US3328197A - Mechanical plating - Google Patents

Description

United States Patent 3,328,197 MECHANICAL PLATIN G John G. Simon, St. Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Filed Feb. 8, 1965, Ser. No. 431,783 13 Claims. (Cl. 117-109) This application is a continuation-in-part of my copending application Ser. No. 41,022, filed July 6, 1960, which in turn is in the nature of a continuation-in-part of my application Ser. No. 789,544, filed Jan. 28, 1959, both now abandoned.

This invention relates to promoter chemicals for facilitating the mechanical plating of finely divided metal particles onto metallic substrates as smooth, dense, adherent, lustrous protective and/or decorative platings or coatmgs.

The process of mechanical plating has been known for perhaps a quarter of a century, but it has become of increasing significance during the last decade. The board principles of the process are well known; see, e.g., British Patent No. 534,888, US. Patents Nos. 2,689,808 and Re. 23,861, and other patents and publications. The process is typically carried out by placing in a tumbling barrel parts to be plated, plating metals in the form of minute malleable particles, impact media such as glass beads and cullet, and water. A variety of inorganic and organic chemicals may also be added to promote the mechanical plating action. As the tumbling barrel is rotated, the plating metal particles are hammered against the surface of the metallic parts to plated, the impact media and the parts themselves serving to flatten the metal particles and insure complete coverage. A properly applied mechanical plating is smooth, uniform, and provides excellent corrosion protection, at the same time requiring simple and inexpensive equipment, particularly when contrasted to electroplating apparatus.

In order to simplify the operation as much as possible and permit unskilled personnel to carry out the process, it is desirable to conduct mechanical plating as a batch operation. Desirably the parts to be plated, the impact media, the Water, the metal plating particles, and any promoter chemicals are all added at the start of an operation and allowed to remain, without change, until the operation is completed. Prior to my invention the results obained by this process were sometimes excellent, but were also unpredictable, erratic, and often wasteful of the metal plating particles. I believe that the reason for this resides in the fact that a mechanical plating operation, to be carried out most efficiently, should involve the gradual addition of the materials used to carry out the mechanical plating process. Unfortunately, as indicated previously, this is difiicult to achieve and undesirable from a point of view of holding the cost of the operation to a minimum.

In accordance with my invention, I provide, for the first time insofar as I am aware, a convenient, simple, economical, and highly reliable method of carrying out mechanical plating operations. My invention includes the provision of a solid bar, or cake, containing a predetermined desirable combination of mechanical plating promoter chemicals. This bar, which is added at the start of a mechanical plating operation, is gradually disintegrated by mechanical and chemical forces as the oper ation proceeds, resulting in a gradual release of the promoter chemical and tending to maintain a constant optimum concentration of the promoter ingredients.

As ingredients for the mechanical plating promoter bar my invention, I include an acidic first material (or one which hydrolyzes to yield hydrogen ions), a second material which prevents the premature agglomeration of ice metal particles in aqueous suspension, and, optionally, such additives as fillers, metal salts, absorbents, adsorbcuts, or chelating agents, or mold release agents to facilitate manufacture of the plating promoter chemical bars. (Although some agglomeration is essential, it is considered premature if it proceeds so rapidly that plating of large clusters of metal particles takes place, thereby imparting a rough nodular appearance to some areas while leaving other areas almost totally unplated.) When the aforementioned ingredients are molded under pressure, with or without the addition of heat, as desired, the dispersant typically functions as a binder to hold the entire bar together. If none of the ingredients just named as components of the plating bar is capable of providing a binding action, I add a binder material separately. Ordinarily, however, this is not necessary.

