EP0978319B1 - Powder spray device with external and internal charging - Google Patents

Powder spray device with external and internal charging Download PDF

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Publication number
EP0978319B1
EP0978319B1 EP98114846A EP98114846A EP0978319B1 EP 0978319 B1 EP0978319 B1 EP 0978319B1 EP 98114846 A EP98114846 A EP 98114846A EP 98114846 A EP98114846 A EP 98114846A EP 0978319 B1 EP0978319 B1 EP 0978319B1
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EP
European Patent Office
Prior art keywords
powder
voltage
electrode
resistance
external
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP98114846A
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German (de)
French (fr)
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EP0978319A1 (en
Inventor
Gunter Dr.-Ing. Börner
Johann Christoph Dr. Rer.Nat. Nienburg
Jörg Dr. rer.nat. Sopka
Josef Wittmann
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ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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ABB Research Ltd Switzerland
ABB Research Ltd Sweden
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Priority to DE59800278T priority Critical patent/DE59800278D1/en
Priority to EP98114846A priority patent/EP0978319B1/en
Priority to JP11223830A priority patent/JP2000061366A/en
Priority to US09/370,688 priority patent/US6220533B1/en
Publication of EP0978319A1 publication Critical patent/EP0978319A1/en
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Publication of EP0978319B1 publication Critical patent/EP0978319B1/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
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/087—Arrangements of electrodes, e.g. of charging, shielding, collecting electrodes
    • 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
    • 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
    • B05B5/053—Arrangements for supplying power, e.g. charging power
    • B05B5/0533—Electrodes specially adapted therefor; Arrangements of electrodes

Definitions

  • the invention relates to a powder spray device with internal and external charging, which is suitable for electrostatic powder coating is.
  • a powder spraying device is known from WO 98/24555 (cf. preamble of claim 1).
  • Fig. 5 shows a known spray gun. It has a chamber 100 into which a powder / air mixture PL can be initiated.
  • the spray gun contains a ground electrode 10 a metallic ring 150 distributed needle-shaped inner high-voltage electrodes 2, and at least one outer high-voltage electrode designed as a needle 5.
  • a high-voltage source designed as a high-voltage cascade 6 supplies high voltage via an electrical connection 30 and the ring 150 to the electrodes 5, 2.
  • the at least one outer high-voltage electrode 5 can be arranged as an option designated additional electrode with which an electric field and an additional Corona are generated outside, which increase the order efficiency should.
  • the electric field generated by the outer needle 5 generates a force on the electrically charged particles.
  • the outer corona can be another Cause charge and repulsion between the ions and the charged Powder particles can cause the spray cloud to expand. Which of the listed physical factors are dominant, depends on the powder output, the properties of the powder (good or poor chargeability) and the distance to the workpiece.
  • both the inner and the external charge required for a sufficiently large charge of the powder particles With larger amounts of powder (greater than 200 g / min), both the inner and the external charge required for a sufficiently large charge of the powder particles.
  • a cascade with a relatively high internal resistance is used for high voltage generation (negative DC voltage).
  • the open circuit voltage U 0 this is the output voltage of the cascade in the unloaded state, is usually in the range from approximately - 80 kV to - 100 kV.
  • the internal resistance of the cascade R i is in the range of approx. 400 M ⁇ to 600 M ⁇ .
  • the maximum output current of the cascade is approx. 80 ⁇ A ... 120 ⁇ A.
  • the usage of cascades with larger output voltages and smaller internal resistances is not possible for security reasons.
  • the relevant standards in Europe and America do not require the air-powder mixture under any circumstances may be ignited by electrical discharges. Among other things limits the performance of the cascade. Further measures to avoid ignition are series resistors and avoidance of electrode arrangements that lead to a high electrical capacity.
  • DE-A1-38 12 358 describes a powder spraying device with several high-voltage electrodes, which cause an external, but no internal powder charge.
  • the Electrodes each with the interposition of a high-impedance resistor connected to a high voltage source.
  • the invention is therefore based on the object of a powder spray device the type known from WO 98/24555, with which there is improved constancy the application efficiency with variable distance between spraying device and Workpiece can be achieved.
  • the ratio of the inner and outer currents is set specifically and changes in distance changes only within narrow limits.
  • the ratio of the inner and outer currents is set specifically and changes in distance changes only within narrow limits.
  • the typical nominal distance of Approx. 70% of the current flows 200 mm to the workpiece via the electrodes for the internal charging and 30% via the external electrode.
  • Fig. 1 shows a front and a side view of a ring 1 from a high-resistance material.
  • a high-resistance material for ring 1 and others - High-resistance components described below can e.g. a plastic can be used, which is filled with graphite, carbon black or other conductive substances.
  • the ring 1 In the ring 1 are - evenly distributed over its inner circumference - several needle-shaped inner high voltage electrodes 2 used.
  • the ring 1 is over one high-resistance rod 3 with a high-voltage source 6 (see FIGS. 2 and 5) connectable.
  • the connection point 11 for the rod 3 is in the middle of a two electrodes 2 lying ring piece.
  • About a high-resistance pin 4 is one needle-shaped outer high-voltage electrode 5 at a connection point 12 connected to the rod 3.
  • FIG. 2 shows the complete electrical equivalent circuit diagram of an arrangement shown in FIG. 1, which is connected to a high-voltage cascade, for better understanding.
  • the cascade 6 is simulated by an ideal voltage source with the voltage U 0 and the resistor R i .
  • the discharge distances for the inner 7 and the outer charge 8 are given by their current-voltage characteristics. Ring pieces lying between the inner electrodes 2 are each modeled by resistors R 1 .
  • the resistance of the rod 3 is divided by the connection point 12 for the pin 4 into resistors R 2 and R 3 .
  • the rod 4 is simulated by the resistor R 4 .
  • the resistor R a combines the resistors R i and R 3 .
  • the components relevant for the internal discharge were combined in a first approximation by a resistor R b and a gas discharge path 9.
  • R c is equal to R 4 .
  • characteristic curve 10 applies to the internal discharge and characteristic curve 11 and 12 for external unloading at two different distances from the workpiece. The The distance is smaller for characteristic curve 11 than for characteristic curve 12.
  • the parameters C i , U i0 , C a and U a0 can be determined from the geometric dimensions and the material parameters using a numerical field calculation. However, an experimental check is recommended.
  • the first approximation for R c is that the larger R c , the greater the edge effect.
  • Resistor R 1 should be in the range of approximately 10 M ⁇ to approximately 30 M ⁇ . This resistance prevents field strength increases and thus high currents when the powder comes into direct contact with the internal needles.

