US3132043A - Metal plating - Google Patents

Description

May 5, 1964 E. T. CLAYTON 3,132,043

' METAL PLATING original Filed June 16, 1949 Mapu Mmczs 44477/ in..

mL P7-lags INVENTOR se/7W Taiwan;

AITORNEYS niilication.

Patented May 1364 v 3,132,043 ,Y METAL PLATING ErithT. Clayton, Baltimore, Md., assig'nor to Peen Plate,

Inc., Baltimore, Md., a corporation of Maryland y Continuation ofapplication Ser. No.- 670,355, May 27,

V`:19.57, which is a" continuation of applications Ser..No. A 99,'S67,`.June 16, 1949, and Ser. N0.V 3,537, Jan. 21,

1948. application Mar. 25, 1963, Ser. No.` 267,854

` loclaims. (Cl. 117-109) This invention relates to metal coatings and particularly to such coatings progressively built upto desired thickness on a base'surface of metal or other material. This application is a continuation of my application Serial No.

670,355, iled May 217, 1957, now abandoned, which is a 1 contacty and the opposite the direction of the base surface extending the area of area of the particle subjected to the blows. f l

Y' For'instance, particles of *zinc dust intermixed in a iluid medium with heavier'particles and the articles to be coated may Vbe treated in a tumbling barrel provided.

" with peripheral riser bars and rotating on its axis to stir continuation of my application Serial No'. 99,567, led

lune/'16, 151949 which, in turn, is a continuation-in-part of Ymyapplication Serial No. 3,537, tiled January 21, 1948,

nowi-Patent`2,640,001, issued May 26, 1953, and application ,Serial No. 14,639, filed March l2, 1948, and Serial No."77,269 filed February 18, 1949, both now abandoned. Airobject `ofthe invention is"to`provide a coating which willbe inexpensive inv application, attractive in appearance and effectively adherent to the base surface Y and protective-against weather, wear and corrosion.

'i To attain this structure a compositeV coating is built upV of1rnacroscopic solid particles of the coating metal and lift lmaterial and'drop it back onto the charge at the bottom, as set forth in my copending applications'above referred to.` Or the coating may be built'up of colloidal particles rubbed oirfr'omzinc coated shot and impacted in intertting Yengagementfto form the protective layer.

Ihave found that it is'of critical importance tothe strength of the bond thatV al most intimate metal-to-metal contact should be attained overtheinterengaging area of each particleand the base surface.l Oxide films and other ilms of inorganic salts of the metals, andmany other compounds, weaken or prevent adhesion, and must be avoided or removedsfrom between the surfaces to permit themetals toadhere. Such films may be reduced or removed mechanically byattrition or chemically by'uxes or both, it beingY important as the depositing operation progresses to prevent or retard reforming of any weakening or corrosive iilmon the surfaces of the particles.

It will thus be seen that there are two things are done to establish thejbes'tgcoating. The result is, as shown'in FIGigZ, an inclusion'throughout the coating of an organic deposited on the base surface and brought into surfaceto-surface contact and adhesion therewith and overlaid with continued similar deposits of said particles interftt'ed in metal'tometal contact and cohesion into a solid surface, covering of desired depth.

Further objects of the invention, particularly in the method ofgapplying-the coating Yto `Ametal and othersurfaces withoutapplication of electric current or melting heat, will appear from the following specitication `and the accompanying drawing forming la partf thereof, whereinif' Y f 1 I f lfis a representative cross-section of a metal coating lembodying myV invention, and

FIGwZ is a portion of the cross-section at great'rnagj Referring to a typical embodiment of the-invention as. .shown FIG. 1, a coating of cleanmetal particles, for` examplezinc, is applied to abase article, for example steel, the undersurface of the coating being formed of `zinc particles broughtto the base surface and adhered thereto by suiciently concentrated ypressureto give a metal-t'o-metal contact ydeveloping interatomic attractive forces'fbetween the metals. This initial or bottom `layer of particles covers the entire coated area continuously,

each particle being Vindividually"'attached to the steel surface by adhesionQfthe adhesive forces brought into play byf-the physical metal-to-metal contact of clean surfaces joined-"together by pressure 4and locally generated heat. `Me'c'zhanical bonding ofthe particles'into the tooth or 'surface irregularities of the base may play a part inthe 1 Vattachment of the coating, but it is believed that the main forces concerned in the'weldment are molecular or atomic in Y nature and involve Van 'der' Waals forces, covalent bonds, metallic linkages and ionic; bonds. All of lthese forces'fcan'" exist when a second metal atom is introduced kinto an assemblage of other metal atoms.

lbouclis .formed securing each particle inl place. This An importantdiference between the flux and the lilm-l substance forming a ilm over the unbonded clean surface areas of the particles; There may also be present,

inclusions of raliuxing compound, or reaction products thereof,ispac ed from the clean metal particle surfaces by the organic lilm.'` j Y Y.

The-flux is used Vto remove oxides and other contaminating lilmsfrom the metal particles and the surface to be coated,"and theilrn forming material is'used to film the ,clan surface of thesmetal particles and the surface toI be coated and protectthem `until theweldment ofthe particles to the surface is accomplished and at which time the film forming material is positioned in interstices in thecoating.v

rlfhese two functions are separate and distinct even thoughjboth ofthem may be confined to thejuseof .a

single filming material'which acts both as a flux and asVV v a' film former.

