US 3287158 A
Description (OCR text may contain errors)
Nov. 22, 1966 M. e. WHITFIELD 3,287,158
COATING OF METAL WITH OTHER METALS Filed Aug. 9, 1962 2 Sheets-Sheet 1 INVENTOR. Mafis/mZZ 6. Whitfield 1966 M. G. WHITFIELD COATING 0F METAL WITH OTHER METALS e 2 mm 7 1 wk mm 1 m A g Q r @m WW w w J? m ou o a o 0% +\N o o vwo ww Z N O .lllllllllllllllllll I I i l I I I I I ll Olxgwmo M M S I} B NQWO vQm E @m mm .Q Npfi F QQ. mg @ml Sun a m m R g ow. D A w a a? b llv @m wk Q a. m .m WN
United States Patent 3,287,158 COATING 0F METAL WITH OTHER METALS Marshall G. Whitfield, Brookfield, Conn. Whitfield Laboratories, Inc., P.O. Box 293, Bethel, Conn.) Filed Aug. 9, 1962, Ser. No. 218,801 2 Claims, (Cl. 117-114) This invention relates to the coating of metal articles or pieces with other metallic substances, and more particularly to the coating of sheets, strips, ribbons and the like, of metals such as steel, iron, etc. with highly oxidizable metals such as aluminum, magnesium, etc.
Such coating of sheets, strips, ribbons and the like has been carried out in the past by passing the material or work to be coated through a bath of molten coating metal. It has been found, however, that difiiculty is experienced in obtaining coatings which have the desired thickness and uniformity. Where there is a bath of highly oxidizable metal in the molten state a film of oxide of a relatively tenacious nature forms on the surface, and it is believed that fragments of this oxide film are deposited on the surface of the metal which is to be coated as the latter enters the bath, thus interfering with the formation of an even coating or deposit of pure coating or donor metal.
The above drawbacks and disadvantages of this prior procedure for coating metal are obviated by the present invention, and one object of the invention is to provide a novel and improved method of and apparatus for coating metal sheets, strips, ribbons and the like with donor metals such as the highly oxidizable metals aluminum, magnesium, etc., by which there is obtained a coating of purer and more uniform nature, consistent as to thickness and devoid to the greatest possible extent of oxides or other impurities.
In carrying out the invention there is provided an improved method of and apparatus for coating metal sheets, strips, ribbons or the like with highly oxidizable coating or donor metals such as aluminum, magnesium, etc. which involves passing the work through a bath of the molten coating metal and surrounding the work at the place of entry with a reducing atmosphere and also a mechanical confining means. The reducing atmosphere is maintained by use of a chamber which surrounds the entering portions of the work and has a passage through which the work enters the molten metal of the bath, such passage being in the form of a snout with an open end which is submerged in the bath. Further, in the said passage there are provided strip-like members constituting the mechanical confining means and which extend across the passage in close proximity to the sides of the entering sheet, strip, ribbon or the like. The strip-like members confine and guide the work, and further confine surface portions of the bath at the point of entry of the work.
Preferably the strip-like confining and guide members are formed of molybdenum or other metal of the long series of Groups 4 to 6 and Group 8 of the Periodic System such as tungsten, niobium, cobalt and tantalum, or of an alloy of one or more of these metals. Or, the guide members may be constituted of substances wherein metals and ceramic materials are combined, or have oxide protection or cermets coatings or the equivalent. The method according to the invention may be carried out in a number of ways, whichwill be described in detail later, in the following specification.
Another object of the present invention is to provide .an improved method and apparatus as above set forth, which is respectively simple to practice, and simple and economical to fabricate.
A further object of the invention is to provide an improved method and apparatus which may utilize to a great extent existing coating equipment of the prior kind mentioned above, utilizing a bath of molten donor or coating metal.
Still another object of the invention is to provide an improved metal coating apparatus as set forth, which is efficient and effective in operation, and reliable in use.
A feature of the invention resides in the provision of an improved metal coating apparatus as above characterized, which does not involve complicated parts or procedures but instead is simple to the extent where it may be readily serviced and maintained.
Other features and advantages will hereinafter appear.
In the drawings accompanying this specification, similar characters of reference are used to designate like components throughout the several views, in which:
FIG. 1 is a diagrammatic representation of an improved coating apparatus as provided by the invention, the illustration being essentially in the form of a vertical sectional view. 1
FIG. 2 is a similar diagrammatic representation of an improved metal coating apparatus made in accordance with the invention, illustrating a modified form thereof.
