US3309217A

US3309217A - Coating method and apparatus

Info

Publication number: US3309217A
Authority: US
Inventors: Fritz J Nagel
Original assignee: Polymer Corp
Current assignee: Polymer Corp
Priority date: 1963-01-08
Filing date: 1963-07-18
Publication date: 1967-03-14
Anticipated expiration: 1984-03-14
Also published as: GB1018486A; JPS508094B1; DE1290336B; DE1577805A1

Description

ach 14, 967 F, J, NAGEL COATING METHOD AND APPARATUS Filed July 18, 1963 INVENTOR FRVTZ J. NAGEL ATTOR'NEY5 ilnited States Patent TO 3,309,217 CATDIG NETHGD AND APPARATUS Fritz J. Nagel, Reading, Pa., assignor, by mesne assignments, to rThe Polymer Corporation, a corporation of Pennsylvania Filed July 18, 1963, Ser. No. 295,977 14 Claims. (Cl. 117-18) This invention relates to process and apparatus for coating the surfaces of articles.

More particularly, the invention relates to the coatings .of the surfaces of metal articles, such as, for eX- ample, washing machine splash tubs, dishwasher tubs and similar open ended or open-topped receptacles on the inside surfaces thereof only, with a plastic coating having a relatively uniform thickness.

It is a primary object of the present invention to provide novel method and apparatus for coating the interior surfaces of .open ended containers such as tubs, pails and the like. A further object of the invention is to coat such surfaces economically and conveniently and to eliminate the need for expensive masking and touch-up procedures.

A still further object of the invention is to ensure a coating on said surfaces of improved evenness or smoothness, uniformity of thickness, and uniformly high quality.

It is yet another object of the invention to provide a relatively simple and economical apparatus for fiuiiingup or fiuidizing coating powders by passing or drawing a distributed liow of gases through the powders, and the apparatus includes means for automatically cutting off the fluidizing gases while simultaneously applying the fluidized powder to the surface of an article to be coated.

It is yet another object of the invention to provide apparatus for coating the interior surfaces of containers which includes means for quickly and effectively securing the container to or releasing the container from the apparatus.

It is still another object of the invention to provide method and apparatus for coating the surfaces of articles by means of fusible powders which are in a pre-flutfed or mobile condition and whereby the final coating is of more uniform thickness than produced by conventional methods and apparatus.

Briefly, the objects .of this invention are achieved by fluidizing a bed of fusible powder within a chamber or tank having an open top while tub-like article or coutainer is secured in inverted position over the upper opening in the chamber or tank, cutting off the fiow of gases through the bed of fusible powder and rotating the tank and article substantially 180 so that the fluidized powder will flow into and fill the article while the article is at a temperature below its melting point, but above the melting point or fusing temperature of the powder so that a film of the powder will fuse and adhere to the interior surface of the article, again rotate the tank and article substantially 180 to their original position so that the excess powder within the article fiows back into the tank. For complete fusion and/or curing of the coating, the article may require a postheat. In other instances, postheatng is not necessary.

The invention will be best understood from a consideration of the following detailed description taken in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a preferred form of the apparatus comprising the invention;

FIG. 2 is an enlarged vertical cross sectional View taken substantially on the plane of line 2 2 of FIG. 1;

FIG. 3 is an enlargement of a portion of FIG. 2;

FIG. 4 is a perspective view of a detail shown in FIGS. 1 and 2;

FIG. 5 is an enlarged perspective view of a portion of a detail shown in FIG. l;

As illustrated in `the drawings, the coating apparatus 1i) includes a tank or hollow housing 12 of suitable size and shape. As illustrated, tank 12 comprises a cylindrical central portion 14 and an annular top or neck 16 integrally connected together by a frusto-conical portion 18. The upper edge of neck 16 terminates in a radial iiange 20. The bottom of the cylindrical portion 14 is closed by a circular bottom 22 slightly larger than the cylindrical portion, and the cylindrical portion 14 is integrally connected to the bottom by a frusto-conical iiange 24.

