Pneumatic powder flow diverting device

Abstract

This invention is directed to a pneumatic flow switching device particularly adapted for the electrostatic coating of tubular workpieces, particularly can bodies, and includes a generally cylindrical chamber, a conduit for peripherally delivering a fluidized admixture of powder and air into the chamber, means for peripherally exhausting the powder-air admixture from the chamber, means adjacent the conduit for directing air tangentially into the chamber whereby the powder-air admixture is directed toward the exhausting means, and means for pneumatically traversing the powder-air admixture generally axially of the chamber for the delivery to an article intended to be treated thereby.

Description

This invention relates to coating articles, and in particular, to electrostatically coating tubular articles such as can bodies or the like.

Can bodies have the interior surfaces thereof coated with an enamel where the cans are intended to contain beverages or varieties of food products. A thin coating of enamel is usually applied to the interior metal surface of the can by a roller coating process before it is shaped to form the can. During the shaping operation the enamel is usually scratched or otherwise subjected to minor damage which exposes small areas of the metal, rendering the interior can surface liable to corrosion by the contents thereof. The damage affected to the interior enamel coating during can shaping is generally repaired by spraying the interior of the can with a coating of lacquer after fabrication and before attachment of an end thereto. This process is extremely wasteful of lacquer because not only is the lacquer sprayed on to the damaged areas but it is also sprayed on those areas which are undamaged and thus consequently do not require further coating.

The enamel coating and/or the lacquer is heated and until recent developments organic solvents were driven off by the heat creating undesirable atmospheric emissions which presently are becoming increasingly regulated by States as well as by the Federal Government. The latter factor has increased the use of coatings without organic solvents for protective or decorative applications, and since the appearance on the market of the latter materials powder coatings have held a strong position among competitive technologies. Flame spraying, fluid bed and similar means have been used for at least twenty years to apply powders and other solvent-free protective coatings.

Approximately one-half dozen years ago electrostatic deposition technology was employed to stripe welded can bodies on a commercial basis and the success thereof has served as a basis for the development of electrostatic powder technology for coating the inside of beer and soft drink containers. The favorable economics associated with electrostatic coating, either full coat, full overcoat, and/or repair coat, is mainly due to lower material costs on a per can body basis, the reduction in air pollution control equipment and, in some instances, reduction of steps in earlier conventional processes (i.e., the elimination of the two coat system).

In the practice of what is termed the "single" mode operation beer can bodies are entirely electrostatically coated in a single step to give a defect-free coating. Since the deposition occurs after the can body blanks are fabricated into cylindrical bodies subsequent scratching does not occur and again conventional lacquer coating operations are eliminated.

In the "single mode" of operation a powder gun pneumatically discharges an admixture of the electrically charged coating powder and air through the can body resulting in a very thin over-all coating. When operating on a commercial basis the can bodies must be rapidly moved into and out of the spray area and of prime concern is the powder flow to the powder gun which must be accurately controlled in order not to waste powder between cans.

In keeping with the foregoing a primary object of this invention is to provide a novel device for pneumatically switching the flow of the powder, the device including a cylindrical chamber, means for delivering a fluidized admixture of powder and air into the chamber, means for exhausting the powder-air admixture from the chamber, first means contiguous to the delivering means for pneumatically directing the powder-air admixture from the delivering means toward the exhausting means, and second means for pneumatically traversing the powder-air admixture during its movement between the delivering and exhausting means for directing the powder-air admixture primarily axially from the chamber toward an area at which an article is to be coated or otherwise effected by the powder portion of the powder-air admixture.

A further object of this invention is to provide a novel pneumatic flow switching device of the type immediately heretofore set forth wherein the first-mentioned directing means is a port opening generally tangentially into the cylindrical chamber whereby air directed into the chamber therethrough tends to propel the powder-air admixture in a circular pattern within the chamber.