FIG. 3 is also a similar diagrammatic representation of an improved coating apparatus, illustrating still another form of the invention.
FIG. 4 is a diagrammatic representation of a type similar to those of FIGS. 1-3, setting forth still another modified form of the invention.
FIG. 5 is a side elevational view of a snout structure constituting yet another embodiment of the invention.
FIG. 6 is a vertical sectional view of the snout, taken on the line 6-6 of FIG. 5, and of a confining means provided by the invention.
FIG. 7 is a bottom plan view of the snout structure of FIGS. Sand 6.
Referring first to FIG. 1, there is shown a tank 10 containing a bath 12 of molten donor or coating metal, such bath being brought to an elevated temperature by any suitable heating means as for example an immersion heater represented generally by the rectangular outline 14. The top surface of the bath 12 is designated 16, and the metal strip or sheet which is passed through t-hebath for the purpose of having a coating applied to it is indicated at 18.
Conveyor means in the form of rollers 20 and 22 are provided, to lead the strip 18 into the bath 12 in an angularly downward or oblique direction, and to guide the strip for leaving the bath in an angularly upward direction, as indicated.
In accordance with the present invention, the strip 18 which is to be coated is brought into the bath 12 at a place of entry 24 which is surrounded by a reducing ati'n-osphere tending to minimize oxidation of the surface of the bath at such location. Further, the strip or sheet which is to be coated is confined, at such place of entry, between strips or members which also confine surface portions of the bath, all to the end that there is minimized the deposit of oxide on the sheet at the point of entry of the latter into the bath.
As shown, for the purpose of maintaining the said reducing atmosphere there is provided an enclosure 26 having entrance and exit openings 28 and 30 respectively, the latter being located in the end of a tapered snout portion 32 of the enclosure. The confining means comprises strips or members 34 and 36 which are guided between roller-shoe pairs 38, 40. The confining strips 34, 36 are preferably so arranged that they constitute a continuous supply, and may be advanced towards the bath 12 as the leading edges thereof are consumed during the operation of the apparatus. Accordingly, as shown, the confining strips 34, 36 extend from supply rolls 42 and 44 respectively, which are shown as being mounted within the enclosure 26.
For the purpose of effecting advance of the confining strips 34, 36, the rollers 38 may be provided with sprocket teeth (not shown), adapted to be received in suitable feed openings in the strips to enable a positive advance of the latter to be effected.
It will be noted that the opening 30 of the snout portion 32 of the enclosure 26 is disposed slightly below the surface 16 of the bath 12 of the molten metal, and that the guide strips 34, 36 extend into the molten metal of the bath a slight distance. The guide strips 34, 36 are preferably formed of molybdenum or another metal of the long series of Groups 4 to 6 and Group 8 of the Periodic System, which include tungsten, niobium, cobalt and tantalum, or the strips may be constituted of alloys of one or more of these metals. Also, the strips may be provided with oxide protection or cermets coatings or the equivalent.
The bath 12 may be of moltenaluminum, for example, and the strip 18 may be of steel or iron which is to be coated with the aluminum.
The confining members or strips 34, 36 may actually touch the sheet 18 which is to be coated, or they may lie in close proximity to such sheet. In each instance, the strips tend to confine the sheet 18 and also to confine surface portions of the bath 12 immediately adjacent the point of entrance of the sheet into the bath.
The feeding or advance of the guide strips 34, 36 is for the purpose of replenishing these as the end portions are gradually oxidized and disintegrated during the operation of the apparatus.
The confining strips 34, 36 in conjunction with the reducing atmosphere provide for a greatly improved coating on the sheet 18, which is of uniform thickness and devoid of impurities, in the following manner: The reducing atmosphere minimizes the formation of oxides at the point of entry of the sheet, whatever small amount of oxide film does form is kept at a minimum by the confining of the surface portions of the bath by the strips 34, 36, and these latter also prevent the deposit of oxide fragments of any magnitude by virtue of the close proximity or wiping action of the strips, with respect to the sheet 18. I
It will now be seen from the foregoing that, by the method and apparatus of the invention there is minimized the formation and transfer of any appreciable oxide film at the surface of the bath immediately adjacent the place of entry of the strip 18 which is to be coated. Accordingly, relatively little oxide will be on the strip 18 as it passes into and through the bath 12, with the desirable result that the desired metallic coating which is applied to and carried off by the strip will be of a purer nature, devoid to the maximum extent of oxidation products and impurities.
