US3929592A

US3929592A - Plating apparatus and method for rotary engine housings

Info

Publication number: US3929592A
Application number: US490688A
Authority: US
Inventors: Otto J Klingenmaier
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1974-07-22
Filing date: 1974-07-22
Publication date: 1975-12-30
Anticipated expiration: 1992-12-30

Abstract

An apparatus and method are disclosed for simultaneously highly uniformly electroplating the working surfaces of a plurality of rotary engine housings. Rotary engine housings are vertically stacked in a box around an insoluble hollow perforated conforming anode. The box is substantially closed except for congruent top and bottom openings that are concentric with and slightly larger than the conforming anode. During plating, the box is completely submerged in an electroplating solution. The box openings allow electroplating solution to enter the box and pass into the anode interior through the anode perforations. Electroplating solution is withdrawn from the anode interior and recirculated back to the tank.

Description

United States Patent 1 1 Klingenmaier Dec. 30, 1975 [75] Inventor: )tto J. Klingenmaier, Warren,

Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 22, 1974 [21] Appl. No.: 490,688

[52] US. Cl. 204/26; 204/237; 204/272; 204/297 W [51] Int. Cl. C25D 7/04; C25D 17/06 [58] Field of Search. 204/272, 26, DIG. 7, 237-239, 204/240, 232, 212, 241, 259, 260, 275, 297 W [56] References Cited UNITED STATES PATENTS 2,487,399 11/1949 Thurber 204/288 3,514,389 5/1970 Stephan et al. 204/237 3,640,799 2/1972 Stephan et a1. 3,840,440 10/1974 Durin 204/25 Primary ExaminerT. M. Tufariello Attorney, Agent, or Firm-Robert J. Wallace [57] 1 ABSTRACT An apparatus and method are disclosed for simulta neously highly uniformly electroplating the working surfaces of a plurality of rotary engine housings. Rotary engine housings are vertically stacked in a box around an insoluble hollow perforated conforming anode. The box is substantially closed except for congruent top and bottom openings that are concentric with and slightly larger than the conforming anode. During plating, the box is completely submerged in an electroplating solution. The box openings allow electroplating solution to enter the box and pass into the anode interiorthrough the anode perforations. Electroplating solution is withdrawn from the anode interior and recirculated back to the tank.

4 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for simultaneously electroplating extremely uniform wearresistant coatings onto the radial working surfaces inside a plurality of i'otary engine housings.

More specifically, this invention involves electrodepositing extremely uniform wear-resistant coatings onto the epitrochoidal working surface inside a rotary engine housing. This surface forms a radial wall of an epitrochoidal chamber within which a generally triangular rotor eccentrically rotates.

It is normal and accepted practice to electroplate a chromium layer onto the epitrochoidal working surface of the rotary engine housing, to reduce working surface wear. Typically, the chromium layer is about 0.003 0.006 inch thick. Accordingly, the housing chamber is normally machined oversize to accommodate this thickness. A chromium layer thicker than needed is then plated onto the working surface, and machined back to the desired thickness. An excess chromium thickness of about 0.005 0.006 inch is generally deposited in the process. In machining the chromium layer to the desired thickness, the final epitrochoidal dimensions are obtained. The chromium plated working surface is ground smooth and relatively flat between axial faces on the rotary engine housing, with sharp comers at those faces. After grinding, the chromium deposit may be anodically etched to provide a more oil retentive working surface.

The chromium can be electrodeposited onto the epitrochoidal working surface by stacking two or more bushings around a conforming anode. One technique for doing so is described in U.S. Pat. No. 3,514,389 Stephan et al.

