US2382868A

US2382868A - Art of metal-coating metals

Info

Publication number: US2382868A
Application number: US423154A
Authority: US
Inventors: Colin G Fink
Original assignee: Metal Alloys Inc
Current assignee: Metal Alloys Inc
Priority date: 1941-12-16
Filing date: 1941-12-16
Publication date: 1945-08-14
Anticipated expiration: 1962-08-14

Description

llg.. 14, Q G. F|NK ART OF METAL-COATING METALS Filed Dec. 16, `1941 Y E N R O T T IN VEN TOR.

CGL/N G. F'YNK ZOTVDJOW atented Aug. 14, 1945 ART OF METAL-COATING METALS Colin G. Fink, New York, N. Y., assignor to Metal Alloys, Inc., Wilmington, Del., a corporation of Delaware Application December- 16, 1941, Serial No. 423,154

2 Claims.

This invention relates to the metal-coating of metals from molten metal baths and provides improvements therein.

Steel and other metals are commonly and extensively coated in molten baths, with tin and zinc, to a less extent with lead and cadmium, to some extent with alloys of the foregoing, and also with some other metals.

Room for improvement lies in the direction of a cleaner coating, greater certainty of complete coverage by the coating metal throughout the course of operations, greater ease of operations, greater speed of operation, and lessened costs.

The present invention provides an advance in the art of metal-coating of metals in most, if not all, of the directions of improvement stated above. The process of the present invention has a simplicity which is disconcerting in the light of the potentialities revealed by a disclosure of the present process and its successful results. To pass a Wet basis metal into a molten bath of a coating metal, as for example tin, aluminum, etc. is contrary to accepted ideas of good practice. The present process appears to be superior to previously known processes of metal-coating metals from molten baths. It operates in the cold up to the point of the introduction of the basis metal into the molten bath, flux adhesions are avoided, and the pretreatment consists ordinarily in applying a simple acid or salt aqueous solution to the basis metal.

Much work has heretofore been done on the cleaning of the basis metal before entering the bath of coating metal, including various pretreatments with reducing gas. I envisage a. gaseous cleaning of the basis metal in the functioning of my process, but my process appears to differ from previous processes and proposed processes, in the gaseous cleaning taking place in the bath of molten coating metal in a space or sleeve in the molten metal created by the expanding vapor and gas followed immediately by contact of the basis metal with the molten coating metal of the bath. The volatilization of the liquid on the basis metal, on entering the molten bath is so sudden as to be explosive, indicating that path of the cleaning of the metals is mechanical.

According to the present invention I wet a basis metal (mild-steel wire for example) with an aqueous cleaning solution (as a concentrated solution of hydrochloric acid) and, while the basis metal is moist with the solution, introduce it into the molten bath of coating metal (tin for example) in such manner that volatilization or giving off of the moist solution and reaction products takes place within the body of the molten metal itself followed immediately by contact of the basis-metal with the molten coating metal, the aforesaid volatilization or gasification or giving off effecting a deoxidation, reduc- -metal coating is fluid or semi-fluid.

tion or cleaning which prepares the basis metal so as to receive an adherent coating of the coating metal, similarly affected. After receiving its coating the basis metal is removed'from the bath of molten metal, and is usually wiped while the It is advantageous to introduce the basis metal article into the molten metal below the liquid-level thereof, as through an orice in the side-wall of the pot or container below the liquid-level of the coating metal therein; itis also advantageous to remove the coated basis-metal article from the molten bath in a similar way.v The method may nevertheless be carried out by introducing and removing the basis metal at the upper surface of the molten coating metal, as for example, through an orifice in a ledge partially submerged in the molten metal.

The volatilized products escape through the surface of the bath of molten coating metal, and are seen to escape through the upper surface of the bath, in line with the passage of a wire or strip of basis metal indicating a space or sleeve of gas and vapor around the Wire or strip extending some distance into the bath of molten metal beneath its surface.

An embodiment of apparatus for carrying out the present process is illustrated in the accompanying drawing, wherein:

Fig. 1 is a diagram of such apparatus.

Fig. 2 is a view of a pot for the molten coating metal.

Referring to said drawing:

Letter X designates a. basis metal article in the form of a Wire, the wire being unwound from a reel I0 and wound, after coating, on a reel l2.

Numeral l5 designates an applicator for wetting the wire X with a suitable reactive cleaning solution, which solution is carried by the wire into the bath for effecting cleaning, reduction or deoxidation as hereinafter described. The applicator may be in the form of a T-tube receiving a constant supply of solution from a receptacle Il. The ends of the T-tube I5 may be partially stopped as indicated at I8 and I9 to admit of the free passage of the wire X and at the same time minimize the escape of solution. The solution in the T-tube I5 is, for example, a cold concentrated solution of hydrochloric acid. Technical grades containing 35% to 50% hydrochloric acid have been used.

Numeral 25 designates a pot or receptacle for containing a molten coating metal, for example tin. A burner A26 may be provided for maintaining the molten metal at a. desired temperature above the volatilization or the melting points of the solutes used in the solutions. Ordinarily the temperature of the molten metal in the pot 2l is kept 50 to 200 C. above its melting point. With tin the temperature of the metal in the pot is maintained between 350 and 400 C.

