US2463342A - Metallic coatings - Google Patents

Description

Patented Mar 1, 1949 Nb Drawing. Application- April 24, 1943; Serial No. 484,479

8 Claims. (01'. 142-4) Thepresent invention relates to a method of rapidly and cheaply plating metal.

It is an object to plate various metals for ex"- ample any stable metal or alloy less active in the electromotive series than the alkali metals upon a base metal. The base metal may consist of. anysolid metal or alloy of general electrical or mechanical use which is desired to be plated and which will withstand high coating temperatures without completely fusing.

It is a further object to apply the metal plate as a chemical mixture of a compound of the plating'metal with other substances which will react whenheat is applied to form the free metal tube plated. 7

It is a, further object to use a base metal that is; ina heated state during some period of its fabricationand use this heat to activate a chemical mixture of the plating substance whereby free metal is produced and plated in situ on the base metal.

I-t is a furtherobject to effect the plating in a manner to remove impurities; such as scale, from the surface of the base metal while it is being plated.

It is a further object to accomplish the plating under conditions of temperature; pressure and fluxes whereby the plating metal is mechanically distributed andpressed upon the surface of the base metal to effect a permanent coating therewith during some normal metal fabrication operatio-n.

Furtherobjects will be inherentin the process as described and will be apparent to one skilled inthis art from the description given.

The base metal will be any metal adapted to carry out the functionof the structure either en.- tirely or in part. The plating metal will be 4 adapted either to modify the stability or corrosive properties of the base metal; the function or hardness. of the. surface for example. to improve we riegpr'bprt s- "such as .ty ctatmg; with soft. bearing metal where the function. will b :e ,as' a hearing or bushingor with a hard cutting or' The mixture of chemicals comprising the platmixture will be adjusted to give a 'stoichio metric reduction of the metal to be plated. The mixture may contain'an additioiial fliixin'g ma:

te'i'ial t'ti ensure proper adherence of the plating 21 metal to the ase metal. The base metal wil l be heated sufficiently to supply enough heat either to initiate the reaction of the chemicals applied to the surface, or to maintain the base metal in a pliable or soft state to allow fabrication while using au'idliars' means to initiate reaction of the plating mixture. h v I Such temperature will tary for different reduc ing metals and 'difier'eht metal fabricating DI'O'C- SSS.

The chemical mixture will contain a-compouiid, such as any reducible commercial ore of the metal to be plated out, preferably an oxide. This will be intimately mixed'with a reducing-agent Such as a free metal more eliemi-call y active in the 91 80 tromotive series than the metal to be plated out.

The chemical reactions may be shown as fol-- lows:

Plating an Taking tin ore from which tin is to be. plated asthe coating agent andmetallicv aluminum as the reducing agent:

4A1+3suow2m2e3+3sn Plating topper Using any common more active metal Y MQuOefiOJF iL gAl+3CuO'= AlzO$ l-3gu ZNi-l GCuONiZOQ-l- GCu Q'd+ Cfi 21Cr+3CuO C I 2 O3+\3 Cu M +2 MsO+ u Mh+2CuO- MriOe+2Cu An alloy may be plated where the active metal is in excess of the metal to be reduced from its oxide. For example'a'bronze from copper and-tin; or from aluminum and copper are shown as:

lsfiaq ib e esnqu 5Al+3CuO+ AliOi+3AlCu Obviously' the proportions will be yariedito'ob aim the desired alloy plate; tbealloy examples being in proportions of 1 to 1 merelyto show the method. w h V X I The same resultsm'aybe obtained byuse of a mixture of compounds with a reducing metal ca iable-of reducing both:

2A1+snoi+ cu0 Ai2o3+sucu Byproper adjustment Of stdicliiometri c p l oportions any number of metals may-be mixed in thepiat'e an alley coatizjig. I

It is aiso posslbie to repeat the operationwith This plate is then treated with the following mix to obtain a chromium plate on a nickel base.

It will be noted that the reducing metal must be not only more active than the-plating metal but will usually be more active than the base metal, in which case any impurities such as metal oxide scale on the base metal will also be reduced. Thus it is desirable in such condition to use a slight excess of the reducing metal.

It will also be apparent that the reaction between the reducing metal is much more active than the metal to be reduced, is usually highly exothermic, and the reduced metal produced on. the surface of the base metal is in a superheated state often highly fluid and in the presence of the higher metal formed oxide tending to act as a flux readily coats the base metal surface.