Fluxes should 'iotbe". confused withor Ycompared to lm'forniers as no flux of the prior art serves both func-V tions therlm-former may serve both functions. On the contrary, however, there `,are film formers lwhich are acid or alkali in character` and oily and lm forming and thus combine` in one; material both functions. Evenv though both functionsfare concentrated in one material they are-both equally/*desirable tol'obtain the best coating. The fluxing operation can be aided by mechanical scrubbing if the plating operation is Icarried, Von in` an environment where reoxid-ation of the metal' isl reduced to a minimum.

ing material is that` the flux vis not sticky, while the surfacefactive@filming"material is not only sticky but adheres most'strongly to clean metal so that it is re'- tained in the interstices of the coating .where it does` exert a deinite'protectiveand beneficial efect.

impacting ofthe zncparticles tends to hatten them in The filmingmaterial, because of its sticky and adherentnature-{is thus retainedV in the coating in much largery traces than the reaction productsof the liux.

In .-tlrose cases where only a' flux such as disclosed in the priorj'art is retained in the coating; theveffects are all harmful its life land usefulness: Such'ux orv other contaminating material acts to reduce-the'thickness and strength and `adhesion of the coating and to increase its porosity and further `reduce the useful life.

' Where corrosive iiuxes are u-sed, such as zinc or ammonium chloride, the harmful effectsrof such retention of such inclusions of :flux in the coating are greatly magnified and cause a 'bloomiand actual disintegration of the coat-ing in time rendering it commercially impractical.

An effective procedure mixes the articles such as steel bolts, nuts and the like with the zinc dust or powder and steel shot in a tumbling container preferably sealed to exclude 'In this case aqueous or other liquid suspending medium is omitted. The tumbling of the container subjects the articles lto direct contact with the zinc particles under conditions of rubbing, attrition Vand impact remorving or penetrating surface iilms andv bonding the metal surfaces together. The exclulsion of oxygen tends to avoid recurrence of oxide films and the clear metal surfaces of the zinc particles become attached directly to the metal of thel articles accumulating and confirming the particles as a covering base` layer of zinc grains having strong adhesion to the steel and strong cohesion to each other at their areas of contact. Upon this ad-` y hering base layer the continued tumbling of the dry mixture deposits and attaches the zinc particles by their clear Y developing bonding forces of great strength brought intov play by the union of the clean metal surfaces under the pressures and -heat generated by the mechanical forces used to distort the particles. These 'forces appear to involve combination of one ro more of `the following forces: Van der Waals forces; covalent'bonds; metallicl linkages; and ionic bonds. The slight inclusions of removedl oxides are negligible and substantially undetectable and there are no intervening-films or deposits from a suspending liquid. The intensified bonding action adapted this procedure to a variety of metal coatings yand at room Vtemperature is effective with aluminum as well as the softer zinc, cadmium, lead and tin giving relatively thick deposits, for instance .006, 'in short times of treatment.

With the metal particles thus surface-worked in the tumbling or other operation, the particle surfaces develop a'highfree energy because of the decrease in the volume of the strain free matrix which in the resultant intimate metal-to-metal contact with each other at the areas of intertting there appears to bel some recrystallization which in some cases merges across grain boundaries.

4 Y the particles reduces and removes them to a degree causing the films to part between the interfitting metal surfaces so that the cohesive forces of metal-to-metal cont tact are accompanied and increased by recrystallization across the boundaries. We then, under such conditions, have areas of metal-to-metal bonding interspersed with areas of intervening thin iilm formations and secondary valence bonds are available to aid in holding the surfaces together in contrast with the reactive inclusions which intervene and weaken and eventually corrode the bondingareas. The building up of the coating of this invention thus provides intimate metal-to-metal bonding with incident recrystallization across the boundaries or at other points a random bonding with incident recrystallization across the boundaries or at still other points combines this with a random mixture of such bonding with film attraction of the surfacesby secondary valence bonds, this f latter combination resulting where there is employment of Some particle apparently grow rapidly in size with resulting grain growth across the particleY boundaries so that invidiualsmaller particlesamalgamate into larger grains. Enlarged crystals of continuous dense metal apparently develop by recrystallization involving the amalgamation of a number of particles originally present in the coating to form large grains. It is also true that some recrystallizationmay occur within the individual boundaries of a particular particle, both types probably proceeding together.

Where, as with processes employing a liquid suspension of the metal particles, there is a wettingV film initially present between the particles at the areas of interiitting,

the impacting thinsthis film and displaces it except for. y

the residue retained chemically as in the case of ionic solu- Vas thosey merely inhibiting oxidation, the compacting of film acting to coat-and protect.