A wide variety of acid, or acid-engendering materials, may be used in the practice of my invention, provided the dissociation constant is at least equal to about 10*. If the dissociation constant exceeds about 10- it will be necessary to add a buffering or protective material to avoid having the acid and the plating metal particles consume each other before adequate plating action can take place. The function of the acidic material in this composition is to clean the surface of the metallic substrate to be plated, generally by the removing of oxide scale or other material which would prevent intimate contact between the plating metal particles and substrate, a concept which is well known. This very necessary cleaning action tends to increase the likelihood of agglomeration. Among the many acids which may be used with effectiveness are the following: acetic, adipic, l-ascorbic, benzoic, butyric, citric, crotonic, diglycolic, formic, gallic, gluconic, hydrochloric, lactic, maleic, malic, phthalic, propionic, succinic, sulfanilic, sulfuric, tartaric, etc. The soluble acidic salts of such acids also prove elfective in this operation. Acidic or acid-engendering materials include aluminum chloride, aluminum sulfate, ammonium 'bifluoride, sodium bisulfate, zinc chloride, zirconium sulfate, and many others.

At one time workers in the field believed that any organic film-forming agent or detergent enhanced the effectiveness of a mechanical plating operation, and it appears that this is true to at least some extent. My co-worker Michael Golben has now determined, however, that the class of materials known as dispersants are unexpectedly superior. Although the exact mechanism is not known with certainty, it appears that dispersants function by preventing premature agglomeration of metal plating particles and the resultant uneven plating. To a considerable extent the plating promoter bar of my invention accomplishes this same end result mechanically; by insuring a gradual release of acid, the pH of the solution is maintained high enough to retard reaction between the acid and the metal particles. Accordingly, then, although the plating bar of my invention is particularly eifective with those materials which are good dispersants, it also proves elfective with those materials which are, e.g., film-forming agents, and have other contributions to make to the plating process.

Among the materials which can be used effectively are the following: gum colloids such as gelatin, alginates and agar and tree exudations such as gum acacia, gum karaya, gum tragacanth, and the like, as set forth in US. Patent 2,689,808; fatty acids or amines, as set forth in US. Patent 3,132,043; substituted primary, secondary, or tertiary amines or amides, as set forth in US. Patent 2,640,002; polyoxyethylene adducts of various amides as set forth in Dutch Patent 98,545; higher alkyl trimethyl ammonium salts, as set forth in US Patent 2,999,767; long chain tertiary amines solubilized with ethylene oxide, as set forth in Us. Patent 3,032,127; amphoteric proteinaceous l compounds such as gelatine glue; certain metal soaps; polyoxypropylene glycol adducts of higher fatty acid amides; and numerous others heretofore known. I have also found that certain discoveries of Michael Golben, my associate, are extremely effective. Among these are polyoxyethylene glycol-terminated nonionic surfactants having a polyoxypropylene-terminated nucleus; anionic sulphonated alkyl aryl salts; compounds containing hydrophilic heterocyclic and hydrophobic alkyl groups.

I have also found that certain high molecular weight polyoxyethylene glycols are excellent dispersants for making the promoter chemical bar of my invention. Although others have suggested the use of low molecular weight glycols in plating operations, I find such materials generally ineffective. Further, a high molecular weight alone is not sufficient to insure effectiveness, still other criteria proving critical. I find that the effective polyoxyethylene glycols are those which have a molecular weight of at least 12,000 and which display a cloud point in 1% solution below 100 C. Speaking in general terms, a branched chain polyoxyethylene glycol compound need not be of as high a molecular weight as a straight chain polyoxyethylene glycol; Thus, a branched chain polyoxyethylene glycol may be made by polymerizing three or four straight chain polyoxyethylene glycol polymers, each having a molecular weight of 6,000, on a polyfunctional nucleus such as a diepoxide; the resultant material has a molecular weight in the range of 18,000 to 24,000 and functions very Well. On the other hand, a straight chain glycol of the same molecular Weight does not prove effective; however, a straight chain glycol having a molecular weight of 50,000 works very satisfactorily. The exact explanation for this is somewhat obscure, but I believe, without being bound thereby, that the effectiveness of the glycol in dispersing the metal plating particles is dependent directly on the degree to which the glycol polymer interferes with the premature agglomeration of the plating metal particles.