Ewample I In rolling steel plate the steel is heated first until it is soft and pliable. The steel slabs are applied to rollers to be rolled into plate. During this operation much scale, iron oxides, are formed and it is common to throw salt on the slabs being rolled to aid in the removal of scale, but the finished plate from ordinary steel does, notwithstanding, containmuch scale on the surface.

According to the present process a highly desirable resistant metal plating, for example chromium, or other desirable coating may be applied to the hot steel plate being rolled whereby a scale free plate is produced.

While the steel plate is being passed under the rollers a mixture of active metal, for example aluminum, and an oxide of the metal to be plated, for example chromic oxide, is thrown on the white hot slab.

The heat of the steel being rolled initiates the reaction between the reducing metal aluminum and the chromium oxide as well as any iron oxide scale on the steel, forming free molten chromium metal and aluminum oxide which acts as a flux. The passage up and back under the rollers distributes and heavily presses the molten chromium evenly over the steel to form a coating. Some of the molten alumina .will be rubbed off in the operation but any finally adhering alumina is additional protection. It may ultimately be removed by pickling, grinding or polishing if desired.

This plating operation would be applied to both sides of the plate as it is turned over as is common while rolling.

Other metal coatings for example copper, cadmium, tin, vanadium, columbium, tantalum,

tungsten, molybdenum, nickel, cobalt, manganese, or mixtures may be applied in a similar way. It is also possible to use additional hardening and fluxing materials to secure harder and more adherent plating. It will be appreciated that some of the highly refractory metals re duced will not be molten, but the softened surface of the steel produced in the reaction to which refraction is compressed under the heavy rollers will give an adherent coating.

It will be further appreciated that the reaction may be varied by using more or less active reducing metals. It will also be possible to secure a coating by use of a low grade ore of the metal to be reduced easier as the pure metal or an alloy thereof. This method will be similarly applicable in fabricating metal strip, rails and discs.

Example II Using an excess of metallic aluminum as a reducing agent and a beryllium salt or ore which has been freed of silica for example AlzOaBeO or BeO alone.

An alloy of beryllium and aluminum is deposited on steel plate, when applied according to Example I. The beryllium need be present only in minor quantity up to 20 percent, usually 1-3% to give the desired properties to the plating. Such coating has hard wearing, non-fatiguing and non-sparking properties desirably imparted to the steel.

This composition may be repeated using the aluminum only in slight excess (as a reducing agent) and an additional oxide of a metal such as copper or nickel adjusted to give, with a small quantity of beryllium oxide or mixed aluminum beryllium oxides, an alloy of nickel or copper with a few percent of beryllium as the metal plate upon the steel.

Thus hot steel is plated by rolling with a powder formed by mixing about 65 parts of aluminum powder, 162 parts of nickel oxide Nizos and 10 parts of beryllium oxide BeO, all parts by weight. This would give an alloy plate of approximately 98% nickel and 2% beryllium, with some impurities such as aluminum oxides, aluminum metal and other oxides. Where copper is substituted for nickel in a 2% beryllium alloy, the quantity of copper oxide would be about 77 parts in the above mixture. It will be apparent to any chemist that the quantities to be used may readily be calculated from the reaction which takes place and the alloy or metal desired as the plating.

If desired the plated sheets or plates may be laminated and joined together by weldin the edges, spot welding or annealing to give a laminated structure of desired properties. Where the coated sheets or plates are to be laminated, they may first be pickled or otherwise cleaned of oxides and fluxes adhering to the'plate.

Refractory or electroresistive or conductive metals may be applied to sheets of steel, and the steel subsequently rolled or welded into tubes having a heat or corrosion resisting or catalytic inner or outer surface; or an electric conducting or re slstive surface. If desired the coated sheet'may' be cut into small buttons for electric contacts where the coating is of tungsten or molybdenum suitable for such use. While some of these metals are infusible per se the surface of the base metal will be sulficiently softened to bond the reduced refractory metal coating.

Example III Metal base wire, such as hard metal Wire of steel or other hard refractory metals nickel, molybdenum, tungsten etc. may be given a coating of copper, silver, lead, zinc or chromium by passing the wire in a heated state rapidly thru a pow-, dered reducing metal such as aluminum or magnesium and an oxide of one of these metals to be plated. The heated base metal wire will activate the chemical mixture to cause a deposit of one of these, metals to coat the wire. The wire may be heated in short sections by an electric current contacting the wire before and after it'is passed thru the chemical mixture.