I amine respectively.

liquid suspensions for the metal particles. It is important that this liquid act to inhibit oxidation and it is also advantageous to combine with this a surface-active effect wetting the surfaces of the particles and the base metal in a manner tending to develop adhesion between-them. By referring to the surface-active effect, it is that class of organic material capable of exhausting itself on clean metal and other surfaces as a thin molecular film, said The film forming substances that are in the interstices of the coating have this surface-active effect. gether into a unitary lstructure by the secondary valence bonds of the intervening iilms of an oxidation inhibitor and by recrystallization `across the interiitting surfaces of f said particles, said recrystallization penetrating and interrupting said intervening films. Y

Ihave found Athat aliphatic carboxylic compounds of the class belonging to fatty acids and their derivatives possess very desirable characteristics in connection with the liquid suspension of the metal particles for plating. Of these compounds asubstituted ammonia compound is particularly efiicaceous. vFor example, if R represent thecarbon chain corresponding to the fatty acid, then the primary amine is RNH2 in which one of the hydrogen ions of the ammoniay hasV been replaced with an alkyl radical. Where two or three of the hydrogen ions are replaced, the amine becomes a secondary or tertiary In the plating of some metals, it is sometimes an advantage to substitute an organic alkali suchas the amines just discussed for the fatty acids, as they are less reactive and cause less gassing in the mill. ln some types of mix, the use of fatty acid causes formation of substantial amounts of metal soaps which may thicken the liquid to the point where good plating is impaired. The use of the organic alkali eliminates the formation of this type of soap.V

A preferred primary amine is one derived from a soya base and has the following approximate composition: Hexadecyl, 10 percent; octadecyl, 10 percent; octadecenyl, 35 percent and octadecadienyl, 45 percent. A tertiary amine derived Vfrom this primary amine is obtained by condensing ethyleneoxide with the primary amine.

Since the amines areY alkaline, theyfmay be reacted with Vother fatty acids or with organic or inorganic acids to produce neutral salts.' Somev of these salts, for example the amine acetate formed by reacting the amine with acetic acid, have the desired-characteristics for platmg.

. Thel amides are another type of aliphatic carboxylic derivative which produce satisfactory results. The primary amide as used in my method is defined-as the l,derivative of an organic acid in which an amine group replaces the OH group.V Therefore, using R as before,A a primary amide is RCONHVZ. Secondary and tertiary amides'are also effective. Both the fatty acids above six carbons in chain length, and the fatty derivatives just discussed, are instances of oily sticky film forming compounds that have The particles are thus massed tofthe fact that recrystalli'zation occurs under stress organic acid or weak alkali such as those previously. menv tioned.

4While notwishing to be limited to 4any theory as to the p surprising fact that any oily lm forming material promotes the welding Vor joining of metal surfaces, it appears that the lm forming material may not attach itself to an oxidized surface, or attaches itself less strongly. In the latter`case it is more apt to beremoved by the abrasive forces involved in the tumbling or agitating operation, thereby exposing the oxide to attack by'abrasion and by any organe acid or weak alkali present. The

fatty acidfilm formers oxides assoaps.

- After this oxide film has Vbeen removed from the surface will directly attack anddissolve of the particle, the oily film former reforms on the clean metal and adheres tightly, thereby shielding it not only from further chemical attack, but also from reoxidation Subsequentimpacts then squeeze out most or all residual traces of `ihnformer which thushas a tendency to collect at the boundaries of the particle and become entrapped in the coating as inclusion in microscopic amount.I These inclusions are also highly beneficial as aholding aid and inzconferring tarnish resistance to the coating, and show inthe-'figures as the approximatelyround black areas concentrated particularly' at the boundariesor 4nnbonded Vsirfacesvof the` grains or particles.l These round dark s'pots"`a1'51` ear occasionally in the interior of the larger masses and are believed to have been left by recrystallization across grain boundaries. When a particle is attened bythe suddendrastic impact, the work done on it raises its lenergy level substantially and imparts considerable -atomicrnobility to the disarranged atoms in the particle. Succeeding impacts, it is thought,factually cause recrystalliz'ationV to occur between particles. This recr'ystallization occurfs during the process and not after the process is completed. 1" Hence, it is not intended to imply that the -material exists in an annealed state. =Normalrecrystallizationprocesses produce an annealed condition with equiaxed grains, but in the instant process y d results in deformation in a preferential manner. When using the amine or amine salt in the carrying or tumblingdliquid during the plating process, the mill can be Aoperated indefinitely at a satisfactory plating eiciency without, the necessity of removing the powder and the liquid for washingand purification. Fresh metal dust mustcontinu'allybe added to replace' that platedl on the objects.' It is also necessary to add fresh amine from time to time, as well as further carrierliquid to 'replace lthat lostinfdragout on the objects removed.'` If desired, the dragoutliquid may be recovered by washing, distillation'or other means, and returned to the mill for reuse. Viln addition to being organic alkalies, the amines are also emulsifying agents. Furthermore, they are cationic wetting agents and "render the surfaces of the metalilakes water rejecting and oil accepting surfaces. Consequently, by, taking advantage of this property, I can use plain waterinlieuV of the organic solvents set forth above as amajor.in'gredientof my tumbling media.` While the the property ofexhausting themselves on the surfaces of fthe metal dusts used'in coating, and on the surfaces-of organic solvents are suitable in some instances, particularly due to their expense, inflammability and their -toxicity, they are sometimes less desirable than plain water.

Therefore, by using amines in water Aas cationic wetting agents either alone or in combination with a water soluble oil the metal being processed, Zinc for example, is coated `with lubricant and satisfactory plating will result.

The amines may be reacted chemically` to produce other Very suitable compounds for use with water as a plating fluid.4 For example, fatty acids may be reacted to form water soluble nonionic surface active agents, the fatty acid amines may be condensed Vin ethylene oxide to produce water soluble cationic wetting agents.