Abstract

Die Erfindung bezieht sich auf eine Pulversprüheinrichtung mit gleichzeitig interner und externer Aufladung, die für eine elektrostatische Pulverbeschichtung geeignet ist. Um eine verbesserte Konstanz des Auftragswirkungsgrades, weitgehend unabhängig vom Abstand der Pulversprüheinrichtung vom Werkstück zu erzielen, wird vorgeschlagen, sowohl innere Hochspannungselektroden (2) als auch äußere Hochspannungselektroden (5) über hochohmige Komponenten (1, 3, 4) mit einer Hochspannungsquelle (6) zu verbinden. <IMAGE>The invention relates to a powder spray device with simultaneous internal and external charging, which is suitable for electrostatic powder coating. In order to achieve an improved consistency of the application efficiency, largely independently of the distance of the powder spraying device from the workpiece, it is proposed to use both high-voltage components (1, 3, 4) with a high-voltage source (6) to create both internal high-voltage electrodes (2) and external high-voltage electrodes (5). connect to. <IMAGE>

Description

Die Erfindung bezieht sich auf eine Pulversprüheinrichtung mit gleichzeitig interner und externer Aufladung, die für eine elektrostatische Pulverbeschichtung geeignet ist.The invention relates to a powder spray device with internal and external charging, which is suitable for electrostatic powder coating is.

