US3750949A

US3750949A - Spray gun for pulverulent material entrained in a gaseous stream

Info

Publication number: US3750949A
Application number: US00196381A
Authority: US
Inventors: M Luderer; A Ettenhofer
Original assignee: Atlas Copco AB
Current assignee: Atlas Copco AB
Priority date: 1971-11-08
Filing date: 1971-11-08
Publication date: 1973-08-07
Anticipated expiration: 1990-08-07

Abstract

A spray gun, for spraying pulverulent material, entrained in a pressurized gaseous stream, onto workpieces comprises a number of interchangeable tubular parts whereby it may be lengthened or shortened, and a plastic composition tube may extend through the spray gun body to transport the pulverulent material. The interchangeable parts constitute a tubular gun barrel extending between an inlet and a discharge orifice, and a thin electrically conductive wire extends in the zone of the bore of the gun barrel and is electrically connected to electrodes in the zone of the discharge orifice to connect the electrodes to a source of electric potential. Baffle bodies are interchangeably pluggable into the gun barrel at the discharge orifice, and may be designed as high voltage electrodes.

Description

United States Patent n91 Luderer et al.

[451 Aug. 7, 1973 1 1 SPRAY GUN FOR PULVERULENT MATERIAL ENTRAINED IN A GASEOUS STREAM [73] Assignee: Atlas Copc. Aktiebolag, Nacka,

Sweden [22] Filed: Nov. 8, 1971 [21] App]. No.: 196,381

Related U.S. Application Data [62] Division of Ser. No. 819,229, April 25, 1969,

2,197,392 4/1940 Hawthorn 339/26 R 3,408,985 ll/1968 Sedlacsik, Jr 239/15 X FOREIGN PATENTS OR APPLICATIONS 1,153,868 5/1969 Great Britain 239/15 Primary Examiner-M. Henson Wood, Jr. Assistant Examiner-John J. Love Atz0rneyJohn J. McGlew et al.

[5 7] ABSTRACT A spray gun, for spraying pulverulent material, en trained in a pressurized gaseous stream, onto workpieces comprises a number of interchangeable tubular parts whereby it may be lengthened or shortened, and a plastic composition tube may extend through the spray gun body to transport the pulverulent material. The interchangeable parts constitute a tubular gun barrel extending between an inlet and a discharge orifice, and a thin electrically conductive wire extends in the zone of the bore of the gun barrel and is electrically connected to electrodes in the zone of the discharge orifice to connect the electrodes to a source of electric potential. Baffle bodies are interchangeably pluggable into the gun barrel at the discharge orifice, and may be designed as high voltage electrodes.

16 Claims, 3 Drawing Figures PAIENILU AUG 7 ms SHEET 2 OF 2 SPRAY GUN FOR PULVERULENT MATERIAL ENTRAINED IN A GASEOUS STREAM CROSS REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 819,229, filed Apr. 25, 1969, for PROCESS AND AP- PLIANCE FOR DUSTING OBJECTS WITH POW- DER," and now abandoned.

FIELD OF THE INVENTION This invention relates to the powder coating of workpieces and, more particularly, to a novel and improved spray gun for applying pulverulent material, entrained in a gaseous stream, onto a workpiece to be coated.

BACKGROUND OF THE INVENTION Various appliances, for dusting or coating objects with powder, are already known in the prior art, but have several disadvantages. One disadvantage is that the powder can not be applied evenly to the workpieces to be coated by means of powder spraying guns. Another disadvantage is that the powder tends to settle in the supply hose, connecting a powder input device to the gun. In operation, such settling causes dust clouds of powder to be suddenly ejected from the gun, making even coating of the workpieces illusive. Another difficulty, in practice, is that the objects to be coated are of different shapes and sizes, having cavities or requiring coating of the lateral surfaces. Known guns, for example, have the disadvantage that the powder jet is ejected from the gun like a projectile. Attempts have been made to break up the powder jet and to influence it, in a spraying direction, by arranging, in front of the spray outlet of the powder spraying gun, so-called baffle bodies which, on various powder spraying guns, have been of adjustable design.