A further object of this invention is to provide a novel pneumatic flow switching device for activating the second directing means only when an article is at a position to be effected by the powder portion of the powder-air admixture.

yet another object of this invention is to provide a novel pneumatic flow switching device including means for supporting an article, preferably a tubular can body, adjacent the axial output of the chamber whereby the article will be coated by the powder of the powder-air admixture.

Still another object of this invention is to provide a novel pneumatic flow switching device of the type aforesaid wherein means are provided for charging the powder and/or article whereby the latter is electrostatically coated.

With the above and other objects in view that will hereinafter appear the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claimed subject matter, and the several views illustrated in the accompanying drawings.

IN THE DRAWINGS

FIG. 1 is a perspective view of the pneumatic flow switching device of this invention, and illustrates powder-air delivery and exhaust port spaced peripherally with respect to a generally cylindrical chamber, an air input port disposed tangentially with respect to the delivery port, and an axially disposed air input port for propelling the normally circularly flowing powder-air admixture to and through a powder gun for subsequent deposition upon an associated article.

FIG. 2 is a fragmentary front elevational view looking from right-to-left in FIG. 1, and illustrates constructional details of the switching device including an annular discharge orifice for the powder-air admixture.

FIG. 3 is a cross-sectional view taken generally along the line 3--3 of FIG. 2, and illustrates details of the chamber construction and a venturi downstream of the axially disposed air inlet port.

FIG. 4 is a cross-sectional view taken generally along line 4--4 of FIG. 3, and illustrates details of the powder-air admixture flow when the axially disposed air inlet port is cut off from a pressurized air source during a non-coating cycle of the device.

The pneumatic flow switching device of this invention is generally designated by the reference numeral 10, and as is best illustrated in FIG. 1, the over-all construction includes a housing 11 defined by a pair of rectangular preferably transparent plates 12, 13 (FIG. 3) secured together by bolts 15 in a conventional manner. The plates are centrally contoured to define a generally cylindrical or circular chamber 16 having a peripheral wall surface 17. Means 18 in the form of a generally radially disposed port functions to deliver an admixture of powder and air into the chamber 16 at approximately the 12 o'clock position thereof, as viewed in FIG. 4. Means, generally designated by the reference numeral 20, in the form of another port is provided for exhausting the powder-air admixture from the chamber in a continuous fashion irrespective of whether or not an article is being coated at a station S (FIG. 3) or being transported to or removed therefrom, in the manner to be described more fully hereinafter. Additional means 21 in the form of another port or conduit is disposed such that air is directed generally tangentially into the chamber 16 at approximately the 12 o'clock position and adjacent the port 18 resulting in the powder-air admixture traveling in a generally circular path augmented by the curvature of the surface 17 from the 12 o'clock position of the chamber 16 to approximately the 7-8 o'clock position at which it is exhausted through the port 20.

Reference is made once again particularly to FIG. 1 in order to indicate the manner in which the switching device 10 is part of a circulating system, generally designated by the reference numeral 25 which includes a source of pressurized air, such as a pump 26 coupled by a conduit 27 to a conventional switch 28. The switch 28 is, in turn, coupled by a conduit 30 to a source 31 of powder, the particular nature of which will be described more fully hereinafter. The air introduced into the powder source 31 through the conduit 32 maintains the powder-air admixture therein in a fluidized state in order that it might be pneumatically moved through the system 25 with its delivery into the interior of the chamber 16 being under the control of an adjustable valve 32 in a conduit 33 which is in turn coupled to the conduit or delivery port 18.

By the same token the air input port 21 is a conduit which is likewise coupled to the valve 28 whereas the exhaust port or conduit 20 is fed back to the powder source 31 for subsequent recirculation. Fresh powder, as necessary, may be fed into the powder source or fluidized bed from any other area through a conduit 34. Thus, in the non-coating or non-application mode of operation the powder-air admixture from the source 31 follows a closed path defined by the conduit 33, the adjustable valve 32, the conduit 18, the interior of the chamber 16, and the conduit 20 augmented by air introduced into the chamber 16 through the conduit 21 with the bed 31 being maintained in a fluidized condition by air introduced thereinto through the conduit 30.

