US 3260611 A
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Description (OCR text may contain errors)
July 12, 1966 B. B. WEIDENHAMMER ETAL COATING METHOD Filed Feb. 15, 1963 Fluidizing Air or Gas INVENTORS BARRY B. WEIDENHAMMER JOHN GHUDOVAN FRITZ J. NAGEL B ZM a M ATTORNEY United States Patent Oflice v 3,266,611 Patented July 12, 1966 3,260,611 COATING METHDD Barry B. Weidenhammer, Temple, John Chudovan, Reading, and Fritz J. Nagel, Reitfton, Pa, assignors, by mesne assignments, to The Polymer Corporation, a corporation of Pennsylvania Filed Feb. 13, 1963, Ser. No. 258,226 2 Claims. (Cl. 117-18) This invention relates to the coating of metal surfaces and is concerned with the formation thereon of durable and decorative, adherent, organic plastic coatings. More particularly, the present invention is concerned with the coating of metal articles, such as, for example, washing machine splash tubs, dishwasher tubs and similar openended or open-topped receptacles on the inside surfaces thereof only.
It is an object of the present invention to provide a novel method of coating the interior surfaces of tub and tub-like articles. A further object is to coat such surfaces economically and conveniently and to eliminate the need for expensive masking and touch-up procedures. A further object of the invention is to insure a coating of improved evenness, uniformity of thickness, and uniformly high quality.
Other objects and advantages will be apparent to one skilled in the art upon reading this disclosure and the accompanying drawing.
' Briefly, the objects of this invention are achieved by rotating and preferably agitating a preheated tub-like article positioned on a vertical or slightly inclined axis, withdrawing a portion of fluidized coating powder from a fluidizing source and contacting the inner surfaces of the article with said powder in an amount which is in excess of the amount necessary to form the desired thickness of coating, continuing the rotating and agitating of the article while slowly pouring off the excess of powder by altering the attitude of the article with respect to a horizontal plane, and then removing the article and allowing the coating to cool and harden. The coated article may be postheated either before or after initial cooling. In other instances, the coated article need not be postheated at all.
For a further description of the invention, reference is made to the accompanying drawing wherein:
FIGURE 1 is a diagrammatic perspective view of a system for carrying out the method of the present invention.
Referring to FIGURE 1 of the drawing, fluidized bed container is an open-topped device of suitable crosssection, which is horizontally divided into an upper and lower chamber, 13b and 13a respectively, by means of porous partition 12. This partition, which should be pervious to the fiuidizing air or gas used but impervious to the particles of coating material, may preferably take the form of a porous ceramic plate, although other similar structure may be advantageously used. The fluidized bed container, which contains fluidized powder 11, is supported by suitable hanger 14 and beam 15 and is adapted to be raised and lowered with respect to supporting beam 15 and also tilted, for example, by means of a rope 16 which can be pulled by the operator so that fluidized powder may be Withdrawn and poured into the opentopped article 17 which is to be coated. Article 17 has an open top 18 adapted to receive the powder 11, bottom portion 19 and side portion 22. The article is supported on rotatable shaft 20 which may be driven by any conventional driving motor and gearing (not shown). In the drawing, the article has a small neck-like opening at its bottom and the shaft 24) is conveniently shown as being jigged and clamped therein by clamping elements 21 (and 21a). It is to be understood that many articles may not have a neck-like opening and the shaft may be clamped to the bottom 19 and/ or lower portion of sides 22 by any convenient clamping device. Vibrator 23 is shown as attached to the shaft 20 for producing vibrations, which preferably are transverse to the shaft. The vibrator may also be attached to a platform positioned on the shaft or the vibrator may be positioned much closer to the article than shown or actually be attached to the article itself. Receptacle 25 is conveniently placed at a position to receive the excess coating powder 24 during the latter stages of the coating operation.