The pot 25 is provided with an inlet opening 21 and an outlet opening 29, both in the sides of the pot below the liquid level of the molten metal therein. To provide for wires of different diameter, the openings 21 and 29 may be made considerably larger than the diameters of the smaller sizes of wire, and the openings stuffed with a suitablestuiiing material, as asbestos. as indicated at 33, the stuiling being effected in such manner as not to impede the passage of the wire, but at the same time to prevent the escape of molten metal through either of the orifices, except of course the molten coating metal adhering to the wire and carried out by the wire X through the exit opening 29. Moreover, by suitably compacting the stuffing in the exit opening 29 it may be made to function as a wiper. Or a wiper 40, as illustrated in Fig. 1, may be employed as is usual in the hot coating of metals for removing surplus metal, smoothing the coating, etc.

trated aqueous solution of hydrochloric acid and was wet by it. For this purpose it was run through the applicator I5 Fig. 1 which was constantly supplied with a concentrated solution of hydrochloric acid. While moist or wet with the hydrochloric acid solution and with reaction products of the hydrochloric acid solution on the steel basis metal, it was introduced beneath the surface of the bath of molten tin coating metal, the introduction, as shown in Fig. 1, being through an orifice 21 in the side wall of the pot 25, containing the molten tin. The wire X had a speed of 150 feet per minute on entering the pot 25 through said orifice, and carried the solution and reaction products on the wire into the molten metal below its upper surface, though higher and lower running speeds have been used. Within the bath of molten tin the solution of hydrochloric acid and reaction products carried by the wire X were volatilized and gasified, bubbles of gas and vapor arising and escaping through the surface of the molten tin in line with the advance of the wire and extending inward about one and one-half inches. While in the bath of moltentin the steel wire X received an adherent coating of tin which it carried with it as it emerged through an exit oriilce 29 in the side of pot 25. While the coating of tin was soft or semi-liquid it was passed through a wiper 40, which removed some of the molten tin coating metal, smoothing the coating, etc. At higher wire speeds, and for larger articles, a larger and longer pot would be used, as found desirable or necessary for best results.

The tin coating on the steel wire was bright and smooth, and adherent and continuous in its coverage.

The tin in the pot was maintained at a temperature of approximately 380 C. In general,

' the temperature of the coating metal is kept about 50 to 200 C. above its melting point (232 C.).

'Ihe minimum speed at which the basis metal, wet with the cleaning solution, is introduced into the bath of molten metal, should be such that the sleeve or zone of gas or vapor evolution extends within the body of the molten metal a distance of about one inch. This minimum speed will vary with the temperature cf the molten coating metal, the conductance and thickness of the basis metal, and perhaps, in a smaller way, with other factors.

Unless the steel wire X is badly oxidized I ilnd that it is not necessary to give it a preliminary cleaning; that is, mildly oxidized steel can be run oi of the reel through the hydrochloric acid solution and into the bath of molten tin. If badly oxidized, the steel wire can be preliminarily deoxidized or cleaned by any one or more of the well-known practices employed in the art for cleaning, as pickling. electro-cleaning, or treatment with a reducing gas.

I have obtained by the practice of the process bright adherent coatings of tin, lead, zinc, and cadmium on steel wire, and also on copper wire and on nickel wire, with a preliminary wetting in each instance with an aqueous solution of hydrochloric acid.

As a cleaning solution for wetting the basis metal just before entering the molten metal in the practice of the present invention, beside an aqueous solution of hydrochloric acid, aqueous solutions of hydriodic acid, hydrouoric acid, hydrobromic acid, acetic acid, oxalic acid and phosphoric acid, stannic chloride,lzinc chloride. and ammonium citrate have each been used.

I have also obtained adherent coatings of aluminum on steel by the practice of the present process, using certain of the cleaning solutions given above, namely aqueous solutions of acetic acid, stannic chloride and hydrochloric acid.

The invention may be carried out by other modes of procedure than that herein specifically described.

What is claimed is: a

1. In a method of coating a basis metal in continuous lengths with a coating metal through contact of the basis metal with the coating metal in a molten state after the basis metal has been wetted with an aqueous volatile acidic solution, the novel step of violently gasifying the acidic solution, within the body of the molten coating metal, from and around the entering portion of the basis metal, thereby forming a gaseous envelope, through an intrusion length of about one inch, by runing the cold basis metal wet with acidic solution directly into fresh molten coating metal below its surface level through a restricted orifice having substantially the same cross-sectional dimensions as those of the basis metal, without first passing through a cover layer of flux, oil, or oxide iilm of the coating metal.

2. A method of coating a basis metal incontinuous lengths with a coating metal. comprising wetting the cold basis metal with a cold aqueous volatile acidic solution, and violently gasifying the acidic solution, Within the body of the molten coating metal, from and around the entering portion of the basis metal, thereby forming a gaseous envelope, through an intrusion length of about one inch, by runing the cold basis metal wet with the acidic solution directly into fresh molten coating metal below its surface level through a restricted oriilce having substantially the same cross-sectional dimensions as those of the basis metal, without first passing through a cover layer oi' flux, oil, or oxide film of the coating metal.

COLIN G. FINE.