EP0236795B1 - Electrostatic spray device for coating powder - Google Patents

Electrostatic spray device for coating powder Download PDF

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Publication number
EP0236795B1
EP0236795B1 EP87102179A EP87102179A EP0236795B1 EP 0236795 B1 EP0236795 B1 EP 0236795B1 EP 87102179 A EP87102179 A EP 87102179A EP 87102179 A EP87102179 A EP 87102179A EP 0236795 B1 EP0236795 B1 EP 0236795B1
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EP
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Prior art keywords
spray
powder
aperture
gas
electrode
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EP87102179A
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German (de)
French (fr)
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EP0236795A2 (en
EP0236795A3 (en
Inventor
Karl Buschor
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Gema Switzerland GmbH
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Gema Switzerland GmbH
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Priority to AT87102179T priority Critical patent/ATE55283T1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
    • B05B5/025—Discharge apparatus, e.g. electrostatic spray guns
    • B05B5/03—Discharge apparatus, e.g. electrostatic spray guns characterised by the use of gas, e.g. electrostatically assisted pneumatic spraying
    • B05B5/032—Discharge apparatus, e.g. electrostatic spray guns characterised by the use of gas, e.g. electrostatically assisted pneumatic spraying for spraying particulate materials

Definitions

  • the invention relates to an electrostatic spray device for coating powder, with a powder channel, the downstream end of which has a spray opening for spraying the coating powder, with at least one gas channel which has at least one gas outlet opening which is arranged essentially in the radial center of the powder channel upstream of its spray opening and axially opens towards this spray opening, with at least one electrode around which the gas of the gas channel flows, which is located in the gas outlet opening and whose downstream electrode end terminates approximately at the downstream opening end of the gas outlet opening.
  • Such an electrostatic spray device is known from US Pat. No. 4,289,278.
  • a gas stream flows around the electrode in the powder channel so that no powder particles are to be deposited on it. It does not matter whether the electrode is located in a gas channel or is in the powder flow and the gas flow is supplied with a gas flow that keeps the electrode clear.
  • the electrode is located relatively far upstream of a spray opening for the coating powder, so that the flow situation there has no influence on the effect of the electrode.
  • the electrode is located in the center of a spray opening that widens in the direction of flow.
  • the powder channel has a section with a reduced cross section, to the downstream end of which the spray opening is connected.
  • a carrier extends axially through the powder channel and through the spray opening, which axially carries an electrode at its front end outside the spray opening.
  • a gas channel leading axially through the carrier opens into the spray opening into an annular nozzle formed in the carrier, which nozzle radially outwards against the Wall of the spray opening is directed, which is widened like a funnel in the flow direction.
  • the powder is atomized by the radial radial gas flow coming into contact with the cross-sectionally circular powder channel flow in the spray nozzle.
  • electrostatic spray devices show DE-OS 16 52 421, 23 12 363, 27 20 458 and 33 10 983, CH-PS 609 585.
  • DE-PS 25 39 627 corresponds essentially to the US -PS 3 940 061 and shows an air-flushed electrode in the center of a spray opening of an electrostatic spray device.
  • the object of the invention is to improve the coating quality and the economy of the coating method of such a spray device. Powder losses on the way from the spraying device to the object to be coated should be reduced. Furthermore, the spray device is said to be able to apply a thicker layer of powder to the object to be coated with good coating quality.
  • the powder channel has a funnel-like channel section which narrows approximately from the gas outlet opening to the spray opening and forms a stowage area which compresses the coating powder and into which the gas outlet opening opens, such that the radial center of the spray opening is in place of the smallest diameter of this channel section is located opposite the gas outlet opening.
  • the powder is compressed in the flow congestion area of the powder channel. Since the electrode does not protrude or only slightly protrudes beyond the end of the gas line and is also flushed with gas flowing out of the gas line, no powder particles can adhere to the electrode.
  • the electrical field lines emanating from the electrode run along ideal trajectories of the powder particles from the electrode to the object to be coated without electrical scattering field lines. Avoiding stray field lines, e.g. in the powder channel opposite to the powder flow direction, with the same electrical energy, leads to a stronger charge of the powder particles, which adhere better to the object to be coated.
  • the gas transfers the electrical charge of the electrode into the compacted powder.
  • the spray opening has the shape of a slot.
  • a flat spray jet has the advantage over a round spray jet that it penetrates better into recesses, openings, cavities and niches of the object to be coated, and thereby better coats the inner surfaces thereof. With a circular cross-section the spray jet creates a strong so-called Faraday cage, i.e. a shielding electrical field, which prevents the electrical field lines of the electrode from penetrating into the recesses or recesses. The effect of Faraday's cage is not as disadvantageous with a flat spray as with a round spray.
  • the electrostatic spraying device according to the invention shown in FIG. 1 has a tubular base body 2, which consists of three individual parts 4, 6 and 8 arranged coaxially one inside the other.
  • a mouthpiece 12 is placed on the downstream end section 10 of the base body 2.