Eine solche Pulversprüheinrichtung ist aus der WO 98/24555 (vgl. Oberbegriff von Anspruch 1) bekannt. Fig. 5 zeigt eine daraus bekannte Sprühpistole. Sie weist eine Kammer 100 auf, in die ein Pulver/Luftgemisch PL einleitbar ist. Die Sprühpistole enthält eine Erdelektrode 10, an einem metallischen Ring 150 verteilt angeordnete nadelförmige innere Hochspannungselektroden 2, sowie wenigstens eine äußere, als Nadel ausgeführte Hochspannungselektrode 5. Eine als Hochspannungskaskade ausgeführte Hochspannungsquelle 6 liefert über eine elektrische Verbindung 30 und den Ring 150 Hochspannung an die Elektroden 5, 2.Such a powder spraying device is known from WO 98/24555 (cf. preamble of claim 1). Fig. 5 shows a known spray gun. It has a chamber 100 into which a powder / air mixture PL can be initiated. The spray gun contains a ground electrode 10 a metallic ring 150 distributed needle-shaped inner high-voltage electrodes 2, and at least one outer high-voltage electrode designed as a needle 5. A high-voltage source designed as a high-voltage cascade 6 supplies high voltage via an electrical connection 30 and the ring 150 to the electrodes 5, 2.

Die wenigstens eine äußere Hochspannungselektrode 5 ist als wahlweise anordenbare zusätzliche Elektrode bezeichnet, mit der ein elektrisches Feld und eine zusätzliche Korona außerhalb erzeugt werden, die den Auftragswirkungsgrad erhöhen sollen. Das durch die äußere Nadel 5 generierte elektrische Feld erzeugt eine Kraft auf die elektrisch geladenen Partikel. Außerdem kann die äußere Korona eine weitere Aufladung bewirken und die Abstoßung zwischen den Ionen und den geladenen Pulverpartikel kann zu einer Aufweitung der Sprühwolke führen. Welche der aufgeführten physikalischen Einflußfaktoren dominierend sind, hängt von der Pulverausstoßmenge, den Eigenschaften des Pulvers (gute oder schlechte Aufladbarkeit) und dem Abstand zum Werkstück ab.The at least one outer high-voltage electrode 5 can be arranged as an option designated additional electrode with which an electric field and an additional Corona are generated outside, which increase the order efficiency should. The electric field generated by the outer needle 5 generates a force on the electrically charged particles. In addition, the outer corona can be another Cause charge and repulsion between the ions and the charged Powder particles can cause the spray cloud to expand. Which of the listed physical factors are dominant, depends on the powder output, the properties of the powder (good or poor chargeability) and the distance to the workpiece.

Bei kleinen Pulvermengen (bis ca. 150 g/min) und normal aufladbaren Pulvern kann allein mit der inneren Aufladung eine hinreichend gute Ladungsmenge auf die Pulverpartikel gebracht werden. Das durch die äußere Nadel aufgebaute elektrische Feld bewirkt eine auf die Pulverpartikel wirkende Kraft F = E*q . Abhängig von der Spannung an der Nadelspitze wird sich ein mehr oder weniger ausgeprägter Kanteneffekt bzw. Umgriff ergeben. Mit der Höhe des Stromes kann die Breite der Sprühwolke beeinflußt werden.With small amounts of powder (up to approx. 150 g / min) and normally chargeable powders with the internal charge alone, a sufficiently good amount of charge on the powder particles to be brought. The electrical built up by the outer needle Field causes a force F = E * q acting on the powder particles. Depends on the Tension at the needle tip will result in a more or less pronounced edge effect or wrap. With the amount of current, the width of the Spray cloud can be affected.

Bei größeren Pulvermengen (größer 200 g/min) ist sowohl die innere als auch die äußere Aufladung für eine hinreichend große Aufladung der Pulverpartikel erforderlich.With larger amounts of powder (greater than 200 g / min), both the inner and the external charge required for a sufficiently large charge of the powder particles.

Der Nachteil einer Anordnung mit metallischer Verbindung zwischen den Elektroden ist jedoch, daß der Strom und die Spannung an der externen Nadel stark abhängig sind vom Abstand zwischen Pistole und Werkstück. Bei einem kleinen Abstand fließt ein viel größerer Strom und die Spannung ist kleiner als bei einem großen Abstand. Dadurch kann sich insbesondere bei hohen Pulverausstoßmengen die Tendenz verstärken, daß der Auftragswirkungsgrad um so größer ist, je kleiner der Abstand ist.The disadvantage of an arrangement with a metallic connection between the electrodes however, the current and voltage on the external needle is highly dependent are the distance between the gun and the workpiece. At a small distance flows a much larger current and the voltage is smaller than at a large distance. This can result in a tendency, particularly with high powder output quantities reinforce that the smaller the distance, the greater the efficiency of the order is.

