EP3551336B1 - Electrostatic spray head - Google Patents

Electrostatic spray head Download PDF

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Publication number
EP3551336B1
EP3551336B1 EP17825362.1A EP17825362A EP3551336B1 EP 3551336 B1 EP3551336 B1 EP 3551336B1 EP 17825362 A EP17825362 A EP 17825362A EP 3551336 B1 EP3551336 B1 EP 3551336B1
Authority
EP
European Patent Office
Prior art keywords
powder
spraying head
electrode
transport direction
powder spraying
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.)
Active
Application number
EP17825362.1A
Other languages
German (de)
French (fr)
Other versions
EP3551336A1 (en
Inventor
André SAIU
Pascal GAUCH
Peter Taiana
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Soudronic AG
Original Assignee
Soudronic AG
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Filing date
Publication date
Application filed by Soudronic AG filed Critical Soudronic AG
Publication of EP3551336A1 publication Critical patent/EP3551336A1/en
Application granted granted Critical
Publication of EP3551336B1 publication Critical patent/EP3551336B1/en
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Classifications

    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
    • B05B1/26—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets
    • B05B1/262—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets with fixed deflectors
    • B05B1/267—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means with means for mechanically breaking-up or deflecting the jet after discharge, e.g. with fixed deflectors; Breaking-up the discharged liquid or other fluent material by impinging jets with fixed deflectors the liquid or other fluent material being deflected in determined directions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B13/00—Machines or plants for applying liquids or other fluent materials to surfaces of objects or other work by spraying, not covered by groups B05B1/00 - B05B11/00
    • B05B13/06—Machines or plants for applying liquids or other fluent materials to surfaces of objects or other work by spraying, not covered by groups B05B1/00 - B05B11/00 specially designed for treating the inside of hollow bodies
    • B05B13/0618—Machines or plants for applying liquids or other fluent materials to surfaces of objects or other work by spraying, not covered by groups B05B1/00 - B05B11/00 specially designed for treating the inside of hollow bodies only a part of the inside of the hollow bodies being treated
    • 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
    • B05B5/081—Plant for applying liquids or other fluent materials to objects specially adapted for treating 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
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/12—Plant for applying liquids or other fluent materials to objects specially adapted for coating the interior of hollow bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/02—Processes for applying liquids or other fluent materials performed by spraying
    • B05D1/04—Processes for applying liquids or other fluent materials performed by spraying involving the use of an electrostatic field
    • B05D1/06—Applying particulate materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D51/00—Making hollow objects
    • B21D51/16—Making hollow objects characterised by the use of the objects
    • B21D51/26—Making hollow objects characterised by the use of the objects cans or tins; Closing same in a permanent manner
    • B21D51/2676—Cans or tins having longitudinal or helical seams

