US2543365A

US2543365A - Method of tin coating ferrous metal articles and bath therefor

Info

Publication number: US2543365A
Application number: US600637A
Authority: US
Inventors: Arch W Harris
Original assignee: American Steel and Wire Company of New Jersey
Current assignee: American Steel and Wire Company of New Jersey
Priority date: 1945-06-20
Filing date: 1945-06-20
Publication date: 1951-02-27
Anticipated expiration: 1968-02-27

Description

Patented Feb. 27, 1951 METHOD OF TIN COATlNG FERROUS METAL ARTICLES AND BATH THEREFOR Arch W. Harris, Euclid, Ulric, assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey No Drawing. Application June 20, 1945,

Serial No. 600,637

This invention relates to improvements in the art of coating metal with tin, and more particularly to the coating of ferrous metal wire with tin for the purpose of providing a lubri cant for the drawing thereof.

My invention comprises applying a tin coating on ferrous metal articles such, for example, as iron or steel wire, by a simple immersion in an aqueous bath of a tin salt. In practicing the improved process, the ferrous metal articles which are to be tin coated are first provided with a coating of copper by immersion in an aqueous solution of a copper salt, such as copper sulphate, acidified with sulphuric acid. This method of coating ferrous articles with copper by simple immersion is Well known in the art, and processes have been proposed heretofore for similarly coating ferrous metals with tin by immersion in a tin-containing solution. In all such prior processes, a prolonged immersion time is required for the formation of the coating of tin, i. e., several hours in the usual operation.

My invention materially reduces the required immersion time to the order of minutes instead of hours, and assures a uniform coating of tin over the entire article being treated,

In a preferred practice, an initial coating of copper is applied in the manner indicated above. After the copper coating has been applied, the resulting copper-coated articles are immersed in a tin coating bath, which preferably is composed of a mixture of stannous chloride or stannous sulphate and zinc chloride, the mixture of tin salt and zinc chloride being dissolved in a suitable quantity of water as will be pointed out in greater detail hereinafter. A quantity of metallic tin is placed in the solution for the purpose of preventing oxidation of the stannous salt and to maintain the soluble tin content of the bath. Feathered metallic tin is preferred, because of the large area of surface presented thereby.

The following specific example illustrates a preferred practice of the invention, but is intended to be illustrative only in character, and not to limit the process in the various aspects thereof to the specific conditions described.

In carrying out the improved process, I provide a bath composed of approximately 0.75 pound of stannous chloride and zinc chloride each, per

gallon of water, and 0.2 pound per gallon of feathered tin. The tin remains in the bath in metallic form for a purpose to be explained shortly. After being coated with copper as explained above, the ferrous articles are immersed filaims. (Cl. 11750) I in the bath just described, which is kept heated approximately to the boiling point. This solution will deposit about three grams of tin coating per kilogram of 0.637 inch high carbon steel wire in approximately ten minutes at boiling temperatures. The copper coating on the article is replaced by tin in the approximate ratio of two atoms of copper by one of tin. Instead of the stannous chloride, stannous sulphate may be em-v ployed. The replaced copper forms the chloride or sulphate, depending upon whether the tin salt employed is stannous chloride or stannous sulphate. Deposition of tin on the article tends to deplete the'tin content of the solution but the depletion isiimmediately made up by solution of the feathered tin at the bottom of the bath. The concentration of the bath thus remains constant and the copper salts formed as a result of replacement of the copper coating by tin crystallize out of solution and settle to the bottom of the bath.

Heating the bath facilitates deposition of the tin, and it is preferred to operate at'about the boiling point of the solution, although lower temperatures may suffice for certain purposes. Any water-soluble tin salt may be em loyed, the stannous chloride and stannous sulphate being the most readily available. The function of the zinc chloride is not understood, but I have observed that its presence is necessary in order to give the desired speed in the deposition of the tin.

I am aware that it has been proposed to coat ferrous articles by dipping them in a fused bath of tin salts, such as those mentioned herein. The use of such bath, however, is characterized by very definite disadvantages. Thus, it is difficult to maintain the established physical properties of the wire after it has passed through a molten salt bath, which must be maintained at 600 F., whereas no difficulty at all is encountered in maintaining the rare-established physical properties of a cold-drawn wire if the same be coated with tin by using the aqueous solution described above, even when it is heated nearly to its boiling point.