SUMMARY OF THE INVENTION An objective of the invention is to provide a spray gun for applying powder, by spraying, into hollow bodies of greater length, with the length of the gun tube of the spray gun being adjustable, as desired, in accordance with the length of the hollow body to be coated. Another objective is to supply the high voltage for the electrostatic field to the front electrodes of the gun head in as reliable a way as possible and with low capacity in relation to the surroundings. Additionally, the invention spray gun is designed to eliminate agglomerations of powder in the .gun barrel at the joints between the assembled gun barrel parts.

In accordance with the invention, a spray gun, for spraying pulverulent material entrained in a gaseous stream onto workpieces, comprises a gun tube, extend: ing between a hand piece and a front end, comprising several parts that may be assembled and disassembled, and the high voltage supply line comprises a thin conductive wire which is arranged in thearea of the-inner bore in such a way that, when assembling the parts, a conductive connection from the high voltage source in the hand piece to theelectrodesat the front end can be made. The wire may be so thin that it canbarely be felt.

Furthermore, the wire may be incorporated into the inner surface or attached thereto, and this can be accomplished either by pressing the wire into the surface, with the application of heat, for example, by the wire being heated by current passage and pressed in, or, alternatively, the wire can also be attached by gluing. In-

stead of the wire, a thin band may be used and this is also glued on by means of epoxy resin, for example. As a further modification, a conductive plastic layer in the form of a narrow-width band or a line may be applied. For this purpose, conductive age-hardenable synthetic varnish can be used, and can be applied as a line inside the parts to be assembled to form the gun tube.

Such an embodiment has a relatively low capacity and, at the same time, such a reliability in transmission that, on the one hand, the high voltage is supplied to the electrodes free of losses and, on the other hand, adequate shock protection is provided.

In another embodiment, the parts can be assembled with relatively long engaging connecting sleeves in such a way that, inside the bored a sleeve, a wire, or a conductive coating, is provided, which is inserted or applied, and which, in the bottom of the recess bore, can be electrically coupled with the wire or corresponding conductive coating of the adjoining part of the gun tube. This embodiment has the great advantage of providing a relatively long creepage distance from the bot tom of the long engaging connecting sleeve to the surface of the gun barrel, and thus eliminates, above all, agglomerations of powder forming at the joints.

In a modification, the creepage distance, in its dimensioning from the point of contact between adjoining part and sleeve, can be designed to be so long that particle agglomerations at the coupling point are eliminated. This length will depend on the insulating material which is used as the gun body, and on the design of the recessed hole. In a further modification, the flange of the sleeve has several grooves which extend or increase the creepage distance.

In another embodiment of the invention, the gun tube, between the hand piece and the front end, comprises several parts capable of being assembled and disassembled relatively to each other, and designed in such a way that an additional continuous insulating plastic hose can be inserted through the parts. A thin conductive wire is incorporated and/or. attached between this hose and the inner wall, with care being taken that the arrangementof the wire complies with the form of the construction. Thus, the wire can barely be felt or can be worked into and onto the inner surface.

The gun can also be designed so that the wire extends loosely throughout the length of the hose. The conductive connection can be worked onto or into the surface of the hose, for example, as a conductive track formed from a conductive plastic material or from metal. Also, in this case, it is possible to applya coat of conductive varnish which is accordingly provided with tenaciously adhering, abrasion-resistant plastic material.

In a furtherembodiment of the invention, the supply hose, extending from the powder feeding appliance, may also be in the form of a hose that can be pulled into the .gun in accordance with the number of parts being assembled. Another supply line, for acceleration air, if

provided, is attached to the supply hose exteriorly of insuch a manner thata screwed-over end cap fixes the hose and, at the same time, connects the wire of the high voltage supply line to the electrodes. This has the great advantage that the hose is sufficiently fixed at the front end and that, at the same time, the high voltage .barrel, and securing means, such as catches or the like,

can be provided in addition.

It is also possible to design the exchangeable bafi'le bodies as high voltage electrodes, with the possibility of conductive electrode parts being attached to a baffle body of plastic material or, alternatively, the baffle bodies themselves are made from metal and serve as electrodes. In another modification, the baffle bodies may carry one or several thin wire electrodes.

