US3406445A - Method for coating steel with white metal - Google Patents

Description

United States Patent O 3,406,445 METHOD FOR COATING STEEL WITH WHITE METAL Giinter Kiipke, Heilbronn (Neckar), and Friedrich Wilhelm Rabenau, Neckarsulm, Wurttemberg, Germany, assignors to Karl Schmidt G.m.b.H., N eckarsulm, Wurttemberg, Germany, a corporation of Germany No Drawing. Filed Sept. 20, 1965, Ser. No. 488,794 Claims priority, application Germany, Oct. 17, 1964, Sch 35,977 8 Claims. (Cl. 29492) ABSTRACT OF THE DISCLOSURE Coating white metal onto a tinned steel sheet by heating the tinned steel sheet to a temperature higher than the melting point of the white metal, applying solid white metal at ambient temperature to the heated tinned steel sheet and pressing the two together between nip rollers.

This invention relates to a method for applying coatings comprising a Pb-Sb-Sn-As alloy commonly referred to as white metal; more specifically, this invention relates to a method for coating steel with white metal.

The prior art teaches that while metal may be applied to steel which is tinned in a hot-tinning process, after which molten white metal is then applied to the hot-tinned steel. The white metal is then reduced to the desired thickness by scraping and milling. These prior art methods of coating are relatively complicated and expensive.

It is therefore an object of the present invention to overcome these and other difiiculties encountered in the art and to obtain a new method for coating with white metal that is quicker and less expensive than the prior art process. It is a further object of this invention to provide a method for coating with white metal in which smooth coatings of a desired thickness may be obtained initially without further machining. A further object of this invention is to provide a method for coating white metal at fine tolerances of coating thickness and smoothness. An additional object is to apply such coatings to steel which has been tinned by either a hot-tinning or galvanic process. An additional object of this invention is to provide a method for applying solid white metal coatings to tinned surfaces, thereby obviating the difficulties encountered in the prior art with molten white-metal coatings. It is another object of this invention to provide as an article of manufacture a precision white metal bearing or anti-friction device.

These and other objects have been obtained by the present invention which comprises coating steel with white metal in which commercially available tinned continuous sheet steel is heated preferably by induction to 320 to 380 C. under a protective gas, and in which white metal in the form of cut or continuous sheets is pressed onto the steel through a roller gap or other suitable press means at room temperature, whereupon the white metal is pressed or plated onto the steel. In this procedure the steel remains practically undeformed, while the white metal is subjected to a deformation of 20 to 50 percent or 60 percent. The adherence of the plating produced according to the invention is perfect. Although commercially available tinned sheet steel is approximately 25 percent more costly than untinned steel, an overall comparison of the present invention shows that it is more economical than the prior art methods and articles produced thereby.

The white metal used in the method of the present invention is known in the art and generally comprises an alloy of lead, antimony, tin and arsenic in ratios which are also Well known in the art.

During the pressing operation of the present invention, the white metal is caused to flow or deform. Deformation and flow are synonymous in this respect and either term is used to indicate that in general the thickness of the white metal is reduced under such pressing conditions. The degree of pressure needed to obtain the bond between the white metal and the tinned steel is directly related to the degree of deformation of the white metal obtained when practicing the method of the present invention.

The adhesive bond is obtained through the intermediate tinning, and although the present invention is directed primarily to a method for obtaining a white metal coating on steel, any tinned surface may be coated in such a manner. Additionally, a non-continuous process may be utilized in place of the nip-roll pressing means used for coating while metal according to the present invention. In this respect, any type of means may be used for applying pressure to the white metal and the surface to which it is applied.

It is one of the essential features of the present invention that White metal may be applied as a coating in substantially a solid state. The prior art difficulties encountered in applying molten white metal coatings are thereby obviated. The non-molten or substantially solid white metal applied according to the method of this invention is preferably coated in the formof continuous or discontinuous sheets, however, the coating may also be applied as a powder according to powder metallurgy techniques which are well known in the art.

The tinned surface to which the white metal coating is applied must be heated to approximately 320 C. to 380 C., and the white metal applied at temperatures lower than the tinned surface, preferably at ambient or room temperature, i.e., 20 C. The temperature of the white metal must be low enough so that the white metal when applied is non-molten or solid. The substrate to which the white metal is applied must be of sufficient strength so that at the elevated temperatures at which the coating is applied, the substrate Will have sufiicient structural integrity so as to permit 20 to 50 percent, or 60 percent deformation of the white metal. In the preferred embodiments of the present invention, the steel substrate exemplifies these properties, whereby, after heating to 320-380 C. and application of the white metal coating, the steel substrate substantially maintains it thickness and other dimensions, Whereas the white metal coating is deformed.