Diese Tendenz ist in der Praxis jedoch nicht erwünscht. Man strebt in einem technisch sinnvollen Bereich (100 mm ... 250 mm) an, daß der Auftragswirkungsgrad unabhängig vom Abstand gleichmäßig hoch ist.However, this tendency is not desirable in practice. You strive in a technical way reasonable range (100 mm ... 250 mm) indicates that the application efficiency is equally high regardless of the distance.

Für die Hochspannungserzeugung (negative Gleichspannung) wird eine Kaskade mit einem relativ hohen Innenwiderstand verwendet. Die Leerlaufspannung U0, dies ist die Ausgangsspannung der Kaskade im unbelasteten Zustand, liegt dabei üblicherweise im Bereich von ca. - 80 kV bis - 100 kV. Der Innenwiderstand der Kaskade Ri liegt im Bereich von ca. 400 MΩ bis 600 MΩ. Die tatsächliche Ausgangsspannung der Kaskade Uc berechnet sich dann mit dem Ausgangsstrom Ic nach folgender Gleichung: Uc = U0 - IcRi A cascade with a relatively high internal resistance is used for high voltage generation (negative DC voltage). The open circuit voltage U 0 , this is the output voltage of the cascade in the unloaded state, is usually in the range from approximately - 80 kV to - 100 kV. The internal resistance of the cascade R i is in the range of approx. 400 MΩ to 600 MΩ. The actual output voltage of the cascade U c is then calculated using the output current I c according to the following equation: U c = U 0 - I c R i

Der maximale Ausgangsstrom der Kaskade beträgt ca. 80 µA ... 120 µA. Die Verwendung von Kaskaden mit größeren Ausgangsspannungen und kleineren Innenwiderständen ist aus Sicherheitsgründen nicht möglich. Die einschlägigen Standards in Europa und Amerika fordern, daß das Luft - Pulver - Gemisch unter keinen Umständen durch elektrische Entladungen gezündet werden darf. Damit wird unter anderem die Leistung der Kaskade begrenzt. Weitere Maßnahmen zu Vermeidung von Zündungen sind Vorwiderstände und eine Vermeidung von Elektrodenanordnungen, die zu einer hohen elektrischen Kapazität führen.The maximum output current of the cascade is approx. 80 µA ... 120 µA. The usage of cascades with larger output voltages and smaller internal resistances is not possible for security reasons. The relevant standards in Europe and America do not require the air-powder mixture under any circumstances may be ignited by electrical discharges. Among other things limits the performance of the cascade. Further measures to avoid ignition are series resistors and avoidance of electrode arrangements that lead to a high electrical capacity.

Bei der Pulverapplikation versucht man mit einem konstanten Abstand zu arbeiten. Jedoch läßt es sich aus verschiedenen Gründen nicht vermeiden, daß sich der Abstand zum Werkstück verändert (z.B. an Kanten).When applying powder, try to work with a constant distance. However, for various reasons, the distance cannot be avoided changed to the workpiece (e.g. on edges).

Die DE-A1-38 12 358 beschreibt eine Pulversprüheinrichtung mit mehreren Hochspannungselektroden, die eine äußere, jedoch keine innere Pulveraufladung bewirken. Um eine Stromkonzentration auf wenige Elektroden zu vermeiden, sind die Elektroden jeweils unter Zwischenschaltung eines hochohmigen Widerstandes mit einer Hochspannungsquelle verbunden.DE-A1-38 12 358 describes a powder spraying device with several high-voltage electrodes, which cause an external, but no internal powder charge. In order to avoid a current concentration on a few electrodes, the Electrodes each with the interposition of a high-impedance resistor connected to a high voltage source.

Der Erfindung liegt daher die Aufgabe zugrunde, eine Pulversprüheinrichtung der aus der WO 98/24555 bekannten Art anzugeben, mit der sich eine verbesserte Konstanz des Auftragswirkungsgrades bei variablem Abstand zwischen Sprüheinrichtung und Werkstück erzielen läßt.The invention is therefore based on the object of a powder spray device the type known from WO 98/24555, with which there is improved constancy the application efficiency with variable distance between spraying device and Workpiece can be achieved.

