Coating device and method for coating a flat workpiece with the coating device

Abstract

Coating device (1) with at least one pair of rollers (2) consisting of a lower conveying roller (3) and an application roller (4) arranged above it, wherein the lower conveying roller (3) projects into a container (5) intended for receiving a medium, wherein a structure-borne sound generator (6) is associated with the container (5), characterized in that at least one spray wire (7) that can be placed under high voltage is adjacent to the application roller (4) and the conveying roller (3) and is arranged on the front of the application roller (4).

Description

[0001] The invention relates to a coating device with at least one pair of rollers consisting of one or more lower conveyor rollers and an application roller arranged above them. The lower conveyor roller extends into a container intended for holding a medium, to which a structure-borne sound generator is assigned, and at least one high-voltage spray wire is arranged adjacent to the application roller and the conveyor roller and on the front side of the application roller. Furthermore, it relates to a method for coating a flat workpiece using the coating device.

[0002] In manufacturing technology, it is often necessary to coat the surfaces of workpieces with powder. With current technology, a light coating of the surface is possible.

[0003] DE 101 63 025 A1 describes a method for coating a substrate comprising a fluidization container, a roller, and a pair of electrodes that generate an electric field between them to convey powder particles to the substrate. DE 40 13 061 A1 shows a device for fluidizing powder contained in a container, which is then applied to a substrate with a spray gun in an electrostatic powder coating system. DE 10 2007 029 578 B4 describes a method for coating a flat workpiece, wherein a container is set in motion by a vibrating device and the powder is transferred by adhesion forces. DE 1 237 143 A shows a powder application device for a brush, in which the brush transfers powder in an electric field through a screen electrode.AT 304 731 B describes a method for electrostatically spraying powdered materials onto workpieces using a spray material carrier immersed in the spray material supply, as well as a device for carrying out this method.

[0004] The object of the present invention is to further develop a coating device such that the layer thickness on a flat workpiece can be controlled. A further object is to provide a method with which, given a given structural design, the layer thickness on a flat workpiece can be increased and controlled. The present invention and the present method enable the application of opaque layers on workpiece surfaces.

[0005] This object is achieved by a coating device having the features of claim 1 and by a method having the features of claim 12. Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims.

[0006] The coating device according to the invention is characterized in particular by the fact that a controllable structure-borne sound generator for atomization is assigned to the container. The structure-borne sound generator transmits structure-borne sound through the container into the medium to be contained therein, the particles or grains of which interact less strongly due to the energy input and can be separated more easily, fluidizing or atomizing the medium for homogeneous contact adhesion of the medium to the surface of the conveyor roller. In other embodiments, the structure-borne sound generator can also be integrated into the container base or container wall. Atomizing the medium also makes it possible to arrange the conveyor roller completely outside the medium. Furthermore, by regulating the structure-borne sound generator, the degree of atomization and ultimately the degree of layer thickness of the medium on the flat workpiece can be influenced.The vibrating motor used for fluidization or the introduction of compressed air into the medium is therefore unnecessary. The structure-borne sound generator is also called a structure-borne sound transducer or body shaker.

[0007] The coating device is assigned at least one spray wire, which increases the effectiveness of the media transfer between the conveyor roller and the application roller, and subsequently also between the application roller and the workpiece, by charging the surface of the application roller. High electrical voltages of 10 kV to 100 kV can be applied to the spray wire, whereby the surface of the application roller is electrostatically charged. To achieve this effect, the spray wire must be parallel to and horizontally offset from the position of the application roller. Its length is adapted to the cylinder height of the application roller to ensure even charging of the application roller. It is also arranged on the front side of the application roller. The front side of the application roller is the side on which a point on the surface of the application roller moves towards the conveyor roller during rotation.The voltage applied to the spray wire and its horizontal and vertical position are adjustable, allowing the degree of charge on the surface of the application roller and, ultimately, the thickness of the coating on the flat workpiece to be adjusted. The horizontal and vertical position of the spray wire is adjusted using two insulators between which the spray wire is clamped. The insulators are made of an electrically insulating material to allow high voltages without undesirable voltage drops. At a minimum, the surface of the application roller must be made of an electrically insulating material to prevent charge equalization and ensure that the medium adheres to the surface of the application roller.

[0008] The surface of the application roller is primarily made of rubber. It is important to ensure that the surface of the application roller is charged before possible contact with the conveyor roller.

[0009] The conveyor roller of the roller pair consists, at least on its surface, of an adhesive material, particularly felt, with respect to the medium to be transferred. The atomized medium is picked up by the conveyor roller's rotation around its own axis and adheres to the conveyor roller through adhesive forces. Electrostatic interactions between the conveyor roller and the atomized medium are not required, but can be used to support this effect if the conveyor roller is also electrostatically charged by the spray wire. Both the conveyor roller and the application roller can rotate independently of each other in both directions around their own axes.

