US3531315A - Mechanical plating - Google Patents

Description

if A nited tates Patent Ofice 3,531,315 Patented Sept. 29, 1970 3,531,315 MECHANICAL PLATING Michael Golben, Maplcwood, Minn., assignor to Minnesota Mining and Manufacturing Company, St. Paul, Minn, a corporation of Delaware No Drawing. Filed July 17, 1967, Ser. No. 653,657 Int. Cl. C23c 17/00 US. Cl. 117-50 23 Claims ABSTRACT OF THE DISCLOSURE Ferrous or other metal parts are acid-cleaned and mechanically metal-plated without any intervening rinsing step, using the acid employed for scale removal. Superior results are attained by providing means for dispersing and inhibiting corrosion of the plating metal particles. Cleaned ferrous metal parts are desirably flashplated by displacement and/or galvanomechanical techniques prior to the mechanical plating step.

BACKGROUND OF THE INVENTION It is common practice to plate ferrous metal parts with a more attractive and/or corrosion-resistant metal. The plating metal may be applied by either electroplating or mechanical plating, depending on such factors as the thickness required and the end use to which the part will be put. Electroplating requires a heavy capital investment, while mechanical plating employs comparatively simple and inexpensive equipment. Since the rate of electroplating is constant for given conditions, cost is directly proportional to the thickness of the plating. In contrast, mechanical plating requires only slightly more time to apply a thick plate than a thin one, and hence cost increases very little with increasing thickness. Where 0.3 to 3 mils of zinc is to be plated on a ferrous metal part, mechanical plating is generally less expensive than electroplating.

Parts to be either electroplated or mechanically plated are usually first cleaned in strong acids, commonly having a dissociation constant of at least When highcarbon steel is exposed to strong acids, it almost inevitably absorbs hydrogen, becoming embrittled and prone to fail when subjected to tensile stress. The plating process itself is also frequently carried on in acidic solution; in electroplating, hydrogen is generated atand absorbed bythe part being plated, causing further hydrogen embrittlement. Mechanically applied platings are somewhat porous, permitting absorbed hydrogen to escape quickly and alleviate the stress, while electroplated platings especially if as thick at l mil-are dense, confining the hydrogen within the ferrous metal lattice. This difference provides a further reason why manufacturers of parts which require a comparatively thick plate find mechanical plating more satisfactory than electroplating, especially where the plated part is to be stressed in use.

Most parts, however, are plated only to improve their appearance, which can be accomplished by a comparatively thin (e.g., 0.1-0.3 mil) coating. Hydrogen readily escapes through such layers, when mechanically plated; in contrast, electroplated parts having a Rockwell C hardness of 40 or more require a special baking step to drive off the hydrogen. Thin layers of zinc and cadmium can be electroplated directly on ferrous metal, while it is gentofore proved both faster and more economical for most thin plating processes.

Before either electroplating or mechanically plating ferrous metal parts, it is almost always necessary to subject them to a cleaning and descaling process. Prior to the present invention, the procedure has been to immerse the parts in an acid solution containing a surfactant until scale, oil and dirt were removed, separate the parts from the dirty cleaning solution, rinse to remove any dirt, scale, or acid clinging to the parts, and then carry out the plating operation.

Since mechanical platingand sometimes electroplatingare typically carried out in acid solution, it might be supposed that costs could be reduced by using the acidic cleaning solution residue for this purpose, but those skilled in both arts have eschewed this possibility. For greatest eifectiveness, the pH of cleaning acid is extremely low, while the pH of plating acid (which is often buffered) is moderate. Accordingly, it has been considered impossible to plate mechanically in strong acid, which would be expected to attack and agglomerate the plating metal particles. Further, cleaning solution is often rendered opaque by suspended scale, carbon, dirt, and oil, and it has been understandably felt that such extraneous material would interfere with plating. Indeed, when an attempt is made to electroplate in such a medium, the resulting plate is irregular, containing minute inclusions of undesirable material.

SUMMARY OF THE INVENTION The present invention provides a simple, straight-forward, rapid, and inexpensive way to provide metal parts with mechanical platings of any desired thickness. Even 0.1-0.3 mil layers can be applied more simply than, and as economically as, by electroplating. The invention involves the surprising and unexpected discovery that mechanical plating can be carried out in the strongly acidic residue remaining after the degreasing and descaling step. This discovery is particularly surprising in view of the fact that an attempt to electroplate in this residue results in a totally unsatisfactory plating.

In accordance with the simplest form of the invention, parts to be cleaned and mechanically plated are placed in a barrel and flooded with an aqueous solution containing surfactant and sufficient acid to lower the pH to 4 or less. The barrel is then rotated, tumbling the parts and media and agitating the solution, until the parts are essentially cleaned and free from oil and scale. Then, without prior rinsing, plating metal particles are added to the solution, desirably providing in the solution means for dispersing the particles and inhibiting their corrosion by the residual acid. The barrel contents are then further agitated until the desired thickness of mechanical plating metal has been applied over the surface of the parts, after which the plated parts are separated from the other contents of the barrel.

Adhesion of the mechanical plating to the substrate, especially to a ferrous metal substrate, is generally enhanced by applying one or more thin flash plates of a nonferrous metal by displacement and/or galvanomechanical techniques. In the latter technique, there is added to the solution remaining after cleaning, small amounts of soluble salt of a galvanomechanical plating metal and 3 finely divided particles of a driving metal which is more anodically active in the solution than is the galvanomechanical plating metal as the solution is agitated, the galvanomechanical plating metal is deposited on the substrate.

For optimum results in carrying out the process just described, it is desirable to employ, during the mechanical plating step, means for inhibiting corrosion of the plating metal particles by the acid, thereby preventing undesirable gassing and permitting the particles to perform their intended function. For maximum smoothness of the mechanical plating, it is also desirable to include means for dispersing the metal particles and preventing their premature agglomeration. In some cases, both of these means may be incorporated in the same compound or composition.

