US2094583A - Manufacture of metal coated products - Google Patents

Description

Oct. 5, 1937. v N.VE. cooK ET AL MANUTACTURE 0F METAL COATED PRODUCTS Filed Mar'cn 22, 1935.

NWN

Patented Oct. ,5, 1.937

' MANUFACTURE or METAL coA'rED PRODUCTS Nelson E. cook, wheeling, W. va.,.Edwara J.

Knopf, Morristown,

Diehl, Wheeling, W. Va., assignors to'v Wheeling Steel Corporation, Wheeling, W. Va., a corporation of Delaware Application March 22, 1935, Serial NoT 12,398 s claims. (ol. :i1-470.2)

' This invention relates to the manufacture of metal coated products, and; while not specifically so limited, has particular application in'the coating, and especially the galvanizing, of sheet metal, such, for example,- as steel sheets. Superior coated products, and particularly galvanized sheet steel products, are produced. Such prod.

ucts are claimed in our Acopending application Serial No. 54,278filed December 13, 1935, which l application is in part a division of this application. This application is in part acontinuation of our copending application Serial No. 741,222,

filed August 24, 1934.

llnirely` for purposes of description and illusfaces are not undesirable, and indeed they are definitely desirable in caseswhere a certain type of finished appearance is Wanted. f

However, for other purposes sheets having both surfaces Spangled are definitely undesirable, as, for example, when the product is to be painted.

Spangledgalvanized surfaces will not take paintlreadily. It has been the practice' heretofore to permit Spangled galvanized sheets to weather, or

`to artificially weather them, as byv treatment` with acid or other chemical having the effect of oxidizing the surfaces ofthe sheets,`in order that the surfaces to be painted may vbecome-some-What roughened so that paint will readily adhere thereto.

We have discovered that galvanized sheets may 40 be produced without the ordinary Spangled surfaces, without the undesirable buckling of the sheets which has attended previous efforts to produce unspangled galvanized sheets, and with a smooth dull matte lor slightly roughened sur.- face which is at the same time highly resistant to corrosion, beautiful in appearance and readily receptive to paint and other similar coating materials. We are well aware of the previous efforts which have been made along these lines in ,v both the practical and the patented art, but no processhaving the features and advantages .of ourprocess has heretofore been proposed and no nish having the desirable qualities of our nish has heretofore been produced.

Before proceeding to explain our invention we f as the results obtained by the two processes are dinary galvanized ware will be produced.` By

'PATENroFFlcE Ohio, and William L.

Wish it understood that we do not claim broadly to have invented theformation o'f unspangled galvanized metal surfaces, as unspangled surfacesA have been produced before. One Way in which unspangled, galvanized 'surfaces have been produced 5 is by dipping the hot, galvanized ware as it comes from the galvanizing pot into a liquid bath, which prevents the formation of spangles,'produces a mottled, irregular, partly bright and partly dull surface and results in warping the ware due to the 10 rapid and uneven temperature changes brought'. about by the dipping. The warping can be reduced to some lextent by heating the bath in which the ware is dipped, but, aside from the question of warping, the nish is unsatisfactory in appearance, isnot highly resistant to corrosion and will not take paint readily. It has also been proposed .to subject galvanized ware to the action of a jety .of water or other liquid, but this has substantially the same results as dipping. Thenish produced is not uniform, being partly bright and partly dull and mottled, is not highly resistant to corrosion and will not take paint satisfactorily. Furthermore, the subjectlng of the hot galvanized? ware to a jet of liquid results in warping of thev ware as in the case of dipping. f l l ,"After considerable experimenting we have dlscovered that the highly desirable unspangled, uniform, dull matte finish may be produced by subjecting the galvanized ware (here considered for lpurposes of illustration as comprising sheets) to the action of a mist or very fine spray. The inist or very line sprayis to be clearly distinguished from the `jet of liquid referred to above,

entirely different. 'Ihe sheets after leaving the galvanizing bath are brought into the presence of the' mist or very ne spray before the large spangles characteristic of ordinary galvanized ware have formed. Almost immediately upon leaving the galvanizing bath the zinc coating begins to lcoolandvcrystallization commences. If this crystallization is allowed to progress unhindered the large spangles characteristic of orbringing the hot sheets into the presence of the mist or very line spray we prevent the formation of the large spangles and the desired uniform dull matte finish results. i

- While we are not certain as to the` theory underlying the process above described, we think that the fine particles of the mist exert a physical effect on the surface of the sheet, creating relatively very closely spaced centers of propagaotheri before the `crystals can attain relatively large size, resulting, as it were, in the squeezing into the same surface area` of a relatively very great number of relatively verysmall crystals which, due to the relative proximity of their centers of propagation or crystallization, have had no opportunity to grow to or. even to approach the .size of \what are commonly known as s'pang1es, which are readily distinguishable to the naked eye even at some distance and which may in some cases extend from their'respective centers of crystallization for/'a distance of an inch or more in various directions; if the size of the crystals is properly controlled the sheet will appear to the naked eye to have a uniform continuous dull matte surface. Underv a powerful magnifying glass this surface will be seen to be crystalline, presenting an appearance similar to an ordinary Spangled surface. However, the relatively gr'eat number of relatively small, relatively' closely spaced crystals afords an ideal surfaceV for the reception of paint and similar. coatings, and this surface is also particularly' well suited for various uses without painting or covering Ywith similar coatings, as, for example, for oven linings.