A pair of axially spaced and parallel rings or

flanges

26 and 28 are integrally secured to the lower inside surface of the cylindrical portion 14. A circular porous partition or plate extends across the lower end of the cylindrical central portion 14 in spaced parallel relationship to bottom 22 so as to divide the interior of housing 12 into upper and lower chambers 34 and 36 -respectively. In use, upper chamber 34 contains a quantity of coating powder 40 and the lower chamber 36 contains a fiuidizing gas. The partition 32 must be impervious to the powder 40 and pervious to the fluidizing gas. The partition 32 preferably is composed of a porous ceramic material, although other porous material may be used. As shown in FIG. 2, the partition 32 extends between the flanges 26 and is secured thereby to cylindrical portion 14. The tank 12 may `also be provided with, in a convenient place, porous sections or plates 32a, for example in the frusto-conical section of the tank or elsewhere. Like the partition 32, porous plate 32a is impervious to the coating powder but pervious to the fiuidizing gases. A pipe (not shown) extending from the very bottom of the tank up through the partition 32 'and t-he powder to a point above the normal powder level, can also be used to exit the gases.

Tank 12 is pivotally supported so as to rotate on a horizontal axis by a hollow axle 42. Axle 42 includes a circular tube 44 surrounding the upper portion of the cylindrical portion 14 and secured thereto as by welding. Secured to diametrically opposite points on the tube 44 are radially extending and coaxially aligned

tubular shafts

46 and 48.

Tubular shafts

46 and 48 extend into horizontal bores formed within vertically extending

posts

50 and 52 which are secured as by bolts 54 to a fixed structure such as a foundation or door S6.

A hand wheel is concentric with shaft 48 and fixed thereto as by a key 59.

The hollow interiors of the

shafts

46 and 48 communicate with the hollow interior of the tube 44 so that gases may flow from one shaft through the tube to the other shaft. The shaft 46 has a radial opening 60 formed in one end thereof which communicates with a vertical passage 62 formed in the post 52 when tank 12 is in a normal upright position as illustrated in FIG. 2. One end of the passage l62 is connected to a suitable source of compressed gas, such as compressed air, -by a conduit 64, a fitting 65, a manual cut-off valve 66, and a conduit 68.

The interior of the shaft 46 is also connected to the source of compressed gas by means of a rotatable pipe coupling 70, conduit 72, elbow tting 74, and Vselector or cut-o valve 76 which is connected to the fitting 65.

The coupling 70 comprises a block 78 of cylindrical shape fixed to the conduit 72 as by threads 80 and extending into the free or open end of the shaft 46 so as to be surrounded by a sealing ring 79 fitted Within a groove within the shaft 46. The central portion of the block 78 is provided with an annular groove which contains the inner race of a ball bearing 82 while the outer race of the bearing is press fitted within the end 3 of the shaft 46 and retained therein by a ring 84 threaded into the end of the shaft 46. Shaft 46 is effectively sealed within the bore and post 52 on opposite sides of the opening 60 by sealing rings S6.

The outer end of the shaft 48 is closed as by a plug 88 threaded therein, and the interiorof the shaft is connected to the lower chamber 36 by a conduit 90.

The article whose interior is to be coated, comprises a container having an open top such as a tub 92 having a radial annular flange 94 formed around its open end. Tub 92 may be secured to the top of the tank 12 by inverting it and placing its flange 94 adjacent to and coaxially of the tub flange 20 as shown in FIG. 2.

The tub may be removably secured to the tank 12 in sealing relationship by encircling the

flanges

94 and 20 by clamping lbelts such as a flexible belt 96 having a hook 98 secured to one end thereof and a toggle device 100 secured to the other end thereof. The toggle device 100 may comprise an elongated lever 102 pivotally connected by a hinge means 104 to one end of the belt. A hollow link 106 is pivotally connected by a suitable fastener 108 to a central portion of the lever 102 as shown in FIG. 5. Thus, when the belt 96 is encircled around the

flanges

20 and 94, the hook 98 may be inserted into the free end of link 106 and the lever 102 may be pivoted away from the hook 9S to an over center position so that the lever lies adjacent the belt and the link 106 tightly draws the two ends of the belt together whereby the belt securely clamps the

flanges

94 and 20 together as shown in FIG. 2. Since the belt is composed of flexible material, it becomes U-shaped in cross section when it is tightly stretched around the flanges as illustrated in FIG. 2.

