EP0455109B1 - Method and installation for coating work pieces in series with a conductive coating product - Google Patents

Description

The invention relates to a method and a system according to the preamble of claims 1 and 5, respectively.

In conventional electrostatic coating systems, such as those used in particular for painting vehicle bodies, the spray head of rotary atomizers or the like is connected to high voltage in order to thereby generate the field which charges the sprayed coating particles between the spray head and the grounded object to be coated. The problem arises here that when using a coating material of high electrical conductivity, such as the environmentally friendly water-soluble paints, the insulation resistance via the line connecting the spray head to the paint supply system is too low if the supply system is at ground potential. The supply system, which usually consists of ring lines for the individual colors, is to be grounded, since otherwise not only would considerable expenditure of insulation be required, but there would also be a risk of explosive discharges due to the large electrical capacity.

In a coating system for electrically conductive materials known from DE-A-30 14 221, a separate storage container is provided for each color, which is arranged insulated from earth and from the other containers and via a color changer and a connecting line spray device at high voltage potential feeds. After the coating operation has ended, the connecting line is flushed with a given color and before changing to a different color with solvent (water) and dried with compressed air in order to maintain the required insulation for the container subsequently connected to the spraying device. In particular with a large number of selectable colors and corresponding containers, this system is structurally complex and bulky. There are also color losses when emptying and flushing the insulating lines and the need to dispose of the flushing agent. The same problem occurs with a method known from DE-A-37 17 929, in which the color changer of an earthed supply system leads to an intermediate container and from there leads to the spraying device for electrical insulation and is dried.

This problem is partially avoided in a system known from DE-C-2900660, in which the coating material first passes from an earthed ring line into an insulated first intermediate container and then from this into a second intermediate container, the output of which is constantly at a high voltage Spray device is connected. By a sufficiently large distance and expediently movable connecting pipes or by moving the first intermediate container up and down, the contents of the first intermediate container are electrically insulated from the second intermediate container and the first intermediate container is isolated from the grounded storage system when the second intermediate container, which is connected to high voltage, is filled. The first intermediate container is electrically charged before emptying into the second intermediate container in order to avoid flashovers. However, the known system is structurally complex and very bulky because of the distances between the first intermediate container and the second intermediate container that are necessary for insulation.

Based on the system known from DE-C-29 00 660, the invention has for its object to provide a method and an installation which require less space and which, in the case of a large number of selectable coating materials of different colors, make it possible to use them Combine intermediate containers into a compact unit in a confined space.

This object is achieved by the method characterized in claim 1 or by the system characterized in the further claims.

The invention not only has the advantage of taking up little space and requiring little construction, it also enables low operating currents. Even if the insulation distances between the first intermediate container of the system known from DE-C-29 00 660 and the supply system or the second container are so large that no flashover occurs, in the known case there is the possibility of a charge exchange by ionization in the insulation gap. This possibility is prevented by the insulating walls of the intermediate container of the system described here.

It is also important that the high voltage does not have to be switched off during the coating operation, since the spray device is always isolated from the supply system during operation. This is achieved according to the invention without the previous need to maintain or set a distance between intermediate containers and the supply system which is greater than the flashover distance of the high voltage applied.

The invention is explained in more detail using an exemplary embodiment shown schematically in the drawing.

The system mainly consists of a permanently grounded supply system, of which only one outlet pipe 1 is shown, a spray device 2 which is constantly at high voltage and two intermediate container chambers A and B which are combined to form a rotatable structural unit and which are arranged in an electrically insulating manner between the supply system and the spray device. The grounded outlet pipe 1 can e.g. be connected to a pressure-controlled ring line or the like.

In the example shown, the two intermediate container chambers A and B essentially consist of elongated cylinders with a semicircular cross-section, which, with their straight base walls 4, 4 ', abut one another, e.g. are attached to each other by screwing the outer flanges. The arcuate walls 3, 3 'and the base walls 4, 4' of the containers consist of insulating material which is sufficiently thick for insulation and are designed to be pressure-resistant, since the containers should be emptied by compressed air, as will be explained. The elongated cylinders forming the intermediate container chambers A, B are divided by transverse walls into a number of individual chambers (not shown) corresponding to the number of selectable coating materials of different colors, each of which has an opening 5 or 5 'at the apex of the arcuate wall 3, 3'. Except for the openings 5,5 ', in which there are valves or other closure means, the cylinders and their individual chambers are completely closed.