A modification of the invention is illustrated in FIG. 2 wherein components similar to those already described in FIG. 1 have been given similar characters. In FIG. 2 the tank 10a contains, a bath 12a of molten metal, the melting having been effected by a heater 14a. The surface of the bath 12a is indicated at 16a, and the strip which is to be coated is shown at 18a.
The conveying and guide means comprise an upper roller 20a and a stationary wiper member 36a, the latter constituting not only a confining means for the strip 18a but also acting as a wiper and a guide around the lower end of which the strip 18a passes before it leaves the bath 12a. The combined confining, wiper and guide member 36a replaces the confining strip 36 of FIG. 1 and also the conveyor roller 22 of this figure.
The reducing atmosphere is maintained by the use of an enclosure 26a, within which there is located a confining strip 34a extending downward in a snout, portion 32a of the enclosure. The confining strip 34a is brought from a supply coil 42a, being guided between a rollerand-shoe pair 38a, 40a.
4 It will be observed that the difference between the constructions of FIGS. 1 and 2 resides in the substitution for FIG. 2 of the combined confining, guide and wiper member 36a for the confining strip 36 and roller 22 of I FIG. 1.
With the arrangement of FIG. 2 there is had the added advantage that a wiping action occurs at the upper side of the strip 18a which is to be coated, in consequence of the provision of the combined guide and wiper member 36a, such wiping action tending to remove any loose oxide or foreign particles from the upper surface of the sheet which is being coated.
Another embodiment of the invention is illustrated in FIG. 3, wherein the work which is to be coated is brought into the side of the bath of molten metal, instead of into the top as in the preceding figures.
In FIG. 3, the strip 18b which is to be coated passes around a conveyor roller 22b located in the bath 12b of the tank 10b. The bath 12b is brought to a melting 1 temperature by the heater 14b. The left wall of the tank 10b as viewed in FIG. 3 has an entrance opening 50 in which there is, disposed the snout portion 32b of the chamber 26b, the latter being provided for the purpose of maintaining a reducing atmosphere at the point .of
surface oxide from the molten metal being deposited on the strip.
Another embodiment of the invention having this same advantage is illustrated in FIG. 4. Here, the strip 18c which is to be coated passes into the bath 12c through the bottom wall of the tank 10c. The temperature of the bath is elevated and maintained at the place of entry of the sheet 18c by means of an enclosure 266 in which there are carried supply rolls 42c and 440 of confining strips 340 and 360 respectively. As with the organization of FIG. 3, the apparatus of FIG. 4 minimizes the deposit of oxide and other foreign particles on the sheet 18c which is to be coated, since the place of entry of the sheet into the coating bath 120 is below the top surface thereof.
Considering the four embodiments of the invention illustrated herein, I have found that where the base metal in the form of the strip 18 (of 18a, 18b or is led into the bath while surrounded by a reducing atmosphere there may still be a tendency for oxide of the coating metal to form at the point of entry, under certain conditions. However, by the provision of the strip-like confining members 34, 36 (or 34a, 36a; 34b, 36b; or 340, 360) there is prevented any continuous appreciable, film of oxide from forming adjacent the surfaces of the strip and being drawn onto those surfaces as the strip enters the bath.
While at present it is preferred to fabricate the strip-like members 34, 36, etc. from molybdenum, other metals of the long series of Groups 4 to 6 of the Periodic System may be used, especially the metals specifically referred to above; also, the members 34, 36 may be fabricated of metallic and ceramic mixtures, some of which are known as cermets. Ceramic coated metals may also be utilized.
It will be seen from the foregoing that the method as provided by the invention embraces the steps of maintaining a reducing atmosphere around the metallic base member at the place of entry of the latter into the bath, and confining surface portions of the bath at the said place of entry and closely adjacent the metallic member, to minimize the deposit of filmfrom the bath onto the member as the latter enters the bath. This method is clearly carried out by the apparatus as above described.
It may now be understood that the method and apparatus are relatively simple and readily practiced and constructed. N0 complicated mechanisms are involved in the apparatus, whereby servicing and maintenance are held to a In connection with the forms of FIGS. 3 and 4 suitable gasket means (not shown) may 'be employed to minimize leakage of the molten metal from the bath.
An arrangement for minimizing the deposit of oxide particles at the place of emergence of a strip from a molten bath forms the subject of separate inventions which are set forth in my copending application Ser. No. 500,468, filed Oct. 11, 1965, and entitled Renewable Doctor Blade, now Patent No. 3,251,339, issued May 17, 1966.