  • a powder channel 14 extends axially through the innermost part 8 of the base body 2 and the mouthpiece 12.
  • this has a funnel-shaped channel section 16 which becomes smaller in diameter in the direction of flow and which is provided centrally with a spray opening 18 for spraying the pneumatically conveyed powder. Due to the funnel-shaped narrowing, the channel section 16 forms a flow stagnation area in which the powder builds up and a higher powder concentration arises.
  • the powder channel 14 there is a device 22 in the channel axis 20 which forms a gas channel 24 which extends along the channel axis 20 and in which also houses an electrical electrode 26 along the channel axis 20 at a distance from the channel wall of the gas channel 24.
  • the electrode 26 is connected in a known manner to an electrical high-voltage source (not shown) and serves to electrostatically charge the coating powder.
  • the high-voltage source can be arranged in a known manner in the base body 2 or externally.
  • the gas is injected through an outlet opening 30 of the gas channel 24, which lies axially opposite the spray opening 18, into the funnel-shaped channel section 16, which forms the flow stagnation area.
  • the end 32 of the electrode 26 and the downstream end 34 of the outlet opening 30 lie approximately in a same cross-sectional plane 36, which is at a distance upstream of the narrowest point 38 of the funnel-shaped channel section 16.
  • the cross-sectional plane 36 is only a short distance in the preferred embodiment of approximately 0.5 to 1.5 mm downstream of the upstream beginning 40 of the funnel-shaped channel section 16.
  • the end 32 of the electrode 26 is also in the cross-sectional plane 36 and should, in a modified embodiment , do not protrude more than 1 mm beyond the gas channel 24, since otherwise the desired electrostatic charging of the powder will deteriorate.
  • cross-sectional plane 36 and thus the ends 32 and 34 of a further cross-sectional plane 42, in which the downstream end 44 of the spray opening 18 is located lies in the range between 3 mm and 5 mm.
  • the distance is preferably approximately 4 mm according to FIG. 1, in which the spray device is shown on a 2: 1 scale.
  • An electrical resistor 46 is accommodated in the gas channel 24, which runs axially to the powder channel axis 20, and is located in an electrical line 48 connecting the high-voltage source to the electrode 26.
  • the electrical resistor 46 serves to prevent electrical flashovers from the electrode 26 to other objects. This is better prevented the closer the resistor 46 is arranged to the electrode 26.
  • the funnel-shaped channel section 16 is conical and its inner channel wall 54 narrows at a cone angle a of 120 °.
  • the cone angle can be in the range between 100 ° and 140 °.
  • the outer end face 52 of the mouthpiece 12 runs parallel and thus at the same angle as the inner channel wall 54.
  • the spray opening 18 is in the form of a slot which extends symmetrically over the central axis 20 of the powder channel 14, the slot with both slot ends 57 extending upstream behind the cross-sectional plane 36, preferably up to a distance 56 of approximately 8 mm from the cone tip 58 of the end face 52 of the mouthpiece 12.
  • the distance 56 should be in the range between 5 mm and 10 mm. However, the preferred distance is 8 mm.
  • Upstream of section 60 is an annular channel section 64 of powder channel 14, which has an increasingly larger opening cross section in the direction of flow up to a largest opening cross section at the beginning of the following section 60.
  • the annular section 64 is defined by the cylindrical wall 62 and the the length of this section 64 is formed as a truncated cone-shaped outer surface 66 of the device 22.
  • the powder channel 14 Upstream of the device 22, the powder channel 14 has a hollow cylindrical section 72.
  • the flow velocity of the powder is accelerated when it flows from the section 72 into the section 68, since the device 22 reduces the opening cross section of the powder channel 14.
  • the opening cross section increases again, so that the flow velocity of the powder particles slows down and the powder distribution is made more uniform.
  • the flow is calmed, and then the powder is compressed in the funnel-shaped channel section 16.
  • the gas of the gas channel 24 injects electrical charge particles from the electrode 26 onto the powder particles in the channel section 16.
  • the slot 2 shows the slit-shaped shape of the spray opening 18 from the front.
  • the ratio of the length to the width of the slit 18 must not be too large.
  • the slot preferably has the dimensions shown in FIGS. 1 and 2.
  • the invention achieves a particularly strong improvement in the electrostatic charging of the powder, the economy and the coating quality, in particular in a spray device in which the spray opening is in the form of a slot, with layers of greater thickness on the object to be coated in a single spraying process can be generated. It is particularly important that the electrode does not protrude substantially from the gas channel and that the distance 41 is approximately 4 mm.

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  • Electrostatic Spraying Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Manufacturing Of Micro-Capsules (AREA)
  • Paints Or Removers (AREA)

Abstract

An electrostatic spray device for coating powder has a powder channel, the downstream end of which has a spray opening for the spraying of the coating powder. At least one gas channel with at least one gas outlet opening is arranged substantially in the radial center of the powder channel upstream of its spray opening, the gas outlet discharging axially in the direction toward the spray opening. At least one electrode, around which gas from the gas channel flows, is located in the gas outlet opening, the downstream electrode end of the electrode terminating substantially at the downstream end thereof. Within the powder channel, directly in front of its spray opening, a funnel-shaped powder channel section is provided for compacting the powder concentration. The gas stream injects electric charges into this section, which the stream of gas has taken up from the electrode. The spray opening preferably has the shape of a slot.