The unit consisting of the two intermediate container chambers A, B is rotatably mounted about a common axis running in the cylinder longitudinal direction through the center of the outer sides of the base walls 4, 4 '. In this example, the axis of rotation is horizontal. At the diametrically opposite openings 5, 5 'on opposite sides of the axis of rotation, one of the chambers for each is parallel to the axis of rotation Various colors corresponding row of connecting devices 6,6 'arranged on one (upper) side for connecting the relevant intermediate container chamber (A) to the supply system and on the other (lower) side for connecting the other chamber (B) to one line 7 leading to the spray device 2.

From the opening 5.5 'of the intermediate container chambers A, B, a conduit 9 or 9' extends into the container which opens in the vicinity of the part of the base wall 4,4 'opposite the opening 5.5'. The conduit 9.9 'is part of a, preferably non-conductive, pipe structure 11 or 11', which is seated in the opening 5.5 'and has two valves and which has a second, additional opening in the interior of the container near the opening 5.5' 10.10 '. The mouth at the end of the tube 9, 9 'and the opening 10 and 10' are each connected to their own, separate connections which, depending on the position of the container, serve as inlet or outlet.

The connecting devices 6, 6 'each contain a valve arrangement 13 or 13' controlled via an electrical or pneumatic control line 14 or 14 ', through which the pipe constructions 11, 11' with their valves can be selected depending on the rotational position of the intermediate container chambers A and B. either with the outlet pipe 1 of the supply system or with the line 7 and / or an air line 15 or 16 containing a valve. The air line 15 serves to vent the intermediate container chamber (A) connected to the supply system when filling, while the air line 16 supplies compressed air with regulated pressure for emptying the intermediate container chamber (B) connected to the line 7 of the spraying device 2. The valve arrangement 13 or 13 'can be coupled to the valves of the tubular construction 11, 11'. The Opening 10, 10 'is the mouth of a short second tube; both tubes are each connected to one of the valves of construction 11 or 11 ', which change their position with respect to the connections of the connection arrangements 13, 13' when they are rotated.

For reasons of insulation, the connection points, that is to say the valves of the construction 11, 11 ', should be arranged generally and independently of the shape of the intermediate container chambers A, B at the point of the container wall which is furthest from the axis of rotation. This enables the smallest possible intermediate container arrangement with regard to the required insulation distances.

The connecting devices 6, 6 'also contain, in accordance with the arrows shown, against the container opening 5, 5' and from them along movable parts which can be displaced along an axis perpendicular to the axis of rotation. The connecting part of the connecting device 6 is connected via the valve arrangement 13 to the outlet pipe 1 and the air line 15, that of the connecting device 6 'to the air line 16 and the line 7 leading to the spray device 2. There may also be a connection between the two air lines. The displaceable connecting parts of the connecting devices 6, 6 'could be firmly connected to the conduits 9, 9', so that these are pulled out of the openings 5,5 'before the intermediate container chambers A, B are rotated and then into the opening 5 or 5' of the each other chamber could be retracted. During the rotational movement, the openings 5 and 5 'can be closed automatically by appropriate means. Preferably, however, the displaceable connecting parts are detached from pipe constructions 11, 11 'remaining in the intermediate container chamber A, B and then coupled again with the other pipe construction.

To explain the mode of operation, it is first assumed that the intermediate container chambers A and B are in the position shown. In this position, coating material can flow from the earthed outlet pipe 1 through the valve arrangement 13 of the connecting device 6 and the mouth at the end of the conduit 9 into the intermediate container chamber A. Since the conduit 9 always opens below the liquid level near the bottom of the container, splashing and blistering of the coating material in the intermediate container are largely avoided. The air displaced by the coating material escapes through the opening 10, which is always above the liquid level during the filling process, and through the valve arrangement 13 into the ventilation line 15. At the same time, coating material contained in the lower intermediate container chamber B can pass through the additional opening located at the lower end of the chamber B. 10 'flow via the valve arrangement 13' of the lower connecting device 6 'into the line 7 leading to the spray device 2, namely through the action of the compressed air from the line 16 through the valve arrangement 13' and the mouth at the end, which lies above the liquid level of the conduit 9 'gets into the intermediate container B.

For example, during the coating break, in which a change is made in a spray booth between a fully coated vehicle body and the coating of the next body, the assembly consisting of the intermediate container chambers A and B can be rotated through 180 ° without time problems. Before the twisting, the displaceable connecting parts of the connecting devices 6 and 6 'are moved away from the intermediate containers, and after the twisting the connection is made again.