Regardless of the dispersant used, it is necessary that it be at least very slightly soluble as that term is defined in Hackhs Chemical Dictionary, i.e., that one part of dispersant dissolves in from 1,000l0,000 parts of water or less, in ten minutes. The amount of dispersant which is effective in combination with the acidic cleaning agent has been found to be as low as the weight of the active hydrogen ion available from the acidic material. The exact amount of dispersant used dependsupon the relative molecular weights of the acidic material and dispersant, the strength of the acidic material, the effective ness of the dispersant, and the particular system involved. Where the dispersant is a polyoxyethylene glycol of the type previously described herein, and where the acid is citric acid, the amount of dispersant is preferably from about 1% to about 4% the weight of the active hydrogen ion available from the acid; additional quantities of dispersant serve no very useful purpose and may, in fact, interfere with the plating operation.

A a guide to securing the proper ratio between dispersant and acidic material I have found it convenient to relate the amount of dispersant to the. amount of available hydrogen ion supplied by the acidic material. As a rule of thumb, at least .05 gram of dispersant, and generally at least 1.5 grams, is required for every gram mol of available hydrogen. Available in this context is intended to mean that the acidic hydrogen has a dissociation constant of at least 10 It will thus be apparent that some polybasic acids have both available and unavailable hydrogen.

In evaluating the etfectiveness of a given dispersant in producing good mechanical platings, I have found it convenient to consider six criteria-plating efficiency, uniformity, cohesion, coverage, brightness, and smoothness of the mechanical plating. The relative significance of these criteria varies with the specific end result sought, but an arbitrary value of 5 is assigned for outstanding performance. According to this somewhat subjective and 4 empirical technique, a perfect mechanical plating would be assigned the value of 30. Generally speaking, a value of 22 is considered fair, and 25 or more is considered very good.

As a guide to interpreting the criteria specified in the preceding paragraph, I offer the following brief statement of qualities which would receive a 5 rating. Plating efficiency-at least of plating metal particles are utilized. Uniformitythickness variation of no more than *-10% over the plated object. Cohesionplating is not removed from the substrate when scored with a razor blade, and tested by applying a strip of pressure-sensitive adhesive tape and quickly removing it. Coverage-none of the uncoated surface shows through. Brightnesssurface closely resembles polished zinc. Smoothness-surface is regular, with no signs of nodularity.

A typical bar may be made in accordance with my invention by comminuting all solid ingredients, uniformly blending them in, e.g., a twin-shell mixer, and pressing into a desired shape at, e.g., 6,000 p.s.i. Bars Weighing approximately 4 ounces each have proved particularly suitable in the practice of this invention, since no more than ten such bars usually need be added to even the largest mechanical plating, and one bar can be used effectively in the smallest equipment commercially available.

The following examples illustrate the use of various compositions of promoter chemical materials in the practice of my invention. These examples are intended to be illustrative only, and numerous equivalents will suggest themselves to the man ordinarily skilled in the art. All parts are by weight unless otherwise noted.

Example 1 1000 grams of shingle brackets were placed in a 1.2 gallon, hexagonal, plastisol-lined steel tumbling mill. The brackets had been previously cleaned by soaking in alkaline solution, pickled in 6% HCl solution and copperflashed by immersion for 15 seconds in a solution of 0.24 pound per gallon of Cuprodine salt and 113 milliliters per gallon of sulfuric acid. The mill was then charged as follows:

(a) Impact media: Grams 5 to 6 mesh spherical glass beads 2100 At the end of 60 minutes rotation, a bright, lustrous, uniform 0.0003 inch thick plate had been deposited about the entire surface of the part. The appearance of the coat approached the smoothness and luster obtained through electroplating; the grain of the coating was not significantly pebbled or rough as is characteristic of many prior art mechanically applied platings. Adherence of the plate was excellent.

In the foregoing example the diammonium citrate serves as a buffer, raising the initial pH of the solution, establishing a more uniform rate of mechanical plating, and facilitating the plating of complex shapes. Where thicker coatings or faster plating action may be desired, the ratio of citric acid to diammonium citrate may be increased or, if desired, the diammonium citrate may be eliminated altogether. The Carbowax 20,000 is formed by polymerizing at least three polyoxyethylene glycol chains having an average molecular weight of 6,000 on a diepoxide nucleus.

