US2702525A - Apparatus for coating wire or strip with molten aluminum - Google Patents

Description

1955 M. G. WHITFIELD 2,702,525

APPARATUS FOR COATING WIRE 0R STRIP WITH HOLTEN ALUMINUM I Filed July 13, 1949 2 Sheets-Sheet 2 INVENTOR.

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dam/1% United States Patent 9 APPARATUS FOR COATING WIRE on smrr wmt MOL'IEN ALUMINUM Marshall c. Whitfield; Garden City, N. Y., nsslgnor m Whitfield & Sheshunotf Incorporated, Garden City, N. ill, a corporation of New York Application July 13, 1949, Serial No. 104,436

11 Claims. (Cl. 118-420) This invention relates to improvements in methods and apparatus for coating metal wire and strip with aluminum.

When wire is coated with aluminum by standard procedures, there is a pronounced tendency for a successive, localized build-up of the coating in thickness in the form of rings or berries" around the wire, as it emerges from the molten aluminum. This uneven coating is undesirable in itself and interferes with the subsequent drawing of the wire, and other operations thereon.

In like manner, when metal strip is coated with molten aluminum by standard procedures, light and heavy striations of coating are frequently produced. The employment of various mechanical means to avoid the formation of light-heavy zones of coating thickness has been suggested. These mechanical means are difficult to construct and maintain in exact adjustment, and are expensive to use.

Also, it should be noted that means and methods used to control coating thickness and uniformity for metals such as zinc and tin have not been found to be of practical application in the case of aluminum. This is due in large part to the great affinity of aluminum for oxygen. The ready formation of aluminum oxide has prevented the successful use of exit apparatus suitable for use with other molten coating metals. Oxide inclusions in the coating are frequent. Tests indicate also that the formation of oxide on the bath and its periodic movement or removal is largely responsible for the uneven coating on wire and strip. Aluminum oxide is not reducible by hydrogen, or other commercial reducing atmospheres.

It is an object of the invention to provide a method of coating wire or strip with aluminum in such a way as to obtain markedly greater uniformity, and to provide apparatus for this purpose.

It is an object of the invention to provide a method and apparatus for the control of oxide at the point or area of emergence of a wire or strip from a bath of molten aluminum.

It is an object of the invention to provide a method and apparatus for coating wire or strip with aluminum, which is economical and positive in use, and which re quires a minimum of equipment.

These fundamental objects, and more specific ones which will be set forth hereinafter or will be apparent to the skilled worker in the art upon reading these specifications, I accomplish by that procedure and in the use of that apparatus of which I shall now describe certain exemplary embodiments.

Reference is made to wherein:

Figure 1 is a diagrammatic vertical section of one embodiment of the apparatus used in conjunction with the invention.

Figure 2 is a top view of the metal delivery means to be later described.

Figures 3 and 4 show in vertical section and plan view an alternative construction of the metal delivery means.

Figure 6 is a side elevation of another form of the apparatus of the invention, and

Figures 5 and 7 are respectively plan and vertical sectional views providing a detailed showing of the device used to divert the molten metal.

Briefly in the practice of the invention, I cause molten coating metal to move with respect to the surfaces ofthe wire or strip being coated in ways hereinafter more spethe accompanying drawings cifically set forth. The movement itself has an effect on the coating operation, particularly leading to uniformity of coating. Also the movement is so controlled as to eliminate the build-up of oxide on the surfaces of the strip or wire and the normal type of accumulation of oxides on the surface of the bath, and is further so controlled as to cause the wire or strip to carry away fresh oxide as it is being'formed thereon at the point or area of emergence of the strand or wire from the bath to prevent its harmful accumulation at the exit point.

In Figure l I have shown an embodiment of one form of the invention. The numeral 10 designates a metal holding pot having channels 13 in a lower insulating structure forming a known type of induction furnace. Induction heating coils 13a surround one or more of the channels, as in conventional furnaces of this type A flow of metal in the induction furnace channels is produced by the action of the induction means, and for illustrative purposes is indicated generally by arrows. direction of flow as respects any particular channel or channels is not a limitation on the invention, since the means hereinafter described may be associated with any channel or channels in which the direction of flow is as desired.