Any of several means for inhibiting corrosion of the plating metal particles may be employed. For example, the acid may be buffered so that its pH does not fall below about 2.5 during plating; alternatively, the acid may be added successively throughout the plating process to maintain the highest pH which is effective. Generally, however, it is preferred to employ an additive which inhibits corrosion of the plating metal particles without affecting acidity.

Among the materials which function as effective means for inhibiting the corrosion of at least some plating metal powders in at least some acid plating solutions are compounded cationic amine inhibitors, such as Armohib (Armour Industrial Chemical Co.); cationic inhibitors such as Inhibitor GC (Sinclair Mineral and Chemical Co.); filming amines such as Nalco 353 (Nalco Chemical Company); triphenyl sulfonium chloride, and mixtures of propargyl alcohol and the reaction product of certain amine hydrochloride with ketones and formaldehyde, such as the Rodines (Amchem Products, Inc.).

Additives which serve as effective corrosion inhibitors are related to both the acid and the specific plating metal. For example, when sulfuric acid is used, Armohib 25 prevents the corrosion of lead or cadmium particles, but not zinc particles. In the same system Nalco 358 inhibits the corrosion of cadmium but not lead. Sinclair Inhibitor GC does not inhibit the corrosion of cadmium in sulfuric acid, but does in hydrochloric acid. The optimum amount of a given additive is related to the specific system in which it is used. Generally, however, the more acidic or more aerated the liquid, the more inhibitor is required.

Among the materials which function as effective means for dispersing at least some plating metal powders in at least some acids are those polyoxyethylene glycols having a cloud point in 1% aqueous solution below 100 C., such as Carbowax 20M (Union Carbide Chemicals Company) or Polyglycol E50,000 (Dow Chemical Company); quaternary aliphatic ammonium salts such as Arquad S-2C, (Armour Industrial Chemical Co.); proteinaceous materials such as Technical Protein Colloids No. 2185, 69, or 70 (Swift and Company); salts of polymerized alkyl aryl sulfonic acids or higher alkyl adducts of diphenyl oxide, such as the Marasperses (Marathon Chemical Company), Orzans (Crown-Zellerbach Compony), Darvans (R. T. Vanderbilt Company), Lomars (Nopco Chemical Company), Tamols (Rohm & Haas), or Benax (Dow Chemical Company); polymers having a hydrophobic polyoxypropyleneterminated nucleus with a plurality of hydrophilic polyoxyethylene glycol-terminated chains attached thereto, such as Pluronics and Tetronics (Wyandotte Chemical Company); polyoxyethylene glycol adducts of alkyl phenols, especially nonyl phenols, such as the Tergitols (Union Carbide Chemicals Co), Surfonics (Jefferson Chemical Company), Igepals (General Aniline and Film Company), and Hyonics (Nopco Chemical Company); hydrophilic heterocyclis adducts of hydrophilic alkyl compounds which contain nitrogen groups, such as Nalquat G8ll or G813 (Nalco Chemical Company); N-cety1 or N-soya-ethyl morpholinium ethosulfate, such as Atlas 271 and 263 (Atlas Chemical Company); amphoteric disodium N-tallow beta imino dipropionate, such as Deriphat 154 (General Mills); the Mannich reaction product of dehydroabietyl amine, formaldehyde, and alpha methyl ketones such as acetone or acetophenone, the reaction product of o-toluidine and formaldehyde.

Additives which function as dispersants are related to both the specific acid and the specific plating metal particles involved. To illustrate, effective dispersants for Zinc in sulfuric acid include Carbowax 20M and Orzan AH3; dispersants for zinc or tin particles in hydrochloric acid include Nalquat G811, while lead can be dispersed in the same acid by Orzan P. Many other examples could be cited.

Whether a given material will function as means for either dispersing or inhibiting the corrosion of specific plating metal particles in a specific milieu can be determined by adding 0.25-0.5 gram of the material to 250 ml. of the acid plating solution in a 400 ml. beaker, adding 10 grams of plating metal powder, stirring vigorously, and allowing the beaker and its contents to stand for 5 minutes. An effective dispersant will keep the metal powder in suspension, rendering the acid plating solution opaque. An effective corrosion inhibitor will essentially prevent both gasing and clumping of the plating metal metal powder into tough balls.

The optimum amount of a given additive is related to the specific system in which it is used. In general, however, large volumes of liquid, open barrels, or highly acidic conditions require more inhibitor than small volumes of liquid, closed barrels, or less acidic conditions. Similarly the optitum amount of dispersant decreases as pH rises or the weight of plating metal particles decr ases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be more easily understood by referring to the following illustrative examples, in which all parts are by weight unless otherwise noted.

Example 1 A 1.2-gallon hexagonal mill provided with a cover was charged with two quarts (3,835 grams) of 1% inch x /8 inch roofing nails, 3,110 grams of glass impact media (3 parts 4-6 mesh spherical, 1 part 8-14 mesh nonspherical, 1 part 12-14 mesh spherical, and 1 /2 parts 31100 mesh spherical), and sufficient F. water to cover the solid materials. To the barrel was then added 20 grams of NaHSO 0.5 gram of the adduct of nonyl phenol and a 9-10 ethylene oxide polyoxyethylene glycol (Surfonic N-95, available from Jefferson Chemical Company), 3.0 grams SnCl and 6.0 grams of 3-micron Zinc powder. The barrel was closed and rotated at 54 rpm. for 5 minutes, after which period the nails were found to be not only free from oil and scale, but also provided with a tin flash coat. To the barrel was then added 57.5 grams of zinc powder and rotation continued for an additional 20 minutes. The pH having risen to about 5, 10 grams of NaHSO was added and rotation continued for an additional 5 minutes. The nails were separated from the remaining contents of the barrel and fouiid to have a uniform bright 0.3-0.4 mil zinc plating having excellent adhesion and uniformity. Presumably because Surfonic N is a borderline dispersant for zinc particles in the system, the zinc plating was somewhat rough, which, was considered desirable for roofing nails. The plated nails could be chromated in standard fashion.

