DE1577922A1 - Electrostatic device for covering objects with finely divided substances - Google Patents

Description

1577923 -9. Jan. 1970

German-lng. Dipl. Oec. publ.

T-JCH LSWiNSKY

. PATlUTANvVALT
8 Munch.sn2l-Gotthard8tr.8T

• Telephone 56 17 62

Societe "Anonyme de Machines Electro statics 17, Rue Duphot, Paris ler, France

"Electrostatic device for coating objects with substances in finely divided form"

. French priority of April 24, 1963 from the French Patent Application No. 932 485

The invention relates to., An electrostatic device for Coating objects with substances present in finely divided form with them a vortex or atomization submitting organs and with them to a corresponding potential compared to the object in question and so "in a cloud of cloth directed at him, on high voltage charging electrode lying opposite the object. =

Such electrostatic devices in which the, Particles along the lines of force between the atomizer head and the object to be coated with them . electrical "field, are conducted compared to the other usual methods for coating objects. significant advantages, in particular greater uniformity in the thickness of the coating layer, lower losses of coating smaterial and better binding of the same to the one to be coated

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Surfaces of the object in question, what a preheating makes these areas superfluous. Such electrostatic devices have therefore gained a wide field of application in recent years, especially since then electrostatic high-voltage generators are available in a practical and compact design.

The invention is based on the object of an electrostatic To create device of the type mentioned, which is in particular for the implementation of this side already previously proposed method for coating objects suitable - in which the coating material is powdery and is in the form of a fluidized bed, the powder being electrostatic is charged and attracted by the objects to be coated as a counter electrode and on this in a Layer sticks. For this purpose, a gas is used in a large number of small streams to swirl the powder into it introduced under pressure, and the particles of matter thus whirled up are electrically opposed to the required potential by means of charging electrodes protruding into this fluidized bed charged to the item to be overdrawn. the Charging electrodes are expediently made of tips, wires or sharp edges, which have been known for a long time are preferably arranged on a porous bottom plate of the container containing the fluidized bed of the powder, through which the compressed gas flows into the powder layer. Besides the already previously known such electrostatic devices adhering to the advantages already mentioned has this Procedures already proposed on this side provide further advantages, as the relatively stable fluidized bed is an extremely suitable means, to a constant source to form charged particles of matter that remain relatively stationary in space at an over & ugs facility on which the au objects in a continuous row with a

minimal amount of work and energy consumption bypassed which is required to create the particle source at the overlay system.

The further development made on this side of this already the previously proposed method and the devices intended to carry it out, however, have shown that they still have a deficiency insofar as the created cloud of particles is responsible for the lack of stability. This has proven to be extremely difficult to control the process parameters with sufficient precision to ensure that the particulate matter is inside the container do a sufficient height to ascend freely through the Covering object to be attracted at the same time but also to avoid that they rise so high that them beyond the container to a considerable extent spilled, especially if the workpiece is on the Übersugsanlage does not exist or it is a proportionate one small object.

It is to fix a particular concern to the present invention> this disadvantage in such electrostatic systems and to provide a device which can increase the Stoffteilchenwolke accurate control and its stability. It is also the aim of the invention to provide improved means with which the spatial extent of electrically charged coating material particles is controlled in such an electrostatic transfer system, regardless of whether it is a spray gun or a device operating according to the vortex process.

This versatile task is the one proposed here Device of the type mentioned at the outset primarily because of the fact that, according to the invention, one or more control!

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Electrodes are provided, which are on a opposite to that of the ' Charging electrodes are substantially different potential and in that between the latter and the object to be coated existing space traversed by the particle cloud are arranged. These control electrodes provided according to the invention limit and regulate the spatial extent of the Cloud of upholstery fabrics.

Further features of the device proposed here, which are claimed with the subclaims, and which are achieved by them Advantages emerge from the following “description of the drawing, which shows a device according to the invention Type in several, for example, selected embodiments illustrated schematically. ·

Fig. 1 shows a first embodiment in a vertical section such a device.

Fig. 2 brings in a, simplified, partially broken off Diagram another embodiment of the proposed here Contraption.

Fig. -3 shows in a simplified perspective view a device according to the invention applied to a spray gun system.

The. Device according to Fig. 1 has a tank or container 1 made of electrically insulating material for receiving the coating material. At a distance from the bottom of this container a horizontal partition 2 is provided, which is partially air-permeable, e.g. made of a porous ceramic plate or one with small breakthroughs provided close together

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provided sheet metal is made; the material of the intermediate wall 2 can be electrically conductive or insulating. Inside the container 1, on the surface of its partition 2, there is a mass 3 of coating material, for example synthetic resin powder, enamel powder, metal powder or other finely dispersible substances. A pipe ^l f is connected to a side wall of the container 1 below its intermediate wall 2 and leads at its other end to .einer compressed gas source, for example compressed air, valves (not shown) for controlling the gas flow through the pipe 4 - are provided. If pressurized gas is entered through the pipe 4 into the bottom chamber of the container below the partition 2 and flows through pores or openings in the partition 2, the gas rises through the powder layer 3 and swirls through it, so that it is in a state of constant movement and turbulence to hold, whereby the particles describe random orbits in the manner of molecules of a fluid, but the particle cloud as a whole remains relatively stationary within the container. In such a state of turbulence, the upper limit of the particle cloud naturally tends to rise significantly above the upper level of the powder layer 3, which is in the static, that is to say not turbulent, state. At the bottom of the container 1, a shaking egg, indicated schematically at 5, is optionally provided in order to initiate and / or improve the vortex effect.