We have found that by lappropriately controlling the mist or spray andthe passage of the` sheet in relation thereto we can form a 4sheet having one side Spangled in the characteristic thus produced. Another use to which sheets hav- A ing one side Spangled in the usual manner and the other side provided with the uniform dull matte iinish'may be put is in the construction of refrigerator cases. The side having the dull matte finish forms the outside of the case and receives the usualfwhite enamel paint, while the Spangled side faces toward the interior of the refrigerator and is naturally well adapted to withstand corrosion due to moisture within the refrigerator. Sheets of this character may also be used for oven linings, the unpainted dull matte nish facing the interior of the oven.

Various materials may be used for producing the mist or very fine spray. Plain water alone -if sufli'cientlyffinelyv divided is fairly satisfactory.

Using a fine mist of plain water does not, however, give as. exact control of surface appearance as is ,desirable for manypurposes. However,`we have found that water solutions of certain chei`nicals produce markedly superior results.Y A few of .thechemicals thus used listed approximately in the order of efficacy are copper sulphate,.

sodium nitrate, sodium chloride, potassium'chromateand potassium permanganate. These salts are precipitated rapidly from their water solutions at temperatures slightly above the solidifying point of zinc or the zinc alloys usually employed' for galvanizing. The solidifying point of aceaasa tion or crystallization from which the crystalsy the galvanizing material `may be in the neighborhood of 760 F. to 800 F.` While we are not certain as to thetheory of action, we believe that the rapid evaporation of the water results in the almost immediate precipitation or deposition on 5 the surface of the. sheet of microscopic, almost unmeasurably small. particles ofthe Salt or of some precipitate formed upon the application of heat to the` mist composed of the salt solution. This precipitate'seems to have the effect of con- 10 trolling the centers of propagation of the crystals so that such centers are distributed quiteuniformly over the surface of the sheet and very close together. Apparently those substances whose solutions most quickly deposit their precipitates onthe'sur'face of the sheet upon the application of heat in the neighborhood of thetemperatures .mentioned above are `mostsatisfactory for our purpose.

Care must be taken to keep the mist very finely. divided. If a relatively coarse spray or jetis methods of treatment. of coatedsheets and certain present preferred-apparatus for carrying out the methodand producing the desired product proceeds.

, In the accompanying drawing we have shown Acertain present preferred forms of apparatus for producing coated'sheets,`in which Figure 1 is a plan vview of one form 'of apparatusf Figure 2 is an elevational view, partly in ver- 40 tical longitudinal cross section, of the apparatus shown in Figure 1; and

Figures 3 and 4 are each a detail elevational View, partly inyertical longitudinal cross section.

of a portion of a modifled form of apparatus.

'I'he steel sheets which are to be coated are rst treated to remove dirt and scale, as, for

example, by pickling, blasting, etc. This step may be omitted if the sheets are originally clean.

The sheets are then treated in apparatus as shown in the drawing and.now to be described.

Referring now more particularly. to Figures 1 f and v2, a set offeed rolls Ill'is located adjacent the entranceof a galya'nizing pot I I of known, construction and provided with entry guides I2 55 and feed rolls I3 by which sheets advancing through the feed rolls I0 are directed downwardly into the pot II through a ux bath. I4 floating on the surface of the molten zinc or spelter contained in the pot II. Guides I5 direct the sheets 60 throughv the spelter between bottom rolls I6.

Guides I'I extend from the rolls I6 upwardly toward the exit rolls I8. 'As the sheets pass between the rolls I8 they are engaged by exit guides I9 which deliver them onto a conveyor 65- 20 or other transporting means.

