US1954462A - Metallic paint - Google Patents

Description

A ril 10,- 1934. u. c. TAINTON 1,954,462

METALLIC PAINT Original Filed June 11, 1932 ---"-$Eoraje Bin Ball MZ'ZZ Coarse Maierz'al CZ'assifier Overflow 3 Thichener 1! Metal P wder Url'yn C. Tainfiavi,

Patented Apr. 10, 1934 PATENT OFFICE METALLIC PAINT Urlyn C. Tainton, Baltimore, Md.

Original application June 11, 1932, Serial No. 616,730. Divided and this application May 29,

1933, Serial No. 673,530

4 Claims. (01. 134-46) This invention relates to a new kind of flaked metallic powder having a bright surface, and to the method of manufacture thereof. Metal powders serving as pigment for paint are frequently generically referred to as bronze powders even though made of metals or alloys of metal which do not have or give what is specifically known as a bronze appearance. The expression "bronze powder and the expression bronze paint as herein used are each employed in the broad or generic sense as including any of the metallic powders or metallic paints even though the same is used and relied upon to give a golden, yellow, silvery or other metallic appear- .ance to an article or surface coated thereby. The present invention is characterized by being very much more economical, both in raw material andmethod of manufacture, than the so-called bronze powders now used for paint and similar purposes. At the present time, bronze powdersare manufactured either from alloys of copper, such as brass, in cases where a golden or yellow tint is required, or from aluminum where the paint is to have a silvery cast. Such present day powders as above mentioned are made by stamping the metal in small hammer mills and subsequently polishing the product so obtained by means of rotating brushes and the addition of a small amount of wax. The metals thus far used are relatively expensive and the operation of preparing the same is slow and costly, so that the price of the finished powder is quite high. For example, aluminum powder suitable for paint ordinarily sells at seventy-five cents to one dollar per pound.

It is well known that metallic zinc affords unusually good protection especially to surfaces of iron and steel. This fact is made use of in a paint which is made by mixing with linseed oil the material known as blue powder or zinc dust, which is obtained as a by-product in the smelter distillation of zinc ores.

A recent circular, issued by the American Zinc Institute, states with reference to this question:

Zinc in'the form of galvanizing is stated by the United States Bureau of Standards, Circular #80, to be by far the best protective metallic coating for the rust-proofing of iron and steel Apparently this characteristic of zinc is equally effective when metallic zinc powder or so-called zinc dust is used in paint as a pigment and applied to metal surfaces Service tests indicate that metallic zinc paint is outstandingly superior from the standpoint of low cost per year of service.

Zinc dust, as used in the paint above mentioned, is of a dirty blue-gray color and the resultant paint does not possess an attractive appearance nor good reflectivity for'light and heat. There would be considerable advantage in producing a metallic powder having the bright appearance like or similar to that of aluminum paint but consisting mainlyof zinc and possessing the advantages of low cost and exceptional protection for metal surfaces. Such a bright zinc powder is, however, unobtainable in the market today.

' The reason for the above condition is as follows: When ordinary zinc is ground it turns dark and if the grinding is long continued, ultimately takes on the appearance of soot. Moreover, the cost of grinding by the ordinary methods is very high as the yield in any given time is remarkably small owing to the fact that ordinary zinc, containing impurities, acts as a rather tough material when subjected to sudden impact.

It has been found that of the disabilities above mentioned, the darkening of the powder is due to superficial oxidation caused by local heat n at the moment of impact. This condition is very so much aggravated if rough surfaces are employed for the hammering action. The diiiiculty of grinding the zinc metal may be minimized by the use of certain alloys consisting of pure zinc to which has been addeda small amount of one or more other elements. We find that a zinc powtier-having a bright surface may be obtained if the grinding is carried on with bright or polished surfaces in the presence of a considerable quan tity of inert liquid, which prevents the local high temperatures referred to above. Proper means must also be provided for dissipating the heat which is generated by grinding. One of the outstanding advantages of the above method is that it is possible to employ ball mills or similar apparatus of large grinding capacity in the manufacture instead of the small hammer mills normally employed. It has been found that grinding equipment as heretofore employed will not produce satisfactory bronze powders. A recent textbook on the subject, Aluminum Bronze Pow- 1 der 8; Aluminum Paint by J. D. Edwards, states that:

"There seems to be but one way to make metallic bronze powders, no matter what the specific mechanical arrangement employed. By pressure, the metal must be forced to flow into flakelike particles. Pressure, such as in stamping, produces a burnishing action and enhances and conserves metallic luster and brilliancy. Abrasion and grinding produce a reduction insize of particle, but the powder so produced is dark in color and granular in nature. -It is almosttotally lacking in the brilliant flakes which give bronze powders their characteristic appearance and value.