Extending upwardly from one of the channels 13 in which the metal flows upwardly into the pot, i provide a pipe-like member 14, connected with an open-ended cylinder 15 in offset relationship. This structure may be supported at the bottom by a flange 16 and may be provided with an arm 17 which can engage the pot ill or a beam extending across it, for further support. The cylinder 15 is so located that its upper end extends somewhat above the level 18 of the molten aluminum in the pot. The connection between the pipe-like member 1 and the cylinder 15 is an upwardly slanting connection such that molten metal from the member will be caused to flow upwardly in the cylinder. Located in the bath of metal is a sheave 19 about which the wire 20 to be coated is passed. The sheave 19 is located below the cylinder 15 of the pipe-like extension 14, and is positioned in the pct 10 by any suitable means such as the bracket 21 and pivot 22. The wire 20 to be coated passes upwardly from the molten bath through the cylinder 15 In the operation of the invention, the coating metal is maintained in molten condition by the action of the induction furnace. Relatively cooler portions of the metal in the pot 10 descend in one or more of the channels 13 and are heated by the coil or coils surrounding one or more of the channels. The action of the coils in causing the heated molten metal to rise rapidly in one or more of the channels is due to electromagnetic forces set up in the molten metal. I take advantage of this propulsion of the molten metal by directing it through the pipe-like member 14 and upwardly through the cylinder 15, the molten metal spilling away from the surface of the wire 20 above the level 18 of the bath, as indicated by the arrows in Figure 1. There is thus provided a sufficient velocity to sweep away or break up the oxides, as they are formed at the surface and around the coated strand as it emerges. The normal accumulation of oxides occurs on the surface of the bath 18 but is kept away from the emerging wire not only by the flow of molten metal as described, but also by the fact that the cylinder 15 extends at its upper end above the level 18 of the molten metal bath.

Molten metal from the bath proper may also be aspirated into the cylinder 15, as indicated by arrows in Figure 1. We have found that with induction furnaces a sufficient flow of molten metal may be produced to accomplish the objects of this invention, although precautions may be taken to increase thevolume and rapidity of the metal propulsion, as may be desired. For example, in a twin-coil, single phase furnace, a high amperage such as 60-kw., combined with a symmetrical magnetic field and the low specific gravity of aluminum produces an energetic metal propulsion. Utilizing the propulsive forces of an induction heating device is of especial value in my arrangement since the maintenance of mechanical propulsive elements beneath the surface gfuzi bath of molten aluminum presents very great difc ties.

Patented Feb. 22, I955.

It should be noted that in the practice of the invention I do not completely eliminate the formation of any oxide on the emerging wire or strip. The still molten aluminum carried out of the bath can and does oxidize slightly at the exposed surfaces before solidifying. It is not my practice to attempt to prevent such oxidation by the maintenance of the reducing atmosphere-over the exit portion of the bath. Rather, the bath is kept .free at the point of emergence of the wire or strip from the relatively continuous layers or rings of oxide ordinarily formed on the bath, which would produce inclusions in the metal and non-uniformity of coating, and hence the practice of the invention is efiective to prevent the formation of large and uneven deposits of oxide and metal in the coating. Actually, wire or strip coated .vith aluminum by the flprocesses of the invention is uniformly covered with ecks or streaks of oxide which has been kept so thoroughly dispersed that it cannotand does not afiect the uniformity-of the coating. Also, the agitation of the metal in the way set forth at the point of emergence of the strand promotes uniformity of coating. The agitation of the metal at the point of emergence is of great importance in the practice of the invention.

Referring to Figures 3 and 4 of the drawings, I have indicated a variation in the form of the cylinder 15 comprising essentially the provision of fingers 24 in the path of the molten metal rising through the cylinder, which fingers produce additional turbulence of the molten metal at the point of exit of the wire 20. Aluminum oxide forming upon the surfaces of molten aluminum creates a layer of great tenacity which is difiicult not only to remove as such, but to break up for purposes of removal. The additional turbulence caused by the fingers 24 is valuable in this connection. The fingers may be integral with the cylinder 15 or they may be formed as parts of a cap-like element 23 which may be slipped over the end of the cylinder and, hence, is replaceable as desired.

In Figures 5, 6 and 7 I have shown a modified form of apparatus particularly designed for the coating of strip. Here, a metal coating pot forming part of an induction heating furnace is indicated at 25, the furnace comprising channels 26 in which the metal is driven upwardly as expelled bv the electromagnetic forces of the induction heating. These channels are provided with pipe-like members 28 provided with supporting rims 29 and, as may be required, with supporting lugs or brackets The pipe-like members extend upwardly from the floor of the pot substantially at or even slightly beyond the level of the molten metal rim. They have curved upper ends or nozzle portions 31 so arranged that the molten metal. which is propelled upwardly through them, will be directed along opposite surfaces of a strip 27. In Figures 5 and 6 the direction of flow of the molten metal is indicated by arrows.