When the form of apparatus shown in Figures 1 and 2 is used the sheets are subjected to a mist or, very fine spray as they are l/carried along by the conveyor 20. 'I'he mistor spray is'in- 70 dicated in Figure 1 by reference numeral 2| and is created kby means of very nely adjusted spray nozzles 22 connected 'with a supply of the fluid being sprayed vand a lsuitable source-of spraying pressure. The position of a sheet on the conveyor is indicated at 23. With this form of apparatus the spray impinges on both sides of the sheet. The nozzles may, however, be so positioned as to direct the spray against one or both sides ,of the sheet. The effect of the mist lor,

on various factors including the character and temperature of the spelter, ythe speed of movement of the sheet, the width.v and thickness of the sheet, 'the weight of the coating,-the factor of whether the mist is applied to one or both sides of the sheet, etc. It is, however, important that the mist shall impinge upon the coated sheet before the process of vcrystallization has advanced A far enough so that the production of crystals clearly distinguishable to thel naked 'eye will result. As crystallization may not set in immediately upon delivery of. the sheet from the spelter bath, particularly when a relatively heavy coating is applied, it is sometimes desirable not to treat the successive portions of the coatedv sheet with the mist until a predetermined time after such portions have emerged from the spelter.

For example, a treatment such as that above described and illustrated in connection with Fig` ures 1 and 2 allows a relatively great time interval before treatment of the sheets with the mist, although, of course, the greater the speed of the sheets the greater the distance from 'the point .of emergence of the sheets from the spelter to the point of impingement of. the mist t ereon may be. f

Ihe apparatus shown in Figure, 3 is similar in all respects to that shown in Figures 1 and 2 except for the positioning of the nozzles 24. These nozzles are arranged in two series extending transversely of 'sthe sheet and substantially op- Dosite each other in the directionof movement of the sheet, the nozzles being directed so that the mist impinges on the sheet at an angle in the direction of movement of the sheet. It has been found that when the nozzles are so positioned superior results are obtained. The reason for this is not definitely known although. it is believed that when the nozzles are directed so that the mist impinges on the sheet at an angle I `in the direction of movement of the sheet the Cil effect is to more rapidly evaporate the mist particles without such a cooling eifect as will produce spangles which may result if the nozzles are directed so that the mist impinges on the sheet at an Iangle in the direction opposite the direction of movement of thesheet. "When it is desired to treat only one side of the sheet only one set of nozzles is operated, the other set being shut off. Alsoy in Figure 3'the nozzles are spaced nozzles 25 arepositioned so as to spray laterally from one or bothsides of the sheet, the spray impinging both on the sheet and also on the exit rolls I8. An arrangement of this character is used on very thin sheets thinly coated in which crystallization tends to commence immediately upon exposure of the coating to the air.

One important advantage of the invention is that y.the necessity for heating the treating substance is eliminated, together with the consequent increased cost. Our treating substance ,may be applied at its. natural storage or room temperature and does not need to be heated. Apparently the very ne state of sub-division of the particles of the mist prevents the mist from having an undesirable cooling effect which might tend to buckle the sheet. Furthermore, the resis'tance 'to corrosion of the coated product does not appear to be substantially lower than the does not', however, produce a product of the' character in which weare interested. The effect t of a jet of dry steam is to wipe the coating, whileu the effect of a jet of wetsteam is to make the coating brighter and more or less non-uniform.-

Also, a cooling air blast has been applied to galvanized sheets on emergence from a zinc bath,

but this treatment does not produce'the uniformv dull unspangled matte finish which we produce but rather tends to increase the brightness and I Spangled effect' of the zinc coating. Our process monly termed spangles and thereafter vand while the coating is at least partially molten subjectlng the coating to an atomized liquid mist d the particles o'f which are -suiiiciently small to inhibit the propagation of crystals visible to Ath naked eye. i

2. In the manufacture of metal coated products, the steps comprising applying to a base a molten zinciferous coating such as would upon cooling normally form crystals of large size commonly termed "spangles and thereafter and while the coating is at` least 4partially molten subjecting tol the coating to an atomized mist of a solution of a chemical which forms a minute precipitate at about the solidication temperature of the coatvsizecommonly termed "spangles and thereafter and while the coating is at least partially molten subjecting the coating to tan atomized liquid mist the particles of which are sufficiently Ismall to inhibit thepropagation of crystals visible to the naked eye.

4. In the manufacture of coated metallic sheets.

the steps comprising applyingvto va base sheet a zinoiferous coating such as would upon cooling normally form crystals of large size commonly termed fspangles and thereafter and during the early stages of crystallization ofthe coating sub- 2,o94,5ss i -iecting the coating to an `atomized liquid mist the particles of `which are, sufficiently small lto inhibit the propagation of crystalsvisible to the naked eye.

O. 6. Inthe manufacture of metal coated products, the steps comprising passing the metal to be .coated through a bath ofla molten zinciferous` vcoating ,material such as wouldupon cooling normally form crystals of large size commonly termed spangles whereby to coat the same and thereafter and while the coating is at least partially molten subjecting the coating to an atomized liquid mist the particles 'of which are'sufllciently small lto inhibit the propagation of crystals visible to the naked eye.

' l l NELSON E. COOK.

EDWARD J. KNOPF.

WIT-11AM LDIEHL.

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