Example 2 1000 grams of parachute harness fittings were placed into a 1.2 gallon, hexagonal, plastisol-lined steel tumbling mill. The fittings had been previously cleaned, pickled and copper-flashed as described in Example 1. The mill was then charged as follows:

Grams (a) Impact media:

2 to 4 mesh spherical glass beads 2100 20 to 50 mesh spherical glass beads 2100 (b) Metal:

Cadmium alloy (60% Cd, 30% Sn, 20% Pb) powder which passes through a 325 US.

Tyler sieve (c) Water: at 50 F. to cover charge. (d) Metal plating bar:

Citric acid 5 Diammonium citrate 5 Carbowax 20,000 0.4 Stannous sulfate 02 Lead Sulfate 0.2 Stearic acid 0.2

In the metal plating bar composition of this example, combination of stannous sulfate and lead sulfate seems to be particularly effective in the plating of cadmium, tin, or lead alloys. The stearic acid functions as a mold release agent during the formation of the plating bars.

Example 3 4800 grams of clean assorted sheet metal screws were given a flash coating of copper by immersion plating in an acid-coppering solution. The parts were then rinsed and placed in a 1.2-gallon, hexagonal, plastisoldined steel tumbling mill. The mill was then charged as follows:

(a) Impact media:

12 to 14 mesh spherical glass beads pints 4 The lid was closed and the mill rotated for minutes, after which an additional 12.5 grams of cadmium powder and 37.5 grams of zinc powder were added. After an additional 20 minutes of rotation, the parts were separated from the media by screening and subjected to a 30-second treatment with iridescent chromate solution. These parts showed excellent resistance to both white and red corrosion in 5% salt spray.

Example 4 56 pounds of brass terminals were cleaned by tumbling them for 15 minutes in an acid cleaning solution maintained at 160 F. There were then given a flash coating of tin and placed in an open-faced vibratory-rotating barrel, together with 90 pounds of spherical glass impact media, one pound of tin powder, and a /1 pound promoter chemical bar containing parts citric acid, 25 parts diammonium citrate, 1 part stannous sulfate, 2 parts Carbowax 20,000, 1 part lead sulfate, and 1 part stearic acid. After plating for 40 minutes, the brass terminals had been provided with a bright tin coating approximately .3 mil thick and covering the surface uniformly.

Example 5 25 pounds of deburred, barb shank nails were cleaned in acid cleaner and immersion coppered. They were then placed in a vibratory-rotary type plating barrel, to which were added 25 pounds of spherical glass impact media, sufiicient water to cover the charge, 624 grams of zinc powder, and two 4-ounce promoter chemical bars. Each promoter chemical bar contained parts of citric acid, ten parts diammonium citrate, 2 parts Carbowax 20,000, 2 parts stannous sulfate, and 2 parts stearic acid. The barrel was then agitated for 30 minutes, after which an additional 624 grams of Zinc powder and 1 promoter chemical bar of a somewhat diiferent composition was added. This bar contained 75 parts citric acid, 25 parts diammonium citrate, 10 parts stannous sulfate, 2 parts Carbowax 20,000, and 2 parts stearic acid. After an additional 30 minutes of agitation, the parts were found to have a coating of excellent brightness and a thickness between 1 and 2.3 mils.

Example 6 700 pounds of inch x 4 /4 inch bolts were cleaned and fiash-coppered in an open-faced barrel, after which they were transferred to an octagonal horizontal barrel containing 900 pounds of spherical glass impact media. Warm water was added to above the level of the mixture at a temperature such that the total charge was warmed to 81 F. To the barrel contents were now added 3 /2 lbs. of zinc, 1 /2 lbs. (6 bars) of promoter chemical composition made up of 54 parts citric acid, 54 parts diammonium citrate, 1 part stannous sulfate, 3 parts gum acacia, and 2 parts stearic acid. The barrel was then rotated at 10 r.p.m. for 30 minutes. The resultant coating had good brightness, adhesion, coverage, and uniform plating between parts.

