US2182132A - Vitreous enameled sheet and method of production thereof - Google Patents

Description

Dec. 5, 1939.

A. l.. MATTHES 2,182,132

VITREOUS ENAMELED SHEET AND METHOD OF ALPRODUCTION THEREOF Filed June 2, 1938 WITNESS INVENT'? Patented Dec. 5, 1939 vortica Archer L. Matthes, Youngstown, Ohio Application .lune 2, 1938', Serial No. 211,359

6 Claims.

My invention relates to vitreous or porcelain enameled sheets such as are commonly used in architectural work, for table tops, refrigerator walls, range bodies, advertising signs, and the like, the. principal object of the invention being to provide a sheet which, when finished, is flatter and to a greater extent devoid of undesirable optical effects than sheets produced by the methods now in vogue, the invention also including a. novel method of producing such improved sheets as well as other objects, advantages, novel steps and operations hereinafter pointed out.

In the manufacture of vitreous enameled sheets it has been customary to provide a metallic base of proper gauge and smooth on both sides and to thoroughly clean it by pickling in a suitable solution or otherwise to prepare it for applcation of the enamel coats; this base may be either plane or may be flanged at the edges or which the finished article is to be put. After the base is cleaned a coat' of fusible enamel is applied to both of its surfaces, cobalt ground coat enamel being generally utilized for this purpose and, after drying, the coated base is then placed in a furnace where'it is heated well above the fusion temperature of the enamel, for example to about 1500 or l600 F., so as to thoroughly fuse the enamel to both of its sides. The coated base is then removed from the furnace and allowed to cool to atmospheric temperature and a second coat of fusible enamel, generally white in color, is applied to the ground or primary coat on one side only, and, after it has dried, the sheet is reintroduced to the furnace or placed in another furnace and the second coat fused desirably, however, at a somewhat lower temperature than that employed for the ground coat. Depending on the use to which the finished sheet is to be put. 4D one or more additional coats may then be successively applied to the secondary or white coat and fused in a similar manner after each such coat has dried, with the result that the finished sheet has at least two separate coats on one side of the base and only one on the other. In consequence, because of the greater total thickness of enamel on the plural coated side of the base, the sheet tends to warp or buckle and present a slightly conveXed surface on that side which produces very undesirable though well known optical eiects and of course detracts from the beauty and salability of the sheet.

In accordance with my invention, however, I am able to produce a at or substantially at vitreous enameled sheet even though it embodies otherwise formed in accordance with'the use to a greater number of coats of enamel on one side than on the other, as by suitable preparation of the metallic base I counteract the tendency of the sheet to crown or become convex as just described. This is not only of advantage in elimi- 5 nating the undesirable optical effects to which I have referred, with consequent enhancement in appearance and beauty of the finished sheet, but also avoids the trouble and expense of backing the sheet in some manner when incorporating it in the article such as a table, refrigerator, range or the like of which it is designed to form a component part in an effort to make it present a plane as distinguished from a warpedsurface to the observer of the article as a whole.

To enable those. skilled in the art to understand and practise the invention, I shall now describe the production of one of my improved sheets in accordance with my aforesaid method and during the course of the description shall refer-to the said drawing in which:

Fig. 1 is a fragmentary plan View of a portion of one face of the metallic base comprised in the sheet, and

Fig. 2 is a transverse section thereof as on the line 2 2 in Fig. 1.

Fig. 3 is a similar transverse section showing the base after the application and fusing of the ground or primary coats to its opposite faces, and

Fig. 4 is a similar view of a finished sheet after the application and fusing of a secondary or finish coat to one of the primary surface coats.

All the said views are on a greatly enlarged scale, and like symbols are used to designate the same parts in each of them.

In the practice of my invention I rst provide a metallic base sheet i of suitable gauge and while this will customarily be of iron or steel it may, if desired, be of other metal. As they come from the rolling mills, sheets intended for manufacture of vitreous enameled articles are usually smoothly finished on both faces and I therefore first subject the sheet to a treatment effective to make one of its faces materially rougher than the opposite face and thereby increase its superficial area.. This treatment may be of any sort adapted to bring about the desired result and may therefore consist in passing the sheet beneath an etched, sand blasted or shot blasted roll, and if this method of roughening the sheet is used a mill having upper and lower rolls of this character is desirably employed and the sheets passed therethrough in pairs face to face so that the outer surface of each sheet in the pair will be roughened as the pair of sheets are simultaneously traversed by the rolls,