Excess chromium is deposited and then machined back to the desired thickness because the chromium plating process inherently tends to produce a nonuniform deposit. A significant proportion, about 60 80 percent, of the cathode current in the process is spent generating hydrogen gas. Increased current density, to accelerate the plating rate, increases gas evolution. The gas which is evolved produces a higher electrical resistance nearer the top of an electroplating bath than the bottom. This results in faster deposition of chromium nearer the bottom of the tank than the top, and corresponding thickness variations in electrodeposits. It is not unusual to obtain, as the result of gas evolution alone, at least 5 percent reduction in thickness for every 3 inches in cathode height in the tank. Such conditions make it exceedingly difficult to chromium plate even one rotary engine working surface when the plate thickness is about 0.002 0.006 inch without a plus or minus 20 percent variation from the average mean thickness. It is most practical to plate a plurality of housings simultaneously, and to stack them vertically. The greater the number of housings in the stack, the larger is the variation in chromium thickness from top to bottom of the stack. Greater solution agitation in the tank can help reduce thickness variation and minimum chromium thickness needed for the stack. However, even with such aids the usual method of preparing rotary engine housings is still to plate an excess thickness of chromium, and then grind it back to size.

I have found a way to simultaneously chromium plate a plurality of vertically stacked rotary engine housings very uniformly. Significantly lesser chromium layer thicknesses can now be used. This conserves both chromium and energy. In many instances no excess chromium need be deposited at all. The chromium layer can be deposited with such uniformity that it is plated exactly to finish thickness. Moreover, in these latter instances, the edges of the working surface are sharp enough so that no machining of the chromium coating is required at all.

OBJECTS AND SUMMARY OF THE INVENTION It is; therefore, an object of this invention to provide a method and apparatus for electrodepositing a wearresistant coating of more uniform thickness onto the epitrochoidal working surface of a rotary engine housanother object of this invention is to provide a method and apparatus for electrodepositing a chromium layer onto the epitrochoidal working surface of rotary engine housings that substantially reduces, if not eliminates, finish machining of the chromium layer.

A further object of this invention is to conserve chromium and energy in the chromium plating of epitrochoidal working surfaces of rotary engine housings.

The objects of this invention are obtained with a method and apparatus in which a plurality of rotary engine housings are vertically stacked directly on each other around a conforming anode within a substantially closed nonconductive container. The container is completely submerged in an electroplating solution in an electroplating tank. The epitrochoidal working surfaces of the housings are in vertical alignment, and metal plates placed at the top and bottom of the stack. The metal plates have openings therein congruent with the aligned epitrochoidal working surfaces of the housings. Top and bottom walls of the container are adjacent the metal plates. These walls have epitrochoidal openings therein smaller than and concentric with the epitrochoidal working surfaces of the aligned housing stack. The conforming anode is insoluble and uniformly perforated opposite the housings. Electroplating solution in the tank enters the closed container through the openings in the container top and bottom walls, passes between the anode and the housings, and into the anode interior through the anode perforations. Means are provided to continuously withdraw electroplating solution from the anode interior and recirculate it back into the electroplating tank.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention will become more apparent from the following description of preferred embodiments thereof and from the drawing, in which:

FIG. 1 is a sectional view along the line 1-1 of FIG. 2, and

FIG. 2 is a top plan view with parts broken away showing an apparatus contemplated by this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to the drawing which shows an electroplating tank 10 filled with a chromium electroplating solution at a temperature of about 60 C. The plating tank is of the usual type, as is the chromium electroplating solution. One solution that can be used is a water solution containing 230 grams per liter Cr O ric acid of about 88 92:1 is preferred over the usual 100:1 ratio to obtain faster deposition rates.

An assembly is suspended within the tank for supporting the workpieces to be plated. The assembly includes two generally U-shaped frame members 12 and a cross member 14, secured to a lower horizontal portion 12 of the frame members 12. A first, or lower, flat plastic plate 16, about 14 inches square, rests on lower horizontal portions 12 of frame members 12. Plastic plate 16v is about '12 inch thick and has a generally central epitrochoidal opening 18 therein.