In operation, the upper chamber 34 of the tank 12 is lled with a suflicient quantity of fusible powder 40 to lill the tub 92. The valve 76 is closed and the cut-off valve 66 is opened so as to connect the lower chamber 36 to a source of suitable compressed gas by means of passage 62 and opening 60. The container 92 is heated to a suitable temperature which is below its melting point but above the melting or fusing temperature of the powder 40. The container 92 is then secured to the tub 12 by means of belt 96 as illustrated in FIG. 2. The compressed gases in chamber 36 ow through the porous partition 32 and upwardly through the powder 40 and then out through porous sections 32a. This causes the powder to become quite fluffy or fluidized. After the powder 40 is properly fluidized, tank 12 and container 92 are rotated approximately 180 about the axes of

shafts

46 and 48. This is accomplished by the operator grasping the hand wheel S and rotating same, After the tank 12 is rotated a few degrees, shaft 46 which is rotating with the tank reaches a point where the opening 60 is no longer aligned with the passage 62 thereby causing the supply of compressed air to chamber 36 to be cut olf. Thus, it is apparent that the opening 30, the pipe 46 and the passageway 62 constitute an automatic cut-off valve which operates when tank 12 is rotated a few degrees from the vertical position shown in FIG. 2. The operator continues to rotate hand wheel S8 until tank 12 is directly above container 92 whereupon the fluidized powder 40 completely fills the container. Since the container 92 is heated, the powder 40 immediately adjacent its interior surfaces melts or fuses and adheres thereto. After a suflicient quantity or thickness of powder has adhered to the interior surface of the container 92, hand wheel 58 and tank 12 are again rotated substantially 180 to the position illustrated in FIGS. l and 2, whereupon the excess powder in the container falls `back into tank 12. The container 92 is then removed from the tank by loosening the belt 96 in an obvious manner, and then, if required, the container is reheated to a sutlicient temperature for a suicient length of time to completely fuse the powder adhering to the interior surface of the container so as to form a smooth coating of substantially uniform thickness. The container is then 4 cooled so that the coating may properly harden and solidify.

For more effectively removing the powder 40 from tank 12 when it is inverted, the tank may be vibrated as by a conventional vibrating device 104. The container 92 may also be vibrated as by a conventional vibration device 106 so as to compact the powder and to ensure that the powder contacts the entire inner surface of the container, particularly the corners and crevices thereof. The vibration devices may comprise air operated vibrators, rotating unbalanced pulleys or wheels, electromagnetic vibrators operated by solenoids with reciprocating armatures, or a device with a rotating crankshaft or eccentric shaft. It is also possible to manually vibrate the tank and container yby repeatedly banging them with a mallet or hammer.

An alternate method of using the coating apparatus is to open both of the valves 66 and 76. This causes a continuous ow of gases through the partition 32 and powder 40 even when tank 12 is inverted whereby the gases force the powder from tank 12 into container 92 to ensure that it is properly lled. When the apparatus is not in use, the cutoff valve 66 is normally closed.

While the apparatus shown in the drawing employs uidizing gases and means to fluidize the powder and thus convert the powder to a flufed lor mobile condition, the invention is not limited thereto, either in terms of apparatus or method. The important feature is that during all or a substantial period of time that the powder is contacting the surface to `be coated, the powder be in a ulfed or mobile condition. This assures uniform distribution of the powder over the surface being coated as well as a uniform appearing and pinhole-free coating or layer. Thus, the powder may be tlutfed or prefluffed without employing uidizing gases, for example, by vibrating the powder while tumbling it; or by vigorous turnbling preferably through a series of screens to aid in breaking up any agglomerates.

