in'a chromic acid plating bath 54. Before doing; so, the. land is preferably vapor blasted to produce an oxide-free surface. The piston is, first electrically connected to the positive terminal of a suitable D.C. source, such for exampleas 6 volts, the lead tape electrode 32 being connected to the, negative terminal by. means of the. lead wires 48. The land. surface 14 is then given a conventional reverse" etch at about 0.5-3 a.s.i. (72 to 432,a.s.f.)' for one-half to several minutes. The electrical connections are then quickly reversed, preferably by a reversing switch, and the land surface 14 is chromium, platedsusing the exposed surface of the lead tape 32 as the. insoluble anode.

The composition: of the, chromium bath is not critical and current densities and temperatures of conventional valuesmay be employed. The same is true when the land surface is to be plated with nickel, copper and other metals as. mentioned hereinbefore. Satisfactory chromium plating of the land surfaces of cast iron diesel engine i pistons was accomplished with a temperature of l 32" F. using a bath containing 36 oz./gal. of chromic acid with sufficient sulfuric acid to give a ratio of CrO to H 80 of 100 to l. The current density must be varied in a conventional manner depending upon the temperature and the basis metal. Values of 0.5 to 3 a.s.i. (72 to 432 a.s.f.) may be used for copper, nickel and most steels. Lands of cast iron pistons were successfully plated by first striking for 1.5 to 2 minutes at 9 a.s.i. (1296 a.s.f.) and then continued deposition at 3 a.s.i (432 a.s.i.).. Steel pistons were successfully plated at the latter value without striking.

By the present invention, lands of new diesel pistons have been plated with 0.5 to 1.0 mil chromium wherein the coating of the deposited metal was sufiiciently uniform over the entire land surface 14 to meet tolerances, thus eliminating the necessity of costly and difiicult regrinding after plating. These pistons showed no appreciable wear on the plated lands after 1,000 hours test run.

It should be understood that the invention may also-be employed to salvage worn pistons in which case the ring groove has been ground to give a true surface with a finish of 16 micro inch R;M.S. or better and chromium has been deposited up to a thickness of 6-12 mil which is not limiting; These heavier coatings may require regrinding to meet dimensional requirements, but even if they do such regrinding will be minimal since, by the present process, the thick chromium deposit issubstantially uniform across the entire face of the land surface.

While a preferred embodiment of the invention has here been shown and described, skilled artisans may-make minor variations without departing from the spirit of the invention and the scope of the appended claims; Thus, it should be understood-that while it is the landsof pistons. which are normally subject to wear and/ or corrosion and therefore require plating, the invention is applicable to. any metallic grooved member for the plating of any one or more surfaces of the groove which require a protective coating of metal.

- I' claim:

1. A process of electroplating a selective surface.

afiixing via insulating adhesion an insoluble deformable.

. metallic Inemberto the surfaces of the groove which are.

not to be plated, said member conforming to the. cone figuration ofthe grooved surfaces to which it, is'affixed, and having a portion within the groove opposing said selective surface to be plated, insulating all surfaces of said structure other than said selective surface andthose. covered by said insoluble metallic member and opera? tively connecting said member and structure to. positive. and negative poles respectively of a' current source. While subjecting said structure to a plating bath until, amating' of metal of desired thickness is deposited on said, selective surface.

2. A process of electroplating a selective. surface within a groove of a metallic structure comprised of afiixing insulating material to the member and to. those. surfaces of the groove which are not to be plated, adhesivcly af fixing to a portion of the insulating material an insolcontour of thesurfaces covered and a portion of. the

tape is disposed within the groove in opposed position to the selective surface to be plated, and connecting the tape and structure tothe positive and negative poles of a current source while subjecting the structure. to a plating bath. i

3. The process of claim 2 wherein the insulating, material is deformable and atfixed to the member ad hesion so that it. conforms to the contour of, the; surfaces covered thereby.

4. The process of claim 2 and adhesively affixing to the outer face of the tape a strip of insulating material in sucha position that the current from the tape tothe selective surface is confined within the groove.

5. A process of chromium plating the land surface of the ring groove of a piston comprised of afiixing an insulating material by adhesion to the surfaces of the piston other than the land surface, afiixing to a portion of the material by adhesion a deformable lead tape so that it conforms to the surfaces covered and a portion of the tape is disposed within the groove in opposed position to the land surface, and connecting the tape and piston to the positive and negative poles of a current source while subjecting the piston to a chromium plating bath.

6. The process of claim 5 and afiixing to the outer face of the tape by adhesion a second strip of insulation which terminates at the corner of the groove opposite the land surface whereby the current from the tape to the selective surface is confined within the groove.

References Cited in the file of this patent UNITED STATES PATENTS 1,335,176 Merritt Mar. 30, 1920 1,798,391 Wurth Mar. 31, 1931 1,809,872 Solderberg June 6, 1931 1,845,052 Laukel Feb. 16, 1932 2,710,834 Vrilalias June 14, 1955 2,859,157 Curtiss Nov. 4, 1958 FOREIGN PATENTS 579,941 Great Britain Aug. 21, 1946

Claims (1)

1. A PROCESS OF ELECTROPLATING A SELECTIVE SURFACE WITHIN A GROOVE OF A METALLIC STRUCTURE COMPRISED OF AFFIXING VIA INSULATING ADHESION AN INSOLUBLE DEFORMABLE METALLIC MEMBER TO THE SURFACES OF THE GROOVE WHICH ARE NOT TO BE PLATED, SAID MEMBER CONFORMING TO THE CONFIGURATION OF THE GROOVED SURFACES TO WHICH IT IS AFFIXED AND HAVING A PORTION WITHIN THE GROOVE OPPOSING SAID SELECTIVE SURFACE TO BE PLATED, INSULATING ALL SURFACES OF SAID STRUCTURE OTHER THAN SAID SELECTIVE SURFACE AND THOSE COVERED BY SAID INSOLUBLE METALLIC MEMBER AND OPERATIVELY CONNECTING SAID MEMBER AND STRUCTURE TO POSITIVE AND NEGATIVE POLES RESPECTIVELY OF A CURRENT SOURCE WHILE SUBJECTING SAID STRUCTURE TO A PLATING BATH UNTIL A COATING OF METAL OF DESIRED THICKNESS IS DEPOSITED ON SAID SELECTIVE SURFACE.

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