These oily film forming detergent materials act to coat the particles of metal and the metal surfaces, and to shield them from reoxidation once they have been cleaned. Many of them are powerful detergents and aid in removal ofv oxide. Others, such as the fatty acids, for example, have chemical oxide solvent properties of their own, and thus also aid in cleaning the particles of oxide. The filming material thus may act in one ormore of several capacities: either as a physical film which acts as a barrier between the metal particles and further corrosion by oxy-` gen; or as a chemical solventfor oxides; or as a detergent or cleansing agent. Cationic and non-ionic wetting agents, detergents, oils and gums, are useful in promoting the coating. Specific examples of materials suitablefor use with water are the water soluble'glycols such as ethylene glycol or a cellulose gum material such as carboxymethyl cellulose used with ammonia or other alkali cleanser.

When high temperatures are necessary, special carrier organic liquids capable of withstanding heats up to 250 degrees centigrade or higher must be used. lOrganic liquids that have been found suitable include certain processed whale oils, some organic phosphates and some of 4the glycols. Some of the saturated fatty acids, such as steal-ic, may be used alone as both the carrier-liquid and the plating agent, lbecause at high temperatures these materials fonn thin liquids. In the plating of metals whose recrystallization temperatures involve heats in excess of approximately 300 degrees centigrade, organic liquids cannot be used and it is necessary to usefused salts as the carrier liquid. v

l `The choice of the chemicals for plating depends on the type and character of the objects to be plated, the kind of metal it is desired to plate, and thickness of the coating desired, as well as its brightness and smoothness, and the speed at which it is to be deposited. Taking zinc by way of example, it may be plated satisfactorily in water using one ofthe water plating agents just discussed.V This will give smooth thick bright coatings. Zinc may be plated equally well in nonaqueous systems at elevated temperatures using whale oil, tin fat, tributyl stearate or otherV in all of these ways. Copper and silver, for example,

must be deposited at elevated temperatures.

In the ,nonaqueous field, some of the surface active agents found useful in promotingplating include the Vvegetable and marine oils and the fatty acids derived` from them, such as oleic, linoleic, cluponadonic, caprylic, cap'Y ric, myristic, palmitic and steario-to name 'a fewl of those specially suitable. In particular," the distilled fatty acids from linseed or soya oils ae very efficacious. It is rather remarkable that an oil or fatty acid which is an ex#V tremely slippery lubricating material should lbe effective' in applying a metallic coating to a metal object. On the face of it, it would appear that if it were desired to apply a metal coating by hammering or rolling with small balls, the last thing for use to accomplish this end would be a lubricating oil.

For successful metal plating in the tumbling mill, it has been found that the volume of liquid to metal powder is extremely important. A large range is permissible and different effects result where the quantity of liquid used is small and where the liquid to metal ratio is large. If too little liquid is used, the mixture is pasty. The material may then pack loosely around the article being plated and it is then shielded from further action; on the other hand, if a large excess of liquid is used, the coating time is increased and the metal deposited on the articles tends to be thinner and brighter.

Where no balls are used, the small objects being plated serve the same purpose as balls. In other words, when plating a charge of small wood screws, for example, these screws are adapted to take the place of balls. This would simplify the process in that it would not be necessary to separate the screws or other small objects from any steel balls and the screws or other small objects would be very nearly as effective.

The use of small balls is especially advantageous in the plating of irregular shaped objects having exterior and interior surfaces inaccessible with large balls Vof the size customarily employed in ball mills. By using shot or small balls a good coating of such irregular shaped objects, both exteriorly and interiorly thereof, is effected. In place of round balls, crushed iron and shotrrnay be used, the sharp broken corners of this type of material assists in reaching into recessed areas that may not be reached even by very small round shot. In lieu of the crushed shot, other broken or sharp pointed pieces of iron may be substituted where it is desired to plate` to the bottom `of threads or under nail heads or other similarly secluded areas. n are: small brads and nails, tacks, nail whiskers, burnishing needles and cones. Care must be taken in selecting the size and character of the grit used to prevent it getting caught in recesses such as they slot on the head of wood screws. Y

The vtemperature at which plating is done depends on the metal being plated. It is necessary to operate within the minimum recrystallization temperatureV range for drastically cold-worked metals. In the case of metals such as zinc, tin and lead which recrystallize at or below room temperature, the plating may advantageously bedone at room temperature. There is no disadvantage, however, to plating these metals at higher temperatures. The operation at more elevated temperatures tends to promote more rapid build-up of the coat and greater adherence. The recrystallization temperatures of other metals ranges on up and is 150 degrees centigrade for aluminum, 200 degrees centigrade for copper and silver, 4S0-degrees centigrade for nickel etc. Heat generated at the point of impacts may be sufficient to raise the temperature locallyV to the minimum'for recrystallization, and thereby secure plating even when the general temperature of the bath is below the recrystallization temperature. i

It has also been found more satisfactory to exclude airA from the interior of the mill and operate with the mill sealed. The exclusion of air is not necessary for plating, but is highly desirable and permitsbright metal plating.