The "normal" generally circular path of travel of the powder-air admixture within the chamber 16 just described is interrupted in order to disrupt the flow path of the powder-air admixture within the chamber 16 and instead redirect the same axially outwardly therefrom. The change in travel of the powder-air admixture is effected by a generally axially disposed nozzle or air inlet port 35 which projects through a bore 36 of the plate 12 into the chamber 16 and is positioned with a discharge opening 37 thereof closely adjacent an inlet end 38 of a venturi tube 40 having a leftwardly (as viewed in FIG. 3) converging tubular passage 41. The venturi 40 has a reduced end 42 received within a bore 43 of the plate 13 and is held therewithin by a tubular flanged member 44 whose flange 45 is conventionally secured to the plate 13. An end portion 46 of a powder nozzle or gun 47 is sandwiched and held captive between the venturi 40 and the tubular member 44 and terminates at its leftmost end in a circular opening 48. Housed within the powder nozzle 47 is a conductive element 50 having a generally bell-shaped end 51 projecting beyond the circular opening 48 and having a maximum diameter as defined by a circular edge 52 slightly less than the circular opening 47 thereby defining a generally annular discharge area 53 between the bell 51, the projecting leftward end of the element 50, and the circular opening 48. This configuration is designed to achieve a generally annular "cloud-like" flow of the powder-air admixture as it departs the orifice 48 for subsequent application to an article supported to the left as viewed in FIG. 3.

Assuming that an article, such as an open-ended tubular can body, is supported to the left of the gun 47 as indicated by the reference numeral S, and preferably coaxial therewith, the "normal" flow of the powder-air admixture heretofore described is interrupted by operating the valve 28 such that air from the pump 26 is additionally directed through the nozzle or conduit into the chamber 16 and/or the inlet 38 of the passage 41 of the venturi tube 40. So long as sufficient air is emitted from the nozzle or jet 35 the powder-air admixture continuously delivered into the chamber 16 will be delivered by the powder gun 47 and particularly through the orifice toward and into the can body in the desired configuration as determined by the particular contour of the area generally designated at 53. It is emphasized that during the redirection of the powder-air admixture from its normal path (generally circular) to a path axial thereto there need be no stoppage of the flow of air to the source 31 through the conduit 30 nor air into the chamber 16 through the conduit 21. The effect of air issuing from the jet 35 simply redirects the powder-air admixture along an axial path to perform the desired coating operation, and upon the termination of air flow to the jet 35 by appropriately operating the switch 28 the "normal" path is reestablished and the powder-air admixture resumes flow from the chamber through the conduit 20 to the source 31 with the latter being augmented by an exhaust pump (not shown) in the line 20.

As was stated earlier the particular use to which the device 11 is applicable is that of electrostatically coating in the single mode of operation. In this mode of operation and variations thereof the fundamental laws of electrostatics apply, namely, like charged bodies repel each and unlike charged bodies attract. Applied first to the coating of a can body this can be interpreted to mean that if charged coating particles are introduced into the inside of the can body at the support S they will be attracted with an appreciable force to an oppositely charged can body. Inasmuch as no particular can body and/or powder charging system forms part of this invention, that for the can body is indicated in FIG. 3 diagrammatically by simply illustrating the support S as part of an electrical system. Insofar as the charging of the powder is concerned, this may be readily effected by a conductor 54 conventionally connected to the element 50 which in turn is preferably insulated by, for example, an insulated spider from the powder nozzle 47. Irrespective of the particular charging system employed the electrostatic forces are desirably sufficiently strong to hold the powder in place against the bare interior surface of the can body in order that the powder will not be displaced during transportation from the coating station to a final fusing station in an oven, an induction heat unit, or the like.

It is further appreciated that all powder directed into the can body by the powder gun 47 will not be attracted to the can body interior by electrostatic forces and the exodus of excess powder therefrom would be costly if simply wasted. Accordingly, the end of the can body most remote from the powder gun 47 is preferably encircled by a hood connected to a vacuum source which is in turn connected to the powder source 31. If as described earlier the conduit 20 includes a vacuum source the conduit may simply be extended and coupled to the hood such that both the chamber 16 and the hood, as well as any can body thereat, are continuously under the effect of the vacuum source to return excess powder to the source 31.