the inner faces of course remaining in their original smooth condition. Other methods of or means for roughening the base sheet may also be employed as long as the ultimately desired result is obtained, namely, the provision of a base sheet smoothon one side and relatively roughened on the other. I have found that good results are obtained when the roughened surface is of a granular nature or provided with small projections of the character of saw teeth, the granulations or teeth being of the order of from 10 to 100 per linear inch but, as hereafter pointed out, the degree of roughness will normally be determined in accordance with the number of coats of' finishing enamel, as distinguished from ground or primary coat enamel, used in producing the vitreous surface which is designed to be exposed when the finished sheet is in use, for example, the top of the sheet when it is to be ultimately used to form a table top. Moreover, the roughening can be either uniform throughout the entire lextent of the base sheet without dening any denite pattern thereon or, if preferred, it may be arranged to define a pattern repeating itself at intervals throughout the roughened area which, of course, preferably extends throughout the entire extent of the sheet or substantially so.

The base, after subjection to the roughening treatment, is next thoroughly cl'l aned in any suitable way to prepare it for th reception of the ground or primary coat, usu,y lly. of cobalt ground coat enamel, which is then applied in any convenient manner to both surfaces of thesheet as 4by dipping or'spraying or in any otherA way adapted to uniformly distribute the fusible enamel over both said surfaces. When the coats arejsuciently dry the coated base is next placed in aL suitable furnace and the enamel fused in the ordinary way and preferably at a temperature of from 1500 to 1600 F. which is materially higher than its fusing point, andthe sheet is then cooled to atmospheric temperature either within or after removal from the furnace.

Now as the roughened surface 2 of the base presents a greater supercial area for the reception of its groundor primary enamel coat 4 than the relatively smoother opposite surface 3 for its ground coat 5, a greater quantity of the enamel adheres to the former per unit of area than to the latter during the dipping, spraying or other operation by which the ground coats .are applied to the base so that after the subsequent fusing and cooling operations, the sheet as a whole has a tendency to warp or buckle in such manner that it becomes slightly convex or dished toward the side carrying the greater quantity of enamel and correspondingly concave on its other side due, apparently, to the unequal tension exerted on the base by the different amounts of enamel upon its opposite faces, and thus appears somewhat as shown in Fig. 3.

The ground coated sheet is now in condition for the reception of the first of the finishing coats on that side which is to be outermost when the sheet is in use. This coat is usually of white fusible enamel and is applied to the concave side of the sheet on the primary ground coat 5 already fused thereon and, as soon as it is dry, the sheet is again introduced to a furnace and the secondary coat 6 fused at a temperature preferably somewhat low- .er than that utilized for fusing the ground coats.

This operation and subsequentcooling of the sheet results in equalizing or substantially equalizing the tension on the base since there is now substantially the same amount of enamel at each side thereof and the sheet consequently warps or dishes in the other direction sufficiently to substantially eliminate the buckled condition existing after the fusing and cooling of the ground coats so that it becomes flat or plane on both sides as indicated in Fig. 4. yIt is thus devoid or substantially devoid of the objectionable optical effects found in vitreous enameled sheets which are not at or very nearly so and may thus be satisfactorily employed without endeavoring to eliminate them by backing the sheet or by other means frequently employed for the purpose.

For certain classes of work, for example the lining of refrigerators, sheets comprising a primary or ground coat on each side and but one secondary or finish coat and thus of the character of the sheet shown in Fig. 4 are satisfactory and such a sheet may therefore be regarded as a finished one within the contemplation of my invention. .However, for other classes of work sheets having additional secondary coats are often preferred as, for

example, in the case of those intended to form the outer Walls of refrigerators and ranges or the tops of tables, two secondary coats upon the ground coat 5 being generally applied and both of such coats being usually of white fusible enamel. Such double nsh coated sheets are also normally employed for architectural Work and for making advertising display signs, and to dene the desired designs thereon color coats. are frequently consecutively applied and fused over the white coats so that ultimately a plurality of fused coats are deposited on one side of the baseand but a single ground coat on the other. Under these conditions vitreous enameled sheets as hitherto w manufactured have an evenv greater tendency to buckle than those having but a single or even two finish coats applied on the ground coat. In accordance With my invention, however, it is possible to substantially neutralize this tendency to buckle by suitably proportioning the roughening of the base sheet in accordance with the number of coats of enamel which are to be applied to the ground coat on the opposite side of the base to produce the nished article since, speaking generally, the greater the enamel-receptive surface per unitof area presented by the roughened face of the base for the reception of the ground coat, the greater will be the amount of material comprised therein and, consequently, the greater the resistance aorded to the buckling tendency resulting from the presence of the plurality of successively applied coats on the opposite side of the base. Thus, for example, where but a single white coat is to be applied to the ground or primary coat 5 the provision of a roughened surface whose granulations or serrations are the order of 10 or 20 to the linear inch may be sufl'icient to insure the production of a flat sheet whereas if a greater number of secondary coats are to be applied it will usually be necessary to increase the number and perhaps the depth of the granulations or serrations per linear inch so as to afford a correspondingly larger surface for the reception of the ground -coat 4.