Four rotary engine housings 20 are stacked in vertical register with the upper axial surfaces of each housing abutting the lower axial surface of the housing above it. The epitrochoidal working surfaces are thus vertically aligned to form a closed vertical passageway 22 of epitrochoidal transverse section. Any passageways (not shown) through the housings that intersect the epitrochoidal working surfaces are preferably plugged in the usual manner for plating. The rotary engine housings can be of cast aluminum, cast iron or the like. The epitrochoidal working surface of each housing 20 forms the radial wall of an epitrochoidal chamber having a major radial dimension of about 9% inches, which dictates a minor radial dimension of about 7 inches. It is contemplated that this invention canbe used with rotary engine housings of any size, but especially for those with epitrochoidal chamber major radial dimensions of about 9 to 11% inches.

The stack of housings is sandwiched between and in direct contact with an upper metal plate 24 and a lower metal plate 26, which are preferably both of steel and about '/4 inch thick. Both plates 24 and 26 have epitrochoidal openings 28 and 30 in them congruent with passageway 22. The aligned housing stack and associated metal plates 24 and 26 are placed on the-square flat plastic plate 16, concentric with the epitrochoidal opening 18 therein. A second, upper, flat and square plastic plate 32 rests on top of the upper conductive plate 24. Upper plastic plate 32 is of the same thickness as lower plastic plate 16 but is only 12 inches square. It has a generally central epitrochoidal opening 34 therein identical to opening 18 in lower plastic plate 16. The upper plastic plate 32 is positioned so that its opening 34 is congruent with opening 18, and therefore also concentric with passageway 22. Epitrochoidal openings 18 and 34 have a major dimension of about 7.5 inches and a minor dimension of about 5 inches. Plastic dowel pins 36 and 36 can be used to maintain alignment and concentricity of the various parts. An open ended, plastic tubular member 38, having a square cross section surrounds the stack of conductive plates and housings. The lower end of tubular member 38 rests on the upper surface 40 of the lower plastic plate 16. The axis of tubular member 38 is perpendicular to the major surfaces of the

plastic plates

16 and 32. Plate 16 substantially closes the lower end of tubular member 38 and plate 32 substantially closes the upper end. Conversely, the lower end of tubular member 38 encloses a portion of surface 40 and plate 16. Tubular member 38 has walls about 1% inch thick and fractionally more than 12 inches wide on their inner surface, to closely receive upper plastic plate 32. Plastic lower and

upper plates

16 and 32 thus cooperate with the foursided tubular member 38 to form a substantially closed box-like container surrounding the stackof rotary engine housings. The

plastic plates

16 and 32 and tubular element 36 can be of different thicknesses, so long as they are rigid and durable in the plating solution and cooperable to form a substantially closed chamber.

A tubular insoluble conforming anode 42 is concentrically positioned within passageway 22, so that its outer surface 44 is parallel the aligned housing working surfaces forming passageway 22. Tubular anode 42 has a constant transverse section along its length. The transverse section is generally epitrochoidal, with a major dimension of about 6.5 inches and a minor dimension of about 4 inches. The composition of the anode forms no part of this invention, and any of the usual insoluble anode compositions for chromium plating canbe used. For example, it can be made of lead, titanium coated with lead, titanium coated with lead oxide, or copper coated with successive layers of iron and a lead-tin alloy containing 93 percent, by weight, lead.

The lower end of anode 42 is opposite lower metal plate 26 and is sealed by an insulated or nonconductive imperforate plate 45. Tubular anode 42 extends upwardly through passageway 22 and the opening 34 in upper. plastic member 32. The upper end of anode 42 is above the level 46 of the electroplating solution in tank 10. Anode 42 has a generally uniform wall thickness of about 0.125 0.250 inch.