We have found that by directing the molten metal in a rapid flow across the surfaces of the strip 27 as it emerges from the bath, a marked improvement in uniformity of coating is achieved. The fiow of metal as such, especially since the'streams are made up of oxidefree metal from the channels 26, helps to keep generaloxide from the surfaces of the bath away from the surfaces of the emerging strip, and the turbulence of the metal helps to keep the accumulating oxidefilm dispersed adjacent the surfaces of the strip.

I prefer also to provide a component of the flow away from the surfaces of the strip as well as to provide means for creating additional turbulence. These purposes are accom lished by providing vanes or fingers 33 directed slantwise toward the surfaces of the strip 27 and inclined in the direction of flow of the molten metal. These vanes or fingers divert some of the metal from the oppositely flowing streams to directions away from the surfaces of the sheet, carrying oxides with them. The vanes or fin ers-also help to break up the oxide film.

The vanes or fin ers are conveniently supported upon bars or brackets 34 so that the arrangement is readily removable for cleaning or replacement.

The component of flow awav from the surfaces of the stri can be increased by directing the nozzles 31 in a slightlv upward direction against the surfaces.

While I have described mechanism and a procedure in connection with controlling conditions at the exit point of'the bath, the same mechanism and procedure can be readily adapted, as will be understood by the skilled worker in the art to control conditions, particularly as to the accumulation of oxide on the bath, at the entrance point, or at both the entrance and exit points. Also, while the invention has been described for the coating of materials in the form of continuous strands, wire or strip, the principles of the invention are applicable to the coatin of individual articles either by dippm in which everi the entrance and exit points of the ba may coincide, or by continuous passage of the articles through the bath by suitable guide or conveyor means.

As an auxiliary control cool air may be blown across the wire, strand or articles at the position of emergence from the bath.

Modifications may be made in the invention without departing from the spirit thereof. Having thus described my invention in certain exemplary embodiments, what I claim as new and desire to secure by Letters Patent is:

1. Apparatus for use in the coating of metal stri with aluminum which comprises a pot for holding a ha of molten metal, an induction furnace mounted beneath said pot having channels through which the metal is inductively propelled, said channels opening into the bottom of said pot, hollow tubes located in the metal holding pot covering the openings of said channels, said tubes arranged to carry the flow of molten metal which rises in certain of said channels, said tubes having openings directed towards each other and arranged to direct the metal flowing in them in streams across the bath of molten metal substantially at the surface. thereof, means for passing said strip into said bath, and means for withdrawing said strip from said bath substantially between said tubes, so as to subject the surfaces of said strip to said streams.

2. The apparatus of claim 1 in which said pot is provided with a row of fingers located in the path of said flow of said streams of metal issuing from each of said tubes, said fingers being partly submerged in the bath of molten metal, and said rows of fingers being arranged so that the coated strip may be withdrawn from the bath between said rows.

. 3. The structure claimed in claim 2, wherein said fingers are inclined toward the surfaces of said strip in directions opposing the flow of said streams.

4. Apparatus for use in the production of an even coating of aluminum on wire or strip, which comprises a pot for holding molten metal, means for passing said wire or strip into a bath of molten metal in said pot and out at the surface of said molten metal at a point separated from the surrounding walls of said pot, induction heating means for the molten metal in said pot, said induction heating means being located externally of said pot and having channels leading into said pot through the walls thereof at points adjacent to the bottom of said pot, one at least of said channels serving as exit means for molten metal from said pot and another at least of said channels serving as entrance means for molten metal into said pot, said induction heating means serving to propel the molten metal through said channels and heat it while being propelled, and a hollow fitting of tubular form connected with said entrance channel beneath the surface of said bath and extending to the surface of said molten metal at the said exit point for said strip or wire, and serving to isolate the entering molten metal from said bath substantially to said exit point whereby to deliver to said exit point the incoming molten metal in a stream of substantially undiminished force and whereby said wire or strip is caused to exit from said bath in said stream.

The apparatus claimed in claim 4 wherein said fitting comprises a body portion and an open-ended upp r portion set in off-set relation to the body of the fitting, said .oif-set portion extending above the surface of the bath so that molten metal flowing through said fitting will cascade into the bath, said off-set portion having projections on its inner walls to create turbulence in the stream of molten metal as the said metal flows from said fitting.

