US3354864A

US3354864A - Apparatus for coating metallic strands

Info

Publication number: US3354864A
Application number: US394158A
Authority: US
Inventors: Earle L Knapp
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1964-09-03
Filing date: 1964-09-03
Publication date: 1967-11-28
Anticipated expiration: 1984-11-28
Also published as: DE1521112A1; ES317083A1; BE669154A; GB1114119A

Description

Nov. 28, 1967 E. KNAPP APPARATUS FOR COATING METALLIC STRANDS 2 Sheets-Sheet 1 R O T W E A N WK I... E IL ,2 A E ATTORNEYS.

NOV. 28, KNAPP APPARATUS FOR COATING METALLIC STRANDS 2 Sheets-Sheet 2 Filed Sept. 3, i964 Hill'll INVENTOR. EARLE L.KNA PP,

ATTORNEYS,

United States Patent ()hio Fiied Sept. 3, 1964, Set. No. 394,158 11 Claims. (Cl. 118-63) This invention relates to the continuous coating of metallic strands with molten metal. The term strand is used in this specification as inclusive of tubing, wire and strip, and hence, while the exemplary embodiment of the invention described hereinafter refers to the coating of wire, the invention is not to be so limited. It may be used with either strip or wire as set out above. Similarly the invention has great and particular utility where the coating metal is aluminum but it may be practiced with any of the conventional coating metals, including zinc and the like.

United States Patents Nos. 2,914,423 and 2,914,419 in the names respectively of E. L. Knapp and K. Oganowski, both relate to a metallic coating process utilizing what may be called a short immersion technique. In each of these patents, a metallic strand is passed upwardly in a vertical path into contact with a pool of molten metal. In each of these patents, the strand to be coated is contacted by molten metal at a point above the normal level of metal in the bath; that is, the moving strand serves to draw the molten metal in the bath upwardly as it passes therethrough. The phrase negative head has been used in these patents to describe this phenomenon.

The short immersion technique'of these patents is especially valuable in the coating of iron or steel strands with aluminum or aluminum rich alloys. By virtue of the short immersion, the pick-up of iron by the molten aluminum bath is greatly reduced, and because of the reduced exposure time, the original physical properties of the strand may to a large extent be retained.

While a short immersion technique is believed to be of significant value, the vertical mode of operation described in these patents involves a great deal of rather expensive equipment, and a very critical set of speeds and relationships. Accordingly, the operating elficiency leaves something to be desired.

Furthermore, especiallyin the case of aluminum coatings, it is very difficult to apply a heavy coating, due to the existence on the surface of the bath of a tough oxide film which tends to be pulled onto the moving strand, and which forms a highly irregular and commercially useless coating.

It is therefore a primary object of this invention to provide a highly efficient apparatus which will serve to continuously coat a metallic strand while maintaining a very short immersion time in the bath of molten metal.

More specifically, it is an object of this invention to provide an apparatus for the coating of metallic strands wherein the strand passes through the molten metal in a horizontal path.

A further object of the invention is to provide an apparatus wherein the strand passes in a horizontal direction through a bath of molten metal at a point below the normal level of molten coating metal in the apparatus.

Another object of the invention is to provide an apparatus by means of which thick coatings (in excess of 0.40 ounce per square foot of strand surface) of high purity aluminum may be applied by a short immersion process to metallic strands.

Still another object of the invention is a short immersion coating apparatus which will consistently produce uniform weight coatings on metallic strands.

; Numerous other objects and advantages of this inven- .-tion will become apparent to the skilled worker in the art as this specification proceeds. Reference will be made to the accompanying drawing which will show in detail an exemplary embodiment of the invention, and in which:

FIG. 1 is a front elevational view showing a portion of the apparatus of this invention, including two coating compartments, the melt reservoir, and pump assembly; and

FIG. 2 is a cross sectional view through a coating compartment according to this invention, as seen along :the line 2-2 of FIGURE 1;

FIG. 3 is a perspective view showing the gas finishing nozzle of this invention.