The portion of the anode above passageway 22 in contact with the electroplating solution has a nonconductive coating 48. The portion of anode 42 in passageway 22, directly opposite the metal plates and the working surfaces of the housings, has a plurality of holes 50 radially arrayed throughout its length that communicate the anode interior with passageway 22. The holes 50 are approximately '74; V4 inch in diameter and are positioned about 1 inch apart radially around the periphery of the anode and alternately spaced axially in rows about k inch apart. Both sides of the anode at its minor transverse dimension, or waist portion, are shielded with a plastic strip 52 and 52' about 1 /4 inch wide along the entire length of the passageway 22. Strip 52 serves as a shield and is only wide enough to maintain a generally constant ratio of anode to cathode area radially around the anode. The minor dimension, or waist, portions of the housing working surfaces are thus prevented from plating at a faster rate than the balance of the housing working surfaces.

Two plastic pipes 54 and 54' are suspended within the interior of anode 42 .from a manifold pipe 56 that communicates with conduit 58. Conduit 58 communicates with the inlet side of pump 60, through a connectionat 62. The outlet side of pump 60 is connected to conduit 64, which communicates with the bottom of tank 10. In this way, electrolyte can be continuously withdrawn from the anode interior during plating and pumped back into the bottom of tank 10. As electrolyte is withdrawn from the anode interior it is continually replenished by electrolyte flowing into passageway 22 through the bottom and top openings 18 and 34 in

plastic members

16 and 32, respectively. Optimum pumping rates are in the range of about 12 24 liters per minute. The electrolyte flows through the openings 18 and 34 and passes between the surfaces being plated and the outer periphery of the anode whereupon it can pass into the anode interior through holes 50 in the anode. Gases generated at the anode are continuously directly swept into the anode interior, to maintain a more uniform anode to cathode resistance throughout the height of the housing stack. Also, it is preferred to agitate the electroplating solution in the tank with suitable means (not shown) to maintain solution uniformity throughout the tank.

A source of negative potential (not shown) is connected to a vertical strap member 66, that is bolted to each of the rotary engine housings and extends up out of the electroplating solution. It is preferred to maintain a current density of about 39 amperes per square decimeter on the housings. The strap 66 is preferably coated (not shown) in all areas contacting the electrolyte and not contacting the rotary engine housings. The positive side of the potential source is connected to the anode to complete the plating circuit. The

nonconductive plates

16 and 32, tubular member 38 and dowel pins 36 and 36' can be of a nonconductive material, or coated with a nonconductive material. They can be of plastic such as a polyniethyl methacrylate material. They can also be of any ceramic or plastic coated metal that is nonconductive and durable.

The spacing between anode 42 and the housing working surfaces is about 1% to 2 inches for rotary engine housings having epitrochoidal chambers with radial major dimensions of about 9 1 1.5 inches. The gap between the anode and the openings 34 and 18 of the top and bottom

plastic members

32 and 16 is about 0.5 inch. In general, the inner edge of

plastic plates

16 and 32 defining epitrochoidal openings 18 and 34 should overlap the openings in their contiguous metal plates. The overlap should be at-least about one-half of and preferably about two-thirds of the radial distance between the openings in the metal plates and the anode. Thus, for anode to plate spacing of about 1% 2 inches, the plastic plate to anode radial spacing should be about f. to inch.

In using my apparatus, metal plate 26 is first placed on lower plastic plate 16. The rotary engine housings prepared for plating in the normal and accepted manner are then stacked on lower metal plate 26. Upper metal plate 24 is then placed on top of the housing stack and plastic plate 32, in turn, placed on top of upper metal plate 24. The housings and metal plates are aligned and concentrically positioned with the plastic plates. Plastic dowel pins 36 and 36 are then placed through them to insure that they stay uniformly positioned. Cathode conductor strap 66 is bolted to the rotary engine housings. Box-like member 38 is then placed around the stacked housings and plates. The assembly can then be lowered into an electroplating tank, with the lower plastic plate 16 spaced at least an inch or two above the bottom of the tank and the upper plastic plate 32 spaced at least an inch or two below the level of the electroplating solution in the tank.

Anode 42 can be permanently attached to cross member 14, and the housings and plates stacked around it. On the other hand it can be removable, and inserted in passageway 22 after the housings and plates have been stacked. It might even be attached to a support above the tank and lowered into the assembly after the assembly is submerged in the electroplating solution.