Diese Aufgabe wird durch eine Pulversprüheinrichtung mit den im Anspruch 1 angegebenen Merkmalen gelöst. Vorteilhafte Ausgestaltungen sind in weiteren Ansprüchen angegeben und ergeben sich aus der nachstehenden Beschreibung eines Ausführungsbeispiels anhand der Zeichnungsfiguren. This object is achieved by a powder spraying device with that specified in claim 1 Features resolved. Advantageous embodiments are in further claims indicated and result from the following description of a Embodiment based on the drawing figures.

Es zeigen:

Fig. 1
eine Anordnung von internen und externen Elektroden einschließlich hochohmiger Verbindungsteile,
Fig. 2
ein vollständiges elektrisches Ersatzschaltbild zu der in Fig. 1 gezeigten Anordnung,
Fig. 3
ein vereinfachtes Ersatzschaltbild,
Fig. 4
zugehörige Strom-Spannungs-Charakteristiken, und
Fig. 5
eine aus dem Stand der Technik bekannte Pulversprüheinrichtung, in die die in Fig. 1 gezeigte Anordnung anstelle der in Fig. 5 gezeigten Elektrodenanordnung einsetzbar ist.
Show it:
Fig. 1
an arrangement of internal and external electrodes including high-resistance connecting parts,
Fig. 2
1 shows a complete electrical equivalent circuit diagram for the arrangement shown in FIG. 1,
Fig. 3
a simplified equivalent circuit diagram,
Fig. 4
associated current-voltage characteristics, and
Fig. 5
a powder spray device known from the prior art, into which the arrangement shown in FIG. 1 can be used instead of the electrode arrangement shown in FIG. 5.

Das angestrebte Ziel einer verbesserten Konstanz des Auftragswirkungsgrades wird mit der erfindungsgemäßen Pulversprüheinrichtung dadurch erreicht, daß das Verhältnis der inneren und äußeren Ströme gezielt eingestellt wird und sich bei Abstandsänderungen nur in engen Grenzen ändert. Beim typischen Nennabstand von 200 mm zum Werkstück fließen etwa 70 % des Stromes über die Elektroden für die interne Aufladung und 30 % über die externe Elektrode.The desired goal of improved consistency in order efficiency will be achieved with the powder spraying device according to the invention in that the ratio of the inner and outer currents is set specifically and changes in distance changes only within narrow limits. At the typical nominal distance of Approx. 70% of the current flows 200 mm to the workpiece via the electrodes for the internal charging and 30% via the external electrode.

Fig. 1 zeigt in einer Vorder- und einer Seitenansicht einen Ring 1 aus einem hochohmigen Material. Als hochohmiges Material für den Ring 1 und weitere - nachstehend beschriebene - hochohmige Komponenten kann z.B. ein Kunststoff verwendet werden, der mit Graphit, Ruß oder anderen leitfähigen Stoffen gefüllt ist.Fig. 1 shows a front and a side view of a ring 1 from a high-resistance material. As a high-resistance material for ring 1 and others - High-resistance components described below can e.g. a plastic can be used, which is filled with graphite, carbon black or other conductive substances.

In den Ring 1 sind - über seinen inneren Umfang gleichmäßig verteilt - mehrere nadelförmige innere Hochspannungselektroden 2 eingesetzt. Der Ring 1 ist über einen hochohmigen Stab 3 mit einer Hochspannungsquelle 6 (siehe Fig. 2 und Fig. 5) verbindbar. Die Anschlußstelle 11 für den Stab 3 liegt in der Mitte eines zwischen zwei Elektroden 2 liegenden Ringstückes. Über einen hochohmigen Stift 4 ist eine nadelförmige äußere Hochspannungselektrode 5 an einer Anschlußstelle 12 mit dem Stab 3 verbunden.In the ring 1 are - evenly distributed over its inner circumference - several needle-shaped inner high voltage electrodes 2 used. The ring 1 is over one high-resistance rod 3 with a high-voltage source 6 (see FIGS. 2 and 5) connectable. The connection point 11 for the rod 3 is in the middle of a two electrodes 2 lying ring piece. About a high-resistance pin 4 is one needle-shaped outer high-voltage electrode 5 at a connection point 12 connected to the rod 3.