Definitions

  • the invention relates to a powder spray head for spraying a coating powder and a powder coating system for coating a can body with powder according to the preambles of the independent claims. See for example WO2014 / 102258 .
  • Powder coating systems with powder spray heads for coating can bodies are known.
  • Such powder spray heads are essentially rod-shaped and have an external diameter such that a previously welded can body can enclose them and is thereby transported in a transport direction along the powder spray head.
  • at least part of the inner surface of the can body is coated with powder.
  • the weld seam of the can body is coated in this way in order to protect it against corrosion.
  • Coating with powder takes place on the basis of electrostatic charging of the powder particles.
  • a charging electrode is used which has a negative high voltage in relation to the frame which is at zero potential. Due to the electrostatic charging of the powder particles, they are deflected in the direction of the can body and adhere to it. In order to additionally support this deflection in the direction of the can body, another so-called guide electrode is used, which is also subjected to a negative voltage. As a result, the powder particles already negatively charged become repelled by the negatively charged lead electrode, which further supports the deflection of the powder in the direction of the can body.
  • a known powder coating system from the company Soudronic from Bergdietikon, Switzerland includes, among other things, a powder spray head in which the charging electrode and the guide electrode are designed as an electrode block.
  • a powder spray head for spraying a powder suitable for coating a can body
  • which powder spray head is designed such that, for coating at least part of an inner surface of the can body, the can body to be coated surrounds the powder spray head and can be moved along the powder spray head in a transport direction .
  • the interior of the powder spray head comprises a working space which has a working opening through which the powder can reach the inner surface of the can body.
  • it comprises a powder tube for providing the powder, the powder tube opening with a powder outlet in the working space of the powder spray head.
  • the powder tube is designed in such a way that it emits the powder essentially in the transport direction into the work space.
  • the lead electrode and the charging electrode have the same polarity.
  • the charging electrode is arranged in the area of the powder outlet and runs in a pointed shape on the powder side (in the direction of the powder flowing through the powder outlet).
  • the arrangement at the powder outlet, where the powder enters the working area ensures that the effect of the electric field on the powder flowing into the working area is increased.
  • the pointed configuration of the charging electrode causes a "concentration" of the electric field at the location where the powder flows through the powder outlet.
  • the guide electrode is plate-shaped and a flat side of the guide electrode is directed towards the working space.
  • This configuration and orientation of the guide electrode allows better detection of the powder located in the work space by the associated electrical field of the guide electrode. Due to the plate-shaped design of the electrode, a more homogeneous electric field with essentially parallel field lines is created in the interior of the working space, similar to a plate capacitor, which causes the powder to be deflected as uniformly as possible away from the guide electrode towards the can body.
  • the design of the charging electrode and the guide electrode consequently result in an improved deflection of the powder in the desired direction in the interaction, but also in isolation. This allows the powder to be fed to the can body more efficiently.
  • the stronger one Electrostatic charging of the powder which is related to the special arrangement and shape of the charging electrode, is not only relevant for the deflection of the powder, but also has the effect that the powder adheres better to the can body, in other words the separation efficiency is higher.
  • a higher quality can body is produced which is even more resistant to external influences, for example corrosion, caused by the later contents of the can.
  • the powder is charged evenly regardless of the particle size.
  • the guide electrode is preferably at such a first distance from the charging electrode in the transport direction that the electrical field of the guide electrode acts on the powder electrostatically charged by means of the charging electrode immediately after the powder has entered the work space.
  • This arrangement of the guide electrode has the advantage that no or only a minimal proportion of the powder particles can flow in a direction other than the can body.
  • the powder coating system according to the invention for coating the can body with powder comprises a powder spray head according to the invention. It also includes a powder delivery device for supplying the powder spray head with powder.
  • the powder feeder can be connected to the powder tube to provide the powder.
  • the powder coating system includes a powder recovery unit for suctioning off excess powder that accumulates during the coating process.
  • the powder recovery unit is arranged downstream of one or more suction nozzles of the powder spray head in the transport direction.
  • the powder coating system has the further advantage that the powder recovery unit can "collect” excess powder, which saves powder.
  • the powder coating system according to the invention is advantageously used for coating a weld seam of the can body.
  • the powder spray head in the work space has at least one wing for guiding the electrostatically charged powder through the work opening to the part of the inner surface of the can body to be coated. In this way, the powder can be guided even better in the direction of the working opening.
  • a plurality of wings are preferably provided, which are arranged one behind the other in the working space in the transport direction in order to capture all powder particles as possible. It is further preferred that the wing or wings are bent in the direction of the working opening. If several wings are present, they each have an ever larger effective area for discharging the electrostatically charged powder. This is a further measure to capture all powder particles as possible, because the powder jet is more concentrated when it enters the work area and expands as it continues. Consequently, the wings, which are getting wider in the transport direction, take this scatter into account.
  • plate-shaped means a flat piece of a hard material, in this case metal, equally thick everywhere, bounded on two opposite sides by a flat surface that is very extensive in relation to the thickness.
  • transport direction relates to a transport direction of the can bodies and is marked with the arrow z, which at the same time also designates the longitudinal axis of the powder spray head.
  • a "working space” refers to a recess in the powder spray head in which the powder is deflected towards the can body.
  • electrically neutral in this context relates to a material that is neither electrically negatively nor electrically positively charged or chargeable.
  • axial and radial refer to a cylindrical coordinate system with the axis z.
  • front relates to the direction of the arrow z and “rear” to the opposite direction.
  • bottom and “top” refer to the direction of gravity.
  • Fig. 1 shows a powder coating system 1 according to the invention with a powder spray head 2 according to the invention in a perspective view.
  • the powder coating system 1 also comprises a powder feed device 15 for supplying the powder spray head 2 with powder, and a powder recovery unit 16 that sucks excess powder from the powder spray head.
  • the arrow 4 shows a working opening of the powder spray head 2 through which powder can pass from a working space 11 to a can body 12.
  • blades 3 are arranged in the working space.
  • Three suction nozzles 5 are arranged downstream of the working space 4.
  • the powder coating system 1 off Fig. 1 also includes a controller (not shown) with which, inter alia, the variables described above are set or monitored. The control is therefore connected to the powder spray head 2, the powder feed device 15 and the powder recovery unit 16.
  • FIG. 11 shows a detailed view of part A of the powder spray head 2 from FIG Fig. 1 in sectional view and Fig. 3 a side sectional view of the detail Fig. 2 .
  • a piece of a powder tube 9 is shown, which ends with a powder outlet 9a.
  • the powder outlet 9a which, like the powder tube 9, is made of an electrically neutral material, represents the opening of the tube 9 in a working space 11.
  • the powder outlet 9a preferably extends in the transport direction z in a conically widening manner. This results in a better distribution of the powder in the work area.
  • the charging electrode 6 is arranged in the area of the powder outlet 9a and runs in a pointed shape on the powder side with a point 6a.
  • the charging electrode 6 is arranged below the powder outlet 9a. However, it could also be arranged further forward in the z-direction in the direction of the working space 11 or further back, which is illustrated by the term “in the area of the powder outlet”. It is preferably rod-shaped and its longitudinal axis is perpendicular to the transport direction z.
  • the charging electrode preferably extends with its tip in an opening in a wall of the powder outlet 9a essentially as far as an inner surface of the powder outlet 9a. This ensures that the charging electrode is arranged as close as possible to the powder.
  • the position of the charging electrode 6 and in particular the pointed shape allow an increased electrostatic charging of the powder when it enters the working space 11.
  • the pointed configuration of the charging electrode 6 at its upper extremity means that the associated electric field is concentrated in a small area within the powder outlet 9a.
  • the powder flowing past can be electrostatically charged more effectively than with previous solutions due to the higher electric field strength in the short time in which it flows past the charging electrode.
  • the powder spray head 2 further comprises a guide electrode 7, which is plate-shaped.
  • a flat side 7a of the lead electrode is directed towards the working space. Due to the flat shape of the guide electrode 7, it is achieved that a second electrical field is generated which is many times more extensive than the electrical field of the charging electrode 6.
  • the alignment of the guide electrode 7 (surface 7a) has the effect that the electric field lines run in such a way that the already electrostatically negatively charged powder in the working space 11 is repelled by the guide electrode 7, which is also negatively charged.
  • the guide electrode 7 can, however, also be formed from several pieces, in particular from several strips. Also a slightly convex or concave shape is conceivable as long as the side 7a of the guide electrode 7 facing the working space has a large extent.
  • a powder particle during flight through the working space 11 has, on the one hand, a speed component essentially in the (axial) transport direction z, which is predetermined by the powder conveyor device 15. For the sake of simplicity, a deviation due to radial scattering of the powder is neglected here.
  • the powder particle has a velocity component in the radial direction (that is, perpendicular to the direction z), which is caused by the electric field of the guide electrode 7.
  • the resulting directional vector of the powder particle therefore depends on the flow velocity into the working space 11, the electrostatic charge through the charging electrode 6 and the strength of the electric field of the guide electrode 7. Another factor is the particle size of the powder particle.
  • the guide electrode 7 has such a first axial distance D1 ( Fig. 3 ) from the charging electrode 6, that the electric field of the guide electrode 7 acts on the powder electrostatically charged by means of the charging electrode 6 immediately after the powder has entered the working space 11. In this way it is avoided that powder particles get a downward velocity component due to their weight force and can possibly fall onto the floor of the working space 11, which is undesirable.
  • the axial distance D1 depends on the above-mentioned factors (flow velocity into the working space 11, electrostatic charge and strength of the electric field of the lead electrode 7). It is conceivable (not shown) that the guide electrode 7 is designed to be displaceable in the z direction in order to have a further degree of freedom in the event of the variation of one of the above parameters.
  • the guide electrode 7 is arranged outside the working space 11 and is preferably separated therefrom at least by means of an insulator 8. This prevents the lead electrode 7 from being coated with a powder layer over time due to the “dirty” working environment. This can e.g. occur due to turbulence or in particular when the electrical field of the guide electrode 7 is switched off, since the powder particles still flying in the work space at this point in time no longer experience any force that would compensate for their own weight and thus fall down. A layer which is formed in this way would change the electrical properties of the guide electrode 7 by forming a dielectric powder layer, which is not desirable.
  • the guide electrode 7 is preferably arranged at a greater distance from the longitudinal axis z of the powder spray head 2 than the tip 6a of the charging electrode 6. This measure serves to avoid impairing the electric field (corona effect) of the charging electrode, since otherwise the powder particles will not be charged.
  • the tip of the charging electrode must be as free as possible from other electrical fields.
  • the guide electrode 7 extends preferably over the end of the working space 11 in the transport direction, for. This will ensure that the entire Powder along the entire longitudinal extent of the work space 11 (and in particular the work opening 4) is detected by the electric field of the guide electrode 7. This is explained in more detail below in connection with the wings 3 of the powder spray head 2.
  • three wings 3 are provided for guiding the electrostatically charged powder through the work opening 4 to the part of the inner surface of the can body 12 to be coated.
  • the wings 3 are made of an electrically neutral material and are arranged one behind the other in the working space 11 in the transport direction z.
  • the powder is deflected upwards by the wings 3 (arrows 10a-d). So your job is to help deflect the powder.
  • the number of blades 3 takes into account the fact that not all powder particles fly in the z-direction at the same speed and consequently their deflection also takes place differently.
  • the different speed of the powder particles is related to the fact that powder bodies collide in the powder flow, which changes their speed.
  • the powder flow is scattered when exiting the powder outlet, whereby the powder particles get different axial components of the speed.
  • the varying mass of the powder particles also plays a role. For these reasons, some powder particles cover a longer distance in the working area than other powder particles. This is the reason why the guide electrode 7 preferably extends to the end of the work space 11.
  • the wings 3 are bent in the direction of the working opening 4 in order to enable the powder to flow past them as laminar as possible.
  • a laminar flow is fundamentally desirable in order to ensure the most even possible powder application on the inner surface of the can body 12. This avoids the time covered for Stretch of the powder particles is not lengthened by any turbulence, while no such delay occurs for other powder particles.
  • the shape of the work space 11 per se can also be designed differently from this point of view than in the exemplary illustrations. In this context is off Fig. 2 and 3 It can also be seen that the front wall of the working space 11 (at arrow 10d), viewed in the transport direction z, has the same or a similar shape as the wings 3.
  • these wings preferably each have an ever larger effective area in the transport direction z for the discharge of the electrostatically charged powder. This is related to the fact that, due to the physically induced scattering of the powder flow, this powder flow on the foremost wing 3 (at arrow 10c) is wider than at the rearmost wing 3 (at arrow 10a). This area variation therefore also causes an effective deflection further forward (in the z-direction).
  • the blades 3 preferably have a second axial distance D2 from the charging electrode 6 in the transport direction z, which is greater than the first distance D1.
  • the second axial distance D2 is understood as the distance from a starting point of a first wing 3, which is closest to the charging electrode 6, to a z-position of the charging electrode 6. This measure is used because, due to the design, the powder arrives in the working space 11 in "bursts". This means that the powder flow does not have a constant density over time, but that the density is approximately sinusoidal. Such a course would have the effect that the coating would also be wavy, i.e. with thicker and thinner sections, which is undesirable. In the “extensive” area up to the wings, the working space 11 brings about a uniformization of the density of the powder flow, so that it arrives at the can body 12 with as constant a density as possible.
  • Fig. 4 shows a cross-sectional view of the powder spray head 2, seen in direction B.
  • FIG Fig. 3 thus opposite to the transport direction z of the can body 12.
  • two sealing lips 14 are shown, which were not shown in the previous figures for reasons of clarity.
  • These sealing lips 14 are attached to a contour of the working opening 4. This can be a single sealing lip or several sealing lips.
  • a free end of the sealing lip 14 rests against the inner wall of the can body 12, so that only the part of the inner wall of the can body 12 to be coated can come into contact with the powder.
  • the coating is to be applied to the weld seam 12a as protection against corrosion, as mentioned at the beginning.
  • the working opening 4 is configured in a correspondingly slot-shaped manner in order to expose only the area around the weld seam 12a.
  • the sealing lips 14 rest on the inner wall of the can body 12, to the side of the weld seam, so that no coating powder can get to other areas of the inner wall and thus only the desired area is coated.
  • the working opening 4 and / or the sealing lips 14 can have a different shape, depending on what is to be coated.
  • the shape and extent of the guide electrode can vary according to the shape of the working opening 4.
  • the powder spray head 2 comprises a high-voltage generator (not shown) which is designed such that it generates a controllable negative voltage between 8 and 40 kV between the charging electrode 6 and the can body 12, which is grounded.
  • the generator can also be designed in such a way that it also generates a controllable negative voltage between 8 and 40 kV between the guide electrode 7 and the can body 12.
  • two different generators can be used.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Electrostatic Spraying Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)

Description

Gebiet der ErfindungField of invention

Die Erfindung betrifft einen Pulversprühkopf zum Sprühen eines Beschichtungspulvers und eine Pulverbeschichtungsanlage zur Beschichtung einer Dosenzarge mit Pulver gemäss den Oberbegriffen der unabhängigen Ansprüche. Siehe zum Beispiel WO2014/102258 .The invention relates to a powder spray head for spraying a coating powder and a powder coating system for coating a can body with powder according to the preambles of the independent claims. See for example WO2014 / 102258 .