After twisting, the previously filled intermediate container A is located at the bottom of the connection of the spraying device, while the previously emptied intermediate container chamber B is located at the top of the connecting pipe 1 of the supply system. Thus, the intermediate container chamber B can now be filled and the intermediate container chamber A can be emptied to the spraying device, which is done in the manner described above. Through the now facing mouth at the end of the conduit 9, compressed air enters the intermediate container chamber A, which is emptied through the opening 10, while coating material flows through the opening at the end of the conduit 9 'into the intermediate container chamber B, which flows through the opening 10 'is vented.

Then the intermediate container chambers A, B are rotated again by 180 ° or turned back. These processes are repeated cyclically during the entire coating operation without the high voltage of the coating device having to be switched off.

The contents of the intermediate container chambers A, B are grounded during the filling and before and during the emptying to the high voltage potential of the spraying device. The electrical charge remaining in the intermediate container after emptying can be removed before the subsequent coupling to the grounded supply system, for example by means of leakage resistors.

An uninterrupted coating operation is also possible if a buffer container 18 is connected to the line 7 leading to the spraying device 2 and is filled by the respective lower intermediate container chamber B and can supply the spraying device 2 during the emptying pauses when the intermediate containers are rotated. The buffer container 18 can by the intermediate container or its own compressed air line 19 are pressurized and thereby emptied. Since this development of the invention does not depend on breaks in operation, there is also the possibility of using a single common intermediate container arrangement (per color) for all connected atomizers, that is to say, for example, for all “levels” of several atomizers in a spray booth.

In order to avoid settling and drying of the coating material in the intermediate containers A and B during longer breaks in operation, the intermediate containers can be rotated continuously and periodically during these breaks or pivoted about their axis of rotation. Furthermore, during breaks in operation, it is possible to periodically control the internal pressure in the chambers A, B (line 16) and the pressure of the buffer tank 18 mentioned (line 19) so that the liquid in the line 7 is constantly acted upon in opposite directions . This means that achieves a constant viscosity of the material and prevents settling.

The system described above can be modified in such a way that the intermediate container arrangement with its two chambers A, B is arranged immovably and periodically for this purpose the connections of the supply system and the coating device, for example the external connecting devices 6, 6 ', with their valves 13, 13' the intermediate container arrangement A, B can be moved around, in particular can be rotated about its axis. The method would then be characterized in that the connections mentioned are rotated from a first position, in which the one intermediate container chamber A is filled by the supply system and its contents are electrically insulated from the spray device, into a second position, in which the content of this chamber A is isolated from the supply system and emptied to the spray device. The same applies vice versa for the other chamber B. The other features of the system described can be retained here.

The connecting devices 6, 6 'contain couplings for automatically connecting the inlet and outlet openings 5 and 5' of the container chambers A, B to the outlet pipe 1 and the air line 15 or to the lines 7 and 16. Preferably, the valve arrangements 13 and 13 ', each containing two changeover valves for the purposes explained above, can be moved along the illustrated double arrows against the container openings 5 and 5' and away from them. This can be useful for coupling and uncoupling, but is also advantageous in terms of electrical insulation. If the connection is interrupted, that is, if the connecting device 6, 6 'is not required for filling or emptying one of the chambers A, B, the valve arrangement 13, 13' can be pushed as far away from the adjacent intermediate container chamber A or B that its distance from the outside of the container is larger than the electrical flashover distance of the high voltage applied in air. This avoids the risk of short-circuits due to condensation, which can form on the outside of the container, particularly in the case of pressurizable containers.

In a modification of this particular embodiment of the invention, there is also the reverse possibility of arranging the intermediate container containing the chambers (A, B) itself to be displaceable against the connecting devices and away from them. When the connection is interrupted, the container is then pushed so far away from the connecting devices that the distance in the manner explained is greater than the electrical flashover distance.

Claims (16)