Die mit einer solchen Anordnung erreichbare Strom- und Spannungsverteilung wird durch die Widerstandswerte der Komponenten 1, 3 und 4 und die Strom-Spannungs-Charakteristik der Gasentladungsstrecken

  • Nadelring - innere Erdelektrode
  • äußere Nadel - Werkstück
bestimmt.The current and voltage distribution achievable with such an arrangement is determined by the resistance values of components 1, 3 and 4 and the current-voltage characteristic of the gas discharge paths
  • Needle ring - inner earth electrode
  • outer needle - workpiece
certainly.

Fig. 2 zeigt zum besseren Verständnis das vollständige elektrische Ersatzschaltbild einer in Fig. 1 gezeigten Anordnung, die mit einer Hochspannungskaskade verbunden ist. Die Kaskade 6 wird durch eine ideale Spannungsquelle mit der Spannung U0 und dem Widerstand Ri nachgebildet. Die Entladungsstrecken für die innere 7 und die äußere Aufladung 8 sind durch ihre Strom-Spannungs-Charakteristiken gegeben. Zwischen den inneren Elektroden 2 liegende Ringstücke sind jeweils durch Widerstände R1 nachgebildet. Der Widerstand des Stabs 3 ist durch die Anschlußstelle 12 für den Stift 4 in Widerstände R2 und R3 aufgeteilt. Der Stab 4 ist durch den Widerstand R4 nachgebildet.FIG. 2 shows the complete electrical equivalent circuit diagram of an arrangement shown in FIG. 1, which is connected to a high-voltage cascade, for better understanding. The cascade 6 is simulated by an ideal voltage source with the voltage U 0 and the resistor R i . The discharge distances for the inner 7 and the outer charge 8 are given by their current-voltage characteristics. Ring pieces lying between the inner electrodes 2 are each modeled by resistors R 1 . The resistance of the rod 3 is divided by the connection point 12 for the pin 4 into resistors R 2 and R 3 . The rod 4 is simulated by the resistor R 4 .

Für eine Auslegung der Widerstände ist eine Vereinfachung des Ersatzschaltbildes zweckmäßig, welches in Fig. 3 dargestellt ist. Der Widerstand Ra faßt die Widerstände Ri und R3 zusammen. Die für die innere Entladung relevanten Komponenten wurden in erster Näherung durch einen Widerstand Rb und eine Gasentladungsstrecke 9 zusammengefaßt. Rc ist gleich R4.A simplification of the equivalent circuit diagram, which is shown in FIG. 3, is expedient for a design of the resistors. The resistor R a combines the resistors R i and R 3 . The components relevant for the internal discharge were combined in a first approximation by a resistor R b and a gas discharge path 9. R c is equal to R 4 .

Zugehörige typische Strom-Spannungs-Charakeristiken sind beispielhaft in Fig. 4 dargestellt. Die Kennlinie 10 gilt für die innere Entladung und Kennlinie 11 und 12 für die äußere Entladung bei zwei unterschiedlichen Abständen zum Werkstück. Der Abstand ist bei Kennlinie 11 kleiner als bei Kennlinie 12.Associated typical current-voltage characteristics are exemplified in FIG. 4 shown. The characteristic curve 10 applies to the internal discharge and characteristic curve 11 and 12 for external unloading at two different distances from the workpiece. The The distance is smaller for characteristic curve 11 than for characteristic curve 12.

Sie können mit folgenden Gleichungen approximiert werden.

  • Innere Entladung Ii = Ci(Ui-Ui0)2 Ci und Ui0 sind Kenngrößen die vom geometrischen Aufbau der Pistole, die insbesondere vom Abstand des Nadelelektrodenringes von der inneren Erdelektrode abhängen.
  • Äußere Entladung Ia = Ca (Ua-Ua0)2 Ca und Ua0 sind Kenngrößen die sowohl vom geometrischen Aufbau der Pistole aber wesentlich stärker vom Abstand der Pistole vom Werkstück als auch von der Form des Werkstückes abhängen. Es ergeben sich also verschiedene Charakteristiken für verschiedene Positionen des Werkstückes.
They can be approximated using the following equations.
  • Internal discharge I. i = C i (U i -U i0 ) 2nd C i and U i0 are parameters which depend on the geometric structure of the gun and which depend in particular on the distance of the needle electrode ring from the inner earth electrode.
  • Outer discharge I. a = C a (U a -U a0 ) 2nd C a and U a0 are parameters which depend both on the geometrical structure of the pistol but much more on the distance of the pistol from the workpiece and on the shape of the workpiece. So there are different characteristics for different positions of the workpiece.