Hintergrundbackground

Pulverbeschichtungsanlagen mit Pulversprühköpfen zur Beschichtung von Dosenzargen sind bekannt. Solche Pulversprühköpfe sind im Wesentlichen stabförmig und haben einen derartigen Aussendurchmesser, dass eine vorgängig geschweisste Dosenzarge sie umschliessen kann und dabei in eine Transportrichtung entlang dem Pulversprühkopf transportiert wird. Während dieser translatorischen Bewegung wird mindestens ein Teil der Innenfläche der Dosenzarge mit Pulver beschichtet. Insbesondere wird auf diese Weise die Schweissnaht der Dosenzarge beschichtet, um sie gegen Korrosion zu schützen.Powder coating systems with powder spray heads for coating can bodies are known. Such powder spray heads are essentially rod-shaped and have an external diameter such that a previously welded can body can enclose them and is thereby transported in a transport direction along the powder spray head. During this translational movement, at least part of the inner surface of the can body is coated with powder. In particular, the weld seam of the can body is coated in this way in order to protect it against corrosion.

Die Beschichtung mit Pulver geschieht auf der Basis elektrostatischer Aufladung der Pulverteilchen. Dabei wird eine Ladeelektrode verwendet, welche eine negative Hochspannung bezogen auf die auf Nullpotential liegende Zarge hat. Aufgrund der elektrostatischen Aufladung der Pulverteilchen werden diese in Richtung der Dosenzarge abgelenkt und haften an diese. Um zusätzlich diese Ablenkung in Richtung der Dosenzarge zu unterstützen, wird eine weitere sogenannte Führungselektrode verwendet, welche ebenfalls mit einer negativen Spannung beaufschlagt ist. Folglich werden die bereits negativ aufgeladenen Pulverteilchen von der negativ geladenen Führungselektrode abgestossen, was die Ablenkung des Pulvers in Richtung der Dosenzarge weiter unterstützt.Coating with powder takes place on the basis of electrostatic charging of the powder particles. A charging electrode is used which has a negative high voltage in relation to the frame which is at zero potential. Due to the electrostatic charging of the powder particles, they are deflected in the direction of the can body and adhere to it. In order to additionally support this deflection in the direction of the can body, another so-called guide electrode is used, which is also subjected to a negative voltage. As a result, the powder particles already negatively charged become repelled by the negatively charged lead electrode, which further supports the deflection of the powder in the direction of the can body.

Eine bekannte Pulverbeschichtungsanlage der Firma Soudronic aus Bergdietikon, Schweiz umfasst unter anderem einen Pulversprühkopf bei dem die Ladeelektrode und die Führungselektrode als Elektrodenblock ausgeführt sind.A known powder coating system from the company Soudronic from Bergdietikon, Switzerland includes, among other things, a powder spray head in which the charging electrode and the guide electrode are designed as an electrode block.

Darstellung der ErfindungPresentation of the invention

Es ist Aufgabe der Erfindung einen Pulversprühkopf und eine Pulverbeschichtungsanlage bereitzustellen, welche eine verbesserte Haftung des Pulvers an der Dosenzarge ermöglicht.It is the object of the invention to provide a powder spray head and a powder coating system which enables improved adhesion of the powder to the can body.

Diese Aufgabe wird mittels eines Pulversprühkopfes und einer Pulverbeschichtungsanlage gemäss den unabhängigen Ansprüchen gelöst.This object is achieved by means of a powder spray head and a powder coating system according to the independent claims.

Demgemäss wird ein erfindungsgemässer Pulversprühkopf zum Sprühen eines für eine Beschichtung einer Dosenzarge geeigneten Pulvers bereitgestellt, welcher Pulversprühkopf derart ausgestaltet ist, dass zur Beschichtung mindestens eines Teils einer Innenfläche der Dosenzarge, die zu beschichtende Dosenzarge den Pulversprühkopf umschliesst und entlang dem Pulversprühkopf in einer Transportrichtung bewegbar ist. Der Pulversprühkopf umfasst in seinem Inneren einen Arbeitsraum, der eine Arbeitsöffnung aufweist, durch welche das Pulver zur Innenfläche der Dosenzarge gelangen kann. Ferner umfasst er ein Pulverrohr zur Bereitstellung des Pulvers, wobei das Pulverrohr mit einem Pulverauslass im Arbeitsraum des Pulversprühkopfes mündet. Das Pulverrohr ist derart ausgestaltet, dass es das Pulver im Wesentlichen in Transportrichtung in den Arbeitsraum abgibt. Weiter umfasst er eine Ladeelektrode zum Beaufschlagen des Pulvers mit einer elektrostatischen Aufladung und eine Führungselektrode, welche in Transportrichtung stromabwärts der Ladeelektrode und unterhalb des Arbeitsraums angeordnet ist, um das im Arbeitsraum befindliche, bereits elektrostatisch aufgeladene Pulver im Wesentlichen in Richtung der Arbeitsöffnung abzulenken. Die Führungselektrode und die Ladeelektrode besitzen eine gleiche Polung.Accordingly, a powder spray head according to the invention for spraying a powder suitable for coating a can body is provided, which powder spray head is designed such that, for coating at least part of an inner surface of the can body, the can body to be coated surrounds the powder spray head and can be moved along the powder spray head in a transport direction . The interior of the powder spray head comprises a working space which has a working opening through which the powder can reach the inner surface of the can body. Furthermore, it comprises a powder tube for providing the powder, the powder tube opening with a powder outlet in the working space of the powder spray head. The powder tube is designed in such a way that it emits the powder essentially in the transport direction into the work space. It further comprises a charging electrode for applying an electrostatic charge to the powder and a guide electrode which is downstream of the charging electrode in the transport direction and is arranged below the work space in order to deflect the already electrostatically charged powder located in the work space essentially in the direction of the work opening. The lead electrode and the charging electrode have the same polarity.

Die Ladeelektrode ist im Bereich des Pulverauslasses angeordnet und verläuft pulverseitig (in Richtung des durch den Pulverauslass strömenden Pulvers) spitzförmig. Durch die Anordnung am Pulverauslass, wo das Pulver in den Arbeitsraum eintritt, wird erreicht dass die Einwirkung des elektrischen Feldes auf das in den Arbeitsraum einströmende Pulver vergrössert wird. Ferner bewirkt die spitzförmige Ausgestaltung der Ladeelektrode eine "Konzentration" des elektrischen Feldes am Ort wo das Pulver durch den Pulverauslass strömt. Diese Massnahmen bewirken eine Erhöhung der elektrostatischen Aufladung des Pulvers, so dass es nach Eintritt in den Arbeitsraum eine stärkere Ablenkung in Richtung der Arbeitsöffnung erfährt.The charging electrode is arranged in the area of the powder outlet and runs in a pointed shape on the powder side (in the direction of the powder flowing through the powder outlet). The arrangement at the powder outlet, where the powder enters the working area, ensures that the effect of the electric field on the powder flowing into the working area is increased. Furthermore, the pointed configuration of the charging electrode causes a "concentration" of the electric field at the location where the powder flows through the powder outlet. These measures cause an increase in the electrostatic charge of the powder, so that after entering the work area it experiences a stronger deflection in the direction of the work opening.

Zusätzlich oder alternativ dazu ist die Führungselektrode plattenförmig und eine flache Seite der Führungselektrode ist zum Arbeitsraum hin gerichtet. Diese Ausgestaltung und Orientierung der Führungselektrode erlaubt eine bessere Erfassung des im Arbeitsraum befindlichen Pulvers durch das zugehörige elektrische Feld der Führungselektrode. Aufgrund der plattenförmigen Ausgestaltung der Elektrode entsteht im Inneren des Arbeitsraums ein homogeneres elektrisches Feld mit im Wesentlichen parallelen Feldlinien, ähnlich wie bei einem Plattenkondensator, das eine möglichst einheitliche Ablenkung des Pulvers von der Führungselektrode weg zur Dosenzarge hin bewirkt.Additionally or alternatively, the guide electrode is plate-shaped and a flat side of the guide electrode is directed towards the working space. This configuration and orientation of the guide electrode allows better detection of the powder located in the work space by the associated electrical field of the guide electrode. Due to the plate-shaped design of the electrode, a more homogeneous electric field with essentially parallel field lines is created in the interior of the working space, similar to a plate capacitor, which causes the powder to be deflected as uniformly as possible away from the guide electrode towards the can body.