Description

Die Erfindung betrifft eine elektrostatische Sprüheinrichtung für Beschichtungspulver, mit einem Pulverkanal, dessen stromabwärtiges Ende eine Sprühöffnung zum Versprühen des Beschichtungspulvers aufweist, mit mindestens einem Gaskanal, der mindestens eine Gasauslaßöffnung aufweist, die im wesentlichen im radialen Zentrum des Pulverkanals stromaufwärts von dessen Sprühöffnung angeordnet ist und in Richtung zu dieser Sprühöffnung hin axial ausmündet, mit mindestens einer vom Gas des Gaskanals umströmten Elektrode, die sich in der Gasauslaßöffnung befindet und deren stromabwärtiges Elektrodenende ungefähr am stromabwärtigen Öffnungsende der Gasauslaßöffnung endet.The invention relates to an electrostatic spray device for coating powder, with a powder channel, the downstream end of which has a spray opening for spraying the coating powder, with at least one gas channel which has at least one gas outlet opening which is arranged essentially in the radial center of the powder channel upstream of its spray opening and axially opens towards this spray opening, with at least one electrode around which the gas of the gas channel flows, which is located in the gas outlet opening and whose downstream electrode end terminates approximately at the downstream opening end of the gas outlet opening.

Eine solche elektrostatische Sprüheinrichtung ist aus der US-PS-4 289 278 bekannt. Bei der bekannten Sprüheinrichtung wird die Elektrode im Pulverkanal von einem Gasstrom umspült, damit sich an ihr keine Pulverpartikel ablagern sollen. Dabei spielt es keine Rolle, ob sich die Elektrode innerhalb eines Gaskanals befindet oder im Pulverstrom liegt und dem Pulverstrom ein die Elektrode freihaltender Gasstrom zugeführt wird. Die Elektrode befindet sich beim Stand der Technik relativ weit stromaufwärts einer Sprühöffnung für das Beschichtungspulver, so daß die dortige Strömungssituation keinen Einfluß auf die Wirkung der Elektrode hat. In anderer Ausführung befindet sich die Elektrode im Zentrum einer sich in Strömungsrichtung erweiternden Sprühöffnung.Such an electrostatic spray device is known from US Pat. No. 4,289,278. In the known spray device, a gas stream flows around the electrode in the powder channel so that no powder particles are to be deposited on it. It does not matter whether the electrode is located in a gas channel or is in the powder flow and the gas flow is supplied with a gas flow that keeps the electrode clear. In the prior art, the electrode is located relatively far upstream of a spray opening for the coating powder, so that the flow situation there has no influence on the effect of the electrode. In another embodiment, the electrode is located in the center of a spray opening that widens in the direction of flow.

Bei einer anderen, aus der US-PS-4 380 320 bekannten elektrostatischen Sprüheinrichtung weist der Pulverkanal einen im Querschnitt reduzierten Abschnitt auf, an dessen stromabwärtigem Ende sich die Sprühöffnung anschließt. Durch den Pulverkanal erstreckt sich axial ein Träger bis durch die Sprühöffnung hindurch, welcher an seinem stirnseitigen Ende außerhalb der Sprühöffnung axial eine Elektrode trägt Ein durch den Träger axial hindurchführender Gaskanal mündet in der Sprühöffnung in eine im Träger gebildeten Ringdüse, welche radial nach außen gegen die Wand der Sprühöffnung gerichtet ist, welche in Strömungsrichtung trichterartig erweitert ist. Die Zerstäubung des Pulvers erfolgt durch Aufeinandertreffen des sternförmig radialen Gasstromes auf den im Querschnitt ringförmigen Pulverkanalstrom in der Sprühdüse.In another electrostatic spray device known from US Pat. No. 4,380,320, the powder channel has a section with a reduced cross section, to the downstream end of which the spray opening is connected. A carrier extends axially through the powder channel and through the spray opening, which axially carries an electrode at its front end outside the spray opening. A gas channel leading axially through the carrier opens into the spray opening into an annular nozzle formed in the carrier, which nozzle radially outwards against the Wall of the spray opening is directed, which is widened like a funnel in the flow direction. The powder is atomized by the radial radial gas flow coming into contact with the cross-sectionally circular powder channel flow in the spray nozzle.

Ebenfalls elektrostatische Sprüheinrichtungen, jedoch ohne die Merkmale vorliegender Erfindung, zeigen die DE-OS 16 52 421, 23 12 363, 27 20 458 und 33 10 983, CH-PS 609 585. Die DE-PS 25 39 627 entspricht im wesentlichen der US-PS 3 940 061 und zeigt eine mit Luft umspülte Elektrode im Zentrum einer Sprühöffnung einer elektrostatischen Sprüheinrichtung.Also electrostatic spray devices, but without the features of the present invention, show DE-OS 16 52 421, 23 12 363, 27 20 458 and 33 10 983, CH-PS 609 585. DE-PS 25 39 627 corresponds essentially to the US -PS 3 940 061 and shows an air-flushed electrode in the center of a spray opening of an electrostatic spray device.