Further, the upper end of anode 42 can be closed with an end wall (not shown), with plastic pipes 54 passing through it. In such instance, anode 42 need not extend up above the level of upper plastic plate 32.

The foregoing describes a plating assembly that is portable and useful in any plating tank with little tank modification. On the other hand, one can permanently install portions of such an assembly in an electroplating tank, should it be desired. For example, the lower plastic member 16 and the surrounding box-like enclosure 38 could be permanently attached to a support on the bottom of the tank. Also, anode 42 can be closed at its upper end, the anode mounted permanently in place, and electroplating solution pumped out of the anode interior through the lower end of the anode.

It should also be noted that this same assembly can be used to uniformly anodically etch the chromium layer after it is deposited. In fact, although not normally preferred, anodic etching can be done in the same tank and solution by merely reversing polarity of the potential source.

I claim:

1. An apparatus for uniformly electrodepositing a wear-resistant coating onto epitrochoidal radial working surfaces of a plurality of rotary engine housings simultaneously, said apparatus comprising:

a nonconductive substantially closed box-like enclosure for containing a vertical stack of abutting and registered rotary engine housings having aligned epitrochoidal inner working surfaces forming a passageway having an epitrochoidal cross section,

a flat metal plate on the top of said housing stack,

a flat metal plate on the bottom of said housing stack,

each of said flat metal plates having a major surface in contact with said stack and having an epitrochoidal opening therein congruent with said aligned inner surfaces,

top and bottom walls on said enclosure adjacent said metal plates with each wall having an epitrochoidal opening therein concentric with and smaller than the epitrochoidal cross section of said passageway,

an insoluble anode having a generally epitrochoidal transverse outer periphery and an interior space, said anode coaxially extending throughout said passageway parallel to and radially spaced inwardly from said aligned inner surfaces,

said anode being radially closer to said concentric epitrochoidal openings in said enclosure top and bottom walls than to said aligned inner surfaces,

said anode having a plurality of radially arrayed openings throughout said passageway that communicate said anode outer periphery with said anode interior space,

means for preventing said solution from entering said anode interior space except through said anode openings in said passageway,

means for supporting said enclosure in a tank of electroplating solution with said enclosure completely immersed in said solution, and

means for continuously withdrawing said solution from said anode interior space and recirculating it to said tank during electrodeposition of said wearresistant coating onto said aligned inner surfaces.

2. An apparatus for uniformly electrodepositing a chromium coating onto epitrochoidal radial working surfaces of a plurality of rotary engine housings simultaneously, said apparatus comprising:

a nonconductive closed box-like enclosure for containing a vertical stack of abutting and registered rotary engine housings having aligned epitrochoidal inner working surfaces forming a passageway having an epitrochoidal cross section with a major dimension of about 1 12 inches, 7

flat metal plates about 0.1 0.2 inch thick contacting the top and bottom of said housing stack, with each plate having an epitrochoidal opening therein congruent with said aligned inner surfaces, flat top and bottom walls on the interior of said enclosure adjacent said flat metal plates with each -wall havingan epitrochoidal opening therein concentric with and having a major dimension of about 1 1.5 inch smaller than said passageway major dimension,

an insoluble anode having a generally epitrochoidal transverse outer periphery and an interior space,

1 said anode coaxially extending throughout said passageway parallel to and radially spaced inwardly from said aligned inner surfaces,

said anode transverse outer periphery having a major dimension about 1.5 2.0 inches smaller than said passageway major dimension,

said major dimension of said concentric epitrochoidal openings in said enclosure top and bottom walls being larger than said anode major dimension by about of the difference between said anode and said passageg major dimensions,

a tank having a bottom wall and containing a solution -for electrodeposition of chromium,

means for supporting said enclosure in said tank completely immersed in said solution and spaced above said tankbottom wall wherein said solution can enter said passageway through said enclosure top and bottom openings, 'saidanode having a plurality of openings radially arrayed throughout said passageway by which said solution can enter said anode interior space from said passageway, "means for preventing said solution from entering said I anode interior space except through said anode openings in said passageway, and means for continuously withdrawing said solution from said anode interior space and recirculating it to said tank during electrodeposition of said chromium coating onto said aligned inner surfaces of 'said housings.