A great disadvantage with appliances for feeding power at powder spraying plants is that very high temperature occur, especially at the receiving cone which is attached adjoining the powder storage container, with the result that powder settles at these spots and may even by sintered on in the case of higher heat. However, there is still another disadvantage due to the fact that the power clings to the lines and also to the guide vanes of whirling devices or acceleration bodies and the like so that, in the course of time, the operation of the appliances is jeopardized. The same disadvantage, however, also occurs in the powder supply hose, in which powder deposits at the walls and thus may result in clogging of the powder supply hose.

An object of the invention is to eliminate the existing disadvantages by covering, with plastics, at least the receiving cone in the area of the input device of the powder into the air or gas current. However, the receiving cone can be made entirely of plastic.

In a further development of the invention, all of the powder carrying parts, for example, the supply hose extending from the ejector to the gun, the hopper, and also other parts may be coated with plastics. It is also possible that receiving cones, guide bodies, guide vanes, accleration bodies, impellers, and the like used with the gun be made of plastics or be coated with plastics.

Plastics which may be used for this purpose include polytetrafluoroethylene or plastic materials of the group of the copolymers from tetrafluoroethylene, hexafluoropropylene, or the like. In this connection, it should be emphasized that other plastic materials also can be used, these being plastics generally known as fluorinated and/or siliconated plastic materials. If layers are used, the plastic materials can be sintered on.

Powder spraying plants provided with a spray gun embodying the invention have the great advantage that sticking or sintering on of powder can no longer occur. In this case, even plastic powder can be sprayed, this having a relatively low melting point. Moreover, it is possible to use even plastic or enamel powder, which has a very high specific weight.

For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a side elevation, partly in section, illustrating somewhat diagrammatically a spray gun embodying the invention;

FIG. 2 is an enlarged front end section of a gun, embodying the invention, provided with a through-type plastic hose; and

FIG. 3 is a sectional view illustrating a gun body as provided with a baffle body designed as a high voltage electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a spray gun embodying the invention comprises a hand piece 41, a part 45, a sleeve 46 and a front section 51. It is, of course, also possible to use several intermediate pieces which, in such event, are connected together by means of sleeves.

Hand piece 41 illustrates how the powder-air mixture is supplied through a hose 42. Hose 42 passes through a bore or passage in hand piece 41, and the powder-air mixture arrives at part 45 which is screwed into hand piece 41 through the medium of a thread 44. Adjacent thread 44, there is a guide piece 69 which rests against a coupling ring 55 which is electrically conductive. The high voltage line 43 is connected to coupling ring 55 so that, upon screwing of part 45, electrical connection is made with a thin wire 54 extending along the inner bore of part 45. In this manner, the high voltage is applied to a coupling ring 56 which is accommodated in the bore of part 45 at the opposite end of this part.

The high voltage is transmitted, through coupling ring 56, to a wire 53 extending in the bore of sleeve 46, and which transmits or conducts the high voltage to a coupling ring 57 at the opposite end of sleeve 46. Coupling ring 57 is arranged to engage a wire 52 extending through the bore of front section 51, to supply the high voltage to this wire. At the front end of front section 51, the high voltage is applied to the electrodes 58 through the wire 52. It will be noted that connecting sleeve 46 has two threaded

couplings

47 and 48, which continue as

guide extensions

49 and 50 engaging the respective coupling rings 56 and 57.

It will be noted that, between coupling ring 57, for example, and the interface 68, there exists a relatively long creepage distance, which prevents build-up of a pontential at coupling ring 57 or at coupling ring 56, and which might result in powder accumulation.

At the front end, baffle body 60 is attached to front section 51 on supports 59, support 59, or baffle body 60, or both, may be designed as electrodes. In FIG. 1, the part 45 is represented cut at 61 in order to illustrate the entire length of the gun.

FIG. 2 illustrates another embodiment of the invention, in which only the front body 62 is shown, in section, and is represented as cut off, as at 67. From FIG. 2, it will be observed that a plastic hose 63, without any joints, extends through front body 62 and has, at the front portion, a widened end 64 which, for example, can be clamped in position by an end cap 65. Plastic hose 63 extends through all the other parts which are included between from body 62 and hand piece 41, and may be constituted by the supply hose for the powderair mixture.