Durch die Erfindung soll die Aufgabe gelöst werden, die Beschichtungsqualität und die Wirtschaftlichkeit des Beschichtungsverfahrens einer solchen Sprüheinrichtung zu verbessern. Dabei sollen Pulververluste auf dem Weg von der Sprüheinrichtung zu dem zu beschichtenden Gegenstand verringert werden. Ferner soll mit der Sprüheinrichtung eine dickere Schicht Pulver auf den zu beschichtenden Gegenstand mit guter Beschichtungsqualität aufgebracht werden können.The object of the invention is to improve the coating quality and the economy of the coating method of such a spray device. Powder losses on the way from the spraying device to the object to be coated should be reduced. Furthermore, the spray device is said to be able to apply a thicker layer of powder to the object to be coated with good coating quality.

Diese Aufgabe wird gemäß der Erfindung dadurch gelöst, daß der Pulverkanal einen ungefähr von der Gasauslaßöffnung bis zur Sprühöffnung trichterartig enger werdenden Kanalabschnitt aufweist, welcher einen das Beschichtungspulver verdichtenden Staubereich bildet, in welchen die Gasauslaßöffnung mündet, daß das radiale Zentrum der Sprühöffnung sich an der Stelle des kleinsten Durchmessers dieses Kanalabschnittes gegenüber der Gasauslaßöffnung befindet.This object is achieved according to the invention in that the powder channel has a funnel-like channel section which narrows approximately from the gas outlet opening to the spray opening and forms a stowage area which compresses the coating powder and into which the gas outlet opening opens, such that the radial center of the spray opening is in place of the smallest diameter of this channel section is located opposite the gas outlet opening.

Dadurch werden folgende Vorteile erreicht: Im Strömungsstaubereich des Pulverkanals wird das Pulver verdichtet. Da die Elektrode nicht oder nur geringfügig über das Ende der Gasleitung hinaussteht und außerdem von Gas, welches aus der Gasleitung ausströmt, umspült wird, können sich keine Pulverteilchen an der Elektrode festsetzen. Die von der Elektrode ausgehenden elektrischen Feldlinien verlaufen längs von idealen Flugbahnen der Pulverteilchen von der Elektrode zu dem zu beschichtenden Gegenstand ohne elektrische Streu-Feldlinien. Die Vermeidung von Streu-Feldlinien, z.B. im Pulverkanal entgegen der Pulver-Strömungsrichtung, führt bei gleicher elektrischer Energie zu einer stärkeren Aufladung der Pulverpartikel, die besser auf dem zu beschichtenden Gegenstand haften. Das Gas überträgt die elektrische Ladung der Elektrode in das verdichtete Pulver. Durch die gleichzeitige Wirkung von Verdichtung des Pulvers und Hineinpressen oder Injektion der Ladungsteilchen der Elektrode mit Hilfe des Gases in das verdichtete Pulver ergibt sich ebenfalls eine verstärkte elektrostatische Aufladung der Pulverteilchen. Diese Wirkungen verringern Verluste an versprühtem Pulver, erzeugen bessere Beschichtungsqualitäten, ermöglichen dickere Pulverschichten auf dem zu beschichtenden Gegenstand pro Sprühvorgang, und können zur Energieeinsparung benutzt werden. Am Ende der Elektrode, also an der Elektrodenspitze, findet eine Koronaentladung statt, durch welche sich das Elektrodenende erwärmen kann. Aber auch bei Erwärmung können keine Pulverteilchen an der Elektrode kleben, weil sie vom Gasstrom von der Elektrode abgehalten werden und weil das Elektrodenende nur unbedeutend, vorzugsweise überhaupt nicht aus der Auslaßöffnung des Gaskanals hinausragt.This achieves the following advantages: The powder is compressed in the flow congestion area of the powder channel. Since the electrode does not protrude or only slightly protrudes beyond the end of the gas line and is also flushed with gas flowing out of the gas line, no powder particles can adhere to the electrode. The electrical field lines emanating from the electrode run along ideal trajectories of the powder particles from the electrode to the object to be coated without electrical scattering field lines. Avoiding stray field lines, e.g. in the powder channel opposite to the powder flow direction, with the same electrical energy, leads to a stronger charge of the powder particles, which adhere better to the object to be coated. The gas transfers the electrical charge of the electrode into the compacted powder. The simultaneous effect of compacting the powder and pressing it in or injecting the charged particles of the electrode with the aid of the gas into the compacted powder likewise results in an increased electrostatic charging of the powder particles. These effects reduce loss of sprayed powder, produce better coating qualities, enable thicker layers of powder on the object to be coated per spraying process, and can be used to save energy. At the end of the electrode, i.e. at the tip of the electrode, there is a corona discharge, through which the end of the electrode can heat up. But even when heated, no powder particles can stick to the electrode because they are kept away from the electrode by the gas flow and because the electrode end protrudes only insignificantly, preferably not at all, from the outlet opening of the gas channel.

