US2496971A - Thermite coating process - Google Patents

Description

l atented Feb. 7, 1950 Sol B. Wiczer, Washington, c.

No Drawing. Original application April 24, 1943.

Serial No. 484,479. Divided and this application April so, 1943, Serial No. 24,410

2 Claims. (c1. 117-50) The present invention relates to a method of rapid and cheaply plating metal.

The present application is a division of my copending application, Serial No. 484,479, filed April 24, 1943, now Patent No. 2,463,342 and the claims herein are directed to thermite coating without hot working as claimed in the parent application.

It is an object to plate various metals for example 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 any solid 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 when heat is applied to form thefree metal to be plated.

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

It is a further object 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 and pressed upon the surface of the base metal to effect a permanent coating therewith during some normal metal fabrication operation.

Further objects will be inherent in the process as described and will be apparent to one skilled in this art from the description given.

The base metal will be any metal adapted to carry out the function of the structure either entirely or in part. The plating metal will be adapted either to modify the stability or corrosive properties of the base metal; the function or hardness of the surface for example to improve wearing properties such as by coating with soft bearing metal where the function will be as a bearing or bushing, or with a hard cutting or wearing surface for dies, tools or rubbing surfaces; or with a highly electric conducting or resistive properties of the base metal where desired electrical properties are to be enhanced as in wire coating or with a refractory metal where heat and oxidation are to be resisted.

The mixture of chemicals comprising the plating mixture will be adjusted to give a stoichio-- metric reduction of the metal to be plated. The mixture may contain an additional fluxing material to ensure proper adherence of the plating metal to the base metal. The base metal will be heated suff ciently 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 auxiliary means to initiate reaction of the plating mixture.

Such temperature will vary for different re ducing metals and different metal fabricating processes.

The chemical mixture will contain a compound, 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 chemically active in the electromotive series than the metal to be plated out.

, The chemical reactions may be shown as follows:

Plating tin Taking tin ore from which tin is to be plated as the coating agent and metallic aluminum as the reducing agent:

a mixture of compounds with a reducing metal capable of reducing both:

By proper adjustment of stoichiometric proportions any number of metals may be mixed in the plate as an alloy coating.

- 3 It is also possible to repeat the operation with different chemical mixes to obtain two platings superimposed one on the other:

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. I It will also be apparent that the reaction be tween the reducing metal is much more active than the metal to be reduced, is usually highly exothermic, and the reduced metal produced on thes'ur'f'ace' of the base metal is in a super heated 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.

Example 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 rolledinto plate. During this operation'rnuch 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, containinuen scale on the surface.

According to the present process a highly desirable resistant metal plating, for example chrom'ium, orother desirable coating may be applied tothe hot steel platebeing rolled'whereby a scale nee. plate is produced.

While the steel plateis 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 aliux. The passage upand-back under the rollers distributes and heavily presses the molten chromium evenly over the steel to form a coating. Some of the molten-*alumina w ill' 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.

Thisyplating operation would-be applied to both sides of the :plate as it is turned over as is comanon 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 mixing materials to secure harder :and more adherent' plating. It will be appreciated that some 'ofthe highly refractory metals reduced will not be molten, but the softened surface of the steel lproduced 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 either as the pure metal or an 4 alloy thereof. This method will be similarly applicable in fabricating metal strip, rails and discs.

Example I) Using an excess of metallic aluminum as a reducing agent and a beryllium salt or ore which has been freed of silica .for example AlzO3,BeO 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% togive thedesired properties to the plating. Such coating has hard wearing, non-fatiguing and nonsparking 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 copperor nickel adjusted to give, with a small quantity of beryllium oxide or mixed aluminum beryllium oxides, analloy of nickel or copper with a fewpercent of beryllium asthe metal plate upon the steel.

Thus hot steel isplated by rolling with a powder formed by mixingabout 65 ,parts of aluminum powder, 162 parts of nickel oxide Nl'zOs and 10 partsof beryllium oxide.Be0, 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 nickelin-a 2% beryllium alloy, the quantity 0! copperoxide 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 welding the edges, spot welding or annealing togive 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 laheat or corrosion resisting or catalytic inner or outer surface; or an electric conducting or resistive surface. If desired the coated sheet maybe cut into smallbuttons for electric contacts where 'the'coating is of tungsten or molybdenum suitable'for suchuse. While some of these metals are infus'ible per se thesurface of the base metal will be sufficiently softened; to bond the reduced refractory metal coating.

Example HI Metal .base wire, such as .hard metal wire or steel .or.other .hard refractory metals nickel, .molybdenum,.tungs'ten, 'etc. may be ,given a coating of copper, silver, lead, zinc ,or chromium -by passingthe wire in .a heated state rapidly thru a powdered reducing metal .such. as aluminum ormagnesium andan. 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 anelectric current contactingthe .wire Ibeforeand after it is passed throughlthe chemicalmixture.

Tubes, pipes or rods may .be coated with the chemical as the tubeis formedby 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 reducing metal may be the most desirable coating agent, such as in anodic oxidation to reduce corrosion as shown in the following:

Example 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 chromic 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 and the treated surface burned a high speed cutting tool. The casting was subjected to corrosive baths and air. lhe 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, such as compounds with another radical may be used. For example hardening agents may be incorporated into the metal surface such as cya-- nides, cyanamids, carbides, or silicides of refractory metals.

6 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 stoichiometric proportions to reduce the tungsten. The resulting product will be a mixture of free metals tungsten, aluminum oxide and tungsten iron and aluminum carbides. The aluminum carbide may be decomposed with water or acid and removed to leave a fused mixture of hard aluminum oxide, tungsten carbide on the base metal.

What I claim is:

1. Method of metal coating a high melting base metal comprising heating the base metal to white hot temperature sufficient to initiate a reaction in a finely divided mixture of an active reducing metal selected from the group consisting of aluminum, magnesium and alloys composed of aluminum and magnesium, and an oxide of a coating metal less active than the reducing metal, the active metal being in proportions at least sufficient to stoichiometrically reduce said oxide, and applying said mixture to the surface of the white hot base metal whereby exothermic reaction is initiated and a molten coating metal is released by the reaction over the surface of the base metal for coating the same.

2. The process of coating an iron casting which comprises, heating the casting until it is white hot, allowing the casting to cool just sufficiently to harden, evenly applying a mixture of two parts by weight of chromic oxide powder and one part by weight of aluminum powder to a surface of the hot casting, whereby a reaction occurs on the surface of the hot casting, between the chromic oxide and aluminum powder mixture to provide a metallic coating on the casting.

SOL B. WICZER.

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

UNITED STATES PATENTS Number Name Date 1,580,647 Breck Apr. 13, 1926 1,943,171 Folliet Jan. 9, 1934

Claims (1)

1. 2. THE PROCESS OF COATING AN IRON CASTING WHICH COMPRISES, HEATING THE CASTING UNTIL IT IS WHITE HOT, ALLOWING THE CASTING TO COOL JUST SUFFICIENTLY TO HARDEN, EVENLY APPLYING A MIXTURE OF TWO PARTS BY WEIGHT OF CHROMIC OXIDE POWDER AND ONE PART BY WEIGHT OF ALUMINUM POWDER TO A SURFACE OF THE HOT CASTING, WHEREBY A REACTION OCCURS ON THE SURFACE OF THE HOT CASTING, BETWEEN THE CHROMIC OXIDE AND ALUMINUM POWDER MIXTURE TO PROVIDE A METALLIC COATING ON THE CASTING.