In carrying out the method of the present invention, coating powder is fluidized in container 10. The article which has first been preheated to a proper temperature is positioned on shaft 20 and the shaft is rotated and vibrator 21 set into action. The article is preferably positioned on a slightly inclined axis, although it may also be vertical at the initial stages of the operation. The container 10 which is ordinarily raised to a position above the article 16, is tilted and fluidizing coating powder is withdrawn therefrom and poured into the rotating and vibrating article in an amout which is in excess of that amount required to form the desired thickness of coating. The attitude of the article with respect to a horizontal plane is then slowly altered or lowered from its initial position while the article continues to vibrate and rotate about its axis until the article is in the position shown in dotted lines in FIGURE 1, whereupon the excess powder 24 is expelled by gravity means and is received by receptacle 23.
In a specific embodiment of the method of the present invention, an automatic washing machine metallic splash tub was preheated in an oven to about 550 F., removed from the oven and positioned on the shaft 20. The shaft was then rotated at about 32 rpm. and the vibrator set in motion to produce vibrations transverse to the shaft. A suitable agitating device is an air operated vibrator known as the Vibralator Vibrator Inducer, Model CCVP- 375, made by Martin Engineering Company of Neponset, Illinois. Polyvinyl chloride coating powder, having a particle size passing through a 40 mesh sieve, in an amount equal to about /5 to /3 the volume of article to be coated, was withdrawn from the container 10 and poured into the rotating and vibrating article. The coating powder particles immediately adjacent to the metal surface began to fuse and sinter to each other and to the metal surface into a continuous layer which was gradually built up into the desired thickness (about l22() mils) while the article was rotated and agitated by vibrating and while the attitude of the article was gradually lowered until the excess of coating material was poured off. The article was then postheated for a few minutes at 475 F. A number of coating runs were performed with polyvinyl chloride coating powder in which the powder contact time varied from about 6 to 15 seconds. The quality of the coating produced was excellent. Not only were the inner sides of the article coated, but also the inner bottom surface of the article was completely coated. Uniformity and evenness were high and, in many cases, the thickness of coating varied by only a few mils, e.g., from a total minimum thickness of about 15 mils to a total maximum thickness of about 18 mils, over the entire inner side and bottom surfaces.
Although polyvinyl chloride was mentioned above, the invention is by no means limited in its practice with that material. Other coating materials which can be used in the practice of this invention include, for example, vinyl chloride resins in general. The term vinyl chloride resins, as used herein, includes vinyl chloride polymers and vinyl chloride oo-polymers, wherein the vinyl chloride is copolymerized with other ethylenically unsaturated compounds, provided said co-polymers contain at least about 50 percent by weight of vinyl chloride. Ethylenically unsaturated compounds which can be copolymerized with vinyl chloride include, for example, vinyl esters such as vinyl acetate, vinyl propionate, vinylidene halides, such as vinylidene chloride and vinylidene bromide, and many others. Other coating materials which may also be used include, for example, cellulosic resins, such as cellulose acetate and cellulose acetate butyrate, epoxy resins, polyamide resins (nylon), polyethylene, chlorinated polyether resins and many others. The coating materials may include conventional additives, for example, pigments, fillers, plasticizers, stabilizers, etc.
With further reference to the fluidization of the coating powder (as in container powder size, etc., reference may be had to the disclosure of Gemmer, U.S. Patent 2,844,489. As further taught in Gemmer, it is common practice to prepare the surface to be coated by removal of oxides or any residual coatings or contaminants, thus presenting a clean surface for reception of the coating resin. Thus, the surfaces may be sandblasted, acid-etched, degreased, phosphated, etc. It may also be desirable to prime the surfaces to be coated with any of a number of conventional primers. Liquid, epoxy-based primers are preferred, for example, the primers taught in U.S. Patent 3,008,848 or the primers taught in U.S. 3,057,746. These primers may be air-dried or ovendried and can provide additional adhesion where ultimate use requirements demand it.
In the practice of the well-known fluidized bed coating process (see, for example, Gemmer U.S. "Patent 2,844,489), a preheated article is immersed in a fluidized bed of pulverulent coating material to form a layer of material thereon. Difliculties arise with this method when the article to be coated is larger than the coating tank or when only one surface or portion of a surface is to be coated. In the latter case, masking must be used to prevent the coating material from adhering to the surfaces or surface portion which are not intended to be coated. The application of masking is a time consuming and expensive operation. In the practice of the present invention, the necessity of building an unwieldy, oversize tank is avoided, as is the necessity of masking the outside surface of the article which is not intended to be coated since the coating material contacts only the inside surface of the article.