Materials of this sort which are suitable The small steel shot or balls serve to hammer the metal derived from fats, tallow, vegetable, marine or organic oils as, for instance, linoleic acid, linolenic acid, oleic acid, caprylic acid, capric acid and especially suitable are those derived from rapeseed, ilaxseed and soyavbeans. In general, any of the fatty acids may be utilized. Y

The solvent may consist of mineral spirits or any Yolatile organic liquid such as toluol, Xylol, hydrocarbon naphthas, chlorinated hydrocarbons, glycol ethers, alcohols (ethyl, butyl and isopropyl) and ketones (di-isopropyl ketones) The mill is then charged with a quantity of small steel l balls approximately 1A@ inch to one inch in diameter. Then, finely powdered dust of the metal or metals to be plated, zinc for example, is added. The mill is then closed and rotated and a bright metallic zinc coating is hammered or impacted onto the articles providing a very smooth, dense, lustrous coating. When'the articles are examined under a microscope, it is found that a solid layer of metallic zinc has been built up thereon.

No heat is necessary in this method, the impact of the steel balls hammering the nely divided metal into chemically clean flake form and plating the same upon the article. The zinc coating on the balls prevents any contamination of the metal powder with iron and likewise prevents the wearing of the balls.

The ratio of the balls to metal is also of importance. The most rapid plating occurs when the ball-to-ball metal ratio is 2 to 1. By increasing this ratio, the metal coat can be made smoother and brighter. If the weight of the ball to metal increases, so does the finish of the plate. How- Y ever, the weight of the metal plated on the article decreases. The range through which plating will occur is any ratio of balls to metal from 0 to 60 parts by weight of balls to l part by weight of metal powder or ake.

The iineness of the metal powder is also a factor in the plating operation and in the quality of the resultant coating. Small particles, for instance, .5 to 10 microns in largest dimension, are effective in producing heavy plating of desirable quality in economical times of treatment. The larger the plating particles Vthe more they tend merely to receive and cushion the impact without developing Y enough intensity in surface to surface pressure to secure v the particle permanently in place. The large impactor units, such as cracked shot, deliver energies in aV certain range for agiven treating apparatus and particles too large to be flattened and xed in place by the impactor blows are ineffective and even interfere with the plating operation. For example, plus mesh material Y screened out of a fine zinc dust hardly plates at all or gives only a light flash coat in a tumbling barrel about three feet in diameter and provided with riserbars lifting and dropping the material. Minus 200 mesh material of the same line zinc dust (about .0025" andV below) gives light coatings of approximately .0003 to .0004" in thickness, whereas the undersize, .5 to 20 microns in smallest dimension, segregated by screening through a ne cloth produces thick, well adhered coatings duefno doubt to the greater efiiciency of the impacting of the smaller particles and the V.decrease in the useless cushioning by the larger particles above V20 microns (in smallest dimension) which wouldV have absorbed'v the blows more electivelyV applied on smaller particles. Such larger particles when present also parasiticallyv accumulate these smaller particles in a manner still further increasing the bulk of the larger particles and aggravating their detrimental elfects. As above noted, line dust particles above 100 mesh were so large as to have practically no plating action and such light flash coat as appeared was largely due to the roughness or tooth of the plated surface.

Such' ,tooth of the surface being plated is produced, for instance, by a brief acid strike and is helpful in gaining adherence of the plating particles. Evenrlarger particles will wear off due to attrition on this roughness giving the characteristic thin film smoothing out the irregularities in a light flash coating which because of its smoothas the treatment continues. This initial innermost layer` of small-.particles at the plated surface is thus driven into intimate metal-to-metal contact with the said surface `and l bonded thereto by mechanical and atomic forces.

Then' the particles are impacted onto these innermost particles -and bonded thereto in metal-to-Inetal contact in continuing deposits overlapping and Vinter'itting in a most intimate surface-to-surface relation.k

The crystalline growth of the particles into'grans proceeds from particle to particle across Athe' interfaces and 'u constitutesaf type of bonding recrystallization.

This growth is ,largely in a rdirectionatwise or along the surface at the innermost particles contributes to the bondingof the coating to the base metal with resultant relativlly tenacious and durable adherence. The zinc coating still is in intimate metal-to-metal bond with the ,steel base even after the specimen was bent through four f' reversals. VThis vcoating was laid down at room temperature-in-a l6-hour run using mineral spirits and long-chain the coatingin providing an inexpensive and durable s urface covering.

The temperatures of treatment particularly inthe'lower ranges may be attained-by retaining the heat-generatedin the mass of material in the barrel. The recrystallization of the worked particles is` initiated and continues during the treatment and subsequently and Ymay be accelerated by subsequent heating after the articles are removedv from the barrel., l f 3 In zinc coating it is desirable to useV dust or powder which not only is tine-but also of highy porosity'a'nd little contaminated with oxide lm. An effective zinc dust will approach 'zinc in color -with only light lmings of oxide and will be uniforniin composition. jThis responds readily to the coating procedure bringing the particles into intimate engagement with they base surface and with the layers 'as they are adhered, c'are being taken to provide` the particle depositing treatment Without excessive simultaneous particle removal.V A satisfactory control of the coating deposit is attained ina rotary container on a hori- Zontal axis andl having a diameter of about eighteen inches with internal riser kor stirring vbars Vor lodges, the` container rotating at about 40 rrpm. A similar smaller unsaturated fatty acid and substantially maintained its integrity-'throughout the bending with `incipient cracking.

.-Such cracking when further developed by bending will often break right through the individual crystals and with some fracture along a portionfof the crystal boundaries. Theredsalso a pronounced tendency of cracks eventually to form and follow along in the general direc- Vtion o'f` the surface while the innermost coating layer metalY under the bending stresses.'