Example 7 To a 1.2-gallon plastisol-lined hexagonal barrel was added 1,000 grams of %-inch mild steel washers which had been cleaned in an acid cleaning solution and flash coated by immersion in an acid coppering solution for one minute. To the barrel was then added spherical glass impact media having the following composition: 1625 grams 46 mesh, 845 grams 12-14 mesh, 359 grams of 90-100 mesh. An ll-gram promoter chemical pellet, formed at 80,000 p.s.i., was then added to the contents of the barrel. The pellet was composed of 5 grams citric acid, 5 grams diammonium citate, 0.2 gram stearic acid, and 0.8 gram of a mixture of quaternary aliphatic ammonium salts available commercially as Arquad S-2C. Next, 20 grams of zinc dust having an average particle size of 3 microns was added, after which plating was carried out at 54 r.p.m. for one hour. The quality index, referred to hereabove, was 27.

Example 8 The process of Example 7 was repeated except that the 0.8 gram of Arquad S2C was replaced with 0.4 gram of Polyglycol E50,000, a straight chain polyoxyethylene glycol having a molecular weight of approximately 50,000 available from the Dow Chemical Company. The quality index of the resultant product was 25. Other straight chain glycols, e.g., a similar product having a molecular weight of only 20,000, proved quite ineffective. It is noted that the cloud point of Polyglycol E50,000, used in this example, is approximately 91 C., while straight chain polyoxyethylene glycols having a molecular weight of only 20,000 do not display a cloud point. Although I am uncertain why this criterion should be significant, I have found that it is extremely useful in determining those polyoxyethylene glycols which are effective for my pur poses.

Example 9 The process of Example 8 was repeated, except that the amount of Polyglycol E50,000 was reduced to 0.2 gram. Results were essentially the same as in Example 8.

Example 10 The process of Example 7 was repeated, except that the 0.8 gram of Arquad S-2C was replaced with 0.7 gram of a polyoxyethylene glycol adduct of oleic amide, available commercially as Nopalcol AO-43 from the Nopco Chemical Company. Quality index of the resultant plated product was 23.

Example 11 The process of Example 7 was repeated except that 0.4 gram of Swift and Company Technical Protein Colloid 2185 was employed as a dispersant. Quality index of the resultant product was 25. Substantially identical results were obtained when Technical Protein Colloids No. 69 and 70 were employed. Likewise, it was found that this hide glue of various viscosities, as well as gelatin, could be substituted with substantially the same effectiveness. Surprisingly, it was found that the quantity required to produce excellent results was considerably less than for any other dispersants which I have tried. For example, only about .05 gram of dispersant is required for each gram mol of available hydrogen supplied by the acid.

The rate at which promotor chemical bars made in accordance with my invention release the components thereof is inversely related to the pressure at which the bars are formed. The relationship is not linear, however, and it depends to a considerable degree on the physical nature of the bar components.

The metal plating bar above described may also contain minute plating metal particles for controlled release into the charge. These metal particles can be admixed with the other ingredients. To avoid contamination, oxidation or other types of reaction, the plating metal particles may receive a protective coating, such as a plastic or resinous coating, abradable by agitation and impact, or they can be incorporated into the bar in the form of distintegrable plastic pellets or capsules, which capsules form a barrier between the metal and the other ingredients.

Metal plating bars of controlled disintegration containing other binders can be made, e.g., by mixing and compacting both liquid and solid ingredients. In such case it is desirable to add an adsorbent or absorbent powder, e.g., a hydrophilic, argillaceous powder like attapulgite clay, diatomaceous earth, fullers earth, and the like.

Other variations will readily occur to the man skilled in the art.