The following are merely typical examples of the type of powders which may be utilized in accordance with the present invention: Type Code Supplier ______________________________________ Epoxy 71 AP 14 Armstrong Products Company, Inc. Epoxy F100C Oxyplast, Ltd. Polyamide Nylon 11 Aquitaine-Organics Polyethylene- Butene SK 4002 Sinclair-Koppers Company Polyethylene SK 7007 Sinclair-Koppers Company ______________________________________

While preferred forms and arrangement of parts have been shown in illustrating the invention, it is to be clearly understood that various changes in details and arrangement of parts may be made without departing from the scope and spirit of this disclosure.

Claims

We claim:

1. A pneumatic flow switching device comprising a generally cylindrical chamber, means delivering a fluidized admixture of powder and air into said chamber, means for exhausting the powder-air admixture from said chamber, first means contiguous said delivering means for pneumatically directing said powder-air admixture from said delivering means toward said exhausting means, and second means for pneumatically traversing said powder-air admixture during its movement between said delivering and exhausting means for directing said powder-air admixture primarily axially from said chamber.

2. The pneumatic flow switching device as defined in claim 1 wherein said first delivering means introduces air into said chamber in a generally tangential direction relative to said cylindrical chamber.

3. The pneumatic flow switching device as defined in claim 1 wherein said exhausting means exhausts the powder-air admixture in a generally tangential direction relative to said cylindrical chamber.

4. The pneumatic flow switching device as defined in claim 1 wherein said delivering means and said exhausting means are separated from each other by at least 90.degree..

5. The pneumatic flow switching device as defined in claim 1 including venturi means into which said axially exhausted powder-air admixture is delivered by said second pneumatic means.

6. The pneumatic flow switching device as defined in claim 1 including means for supporting an article to be coated by the powder of said powder-air admixture adjacent the axial output thereof from said chamber.

7. The pneumatic flow switching device as defined in claim 1 including a source for said powder-air admixture, and means for returning said peripherally exhausted powder-air admixture to said powder-air source.

8. The pneumatic flow switching device as defined in claim 1 including means for supporting an article to be coated by the powder of said powder-air admixture adjacent the axial output thereof from said chamber, and means for charging the powder prior to reaching the article whereby the latter is electrostatically coated.

9. The pneumatic flow switching device as defined in claim 2 wherein said exhausting means exhausts the powder-air admixture in a generally tangential direction relative to said cylindrical chamber.

10. The pneumatic flow switching device as defined in claim 2 wherein said delivering means and said exhausting means are separated from each other by at least 90.degree..

11. The pneumatic flow switching device as defined in claim 2 including venturi means into which said axially exhausted powder-air admixture is delivered by said second pneumatic means.

12. The pneumatic flow switching device as defined in claim 2 including means for supporting an article to be coated by the powder of said powder-air admixture adjacent the axial output thereof from said chamber, and means for charging the powder prior to reaching the article whereby the latter is electrostatically coated.

13. The pneumatic flow switching device as defined in claim 3 wherein said delivering means and said exhausting means are separated from each other by at least 90.degree..

14. The pneumatic flow switching device as defined in claim 3 including venturi means into which said axially exhausted powder-air admixture is delivered by said second pneumatic means.

15. The pneumatic flow switching device as defined in claim 3 including means for supporting an article to be coated by the powder of said powder-air admixture adjacent the axial output thereof from said chamber, and means for charging the powder prior to reaching the article whereby the latter is electrostatically coated.

16. The pneumatic flow switching device as defined in claim 112 including a source of said powder-air admixture, and means for returning said peripherally exhausted powder-air admixture to said powder-air source.

17. The pneumatic flow switching device as defined in claim 12 including a source of said powder-air admixture, and means for returning said peripherally exhausted powder-air admixture to said powder-air source.