Bei einer besonders bevorzugten Ausführungsform der Erfindung hat die Sprühöffnung die Form eines Schlitzes. Dadurch wird beim Versprühen des Pulvers ein flacher Sprühstrahl erzeugt. Ein flacher Sprühstrahl hat gegenüber einem runden Sprühstrahl den Vorteil, daß er besser in Vertiefungen, Öffnungen, Hohlräume und Nischen des zu beschichtenden Gegenstandes eindringt, und dadurch deren Innenflächen besser beschichtet. Bei einem im Querschnitt kreisrunden Sprühstrahl entsteht ein starker sogenannter Faradayscher Käfig, also ein abschirmendes elektrisches Feld, welches das Eindringen der elektrischen Feldlinien der Elektrode in die Vertiefungen oder Ausnehmungen verhindert. Die Wirkung des Faradayschen Käfigs tritt bei einem flachen Strahl nicht in so nachteiliger Weise ein wie bei einem runden Sprühstrahl.In a particularly preferred embodiment of the invention, the spray opening has the shape of a slot. This creates a flat spray when the powder is sprayed. A flat spray jet has the advantage over a round spray jet that it penetrates better into recesses, openings, cavities and niches of the object to be coated, and thereby better coats the inner surfaces thereof. With a circular cross-section the spray jet creates a strong so-called Faraday cage, i.e. a shielding electrical field, which prevents the electrical field lines of the electrode from penetrating into the recesses or recesses. The effect of Faraday's cage is not as disadvantageous with a flat spray as with a round spray.

Weit Merkmale der Erfindung sind in der nachfolgenden Beschreibung und insobesondere in Unteransprüchen enthalten.Wide features of the invention are contained in the following description and in particular in subclaims.

Die Erfindung wird im folgenden anhand einer Ausführungsform als Beispiel beschrieben, die in den Zeichnungen dargestellt ist. Im einzelnen zeigen.

  • Fig. 1 einen Längsschnitt einer elektrostatischen Sprüheinrichtung nach der Erfindung, im Maßstab 2:1, wobei der stromaufwärtige Einrichtungsteil weggelassen wurde, zur Zerstäubung ohne Prallplatte,
  • Fig. 2 eine Vorderansicht der Sprüheinrichtung von Fig. 1, im Maßstab 1:1.
The invention is described below using an embodiment as an example, which is illustrated in the drawings. Show in detail.
  • 1 shows a longitudinal section of an electrostatic spray device according to the invention, on a scale of 2: 1, with the upstream device part being omitted, for atomization without a baffle plate,
  • Fig. 2 is a front view of the spray device of Fig. 1, on a scale of 1: 1.