In addition, wire 66 extends through all the parts which are threaded together, as far as the hand piece. The wire is positioned between plastic hose 63 and the internal surface of the front body 62, in the bore therethrough. At its front end, wire 66 is electrically connected with an electrode 58.

The embodiment of the invention shown in FIG. 2 has the great advantage that a spray gun, for powder spraying, can be set up in any length desired. Moreover, there is a great advantage that the thin wire provides a low capacity conductor for the high voltage to the electrode. Another advantage is that the gun also can be used as a short gun by simply screwing front section 62 to hand piece 41. It is also possible, of course, to provide expanding parts which may serve for guiding the gun tube into a larger hole for spraying the surface of the hole with powder.

The spray gun embodying the invention and incorporating the unit construction is completely adaptable to various holes of pipes, it being also possible to use a flexible front section which can pass through pipe bends. In such a case, a guide piece can be used and is, for example, attached to the pipe body.

In the further embodiment of the invention shown in FIG. 3, the gun barrel comprises a basic part 51 into which a connecting sleeve 52' can be threaded, and front section 53 can be threaded onto sleeve 52'. This provides a gun barrel which can be used for applying powder inside pipes or hollow spaces. The sleeve extensions 56' and 57' of sleeve 52' are relatively long to provide, toward the exterior, a long creeping interface for high voltage.

A plastic hose 58' is threaded in the interior, and ei ther may be electrically conductive or may contain a current conductor. The plastic hose extends through the entire gun barrel and terminates at the front in the receiving sleeve 59 which is held in position by a clamping collar 60'. The individual parts are connected to each other by coupling rings 54' and 55', which also may serve for transmitting the high voltage.

At the front section, a baffle body 49', on supports 48', can be inserted, and is connected to the high voltage through ring 60. At its front end, baffle body 49- can carry point electrodes 50' which are also connected to the high voltage.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be un' derstood that theinvention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A spray gun, for spraying pulverulent material, entrained in a gaseous stream, onto the surfaces of work pieces with the application of a high voltage elactrostatic field between an electrode and a workpiece, comprising, in combination, a feed line, for the gaseous stream carrying the pulverulent material, having an outlet; means forming a discharge orifice; a rigid tubular gun barrel of insulating material extending between an inlet, communicating with said outlet, and said discharge orifice; the pulverulent material, during passage thrugh said gun barrel, being electrostatically charged by friction with said gun barrel; said gun barrel comprising plural disengageably interconnected compo nents, a thin electrically conductive wire extending in the zone of the boreof said gun barrel; an insulated conductor connected to a source of high voltage electric potential, connected to said wire at said inlet; and electrodes in the zone of said discharge orifice electrivoltage electric potential through said insulated conductor.

2. A spray gun, as claimed in claim 1, in which said wire has a diameter so small that the wire can barely be gripped.

3. A spray gun, as claimed in claim 1, in which said wire is combined with the internal surface of said gun barrel.

4. A spray gun, as claimed in claim 1, in which said components include at least one relatively elongated connection sleeve having a portion of said wire extending throughout the length of its bore; each sleeve having ends seating in axially elongated bore recesses in adjacent components; and means in said bore recesses electrically interconnecting the wire portions in adjacent components.

5. A spray gun, as claimed in claim 4, in which the zone of contact between each sleeve and the adjacent components is so dimensioned, as to creep distance, that pulverulent material agglomerations at the junction points of adjacent components are avoided.

6. A spray gun, as claimed in claim 1, including a continuous insulating conduit, of plastic composition material, inserted in said gun barrel; said wire being in contact with said conduit.

7. A spray gun, as claimed in claim 6, in which said wire extends loosely through said conduit.

8. A spray gun, as claimed in claim 6, in which said conduit has a strip of electrically'conductive material extending longitudinally of a surface thereof and constituting said wire.

9. spray gun, as claimed in claim 6 in which the length of said conduit disposed in said gun barrel can be adjusted, by pulling said conduit into or out of said gun barrel, in accordance with the number of saidcomponents dis'engageably assembled to form said gun barrel.