Another embodiment of the invention is illustrated in FIGS. 5, 6 and 7, wherein further details of a snout structure are given. in these figures, the snout structure is constituted of eight separate pieces or members, designated 50, 52, 54, 56, 58, 60, 62 and 64. The members 50-64 may advantageously be cast iron; or they may be constit-uted of cermets or oxides, formed into the desired shapes and thereafter fired to make a solid bonded mass. Sintered silicon nitride bonded silicon carbide known as Refrax is suitable for this purpose.
The pieces 50, 52, 62 and 64 are end or corner pieces, whereas the pieces 54, 56, 58 and 60 are side pieces or members. Each of the pieces 50-64 has a top, mounting flange portion indicated by a similar numeral with the suflix "12 added. Further, the pieces 50-64 have depending portions 5012-641) arranged in converging relation and providing a narrow elongate slot or opening 66 through which the strip 18b, which is to be coated, may pass.
The mounting flange portions 50a-64a are provided with screw holes, as shown, to enable the snout to be secured to a suitable enclosure, as will be readily understood.
The pieces or members 50-64 have tongue-and-groove joints 54c-64c and 54d-64d by which there is facilitated the fitting and cementing together of the pieces in the snoutconfiguration shown. The firing of the pieces is done after such cementing, and the assembly is effected as follows. The pieces 50, 54, 58 and 62 are cemented to each other in the assembled relation shown, and such assemblage is equivalent to a single unitary fused mass. The pieces 52, 56, 60 and 64 are likewise cemented together and thereafter tired to form a second fused mass. 7 Thus, the snout is made up of two separate fused assemblages, being split along a longitudinal center line.
Also, bushings 68 and 70 to feed gas into the snout under pressure are inserted in the depending portions 54b and 58b respectively, and are cemented in place before the firing of the assemblage containing these pieces. The bushings and the depending portions of the supporting pieces have aligned bores which communicate with the interior of the snout.
Referring to FIG. 6, confining and guide means are provided in the form of flexible strips or sheets 72 and 74, such sheets being supplied from supply rolls 76 and 78 carried on turnable spindles 80 and 82. Cooperable feed rollers 84 and 86 engage the supply rolls 76 and 78 to prevent undesired unwinding of the strip or sheet material, and to facilitate the feeding or advancing of the same as the leading edges wear. The confining strips 72, 74
function in the manner of the strips 34, 36, etc. already described above, and may be constituted of similar material.
The snout construction and confining means shown in FIGS. 5-7 illustrate a preferred form of the apparatus, which may be used in the various arrangements illustrated in FIGS. l-4, in conjunction with suitable enclosure means providing a confined space or area where a reducing atmosphere is to be maintained.
The construction shown in FIGS. 5-7 is relatively simple, and constitutes a practical example of a snout and confining means which is rugged and wear-resistant.
Variations and modifications may be made within the scope of the claims, and portions of the improvement may be used without others.
1. The method of coating an elongate metallic member with a molten metallic substance, which includes the steps of:
(a) passing the member lengthwise into a bath of said molten metallic substance at a place of entry,
(b) rotatably supporting a thin, coiled metallic confining strip adjacent said bath,
(c) guiding the free end portion of said coiled confining strip independently of the said member and near the place of entry of the member into the bath and in a position broadside to and spaced from the member, to confine surface portions of the bath at a side of the metallic member so as to minimize the deposit of film from the bath onto the member as the latter enters the bath, and
(d) periodically feeding additional portions of said confining strip from the coiled supply thereof lengthwise toward the bath surface as the strip is consumed, to maintain the said confinement.
2. The method of claim 1, and including the additional step of curving the confining strip away from the member at locations between the member and the place where the strip is being guided. 1
References Cited by the Examiner UNITED STATES PATENTS 2,054,549 9/ 1936 Smith.
2,294,750 9/1942 Harris 117-114 2,345,058 3/ 1944 Matteson.
2,382,868 8/ 1945 Fink.
2,394,545 2/ 1946 Grupe 117-5 1 X 2,410,420 11/ 1946 Bennett 15-236 2,424,034 7/ 1947 Hopper.
2,449,329 9/ 1948 Schell.
2,875,096 2/1959 Diehl et a1.
2,989,944 6/1961 Harris et a1.
3,081,191 3/1963 Smith 118-413 X ALFRED L. LEAV-ITT, Primary Examiner.
RICHARD D. NEVIUS, WILLIAM D. MARTIN,
R. S. KENDALL, I. P. MCINTOSH, Assistant Examiners.