1. Method of serially electrostatically coating work pieces with electrically conductive coating material in which the coating material flows from a supply system at low potential or earth potential initially into an intermediate container comprising two chambers (A,B) and is fed from it to a spraying device at high voltage potential, the intermediate container constantly insulating the spraying device from the supply system,
   characterised in that the intermediate container (A,B) is rotated from a first position, in which it is filled from the supply system through an opening in the container whilst its contents are electrically insulated from the spraying device, into a second position, in which its contents are insulated from the supply system and are emptied into a conduit leading to the spraying device, whereby the two chambers (A,B) of the intermediate container are each filled and, after rotation, emptied, alternately.
2. Method as claimed in Claim 1, characterised in that the second chamber (B) is filled from the same outlet of the supply system and is emptied into the same conduit to the coating device as the first chamber (A).
3. Method as claimed in one of the preceding claims, characterised in that the chambers (A,B) are emptied by compressed air.
4. Method as claimed in one of the preceding claims, characterised in that the chambers (A,B) are constantly or periodically rotated or tilted in operational interruptions so that deposition of the coating material on the internal walls of the container is prevented.
5. Installation for carrying out the method as claimed in one of the preceding claims for serially electrostatically coating work pieces with electrically conductive coating material including a supply system at a low potential or earth potential, a spraying device at a high voltage, two intermediate container chambers (A,B) constantly insulating the supply system from the spraying device and connecting devices (6,6') which may be controlled to connect the intermediate container chambers (A,B) to an outlet (1) of the supply system or to a conduit (7) leading to the spraying device and to release these connections, characterised in that the two intermediate container chambers (A,B) are sealed with the exception of closable openings (5,5') serving as an inlet and an outlet, have walls (3,3', 4,4'), which comprise insulating material and seal the chambers from the exterior and from one another, and are mounted to be rotatable about a common axis.
6. Installation as claimed in Claim 5, characterised in that the two intermediate container chambers (A,B) are arcuate in cross-section and are so secured to one another that their flat base walls (4,4') engage one another and that their common axis of rotation is disposed in the centre between the two base walls (4,4')
7. Installation as claimed in Claim 5 or 6, characterised in that extending within the intermediate container (A,B) from the opening (5,5') of the intermediate container chamber (A,B) there is a conduit (9,9') of a pipe construction (11,11') disposed in the container opening (5,5') which opens out in the vicinity of the container wall (4,4') opposite to the opening (5,5'), that the pipe construction (11,11') has an additional opening (10,10') in the intermediate container (A,B) in the vicinity of the container opening (5,5') and that the pipe construction (11,11') has two separate connections, of which one is connected to the opening at the end of the conduit (9,9') and the other is connected to the additional opening (10,10').
8. Installation as claimed in Claim 7, characterised in that when filling the intermediate container chamber (A,B) the coating material flows through the opening at the end of the conduit (9,9') into the intermediate container chamber (A,B) and air escapes through the additional opening (10,10') of the pipe construction (11,11'), that when emptying the intermediate container chamber (A,B) the coating material leaves the chamber through the additional opening (10,10') and that the connecting devices (6,6') at the outlet (1) of the supply system and at the conduit (7) leading to the spraying device include a respective controlled valve arrangement (13,13') with which the pipe construction (11,11') may be connected in dependence on the rotational position of the intermediate container chambers (A,B) to the supply system, the conduit leading to the spraying device and/or to an air conduit (15,16).
9. Installation as claimed in Claim 8, characterised in that connected to the valve arrangements (13,13') there is a venting conduit (15) and a compressed air conduit (16) serving to empty the intermediate container chambers (A,B).
10. Installation as claimed in one of Claims 5 to 9, characterised in that the connecting devices (6,6') include connector portions which are movable towards the container opening (5,5') and away from it, one of which connector portions is connected to the supply system and the other is connected to the conduit (7) leading to the spraying device.
11. Installation as claimed in one of Claims 7 to 10, characterised in that each pipe construction (11,11') includes two valves, of which one is connected to the conduit (9,9') and the other is connected to a shorter, second pipe, whose mouth constitutes the additional opening (10,10').
12. Installation as claimed in one of Claims 5 to 11 for a plurality of selectable coating materials of different colour, characterised in that each intermediate container chamber (A,B) comprises an elongate insulated container with individual chambers which constitute a unit and correspond to the number of the colours and are separated from one another by transverse walls and for which a corresponding number of outlets (1) from the supply system and connections for the spraying device are arranged in respective rows parallel to the axis of rotation of the container.
13. Installation as claimed in one of Claims 5 to 12, characterised in that connected to the conduit leading to the spraying device is a buffer container (18) which may be filled and acted upon by pressure from the intermediate container (A, B).
14. Installation as claimed in one of Claims 5 to 13, characterised in that the connecting devices (6,6') include couplings for automatically connecting inlet and outlet openings (5,5') of the container chambers (A,B) with external conduits (1,7,15,16).
15. Installation as claimed in one of Claims 5 to 14, characterised in that the connecting devices (6,6') include a connector arrangement (13,13') which may be moved towards the container openings (5,5') and away from them and which, when the connection is interrupted, is moved so far away from the adjacent intermediate container chamber (A,B) that its spacing from the external surface of the container is greater than the electrical spark-over distance of the applied high voltage in air.
16. Installation as claimed in one of Claims 5 to 14, characterised in that the intermediate container is arranged to be movable towards the connecting devices (6,6') and away from them, whereby when the connection is interrupted the container is moved so far away from the adjacent connecting devices that the spacing is greater than the electrical spark-over distance of the applied high voltage in air.

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