[0010] To further increase the possible layer thickness on the flat workpiece, several conveyor rollers can be arranged horizontally offset next to each other. The resulting multiplied conveyance of the atomized medium from the container and the resulting overlap of the layers on the flat workpiece enable the application of a layer thickness many times greater than that achieved with just one pair of rollers.

[0011] Before using the coating device, the diameters of both rollers in the roller pair can be freely selected. By selecting the diameters, the coating thickness on the flat workpiece can be further increased. For example, if the diameter of the conveyor roller is half the diameter of the application roller, a coating thickness twice as thick can be achieved on the flat workpiece. By increasing the number of conveyor rollers, the coating thickness on the flat workpiece can also be increased. Twice as many conveyor rollers result in twice the coating thickness.

[0012] At least one pair of guide rollers is provided to guide and stabilize the flat workpiece during coating. The guide rollers are grounded and guide the workpiece over the application roller either at a suitable distance or without a gap. The selection of the distance between the workpiece and the higher roller depends on the desired coating thickness on the workpiece. In this embodiment, a pressure roller is arranged above the application roller, which additionally presses the workpiece onto the application roller via its upper surface, assuming the desired contact between the workpiece and the application roller. This improves the mechanical media transfer from the surface of the application roller to the workpiece.

[0013] One or more scrapers are assigned to the conveyor roller, which regulate the dosage of the medium on the surface of the conveyor roller. The position of the scraper is adjustable for this purpose. The amount of medium absorbed by the conveyor roller has a proportional effect on the layer thickness of the medium on the flat workpiece. Thus, the scraper also influences the layer thickness of the medium on the flat workpiece.

[0014] The advantages, advantageous embodiments and effects described in connection with the coating device according to the invention apply to the same extent to the method according to the invention.

[0015] The coating device, as described in this section, uses a process for coating a flat workpiece in which the layer thickness is regulated. The atomization or fluidization of the medium held in the container is achieved with the aid of an adjustable structure-borne sound generator for homogenization and thus also for increasing the media absorption by the conveyor roller. By controlling the structure-borne sound generator, the degree of media absorption is adjusted and the conveyor roller can be positioned in or above the medium.

[0016] The atomized medium is absorbed by the surface of the conveyor roller through adhesion forces and, optionally, by rotation of the conveyor roller around its own axis. The conveyor roller's scraper is then used to meter the layer thickness of the medium on the surface of the conveyor roller. The spray wire charges the surface of the application roller, and the medium can then be transferred from the conveyor roller to the application roller. The direction of rotation within the roller pair is freely selectable. The grounded workpiece is guided over the application roller using the grounded guide rollers, which serve to stabilize the workpiece.The transfer of the medium located on the surface of the application roller to the grounded workpiece to be coated takes place via the effect of the electric field created by the potential difference between the surface of the application roller and the grounded workpiece.

[0017] The process can also be carried out with multiple horizontally arranged roller pairs. Increasing the number of roller pairs results in a significantly increased layer thickness of the medium on the workpiece by applying the medium multiple times. The conveyor roller and the application roller are designed to rotate in opposite directions for more effective media transfer.

[0018] The features and feature combinations mentioned above in the description, as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figure, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed and disclosed by the invention that are not explicitly shown or explained in the figure, but which emerge and can be produced through separate feature combinations from the explained embodiments.

[0019] Further advantages, features, and details of the invention will become apparent from the claims, the following description of preferred embodiments, and the drawings. Herein: Fig. 1 a side view of the coating device.

[0020] In the Fig.1 shows a coating device 1, which comprises a pair of rollers 2 consisting of a conveyor roller 3, which is positioned lower during normal use, and an application roller 4, which is positioned higher during normal use, a container 5, and a structure-borne sound generator 6. The pair of rollers 2 is arranged above the container 5 such that the conveyor roller 3 protrudes into a medium located in a container 5 or is arranged just above the medium. An adjustable structure-borne sound generator 6 is arranged below the container 5 such that it introduces structure-borne sound into the medium and can atomize or fluidize the medium located in the container. Both rollers 3, 4 can rotate about their cylindrical axes in both directions. The diameter of the rollers 3, 4 can be freely selected before use of the coating device 1, so that the layer thickness on the flat workpiece can be further increased.By regulating the structure-borne sound generator 6, the degree of layer thickness of the medium on a flat workpiece that is guided over the application roller 4 is adjusted and, in addition, the structure-borne sound generator 6 causes the homogenization of the layer on the conveyor roller 3 by coupling sound waves into the medium located in the container 5.