3. An apparatus for uniformly electrodepositing a chromium coating onto epitrochoidal radial working surfaces of a plurality of rotary engine housings simultaneously, said apparatus comprising:

a frame for supporting workpieces to be electroplated in a tank containing chromium electroplating solution,

a horizontal first flat nonconductive plate on said frame,

a vertically oriented tubular nonconductive member with open upper and lower ends, the lower end of which, is sealed on and encloses an upper surface portion of said first nonconductive plate, 1 a first horizontal flat metal plate on said enclosed upper surface portion within said tubular member for contact with the bottom of a vertical stack of abutting and registered rotary engine housings within said tubular member, said housings having aligned epitrochoidal inner working surfaces forming a vertical passageway of epitrochoidal horizontal cross section,

a second horizontal flat metal plate within said tubular member for contact with the top of said stack of rotary engine housings,

a second horizontal flat nonconductive plate on top of said second metal plate, and substantially closing the upper end of said tubular member,

said first and second flat metal plates each having an epitrochoidal opening therein congruent with said aligned inner surfaces of said rotary engine housin s,

said first and second flat nonconductive plates each having an epitrochoidal opening therein concentric with and smaller than said metal plate openings through which said electroplating solution in said tank can enter top and bottom ends of said passageway, v

vertical tubular insoluble anode having an epitrochoidal horizontal outer periphery concentric with and smaller than said nonconductive plate openings coaxially disposed in said housing passageway and uniformly radially spaced inwardly from said aligned inner surfaces, the radial spacing between said anode and said passageway being about two to three times greater than the radial spacing from said nonconductive plates,

said anode extending upwardly along the entire length of said passageway and through said second plate opening to a level above them,

a nonconductive coating covering all anode portions outside said passageway and anode waist portions within said passageway, and

said anode having a closed bottom end and a plurality of uniformly radially arrayed openings therein along its length through which electroplating solution from said passageway can pass within said tubular anode and be recirculated to said tank during electroplating.

4. A method of uniformly electrodepositing a wearresistant coating onto epitrochoidal working surfaces of a plurality of rotary engine housings simultaneously, said method comprising the steps of:

vertically stacking a plurality of rotary engine housings having epitrochoidal inner working surfaces in alignment to form a passageway having an epitro-v choidal cross section,

stacking metal plates at the top and bottom of the housing stack with the metal plates each having an epitrochoidal opening therein congruent with said passageway,

substantially enclosing said stack of housings and metal plates in a nonconductive container having top and bottom epitrochoidal openings therein adjacent the stack that are concentric with and smaller than the epitrochoidal cross section of said passageway,

coaxially positioning a tubular insoluble anode having a hollow interior and a generally epitrochoidal cross section within said passageway, with said anode paralleling the entire length of said passageway and spaced radially inwardly therefrom about two or three times its radial spacing from said container openings, said anode having radially arrayed openings throughout said passageway communicating said passageway with the anode interior,

completely immersing said container and said anode in an electroplating bath so that electroplating solution can enter said container through said top and bottom openings,

preventing electroplating solution from entering the anode interior except through said radially arrayed openings,

applying a negative potential to said housing stack and a positive potential to said anode, and

' tank.