What I claim is:

1. As a means to promote the mechanical plating, in an aqueous medium, of metal powder particles onto a substrate to be plated therewith, a water-disintegrable solid bar capable of gradually releasing plating promoter chemicals to the aqueous medium over a period of time during the plating operation to enhance and facilitate uniformity of plating, said solid bar comprising an acidic first material having a dissociation constant of at least 10" and a second at least very slightly soluble material capable of slowing up or preventing the premature agglomeration of metal powder particles in aqueous suspension, said second material being present in an amount equal to at least about .05 gram per gram mol of available hydrogen supplied by said acidic material, said bar including ingredients which impart mechanical stability by binding the bar together, said bar further containing a buffering or protective material where the dissociation constant of said acidic first material exceeds 10* 2. As a means to promote the mechanical plating, in an aqueous medium, of metal powder particles onto a substrate to be plated therewith, a water-disintegrable solid bar capable of gradually releasing plating promoter chemicals to the aqueous medium over a period of time during the plating operation to enhance and facilitate uniformity of plating, said solid bar comprising an acidic material having a dissociation constant of at least 10- and a solid, at least very slightly soluble, polyoxyethylene glycol having a molecular weight of at least 12,000 and a cloud point in 1% solution below C., said polyoxyethylene glycol functioning as a dispersant and further serving to impart stability to said bar by binding the ingredients thereof together, said bar further containing a bufi'en'ng or protective material where the dissociation constant of said acidic material exceeds 10 3. The product of claim 2 in which the polyoxyethylene glycol is a straight chain glycol having a molecular weight of about 50,000.

4. The product of claim 2 in which the polyoxyethylene glycol is a branched chain glycol having a molecular weight of at least about 20,000.

5. The product of claim 2 in which at least about 1.5 grams of polyoxyethylene glycol is present for every gram mol of available hydrogen provided by said acidic material.

6. As a means to promote the mechanical plating, in an aqueous medium, of metal powder particles onto a substrate to be plated therewith, a water-disintegrable solid bar capable of gradually releasing plating promoter chemicals to the aqueous medium over a period of time during the plating operation to enhance and facilitate uniformity of plating, said solid bar comprising an acidic material having a dissociation constant of at least 10-", a small amount of a water-soluble tin salt, and an at least very slightly soluble dispersant for metal particles in agitated acid solution capable of slowing up or prevent-. ing the premature agglomeration of metal powder particles, said dispersant being present in an amount equal to at least about .05 gram per gram mol of available hydrogen supplied by said acidic material, said bar including ingredients which impart mechanical stability by binding the bar together, said bar further containing a buffering or protective material where the dissociation constant of said acidic material exceeds 10 7. As a means to promote the mechanical plating, in an aqueous medium, of metal powder particles onto a substrate to be plated therewith, a water-disintegrable solid bar capable of gradually releasing plating promoter chemicals to the aqueous medium over a period of time during the plating operation to enhance and facilitate uniformity of plating, said solid bar comprising an acidic material having a dissociation constant of at least '10- and an at least very slightly soluble dispersant for metal particles in agitated acid solution material capable of slowing up or preventing the premature agglomeration of metal powder particles, said dispersant being present in an amount equal to at least about .05 gram per gram mol of available hydrogen supplied by said acidic material, said bar including a chelating agent and ingredients which impart mechanical stability by binding the bar together, said bar further containing a buffering or protective material where the dissociation constant of said acidic material exceeds 10- 8. In a method of mechanically plating parts which includes the steps of placing said parts in a plating barrel together with finely divided plating metal, impact media, acid and water, and thereafter agitating the contents of the barrel until said parts have been plated with said plating metal, the improvement comprising adding to the contents of said barrel an at least very slightly soluble nonionic material which consists essentially of a polyoxyethylene glycol having a molecular weight of at least 10 and (2) an at least very slightly soluble polyoXyethylene glycol having a molecular weight of at least about 12,000 and a cloud point in 1% solution below 100 C., the ratio of said glycol to said acid being such that there is at least 1.5 grams of glycol per gram mol of hydrogen available from said acid, said bar further containing a buffering or protective material where the dissociation constant of said acid exceeds 10 10. As a mechanical plating promoter, the combination of (1) citric acid and (2) an at least very slightly soluble polyoxyethylene glycol having a molecular weight of at least about 12,000 and a cloud point in 1% solution below 100 C., the ratio of said glycol to said acid being such that there is at least 1.5 grams of glycol per gram mol of hydrogen available from said acid.