10. A spray gun, as claimed in claim 6, including baffle bodies interchangeably pluggable into the wall of the gun barrel component at said discharge orifice.

11. A spray gun, as claimed in claim 10, in which said baffle bodies are designed as high voltage electrodes.

12. A spray gun, as claimed in claim 10, in which said baffle bodies carry said electrodes.

13. A spray gun, as claimed in claim 8, including a powder comprise plastic composition materials of the cally connected to said wire, said wire serving for connection of only said electrodes to said source of high group consisting of polytetrafluoroethylenes.

15. A spray gun, as claimed in claim 1, in which at least a part of those walls which come in contact with powder compriseplastic composition materials of the group consisting of copolymers of 'tetrafluoroethylene, hexafluoropropylene, and the like.

16. A spray gun, for spraying pulverulentmaterial, entrained in a gaseous stream, onto the surfaces of workpieces with the application of an electrostatic field between an electrode and a workpiece, comprising, in combination, a feed line, for the gaseous stream carrying the pulverulent material, having an outlet; means forming a discharge orifice; a tubular gun barrel extending between an inlet, communicating with said outlet, and said discharge orifice; said gun barrel comprising plural disengageably interconnected components; a

conduit, the end of said conduit adjacent said discharge orifice being flared out over the end of a gun barrel component; and an end cap threaded onto said lastnamed gun barrel component to secure said conduit in position and establishing connection between said wire and said electrodes;

Claims

1. A spray gun, for spraying pulverulent material, entrained in a gaseous stream, onto the surfaces of workpieces with the application of a high voltage elactrostatic field between an electrode and a workpiece, comprising, in combination, a feed line, for the gaseous stream carrying the pulverulent material, having an outlet; means forming a discharge orifice; a rigid tubular gun barrel of insulating material extending between an inlet, communicating with said outlet, and said discharge orifice; the pulverulent material, during passage thrugh said gun barrel, being electrostatically charged by friction with said gun barrel; said gun barrel comprising plural disengageably interconnected components, a thin electrically conductive wire extending in the zone of the bore of said gun barrel; an insulated conductor connected to a source of high voltage electric potential, connected to said wire at said inlet; and electrodes in the zone of said discharge orifice electrically connected to said wire, said wire serving for connection of only said electrodes to said source of high voltage electric potential through said insulated conductor.

8. A spray gun, as claimed in claim 6, in which said conduit has a strip of electrically conductive material extending longitudinally of a surface thereof and constituting said wire.

9. A spray gun, as claimed in claim 6, in which the length of said conduit disposed in said gun barrel can be adjusted, by pUlling said conduit into or out of said gun barrel, in accordance with the number of said components disengageably assembled to form said gun barrel.

13. A spray gun, as claimed in claim 8, including a baffle body supported on the gun barrel component adjacent said discharge orifice, and serving as a high voltage electrode.

14. A spray gun, as claimed in claim 1, in which at least a part of those walls which come in contact with powder comprise plastic composition materials of the group consisting of polytetrafluoroethylenes.

15. A spray gun, as claimed in claim 1, in which at least a part of those walls which come in contact with powder comprise plastic composition materials of the group consisting of copolymers of tetrafluoroethylene, hexafluoropropylene, and the like.

16. A spray gun, for spraying pulverulent material, entrained in a gaseous stream, onto the surfaces of workpieces with the application of an electrostatic field between an electrode and a workpiece, comprising, in combination, a feed line, for the gaseous stream carrying the pulverulent material, having an outlet; means forming a discharge orifice; a tubular gun barrel extending between an inlet, communicating with said outlet, and said discharge orifice; said gun barrel comprising plural disengageably interconnected components; a thin electrically conductive wire extending in the zone of the bore of said gun barrel; electrodes in the zone of said discharge orifice electrically connected to said wire, said wire serving for connection of said electrodes to a source of electric potential; a continuous insulating conduit, of plastic composition material, inserted in said gun barrel; said wire being in contact with said conduit, the end of said conduit adjacent said discharge orifice being flared out over the end of a gun barrel component; and an end cap threaded onto said last-named gun barrel component to secure said conduit in position and establishing connection between said wire and said electrodes.