As is well known in the art, a metallic strand must be thoroughly cleaned or otherwise prepared prior to entering the coating bath, so -that the coating metal will adhere properly to the strand surface; and it will be understood that this invention is not directly concerned with the preparatory steps of a coating process, so long as the strand arrives at the apparatus of this invention with its surface properly prepared. By way of example, US. Patents Nos. 2,110,893 and 2,136,957, in the name of T. Sendzimir teach a process wherein a light oxide film is first for-med on the surface of the strand, and the strand is then passed through a reducing furnace to remove the prior formed oxide layer. Finally, without re-exposing the strand to atmosphere, it is passed into a bath of molten coating metal. Another satisfactory series of pre-coating steps are taught in the co-pending application Serial No. 397,538 entitled Method of Producing Metallic Coated Ferrous Strands.

Briefly considered, the instant invention is adapted to receive a properly prepared strand, which is passed in a horizontal direction through a restricted aperture in a die formed of a material which is not Wetted by the coating metal, into a pool of molten metal. The coating compartment itself is of a relatively short length, so that the total time during which the moving strand is in contact with the coating metal bath is quite short.

The strand then exits through another restricted aperture in a die of non-wettable material, with gas jets directed at the exit die from its outer side, thereby limiting excessive melt drag out, and forming a thick, uniform coating on the strand.

Referring now to FIG. 2, the coating compartment has been indicated generally at 10, through which the strand 12 to be coated passes in a substantially horizontal path. (When viewed as in FIG. 2, the strand 12 will be passing from right to left.) At the right hand portion of the figure is seen a heat resistant tube 14 through which the strand has passed since leaving the last stage of the pre-coating processing, which in the case of the Sendzimir process outlined above, will be a hydrogen reducing furnace.

The tube 14 is secured in any suitable manner to the entrance chamber 15, which is provided with the inlet 16 for a suitable reducing gas such as dissociated ammonia. The inlet 16 communicates with the annular groove 17 in the plug 18, and the incoming gases are directed thereby back through the tube 14. The entrance chamber 15 may also be provided with a dust pocket, as at 19.

Between the entrance chamber 15 and the coating compartment 10 is the coating metal trap 20, including the inlet 21 for a suitable inert or reducing gas, such as dry nitrogen gas. The trap 20 also includes the passage 22, by means of which any coating metal passing through the entrance die to be described, is returned to the supply trough.

The right hand wall of the coating compartment (as seen in FIG. 2) is provided with a recess which receives the entrance die 23. The die 23 must be of a material which is not wet by the coating metal, to minimize escape of the coating metal therethrough. It is also important that the die 23 be of a material which will not flake off during the passageof the wire 12, and might thereby prevent the wire itself from being wet. Removably secured to the left hand wall of the coating compartment is the exit die holder 24, which receives the exit die 28. This die should also be formed of some material which will not be wetted by the coating metal; in the preferred form of the invention, the

dies

23 and 28 will both be made of a refractory material such as a stabilized zirconium silicate.

As is clearly shown in he drawings, the die 28 is received in the recess in the holder 24 with substantial clearance. By virtue of this construction, the die 28 is free to float with respect to the coating compartment 10 as the wire or strand 12 passes therethrough. This floating die arrangement makes it possible to secure a uniform coating on wire, despite helical movement due to the uncoiling step, it being understood that the molten metal drawn by the strand 12 into the enlarged entrance opening of the die 28 will exert suflicient force to maintain a uniform radial distance between the strand and the die. An analogous floating die set up is taught in recently issued U.S. Patent No. 3,060,889 in the name of E. L. Knapp.

By virtue of this arrangement, the strand to be coated passes from the last stage of the pre-coating processing, through the coating compartment, without passing over guide sheaves or rollers of any kind. This insurers that the surface of the strand is uniformly prepared and insures an even coating.