Applicant has discovered and ascertained that in the presence of a large volume of inert liquid, it is possible to quite successfully employ standard grinding equipment. To accomplish the desired end, applicant preferably passes a stream of relatively inert liquid through the mill and thereby carries in suspension the metal powder which is undergoing treatment. This inert carrying liquid from the mill then passes to and through settling chambers or classifiers, in which the coarser material settles and from which the coarser material is returned to the head of the grinding circuit along with the new feed material, while at the same time the fine powder and inert liquid carrying the fine powder. is allowed to overflow and is passed to a filter or other suitable separating-out medium, when the fine filtered out powder or particles are recovered as by filtration, centrifuging or similar treatment and from which the inert liquid freed of the major portion, if not all, of the fine powder is returned to the head of the grinding circuit. In this way, the operation is made continuous and the operating costs are very low.

Itis preferred to employ for the lining of the grinding apparatus, to wit, the mill, as it is usually called and the grinding media, hard material capable of taking a high polish. Manganese steel or nickel-chrome alloys provide materials which may be used with advantage. It is also preferable to add to the inert grinding medium, reducing agents such as linseed oil, which will combine with and counteract any oxygen introduced into the circuit; and also small amounts of organic acids such as stearic and oleic acid, which will combine with and thereafter counteract any zinc oxide that may be formed.

There is usually employed as an inert liquid, a light hydrocarbon such as kerosene or benzene. The linseed oil or similar material which is used as a reducing agent is added to this hydrocarbon in appropriate amounts, say ten to twenty per centum of linseed oil to ninety to eighty per centum of the inert light hydrocarbon. It is within the contemplation of this invention that other liquids such as carbon tetrachloride, butyl alcohol, et cetera, may be used to provide the inert liquid.

Before grinding in the mill, the metal is reduced to the form of sheet, ribbon, granules, shavings, et cetera, and preferably to a thin, finely divided form and one in which the zinc pieces are clear and bright. The operation may be advantageously carried out as a method of using scrap zinc foil obtained in connection with the process described in pending applica tion, Serial No. 531,610, filed April 20, 1931, or

in pending application,'Serial No. 608,348, filed April 29, 1932, covering joint inventions of myself and Frank W. Harris. The zinc foil of these applicationsor produced according to either of them-is particularly useful as providing the basic material from which to manufacture a zinc paint pigment according to the present inven- 'tion. Another suitable method for preliminary preparation of the metal is to melt the metal and allow it to fiow in a molten form onto the periphery of a rapidly revolving metal drum. By this means, extremely thin sheets 0; ribbons may be obtained.

.when' inetalsare classified in the However, for effective commercial production, it is advisable to have the zinc which is to be ground in relatively thin, slender or finely divided form whereby the grindingoperation can be most effectively carried out so that most of the work and energy of grinding is employed in the actual converting of the fine particles into brightly polished flake-like form.

The grinding operation employed and relied upon for carrying out and realizing the present invention is one in which the application of impact pressure and frictional rubbing contact is suflicient to break up and flatten out the metal particles and so completely to change their form by pressure applied in a manner so as to effeet a flow of the metal into flake-like particles. In short, the grinding of this invention includes such steps and operations as may be described as grinding, disintegrating and'fiattening out. In other words, the grinding of the invention accomplishes a crushing and corresponding spreading or extending of the surface of the pieces or particles of raw material operated upon in order to produce the desired finished product. Moreover, this type of grinding is carried out in the presence of inert liquids as is herein pointed out. The grinding of this invention should not be confused with grinding sometimes so called which may involve nothing more than the introducing of metal pigment into a grinding machine to thereby effect an intimate mixing of the pigment portions in or with a liquid with which it is being mixed in the grinding machine, and which mixing operation is carried out without disintegrating of the pigment particles and without an extending of the surfaces of the pigment particles.