The shielding gas employed according to the method of the present invention can be any gas known in the art suitable for this purpose, such as the -so-called noble gases or reducing gases such as carbon monoxide or hydrogen or nitrogen or any gas that will prevent oxidation of the metal during the heating and pressing operations without adversely combining with the metal.

The following non-limiting examples are included as certain preferred embodiments of the invention and are not to be construed as narrowing the scope of the invention.

Example I A low-carbon sheet steel (approximately St4 supplied in coil form is galvanically tinned on one side in the customary manner with a coating of 5 to 8 mu of tin. A white metal composed of 13.5 percent Sb, 1.5 percent Sn, 1 percent As, and the balance Pb is cast into rolling ingots of 20 mm. thickness, rolled down to 1 mm. at approximately 180 C., and roughened on one side with wire brushes. The tinned sheet steel is then continuously heated by induction at medium frequency to 280 C., and fed through an induction coil directly into the nip of a rolling mill under a shielding gas.

The sheet, roughened on one side, is likewise fed to the rolling mill nip, and squeezed in the roller gap onto the hot, tinned steel sheet, the steel undergoing no deformation and the white metal of 1 mm. thickness being reduced to 0.5 mm. thickness. When the white metal has been sweated onto the tinned surface of the steel, it can be further formed into rolled bushings or split bushings for friction bearings. The surface of the white metal and of the steel remains smooth, having a roughness of less than 1 mu, so that no further machining is needed.

Example 11 The procedure of Example I is repeated using a commercially available hot, tinned steel with a tin coating of 4 to 12 mu which is inductively heated to 300 C. under a shielding gas. Just ahead of the roller gap, a white metal alloy of the Pb-Sb-Sn-As type, rolled from east ingots into sheet form, is cold-rolled'onto the steel. The final coating thickness of the white metal in this example is 0.2 mm. The white-metal sheet was rolled to a thickness of 0.35 mm. from the ingot, before application to the tinned steel sheet. The white metal adhered to the steel sheet is used as a bearing.

Example 111 A white-metal-coated steel strip is prepared for socalled micro-bearings, in which the white metal thickness amounts to only 50 to 70 mu. In this example, a white metal sheet, 0.1 mm. thick, is rolled onto galvanically or hot tinned, heated steel strip. The laminating is effected and takes place in the same manner as described in Example I, although the easily torn, thin foil had to be fed to the roller gap in the cold state by means of a foil dispenser, according to methods known in the art. In this case again, any subsequent machining of the white metal or of the steel surface is unnecessary, and is even impossible in the latter case.

Thus, there has been described a novel method and article of manufacture, whereby a solid white-metal coating is applied to a tinned substrate, whereby smooth coatings of a desired thickness are obtained initially without further machining, the coatings being held to fine tolerances of coating thickness and smoothness. The coatings are formed by pressing the white metal onto a hot, tinned substrate in such a manner so that the white metal under-v goes between 20 to 50, or 60 percent deformation. By the application of white-metal coatings to a tinned steel substrate, according to the method of the present invention, an article of manufacture is obtained comprising a precision white metal bearing or anti-friction device.

Although the invention has been described with reference to certain preferred embodiments, it is not intended that the invention be limited thereby, and certain modifications of thenovel method and article of manufacture are intended to be included within the broad scope of the fo'llowing claims.

1. A method for plating white metalonto steelj'comprising heating a tinned steel surface to'a' temperature from 280 C. to 380 'C., pressing asolid'white metal strip at ambient temperature onto said tinned steel, leading said white metal and said steel simultaneously through nip rollers and pressing said white metal into a plating relationship with said steel in said nip rollers at pressures sufficient to-plate said White metal ontosaid steel and to exclusively deform saidwhite metal, with said steel remaining substantially undeformed, whereby a white metal coating is obtained having a surface smoothness of less than one micron.

2. Method as claimed in claim 1 wherein said steel surface is heated to a temperature of about 320 to 380 C.

3. The method of claim 2 where said heating is conducted inductively.

4. The method of claim 2, where said pressing is conducted under a shielding gas.

5. The method of claim 2, where said white metal comprises an alloyfof Pb, Sb, Sn, and As.

6. The method of claim 5, where said alloy comprises 13.5 percent Sb, 1.5 percent Sn, 1 percent As and the balance Pb. z

7. The method of claim 2 where said white metal is reduced by an amount comprising 20 percent to percent during said pressing.

8. The method of claim 2, where said white metal before plating varies from 0.35 to 1.0 mm. in thickness.

References Cited V UNITED STATES PATENTS 1,956,464

JOHN F. CAMPBELL, Primary Examiner.

D. C. REILEY, Assistant Examiner.