Example 2 The mill of Example 1 was charged with 3,835 grams of roofing nails, and 5,099 grams of the impact media, and water as in Example 1. To the barrel was then added 41.54 grams of a cleaner-promoter having the following composition:

Grams NaHSO 35 SnSO 1.13 Surfonic N95 0.75

Precipitated hydrous silica (Zeo 458D, commer- Ammonium lignosulfonate (Orzan AH-3, available from Crown-Zellerbach) 0.75

The mill was then run for minutes, at the end of which time the roofing nails had been thoroughly cleaned and had acquired a bright tin plating. The barrel was opened, 58 grams of zinc powder added, the barrel reclosed, and rotation continued for an additional minutes. The nails were then rinsed, removed from the mill, and found to have a very good zinc plating. Presumably because "()rzan AH-3 is a good dispersant for zinc particles, the plating was somewhat smoother than that obtained in Example 1.

Example 3 The mill of Example 1 was charged with roofing nails, impact media, and water, all as in Example 1.

A solid granular cleaner and plating promoter was prepared by blending 35 grams NaHSO 1.7 grams SnSO (water-soluble flash plating salt), 0.7 gram Surfonic N95 (detergent), 0.1 gram of silicone defoamer absorbed on puffed borax (as in Example 2), and 0.75 gram Orzan AH-3 (dispersant).

A protected driving and mechanical plating metal powder was prepared as follows: 18 grams of a watersoluble binding and coating polymermethylcellulose (Methocel HG, commercial available from Hercules Powder Co.)-was dissolved in 100 cc. of isopropanol, added to 200 cc. water, and stirred to yield a uniform solution. Next 36 grams of powdered zinc was added and stirred vigorously to disperse it throughout the solution. The zinc-containing solution was then poured into a large Petri dish and heated 4 hours at 200 F. to remove the solvent and decrease the water-solubility of the methylcellulose, thereby retarding the rate at which the zinc powder could be subsequently made available. The resultant film was broken into small flakes and shreads and blended with the granular plating promoter described in the preceding paragraph to yield a generally uniform mixture of granular material for use in cleaning, galvanomechanically flash plating and mechanically plating.

The granular mixture was then added to the mill,- which was then closed and rotated at 30 rpm. for 10 minutes; when opened, it was found that the nails had been uniformly tin plated. The mill was then closed and rotated for an additional 10 minutes, yielding a bright, uniform zinc plate which chromated well.

The advantage of the procedure described in this example is that all components for cleaning, tinning, and mechanically plating can be initially added to the mill without separate measurement, so that the mill can then remain closed throughout the entire cleaning and plating operation. It will be appreciated that numerous equivalents for the component maerials can be used.

Example 4 The mill of Example 1 was charged with 6,500 grams of moderately soiled /3inch mild steel washers and 4,000 grams of the impact media used in Example 1, sufficient water being added to cover the charge. A combination cleaner: tin flash coaterzplating promoter grams NaHSO 3 grams SnCl 0.5 gram Surfonic N95, and 5 grams Zinc) was added, after which the barrel was rotated at 63 rpm. for 5 minutes. A uniform tin plating was obtained. An additional 35 grams of zinc was added and rotation at 63 rpm. continued for 20 minutes. A 0.15-0.25 mil zinc plate was obtained.

Example 5 The mill of Example 1 was charged with 5,020 grams of heavily scaled, soiled -inch hot rolled steel washers (1105 square inches of surface), 4,000 grams of the impact media described in Example 1, and sufficient water to cover the charge. To the mill was then added 20 grams of concentrated H and 8 grams of a cleaner having 'the following composition:

NaCl 5.71 Surfonic N 0.67 Heterocyclic tertiary amine (Amine 0, available from Geigy Industrial Chemicals) 0.19 Diatomaceous earth (Celite Super Floss, available from Johns-Manville Sales Corp.) 1.43

Steam was used to raise the temperature of the mill contents to 130 F., and rotation continued for 15 minutes. The steam was then turned off, the mill opened, and the washers found to be free from dirt, oil, and scale; the liquid contents of the mill, however, were opaque with dissolved and suspended soil. Next Was added 2.1 grams SnCl and 3.5 grams powdered zinc, and the mill rotated for an additional 5 minutes; it was found that the washers had been uniformly tin flash plated. To the mill was then added 26.5 grams of zinc powder and a mixture of 0.5 gram Zeo 458D and 0.5 gram Additive R The barrel was then closed and rotated for an additional 20 minutes, after which time it was found that the washers had been provided with a reasonably bright, uniform, very smooth 0.13-0.25 mil zinc plating. Additive R seems to combine the features of corrosion inhibition, hydrogen embrittlement prevention, and zinc dispersion in this system, making it an especially interesting additive.

Example 6 The mill of Example 1 was charged with 6,500 grams of /S-ll'lCh mild steel washers, 4,000 grams of impact media of the type used in Example 1, and sufficient water to cover the solid material. Next 40 grams of an aqueous cleaner-plating promoter chemical (27% H 80 58% NH HSO and 10% ammonium acrylate) was added. The mill was closed and rotated for 15 minutes at F., opened, and 2 grams of SnCl and 3.6 grams of zinc added. The barrel was again closed and rotated for 5 minutes, providing the washers with a thin uniform tin plating. 32.5 grams of zinc was then added and rotation continued for an additional 20 minutes. The washers were found to have a uniform well-adhered 0.2-0.4 mil zinc plating.