'At ordinarytemperatures there is no visiblediifusion between the coating and the base metal, neither penetrat-- ing the other to any visibly'evident extent. The metal- Vto-metal contact, howevenuis so intimate that a zinc coating laiddown by this process `will diffuse into-the base metal (steel) attemperatures such as 225 C. well below the temperature atV which such diffusion would be expected.' This indicates that the bond is partly atomic and that there is atomic penetration between the* metals long before a visible diifusion becomes apparent.

11 The bond between the coating and thebase metal Y mayfth'us be improved by heating within the-'melting point and this is increasingly true where between the base and the innermost layer` of particles there are areas of an'interface lm intervening'toV reduce or prevent metaltofmetalcontact. The longeror higher the heatingthe moreevident the resulting diffusion. The large increase y Y in;surface area which takes place when the particle is flattened ruptures the thin lm through the increase in surface area. Apparently this ruptured film is squeezed Qutby the forces involved between the cleanV surfaces which weld. Locally generated heat which is concentrated in the particle also might `play a part in aiding the removal ofthe residual film. The very small size of the particle is of importance-in the elimination of the major part l.offany rfilm between the` mating surfaces. Forces Hofcapillarity may also function over the short distances involved. At the.V same time thebonding and recrystal- VI.lizatioubetween the particles is accelerated. This final heating when employed may be Yto-any desired degree preferably below the melting point of the softer metal andmayl advantageously involve an annealing of the base metal, simultaneouslydmproving its structure. It does `not change and merelyv accentuates the characteristics of cylinder of seven and one-half iches diameter is 'also effective rotating at about 60 r.p.m., the times of r'treatment varying from a few hours to sixteenor more ,hours as above explained and with various admixtures of coarser materialsuch ascracked shot.

The following are examples of articlesand coatings.

ExampleV 1.--Twolbs.V ofroofing nails were degreasedvr in a commercial alkali soak cleaner at 180 Fffor ve minutes. The nails vvczrerthenrinsedk in water and pickled in a 10% hydrochloric acid solution of 150 F. forvve minutes. They were then rinsed in `vvater. The nails Ywere then placedl in a one-gallon cylindrical can withjsix lbs.V of zinc coated iron shot. AThe mixture was their covered` with water. A` few drops of v an anti-foaming material were added together `with 50 cc'. of a solution containing 2 grams citric acid andl 0.8 grfamwater solubleethylene'" oxide condensed' fatty acid ftypezlm-formerfsuch-as is; described in U.S. Patentlpe. 23,1861. "grams of lzinc dust of 3 to 8 microns inparticlesize were added to' the mixture before the can wasclosed. The'canwas lthenV closed and placed in apaint shaking'mechanism of-a R'ed Devil paint shaker and shaken for 10 minutes. On `opening the can, the zinc`dust had been ldeposited orirthe nails asa dense, bright zinc coating of .approximately .002

yExample Z.-An :assortment of small steel hardware two lbs. in weight were added yto avsmallironmill, approximately one-gallon capacity, containing tin fats, tin fats being ahydrogenatedfmixture .of fatty materials solid at room temperature used in theV hot tinnin'g of steel sheets. Torthe. ,tin fats was added 5 0 cc.` of oleic acid, 50` grams of copper powder and eight lbs. of iron shot which had been previously coated with copper in accordance with this example. The mill was closed and sealed with an asbestos gasket and operated inan insulated cabinet, maintained at a temperature of 200 C'.

When the mill was vopened the hardware was found to be coated with a bright, attractive coating fof copper approximately .001."'thicktf J g.

Example 3.-A piece of steel degre'ased and acid pickled as described in Example 1, was'taped round the edges to the'bottom of adish'so Sit could not move and the `dish was lled to a depth of..1 inch with a mixture of zinc dust, Water and chemicals asdescribd in Example l. A brush having brass bristles .was rotated over the 'surface4 of this steel plate rotating at a speed of 450 linear feet per minute. During rotation the dish was moved so as to place all portions of the steel vsurface under the action of the rotating brush. The plating operation was continued for two'minutes, at ,the end 4of `vwhich time" the steel was found to be coated with abri'ght, smooth',`at tractive'coatingofzincjf'f`Y- i f `Example 4.\-A charge-comprising 500 pounds of steel,

spring wire, hose clamps was descaled by blasting withV steel grit and dipped for one minute in a solution of 2% CuSO4 and 3% H2504 plus a commercial inhibitor at room temperature to deposit a thin Coating of copper by chemical replacement. After rinsing, these werev placed in a horizontal, octagonal tumbling barrel of 30" diameter andv 30" length with 800 pounds steel pellets of .053" d. previously plated by similar operation of this process. To these were added 71/2 pounds of zinc dust of 3-8 micron particle size, and 1/2 pound of tin powder of -325 mesh. Then 3 pounds of citric acid and I pound of a water soluble ethylene oxide-condensed fatty acid type film-former such as is described in U.S. Patent Re.V 23,861 were added together with sufficient water to cover the solid contents of the barrel. The barrel was then closed and rotated at a speed of 22 r.p.m. for one hour. The hose clamps were thus plated with a bright metallic coating of .0005 thickness containing zinc and tin.

vAs a result of tests that have Lbeen made and supervised by a United States Government testing agency for the Aeronautics Branch of the Department .of the` Navy in connection with the present invention, the` following results were found to be factual rand were so reported by that testing agency.

