EP0754498A2 - Device for depositing solid or fluid substances on surfaces - Google Patents

Abstract

The coating device has a supply container (34) of a HV supply system (33) for the solid or liquid material, coupled to a filling valve (15) of a feed system (11) via a transfer system with a transfer container (19). The transfer container is filled via the filling valve when the transfer system is at earth potential and is fed from the transfer container to the HV supply system when the transfer container is at the same HV potential.

Description

The invention relates to a device according to the preamble of claim 1.

For a long time, electrostatic application technology with the help of direct high voltage has been used to coat objects or surfaces with solid or liquid media, in which the medium to be applied is charged directly or indirectly in an electrical field and is thus forced to deposit on the opposite pole surface.

Electrically neutral application or application media are first mechanically atomized and then brought into the influence of an electric field, the neutral media particles being indirectly charged by the polarity of the highest field line density and thereby being attracted to the opposite pole, the surface. This method allows the coating of all so-called electrically conductive as well as electrically poorly conductive media from a neutral, earthed source. However, it has a reduced application efficiency.

The method in which the application medium is charged directly leads to a considerable increase in the application efficiency and is therefore preferred. Here, the medium is fed directly to an electrode generating the electrostatic field with the highest field line density and is thereby directly electrically charged. This electrode is used in practice, for. B. formed by a high-voltage potential rotating body, which mechanically atomizes and simultaneously charges the medium mechanically by its rotational speed and by the electrical forces acting on the medium.

If the medium is poorly conductive, ie it has a relatively high electrical resistance, it can be easily connected from a grounded supply line via a non-metallic hose line to the atomizing electrode, which is at high voltage potential, without causing an electrical short circuit (see calculations according to VDE 0147).

On the other hand, if the medium is electrically highly conductive, e.g. B. a water-based paint, there would be a short circuit between the atomizing electrode connected to the high voltage potential and the grounded supply line if the medium forms an electrically conductive connection between the supply line and the atomizing electrode with the same structure.

In order to avoid this, two methods have become known. In the first method, a connection to an earthed supply system is basically dispensed with and the atomizing electrode is fed directly from an insulated supply container which is at the same high-voltage potential as the atomizing electrode. However, there is the disadvantage that the application or coating process must be interrupted by refilling the supply container in order to avoid a short circuit when filling from a grounded supply system.

In another process method (see DE-PS 29 00 660), a so-called transfer or buffer container is switched on between the grounded supply system and a supply container which is at high voltage potential, in order to enable filling of the supply container at least intermittently without having to interrupt the application process. The device required for this is called potential isolator. In this potential isolator, a shut-off element which is connected to the grounded supply system and can be moved downward is provided in an upper level, the outlet opening of which lies at a safety distance corresponding to the high-voltage potential above an underlying transfer container. This transfer container is insulated from the environment and has a shut-off element which can also be moved downward in the lower region, the outflow opening of which, in turn, lies at an appropriate safety distance above an underlying supply container. This supply container is also insulated from the environment and is constantly connected to high-voltage potential so that the atomizing electrodes at the same potential can be continuously supplied with the medium. When starting for the first time, the transfer container must first be filled with the medium from the earthed supply system. For this purpose, the insulated transfer container and any metal parts located in its area are connected to earth potential via a switching element. Then the filling valve of the supply system connected to earth potential lowered and opened via the transfer container. When a corresponding level control registers the maximum fill level in the transfer container, the filling process is ended. The filling valve, which has been lowered for filling, is returned to the starting position and the transfer container is connected to the high-voltage potential of the supply container by means of the switching element. After this connection to high-voltage potential, there is a potential difference between the grounded filling valve on the supply system and the transfer container, whereas there is no longer a potential difference between the transfer container and the supply container itself. As a result, any medium drops still adhering to or forming on the discharge pipe of the filling valve of the supply system are electrostatically drawn off and atomized by the electrostatic field. This process creates an uncontrolled contamination in the immediate vicinity by the medium. After connecting the transfer container to the high-voltage potential, the filling valve of the transfer container is lowered via the supply container and opened until a corresponding level control in the supply container registers the maximum fill level and then closes the filling valve. Here, too, there can be problems with adhering drops.

After completing this process, the transfer container is filled as described above.

The disadvantage of this configuration is on the one hand the use of the switching element, which is formed by an expensive, oil-filled high-voltage disconnector earthing switch with a limited service life; elaborate control of the switches is necessary in order to avoid incorrect switching and short circuits; on the other hand, there is a risk of current surges in the earth potential circuit due to sudden switching on or off of the full high voltage of capacitive transfer container components, which u. a. can lead to the destruction of electronic components; and there is the problem that the system can become contaminated by drops of electrostatically atomized medium adhering to the filling devices.