Die Ausgestaltung der Ladeelektrode und der Führungselektrode bewirken folglich im Zusammenspiel, aber auch für sich genommen, eine verbesserte Ablenkung des Pulvers in die gewünschte Richtung. Dadurch kann das Pulver effizienter an die Dosenzarge geführt werden. Die stärkere elektrostatische Aufladung des Pulvers, die mit der speziellen Anordnung und Form der Ladeelektrode zusammenhängt, ist aber nicht nur für die Ablenkung des Pulvers relevant, sondern sie bewirkt auch, dass das Pulver besser an der Dosenzarge haftet, mit anderen Worten ist der Abscheidewirkungsgrad höher. Dadurch wird eine Dosenzarge höherer Qualität hergestellt, die noch resistenter gegen äussere Einflüsse, z.B. Korrosion, hervorgerufen durch den späteren Inhalt der Dose, ist. Ausserdem wird das Pulver unabhängig von der Partikelgrösse gleichmässig aufgeladen.The design of the charging electrode and the guide electrode consequently result in an improved deflection of the powder in the desired direction in the interaction, but also in isolation. This allows the powder to be fed to the can body more efficiently. The stronger one Electrostatic charging of the powder, which is related to the special arrangement and shape of the charging electrode, is not only relevant for the deflection of the powder, but also has the effect that the powder adheres better to the can body, in other words the separation efficiency is higher. As a result, a higher quality can body is produced which is even more resistant to external influences, for example corrosion, caused by the later contents of the can. In addition, the powder is charged evenly regardless of the particle size.

Bevorzugt hat die Führungselektrode in Transportrichtung einen derartigen ersten Abstand von der Ladeelektrode, dass das elektrische Feld der Führungselektrode auf das mittels der Ladeelektrode elektrostatisch aufgeladene Pulver unmittelbar nach Eintritt des Pulvers in den Arbeitsraum einwirkt. Diese Anordnung der Führungselektrode hat den Vorteil, dass keine oder nur ein minimaler Anteil der Pulverpartikel in eine andere Richtung als zur Dosenzarge hinströmen kann.The guide electrode is preferably at such a first distance from the charging electrode in the transport direction that the electrical field of the guide electrode acts on the powder electrostatically charged by means of the charging electrode immediately after the powder has entered the work space. This arrangement of the guide electrode has the advantage that no or only a minimal proportion of the powder particles can flow in a direction other than the can body.

Die erfindungsgemässe Pulverbeschichtungsanlage zur Beschichtung der Dosenzarge mit Pulver umfasst einen erfindungsgemässen Pulversprühkopf. Ferner umfasst sie ein Pulverfördergerät für eine Versorgung des Pulversprühkopfes mit Pulver. Das Pulverfördergerät ist zur Bereitstellung des Pulvers am Pulverrohr anschliessbar. Schliesslich umfasst die Pulverbeschichtungsanlage eine Pulverrückgewinnungseinheit zum Absaugen von überschüssigem Pulver, das während der Beschichtung anfällt. Die Pulverrückgewinnungseinheit ist in Transportrichtung stromabwärts von einer oder mehreren Absaugdüsen des Pulversprühkopfes angeordnet.The powder coating system according to the invention for coating the can body with powder comprises a powder spray head according to the invention. It also includes a powder delivery device for supplying the powder spray head with powder. The powder feeder can be connected to the powder tube to provide the powder. Finally, the powder coating system includes a powder recovery unit for suctioning off excess powder that accumulates during the coating process. The powder recovery unit is arranged downstream of one or more suction nozzles of the powder spray head in the transport direction.

Ausser den bereits genannten Vorteilen des Pulversprühkopfes hat die Pulverbeschichtungsanlage den weiteren Vorteil, dass die Pulverrückgewinnungseinheit überschüssiges Pulver wieder "einsammeln" kann, wodurch Pulver gespart wird.In addition to the advantages of the powder spray head already mentioned, the powder coating system has the further advantage that the powder recovery unit can "collect" excess powder, which saves powder.

Mit Vorteil wird die erfindungsgemässe Pulverbeschichtungsanlage für die Beschichtung einer Schweissnaht der Dosenzarge verwendet.The powder coating system according to the invention is advantageously used for coating a weld seam of the can body.

In einer Ausführungsform besitzt der Pulversprühkopf im Arbeitsraum mindestens einen Flügel zum Leiten des elektrostatisch aufgeladenen Pulvers durch die Arbeitsöffnung an den zu beschichtenden Teil der Innenfläche der Dosenzarge. Auf diese Weise kann das Pulver noch besser in Richtung der Arbeitsöffnung geleitet werden.In one embodiment, the powder spray head in the work space has at least one wing for guiding the electrostatically charged powder through the work opening to the part of the inner surface of the can body to be coated. In this way, the powder can be guided even better in the direction of the working opening.

Bevorzugt sind mehrere Flügel vorgesehen, welche im Arbeitsraum in Transportrichtung hintereinander angeordnet sind, um möglichst alle Pulverpartikel zu erfassen. Es ist weiter bevorzugt dass der Flügel oder die Flügel in Richtung der Arbeitsöffnung gebogen sind. Vorzugsweise besitzen bei Anwesenheit mehrerer Flügel diese jeweils eine immer grössere Wirkfläche für die Ableitung des elektrostatisch aufgeladenen Pulvers. Dies ist eine weitere Massnahme zur Erfassung möglichst aller Pulverpartikel, denn der Pulverstrahl ist beim Eintritt in den Arbeitsraum konzentrierter und dehnt sich im weiteren Verlauf aus. Folglich berücksichtigen die in Transportrichtung immer breiteren Flügel diese Streuung.A plurality of wings are preferably provided, which are arranged one behind the other in the working space in the transport direction in order to capture all powder particles as possible. It is further preferred that the wing or wings are bent in the direction of the working opening. If several wings are present, they each have an ever larger effective area for discharging the electrostatically charged powder. This is a further measure to capture all powder particles as possible, because the powder jet is more concentrated when it enters the work area and expands as it continues. Consequently, the wings, which are getting wider in the transport direction, take this scatter into account.

Kurze Beschreibung der ZeichnungenBrief description of the drawings

Weitere Ausgestaltungen, Vorteile und Anwendungen der Erfindung ergeben sich aus den abhängigen Ansprüchen und aus der nun folgenden Beschreibung anhand der Figuren. Dabei zeigen:

  • Fig. 1 eine perspektivische Ansicht einer erfindungsgemässen Pulverbeschichtungsanlage mit einem erfindungsgemässen Pulversprühköpf,
  • Fig. 2 eine Detailansicht eines Teils A des Pulversprühkopfes aus Fig. 1 in Schnittansicht,
  • Fig. 3 eine seitliche Schnittansicht des Details aus Fig. 2, und
  • Fig. 4 eine Querschnittansicht des Pulversprühkopf, gesehen in Richtung B aus Fig. 3.
Further refinements, advantages and applications of the invention emerge from the dependent claims and from the description that follows based on the figures. Show:
  • Fig. 1 a perspective view of a powder coating system according to the invention with a powder spray head according to the invention,
  • Fig. 2 a detailed view of part A of the powder spray head Fig. 1 in sectional view,
  • Fig. 3 a side sectional view of the detail Fig. 2 , and
  • Fig. 4 a cross-sectional view of the powder spray head, seen in direction B. Fig. 3 .

Weg(e) zur Ausführung der ErfindungWay (s) for carrying out the invention Definitionen und Anmerkungen:Definitions and Notes:

Im vorliegenden Zusammenhang bedeutet der Begriff plattenförmig ein flaches, überall gleich dickes, auf zwei gegenüberliegenden Seiten von je einer im Verhältnis zur Dicke sehr ausgedehnten ebenen Fläche begrenztes Stück eines harten Materials, in diesem Fall Metall.In the present context, the term plate-shaped means a flat piece of a hard material, in this case metal, equally thick everywhere, bounded on two opposite sides by a flat surface that is very extensive in relation to the thickness.

Der Begriff "geeignet" in Zusammenhang mit Pulvers definiert jedes Pulver, das der Fachmann für die Beschichtung von Metallflächen verwenden würde.The term “suitable” in connection with powder defines any powder which the person skilled in the art would use for the coating of metal surfaces.

Der Begriff "Transportrichtung" bezieht sich auf eine Transportrichtung der Dosenzargen und ist mit dem Pfeil z gekennzeichnet, der gleichzeitig auch die Längsachse des Pulversprühkopfes bezeichnet.The term "transport direction" relates to a transport direction of the can bodies and is marked with the arrow z, which at the same time also designates the longitudinal axis of the powder spray head.