Die in Fig. 1 dargestellte elektrostatische Sprüheinrichtung nach der Erfindung hat einen rohrartigen Grundkörper 2, welcher aus drei koaxial ineinander angeordneten Einzelteilen 4, 6 und 8 besteht. Auf den stromabwärtigen Endabschnitt 10 des Grundkörpers 2 ist ein Mundstück 12 aufgesetzt. Durch den innersten Teil 8 des Grundkörpers 2 und das Mundstück 12 erstreckt sich axial ein Pulverkanal 14. Dieser hat im Mundstück 12 einen in Strömungsrichtung im Durchmesser kleiner werdenden trichterförmigen Kanalabschnitt 16, welcher zentrisch mit einer Sprühöffnung 18 zum Versprühen des pneumatisch geförderten Pulvers versehen ist. Durch die trichterförmige Verengung bildet der Kanalabschnitt 16 einen Strömungsstaubereich, in welchem sich das Pulver staut und eine höhere Pulverkonzentration entstehtlm Pulverkanal 14 befindet sich in der Kanalachse 20 eine Einrichtung 22, welche einen Gaskanal 24 bildet, der sich längs zur Kanalachse 20 erstreckt, und in welchem ebenfalls längs zur Kanalachse 20 eine elektrische Elektrode 26, mit Abstand zur Kanalwand des Gaskanals 24, untergebracht ist. Die Elektrode 26 ist in bekannter Weise an eine elektrische Hochspannungsquelle (nicht dargestellt) angeschlossen und dient zur elektrostatischen Aufladung des Beschichtungspulvers. Die Hochspannungsquelle kann in bekannter Weise im Grundkörper 2 oder extern angeordnet sein. Die Elektrode 26 wird vom Gas des Gaskanals 24, welches von einem Anschluß 28 zugeführt wird, in Längsrichtung umströmt. Das Gas wird durch eine Auslaßöffnung 30 des Gaskanals 24, welche der Sprühöffnung 18 axial gegenüberliegt, in den trichterförmigen Kanalabschnitt 16 injiziert, welcher den Strömungsstaubereich bildet. Das Ende 32 der Elektrode 26 und das stromabwärtige Ende 34 der Auslaßöffnung 30 liegen ungefähr in einer gleichen Querschnittsebene 36, die sich mit Abstand stromaufwärts der engsten Stelle 38 des trichterförmigen Kanalabschnittes 16 befindet. Die Querschnittsebene 36 liegt bei der bevorzugten Ausführungsform nur ein kurzes Stück von ungefähr 0,5 bis 1,5 mm stromabwärts des stromaufwärtigen Anfangs 40 des trichterförmigen Kanalabschnitts 16. Das Ende 32 der Elektrode 26 liegt ebenfalls in der Querschnittsebene 36 und sollte, in abgewandelter Ausführungsform, nicht mehr als 1 mm über den Gaskanal 24 hinausragen, da sonst die angestrebte elektrostatische Aufladung des Pulvers verschlechtert wird. Wichtig ist außerdem, daß die Querschnittsebene 36 und damit die Enden 32 und 34 von einer weiteren Querschnittsebene 42, in welcher sich das stromabwärtige Ende 44 der Sprühöffnung 18 befindet, in dem Bereich zwischen 3 mm und 5 mm liegt. Vorzugsweise beträgt der Abstand ungefähr 4 mm entsprechend Fig. 1, in welcher die Sprüheinrichtung im Maßstab 2:1 dargestellt ist.The electrostatic spraying device according to the invention shown in FIG. 1 has a tubular base body 2, which consists of three individual parts 4, 6 and 8 arranged coaxially one inside the other. A mouthpiece 12 is placed on the downstream end section 10 of the base body 2. A powder channel 14 extends axially through the innermost part 8 of the base body 2 and the mouthpiece 12. In the mouthpiece 12, this has a funnel-shaped channel section 16 which becomes smaller in diameter in the direction of flow and which is provided centrally with a spray opening 18 for spraying the pneumatically conveyed powder. Due to the funnel-shaped narrowing, the channel section 16 forms a flow stagnation area in which the powder builds up and a higher powder concentration arises. In the powder channel 14 there is a device 22 in the channel axis 20 which forms a gas channel 24 which extends along the channel axis 20 and in which also houses an electrical electrode 26 along the channel axis 20 at a distance from the channel wall of the gas channel 24. The electrode 26 is connected in a known manner to an electrical high-voltage source (not shown) and serves to electrostatically charge the coating powder. The high-voltage source can be arranged in a known manner in the base body 2 or externally. The gas 26 of the gas channel 24, which is supplied from a connection 28, flows around the electrode 26 in the longitudinal direction. The gas is injected through an outlet opening 30 of the gas channel 24, which lies axially opposite the spray opening 18, into the funnel-shaped channel section 16, which forms the flow stagnation area. The end 32 of the electrode 26 and the downstream end 34 of the outlet opening 30 lie approximately in a same cross-sectional plane 36, which is at a distance upstream of the narrowest point 38 of the funnel-shaped channel section 16. The cross-sectional plane 36 is only a short distance in the preferred embodiment of approximately 0.5 to 1.5 mm downstream of the upstream beginning 40 of the funnel-shaped channel section 16. The end 32 of the electrode 26 is also in the cross-sectional plane 36 and should, in a modified embodiment , do not protrude more than 1 mm beyond the gas channel 24, since otherwise the desired electrostatic charging of the powder will deteriorate. It is also important that the cross-sectional plane 36 and thus the ends 32 and 34 of a further cross-sectional plane 42, in which the downstream end 44 of the spray opening 18 is located, lies in the range between 3 mm and 5 mm. The distance is preferably approximately 4 mm according to FIG. 1, in which the spray device is shown on a 2: 1 scale.

In dem axial zur Pulverkanalachse 20 verlaufenden Gaskanal 24 ist ein elektrischer Widerstand 46 untergebracht, der sich in einer die Hochspannungsquelle mit der Elektrode 26 verbindenden elektrischen Leitung 48 befindet. Der elektrische Widerstand 46 dient dazu, elektrische Überschläge von der Elektrode 26 zu anderen Gegenständen zu verhindern. Dies wird besser verhindert, je näher der Widerstand 46 bei der Elektrode 26 angeordnet ist.An electrical resistor 46 is accommodated in the gas channel 24, which runs axially to the powder channel axis 20, and is located in an electrical line 48 connecting the high-voltage source to the electrode 26. The electrical resistor 46 serves to prevent electrical flashovers from the electrode 26 to other objects. This is better prevented the closer the resistor 46 is arranged to the electrode 26.

Der trichterförmige Kanalabschnitt 16 ist kegelförmig ausgebildet und seine innere Kanalwand 54 verengt sich unter einem Kegelwinkel a von 120°. In abgewandelter Ausführungsform kann der Kegelwinkel im Bereich zwischen 100° und 140° liegen. Die äußere Stirnfläche 52 des Mundstücks 12 läuft parallel und damit unter dem gleichen Winkel wie die innere Kanalwand 54.The funnel-shaped channel section 16 is conical and its inner channel wall 54 narrows at a cone angle a of 120 °. In a modified embodiment, the cone angle can be in the range between 100 ° and 140 °. The outer end face 52 of the mouthpiece 12 runs parallel and thus at the same angle as the inner channel wall 54.