[0021] A spray wire 7 is located parallel and horizontally offset to the position of the axes of both rollers 3, 4. Since the spray wire 7 is intended to charge the application roller 4 in order to support the media transfer from the conveyor roller 3 to the application roller 4, and the media transfer from the application roller 4 to the workpiece, the spray wire 7 must be located parallel and horizontally offset in relation to the position of the application roller 4. The spray wire 7 must be made of a material that allows the application of high voltages (10 kV to 100 kV). In this embodiment, the spray wire 7 is made of platinum. Any other material that meets the voltage requirement would be conceivable as a material for the spray wire 7. The length of the spray wire 7 is adapted to the cylinder height of the rollers 3, 4 in order to achieve a uniform charging of the atomized medium.The spray wire 7 is arranged on the front side of the application roller 4, wherein the front side is defined by the fact that a point located on the surface of the application roller 4 moves towards the conveyor roller 3 as the application roller 4 rotates. The tension of the spray wire 7 is adjustable, whereby the degree of charging of the atomized medium and thus also the degree of layer thickness on the flat workpiece can be adjusted. The adjustment of the spray wire 7 in the horizontal and vertical directions is carried out via two insulators 8, between which the spray wire 7 is clamped. In this embodiment, the insulators 8 are designed as length-adjustable rods in order to carry out the vertical adjustment of the spray wire 7. The rods can be attached to the container 5 at various positions in order to carry out the horizontal adjustment of the spray wire 7.Any other shape that facilitates clamping and adjustment of the position in the horizontal and vertical directions of the spray wire 7 can be used as the shape of the insulators 8. The choice of the position of the insulator 8 and thus also of the spray wire 7 also influences the degree of charging of the surface of the application roller 4 and thus the layer thickness of the medium on a flat workpiece. The insulators 8 are made of electrically insulating material to enable high voltages on the spray wire 7 without an unwanted voltage drop. In this embodiment, the insulators 8 are made of PVC.

[0022] In this embodiment, the application roller 4 is hollow to reduce the weight of the coating device 1. At least the surface of the application roller 4 is made of an electrically insulating material to prevent charge equalization and ensure the adhesion of the medium to the surface of the application roller 4. In this embodiment, the surface of the application roller 4 is made of rubber.

[0023] The surface of the conveyor roller 3 consists of at least one material that is adhesive to the medium to be transferred. This allows the atomized medium to be absorbed by a rotational movement of the conveyor roller 3 around its own axis, whereby no electrostatic interactions are necessary between the conveyor roller 3 and the atomized medium. However, the electrostatic interactions can be used in a supporting manner if the conveyor roller 3 is also electrostatically charged by the spray wire 7.

[0024] The conveyor roller 3 and the application roller 4 are both independently rotatable about their own axis.

[0025] To further increase the possible layer thickness on the flat workpiece, several conveyor rollers 3 can be arranged horizontally offset next to one another. To increase the possible layer thickness on the flat workpiece, the roller pair 2 can also be arranged horizontally next to one another several times in the coating device 1. Since this allows for a multiple conveyance of the medium from the container 5, the superimposition of the layers on the flat workpiece allows for the application of a layer thickness many times greater than that possible with just one roller pair 2.

[0026] In order to stabilize the flat workpiece during coating by the coating device 1, one or more pairs of guide rollers 9 are arranged so that the flat workpiece is guided over the application roller 4. In order not to weaken the electrostatic interaction between the grounded, flat workpiece and the charged, atomized medium, the guide rollers 9 are also grounded. The flat workpiece can be guided over the application roller 4 with no clearance or with a suitable clearance. This adjustment allows the layer thickness of the medium on the flat workpiece to be further regulated. In this embodiment, a pressure roller 11 is arranged above the application roller 4 so that the workpiece can be additionally pressed onto the application roller 4 via its upper side by the pressure roller 11, provided contact with the application roller 4 is desired.The mechanical media transfer from the application roller 4 to the workpiece can thus be promoted.

[0027] In the coating device 1 there is a scraper 10 for reducing the layer thickness on the conveyor roller 3. The position of the scraper 10 is adjustable so that a dosage of the layer of the medium on the conveyor roller 3 and thus also on the flat workpiece is achieved.