Normally, the container 92 which is to be coated is composed of a suitable metal and powder 40 is composed of a suitable fusible coating material. Specific suitable materials for making the powder 40 may comprise polyvinyl chloride, other vinyl chloride resins, such as vinyl chloride polymers and vinyl chloride copolymers, wherein the vinyl chloride is copolymerized with other ethylenically unsaturated compounds, provided such copolymers contain at least 50% 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 be used include, for example, polyethylene, 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 also include conventional additives, for example, pigments, fillers, plasticizers, stabilizers, etc. The coating material preferably has a particle size of between yabout 0.001 inch and about 0.024 inch. Best results are usually obtained with a particle size of between 0.002 and about 0.012 inch.

Before the interior surface of the container 92 is coated, it is preferable to prepare the surface by removal of oxides or any residual coatings or contaminants, in order to present a clean surface for reception of the coating resin. Thus, the surface may be sandblasted, acid-etched, degreased, phosphated, etc. It may also be desirable to prime the surfaces to be coated with any lof a number of conventional primers. Liquid, epoxy-based primers are preferred. For example, the primers taught in U.S. Patents 3,008,848, 3,057,746, `as well as other similar epoxyacrylic-based primers, may be used. These primers may be air dried or oven dried and can provide additional adhesion where ultimate use requirements demand it.

Preferably, when the tank 12 and container 92 are secured together as viewed in FIG. 2, the center of gravity of the tank and container without the powder 40 is slightly below the axis of

shaft

46, 48, so that gravity will normally maintain the tank in its upright position. However, when the tank is inverted and the powder 40 flows into container 92, the center of gravity of the tank, container and powder combined, is slightly below the axis of

shaft

46, 48, or in other words, is between the shaft and container so that once the tank has been inverted, it will automatically remain inverted until returned to its original position.

In the practice of the well known uidized bed coating process, a preheated article is immersed in a uidized bed of pulverulent coating material to form a layer of material thereon. Diiiculties 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 eX- pensive operation. In the practice of the present invention, the necessity of building an imwieldly, 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.

When plastic powders such as polyethylene or polyvinylchloride are used for coating the interior of the container or tub 92, the container is heated to a temperature of about 550 F. before it is placed on and secured to the tank 12. After the container is removed from the tank, it is preferable to postheat it for a few minutes `at about 475 F. so as to completely fuse or melt the powder so that it may form a smooth layer of uniform thickness over the interior surface of the container.

Inasmuch as various changes may be made in the form, location and relative arrangement of the several parts without departing from the essential characteristics of the invention, it will be understood that the invention is not to be limited except by the scope of the appended claims.

I claim:

1. A coating process which comprises inverting a tank lof lluidized powder with the open end of a heated openended container to be coated secured to the tank so that the fluidized powder flows from the tank into the container and is coalesced into an adherent layer on an inner surface of the container.

2. The process of coating the interior surfaces of a hollow, open-ended container, which comprises the steps of:

fluidizing a bed of pulverulent, heat-fusible coating materials contained within an open-topped fluidization vessel by passing a stream of iluidizing gases upwardly through said coating materials;

heating said container to a temperature in excess of the fusion temperature of said coating materials but below the melting point of said article; discontinuing said stream of fluidizing gases;

securing the open end of said heated article to the open top of said uidization vessel so that the interiors Iof said article and said vessel are in open communication with each other;

inverting said vessel to enable the coating materials to flow into and substantially fill the article by gravity;

maintaining said coating material in said article for a suicient length of time to cause a portion of said coating materials to fuse onto the interior surfaces of said article;

returning said vessel and said article to their original positions whereby unfused coating ymaterials are returned by gravity to the interior of said vessel; and removing said article from said vessel.

3. The process of claim 2 including the step of postheating said article above the melting point of said coating material whereby the coating material adhering to said article becomes completely fused and forms a smooth coating of uniform thickness on the interior surfaces thereof.

4. A process as defined in claim 2 wherein said 'coating material comprises a vinyl chloride polymer.

5. A process as defined in claim 2, wherein said coating material comprises polyethylene.

6. A process as defined in claim 2 including the step of vibrating said vessel and article while in an inverted position.

7. The process of claim 2 including the step of vibrating said article after it is moved to its original position so as to cause additional unfused powder to return to said vessel.