A device of the type mentioned is known from US Pat. No. 3,122,320. There is a transfer system above a supply system, from which the actual spray nozzles for applying media to surfaces are supplied, which is insulated from earth. If the supply system is filled with medium from this transfer system, the transfer system reaches high voltage potential and if the transfer container of the transfer system is to be refilled, then a short circuit can occur between the supply system and the transfer system occur; Since the transfer system can remain at high voltage potential for a long time, there is an acute risk to the operating personnel.

The object of the invention is to provide a device of the type mentioned, which is more easily installed than the known device, in which current surges in the earth potential circuit are avoided and in which the system pollution is reduced. In addition, the aim is to prevent the transfer system from being at high voltage potential for a long time.

This object is achieved according to the invention by the characterizing features of claim 1. According to the invention, the transfer container is connected to the earth and the high-voltage source via a high resistance.

This takes advantage of the fact that the medium itself is electrically conductive, so that the media jet from the supply system to the transfer container on the one hand and from the transfer container to the supply system on the other hand creates the electrically conductive connection between the individual components. When the media jet flows from the delivery system into the transfer container, the transfer container is connected to earth and is connected to earth via the resistor, which has a high resistance with a few gigohms. After the filling process of the transfer container has been completed, it is electrically separated from the earth potential by interrupting the media jet and, by opening the filling valve in the transfer container, it is electrically conductively connected to the supply container at high voltage potential.

The current flowing from the transfer container via the resistor in the case when the transfer container fills the supply container is at a few microamperes, which hardly stress the high voltage source. It is important that the transfer system, that is to say the medium and associated metal parts, is back to earth potential after a relatively short time after the filling process of the supply container has ended. This avoids endangering the operating personnel.

It is only through the insertion of the resistance that it is practically possible to use the medium itself in order to safely place the transfer system on the one hand on the ground and on the other hand on the high-voltage potential.

A further advantageous embodiment of the invention can be found in the characterizing features of claim 2. Thereafter, both the transfer and the supply container each have a vertically displaceable filling tube that is used for filling the transfer container or the supply container is raised so that at the beginning of the filling process the lower end of the filling tube is free of the medium of the associated container. This ensures that splashing of the medium is prevented.

Below the filling valve of both the transfer container and the feed system there is a Faraday cage into which the upper end of the filling tube of the transfer container or of the supply container can be inserted without being touched.

Based on the drawing, in which an embodiment of the invention is shown schematically, the invention and advantageous refinements and further improvements and further advantages are to be explained and described in more detail.

Fig. 1

eine erfindungsgemäße Ausgestaltung der Vorrichtung,

Fig. 2

die Vorrichtung nach Fig. 1 während des Befüllvorgangs des Transferbehälters und

Fig. 3

die Vorrichtung gemäß Fig. 1 beim Befüllen des Versorgungsbehälters.

Show it

Fig. 1

an embodiment of the device according to the invention,

Fig. 2

the device of FIG. 1 during the filling process of the transfer container and

Fig. 3

the device of FIG. 1 when filling the supply container.

1 shows a device according to the invention before so-called commissioning. The device, which as a whole has the reference number 10, has a feed system 11 which is shown in dash-dot lines and is grounded at 12. A feed ring system 13 for paint or washing-up liquid belongs to the supply system, from which a line 14 runs to a filling valve 15, to which an outflow pipe 16 is assigned, which is surrounded by a Faraday cage 17.

Below the feed system 11 there is a transfer system 18 with a transfer container 19, on the lower side of which a filling valve 20 is arranged, to which an outflow pipe 21 connects, the end of which is surrounded by a Faraday cage 22 in the same way as the outflow pipe 16. A filling tube 23 is arranged within the transfer container 19 and can be moved up and down in the double arrow direction P with a hydraulic device 24. The hydraulic device 24 has a cylinder 25, in which a piston 26 is arranged, the piston rod 27 of which is fixedly connected to the filling tube 23 via a carrier 28. The transfer system 18 is via an electrical line 29 with the interposition of a high-resistance in the gigohm range connected to a branch point 31 which is connected to earth 12.

A supply system 33 is provided vertically below the transfer system 18, in which a supply container 34 is inserted, on the underside of which a feed pump 35 connects, which is switched into an internal ring or spur line 26. A supply electrode 34 supplies a spray electrode, not shown in detail, with fluid, that is to say with medium, for coating surfaces.