Die Sprühöffnung 18 hat die Form eines Schlitzes, welcher sich symmetrisch über die Mittelachse 20 des Pulverkanals 14 erstreckt, wobei sich der Schlitz mit beiden Schlitzenden 57 stromaufwärts bis hinter die Querschnittsebene 36 erstreckt, vorzugsweise bis zu einem Abstand 56 von ungefähr 8 mm von der Kegelspitze 58 der Stirnfläche 52 des Mundstückes 12. In abgewandelter Ausführungsform sollte der Abstand 56 im Bereich zwischen 5 mm und 10 mm liegen. Der bevorzugte Abstand ist jedoch 8 mm.The spray opening 18 is in the form of a slot which extends symmetrically over the central axis 20 of the powder channel 14, the slot with both slot ends 57 extending upstream behind the cross-sectional plane 36, preferably up to a distance 56 of approximately 8 mm from the cone tip 58 of the end face 52 of the mouthpiece 12. In a modified embodiment, the distance 56 should be in the range between 5 mm and 10 mm. However, the preferred distance is 8 mm.

Stromaufwärts des trichterförmigen Kanalabschnittes 16 befindet sich ein Abschnitt 60 des Pulverkanals 14, welcher die Form eines zylindrischen Ringraumes hat, da längs dieses Abschnittes sowohl die Einrichtung 22 als auch die Kanalwand 62 des Pulverkanals 14 zylindrisch ausgebildet sind. Stromaufwärts schließt sich an den Abschnitt 60 ein ringkanalförmiger Abschnitt 64 des Pulverkanals 14 an, welcher in Strömungsrichtung einen zunehmend größeren Öffnungsquerschnitt hat, bis zu einem größten Öffnungsquerschnitt am Anfang des folgenden Abschnittes 60. Der ringförmige Abschnitt 64 wird durch die zylindrische Wand 62 und die auf der Länge dieses Abschnittes 64 kegelstumpfförmig verjüngte äußere Mantelfläche 66 der Einrichtung 22 gebildet. Stromaufwärts des Abschnittes 64 befindet sich ein ringförmiger Kanalabschnitt 68 des Pulverkanals 14, welcher durch die zylindrische Wand 62 und eine zylindrische Mantelfläche 70 der Einrichtung 22 gebildet ist. Stromaufwärts der Einrichtung 22 hat der Pulverkanal 14 einen hohlzylindrischen Abschnitt 72. Die Strömungsgeschwindigkeit des Pulvers wird beschleunigt, wenn es vom Abschnitt 72 in den Abschnitt 68 strömt, da die Einrichtung 22 den Öffnungsquerschnitt des Pulverkanals 14 verkleinert. Im Abschnitt 64 wird der Öffnungsquerschnitt wieder größer, so daß sich die Strömungsgeschwindigkeit der Pulverteilchen verlangsamt und eine Vergleichmäßigung der Pulververteilung bewirkt wird. Im folgenden Abschnitt 60 erfolgt eine Strömungsberuhigung, und dandach erfolgt im trichterförmig enger werdenden Kanalabschnitt 16 eine Komprimierung des Pulvers. Das Gas des Gaskanals 24 injiziert eletrische Ladungsteilchen von der Elektrode 26 auf die Pulverteilchen im Kanalabschnitt 16.Upstream of the funnel-shaped channel section 16 there is a section 60 of the powder channel 14, which has the shape of a cylindrical annular space, since both the device 22 and the channel wall 62 of the powder channel 14 are cylindrical along this section. Upstream of section 60 is an annular channel section 64 of powder channel 14, which has an increasingly larger opening cross section in the direction of flow up to a largest opening cross section at the beginning of the following section 60. The annular section 64 is defined by the cylindrical wall 62 and the the length of this section 64 is formed as a truncated cone-shaped outer surface 66 of the device 22. Upstream of section 64 there is an annular channel section 68 of the powder channel 14 which passes through the cylindrical one Wall 62 and a cylindrical lateral surface 70 of the device 22 is formed. Upstream of the device 22, the powder channel 14 has a hollow cylindrical section 72. The flow velocity of the powder is accelerated when it flows from the section 72 into the section 68, since the device 22 reduces the opening cross section of the powder channel 14. In section 64, the opening cross section increases again, so that the flow velocity of the powder particles slows down and the powder distribution is made more uniform. In the following section 60, the flow is calmed, and then the powder is compressed in the funnel-shaped channel section 16. The gas of the gas channel 24 injects electrical charge particles from the electrode 26 onto the powder particles in the channel section 16.

Fig. 2 zeigt von vorne die schlitzförmige Form der Sprühöffnung 18. Das Verhältnis von Länge zu Breite des Schlitzes 18 darf nicht zu groß sein. Der Schlitz hat vorzugsweise die in den Fig. 1 und 2 dargestellten Abmessungen.2 shows the slit-shaped shape of the spray opening 18 from the front. The ratio of the length to the width of the slit 18 must not be too large. The slot preferably has the dimensions shown in FIGS. 1 and 2.