Turning now to FIG. 1, a pair of coating compartments 10 and 16a have been shown as adapted to be supplied with molten metal from a common source, including the supply trough 34, the melt reservoir 36, and the supply tube 38. Molten metal in the supply trough will enter the pump body 40 through aperture 42, and will rise to approximately the level indicated by the line 44. Pulsed gas, preferably nitrogen, will be admitted to the pump 40 through the conduit 46, and will serve to force a supply of molten metal through the pump feed tube 48, into the melt reservoir 36, which will be filled to approximately the level indicated by the line 50.

Metal passes from the melt reservoir 36 into the supply tube 38 via the pump drain tube 52. Each of the

coating compartments

10 and 10a are provided with the snorkel tube 54 (see FIG. 2) the end of which is in communication with the interior of the supply tube 38. Thus the level of molten metal in the

coating compartments

10 and 10a will be exactly equal to the level in the melt reservoir 36.

When continuous operation of a coating line is contemplated, molten metal from a suitable supply will be fed into the melt reservoir 36 by gravity, and from there to the coating compartments 10 and 10a in the manner described above. The pump will only be used intermittently to return molten metal which has escaped into the supply trough 34, to the melt reservoir.

Preferably, the level of molten metal in the coating compartments will be maintained very slightly above the top of the strand passing therethrough, so that the hydrostatic pressure is held fairly low. This will limit excessive melt drag out with the exiting wire. It is also believed that by passing the wire below the surface of molten metal, pick up of the surface oxide layer by the moving strand is very greatly reduced. In some cases it may be desirable to provide a ring of material about the inside of the coating compartment at the normal, molten metal level, which is wettable by the coating metal in the compartment; this prevents the oxide layer from being drawn out with the strand.

It should be pointed out at this time that according to the teachings of the co-pending application entitled Method of Producing Metallic Strands referred to earlier, the wire being coated enters the molten bath at a temperature below that of the finishing temperature for the given coating metal. To prevent freezing of the bath by the relatively cold entering wire, the molten metal supply should be continuously heated, and the coating compartment may be provided with the cover 56 to reduce heat loss to atmosphere. Bath heating means may be included as a part of this cover 56.

In some applications (e.g. with high bath temperatures, where thermal cycling of the strand is not critical) the use of an insulating type cover 56, along with circulation of coating metal from the melt reservoir 36, through the overflow aperture 57 in its front wall, into the supply trough 34, and back to the melt reservoir through the pump 40, will be sufiicient to hold a satisfactory bath temperature.

Upon leaving the exit die 28, the wire 12 passes into the gas finishing chamber, formed between the

mating elements

58 and 60. As seen in FIG. 3, the element 58 is provided with the passage 62 which is supplied with a non-oxidizing or reducing gas according to the teachings of U.S. Patent 2,526,731, in the name of K. G. Coburn. The finishing gas passes through the

apertures

64 and 66 into the finishing chamber. It will be seen that according to this construction, all of the finishing gas impinges on the coated strand from below. It is believed that the gas therefore performs the additional function of supporting the still molten coating in a position concentric with the wire 12, so that a uniform thickness coating is obtained.

It will also be noted that the finishing gases emerging from the passage 66 are directed at the exit die 28, this serving to narrow the meniscus of the molten metal and confine it within the clearance of the die 28. The narrowness of the meniscus, along with the control of molten aluminum oxidation causes an even flow of coating metal onto the strand without the formation of surface irregularities. It is, of course, within the scope of this invention to provide additional gas finishing jets if desired.

Numerous modifications in the details of the invention may be made without departing from its scope and spirit, and it should be understood that no limitations are intended except insofar as set forth in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An apparatus for coating a metallic strand with a molten coating comprising:

(a) a coating compartment adapted to be supplied with molten coating metal to not more than a normal level, and having entrance and exit apertures for the passage of a strand in a horizontal path in opposed walls thereof, said apertures being disposed immediately below said normal level;

(b) an exit die having a restricted die orifice;

(c) means floatingly securing said exit die to said compartment in alignment with said exit aperture; and

(d) a gas finishing nozzle disposed closely adjacent said exit die and adapted to direct at least a portion of the gas passing therethrough into said exit die.