Example 7 A cleaning powder was prepared by absorbing on 70 grams of Zeo 455D, 148.5 grams of concentrated H 80 and 12 grams of the reaction product of a straight chain alcohol and ethylene oxide (Arosurf EO-66, commercially available from Archer Daniels Midland Co.), and then mixing with 6 grams of Orzan AH-3 and 91.5 grams of (NI-19 80 As used hereinafter, Additive R is a product made as follows: To 23.4 grams of dehydroabietyl amine (Amine D, available from Hercules Chemical Company) was slowly added 7.5 grams of acetophenone, with stirring; 10 grams of 20 B. HCl solution in water was added slowly in the same manner. Next 9.7 grams of 37% formaldehyde was added in small increments and the mixture refluxed intermittently at 80 C. over a period of 3 days. At this point 25.0 grams of acetone was added directly and 9.5 grams of 37% formaldehyde added incrementally, continuing to reflux for an additional 24 hours. The solution was evaporated to leave a solid material, 0.82 gram of which was dissolved in 0.66 gram of p a 70: 15 z 15 isopropanol acetone: methanol solvent. In 0.42 gram of water 0.82 gram of nonionic polyoxyethylene adduct of nonyl phenol (Tergitol NP-25, available from Union Carbide Chemicals Co.) was dissolved, and the two solutions mixed together.

The mill of Example 1 was charged with washers, impact media, and water, as in Example 5. To the charge was then added 20 grams of the powdered cleaning material described in the opening paragraph of this example, and the mill closed and rotated at 60 rpm. for minutes at 120 F. The mill was opened, 2 grams of SnCI and 3.5 grams of zinc added, closed, and rotated an additional 5 minutes; the washers had been thoroughly cleaned and provided with a uniform tin flash plate. Next .23 grams of zinc powder was added, and the mill closed and rotated an additional minutes at 90 F., providing the washers with a uniform 0.15-0.2 mil Zinc plating.

Example 8 The mill of Example 1 was charged with 2,500 grams of As-inch mild steel washers, 3,110 grams of glass impact media (75% 12-14 mesh spherical, 91-100 mesh spherical), sufiicient Water to cover the solid material, and 20 ml. of the following composition:

Parts by weight 54.3" B. H 80 568.0 Water 74.0 Surfonic N-95 22.3 Surfonic N-lO 2.7 Additive R (commercial equivalent), as in Example 5 12.0 Propargyl alcohol 11.0

The mill was closed and rotated for 10 minutes, steam being supplied to heat the charge. The mill was then opened, 2 grams of CL1SO4'H2O and 1 gram of NaCl added, closed, and rotated an additional 5 minutes, providing the washers with copper flash-plated by displace ment. Next 1.2.5 grams of zinc powder and 5 grams phthalic anhydride were added, the mill again closed, and steam used to raise the temperature to 160-180 F.. while rotating for about 10 minutes. The washers were plated very effectively, although there was some tendency to roughness. Phthalic anhydride becomes acidic only when the temperature is raised sufficiently above room temperature to cause hydrolysis.

Example 9 The mill of Example 1 was charged with 3,835 grams of roofing nails, 2,100 grams of glass impact media (3 parts 12-14 mesh spherical, 1 part 20-45 mesh spherical, and 1 part 31-100 mesh spherical), and sufficient water to cover the solid material.

Ten parts of Surfonic N-95, 1,200 parts of NaHSO and 40 parts Celite Super Floss were mixed together, the NaHSO becoming coated with the Super Floss (diatomaceous earth) and rendered less corrosive to materials with which it came into contact. Five parts of 50% active Technical Protein Colloid (Swift 69), parts of Surfonic N-95, 3 parts Orzan AH-3, 8 parts of zinc powder, 6 parts of Celite Super Floss, and 3 parts of pine sawdust were separately mixed; here the diatomaceous earth protectively coated the zinc powder. The two separately prepared powdered compositions were then mixed together and pressed at 5,000 p.s.i. to form a 34-gram A pellet, the diatomaceous earth serving to prevent the Zinc from reacting with the NaHSO A 1.3-gram B pellet was formed by mixing and pressing together at 5,000 p.s.i. parts stannous chloride, 10 parts 58-202, 15 parts Celite Super Floss, and 1.5 parts sifted pine sawdust.

The two promoter pellets were added to the mill, which was then closed, rotated at 60 rpm. for 5 minutes, opened, and 57.5 grams of Zinc powder added. The mill was again closed and rotated for 20 minutes; no foam developed, and the mill was not subjected to increased pressure. The nails were uniformly plated with zinc, showing good brightness and receptivity to chromating.

8 Example 10 The mill of Example 1 was charged with 3,835 grams of roofing nails, 3,000 grams of glass impact media (3 parts 4-6 mesh spherical, 1 part 8-14 mesh nonspherical, 1 part 12-14 mesh spherical, 1 part 20 mesh spherical), and sufiicient water to cover the solid materials. A cleaner-promoter chemical pellet was formed by pressing at 5,000 p.s.i. the following materials:

Grams Citric acid 11.2 Diammonium citrate (buffer) 3.7 Stearic acid 0.3 Polyoxyethylene glycol (Carbowax 20M) 0.3 Stannous sulfate 1.5 Surfonic N-95 0.5 Sifted pine sawdust 0.4 Powdered zinc 2.0

The mill was closed and rotated for 5 minutes at r.p.m., uniformly tinning the nails without developing any foam or pressure. Next 57.5 grams of zinc was added, the barrel closed, and rotation continued for 20 minutes at 60 r.p.m. and F. The nails were then removed, rinsed and examined, revealing a 0.35-mil zinc coating with good adhesion and brightness. The diammonium citrate maintained the pH high enough that acid did not significantly attack the zinc plating metal particles.