As a means of electrically charging the particles in the finely distributed particle cloud, several pointed electrodes or ionizers 6 arranged in a row are provided, which can be metallic or can be made of a semiconductor. The electrodes 6 are supported by a support rod supported above the porous partition 2, the tips of these electrodes are directed upwards and

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the electrodes in operation within the fluidized bed or the Particle cloud come to rest. The electrodes 6 are on the support rod 10 and an insulated connection line 11 to a Terminal of a high voltage source 7 electrically connected, which has a high DC voltage of about 100 kV and more, e.g. an electrostatic generator, the other terminal of this high voltage source being earthed, Preferably, the electrodes 6 are arranged in spatial relationship in a planar row that extends horizontally through the Particle cloud extends.

In operation of this previously proposed device, ie with a connected high voltage source 7 and with compressed air output through the pipe ¹ I- into the container 1, the initially compressed powder layer 3 is converted into a fluidized bed, and the tip electrodes 6 act on the one hand by direct contact with the whirled up particles and on the other hand via ionized air molecules, um.all particles of the cloud of matter to convey a high ... electrical potential corresponding to the high voltage source 7. If the not shown, earthed objects to be coated, for example by a chain conveyor at a short distance above the upper opening of the container 1, the strong electric field, which then builds up between the ionizing electrodes 6 and the object in question, causes the Particles of the substance cloud are guided along the lines of force of this field to the surface of the object in question to be coated, which is thus quickly and effectively covered with the powder, which remains adhering to the surface of the object through electrostatic attraction. «'

As I said, it had proven difficult to be able to effectively control the altitude in order to make the cloud more finely divided Particles in the container increases. During this height

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of course partly on the flow rate and flow rate of the entered through pipe 4 Pressure gas depends, but electrical factors also play a role. The'charged particles tend to each other to repel. In particular, in the absence of an object of relatively large size, which is part of the particle cloud presents, electrical stray or interference fields tend to cause particles of matter to settle on surrounding earthed objects drop. As a result, the particulate cloud is lacking of stability and is uneven in its properties and tends to rise too high and over the edge of the container to be spilled. j

According to the invention, this difficulty is countered by that control electrodes 8 are provided 'These control electrodes' have, for example, the form of tip electrodes that are; homely like the charging electrodes 6 and made of metal or a j Resistance or semiconductor material can be made. You j are from the side walls of the container 1 in a vorbe- j correct height above the charging electrodes 6, and their tips protrude into the container 1. The control electrodes, 8 are connected to earth. ;

In operation, the control electrodes 8 cause them to be approaching particles of the cloud of matter either by immediate Touch, but above all through ionization of the air molecules discharged, creating the ions with the opposite polarization of the powder particles. Experience shows that the The number and position of the control electrodes 8 can be determined in such a way that that the height of the particle cloud with a good measure of accuracy Regardless of the presence or absence of an earthed object above the container

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can. Likewise, the presence of control electrodes makes ■ According to the invention it is possible to coat objects of small dimensions with powder without powder from the container in spilled or wasted to an undesirable extent. The electrodes 8 can build up an electrostatic control field within the container 1, which is contained in it makes charged particle cloud less sensitive to undesired secondary fields and thus the stability of the particle cloud improved.

In the embodiment shown in FIG. 2, a container 1 is provided which holds a powder layer 3 in it. Furthermore, means corresponding to those in FIG 3 blow through it to transform it into a fluidized bed and particle cloud. Furthermore, charging elements are provided, for example, corresponding to the electrodes 6 in FIG. 1, but they can also take other forms, for example the perforated horizontal partition carrying the powder layer 3 can be metallic and designed as a charging electrode according to suggestions made earlier. In this embodiment the control electrodes according to the invention are in the form of fine wires 8 ', for example stainless steel wires with a diameter of 0.1 or 0.2 mm. For example, two such wires are provided here, both of which extend around the inner wall of the container at a perpendicular distance from one another and are held by the container wall by insulating supports 9. Both wires 8 ¹ are connected to earth. Of course, a single such wire 8 'or more than two can also be used. To be the operation of the embodiment according to FIG. 2 described braucht'nicht, since it is substantially the same as in the embodiment of FIG. 1. ^

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Fig. 3 illustrates a typical electrostatic atomizing, st. Spray gun system instead of a system that works according to the fluidized bed process described above. This plant of the Fig. 3 has a spray gun 21 made of insulating material, which is equipped with an atomizer head 22, the one Forms or has ionizing electrode, which consists of conductive or semiconducting material and is electrically connected to the insulated Cooking voltage pole of an electrostatic generator 23 grounded with its other terminal connected is. Finely distributed coating material such as plastic powder is in a compressed air stream from a corresponding, Source, not shown, via an ifexible hose 24 entered into the atomizer gun and sprayed from the atomizer head 22.