Ein "Arbeitsraum" bezeichnet eine Ausnehmung im Pulversprühkopf, in der das Pulver zur Dosenzarge hin abgelenkt wird.A "working space" refers to a recess in the powder spray head in which the powder is deflected towards the can body.

Der Begriff "elektrisch neutral" ist in diesem Zusammenhang auf ein Material bezogen, das weder elektrisch negativ noch elektrisch positiv geladen bzw. aufladbar ist.The term “electrically neutral” in this context relates to a material that is neither electrically negatively nor electrically positively charged or chargeable.

Die Begriffe "axial" und "radial" beziehen sich auf ein zylindrisches Koordinatensystem mit der Achse z. Entsprechend bezieht sich der Begriff "vorne" auf die Richtung des Pfeils z und "hinten" auf die Gegenrichtung. Die Begriffe "unten" und "oben" beziehen sich auf die Richtung der Schwerkraft.The terms "axial" and "radial" refer to a cylindrical coordinate system with the axis z. Correspondingly, the term “front” relates to the direction of the arrow z and “rear” to the opposite direction. The terms "bottom" and "top" refer to the direction of gravity.

Fig. 1 zeigt eine erfindungsgemässe Pulverbeschichtungsanlage 1 mit einem erfindungsgemässen Pulversprühkopf 2 in perspektivischer Ansicht. Ferner umfasst die Pulverbeschichtungsanlage 1 ein Pulverfördergerät 15 für eine Versorgung des Pulversprühkopfes 2 mit Pulver, und eine Pulverrückgewinnungseinheit 16, welche überschüssiges Pulver aus dem Pulversprühkopf absaugt. Ferner ist mit dem Pfeil 4 eine Arbeitsöffnung des Pulversprühkopfes 2 dargestellt, durch die Pulver aus einem Arbeitsraum 11 an eine Dosenzarge 12 gelangen kann. Ferner sind im Arbeitsraum 11 Flügel 3 angeordnet. Drei Absaugdüsen 5 sind stromabwärts des Arbeitsraums 4 angeordnet. Diese Elemente werden im Folgenden in Zusammenhang mit dem Pulversprühkopf 2 im Detail beschrieben. Ausserdem zeigt Fig. 1 die Dosenzarge 12 in einer Position in der ihre geschweisste Längsnaht 12a schon beschichtet wurde, wobei die Beschichtung an der Innenfläche der Dosenzarge vorgenommen wurde und daher in der Figur nicht sichtbar ist. Fig. 1 shows a powder coating system 1 according to the invention with a powder spray head 2 according to the invention in a perspective view. The powder coating system 1 also comprises a powder feed device 15 for supplying the powder spray head 2 with powder, and a powder recovery unit 16 that sucks excess powder from the powder spray head. Furthermore, the arrow 4 shows a working opening of the powder spray head 2 through which powder can pass from a working space 11 to a can body 12. Furthermore, blades 3 are arranged in the working space. Three suction nozzles 5 are arranged downstream of the working space 4. These elements are described in detail below in connection with the powder spray head 2. Also shows Fig. 1 the can body 12 in a position in which its welded longitudinal seam 12a has already been coated, the coating being carried out on the inner surface of the can body and therefore not visible in the figure.

Die Pulverbeschichtungsanlage 1 aus Fig. 1 umfasst ferner eine Steuerung (nicht gezeigt) mit der unter anderem die oben beschriebenen Variablen eingestellt bzw. überwacht werden. Die Steuerung ist also mit dem Pulversprühkopf 2 dem Pulverfördergerät 15 und der Pulverrückgewinnungseinheit 16 verbunden.The powder coating system 1 off Fig. 1 also includes a controller (not shown) with which, inter alia, the variables described above are set or monitored. The control is therefore connected to the powder spray head 2, the powder feed device 15 and the powder recovery unit 16.

Fig. 2 zeigt eine Detailansicht eines Teils A des Pulversprühkopfes 2 aus Fig. 1 in Schnittansicht und Fig. 3 eine seitliche Schnittansicht des Details aus Fig. 2. Fig. 2 FIG. 11 shows a detailed view of part A of the powder spray head 2 from FIG Fig. 1 in sectional view and Fig. 3 a side sectional view of the detail Fig. 2 .

In den Figuren ist der Weg des Pulvers mittels der Pfeile 10, 10a-d schematisch dargestellt.In the figures, the path of the powder is shown schematically by means of arrows 10, 10a-d.

Links in den Figuren ist ein Stück eines Pulverrohrs 9 gezeigt, das mit einem Pulverauslass 9a endet. Der Pulverauslass 9a, der wie das Pulverrohr 9 aus einem elektrisch neutralen Material hergestellt ist, stellt die Mündung des Rohrs 9 in einem Arbeitsraum 11 dar. Vorzugsweise erstreckt sich der Pulverauslass 9a in Transportrichtung z auf konisch ausweitende Weise. Dadurch wird eine bessere Verteilung des Pulvers im Arbeitsraum erreicht.On the left in the figures, a piece of a powder tube 9 is shown, which ends with a powder outlet 9a. The powder outlet 9a, which, like the powder tube 9, is made of an electrically neutral material, represents the opening of the tube 9 in a working space 11. The powder outlet 9a preferably extends in the transport direction z in a conically widening manner. This results in a better distribution of the powder in the work area.

Die Ladeelektrode 6 ist im Bereich des Pulverauslasses 9a angeordnet und verläuft pulverseitig spitzförmig mit einer Spitze 6a. Die Ladeelektrode 6 ist unterhalb des Pulverauslasses 9a angeordnet. Sie könnte aber auch in z-Richtung weiter vorne in Richtung des Arbeitsraums 11 oder weiter hinten angeordnet sein, was durch den Begriff "im Bereich des Pulverauslasses" verdeutlicht ist. Sie ist vorzugsweise stabförmig und ihre Längsachse ist senkrecht zur Transportrichtung z. Vorzugsweise erstreckt sich die Ladeelektrode mit ihrer Spitze in einer Öffnung in einer Wand des Pulverauslasses 9a im Wesentlichen bis zur einer Innenfläche des Pulverauslasses 9a. Dadurch wird erreicht, dass die Ladeelektrode so nah wie möglich am Pulver angeordnet ist. Die Lage der Ladeelektrode 6 und insbesondere die spitze Form ermöglichen eine erhöhte elektrostatische Aufladung des Pulvers, wenn es in den Arbeitsraum 11 eintritt. Wie bereits angemerkt, bedeutet die spitze Ausgestaltung der Ladeelektrode 6 an ihrer oberen Extremität eine Konzentrierung des zugehörigen elektrischen Feldes auf einen kleinen Bereich innerhalb des Pulverauslasses 9a. Daraus resultiert dass das vorbeiströmende Pulver aufgrund der höheren elektrischen Feldstärke in der kurzen Zeit, in der es an der Ladeelektrode vorbeiströmt effektiver als bei bisherigen Lösungen elektrostatisch aufgeladen werden kann.The charging electrode 6 is arranged in the area of the powder outlet 9a and runs in a pointed shape on the powder side with a point 6a. The charging electrode 6 is arranged below the powder outlet 9a. However, it could also be arranged further forward in the z-direction in the direction of the working space 11 or further back, which is illustrated by the term “in the area of the powder outlet”. It is preferably rod-shaped and its longitudinal axis is perpendicular to the transport direction z. The charging electrode preferably extends with its tip in an opening in a wall of the powder outlet 9a essentially as far as an inner surface of the powder outlet 9a. This ensures that the charging electrode is arranged as close as possible to the powder. The position of the charging electrode 6 and in particular the pointed shape allow an increased electrostatic charging of the powder when it enters the working space 11. As already noted, the pointed configuration of the charging electrode 6 at its upper extremity means that the associated electric field is concentrated in a small area within the powder outlet 9a. As a result, the powder flowing past can be electrostatically charged more effectively than with previous solutions due to the higher electric field strength in the short time in which it flows past the charging electrode.