A further disadvantage is that the tin coating obtained by using the fused salt bath is the same type obtained by using a bath of molten tin, that is to say, the coating is many times heavier than needed to serve as a lubricant in drawing the wire, the tin forming an alloy with the steel base. In using the fused salt bath, moreover, it is necessary, as in the case of hot-dip tinning, to wipe the coated wire in order to obtain a smooth coating which is necessary to facilitate drawing. My process results in a tin coating which is smooth enough without wiping to serve satisfactorily as a lubricant when drawing the wire. In drawing wire with a tin coating a plied by my invention it has been found possible to make twelve drafts on the cone machine producing a music wire finish.

It will be apparent that various modifications in the procedure described may be made without departing from the spirit of the invention or the appended claims.

I claim:

1. In a process of coating ferrous articles with tin, the steps including immersing the articles in an acidified aqueous solution of a copper salt, thereby causing a layer of copper to be deposited on the article, thereafter immersing the coppercoated articles in a bath of an aqueous solution of a water-soluble stannous salt and zinc chloride. having a quantity of metallic tin therein and holding the articles in the said bath until the copper coating thereof is substantially entirely replaced by tin, the metallic tin in the bath replacing the tin plated out of the bath.

2. A process as defined by claim 1 characterized by said aqueous solution being composed of approximately 0.75 pound per gallon of water each of stannous salt and zinc chloride.

3. A process as defined by claim 1 characterized by heating the bath to a temperature approaching the boiling point of the solution.

4. A process as defined by claim 1, wherein the stannous salt is stannous sulphate.

5. A process as defined by claim 1, wherein the stannous salt is stannous chloride.

6. In a process of finish-coating a ferrous product having an initial coating of copper thereon, the steps including immersing the product in a bath of an aqueous solution of a water-soluble stannous salt and zinc chloride, having a quantity of metallic tin therein and continuing the immersion until the copper coating on the prodnot has been substantially replaced by tin.

7. A coating bath for depositing tin by displacement of a copper coating on ferrous articles comprising an aqueous solution of substantially equal parts of a water-soluble tin salt and zinc chloride and containing metallic tin.

8. A coating bath as defined by claim '7 characterized by said solution being composed of substantially 0.75 pound per gallon of water each of a water-soluble tin salt and zinc chloride, and containing approximately 0.2 pound of metallic tin per gallon.

9. A coating bath as defined by claim 7, wherein the tin salt is stannous sulphate.

10. A coating bath as defined by claim 7, wherein the tin salt is stannous chloride.

ARCH W. HARRIS.

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

UNITED STATES PATENTS Number Name Date 97,417 Lothrop Nov. 30, 1869 1,256,084 Watkins Feb. 12, 1918 2,144,798 Epperson Jan. 24, 1939 2,159,510 Pavlish May 23, 1939 2,282,511 Bradley May 12, 1942 2,369,620 Sullivan Feb. 13, 1945 FOREIGN PATENTS Number Country Date 240 Great Britain 1857

Claims

1. IN A PROCESS OF COATING FERROUS ARTICLES WITH TIN, THE STEPS INCLUDING IMMERSING THE ARTICLES IN AN ACIDIFIED AQUEOUS SOLUTION OF A COPPER SALT, THEREBY CAUSING A LAYER OF COPPER TO BE DEPOSITED ON THE ARTICLE, THEREAFTER IMMERSING THE COPPERCOATED ARTICLES IN A BATH OF AN AQUEOUS SOLUTION OF A WATER-SOLUBLE STANNOUS SALT AND ZINC CHLORIDE, HAVING A QUANTITY OF METALLIC TIN THEREIN AND HOLDING THE ARTICLES IN THE SAID BATH UNTIL THE COPPER COATING THEREOF IS SUBSTANTIALLY ENTIRELY REPLACED BY TIN, THE METALLIC TIN IN THE BATH REPLACING THE TIN PLATED OUT OF THE BATH.