Die Kenngrößen Ci, Ui0, Ca und Ua0 sind aus den geometrischen Abmessungen und den Materialkennwerten mit einer numerischen Feldberechnung ermittelbar. Eine experimentelle Überprüfung ist aber empfehlenswert.The parameters C i , U i0 , C a and U a0 can be determined from the geometric dimensions and the material parameters using a numerical field calculation. However, an experimental check is recommended.

Der Einfluß der Menge des geförderten Pulvers kann hier vernachlässigt werden.The influence of the amount of powder conveyed can be neglected here.

Das Ersatzschaltbild wird durch folgendes Gleichungssystem beschrieben: U0= RaCa(Ua-Ua0)2+(Ra+Rb)Ci(Ui-Ui0)2+Ui U0= RaCi(Ui-Ui0)2+(Ra+Rc)Ci(Ua-Ua0)2+Ua The equivalent circuit diagram is described by the following system of equations: U 0 = R a C. a (U a -U a0 ) 2nd + (R a + R b ) C i (U i -U i0 ) 2nd + U i U 0 = R a C. i (U i -U i0 ) 2nd + (R a + R c ) C i (U a -U a0 ) 2nd + U a

Mit diesen Gleichungen lassen sich die Werte für die Widerstände optimieren. In einem Ausführungsbeispiel haben sich folgende Richtwerte ergeben:

  • Ra = 400 MΩ ...600 MΩ
  • Rb = 20 MΩ ... 200 MΩ
  • Rc = (2 ...5) * Rb
    • The values for the resistances can be optimized using these equations. The following guide values have resulted in one exemplary embodiment:
  • R a = 400 MΩ ... 600 MΩ
  • R b = 20 MΩ ... 200 MΩ
  • R c = (2 ... 5) * R b

    • Für Rc gilt in erster Näherung, daß je größer Rc, desto größer der Kanteneffekt.The first approximation for R c is that the larger R c , the greater the edge effect.

    Der Widerstand R1 sollte im Bereich von ca. 10 MΩ bis ca. 30 MΩ liegen. Dieser Widerstand verhindert, daß es bei einem unmittelbaren Kontakt des Pulvers an den internen Nadeln zu Feldstärkeüberhöhungen und damit hohen Strömen kommt.Resistor R 1 should be in the range of approximately 10 MΩ to approximately 30 MΩ. This resistance prevents field strength increases and thus high currents when the powder comes into direct contact with the internal needles.

    Claims (7)

    1. Powder-spraying apparatus, which has a high-voltage source (6) and
      as a result of the arrangement of an earth electrode (10) and a number of internal high-voltage electrodes (2) is equipped for internal powder charging, and, in addition,
      as a result of the arrangement of at least one external high-voltage electrode (5) is equipped for external powder charging,
      characterized in that for the purpose of dividing the overall electrode current to the internal electrodes (2) and the at least one external electrode (5) in a desired ratio
      a) the high-voltage source (6) is connected, via connection elements (3,4) of high-resistance material, to the external high-voltage electrode (5) or all the external high-voltage electrodes (5) present, and to a ring (1) of high-resistance material, over the circumference of which the inner high-voltage electrodes (2) are connected, distributed uniformly, and
      b) the d.c. resistance (R1) of the portion of the ring respectively located between two electrode connections has a value in the range from 10 MΩ to 30 MΩ.
    2. Powder-spraying apparatus according to Claim 1, characterized in that the material used for the high-resistance components (1, 3, 4) is a plastic which is filled with graphite, carbon black or other conductive materials.
    3. Powder-spraying apparatus according to Claim 1 or 2, characterized in that the d.c. resistance of the high-resistance connection elements (3, 4) is in each case around more than 1 MΩ.
    4. Powder-spraying apparatus according to one of the preceding claims, characterized in that the at least one external high-voltage electrode (5) is connected by means of a high-resistance pin (4) to a feed rod (3) leading to the ring (1).
    5. Powder-spraying apparatus according to one of the preceding claims, characterized in that the d.c. resistances of the high-resistance components (1, 3, 4) are selected such that with a nominal distance of 200 mm between the spraying apparatus and a workpiece, the result is a division of the current of about 70% via the internal electrode (2) and about 30% via the external electrode or electrodes (5).
    6. Powder-spraying apparatus according to one of the preceding claims, characterized in that the high voltage is fed to the ring (1) by means of a high-resistance rod (3) at a connection point (11) which is located at the centre of a ring portion located between two electrode connection points.
    7. Powder-spraying apparatus according to Claim 6, characterized in that there is only one needle-like external high-voltage electrode (5), which is connected to the high-resistance rod (3) at a connection point (12) with the interposition of a high-resistance pin (4).
    EP98114846A 1998-08-07 1998-08-07 Powder spray device with external and internal charging Expired - Lifetime EP0978319B1 (en)