Example 11 The mill of Example 1 was charged with 1,700 grams of golf cleats, 2,000 grams of glass impact media (4 parts 4-6 mesh spherical, 2 parts 14-20 mesh nonspherical, 1 part -100 mesh spherical), and sulficient water to cover the solid materials. To the barrel were then added a watersoluble bag containing 19 grams of chemicals and a 7.2- gram pressed bar. Formulations of these two additives were as follows:

WATER SOLUBLE BAG Sifted pine sawdust 1.2

The contents were preheated with steam to 125 -l30 F., after which the mill was closed and rotated at 60 rpm. for 5 minutes, cleaning and tin flash coating the cleats. Next 17 grams of zinc powder was added, and the mill closed and rotated for 20 minutes maintaining a temperature of approximately F.; the cleats were found to have a good coating of zinc.

Example 12 The mill of Example 1 was charged with 450 grams of fiat nominally Az-inch copper washers (0.693-inch O.D.), 1,000 grams of glass impact media (3 parts 4-6 mesh spherical, 1 part 8-14 mesh nonspherical, 1 part 12-14 mesh spherical, and 1 part 30-100 mesh spherical), and sufiicient water to cover the solid materials. A cleanerpromoter consisting of 5 grams citric acid, 5 grams diammonium citrate, 0.2 gram Carbowax 20M, and 0.1 gram Surfonic N-95, was then added, and the mill closed and rotated at 45 rpm. for 10 minutes to clean Example 13 To a 4.75-ft. octagonal horizontal barrel, adapted to be closed at both ends, was added 300 lbs. of /s-inch flat mild steel washers, 270 lbs. of glass impact media (3 parts 12-l4 mesh spherical, 1 part 20-45 mesh spherical, 1 part 31100 mesh spherical), and sufficient water to cover the charge. Next 1,500 grams of a cleaner having the following composition was added:

Parts Water 50 Concentrated H SO 90 Arosurf EO-66 3 .75

Armohib 25 0.375

The barrel was then closed, rotated 15 minutes at 125 F. to clean the parts, opened, and a 320-gram promoter chemical bar of the following composition added:

Parts Additive R (commercial equivalent) 40 Zinc powder 160 Tri(butoxyethyl) phosphate defoamer 20 Surfynol 485 5.5 Celite Super Floss 80.0

NaHCO 160.0

High viscosity water-soluble hydroxyethyl cellulose (NatrosoP 250H, commercially available from Hercules Powder Co.) 11.0

SnCl 80.0

The barrel was closed and rotated 5 minutes to tin the washers, opened, and 1 /2 lbs. Zinc powder added. The barrel was again closed and rotated for 30 minutes at 20 r.p.m., providing the washers with a bright, well-adhered 0.150.25 mil zinc plating. The NaHCO in the promoter chemical bar reacted with the acid, thereby hastening disintegration of the bar.

Example 14 Zinc powder and rotation continued for an additional 20 1 minutes. When removed from the barrel and rinsed, the nails were found to have a zinc plating which was extremely well-adhered, uniformly covered and 0.3 mil thick.

Example 15 To a tulip barrel of the type described in Example 14 was added 1 quart of lock washers (1,107 grams), 1 /2 quarts of spherical glass impact media (8 parts 12-14 mesh, 2 parts 45 mesh, and 1 part 91-100 mesh), sufficient water to cover the charge, and 20 grams of cleaner having the following composition:

Water 135 Concentrated H 50 243 Alcohol polyether (Arosurf E066) 20 Additive R (commercial equivalent) 5 Propargyl alcohol 5 The barrel was then rotated for 15 minutes at room temperature, after which time the lock washers were found to be celan and free from scale and oil. To the barrel was then added 7.93 grams of powder having the following composition:

Zinc powder 30.0 2,4,7,9-tetramethyl 5-decyne-4,7 diol reacted with 30 mols of ethylene oxide (SurfynoP 485, sold by Air Reduction Chemical and Carbide Co.) 1.0 Natrosol 250H 3.0 NaCl 5.0 Sodium formate (buffer) 100.0 Orzan AH-3 0.5 Carbowax 20M 0.5

At the same time 1 gram of a promoter chemical having the following composition was added:

SnCl 30.37 SS-202 0.585 Maple sawdust 4.72

The barrel was rotated for an additional 5 minutes, after which time the lock washers were found to have been uniformly tinned. To the barrel was then added 38.7 grams of zinc powder and rotation continued for 30 minutes at 52 r.p.m. An extremely adherent 0.3-mil zinc plating was found to have been applied, of the available zinc powder having been utilized.

Example 16 To a tulip barrel of the type described in Example 14 was added 1,276 grams of spring wire hose clamps (SAE 1065 steel) having a total surface area of 320 square inches, 10 lbs. of spherical glass impact media (4 parts 4-6 mesh, 1 part 12-14 mesh, 1 part 2045 mesh, 1 part -100 mesh) and one liter of water. To the barrel was then added 12 cc. of one composition containing 24.95% water, 74.71% 52 B. H 80 and 0.34% Additive R (commercial equivalent), and 12 cc. of another composition containing 48.6% water, 27.1% 52 B. H SO 10.0% CuSO -5H O, and 14.3% NaCl. The barrel was rotated at 60 r.p.m. for 15 minutes to clean the parts, after which 0.110 gram Additive R (commercial equivalent), 0.634 gram Additive A and 0.45 gram SnCl together with 1.8 grams cadmium powder, were added. After 5 minutes a uniform tin flash plate was obtained. Fourteen grams of powdered cadmium were added and rotation continued for another 25 minutes. An excellent cadmium plate was obtained.