It is a feature of the present invention that the powder contacting the article is taken from a fluidizing container or fluidizing source and thus, initially, and during a substantial portion of the coating operation, is in a flulfed and semi-fluidized state. While the drawing shows as the fluidizing source, a container positioned above the article being coated, and the pouring of fluidized powder therefrom into the article, it is apparent that the fiuidizing source or container could be below the article and a hose or tubular member used therewith to convey fluidized coating material from the source to the article. Such a procedure might be more desirable where overhead space is limited. When the powder is taken from a fluidizing source, as discussed above, there is assured a much more even distribution of powder over the article surfaces and much improved coating than could be obtained if dead powder were used, as is taught in the Heisler et al. patent, U.S. No. 2,737,461. Furthermore, contrary to the teaching of the Heisler et al. patent, it has been found that by starting the coating operation while the article is being agitated, as by imparting vibrations thereto, and rotated in a substantial vertical position and then gradually lowering the article while continuing the rotation and agitation and, of course, the coating, the inside bottom surfaces of the article, as well as the inside wall or side surfaces of the article, can be substantially evenly and uniformly coated.
The manner of agitating the article, and it is to be understood that any agitation imparted to the article merely by rotating the same is ordinarily negligible, may vary. Preferably, suitable agitation of the article is accomplished by means of a vibrating device, such as the air operated vibrator previously disclosed, or by means of one or more unbalanced pulleys; electromagnetic vibrations induced by one or more solenoids or a reciprocating armature; or by means of a crankshaft or eccentric shaft. It is additionally possible to manually agitate the article by repeatedly banging it with a mallet or hammer.
Although the present invention has been illustrated with a splash tub which is substantially circular in cross section, it is a surprising feature that it is also applicable to essentially square shaped tubs as well as many other utilitarian tub-like articles, for example, pails, buckets, barrels, short lengths of pipe, etc. In the case of a square shaped article, it is preferred to reverse the rotation periodically.
Obviously, many modifications and variations of the present invention are possible in the light of the above teachings.
It is to be understood, therefore, that the scope of the invention is not limited by the details of the foregoing description but will be defined in the following claims.
1. A method of coating the interior surface of a hollow tub-like article that has one open end and one substantially closed end comprising preheating the article to above the fusion temperature of resinous pulverulent coating materials; mounting said article for rotation about an axis with said open end substantially uppermost; fluidizing a bed of said pulverulent resinous coating materials; pouring such fluidized coating materials directly into a lower portion of said article; rotating said article about said first axis; gradually inclining said first axis from a substantially vertical position to one that will cause said open end to point below a horizontal plane while continuing said rotation; and allowing unfused coating materials to spill out of said opening.
2. A method according to claim 1 in which said article is vibrated during said rotation.
References Cited by the Examiner UNITED STATES PATENTS 2,166,945 7/ 1939 Eberhart. 2,723,054 11/1955 Louden et a1 222-195 2,737,461 3/ 1956 Heisler et al. 117-18 3,004,861 10/1961 Davis 11718 3,008,847 11/1961 Berge 11772 3,062,414 11/1962 Morris 222 3,063,860 11/1962 Gemmer 117-18 3,090,696 5/ 1963 Gemmer 11721 3,102,603 9/1963 Kerr 222145 X 3,132,038 5/1964 Ward 11718 3,138,483 6/1964 Dettling et al. 11721 X 3,167,442 1/1965 Brooks 11719 X FOREIGN PATENTS 115,735 1876 France. 1,238,170 6/1960 France. 1,051,175 2/1959 Germany.
OTHER REFERENCES Kunststolfe BD. 47,1957, Heft 8, pp. 510, 511, and 512.
WILLIAM D. MARTIN, Primary Examiner.
G. L. HUBBARD, Assistant Examiner.