Tubes, pipe or rods may be coated withthe chemical as the tube is formed by extrusion from a die or otherwise preheated.

It will be apparent that various base metals may be used as well as reducing metals, the latter being selected within the limits of its chemical capacity to reduce the metal to be plated.

Sometimes the oxidation product of the re ducing metal may be the most desirable coating agent, such -as in anodic oxidation to reduce corrosion as shown in the following:

Eardmple IV A heat rolled magnalium sheet is treated with a small quantity of aluminum or magnesium metal powder and an oxide of a metal which will slow down oxidation, such as boric oxide, and another oxide tending to form a slight coating such as beryllium oxide, chromic oxide, nickel oxide etc. Upon reaction the plating metal will be plated and alloyed with the surface of the light metal and a coating of noncorrosive magnesium or aluminum oxide will be formed.

Example V White hot iron castings, cooled only enough to set, are coated with the composition described to give a desirable coating on surfaces to be left unfinished. A white hot casting, cooled only sufficient to harden, was treated on one surface only with a mixture of two parts by weight of chromio oxide and one part of aluminum powder. The powder was dusted evenly over this surface, a reducing reaction set up and moved evenly over the surface. After cooling the surface was brushed clean. The treated surface showed a hardness of 35-40 on the scleroscope while the untreated surface showed a hardness of only -20. On machining the treated surface burned a high speed cutting tool. The casting was sub jected to corrosive baths and air. The untreated surfaces began to rust in a few days while the treated surfaces remained bright and clean.

Other compounds of the metal to be plated than the oxide as they are more available commercially or as the reduction product may be more desirable with another radical may be used, for example hardening agents may be incorporated into the metal surface such cyanides, eyanamids, as carbides, silicides of refractories may be fused into the surface of steel or other base metal as follows:

Example VI Steel plate, as rolled in Example I, is treated with a mixture of aluminum powder, tungsten oxide and an excess of free carbon adjusted in mite reaction, applying to the surface of the base metal a mixture of finely divided thermite solids comprising a mixture of oxide of the coating metal and a reducing metal more active chemically than the coating metal capable of reacting exothermically after the reaction is initiated by the heat of the base metal and releasing a molten coatinggmetal and working the melted coating metal into the surface of the base metal by rolling.

2. In a process of pressure fabrication of metals the steps of heating a base metal to a hot working temperature and to initiate a thermite reaction, applying to the surface of the base metal a mixture of finely divided thermite solids comprising a mixture of oxide of the coating metal and a reducing metal more active chemically than the coating metal capable of reacting exothermically after the reaction is initiated by the heat .of the base metal releasing a molten coating metal, and hot working to reduce the cross sectional dimensions of the base metal and forcibly impregnate the surface thereof with the coating metal.

3. Method according to claim 2 wherein a plurality of reducible metal compounds are used and the reducing metal more chemically active than either is in sufficient excess to reduce all of the metal compounds and to alloy therewith as part of the plating.

4. Method of claim 2 where the base metal is steel.

5. Method of claim 2 wherein the base metal is non-ferrous.

6. Method of claim 2 wherein the base metal is steel and the coating metal contains a substantial proportion of chromium released from a thermite mixture of the plating metal oxide and a more active reducing metal.

7. Method of claim 2 wherein the base metal is steel and the coating metal contains 'a substantial proportion of copper.

8. Method of claim 2 wherein the base metal is steel and coating metal contains a substantial proportion of beryllium released from a thermite mixture of the plating metal oxide and a more active reducing metal.

SOL B. WICZER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 148,795 Wood Mar. 17, 1874 1,178,551 Stolle Apr. 11, 1916 1,365,499 Kelley -1 Jan. 11, 1921 1,580,847 Break Apr. 13, 1926 1,899,569 Howe Feb. 28, 1933 1,943,171 Folliet Jan. 9, 1934 2,100,537 Conway Nov. 30, 1937 2,107,328 Fowler et a1. Feb. 8, 1938 2,158,461 Kochring May 16,1939 2,241,094 Marvin May 6, 1941 2,282,175 Emerson May 5, 19'42