According to certain broader aspects of the invention, ordinary zinc may serve as the raw material. However, for many purposes, it is especially advantageous to use alloys consisting of high grade zinc and containing a small quantity of another element in solid solution as described in co-pending application, Serial No. 608,348, previously referred to. For example, an alloy which gives exceptionally brilliant paint is one consisting of more than 99.9 percentum of zinc and 0.07 percentum of manganese, other impurities such as cadmium and lead being as small in amount as possible. One purpose of manganese as an alloy is to prevent the recrystallization of the zinc as is described in said application, Serial No. 608,348, and other alloying metals may be used instead of manganese as is described'in said application. It is to be understood, however, that while the process herein described is especially applicable to the production of zinc and zinc alloy powders, it is not to be construed as being limited to this field, for the process to which the invention is directed has broad fields of application, and, for example, may be applied to the manufacture of powders of other metals such as aluminum, copper, brass, cadmium, lead, nickel, silver, gold, tin, etc. It is of especial value for the production of large tonnages as it permits the use of large grinding equipment and the minimum of supervision. It also obviates the danger of explosion which is a constant hazard presence of air as is done at present.

The single sheet of drawing diagrammatically illustrates an arrangement of apparatus by which the desired metallic zinc pigment suitable for paint may be made. The apparatus shown employs a wet grinding process and includes in combination and in operative relationship any suitable grinding mill, as, for example, a ball mill 1--although any other type of mill such as a tube or rod mill could well be employed---; a

classifier, for example, a drag classifier, 2, intowhich the pulp from the delivery end of the ball mill flows through suitable pipe line to the classifier; a thickener 3 into whichwthere is an overflow from the delivery end of the classifier through suitable pipe line that carries fine metallic particles in suspension with the grinding liquid from the classifier to the thickener wherein the pulp or metallic pigment settles-this settled material is sometimes referred to as the metallic sludge-; and a filter 4 into which there is an underfiow leading through any suitable pipe line from the thickener to the filter. 'These parts are connected so that liquid freed, or freed to a certain extent. from the metallic particles is returned (a) from a portion of the classifier, (b) from an overflow leading from the thickener, and

@(c) from the lower portion of the filter-from' below or behind the filtering septum--, back to the entrance end of the ball mill whereby the wet grinding process can be properly carried out and in a continuous manner. The apparatus also has any suitable feeding or storage means 5 that delivers the zinc pieces to be ground into the return line leading to the entrance end of the ball mill.

While it is feasible to have all the return lines leading to the ball mill embodied in a single line, still it is possible to have independent lines for any one or more of these returns. In the drawing, as shown, there is provided an independent return line leading from the classifier back to the ball mill whereby the coarser material is re turned and handled through that line and in this return line for this coarse material there is also delivered the material from the storage bin preparatory to introduction of material from the storage bin into the ball mill. It will be maniiest that in the functioning of this apparatus, the ball mill serves to progressively grind and reduce the metal particles. In this wet grinding, some of the larger particles, as well as the sufiiciently fine particles, pass from the ball mill to the classifier. This mill is preferably lined with, and the balls or rods used therein are preferably made of, hardened steel, manganese steel or nickelchrome alloys. The classifier is intended to separate out the coarse material which is not sufficiently fine for paint pigment. Therefore, this material is directly returned from one end of the classifier to the entrance end of the ball mill where the reducing operation is repeated. I

The fine material passes from the delivery end of the classifier through suitable piping into the thckener whereby the operations incident to the thickener take place; namely, the lighter over flow liquid or the overflow liquid to a large extent freed from the metallic particles. pass to an overfiow line leading baclr to the ball mill while from the delivery end of the thickener the fine particles together with a certain amount of the liquid employed in the process, to wit, collectively, the thickened sludge that collects in the bottom of the thickener, are conveyed or conducted to the filter a. While the apparatus l may be referred to as a filter which may. more broadly be referred to as a separator, the functioning thereof is definitely to cause a filtering or separating-out of the fine metallic particles from the liquid employed in the process. After this operation has been effected, the filtered liquid is returned to the ball mill or classifier. The deposited, or concentrated and collected metallic, particles are then removed from the filter or separator. As previously indicated, there is suflicient liquid in the deposited material, however, to prevent oxidation and by the process herein described, and due to the retention of the fine metallic pigment particles in a certain amount of this liquid vehicle, there is revented any oxidizing contact which would cause a tarnishing of the metal pigment prior to its introduction into the proper vehicle with which the paint particles are mixed for the formation of paint.

The fine metal particles from the filter or filter press may, if desired, be washed with fresh liquid to separate any dirt or oxide and may then be dried or used in the wet state for mixing with the proper vehicle to form a pa nt. The dry powder may, if desired, be subjected to a polishing operation but this is usually unnecessary as it will be found that the powder produced in this way already has a brilliant surface similar to the best metallicpigment. When the paint part cles have been mixed with this proper vehicle to provide the paint, it is manifest that they are still retained in such condition and manner that oxidation w'll not occur so'that when the paint is applied the resulting painted article is one having a brilliant, bright metallic surface, and these characteristics are enabled to be realized because the metallic particles are in the form of flakes having smooth, bright surfaces. It w ll also be noied that the ball mill and the grinding operation carried out therein effects not merely a disintegrating of the metallic substances into fine powders but it in fact also effects a burnishing and polishing of the nietallc particles under con ditions where the surface of each particle is rendered smooth and bright and of a character such as to remain so.