6. Apparatus for use in the coating of metal strip with aluminum which comprises a pot for holding a bath of molten metal, means for passing said strip into saidbath and for withdrawing said strip, an induction furnace mounted externally of said pot and having channels through which the molten metal is inductively propelled, said channels opening into said pot at points adjacent to the bottom thereof, two of said channels being entrance channels through which the molten metal flows into said t and at least one of said channels being an exit channel or metal flowing from said pot, hollow tubes located in the metal holding pot and extending from said entrance channels respectively to the surface of said bath, said tubes acting to isolate streams of molten metal from the molten metal in said bath and to carry said streams with substantially undiminished force to the surface of said bath, where said tubes have openings directed toward each other, said tubes at the surface of said bath lying in spaced relationship to each other and positioned off the edges of said strip where said strip leaves said bath, said openings being directed so that each produces a stream of metal flowing across a surface of said strip at the surface of said bath, said streams being respectively oppositely directed.

7. The apparatus claimed in claim 6 wherein the free end of said tube is positioned so as to direct the stream of molten metal across the surface of the bath, and wherein said pot is provided with a row of bafiles located in the path of said stream, said bafiles being positioned so as to be partially submerged in said bath.

8. The structure claimed in claim 6 in which said pot is provided with a row of fingers located in the path of flow of said streams of metal issuing from each of said tubes, said fingers being partly submerged in the bath of molten metal, and said rows of fingers being arranged so that the coated strip may be withdrawn from the bath between said rows.

9. The structure claimed in claim 8 wherein said fingers are inclined toward the surfaces of said strip in directions opposing the flow of said streams.

10. Apparatus for use in the production of an even coating of aluminum on wire .or strip which comprises a.

ing to heat molten metal and propel it through said channels, a hollow fitting on a channel through which molten metal is propelled into said pot, said fitting extending through said pot from the bottom thereof to the surface of the metal in said pot, and means for passing said wire or strip into the bath of molten metal in said potand out through said molten metal at a point where the metal delivered by said hollow fitting will flow about the wire or strip as it leaves the bath.

11. Apparatus claimed in claim 10 wherein said fitting comprises a body portion and an open ended upper portion in ofiset relation to said body portion, said offset portion extending above the surface of the bath so that molten metal flowing through said fitting will cascade into the bath, said offset portion having projections on its inner walls to create turbulence in the stream of molten metal as the said metal flows from said fitting.

References Cited in the file of this patent UNITED STATES PATENTS 2,166,250 Herman July 18, 1939 2,398,034 Oganowski Apr. 9, 1946 2,520,349 Tama Aug. 29, 1950 2,528,208 Bonsack et al Oct. 31, 1950 2,528,209 Bonsack et al Oct. 31, 1950

Claims (1)

1. 4. APPARATUS FOR USE IN THE PRODUCTION OF AN EVEN COATING OF ALUMINUM ON WIRE OR STRIP, WHICH COMPRISES A POT FOR HOLDING MOTEL METAL, MEANT FOR PASSING SAID WIRE OR STRIP INTO A BATH OF MOLTEN METAL IN SAID POT AND OUT OF THE SURFACE OF SAID MOLTEN METAL AT A POINT SEPERATED FROM THE SURROUNDING WALLS OF SAID POT, INDUCTION HEATING MEANS FOR THE MOLTEN IN SAID POT, SAID INDUCTION HEATING MEANS BEING LOCATED EXTERNALLY OF SAID POT AND HAVING CHANNELS LEASING INTO SAID POT THROUGH THE WALLS THEREOF AT POINTS ADJACENT TO THE BOTTOM OF SAID POT, ONE AT LEAST OF SAID CHANNELS SERVING AS EXIT MEANS FOR MOLTEN METAL FROM SAID POT AND ANOTHER AT LEAST OF SAID CHANNELS SERVING AS ENTRANCE MEANS FOR MOLTEN METAL INTO SAID POT, SAID INDUCTION HEATING MEANS SERVING TO PORPEL THE MOLTEN METAL THROUGH SAID CHANNELS AND HEAT IT WHILE BEING PROPELLED, AND A HOLLOW FITTING OF TUBULAR FROM CONNECTED WITH SAID ENTRANCE CHANNEL BENEATH THE SURFACE OF SAID BATH AND EXTENDING TO THE SURFACE OF SAID MOLTEN AT THE SAID EXIT POINT FOR SAID STRIP OR WIRE, AND SERVING TO ISOLATE THE ENTERING MOLTEN METAL FROM SAID BATH SUBSTANTIALLY TO SAID EXIT POINT WHEREBY TO DELIVER TO SAID EXIT POINT THE INCOMING MOLTEN METAL IN A STREAM OF SUBSTANTIALLY UNDIMINISHED FORCE AND WHEREBY SAID WIRE OF STRIPS IS CAUSED TO EXIT FROM SAID BATH IN SAID STREAM.

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