8. The process of claim 3 wherein said article is heated to at least 500 F. when it is placed on said vessel and is post heated to at least 475 F.

9. Apparatus for coating the inside surfaces of a hollow, open-ended container with heat-fusible coating materials comprising a fiuidization vessel divided into an upper and lower portion by means of a gas-pervi-ous plate adapted to support a fiuidized bed of said coating materials thereover;

conduit means to introduce fluidizing gases into the lower portion of said vessel; means for securing said container in sealing relationship onto the open end of said fluidization vessel so that the interior of said container is in communication with the upper portion of said chamber; and

support means for rotatably mounting said fluidization vessel and said container so that they may be rotated into an inverted position.

10. Apparatus as defined in claim 9 wherein said support means includes a rotatably mounted horizontally extending hollow shaft connected to said conduit means.

11. Apparatus as defined in -claim 10 including auto- -rnatic valve means operatively connected to said shaft so that said automatic valve is open when said vessel is in upright position and is automatically closed when said Vessel is rotated to an inverted position.

12. Apparatus as defined in claim 11 including a bypass conduit connected to said shaft and a selector valve in series with said bypass conduit.

13. Apparatus as defined in claim 9 wherein the center of gravity of said vessel is below said shaft when said vessel is in upright position.

14. Apparatus as defined in claim 9, including a vibration means on said uidization vessel.

References Cited by the Examiner UNITED STATES PATENTS 2,844,489 7/ 1958 Gemmer 117-21 2,969,038 1/ 1961 Neumann 118-429 3,063,860 11/1962 Gemmer 117-18 3,138,483 6/1964 Dettling et al. 117-18 3,142,579 7/1964 Brooks 117-18 3,196,033 7/1965 Brooks 117-18 3,199,923 8/1965 Brooks 302-29 3,207,618 9/1965 DeHart 117-18 3,227,135 l/l966 Brooks 118-408 FOREIGN PATENTS 700,177 11/ 1953 Great Britain.

WILLIAM D. MARTIN, Primary Examiner.

S. W. ROTHSTEIN, P. F. ATTAGUILE,

Assistant Examiners.

Claims

2. THE PROCESS OF COATING THE INTERIOR SURFACES OF A HOLLOW, OPEN-ENDED CONTAINER, WHICH COMPRISES THE STEPS OF: FLUIDIZING A BED OF PULVERULENT, HEAT-FUSIBLE COATING MATERIALS CONTAINED WITHIN AN OPEN-TOPPED FLUIDIZATION VESSEL BY PASSING A STREA OF FLUIDIZING GASES UPWARDLY THROUGH SAID COATING MATERIALS; HEATING SAID CONAINER TO A TEMPERATURE IN EXCESS OF THE FUSION TEMPERATURE OF SAID COATING MATERIALS BUT BELOW THE MELTING POINT OF SAID ARTICLE; DISCONTINUING SAID STREAM OF FLUIDIZING GASES; SECURING THE OPEN END OF SAID HEATED ARTICLE TO THE OPEN TOP OF SAID FLUIDIZATION VESSL SO THAT THE INTERIORS OF SAID ARTICLE AND SAID VESSEL ARE IN OPEN COMMUNICATION WITH EACH OTHER; INVERTING SAID VESSEL TO ENABLE THE COATING MATERIALS TO FLOW INTO AND SUBSTNATIALLY FILL THE ARTICLE BY GRAVITY; MAINTAINING SAID COATING MATERIAL IN SAID ARTICLE FOR A SUFFICIENT LENGTH OF TIME TO CAUSE A PORTION OF SAID COATING MATERIALS TO FUSE ONTO THE INTERIOR SURFACES OF SAID ARTICLE; RETURNING SAID VESSEL AND SAID ARTICLE TO THEIR ORIGINAL POSITIONS WHEREBY UNFUSED COATING MATERIALS ARE RETURNED BY GRAVITY TO THE INTERIOR OF SAID VESSEL; AND REMOVING SAID ARTICLE FROM SAID VESSEL.