[0028] With such a coating device 1, a process can be carried out in which the atomization or fluidization of the medium with the aid of an adjustable structure-borne sound generator 6 is initiated for homogenization and thus also for increasing the media absorption by the conveyor roller 3. The control of the structure-borne sound generator 6 enables the degree of media absorption of the conveyor roller 3 to be adjusted, thereby allowing the conveyor roller 3 to be inserted into the medium or above the medium located in the container 5. The atomized medium is absorbed via the surface of the conveyor roller 3 by the existing adhesion forces. The dosage of the layer thickness of the medium on the conveyor roller 3 and thus also on the flat workpiece is carried out via the scraper 10, the position of which is adjustable.The surface of the application roller 4 is electrostatically charged by the spray wire 7, after which the medium can be transferred from the conveyor roller 3 to the application roller 4. The direction of rotation within the roller pair 2 is freely selectable. The layer thickness of the medium on the application roller 4 is metered via the position-adjustable scraper 12. In a preferred embodiment, the scraper 12 is designed as a broom so that the scraped-off medium can fall back into the tub. It is also conceivable to use a rubber lip or a plate as the scraper 12. The guide rollers 9 guide the workpiece in a stabilized manner over the application roller 4, whereby the atomized medium located on the surface of the application roller 4 is transferred to the grounded workpiece to be coated.This transfer takes place via the effect of the electric field that is created by the potential difference between the surface of the application roller 4 and the grounded flat workpiece.

[0029] This method can also be carried out with a plurality of horizontally arranged roller pairs 2, so that a multiple of the layer thickness equivalent to the plurality is possible on the flat workpiece.

[0030] The conveyor roller 3 and the application roller 4 rotate in opposite directions, enabling more effective media transfer. LIST OF REFERENCE SYMBOLS 1 coating device 2 pairs of rollers 3 conveyor roller 4 application roller 5 containers 6 structure-borne sound generators 7 spray wire 8 Insulator 9 leadership roles 10 scrapers 11 Pressure roller 12 scrapers

Claims

[1] Coating device (1) with at least one pair of rollers (2) consisting of a lower conveyor roller (3) and an application roller (4) arranged above it, wherein the lower conveyor roller (3) projects into a container (5) intended to hold a medium, wherein a structure-borne sound generator (6) is assigned to the container (5), characterized by that at least one spray wire (7) which can be placed under high voltage is arranged adjacent to the application roller (4) and the conveyor roller (3) and on the front side of the application roller (4). [2] Coating device (1) according to claim 1, characterized by that the spray wire (7) is clamped between two insulators (8) and the insulators (8) are adjustable horizontally and / or vertically. [3] Coating device (1) according to claim 1 or 2, characterized by that the tension of the spray wire (7) is adjustable. [4] Coating device (1) according to one of claims 1 to 3, characterized bythat at least the surface of the application roller (4) consists of an electrically insulating material. [5] Coating device (1) according to claim 4, characterized by that the surface of the application roller (4) is made of rubber. [6] Coating device (1) according to one of claims 1 to 5, characterized by that the electrical charge of the application roller (4) is adjustable. [7] Coating device (1) according to one of claims 1 to 6, characterized by that at least the surface of the conveyor roller (3) consists of an adhesive material with respect to the medium to be transferred. [8] Coating device (1) according to one of claims 1 to 7, characterized by that several conveyor rollers (3) are arranged offset next to one another. [9] Coating device (1) according to one of claims 1 to 8, characterized bythat several pairs of rollers (2) with the associated spray wire (7) are arranged horizontally next to one another in the conveying direction of the workpiece to be coated. [10] Coating device (1) according to one of claims 1 to 9, characterized by that at least one pair of guide rollers (9) are arranged to guide the workpiece. [11] Coating device (1) according to one of claims 1 to 10, characterized by that a scraper (10) is assigned to the conveyor roller (3). [12] Method for coating a flat workpiece with a coating device (1) according to claim 11, comprising the following steps: - atomising the medium held in the container (5) with the aid of an adjustable structure-borne sound generator (6) for homogenisation and thereby also for increasing the media absorption by the adhesive material of the conveyor roller (3), whereby the degree of media absorption is adjusted by the control of the structure-borne sound generator (6) and the insertion of the conveyor roller (3) into the medium or above the medium is enabled, - Absorption of the atomized medium by the surface of the conveyor roller (3) by means of adhesion forces, - stripping the conveyor roller (3) with the associated stripper (10) for dosing the layer thickness of the medium on the conveyor roller (3), - electrostatic charging of the application roller (4) by the spray wire (7), - Transfer of the medium from the conveyor roller (3) to the loaded application roller (4), whereby the direction of rotation within the roller pair (2) is freely selectable, - guiding the earthed workpiece over the application roller (4) using the earthed guide rollers (9) for stabilisation, - Transfer of the charged medium located on the surface of the application roller (4) to the earthed workpiece to be coated via the effect of the electric field created by the potential difference between the application roller (4) and the earthed workpiece. [13] Method according to claim 12, characterized by that by increasing the number of roller pairs (2) in the horizontal direction and / or increasing the number of conveyor rollers (3) and / or freely selecting the diameters of both rollers of a roller pair (2), a higher layer thickness of the medium on the substrate is achieved. [14] Method according to claim 12, characterized by that the conveyor roller (3) and the application roller (4) rotate in opposite directions during media transfer.

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