An object to be covered, such as a flat one here Plate 25 made of metal or plastic is covered by an appropriate Chain conveyor or the like on the atomizer head 2 2 passed while he himself is grounded. In well-known In this way, the particles of the coating material are charged to a high potential corresponding to that of the generator 23, when they leave the atomizer head 22 or pass the ionizing electrode (not shown) assigned to it > and form a cloud of particles that are relatively low speed along the lines of force between the atomizer head 22 and the object 25 to be coated existing electric field and then on the Set down the relevant surfaces of the object to be coated evenly. Frequently, however, it has been found that that particles of this cloud tend to migrate, for example under the effect of electrical stray fields, and according to the invention means are provided which such stray particles -ent-

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load and prevent their further migration. To this end are behind the. to be coated object 25, i.e. on the side facing away from the atomizer gun 22 in a Row or in the form of a network of 26 fine conductive wires, here e.g. four wires in a vertical direction and a long distance from one another, provided and electrically connected to earth potential.

Depending on requirements, the network 26 can be on a .Vibrier- or Shaking device 27 may be arranged, which helps to keep the powder particles deposited on the wires of the network 26, to shake off. Under the discharge device 26 are for To collect the discharged powder, appropriate collecting organs are provided, but not shown. Thus becomes any Coating material that accidentally deviates from the prescribed area during an atomization process due to the ionizing Action of the wires 26 discharged, therefore falls to the ground and is collected and returned to the actual process. Behind the wire mesh 26 at a distance from this is preferably a electrically insulating screen 28 is provided, which serves as a reflector, the particles migrating backwards into the space of the wires 26 throws back.

In the embodiment of FIG. 3 using a Atomizer gun can attach the ionizing elements like wires different places, e.g. on the sides of the atomizer system * The device according to the invention is also for the electrostatic atomization of liquid coating. materials such as paint can be used, as the electrically charged fine liquid droplets are discharged "and the powder particles are collected in the same way. The control electrodes can take a wide variety of forms. This one The electrodes are supposed to act mainly duroh ionization

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effective parts of the control electrode that of the particle cloud ^! are exposed, have a small radius of curvature, ie in the form of sharp points, thin wires or the like. Other parts of the control electrodes with large radii of curvature can be covered with insulating material if necessary. The control electrodes _r should be spaced apart a sufficient distance to enable them to perform their lonisierfunktion effective.

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Claims (13)

Patent claims: 1. Electrostatic device for covering objects with substances present in finely divided form with organs subjecting them to turbulence or atomization and with them charging up to a potential corresponding to the object in question and thus directing them in a cloud of matter onto it, <to high voltage opposite Charging electrodes lying on the object, characterized by control electrodes (8) which are at a potential that is substantially different from that of the charging electrodes (6) and in the between the latter and the object to be coated ο available space "traversed by the particle cloud. are arranged. 2. Apparatus according to claim 1 , characterized in that the control electrode! -; (8) have a small radius of curvature in their area facing the particle cloud. 3. Apparatus according to claim 2, characterized in that the Control electrodes are designed as tip electrodes (8) (Fig. 1). 4. Apparatus according to claim 2, characterized in that one or more wires (8 ^f ) are provided as control electrodes (Fig. 2). 5. Device according to one of claims 1 to 4, characterized in that that the control electrodes (8, 8 ') on the same Potential like the object to be coated. 6 _t . Device according to one of Claims 1 to 5, characterized in that the control electrodes (8, 8 ') are earthed. • '·. - 13 - 009813/078 3 BATH 7. Device according to one of the preceding claims, characterized in that it is equipped with an atomizer gun (21> 22) '- ..'"'is equipped (Fig. 3). 8. Device according to one of claims 1 to B, characterized through a container (1) which receives the coating material (3) in finely divided form and into which a swirling of the Substance-causing pressurized gas flows. 9. Apparatus according to claim 8, characterized in that the Control electrodes (8) from the inner wall of the container (1) above the charging electrodes (3) are supported (Fig. 1). 10. Apparatus according to claim 8 or 9, characterized in that that the control electrodes (8, 8 ') in the edge region of the cloud of matter pervading space. 11. Apparatus according to claim 6 or 7, characterized in that that the control electrodes (26) on the atomizer gun (21, 22) or the like. facing away from the object to be coated (25) are arranged (Fig. 3). 12. The device according to claim 11, characterized by means for collecting, collecting and returning the from the control electrodes (26) discharged coating material particles (Fig. 3), 13. Device according to one of claims 1 to 12, - characterized by means (5; 27) for shaking the control electrodes (8; 26) (Figs. I and 3). · lh. Device according to one of Claims 1 to 13, characterized by a reflective screen (28) which is arranged at a distance from the control electrodes (26) and consists of an electrically insulating • "'the material (Fig. 3).