Ferner umfasst der Pulversprühkopf 2 eine Führungselektrode 7, welche plattenförmig ist. Eine flache Seite 7a der Führungselektrode ist zum Arbeitsraum hin gerichtet. Aufgrund der flachen Form der Führungselektrode 7 wird erreicht, dass ein zweites elektrisches Feld erzeugt wird, welches um ein Vielfaches ausgedehnter als das elektrische Feld der Ladeelektrode 6 ist. Die Ausrichtung der Führungselektrode 7 (Fläche 7a) bewirkt, dass die elektrischen Feldlinien derart verlaufen, dass das bereits elektrostatisch negativ aufgeladene Pulver im Arbeitsraum 11 von der Führungselektrode 7, die auch negativ geladen ist, abgestossen werden. Die Führungselektrode 7 kann aber auch aus mehreren Stücken, insbesondere aus mehreren Streifen, gebildet sein. Auch eine leicht konvex oder konkave Form ist denkbar, solange die dem Arbeitsraum zugewandte Seite 7a der Führungselektrode 7 eine grosse Ausdehnung hat. Dadurch wird eine Ablenkung des Pulvers nach oben in Richtung der Arbeitsöffnung 4 erreicht. Folglich besitzt ein Pulverteilchen während des Flugs durch den Arbeitsraum 11 einerseits eine Geschwindigkeitskomponente im Wesentlichen in (axialer) Transportrichtung z, die vom Pulverfördergerät 15 vorgegeben ist. Eine Abweichung wegen einer radialen Streuung des Pulvers wird hier der Einfachheit halber vernachlässigt. Andererseits besitzt das Pulverteilchen eine Geschwindigkeitskomponente in radialer Richtung (also senkrecht zur Richtung z), die durch das elektrische Feld der Führungselektrode 7 verursacht wird. Der resultierende Richtungsvektor des Pulverteilchens hängt also von der Einströmungsgeschwindigkeit in den Arbeitsraum 11, der elektrostatischen Aufladung durch die Ladeelektrode 6 und der Stärke des elektrischen Feldes der Führungselektrode 7 ab. Ein weiterer Faktor ist die Teilchengrösse des Pulverpartikels. Auf diese Grösse wird aber im vorliegenden Zusammenhang nicht eingegangen, da die Verwendung eines herkömmlichen Standardpulvers vorausgesetzt wird. Vielmehr werden die oben genannten Grössen variiert, um der Teilchengrösse (und folglich Masse) des Pulvers Rechnung zu tragen. Die Wahl einer anderen Partikelgrösse für das Pulver ist aber auch denkbar.The powder spray head 2 further comprises a guide electrode 7, which is plate-shaped. A flat side 7a of the lead electrode is directed towards the working space. Due to the flat shape of the guide electrode 7, it is achieved that a second electrical field is generated which is many times more extensive than the electrical field of the charging electrode 6. The alignment of the guide electrode 7 (surface 7a) has the effect that the electric field lines run in such a way that the already electrostatically negatively charged powder in the working space 11 is repelled by the guide electrode 7, which is also negatively charged. The guide electrode 7 can, however, also be formed from several pieces, in particular from several strips. Also a slightly convex or concave shape is conceivable as long as the side 7a of the guide electrode 7 facing the working space has a large extent. As a result, the powder is deflected upwards in the direction of the working opening 4. Consequently, a powder particle during flight through the working space 11 has, on the one hand, a speed component essentially in the (axial) transport direction z, which is predetermined by the powder conveyor device 15. For the sake of simplicity, a deviation due to radial scattering of the powder is neglected here. On the other hand, the powder particle has a velocity component in the radial direction (that is, perpendicular to the direction z), which is caused by the electric field of the guide electrode 7. The resulting directional vector of the powder particle therefore depends on the flow velocity into the working space 11, the electrostatic charge through the charging electrode 6 and the strength of the electric field of the guide electrode 7. Another factor is the particle size of the powder particle. However, this parameter is not discussed in the present context, since the use of a conventional standard powder is assumed. Rather, the sizes mentioned above are varied in order to take into account the particle size (and consequently the mass) of the powder. The choice of a different particle size for the powder is also conceivable.

Die Führungselektrode 7 hat in Transportrichtung einen derartigen ersten axialen Abstand D1 (Fig. 3) von der Ladeelektrode 6, dass das elektrische Feld der Führungselektrode 7 auf das mittels der Ladeelektrode 6 elektrostatisch aufgeladene Pulver unmittelbar nach Eintritt des Pulvers in den Arbeitsraum 11 einwirkt. Auf diese Weise wird vermieden, dass Pulverteilchen aufgrund ihrer Gewichtskraft eine Geschwindigkeitskomponente nach unten bekommen und ggf. auf den Boden des Arbeitsraums 11 fallen können, was unerwünscht ist. Der axiale Abstand D1 hängt von den oben genannten Faktoren ab (Einströmungsgeschwindigkeit in den Arbeitsraum 11, elektrostatische Aufladung und Stärke des elektrischen Feldes der Führungselektrode 7). Es ist denkbar (nicht gezeigt) dass die Führungselektrode 7 in z-Richtung verschiebbar ausgestaltet ist, um einen weiteren Freiheitsgrad im Falle der Variation eines der obigen Parameter zu haben. Durch geeignete Wahl des axialen Abstands D1 wird also erreicht dass die Pulverteilchen sofort bei Eintritt in den Arbeitsraum 11 vom elektrischen Feld der Führungselektrode 7 "übernommen" werden und folglich sofort eine Ablenkung nach oben erfahren.The guide electrode 7 has such a first axial distance D1 ( Fig. 3 ) from the charging electrode 6, that the electric field of the guide electrode 7 acts on the powder electrostatically charged by means of the charging electrode 6 immediately after the powder has entered the working space 11. In this way it is avoided that powder particles get a downward velocity component due to their weight force and can possibly fall onto the floor of the working space 11, which is undesirable. The axial distance D1 depends on the above-mentioned factors (flow velocity into the working space 11, electrostatic charge and strength of the electric field of the lead electrode 7). It is conceivable (not shown) that the guide electrode 7 is designed to be displaceable in the z direction in order to have a further degree of freedom in the event of the variation of one of the above parameters. By a suitable choice of the axial distance D1 it is achieved that the powder particles are "taken over" by the electric field of the guide electrode 7 immediately upon entering the working space 11 and consequently experience an upward deflection immediately.

Die Führungselektrode 7 ist ausserhalb des Arbeitsraums 11 angeordnet und ist vorzugsweise mindestens mittels eines Isolators 8 von diesem getrennt. Dadurch wird vermieden, dass die Führungselektrode 7 mit der Zeit aufgrund der "schmutzigen" Arbeitsumgebung mit einer Pulverschicht beschichtet wird. Dies kann z.B. durch Verwirbelungen oder insbesondere beim Abschalten des elektrischen Feldes der Führungselektrode 7 auftreten, da die zu diesem Zeitpunkt noch im Arbeitsraum fliegenden Pulverteilchen keine Kraft mehr erfahren, die ihre eigene Gewichtskraft kompensieren würde und somit herunterfallen. Eine sich auf diese Weise bildende Schicht würde die elektrischen Eigenschaften der Führungselektrode 7 durch Bildung einer dielektrischen Pulverschicht verändern, was nicht erwünscht ist.The guide electrode 7 is arranged outside the working space 11 and is preferably separated therefrom at least by means of an insulator 8. This prevents the lead electrode 7 from being coated with a powder layer over time due to the “dirty” working environment. This can e.g. occur due to turbulence or in particular when the electrical field of the guide electrode 7 is switched off, since the powder particles still flying in the work space at this point in time no longer experience any force that would compensate for their own weight and thus fall down. A layer which is formed in this way would change the electrical properties of the guide electrode 7 by forming a dielectric powder layer, which is not desirable.

Vorzugsweise hat die Führungselektrode 7 einen grösseren Abstand zur Längsachse z des Pulversprühkopfes 2 als die Spitze 6a der Ladeelektrode 6 angeordnet. Diese Massnahme dient dazu, das elektrische Feld (Corona-Effekt) der Ladeelektrode nicht zu beeinträchtigen, da sonst die Pulverpartikel nicht aufgeladen werden. Die Spitze der Ladeelektrode muss möglichst frei von anderen elektrischen Feldern sein.The guide electrode 7 is preferably arranged at a greater distance from the longitudinal axis z of the powder spray head 2 than the tip 6a of the charging electrode 6. This measure serves to avoid impairing the electric field (corona effect) of the charging electrode, since otherwise the powder particles will not be charged. The tip of the charging electrode must be as free as possible from other electrical fields.

Die Führungselektrode 7 erstreckt sich vorzugsweise über das Ende des Arbeitsraums 11 in Transportrichtung z. Dadurch wird sichergestellt dass das gesamte Pulver entlang der gesamten Längserstreckung des Arbeitsraums 11 (und insbesondere der Arbeitsöffnung 4) vom elektrischen Feld der Führungselektrode 7 erfasst wird. Dies wird im Folgenden in Zusammenhang mit Flügeln 3 des Pulversprühkopfes 2 näher erläutert.The guide electrode 7 extends preferably over the end of the working space 11 in the transport direction, for. This will ensure that the entire Powder along the entire longitudinal extent of the work space 11 (and in particular the work opening 4) is detected by the electric field of the guide electrode 7. This is explained in more detail below in connection with the wings 3 of the powder spray head 2.

