US3429734A

US3429734A - Method and apparatus for coating metal strip

Info

Publication number: US3429734A
Application number: US504605A
Authority: US
Inventors: Brian C Coad
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1965-10-24
Filing date: 1965-10-24
Publication date: 1969-02-25
Anticipated expiration: 1986-02-25

Description

Feb. 25, 1969 B. c. coAD 3,429,734

METHOD AND APPARATUS FOB COATING METAL STRIP Filed oct. 24, 1965 H613.- 5/ FIGA.

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United States Patent Ofi 'ice 3,429,734 Patented Feb. 25, 1969 Ciaims ABSTRACT OF THE DISCLOSURE A crucible for a melt of a metallic coating material is provided with a rectangular slot in its bottom. The slot is of substantially the same size and shape as the transverse cross section of a solid metal strip to be coated. The strip is continuously drawn up through the slot. The crucible up to a certain level contains a melt of the coating material through which the core material is drawn and leaves the melt at said level. The strip being cooler than the melt absorbs heat therefrom to congeal it on the strip. Extending from the bottom of the crucible to points above said level and located at opposite ends of the slot are members grooved to slidably tit with the margins of the core material so as to act as shields against the melt reaching marginal portions of the strip, whereby the effect of the uneven marginal heat-How pattern is avoided and a constant thickness of coating congeals on the strip between its uncoated margins. The uncoated margins may later be trimmed off.

This invention relates to the manufacture of coated materials, and more particularly to the application to a core `by a dip-coating process of a coating of substantially constant thickness.

Among the several objects of the invention may be noted the provision of a method and apparatus for applying a coating of substantially constant thickness to a core by dip-coating the core in a melt of the coating metal; the provision of a method and apparatus of the class described for coating a metal core with a like or different metal coating of substantially uniform thickness; the provision of a method and apparatus for the manufacture of a coated core by a continuous process wherein the coating is excluded from certain portions of the core; and the provision of an article coated in accordance with the method of the invention. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the methods, constructions and products hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying diagrammatic drawings, in which one of various possible embodiments of the invention is illustrated:

FIG. 1 is an illustrative cross section through a coated strip manufactured by a prior-art process;

FIG. 2 is a similar section through a coated strip manufactured laccording to the present invention;

FIG. 3 is a top plan view of apparatus useful for manufacturing coated strip according to the invention;

FIG. 4 is a bottom plan view of the FIG. 3 apparatus;

FIG. 5 is a fragmentary perspective view of parts of the apparatus; and

FIGS. 6 and 7 are enlarged fragmentary sections taken along lines 6-6 and 7 7, respectively, of FIG. 3.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

In the present application, reference yto metals is intended to include alloys thereof. Coating of elongate core material may be with a material which may be the same as or different from that of the core. For clarity of illustration, the sizes, thicknesses, etc. are exaggerated. Therefore the drawings are not to scale. The term core means that which is coated or clad and may be in the form of strip, rod, wire or any other appropriate cross section. The invention has primary, although not exclusive, use when both the core and the cladding are composed of dfferent metals.

It is known in the art to form clad metal wire, rod, strip or the like by drawing a cold core through molten metal to congeal or freeze a lm or layer of the melt on `the core. The thickness of the congealed metal depends (in part) on the heat-flow pattern developed in the solid core. This heat-flow pattern, and thus the layer coated on the core, are asymmetrical across a core which has an unsymmetrical heat-flow pattern; for example, a strip which is rectangular in transverse section.

In FIG. l of the drawings is shown a metal core strip 1 of rectangular cross section, coated with metal 3 which has been congealed on the core by drawing it through a melt of the coating metal in accordance with a process previously known to the art. As shown in FIG. l, the surface of the coating metal is somewhat oval in section, a shape which is undesirable in that the cladding on the wide faces of the strip is of variable thickness. Thus even if the edges are trimmed off, as on the dotted lines 2, an uneven coating occurs on the flat sides of the strip. This asymmetrical coating results from an uneven heat-iiow pattern at the corners of the core, and it is avoided by the present invention.

Referring now to FIGS. 3-7 of the drawings, apparatus for manufacturing a metal strip having on it a congealed coating `of substantially uniform thickness Iis `shown to comprise a refractory container or Crucible 5 having a bottom or base 7 and a wall 9 projecting upward from the base. Crucible `S is adapted to receive a melt of the coating metal. In the base 7 of the Crucible is a hole 11 which is substantially the `same `size and shape as the transverse cross section of the core to be coated. As illustrated in the drawings, the hole 11 is in the shape of a rectangle but it will be understood that other shapes can he used. The core or so-called seed strip to be coated is designated 13 and, as shown in the drawings, is an elongated strip which is rectangular in cross section. Crucible 5 is open at the top as illustrated in FIG. 4 so that strip 13 may be drawn upward through hole 11 and through the melt l5 of the coating metal (FIGS. 6 and 7) and then out through the top of the crucible. The core is cooler than the melt when it first enters the crucible. If desired, this temperature differential can be established and regulated by contr-olling the temperature `of the strip as it enters the melt.