    Priority Applications (4)

    Application Number Priority Date Filing Date Title
    DE59800278T DE59800278D1 (en) 1998-08-07 1998-08-07 Powder spraying device with internal and external charging
    EP98114846A EP0978319B1 (en) 1998-08-07 1998-08-07 Powder spray device with external and internal charging
    JP11223830A JP2000061366A (en) 1998-08-07 1999-08-06 Powder spray device with external and internal charging
    US09/370,688 US6220533B1 (en) 1998-08-07 1999-08-09 Powder-spraying apparatus with internal and external charging

    Applications Claiming Priority (1)

    Application Number Priority Date Filing Date Title
    EP98114846A EP0978319B1 (en) 1998-08-07 1998-08-07 Powder spray device with external and internal charging

    Publications (2)

    Publication Number Publication Date
    EP0978319A1 EP0978319A1 (en) 2000-02-09
    EP0978319B1 true EP0978319B1 (en) 2000-09-20

    Family

    ID=8232417

    Family Applications (1)

    Application Number Title Priority Date Filing Date
    EP98114846A Expired - Lifetime EP0978319B1 (en) 1998-08-07 1998-08-07 Powder spray device with external and internal charging

    Country Status (4)

    Country Link
    US (1) US6220533B1 (en)
    EP (1) EP0978319B1 (en)
    JP (1) JP2000061366A (en)
    DE (1) DE59800278D1 (en)

    Families Citing this family (5)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    US6874712B2 (en) * 2002-09-27 2005-04-05 Abb Inc. Swirl gun for powder particles
    US7360724B2 (en) * 2004-10-20 2008-04-22 The Procter & Gamble Company Electrostatic spray nozzle with internal and external electrodes
    US7455249B2 (en) * 2006-03-28 2008-11-25 Illinois Tool Works Inc. Combined direct and indirect charging system for electrostatically-aided coating system
    FR2942415B1 (en) * 2009-02-24 2011-03-11 Sames Technologies ELECTROSTATIC PROJECTOR COMPRISING MOBILE ELECTRODES AND ELECTROSTATIC PROJECTION METHOD USING SUCH A PROJECTOR
    JP6112130B2 (en) * 2015-03-25 2017-04-12 トヨタ自動車株式会社 Electrostatic nozzle, discharge device, and method for manufacturing semiconductor module

    Family Cites Families (8)

    * Cited by examiner, † Cited by third party
    Publication number Priority date Publication date Assignee Title
    US3167255A (en) * 1961-05-08 1965-01-26 Sames Mach Electrostat Electrostatic sprayer system having a separate high resistivity conductor
    US4027050A (en) * 1975-07-10 1977-05-31 Frederic David Haig Method and apparatus for electrostatic coating
    CH622972A5 (en) * 1977-09-09 1981-05-15 Gema Ag Device for electrostatic powder coating of objects
    US4576827A (en) * 1984-04-23 1986-03-18 Nordson Corporation Electrostatic spray coating system
    AU580147B2 (en) * 1985-04-18 1989-01-05 Nordson Corporation Particle spray gun
    DE3812358A1 (en) * 1988-04-14 1989-10-26 Hestermann Gerhard Spray unit for electrostatic polymer powder coating
    US5904294A (en) * 1996-09-13 1999-05-18 Nordson Corporation Particle spray apparatus and method
    CA2273830A1 (en) 1996-12-06 1998-06-11 Abb Research Ltd. Powder spraying device

    Also Published As

    Publication number Publication date
    DE59800278D1 (en) 2000-10-26
    US6220533B1 (en) 2001-04-24
    EP0978319A1 (en) 2000-02-09
    JP2000061366A (en) 2000-02-29

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