Im Arbeitsraum 11 sind drei Flügel 3 zum Leiten des elektrostatisch aufgeladenen Pulvers durch die Arbeitsöffnung 4 an den zu beschichtenden Teil der Innenfläche der Dosenzarge 12 vorgesehen. Die Flügel 3 sind aus einem elektrisch neutralen Material hergestellt und im Arbeitsraum 11 in Transportrichtung z hintereinander angeordnet. Wie aus den Figuren zu erkennen ist, wird das Pulver von den Flügeln 3 nach oben abgelenkt (Pfeile 10a-d). Ihre Aufgabe ist also die Ablenkung des Pulvers zu unterstützen. Die Anzahl der Flügel 3 berücksichtigt die Tatsache, dass nicht alle Pulverteilchen mit gleicher Geschwindigkeit in z-Richtung fliegen und folglich ihre Ablenkung auch unterschiedlich stattfindet. Die unterschiedliche Geschwindigkeit der Pulverteilchen hängt einerseits damit zusammen, dass Pulverteichen im Pulverstrom zusammenstossen, wodurch sich ihre Geschwindigkeit ändert. Andererseits wird der Pulverstrom beim Austritt aus dem Pulverauslass gestreut, wodurch die Pulverteilchen unterschiedliche Axialkomponenten der Geschwindigkeit bekommen. Schliesslich spielt auch die variierende Masse der Pulverteilchen eine Rolle. Aus diesen Gründen legen manche Pulverteilchen eine längere Strecke im Arbeitsraum hinter sich als andere Pulverteilchen. Dies ist der Grund warum sich die Führungselektrode 7 vorzugsweise bis zum Ende des Arbeitsraums 11 erstreckt.In the work space 11, three wings 3 are provided for guiding the electrostatically charged powder through the work opening 4 to the part of the inner surface of the can body 12 to be coated. The wings 3 are made of an electrically neutral material and are arranged one behind the other in the working space 11 in the transport direction z. As can be seen from the figures, the powder is deflected upwards by the wings 3 (arrows 10a-d). So your job is to help deflect the powder. The number of blades 3 takes into account the fact that not all powder particles fly in the z-direction at the same speed and consequently their deflection also takes place differently. On the one hand, the different speed of the powder particles is related to the fact that powder bodies collide in the powder flow, which changes their speed. On the other hand, the powder flow is scattered when exiting the powder outlet, whereby the powder particles get different axial components of the speed. Finally, the varying mass of the powder particles also plays a role. For these reasons, some powder particles cover a longer distance in the working area than other powder particles. This is the reason why the guide electrode 7 preferably extends to the end of the work space 11.

Für eine effiziente Ablenkung sind die Flügel 3 in Richtung der Arbeitsöffnung 4 gebogen, um eine möglichst laminare Strömung des Pulvers an ihnen vorbei zu ermöglichen. Eine laminare Strömung ist grundsätzlich erwünscht um einen möglichst gleichmässigen Pulverauftrag auf der Innenfläche der Dosenzarge 12 zu gewährleisten. Damit wird vermieden, dass die Zeit für die zurückgelegte Strecke der Pulverteilchen nicht durch etwaige Verwirbelungen verlängert wird, während für andere Pulverteilchen keine solche Verzögerung auftritt. Es wird angemerkt dass auch die Form des Arbeitsraums 11 an sich unter diesem Gesichtspunkt anders gestaltet werden kann als in den beispielhaften Abbildungen. In diesem Zusammenhang ist aus Fig. 2 und 3 auch zu erkennen dass die Vorderwand des Arbeitsraums 11 (beim Pfeil 10d), in Transportrichtung z gesehen, eine gleiche oder ähnliche Form wie die Flügel 3 besitzt.For efficient deflection, the wings 3 are bent in the direction of the working opening 4 in order to enable the powder to flow past them as laminar as possible. A laminar flow is fundamentally desirable in order to ensure the most even possible powder application on the inner surface of the can body 12. This avoids the time covered for Stretch of the powder particles is not lengthened by any turbulence, while no such delay occurs for other powder particles. It is noted that the shape of the work space 11 per se can also be designed differently from this point of view than in the exemplary illustrations. In this context is off Fig. 2 and 3 It can also be seen that the front wall of the working space 11 (at arrow 10d), viewed in the transport direction z, has the same or a similar shape as the wings 3.

Bei Anwesenheit mehrerer Flügel haben diese vorzugsweise jeweils eine immer grössere Wirkfläche in Transportrichtung z für die Ableitung des elektrostatisch aufgeladenen Pulvers. Dies hängt damit zusammen, dass aufgrund der physikalisch bedingten Streuung des Pulverstroms dieser Pulverstrom am vordersten Flügel 3 (beim Pfeil 10c) breiter ist als beim hintersten Flügel 3 (beim Pfeil 10a). Daher bewirkt diese Flächenvariation auch weiter vorne (in z-Richtung) eine effektive Ablenkung.If several wings are present, these preferably each have an ever larger effective area in the transport direction z for the discharge of the electrostatically charged powder. This is related to the fact that, due to the physically induced scattering of the powder flow, this powder flow on the foremost wing 3 (at arrow 10c) is wider than at the rearmost wing 3 (at arrow 10a). This area variation therefore also causes an effective deflection further forward (in the z-direction).

Bevorzugt haben die Flügel 3 in Transportrichtung z einen zweiten axialen Abstand D2 von der Ladeelektrode 6, der grösser als der erste Abstand D1 ist. Der zweite axiale Abstand D2 ist als der Abstand von einem Anfangspunkt eines ersten Flügels 3, der der Ladeelektrode 6 am nächsten ist, bis zu einer z-Position der Ladeelektrode 6 verstanden. Diese Massnahme wird angewandt, da konstruktionsbedingt das Pulver in "Schüben" in den Arbeitsraum 11 ankommt. Damit ist gemeint dass der Pulverstrom keine konstante Dichte über die Zeit hat, sondern die Dichte in etwa sinusförmig verläuft. Ein solcher Verlauf würde bewirken, dass auch die Beschichtung wellenförmig wäre, also mit dickeren und dünneren Abschnitten, was unerwünscht ist. Der Arbeitsraum 11 bewirkt in dem "weitläufigen" Bereich bis zu den Flügeln gewissermassen eine Uniformierung der Dichte des Pulverstroms, so dass es mit möglichst konstanter Dichte an der Dosenzarge 12 ankommt.The blades 3 preferably have a second axial distance D2 from the charging electrode 6 in the transport direction z, which is greater than the first distance D1. The second axial distance D2 is understood as the distance from a starting point of a first wing 3, which is closest to the charging electrode 6, to a z-position of the charging electrode 6. This measure is used because, due to the design, the powder arrives in the working space 11 in "bursts". This means that the powder flow does not have a constant density over time, but that the density is approximately sinusoidal. Such a course would have the effect that the coating would also be wavy, i.e. with thicker and thinner sections, which is undesirable. In the “extensive” area up to the wings, the working space 11 brings about a uniformization of the density of the powder flow, so that it arrives at the can body 12 with as constant a density as possible.

Fig. 4 zeigt eine Querschnittansicht des Pulversprühkopfes 2, gesehen in Richtung B aus Fig. 3, also entgegengesetzt der Transportrichtung z der Dosenzarge 12. In dieser Figur sind zwei Dichtlippen 14 dargestellt, die aus Klarheitsgründen in der vorherigen Figuren nicht eingezeichnet wurden. Diese Dichtlippen 14 sind an einer Kontur der Arbeitsöffnung 4 befestigt. Dabei kann es sich um eine einzige Dichtlippe oder um mehrere Dichtlippen handeln. Ein freies Ende der Dichtlippe 14 liegt bei Anwesenheit einer Dosenzarge 12 an der Innenwand der Dosenzarge 12 an, so dass nur der zu beschichtende Teil der Innenwand der Dosenzarge 12 in Kontakt mit dem Pulver kommen kann. In diesem Beispiel soll die Beschichtung auf die Schweissnaht 12a als Schutz gegen Korrosion aufgebracht werden, wie eingangs erwähnt. Da sich diese Schweissnaht 12a in Längsrichtung z der Dosenzarge 12 erstreckt, ist die Arbeitsöffnung 4 entsprechend schlitzförmig ausgestaltet, um nur die Umgebung der Schweissnaht 12a freizulegen. Wenn eine Dosenzarge 12 über der Arbeitsöffnung 4 anwesend ist, liegen die Dichtlippen 14 an der Innenwand der Dosenzarge 12 an, seitlich der Schweissnaht, so dass kein Beschichtungspulver an anderen Bereichen der Innenwand gelangen kann und somit nur der gewünschte Bereich beschichtet wird. Fig. 4 shows a cross-sectional view of the powder spray head 2, seen in direction B. FIG Fig. 3 , thus opposite to the transport direction z of the can body 12. In this figure, two sealing lips 14 are shown, which were not shown in the previous figures for reasons of clarity. These sealing lips 14 are attached to a contour of the working opening 4. This can be a single sealing lip or several sealing lips. When a can body 12 is present, a free end of the sealing lip 14 rests against the inner wall of the can body 12, so that only the part of the inner wall of the can body 12 to be coated can come into contact with the powder. In this example, the coating is to be applied to the weld seam 12a as protection against corrosion, as mentioned at the beginning. Since this weld seam 12a extends in the longitudinal direction z of the can body 12, the working opening 4 is configured in a correspondingly slot-shaped manner in order to expose only the area around the weld seam 12a. When a can body 12 is present above the working opening 4, the sealing lips 14 rest on the inner wall of the can body 12, to the side of the weld seam, so that no coating powder can get to other areas of the inner wall and thus only the desired area is coated.