11. As a mechanical plating promoter, the combination of (1) citric acid and (2) an at least very slightly soluble adduct of a short-chain polyfunctional compound and at least three molecules of polyoxyethylene glycol, the molecular weight of said adduct being at least about 20,000, the ratio of said glycol to said acid being such that there is at least 1.5 grams of glycol per gram mol of hydrogen available from said acid.

12. As a promoter for use in the mechanical plating of cadmium, the combination of (1) an acid having a dissociation constant of at least 10 (2) an at least very slightly soluble polyoxyethylene glycol having a molecular weight of at least about 12,000 and a cloud point in 1% solution below 100 C., the ratio of said glycol to said acid being such that there is at least 1.5 grams of glycol per gram mol of hydrogen available from said acid, (3) a tin salt, (4) a lead salt, and (5) where the dissociation constant of said acid exceeds a buffering or protective material.

13. As a means to promote the mechanical plating of metal powder particles onto a substrate to be plated therewith, a water-disintegrable solid bar capable of gradually releasing plating promoter chamicals to the aqueous medium over a period of time during the plating operation to enhance and facilitate uniformity of plating, said solid bar comprising an acidic material having a dissociation constant of at least 10 a small amount of a water-soluble tin salt, a small amount of lead salt, and an at least very slightly soluble dispersant for metal particles in agitated acid solution capable of slowing up or preventing the premature agglomeration of metal powder particles, said dispersant being present in an amount equal to at least about .05 gram per gram mol of available hydrogen supplied by said acidic material, said bar including ingredients which impart mechanical stability by binding the bar together, said bar further containing a buffering or protective material where the dissociation constant of said acidic material exceeds 10 References Cited UNITED STATES PATENTS 2,434,855 1/ 1948 Kosterlitzky 1061 X 2,519,672 8/1950 Lawless 1061 2,640,002 5/1953 Clayton '117109 2,689,808 9/1954 Clayton 117109 X 2,793,965 5/1957 Myers et a1. 1061 X 2,940,867 6/1960 Streicher 117130 X 3,023,127 2/1962 Clayton 117131 X OTHER REFERENCES Carbowax Compounds and Polyethylene Glycols, by Carbide and Carbon Chemicals Corp., New York, N.Y., June 30, 1946.

Hill, F. N., et al.: Industrial and Engineering Chemistry, High Molecular Weight Polymers of Ethylene Oxide, Hill, F. N., et al., Detergent Digest, vol. 50, No. 1, January 1958, p. 5.

Carbowax, Polyethylene Glycols, Union Carbide Chemicals Co., New York, N.Y., 1960 pamphlet, pp. 1, 9 and 22.

ALFRED L. LEAVITT, Primary Examiner.

JOSEPH B. SPENCER, RALPH S. KENDALL,

Examiners. J. P. MCINTOSH, Assistant Examiner.

Claims (1)

1. 8. IN A METHOD OF MECHANICALLY PLATING PARTS WHICH INCLUDES THE STEPS OF JPLACING SAID PARTS IN A PLATING BARREL TOGETHER WITH FINELY DIVIDED PLATING METAL, IMPACT MEDIA, ACID AND WATER, AND THEREAFTER AGITATING THE CONTENTS OF THE BARREL UNTIL SAID PARTS HAVE BEEN PLATED WITH SAID PLATING METAL, THE IMPROVEMENT COMPRISING ADDING TO THE CONTENTS OF SAID BARREL AN AT LEAST VERY SLIGHTLY SOLUBLE NONIONIC MATERIAL WHICH CONSISTS ESSENTIALLY OF A POLYOXYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT OF AT LEAST ABOUT 12,000 AND A CLOUD POINT IN 1% SOLUTION BELOW 100*C., THE AMOUNT OF SAID MATERIAL ADDED BEING AT LEAST ABOUT 1.5 GRAMS PER GRAM MOL OF HYDROGEN AVAILABLE FROM SAID ACID.