Inside the supply container 34 there is a filling pipe 37, the central axis of which is aligned with the central axis of the filling pipe 23 and the outflow pipes 16 and 21 and which can be moved up and down in the double arrow direction P by means of a piston-cylinder arrangement 38. For this purpose, the piston-cylinder arrangement 38 has a cylinder 39 in which a piston 40 can be moved up and down, the piston rod 41 of which is connected to a carrier 42 which connects the piston rod 41 to the filling tube 37. The supply system 33 is connected via a line 43 to a high-voltage generator 32, the other end of which is connected to earth.

In the state according to FIG. 2, the supply container 34 is filled with medium 50. The task now is to fill the transfer container 19 with medium 51. For this purpose, the filling tube 23 is moved upwards via the piston-cylinder arrangement 24 until the upper end of the filling tube 23 engages in the Faraday cage 17. Then the filling valve 15 is opened and the medium 51 flows through the filling tube 23 into the transfer container, the transfer system 18 being applied to earth by the jet 52 of the medium.

As soon as the transfer container is filled, see FIG. 3, the filling tube 23 is again moved downward into the transfer container 19 in the transfer system 18 by the piston-cylinder arrangement 24, the feed system 11 with the closed filling valve 15, the outflow tube 16 and the Faraday cage 17 is electrically separated from the transfer system 18 and the earth 12 is only electrically conductively connected to the transfer system 18 via the resistor 30.

In the position shown in FIG. 3, after the filling tube 23 has been pulled or moved into the transfer system 18, the filling tube 37 has been extended upwards until the upper end engages in the Faraday cage 22 of the transfer system 18 without the to touch Faraday cage 22 or the outflow pipe 20. The filling valve 20 is then opened and a medium jet 53 can flow downward into the supply container 34, the transfer system through the jet 53 18 is brought to high voltage potential and a current I in the microampere range can only flow via the resistor 30.

As a result, the supply system 33, which is at high voltage potential, no longer needs to be isolated from high voltage potential; the transfer system is switched to high-voltage potential by means of the fluid jet 53, as is its separation, and the electrically conductive connection of the feed system 11 to the transfer system 18 is effected by the jet 52, as indicated above.

Both the fill pipe 38 and the fill pipe 37 are made of plastic; the hydraulic cylinder 24 or 38 can also be designed as a pneumatic piston-cylinder arrangement; It is of further importance that the filling tubes 51 and 37 are free of the level of the medium 51 and 50 in the transfer container 19 and in the supply container 34 when the respectively associated filling valves 15 and 20 are opened.

Minimum and maximum level monitors are arranged in the transfer container 19 and in the supply container 34 (not shown), each of which signals when a filling process of the respective container must be started or ended.

When the container 34 is filled, i. that is, the medium in the transfer container 19 has overflowed into the container 34, the filling tube 37 is moved down again into the supply container 34 and the position of the device 10 shown in FIG. 1 is reached.

Any charges present in the individual system, for example by influence from the supply container 34, which is separated via the dielectric and connected to high-voltage potential, to the transfer container 19 are dissipated by means of the resistance 30 to earth. The high-voltage potential of the transfer system is also equalized via the resistor 30 after the transfer process to earth has ended, which due to the resistance, which is in the giga-ohm range, is completed within a short time, preferably a few seconds.

It should also be added that when the transfer element is filled, the beam 52 runs electrically parallel to the resistor 30, whereas the beam 53 is in series with the resistor 30 when the supply system 33 is filled.

Claims (3)

Device for filling a high-voltage supply system with a supply container in a system for coating surfaces with a liquid or solid, electrically highly conductive medium, a transfer system with a transfer container being provided between the supply container and a first filling valve of a supply system, in which the Medium can be filled from the first filling valve when the transfer system is at ground potential, and from which the medium can be filled into the storage container when the transfer system is at the same high-voltage potential as the supply system, the jet of the medium transferring the transfer container and thus the Transfer system electrically connected to the supply container and thus the supply system, characterized in that the transfer system (18) is connected to earth via a high resistance (30), preferably in the giga-ohm range. Apparatus according to claim 1, characterized in that the transfer and the supply container are each assigned a vertically displaceable filling tube (23, 37) which, when the transfer container (19) and the supply container (34) are filled, is raised so far that to At the beginning of the filling process, the lower end of the filling tube (23, 34) is free of the medium of the associated container. Apparatus according to claim 1 or 2, characterized in that a Faraday cage (17, 22) is arranged in the transfer system (18) below the first filling valve and a second filling valve (20) arranged below the transfer container, into which the upper end of the filling tube (23) of the transfer container (19) or the filling tube (37) of the supply container (34) can be inserted without being touched.

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