Selbstverständlich kann die Arbeitsöffnung 4 und/oder können die Dichtlippen 14 eine andere Form haben, je nachdem was beschichtet werden soll. Entsprechend kann die Form und Ausdehnung der Führungselektrode entsprechend der Form der Arbeitsöffnung 4 variieren.Of course, the working opening 4 and / or the sealing lips 14 can have a different shape, depending on what is to be coated. Correspondingly, the shape and extent of the guide electrode can vary according to the shape of the working opening 4.

Schliesslich umfasst der Pulversprühkopf 2 einen Hochspannungsgenerator (nicht gezeigt) welcher derart ausgestaltet ist, dass er zwischen der Ladeelektrode 6 und der Dosenzarge 12, welche geerdet ist, eine regelbare negative Spannung zwischen 8 und 40 kV erzeugt. Der Generator kann ausserdem derart ausgestaltet sein, dass er auch zwischen der Führungselektrode 7 und der Dosenzarge 12 eine regelbare negative Spannung zwischen 8 und 40 kV erzeugt. Alternativ können zwei unterschiedliche Generatoren verwendet werden.Finally, the powder spray head 2 comprises a high-voltage generator (not shown) which is designed such that it generates a controllable negative voltage between 8 and 40 kV between the charging electrode 6 and the can body 12, which is grounded. The generator can also be designed in such a way that it also generates a controllable negative voltage between 8 and 40 kV between the guide electrode 7 and the can body 12. Alternatively, two different generators can be used.

Während in der vorliegenden Anmeldung bevorzugte Ausführungen der Erfindung beschrieben sind, ist klar darauf hinzuweisen, dass die Erfindung nicht auf diese beschränkt ist und in auch anderer Weise innerhalb des Umfangs der folgenden Ansprüche ausgeführt werden kann. Insbesondere sind Begriffe wie "vorteilhaft" und "vorzugsweise" lediglich mit beispielhaften Ausführungsformen verknüpft und haben keine einschränkende Wirkung auf den Umfang der Erfindung.While preferred embodiments of the invention are described in the present application, it should be clearly pointed out that the invention is not restricted to these and can also be carried out in other ways within the scope of the following claims. In particular, terms such as “advantageous” and “preferably” are only associated with exemplary embodiments and have no restrictive effect on the scope of the invention.

Claims (16)

  1. Powder spraying head (2) for spraying a powder which is suitable for coating a can body (12), wherein the powder spraying head (2) is adapted in such a way that the can body (12) to be coated encloses the powder spraying head (2) and is movable along the powder spraying head (2) in a transport direction (z), for coating at least a part (12a) of an inner surface of the can body (12), comprising
    a work chamber (11) inside the powder spraying head (2), which has a work opening (4) through which the powder can reach the inner surface of the can body (12),
    a powder tube (9) for providing the powder, wherein the powder tube (9) with a powder outlet (9a) opens into the work chamber (11) of the powder spraying head (2) and is adapted to deliver the powder substantially in transport direction (z) into the work chamber (4),
    a charging electrode (6) for charging the powder with an electrostatic charge,
    a guiding electrode (7), which is arranged in transport direction (z) downstream of the charging electrode (6) and below the work chamber (11), for deflecting the powder present inside the work chamber (11), which is already electrostatically charged, substantially in the direction of the work opening (4), wherein the guiding electrode (7) and the charging electrode (6) have a same polarity,
    wherein the charging electrode (6) is arranged in the area of the powder outlet (9a) and is formed with a tip (6a) in the direction of the powder streaming into the work chamber (11) and/or
    wherein the guiding electrode (7) is plate-shaped and a flat side (7a) of the guiding electrode (7) is oriented towards the work chamber (11).
  2. Powder spraying head according to claim 1, wherein the charging electrode (6) is rod-shaped and its longitudinal axis is perpendicular to the transport direction (z).
  3. Powder spraying head according to claim 1 or 2, wherein the charging electrode (6) extends with its tip (6a) through an opening (9b) in a wall of the powder outlet (9a) substantially up to an inner surface of the powder outlet (9a).
  4. Powder spraying head according to one of the preceding claims, wherein the guiding electrode (7) extends at least up to an end of the work chamber (11) in transport direction (z).
  5. Powder spraying head according to one of the preceding claims, wherein the guiding electrode (7) is formed by multiple parts, particularly by multiple strips.
  6. Powder spraying head according to one of the preceding claims, wherein the guiding electrode (7) is arranged outside the work chamber (11) and is particularly separated from it by at least an isolator (8).
  7. Powder spraying head according to one of the preceding claims, wherein the guiding electrode (7) is arranged at a greater distance to the longitudinal axis (z) of the powder spraying head (2) than the tip (6a) of the charging electrode (6).
  8. Powder spraying head according to one of the preceding claims, wherein the guiding electrode (7) has such a first axial distance (D1) from the charging electrode (6) in transport direction (z), that the electric field of the guiding electrode (7) acts upon the powder, which is electrostatically charged by the charging electrode (6) immediately after the powder enters the work chamber (11).
  9. Powder spraying head according to one of the preceding claims, wherein at least a blade (3) for guiding the electrostatically charged powder through the work opening (4) to the part (12a) to coat of the inner surface of the can body (12) is provided inside the work chamber (11), particularly wherein multiple blades (3) are provided, which are arranged inside the work chamber (11) in succession in transport direction (z), particularly wherein the blade (3) or the blades (3) are curved in direction of the work opening (4), particularly wherein in case multiple blades (3) are present they have an increasing acting surface in transport direction (z) for deflecting the electrostatically charged powder.
  10. Powder spraying head according to claims 8 and 9, wherein the blade (3) or the blades (3) have a second axial distance (D2) from the charging electrode (6) in transport direction (z), which is greater than the first distance (D1).
  11. Powder spraying head according to one of the preceding claims, wherein the powder outlet (9a) extends in transport direction (z) in a conically expanding way.
  12. Powder spraying head according to one of the preceding claims, further comprising a high voltage generator which is adapted to generate a negative voltage, which can be regulated in a range from 8 to 40 kV, between the charging electrode and the grounded can body and/or which is adapted to generate a negative voltage, which can be regulated in a range from 8 to 40 kV, between the guiding electrode and the grounded can body.
  13. Powder spraying head according to one of the preceding claims, wherein at least a sealing lip (14) is attached to a contour of the work opening (4), wherein a free end of the sealing lip (14) snugs to the inner surface of the can body (12) when a can body is present (12), such that only the part (12a) to be coated of the inner wall can come into contact with the powder.
  14. Powder spraying head according to one of the preceding claims, further comprising at least a suction nozzle (5) for the excess powder, particularly wherein multiple, particularly three, suction nozzles (5) are arranged in succession in transport direction (z).
  15. Powder coating installation (1) for coating a can body (12) with powder, with a powder spraying head (2) according to one of the preceding claims, further comprising
    a powder transport device (15) for supplying the powder spraying head (2) with powder, wherein the powder transport device (15) is connectable to the powder tube (9) for providing the powder, and
    a powder recycling unit (16) for sucking the excess powder which is generated during the coating, wherein the powder recycling unit (16) is arranged in transport direction (z) downstream of one or more suction nozzles (5) of the powder spraying head (2).
  16. Use of the powder coating installation (1) according to claim 15 for coating a welding seam (12a) of the can body (12).
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CH713662A2 (en) 2018-10-15
ES2828068T3 (en) 2021-05-25
PT3551336T (en) 2020-12-11
TWI749148B (en) 2021-12-11
CN110325285A (en) 2019-10-11
US20200360942A1 (en) 2020-11-19
WO2018176164A1 (en) 2018-10-04
TW201838719A (en) 2018-11-01
EP3551336A1 (en) 2019-10-16
CN110325285B (en) 2021-07-09

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