2. The coating apparatus claimed in claim 1 wherein said exit die is formed of a material which is not wettable by said coating metal.

3. The coating apparatus claimed in claim 2 including an entrance die secured to said coating compartment in alignment with said entrance aperture, said entrance die being of a material which is not wettable by said coating metal.

4. The coating apparatus claimed in claim 3 including means for providing a protective atmosphere for said strand up to its point of entry into said coating compartment.

5. The coating apparatus claimed in claim 4 wherein said gas finishing nozzle is adapted to direct a portion of the gas passing therethrough at the underside of said strand, whereby said still molten coating is maintained concentric with said strand during at least its initial cool- 6. The coating apparatus claimed in claim 5 including means for supplying molten metal to said coating compartment, and a molten metal trap associated with said entrance die, and with said metal supplying means, whereby molten metal, passing through said entrance die is returned to said supply means.

7. An apparatus for coating a metallic strand with molten coating metal comprising:

(a) means containing a supply of molten metal;

(b) a melt reservoir having a normal molten metal level;

(0) pump means for conveying molten metal from said supply to said melt reservoir;

(d) a coating compartment having entrance and exit apertures for the passage of a strand in a horizontal direction in opposed walls thereof; and

(e) passage means for conveying said molten metal from said reservoir to said coating compartment and to maintain said metal in said compartment at a normal level substantially equal to said normal level of molten metal in said melt reservoir, said normal level of said coating compartment being immediately above said entrance and exit apertures in said compartment.

8. The coating apparatus claimed in claim 7 including an exit die floatingly secured to said compartment in alignment with said exit aperture.

9. The coating apparatus claimed in claim 8 includ- 6 ing a gas finishing nozzle disposed closely adjacent said exit die and adapted to direct at least a portion of the gas passing therethrough said exit die.

10. The coating apparatus claimed in claim 9 wherein said gas finishing nozzle is adapted to direct a portion of the gas passing therethrough at the underside of said strand, whereby said still molten coating metal is maintained concentric with said strand during at least its initial cooling.

11. The coating apparatus claimed in claim 7 including means for preventing the level of molten metal in said melt reservoir from exceeding said normal level.

References Cited UNITED STATES PATENTS Re. 19,758 11/ 1935 Underwood 118-420 X 1,583,844 5/1926 Kochendorfer et a1. l186'3 2,214,108 9/1940 Nichols 18405 X 2,405,220 8/1946 Mann 118-405 X 2,914,423 11/1959 Knapp 118125 X 3,060,889 10/1962 Knapp 1l863 CHARLES A. WILLMUTH, Primary Examiner.

I. P. MCINTOSH, Assistant Examiner.

Claims

1. AN APPARATUS FOR COATING A METALLIC STRAND WITH A MOLTEN COATING COMPRISING: (A) A COATING COMPARTMENT ADAPTED TO BE SUPPLIED WITH MOLTEN COATING METAL TO NOT MORE THAN A NORMAL LEVEL, AND HAVING ENTRANCE AND EXIT APERTUES FOR THE PASSAGE OF A STRAND IN A HORIZONTAL PATH IN OPPOSED WALLS THEREOF, SAID APERTURE BEING DISPOSED IMMEDIATELY BELOW SAID NORMAL LEVEL; (B) AN EXIT DIE HAVING A RESTRICTED DIE ORIFICE; (C) MEANS FLOATINGLY SECURING SAID EXIT DIE TO SAID COMPARTMENT IN ALIGNMENT WITH SAID EXIT APERTURE; AND (D) A GAS FINISHING NOZZLE DISPOSED CLOSELY ADJACENT SAID EXIT DIE AND ADAPTED TO DIRECT AT LEAST A PORTION OF THE GAS PASSING THERETHROUGH INTO SAID EXIT DIE.