A pair of refractory guides or shields 17 are secured to base 7 at opposite ends -of the slot 11. Each `of guides 17 has a notch or guide slot 19 on its inner or facing surfaces, the innermost portions of the slots being spaced apart a distance just adequate to receive the side edges of the core 13 as it is drawn upward through hole 11. Guides 17 not only guide the core upward but also serve to shield or mask the edge portions of the core from the melt 15 as the core is drawn through the melt. The guides 17 extend from the base 7 upward to a point yabove the upper level of the melt in the crucible. Thus there is substantially no contact between edge portions of the core and the melt as the core is moved through the guides.

As the core 13 moves upward through the crucible, as indicated by the arrows in FIG. 5, the relatively hot liquid metal 15 in the crucible will engage the Unshielded center portions `of core 13 (i.e., the portions between the guides 1-7). This material will be cooled by contact with the cooler surface of the core and will congeal on the unshielded core surface. The coating strips which have been designated 21, increase in thickness as the core moves from the bottom to the top of the melt, and this buildup is illustrated in FIG. 7 of the drawings. The thickness of strips 21 will depend upon the mass of core 13, the speed at which it is moved through melt 15, and the temperature diiferential between the core and the melt.

In order to obtain a coating of constant thickness, an even heat-flow pattern must be developed across -all surfaces to be coated. The only areas of core 16 exposed to the melt are the hat central surfaces on its opposite sides. The heat transfer along these surfaces is substantially even 4or regular, there being no irregular configuration as at the shielded corners, or variance in thickness of Ithe strip which would tend to develop an irregular heat-flow pattern along these areas. The end portions of the core or strip 13 which are shielded by the guides 17 contain the corners or edges `of the strip across which irregular heat-flow patterns are developed. Were these edge surfaces exposed to the melt, an irregular coating thickness would occur on the at side surfaces, similar in shape to the coating 3 illustrated in lFIG. 1, since an uneven heat-flow pattern would be developed. Thus by shielding the areas of the core being coated which might develop irregular heat-dow patterns, constant thickness of coatings can be applied to the fiat surfaces of the core.

A transverse cross lsection of the coated strip is illustrated in FIG. 2 of the drawings. It will be noted that coatings 21 on each side of core 13 are substantially the same thickness and are constant in their thickness throughout a substantial width. If desired, the uncoated ends of core 1'3 may be trimmed off. The resulting article thus produced diers significantly from the coated strip of the prior art illustrated in FIG. l which has a coating of variable thicknesses on its flat sides. The article illustrated in FIG. 2 is useful in many applications requiring clad strips or the like.

The process of the invention has been described in connection with coating of a thin metal strip of rectangular cross section. However, it is to be understood that cores of other shapes or configurations may also be coated according to -this process. It will also be recognized that coating material can be excluded from areas of the core other than edges `or other areas which might produce uneven coatings. For example, narrow strips might be applied to opposite sides of a circular core in which the heat-flow pattern is even. Other variations will be clear to those skilled in the art.

It will be understood that while the materials of the core and of the congealable cladding material are in general different, these materials may be the same if the object of the method is simply to increase the thickness of the strip by dip-forming. In the preferred form, both materials are metal, but other materials may be employed.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

What is claimed is:

1. The method of continuously evenly applying and congealing melted metal coating material on at least one face of an elongate solid metal strip having a crosssectional shape providing at least one face area over which an even heat-How pattern may be developed and marginal areas at which irregular heat-flow patterns ordinarily develop to distort said even heat-ow pattern, comprising sliding the strip through grooved guides for shielding the margins of the strip while leaving unshielded at least one face of the strip, and immersing the strip in a melt of the metal coating material only in the region of its movement through said guides, whereby the melted metal congeals substantially evenly on said face.

2. The method according to claim 1, wherein both faces of the strip are left unshielded during immersion.

3. Apparatus for continuously evenly coating a metal on at least one face of an elongate solid metal strip having a cross-sectional shape of substantially constant thickness providing opposite face areas over which even heatow patterns may be developed except for marginal areas at which irregular heat-ow patterns ordinarily develop to distort said even heat-dow patterns, the apparatus comprising a crucible adapted to hold a melt of the coating metal up to a certain level, the crucible having a slot in its space conforming generally to the transve-rse cross section of the strip to be coated, means for moving the strip upwardly through the slot and through the melt to absorb heat therefrom to congeal on the strip, and grooved means in the crucible extending from the 'base of the crucible adjacent the ends of the slot to points above said level of the melt for slidably receiving and shielding said marginal areas of the strip from the melt during passage of the strip therethrough, whereby development of said irregular heat-ow patterns is substantially prevented from occurring and said even heat-flow patterns are substantially maintained.

4. Apparatus made according to claim 3, wherein the strip and the slot in the base of the crucible are of rectangular cross section.

References Cited UNITED STATES PATENTS 3,320,084- 5/1967 Lirones 117-38 X 3,134,150 5/1964 Parke et al. 118-405 3,060,055 10/ 1962 Bixler 118-405 1,711,948 5/1929 Jones 118-406 ALFRED L. LEAVITT, Primary Examiner.

A. GRIMALDI, Assistant Examiner.

U.S. Cl. X.R. 118-405; 117-114