Example 17 T o the barrel of Example 14 was added the same load of hose clamps, impact media, and cleaners as in Example 16 for cleaning carried out in the same manner. Next a promoter containing 0.7 gram CdO and 0.136 gram Additive A was added and allowed to dissolve for 5 minutes, and 2 grams of powdered zinc then added. The barrel was again rotated, and a cadmium flat plate obtained after 5 minutes. 8.8 grams of cadmium powder was added and rotation continued for 20 minutes, yielding an excellent cadmium plate.

Example 18 A load of hose clamps was cleaned as in Example 16. Next 0.110 gram of Additive R (commercial equivalent), 0.364 gram Additive A (as in Example 16) and 0.45 gram SnCl were added, together with 1.2 grams zinc powder. A uniform tin flash plate was obtained in 5 minutes, after which 11 grams of tin powder was added. Rotation was continued for 20 minutes, yielding a welladhered mechanically applied tin plate; the plating was somewhat rough, indicating the desirability of slightly more dispersant.

1 As used hereinafter, Additive A is the reaction product of 102 parts water, 63 parts Carbowax 20M, S) parts HCL 13 parts o-toluidine, and 13 parts 36% aqueous solutlon of HCHO.

1 1 Example 19 A barrel of the type employed in Example 14 was loaded with hose clamps, impact media, and water as in Example 16. To the barrel was then added a cleaning composition consisting of 8.25 grams 66 B. H 80 0.055 gram Addi tive R, 1.58 grams CuSO -5H O, 2.27 grams NaCl, and 7.7 grams of water. The barrel was then rotated at 60 r.p.m. for 15 minutes to clean the parts, after which promoter chemical consisting of 0.114 gram Additive R, 0.0364 gram Additive A, and 0.45 gram SnCl was added, and the barrel rotated for 5 minutes to effect solution. Next 0.9 gram of powdered zinc was added and the barrel rotated for 5 minutes to provide the hose clamps with a tin flash plate. An additional 11 grams of zinc was then added, and rotation continued for 20 minutes, yielding a uniform zinc plating.

Example 20 To a tulip barrel of the type described in Example 14 were added 400 grams of hose clamps, 1,558 grams of glass impact media (3 parts 46 mesh spherical, 1 part 814 mesh spherical, 1 part 12-14 mesh spherical, 1 /2 parts 90-100 mesh spherical), and suflicient water to impart fluidity. The barrel was set in rotation and the following cleaning composition added:

Grams NaHSO 10.0 CdCl 0.4 Additive R (commercial equivalent) 0.1 Additive A 0.0

Example 21 The plating barrel of Example 14 was charged with hose clamps, impact media, and water as in Example 18 and the following cleaner added:

Concentrated HCl ml.

Additive R (commercial equivalent)0.05 gram Additive A"0.05 gram PbCl 0.5 gram The barrel was rotated at 52 r.p.m. for 10 minutes to clean the parts and 1.0 gram of zinc dust then added; after 5 minutes further rotation, it was found that a lead flash plate had been galvanically deposited. Next 3 grams of zinc dust and 0.1 gram of Additive A were added and rotation continued for 20 minutes; a 0.2-mil zinc plating was obtained.

Example 22 The plating barrel of Example 14 was charged With hose clamps, impact media, and water, and the following cleaner added:

Concentrated HC15 ml.

Additive R (commercial equivalent)--0.05 gram Additive A0.05 gram HgSO 0.S gram Surfonic N-100-0.05 gram The barrel was rotated at 52 r.p.m. for 5 minutes to clean the parts and 1 gram of zinc dust then added; after 5 minutes further rotation it was found that a bright mercury coating had been galvanically deposited. Next 3 grams of zinc dust and 0.1 gram Additive A were added to the barrel and rotation continued for min- 12 utes. It was noted that the pH had risen to 5.5, while a fairly bright coating of zinc had been mechanically applied.

Example 23 To a large open, tapered barrel was added 100 lbs. of 8d nails, and 275 lbs. of glass impact media of the type used in Example 1. Suflicient Water was added to cover the nails, after which cleaner having the following composition was added:

Grams NaHSO 706 NaCl 91 CuSO 5H O 64 Additive R (commercial equivalent) 1.9

The barrel was rotated for 15 minutes at 66 F., cleaning and flash-coppering the nails. To the barrel was then added 500 grams of zinc powder and rotation continued for 10 minutes, after which an additional 500 grams of zinc powder and 500 grams of NaHSO was added. Rotation was continued for an additional minutes, after which the nails were found to have been provided with a bright uniform zinc plating.

Example 24 This example was carried out in an open-ended cylindrical barrel having an effective axial length of 18 inches, an outer diameter of 36 inches, a 7-inch diameter opening at one end, and a 16-inch diameter opening at the other end. To the barrel, which was provided with internal lifter bars, was then added 100 lbs. of 8d nails, 275 lbs. of impact media as in Example 23, 706 grams NaHSO 20 grams SnSO 23.6 grams Zinc powder, and enough water to leave a small puddle as the barrel was rotated. The barrel was then rotated for 2 minutes to clean and tin-plate the nails, after which 1.5 grams of Additive R (commercial equivalent) was added and rotation continued for an additional minute. Next 500 grams of zinc powder was added and the rotation continued for 10 minutes, providing the nails with an unusually smooth 0.2-0.5 mil zinc plating. An additional 500 grams of zinc powder was then added and rotation continued for an additional 20 minutes. The resultant coating was bright, smooth, well-adhered, and excellent in coverage, the average thickness being 0.6 mil.