' Electro-plate zinc coatings- .0002 thick lasted between t190 'and 273 days without rust-ing. Electro-deposited cadmium coating .0002" thick lasted 364 days to first rust. Electro-deposited cadmium coating .0005" thick no rust after 812 days. Coatings of instant process .0002 thick no rust after 812 days.

It should be pointed'out that cadium has always been particularly good for exposure in marine atmosphere and in this particular test, as reported by the Government agency, the instant coating .0002 thick lasted as well as electro-deposited cadium of 21/2 times the thickness.

The above tests were vmade on coatings of steel bolts in out-door marine atmosphere.

The details of the polishing of surfaces of 125 and 5 60 and 500 diameters respectively are as follows:

'Ihe polishing and etching of the reproduction 1000 diameters is as follows:

(l) Mount specimen in' circular steel ring in Bakelite matrix.

(2) Rouge polish with coarse abrasive ory file making 'sure steel is removed to a point where va full coat is exposed.

(3) Wet polish in the following order on Carborundum papers', grit 240, grit 320, and grit 400. Y A (4) Polish `on vlead lap -with 3031/2 emory. Y (5) -Polish on wax lap with'600X crystalline Alundum. (6) Polish on AB microcloth lap with Linde B polishing compound, after having treated the lap vwith a light solution of castile soap.

(7) Maximum amount of pressure should be used on the final wheel, solution kept as thickas possible 'and polishing time-kept to a minimum.

(8) Etch with a chromic anhydride reagent, such as the following: 50 grams of pure VCrO3; 4V grams NaSO4; 1000 mls. of H2O.

(9) Etching time normally should not exceed 2 seconds, ilushingoff excess reagent withvvvater, following by swab with alcohol.

Another specimen at 500 diameters and etched as above described has the grain characteristics at adjacent areas of variable working. The particles `are similar in general `form to those previously described, and intensified attrition and impacting of the coating particles as they round a corner bend stretches Vand thins out the graining to films along closely packed lines following the contour of the base surface.

The coatings are thoroughly protective. They are at least equal to hot dip and electro deposited coatings in durability and service. In uniformity `of thickness, ad- Iherence, flexibility and continuity they are similarly comparable to Vthe hot dipped and electroplated coatings of the same metal.

While the treatmentsv above `described have dealt mainly with the deposit of particles of a single metal such as zinc, the process of this invention is also applicable with 'a plurality of-powders of different metals or of particles of alloys both solid solution and two-phase, as explained in my applications, Serial Nos. 14,639 and 77,269, and the metal coatings referred to in the appended claims are of one or .more metals or alloys.

I claim: n I

1. An article having a pressure applied metallic coating of built-up layers of numerous mechanically flattened overlapping land interf'itting discrete and distinct particles of metal, said particles having clean substantially pure metal surfaces and being atomically bonded together by intimate metal tometal contact Iat portions of said clean surfaces; and a film-forming, surface-active organic substance interspersed throughout the coating in the form of inclusions of thin, strongly adherent film on and between the unbonded clean surfaces of the particles to prevent exposure land inhibit oxidation `of the unbonded clean surfaces of the particles, each inclusion aiding in holdingV together the particles adjacent the inclusion through the said unbonded surfaces of the particles to which the organic substance adheres, saidV organic substance being substantially chemically inert to the clean metal and hav'- ing a polar molecular structure including a carbon chain and capable of exhausting itself through adsorption of molecularly thinV lms onto the clean surfaces of the metal, Vand the thin film being physically aflinitive and strongly adherent to clean surfaces of the metal.

1 2. An article according to claim 1 and further having distributed inclusions of a water Isoluble fluxing compound chemically reactive to oxides of the metal when in laqueous solution, the film-forming organic substance having selectively greater adherence to the clean metal surfaces such thatthe inclusions of the fluxing compound are spaced'from the Vclean metal surfaces by the molecularly thin film of the film-forming substance.

3. An article according to claim 1 wherein all of the particles before mechanical attening are between .5 and 20 microns in their largest dimension.

4; An article having a pressure applied metallic coating of built-up layers of numerous mechanically flattened overlapping and interfitting discrete and distinct particles of metal, said particles having .clean substantially pure metal surfaces and being atomically bonded together by intimate metal to metal contact at portions of said clean surface; a film-forming, surface-active organic substance interspersed throughout the coating in the form of inclusions of thin, strongly adherent film onv and between the unbonded clean surfacesv of the particles to-prevent exposure and inhibit oxidation of theV unbonded clean surfaces of the particles and to aid in holding together the particles through the said unbonded surfaces to which the organic substance adheres, said organic substance being` substantially chemically inert to the clean metal and having a molecular structure 'including a carbon chain and capable of exhausting itself through adsorption of molecularly thin films onto the clean surfaces of the metal, and the thin film being physically afiinitive and strongly adherent to clean surfaces of the metal; and Va water soluble iuxing compound chemically reactive to oxides of the metal' when in aqueous solution distributed inV inif Vvclusions 'in the coating to a lesser extent than said film-v t forming substance. i

5. An article according to claim 4'wherein all'of the i particles before mechanical flattening are between .5 and Y 20 microns in their largest dimension.