Claims

1. AN APPARATUS FOR UNIFORMLY ELECTRODEPOSITING A WEARRESISTANT COATING ONTO EPITROCHOIDAL RADIAL WORKING SURFACES OF A PLURALITY OF ROTARY ENGINE HOUSINGS SIMULTANEOUSLY, SAID APPARATUS COMPRISING: A NONCONDUCTIVE SUBSTANTIALLY CLOSED BOX-LIKE ENCLOSURE FOR CONTAINING A VERTICAL STACK OF ABUTTING AND REGISTERED ROTARY ENGINE HOUSINGS HAVING ALIGNED EPITROCHOIDAL INNER WORKING SURFACES FORMING A PASSAGEWAY HAVING AN EPITROCHOIDAL CROSS SECTION, A FLAT METAL PLATE ON THE TOP OF SAID HOUSING STACK, A FLAT METAL PLATE ON THE BOTTOM OF SAID HOUSING STACK, EACH OF SAID FLAT METAL PLATES HAVING A MAJOR SURFACE IN CONTACT WITH SAID STACK AND HAVING AN EPITROCHOIDAL OPENING THEREIN CONGRUENT WITH SAID ALIGNED INNER SURFACES, TOP AND BOTTOM WALLS ON SAID ENCLOSURE ADJACENT SAID METAL PLATES WITH EACH WALL HAVING AN EPITROCHOIDAL OPENING THEREIN CONCENTRIC WITH AND SMALLER THAN THE EPITROCHOIDAL CROSS SECTION OF SAID PASSAGEWAY, AN INSOLUBLE ANODE HAVING A GENERALLY EPITROCHOIDAL TRANSVERSE OUTER PERIPHERY AND AN INTERIOR SPACE, SAID ANODE COAXIALLY EXTENDING THROUGHOUT SAID PASSAGEWAY PARALLEL TO SAID RADIALLY SPACED INWARDLY FROM SAID ALIGNED INNER SURFACES, SAID ANODE BEING RADIALLY CLOSER TO SAID CONCENTRIC EPITROCHOIDAL OPENINGS IN SAID ENCLOSURE TOP AND BOTTOM WALLS THAN TO SAID ALIGNED INNER SURFACES, SAID ANODE HAVING A PLURALITY OF RADIALLY ARRAYED OPENINGS THROUGHOUT SAID PASSAGEWAY THAT COMUNICATE SAID ANODE OUTER PERIPHERY WITH SAID ANODE INTERIOR SPACE, MEANS FOR PREVENTING SAID SOLUTION FROM ENTERING SAID ANODE INTERIOR SPACE EXCEPT THROUGH SAID ANODE OPENINGS IN SAID PASSAGE WAY, MEANS FOR SUPPORTING SAID ENCLOSURE IN A TANK OF ELECTROPLATING SOLUTION WITH SAID ENCLOSURE COMPLETLY IMMERSED IN SAID SOLUTION, AND MEANS FOR CONTINUOUSLY WITHDRAWING SAID SOLUTION FROM SAID ANODE INTERIOR SPACE AND RECIRCULATING IT TO SAID TANK DURING ELECTRODEPOSITION OF SAID WEAR-RESISTAND COATING ONTO SAID ALIGNED INNER SURFACES.

2. An apparatus for uniformly electrodepositing a chromium coating onto epitrochoidal radial working surfaces of a plurality of rotary engine housings simultaneously, said apparatus comprising: a nonconductive closed box-like enclosure for containing a vertical stack of abutting and registered rotary engine housings having aligned epitrochoidal inner working surfaces forming a passageway having an epitrochoidal cross section with a major dimension of about 1 - 12 inches, flat metal plates about 0.1 - 0.2 inch thick contacting the top and bottom of said housing stack, with each plate having an epitrochoidal opening therein congruent with said aligned inner surfaces, flat top and bottom walls on the interior of said enclosure adjacent said flat metal plates with each wall having an epitrochoidal opening therein concentric with and having a major dimension of about 1 - 1.5 inch smaller than said passageway major dimension, an insoluble anode having a generally epitrochoidal transverse outer periphery and an interior space, said anode coaxially extending throughout said passageway parallel to and radially spaced inwardly from said aligned inner surfaces, said anode transverse outer periphery having a major dimension about 1.5 - 2.0 inches smaller than said passageway major dimension, said major dimension of said concentric epitrochoidal openings in said enclosure top and bottom walls being larger than said anode major dimension by about 2/3 of the difference between said anode and said passage major dimensions, a tank having a bottom wall and containing a solution for electrodeposition of chromium, means for supporting said enclosure in said tank completely immersed in said solution and spaced above said tank bottom wall wherein said solution can enter said passageway through said enclosure top and bottom openings, said anode having a plurality of openings radially arrayed throughout said passageway by which said solution can enter said anode interior space from said passageway, means for preventing said solution from entering said anode interior space except through said anode openings in said paSsageway, and means for continuously withdrawing said solution from said anode interior space and recirculating it to said tank during electrodeposition of said chromium coating onto said aligned inner surfaces of said housings.