Thus in accordance with my invention I am able to produce a substantially flat sheet free from undesirable optical effects irrespective,.

with the roughness thereof, nevertheless as the cost of the ground coat enamel is relatively low Vin comparison with that used for the secondary coats, the cost of a sheet of a given size produced in accordance with my invention will ordinarily be but little greater than that of an ordinary sheet of similar size having a corresponding number of secondary coats, while the advantages possessed by my improved sheets render them more readily marketable and distinctly more satisfactory to the ultimate user.

While I have herein described with considerable particularity one-manner of practising the method of my invention with resulting production of one of my improved sheets embodying but a single secondary coat of vitreous enamel, it will be understood as hitherto explained that sheets having a greater number of secondary coats consecutively applied and fused may be as readily produced and are equally comprehended by the invention. Furthermore, while I have referred more particularly to a vitreous enameled sheet and to the use of fusible enamel in its preparation, the invention is equally applicable to the production of sheets embodying coatings of other fusible materials such as porcelains and the like, and I have therefore herein employed the term enamel in a comprehensive as distinguished from a restrictive sense and thus as including such other fusible materials. Finally, it is to be understood also that the method of my invention is susceptible of considerable variation from the particular and normally preferred practice thereof which I have herein outlined Without departing from the spirit and scope of the invention as dened in the appended claims.4

Having thus described my invention, I claim and desire to protect by Letters Patent of the United States:

1. As an article of manufacture, a vitreous enameled sheet comprising a metallic base roughened on one side and relatively smooth on the other, a coat of fused vitreous material on said roughened side and a plurality of coats of fused vitreous material on the opposite side.

2. As an article of manufacture, a vitreous enameled sheet comprising a metallic base sheet relatively smoother on onesurface than on the surface opposed thereto, a ground coat of fused vitreous material on each of said surfaces, the coat on the smoother surface embodying less material per unit of area than the other coat, and a. coat of fused vitreous material on the rst mentioned coat.

3. In a method of producing a vitreous enameled sheet, the steps of initially forming a metallic base sheet having a smooth surface on one side and a relatively rougher surface on the other, applying a ground coat of fusible enamel to the opposed surfaces of the base, fusing said coat, applying a second coat of fusible enamel to the fused coat adjacent the smooth surface of the base, and then fusing said second coat thereto.

4. In a method of producing a vitreous enameled sheet, the steps of initially forming a metallic base sheet having a smooth surface on one side and a relatively rougher surface on the other, applying a ground coat of fusible enamel to both surfaces of the base, fusing said coats thereon simultaneously at a temperature materially higher than the fusing point of the enamel, applying a second coat of fusible enamel to the fused coat adjacent the smooth side of the base,

and then fusing said second coat thereto at a lower temperature than that utilized to fuse the ground coats.

5. The method. of producing a finished, subl stantially iiat vitreous enameled sheet which comprises the steps of treating one side of a metallic base sheet to increase its superficial area overy that of the other side, applying and fusing a coat of enamel to each side of the base to thereby produce after cooling a ground coated sheet slightly concave on the side remote from the treated side of the base, and then applying and fusing to the ground coat on the concave side suiicient enamel to apprommately equalize the forces exerted by the ground coats on the base and thereby reduce the sheet to substantial ilatness.

6. The method of producing -a finished, substantially fiat vitreous enameled sheet which comprises the steps of treating one side of a metallic base sheet so as to increase its superficial area over that of the-other side in an amount proportional to the total quantity of enamel to be ultimately applied to the untreated side of the base, then applying andlfusing a coat of ground enamel to each side of the base whereby after.

cooling it is subjected to unequal stresses with corresponding tendency to buckle toward its treated side, and then applying to and fusing on the ground coat remote from said side the rest of the enamel designed to be applied on said side to thereby substantially equalize said stresses and negative said tendency to buckle.

ARCHER L. MA'I'rHEs.

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