Example This example was carried out in an open-end barrel similar to that of Example 24, except that the effective inner axial length was 24 inches and the outer diameter 48 inches. To the barrel was added 191 lbs. of spring washers, having a total area of approximately 572 square feet, 220 lbs. of glass impact media (4 parts 46 mesh spherical, and 1 part 8-14 mesh nonspherical, 2 parts 12-14 mesh spherical, and 1 part 100 mesh spherical), and 2,900 ml. of each of the following cleaner components:

Sufficient water was added so that small puddles remained near the bottom of the barrel while rotating at 15 r.p.m. Temperature was adjusted to 67 F. and the barrel rotated for 15 minutes to clean the washers and provide them with a copper displacement flash plate. Next, 215

13 grams of zinc powder and 91-gram bars of promoter chemical having the following composition were added:

NaHSO 45.0

Additive R (commercial equivalent) 5.0 Additive A 2.0 Pine sawdust 26.0 SnCl 21.0 Stearic acid 1.0

Rotation was continued for 5 minutes to tin the Washers, after which 4,050 grams of Zinc powderwas added and rotation continued for 30 minutes to provide a 0.4-0.5 mil zinc plate having good appearance and excellent adhesion.

The composition and method described in this example has been used to plate zinc on hardened steel, mild steel, stainless steel, ferrous powder metallurgy parts, malleable cast iron, and tungsten carbide tire studs. With omission of the CuSO -5H O and NaCl, the composition and method have also been used to plate zinc on copper, brass, zinc, stainless steel, and white metal.

Various metal powder other than zinc have also been plated in accordance with this example. To illustrate, cadmium, lead, tin, 60/40 tin/lead alloy, and 50/50 tin/ zinc mixture have all been plated effectively on steel, brass, copper, and stainless steel, no copper flash being needed for the last three named substrates.

Example 26 To an open-ended barrel of the type described in the preceding example was added 3 cubic feet (210 lbs.) of Palnut lock washers, and 3 cubic feet of glass impact media (8 parts 12-14 mesh spherical, 2 parts 20-45 mesh spherical, 1 part 31-100 mesh spherical), and 1,368 grams of a cleaner having the following composition:

Grams Water 453 Concentrated H 50 815 Arosurf EO-lOS 67 Additive R (commercial equivalent) 16.7 Propargyl alcohol 16.7

The barrel was then rotated 7 minutes at 6-5" F. to clean the parts, after which powdered material having the following composition was added:

Grams Zinz powder 131 Surfynol 485 4.4 Natrosol 250H 13.1 NaCl 21.8 Orzan AH-3 2.2 Orzan S 2.2 Carbowax 20M 4.4 Sodium formate (buffer) 680 At the same time a powder having the following composition was added:

Grams SnCl 66.5 85.202 1.27 Maple sawdust 10.25

The barrel was then rotated for minutes to tin the lock washers, after which 5,900 grams of zinc was added and the barrel rotated an additional 30 minutes at 16 r.p.m. The plating was found to be firmly adhered and to have an average thickness of 0.57 mil:7%. When individual parts were pounded vigorously with a hammer and then tested for adhesion by applying a stri of normally tacky and pressure-sensitive adhesive tape, rolling down firmly, and stripping it free quickly, virtually no zinc was removed.

Example 27 This example was carried out in an open-end barrel similar to that of Example 24 except that the effective inner axial length was 48 inches. To the barrel was added 325 lbs. of mild steel washer-type lock nuts having a surface area of 1,040 square feet, 840 lbs. of glass impact media (4 parts 4-6 mesh spherical, 1 part 12-14 mesh spherical, 1 part 8-14 mesh nonspherical, 1 part -100 mesh spherical), and about 15 gallons of water. The barrel was rotated at 24 r.p.m. while adding 5 /2 quarts each of Part A and Part B, as described in Example 25. After 15 minutes the parts were found to be clean and provided with a copper flash plate. Eleven 91-gram bars having the following composition were added:

NaHSO 44.6 Additive R (commercial equivalent) 5.4 Additive A 1.7 Wood flour 26.1 4 parts SS-202 absorbed in 3 parts puffed borax 0.57 SnCl 20.5 Stearic acid 1.13

The barrel was rotated for 5 minutes to dissolve the bars, after which 14 lbs. of zinc was added and rotation continued for an additional 25 minutes. A thin galvanornechanical flash plate, with a mechanical plating of zinc overlying the flash plate, was obtained. Plating was considered acceptable, but the speed and efliciency were both lower than when one pound of zinc was added as a driving metal 5 minutes before the plating zin powder was added.

What I claim is:

1. A method of providing a metal substrate with a firmly adherent uniform plating of a mechanical plating metal, comprising the steps of:

(1) flooding the surface of said substrate with an agitated aqueous solution which contains components essentially comprising strong acid,

(2) continuing to agitate acid solution until the surface of the substrate is essentially clean and free of oxide,

(3) without prior rinsing of said substrate, adding to said solution a quantity of finely divided mechanical plating metal which is suflicient to provide the desired thickness of said mechanical plating metal,

(4) continuing to agitate said solution and the components therein until the desired thickness of said mechanical plating metal has been mechanically applied over the surface of said substrate, and

(5) removing said solution and components suspended therein from the plated substrate.

2. A method of providing a metal substrate with a firmly adherent uniform plating of a mechanical plating metal, comprising the steps of:

(1) flooding the surface of said substrate with an agi tated aqueous solution which contains components essentially comprising sufi'lcient acid having a dissociation constant of at least 10 to lower the pH to not more than 4,

(2) continuing to agitate said solution until the surface of the substrate is essentially clean and free of oxide,

(3) without prior rinsing of said substrate, adding to said solution (a) a quantity of finely divided mechanical plating metal which is suflicient to provide the desired thickness of said mechanical plating metal,

(b) means for (i) dispersing particles of said mechanical plating metal in acidic solution and (ii) inhibiting corrosion of said mechanical plating metal by acid, and

(4) continuing to agitate said solution and the components therein until the desired thickness of said mechanical plating metal has been mechanically applied over the surface of said substrate, and

(5 removing said solution and components suspended therein from the plated substrate.