3. An apparatus for uniformly electrodepositing a chromium coating onto epitrochoidal radial working surfaces of a plurality of rotary engine housings simultaneously, said apparatus comprising: a frame for supporting workpieces to be electroplated in a tank containing chromium electroplating solution, a horizontal first flat nonconductive plate on said frame, a vertically oriented tubular nonconductive member with open upper and lower ends, the lower end of which is sealed on and encloses an upper surface portion of said first nonconductive plate, a first horizontal flat metal plate on said enclosed upper surface portion within said tubular member for contact with the bottom of a vertical stack of abutting and registered rotary engine housings within said tubular member, said housings having aligned epitrochoidal inner working surfaces forming a vertical passageway of epitrochoidal horizontal cross section, a second horizontal flat metal plate within said tubular member for contact with the top of said stack of rotary engine housings, a second horizontal flat nonconductive plate on top of said second metal plate, and substantially closing the upper end of said tubular member, said first and second flat metal plates each having an epitrochoidal opening therein congruent with said aligned inner surfaces of said rotary engine housings, said first and second flat nonconductive plates each having an epitrochoidal opening therein concentric with and smaller than said metal plate openings through which said electroplating solution in said tank can enter top and bottom ends of said passageway, a vertical tubular insoluble anode having an epitrochoidal horizontal outer periphery concentric with and smaller than said nonconductive plate openings coaxially disposed in said housing passageway and uniformly radially spaced inwardly from said aligned inner surfaces, the radial spacing between said anode and said passageway being about two to three times greater than the radial spacing from said nonconductive plates, said anode extending upwardly along the entire length of said passageway and through said second plate opening to a level above them, a nonconductive coating covering all anode portions outside said passageway and anode waist portions within said passageway, and said anode having a closed bottom end and a plurality of uniformly radially arrayed openings therein along its length through which electroplating solution from said passageway can pass within said tubular anode and be recirculated to said tank during electroplating.

4. A method of uniformly electrodepositing a wear-resistant coating onto epitrochoidal working surfaces of a plurality of rotary engine housings simultaneously, said method comprising the steps of: vertically stacking a plurality of rotary engine housings having epitrochoidal inner working surfaces in alignment to form a passageway having an epitrochoidal cross section, stacking metal plates at the top and bottom of the housing stack with the metal plates each having an epitrochoidal opening therein congruent with said passageway, substantially enclosing said stack of housings and metal plates in a nonconductive container having top and bottom epitrochoidal openings therein adjacent the stack that are concentric with and smaller than the epitrochoidal cross section of said passageway, coaxially positioning a tubular insoluble anode having a hollow interior and a generally epitrochoidal cross section within said passageway, with said anode paralleling the entire length of said passageway and spaced radially inwardly therefrom about two or three times its radial spacing from said container openings, said anode having radially arrayed opeNings throughout said passageway communicating said passageway with the anode interior, completely immersing said container and said anode in an electroplating bath so that electroplating solution can enter said container through said top and bottom openings, preventing electroplating solution from entering the anode interior except through said radially arrayed openings, applying a negative potential to said housing stack and a positive potential to said anode, and while applying said potentials, continuously withdrawing said electroplating solution from said anode interior and recirculating it back to said tank.