Alle Teile der Spritzpistole, welche vom Pulver berührt werden, bestehen aus Kunststoff.All parts of the spray gun that are touched by the powder are made of plastic.

Durch die Erfindung wird insbesondere bei einer Sprüheinrichtung, bei welcher die Sprühöffnung die Form eines Schlitzes hat, eine besonders starke Verbesserung der elektrostatischen Aufladung des Pulvers, der Wirtschaftlichkeit und der Beschichtungsqualität erreicht, wobei in einem einzigen Sprühvorgang auch Schichten größerer Dicke auf dem zu beschichtenden Gegenstand erzeugt werden können. Besonders wichtig ist dabei, daß die Elektrode im wesentlichen nicht aus dem Gaskanal herausragt, und daß der Abstand 41 ungefähr 4 mm beträgt.The invention achieves a particularly strong improvement in the electrostatic charging of the powder, the economy and the coating quality, in particular in a spray device in which the spray opening is in the form of a slot, with layers of greater thickness on the object to be coated in a single spraying process can be generated. It is particularly important that the electrode does not protrude substantially from the gas channel and that the distance 41 is approximately 4 mm.

Die Anwendung der Erfindung ist jedoch nicht auf schlitzförmige Sprühöffnungen beschränkt.However, the application of the invention is not restricted to slot-shaped spray openings.

Claims (7)

1. An electrostatic spray device for coating powder, having a powder conduit (14), the downstream end of which comprises a spray aperture (18) for spraying the coating powder, having at east one gas conduit (24), which comprises at least one gas outlet aperture (30), which is disposed substantially in the radial centre of the powder conduit upstream from its spray aperture (18) and discharges axially in the direction of this spray aperture (18), having at east one electrode (26) around which gas from gas conduit (24) flows and which is located in the gas outlet aperture (30) and the downstream electrode end (32) of which ends approximately at the downstream end (34) of the gas outlet aperture, characterised in that the powder conduit (14) comprises a conduit section (16) which tapers in a funnel shape roughly from the gas outlet aperture (30) to the spray aperture and which forms a pressure region compressing the coating powder, into which region the gas outlet aperture (30) opens, and in that the radial centre of the spray aperture (18) is located at the point of the smallest diameter of this conduit section (16) opposite the gas outlet aperture (30).
2. A spray device as specified in Claim 1, characterised in that the funnel angle (a) of the powder conduit section (16), which becomes smaller in a funnel shape in the downstream direction, lies between 100° and 140°, preferably 120°.
3. A spray device as specified in Claim 1 or 2, characterised in that the distance (41) from the end (34) of the gas outlet aperture (30) to the end (44) of the spray aperture (18) lies between 3 mm and 5 mm, and is preferably approximately 4 mm.
4. A spray device as specified in one of Claims 1 to 3, characterised in that the spray aperture (18) is shaped like a slit.
5. A spray device as specified in Claim 4, characterised in that the slit, which forms the spray aperture (18), extends symmetrically to the radial centre (20) of powder conduit (14) in the conduit wall upstream right over the downstream end (34) of gas outet aperture (30).
6. A spray device as specified in Claim 5, characterised in that the slit, which forms the spray aperture (18), extends upstream with both slit ends (57) to a distance (56) of 5 mm to 10 mm, preferably 8 mm from the apex of the cone (58) of the cone-shaped outer front surface (52) of a nozzle (12) comprising the spray aperture (18).
7. A spray device as specified in one of Claims 1 to 6, characterised in that the end (32) of the electrode (26) and the downstream end (34) of the gas outlet aperture (30) lie roughly 0.5 mm to 1.5 mm downstream from the upstream beginning (40) of the funnel-shaped conduit section (16).
EP87102179A 1986-03-13 1987-02-16 Electrostatic spray device for coating powder Expired - Lifetime EP0236795B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT87102179T ATE55283T1 (en) 1986-03-13 1987-02-16 ELECTROSTATIC SPRAYING DEVICE FOR COATING POWDER.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3608415 1986-03-13
DE19863608415 DE3608415A1 (en) 1986-03-13 1986-03-13 ELECTROSTATIC SPRAYING DEVICE FOR COATING POWDER

Publications (3)

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EP0236795A2 EP0236795A2 (en) 1987-09-16
EP0236795A3 EP0236795A3 (en) 1988-09-14
EP0236795B1 true EP0236795B1 (en) 1990-08-08

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US (1) US4802625A (en)
EP (1) EP0236795B1 (en)
JP (1) JPS62269766A (en)
AT (1) ATE55283T1 (en)
DE (1) DE3608415A1 (en)
ES (1) ES2016577B3 (en)

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Also Published As

Publication number Publication date
ATE55283T1 (en) 1990-08-15
JPS62269766A (en) 1987-11-24
DE3608415A1 (en) 1987-09-24
JPH0525552B2 (en) 1993-04-13
US4802625A (en) 1989-02-07
DE3608415C2 (en) 1989-01-19
EP0236795A2 (en) 1987-09-16
EP0236795A3 (en) 1988-09-14
ES2016577B3 (en) 1990-11-16

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