3. The method of claim 2 wherein the substrate is a ferrous metal which is provided with at least one thin flash plate of nonferrous metal not later than Step (3).

4. The method of claim 3 wherein the flash plate is ap plied by displacement plating.

5. The method of claim 3 wherein the flash plate is applied by galvanomechanical plating.

6. The method of claim 3 wherein a first flash plate is applied by displacement plating and a second flash pate is applied by galvanomechanical plating.

7. The method of claim 2 wherein the aqueous solution contains a hydrogen embrittlement inhibitor.

8. A method of providing small metal parts with a firmly adherent uniform coating of a mechanical plating metal, comprising the steps of:

(1) placing said parts in a mill with aqueous solution which contains ingredients comprising suflicient acid to lower the pH to not more than 4,

(2) continuing to agitate said solution until said parts are essentially clean and oxide-free,

(3) without rinsing said parts, and not later than at this time, adding to the mill a small amount of a salt of a galvanomechanical plating metal, said salt being soluble in said solution, and

(4) without rinsing said parts adding to the mill finely divided particles of a driving metal which is more anodically active in said solution than said galvanomechanical plating metal,

(5) continuing to agitate said solution, whereby said galvanomechanical plating metal is deposited on said parts,

(6) providing in said solution after the parts are cleaned and not later than at this time finely divided particles of said mechanical plating metal in quantity sufiicicut to provide the desired thickness of said mechanical plating metal,

(7) providing in said solution not later than at this time means for (a) dispersing particles of said mechanical plating metal in acidic solution and (b) inhibiting corrosion of said mechanical plating metal by acid,

(8) continuing agitation of said solution and the components therein until the desired thickness of said mechanical plating metal has been mechanically applied to said galvanomechanical plating metal over said substrate, and

(9) removing the plated parts from said solution.

9. The method of claim 8 wherein impact media are present in the solution throughout the process.

10. The method of claim 8 wherein the mill is provided, not later than Step (3) with the dissolved salt of a displacement plating metal which will displacement plate on said substrate metal.

11. The method of claim 10 wherein the substrate is a 4 ferrous metal and the displacement plating metal is copper.

12. The method of claim 10 wherein a hydrogen embrittlement inhibitor is included in the solution during the acid cleaning step.

13. The method of claim 8 wherein the solution in Step (1) contains a surfactant.

14. The method of claim 8 wherein a plurality of small parts are treated simultaneously in a rotary barrel.

15. The method of claim 14 wherein the rotary barrel is open to the atmosphere.

16. The method of claim 14 wherein the driving metal particles and the mechanical plating metal particles are formed of the same metal.

17. The method of claim 16 wherein the metal particles are all added at the same time, the means for dispersing and inhibiting corrosion of said particles being added therebefore.

18. The method of claim 14 wherein the particles of mechanical plating metal are added to the solution after the desired degree of galvanomechanical plating has been achieved, the means for dispersing and inhibiting corrosion of the mechanical plating metal particles being added to said solution after galvanomechanical plating and no later than the time said mechanical plating metal particles are added.

19. The method of claim 14 wherein the same means disperses particles of the mechanical plating metal and inhibits the corrosion thereof.

20. The method of claim 19 wherein the means is a blend of propargyl alcohol, dispersants, and the reaction product of acidified dehydroabietyl amine, acetone and formaldehyde.

21. The method of claim 14 wherein the galvanomechanical plating metal is tin and the driving metal is zinc.

22. The method of claim 21 wherein the mechanical plating metal is zinc.

23. A no-rinse method of providing small ferrous metal parts with a firmly adherent uniform plating of a dif- 0 ferent metal, comprising the steps of (l) placing said parts in a rotary treating barrel together with components comprising (a) water (b) impact media (c) surfactant (d) sufiicient acid having a dissociation constant of at least 10 to lower the pH to not more than 4,

(e) water-soluble salt of a displacement plating metal which will displacement plate on clean iron, and

(f) hydrogen embrittlement inhibitor,

(2) rotating said barrel until (a) the parts are essentially clean and oxide-free,

and

(b) a thin layer of said displacement metal has plated out on the clean, oxide-free surfaces of said parts, thereby tending to (i) reduce hydrogen embrittlement of said parts (ii) prevent the cleaned metal from dissolving, and

(iii) improve the adhesion of subsequently applied layers,

(3) without rinsing or separating said parts from the remaining contents of said barrel, adding to said barrel (a) salt of galvanomechanical plating metal, said salt being soluble in the liquid contents of said barrel,

(b) means for (i) dispersing particles of said mechanical plating metal in acidic solution and (ii) inhibiting corrosion of said mechanical plating metal (c) a small amount of particulate driving metal which is more anodically active than said galvanomechanical plating metal,

(4) continuing to rotate said barrel, whereby a layer of said galvanomechanical plating metal is deposited on said displacement metal layer over said parts,

(5) without rinsing or separating said parts from the remaining contents of said barrel, adding to said barrel, particulate mechanical plating metal (6) continuing to rotate said barrel until the desired thickness of mechanical plating metal has been mechanically applied to the layer of galvanomechanical plating metal over said parts, and

(7) separating the plated parts from the remaining contents of said barrel.

References Cited UNITED STATES PATENTS 2,689,808 9/1954 Clayton 117109 (Other references on following page) 17 18 References Cited ALFRED L. LEAVITT, Primary Examiner 3,141,780 7/1964 Simon et a1. 1061 J. A, BELL, Assistant Examiner 3,328,197 6/1967 Simon 1061 3,400,012 9/1968 Golben 106-1 US. Cl. X.R.

5 OTHER REFERENCES 106 1,117 160 Chemical Abstracts, vol. 65, 1966, p. 14963f.