6."-An article having a pressure applied metallicrcoat- Ving of built-up layers of numerous mechanically tiattened r overlapping and interiitting discrete and distinct particles of metal, lsaid particles having clean substantially pure metal surfaces and being atomically bonded together byl intimate metal to metal contact at portions ot said clean surfaces; and a film-forming, surface-active organic substance interspersed throughout the coating inthe `forni of inclusions of thin, strongly adherent film on and between theunbonded clean surfaces of the particles to prevent exposure and inhibit oxidation of the unbonded clean Y, surfaces of the particles, each inclusion aiding in holding together the particles adjacent the inclusion through the said unbonded surfaces of the particles to which the organic substance adheres, said organic substance being substantially chemically inert to the clean metal and havinga polarmolecular structure including a carbon chain and'capable .of exhausting itself through adsorption of molecularly thin lilmsonto the clean surfaces of the metal, Vand 'the thin ilrn being physically aiiinitiveand film of organic substance further being adherent to the clean metal to a degree greater than to oxides of the metal v 7. An article having a pressure applied metallic'coatposure 4and inhibit oxidation of the unbonded clean surf faces of the particles and to aid in holding together thev particles through the said unbonded surfaces to which the Y organic substance adheres, ysaid organic substance being substantially chemically inert to the clean metal and hav- *ing* a/molecular structure including a carbonchain andcapable of exhausting itself through adsorption of molecl Ystrongly adherent to clean surfaces of the metal, the thin y aiaaoas Y lli ularly thin filmsV onto theclean surfaces of the metal, and the thin ilm being physically ainitive and strongly adherent to clean surfaces of the metal; and a Water soluble iuxing compound chemically reactive to oxides of the metal when in aqueous solution distributed in inclusions in the coating to a lesser extent than said film-forming substance, the thin film of organic substance further being adherent to the clean metal yto adegree greater than to oxides of the metal.

8. An article having a pressure applied metallic coatp ing of built-up layers of numerous mechanically tlattened overlapping and intertitting discrete and distinctparticles of metal, the particles before mechanical flattening being .54.0 microns in their largest dimension, said particles having clean substantially pure metal surfaces and being atomically bonded together by intimate metal` to metal contact at portions of said clean surfaces; and a iilmforming, surface-active organic substance interspersed throughout the coating in the form of inclusions `of thin, strongly adherent film on and between the unbonded clean surfaces of the particles to prevent exposure and inhibit oxidation of the unbonded clean surfaces of the particles and to aid in holding together the particles through the' said unbonded surfaces to which the organic substancel adheres, said organic substance being substantially chemically inert to the clean metal and having a molecular structure including a carbon chain and capable of exhausting itself through adsorption of molecularly thin films onto the clean surfaces of the metal, andthe thin iilm being physically aiiinitive and strongly adherent to clean surfaces of the metal, the thin film of organic substance further being adherent to the metal to a greater degree than to oxides ofthe metal.l 1

9. An article according to claim 8 wherein the organic substance is a cationic, emulsifying agent capable of rendering the metal sunfaces waterv rejecting.

l0. An article according to claim 8 whereinl the or-V ganic substance comprises a cationic wetting agent, an includes a water soluble oil mixed therewith.

References Cited in the file lof this patent UNITED STATES PATENTS Y 1,873,223 Sherwood a Aug. 23, 1932 2,640,001 Clayton p May 26, 1953 v f l FOREIGN PATENTS n v I 534,888 Great Britain Man 21., 1941l Podszus aan Dec. 16, 1930

Claims (1)

1. AN ARTICLE HAVING A PRESSURE APPLIED METALLIC COATING OF BUILT-UP LAYERS OF NUMEROUS MECHANICALLY FLATTENED OVERLAPPING AND INTERFITTING DISCRETE AND DISTINCT PARTICLES OF METAL, SAID PARTICLES HAVING CLEAN SUBSTANTIALLY PURE METAL SURFACES AND BEING ATOMICALLY BONDED TOGETHER BY INTIMATE METAL TO METAL CONTACT AT PORTIONS OF SAID CLEAN SURFACES; AND A FILM-FORMING, SURFACE-ACTIVE ORGANIC SUBSTANCE INTERSPERSED THROUGHOUT THE COATING IN THE FORM OF INCLUSIONS OF THIN, STRONGLY ADHERENT FILM ON AND BETWEEN THE UNBONDED CLEAN SURFACES OF THE PARTICLES TO PREVENT EXPOSURE AND INHIBIT OXIDATION OF THE UNBONDED CLEAN SURFACES OF THE PARTICLES, EACH INCLUSION AIDING IN HOLDING TOGETHER THE PARTICLES ADJACENT THE INCLUSION THROUGH THE SAID UNBONDED SURFACES OF THE PARTICLES TO WHICH THE ORGANIC SUBSTANCE ADHERES, SAID ORGANIC SUBSTANCE BEING SUBSTANTIALLY CHEMICALLY INERT TO THE CLEAN METAL AND HAVING A POLAR MOLECULAR STRUCTURE INCLUDING A CARBON CHAIN AND CAPABLE OF EXHAUSTING ITSELF THROUGH ADSORPTION OF MOLECULARLY THIN FILMS ONTO THE CLEAN SURFACES OF THE METAL, AND THE THIN FILM BEING PHYSICALLY AFFINITIVE AND STRONGLY ADHERENT TO CLEAN SURFACES OF THE METAL.

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