This application is a division of my application filed on June 11, 1932. Serial No. 616,730.

I claim:

1. The manufacture of metallic zinc powder by the method comprising producing zine foil with a bright metallic appearance, subjecting pieces of said foil to a wet grinding operation wherein the zinc particles are maintained within an inert liquid during the grinding operation, withdrawing liquid bearing the thus ground particles, subjecting said withdrawn liquid to a class fying operation wherein the larger particles and one portion of the withdrawn liquid pass in one direction and thence from the classifying operation and the finer particles and theother portion of the with drawn liquid passin another direction and thence from the classifying operation, returning the portion containing the larger or coarser particles to the grinding operation, conducting the portion containing the finer particles to a place where a separating of said finer particles from the liquid bearing the same is largely effected, returning to the grinding operation the liquid from which said finer particles have thus been separated, conveying sad finer particles thus separated and some of the liquid containing the same to a further separating operation whereby said finer particles can be concentrated and collected, returning to the grinding operation the liquid thus finally separated and substantially freed of said finer 1 divided form with a bright metallic appearance, subjecting zinc of said form to a wet grinding process wherein the zinc undergoing grinding is maintained within a liquid inert with respect to the zinc, withdrawing liquid bearing the resulting ground particles, subjecting withdrawn liquid to a classifying operation whereby entrained large particles can pass in'one direction and the fine particles in the liquid pass-with the major portion of the liquid in the other direction, returning the large particles to the grinding process, conducting the liquid containing the fine particles to a place wherein a separating of fine particles in the liquid can take place, returning to the grinding process the liquid from which the particles have thus been settled, conducting the settled particles and some of the liquid within which the settled particles are located to a further separating operation whereby the finer particles can be further concentrated and collected, returning the liquidthus freed from the concentrated and collected zinc particles to the grinding operation, and removing for use the thus collected and concentrated zinc particles.

3. An apparatus comprising means for supplying pieces of zinc, in bright, finely divided form, a grinding apparatus to which there is a continuous supply of liquid inert to zinc, a classifier, a thickener and a filtering means, piping for conducting liquid and ground particles carried by the liquid from the delivery portion of the grinding apparatus to the classifier wherein the ground particles carried thereto with the liquid is separated whereby the coarser particles can be returned to the mill and whereby the finer particles can pass with the liquid in which they are carried on the way to the thickener, means for conducting said liquid and fine particles carried thereby from the classifier to the thickener the latter of which is constructed so that metallic sludge can collect in one portion thereof and so that a portion of the liquid supplied thereto can overfiow from the thickener after some of the metallic particles therein have settled into the sludge portion of the thickener, means for conducting the metallic sludge from the portion or the thickener in which it collects to the filtering means, within which filtering means the sludge can be further filtered in order to collect the fine particles, and means for returning to the grinding apparatus the filtered-out liquid from the filter, the overflow from the thickener and the coarse particles from the classifier, the means for supplying pieces of zinc being arranged whereby said pieces of zinc are placed into the entrance end of the ball mill.

4. An apparatus comprising means for supplying zinc in condition and form suitable for grinding, a ball mill to which there is a continuous supply of liquid inert to zinc, a classifier, a thickener, a filtering means, piping for conducting liquid and ground particles carried by the liquid from the delivery portion of the ball mill to the classifier in which classifier the ground particles carried thereto with the liquid is separated whereby the coarser particles can be returned to the mill and whereby the finer particles can be conveyed with the liquid in which they are carried to the thickener, means for conducting said fine particles and liquid conveying the same from the classifier to the thickener, the latter of which is constructed so that a metallic sludge can collect in one portion thereof and so that a por tion of the liquid supplied thereto can pass from the thickener back toward the mill after some of the metallic particles therein have dropped into the sludge portion of the thickener, means for conducting the metallic sludge from the portion of the thickener in which it collects to the filtering means, in which filtering means the sludge can be further filtered preparatory to separating out and collecting the fine particles and means for returning to the ball mill the filtered-out liquid from the filter, the liquid passing from the thickener back toward the mill, and the coarse particles from the classifier, the means for supplying zinc being arranged for delivering said zinc into the liquid flowing toward and into the entrance end of the ball mill.

URLYN C. TAINTON.

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