EP0455107B1 - 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 8, 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 sprayed coating particles on the charging field 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 which is at high voltage potential horizontal spray device 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-29 00 660, in which the coating material first arrives from an earthed ring line in an insulated first intermediate container and then from this into a second intermediate container, the output of which is constantly the same High voltage lying 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 the aforementioned DE-PS 29 00 660, the invention has for its object to provide a method and a system that require less space and allow in the case of a large number of selectable coating materials of different colors, the intermediate container required for this can be combined into a compact unit in the smallest of spaces.

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

According to the invention, the spatial distances between the intermediate containers from one another and from the supply system can be substantially reduced by the described insulating means, which in the simplest case consist of a rotatable container.

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 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 zone. This possibility is prevented by the insulating walls of the intermediate containers.

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, either between the two intermediate containers or between the first intermediate container and the outlet opening of the supply system. This is achieved according to the invention without the previous need to maintain or set a distance between the intermediate containers and the supply system which is greater than the flashover distance of the high voltage applied.

Fig. 1

eine Anlage mit zwei Zwischenbehältern gemäß einem ersten Ausführungsbeispiel;

Fig. 2

eine Anlage gemäß einem zweiten Ausführungsbeispiel;

Fig. 3

eine Anlage gemäß einem dritten Ausführungsbeispiel;

Fig. 4

eine schrägbildliche Ansicht einer Anlage für eine Vielzahl verschiedenfarbiger Beschichtungsmaterialien; und

Fig. 5

eine besondere Ausführungsform des zweiten Zwischenbehälters.

The invention is explained in more detail using various exemplary embodiments. In the drawing show schematically

Fig. 1

a system with two intermediate containers according to a first embodiment;

Fig. 2

a system according to a second embodiment;

Fig. 3

a system according to a third embodiment;

Fig. 4

an oblique view of a plant for a variety of different colored coating materials; and

Fig. 5

a special embodiment of the second intermediate container.

1 shows two intermediate containers A and B connected between an earthed supply system, of which only one outlet pipe 1 is shown, and an electrostatically operating spray device (not shown). The intermediate containers A and B each consist of an elongated hollow cylinder, the circular cylindrical outer wall 2 or 3 (outer shell) of insulating material of a thickness sufficient for electrical insulation in this embodiment. These cylinders forming the intermediate containers are divided in their longitudinal direction by transverse walls in each case into a number of partial containers corresponding to the number of selectable coating materials of different colors (as is shown in FIG. 4 for another exemplary embodiment). In the embodiment shown in FIG. 1, both intermediate containers A and B are immovably mounted. They lie with their longitudinal axes horizontally parallel to one another and to a row of outlet pipes 1 corresponding to the number of colors that can be selected, the two intermediate containers A and B being vertically one above the other are arranged and the vertical longitudinal axis of the outlet pipe 1 intersects both cylinder axes.

Each sub-container of the intermediate container A has at its upper end an inlet opening 4, for example in the form of a valve, which lies on the longitudinal axis of the outlet pipe 1, and at the lower end an outlet opening 5 likewise in the form of a valve an inlet opening 6, for example in the form of a valve, which lies axially below the outlet opening 5.

The entire intermediate container A is concentrically enclosed by a likewise cylindrical insulating shell 7 of sufficiently thick insulating material which is circular in cross section and which can be rotated by at least 180 °, for example by 360 °, about the horizontal longitudinal axis relative to the intermediate container A in accordance with the arrows shown. The insulating shell 7 contains an opening 8 at the positions corresponding to the inlet openings 4 of the various partial containers in the horizontal direction. In the position of the rotatable insulating shell 7 shown, its opening 8 is located exactly between the mouth of the outlet pipe 1 and the inlet opening 4 of the intermediate container A.

The second intermediate container B is also concentrically surrounded over its entire length by an insulating shell 9 which, according to the arrows shown, can be rotated in two directions relative to the intermediate container B about its longitudinal axis, for example by 90 °. The insulating shell 9 only has to be partially cylindrical, so that it covers the opening 6 and can be pivoted away from it. The intermediate container B has permanent line connections (not shown) to the spray device.

A distance which improves the insulation is maintained between the insulating shells 7, 9 and the associated containers A, B. The insulating shells can also be arranged so that they serve as a cover for the openings and prevent loss of solvent and drying of the paint, especially when the inlet and outlet openings of the containers do not contain any valves.

The operation of the system shown is known in principle (see. DE-C-29 00 660). Accordingly, the outlet pipe 1 is always at a low or earth potential, while the content of the intermediate container B is constantly connected to the high voltage of the spraying device and the potential of the intermediate container A changes cyclically between high voltage and earth potential. When the intermediate container A is filled by the supply system, its contents are grounded and isolated from the contents of the intermediate container B. Before and during the intermediate container A is emptied into the intermediate container B, the contents of the intermediate container A, on the other hand, are set to high voltage and isolated from the grounded supply system. While the intermediate container B is then emptied to the spraying device, the intermediate container A can be filled again.

In contrast to the known system, the insulation required in each case is not achieved by a spatial distance which is greater than the respective flashover width of the high voltage, but by the insulating material of the container walls and by the insulating shells 7 and 9. This allows the distance between the mouth of the outlet pipe 1 and the liquid in the intermediate container A and the distance between the outlet opening 5 and the liquid in the intermediate container B, between which an electrical flashover distance would otherwise exist, would be smaller than the respective electrical flashover distance.

As shown, when filling the intermediate container A, the opening 8 of the insulating shell 7 is located between the outlet pipe 1 and the inlet opening 4, while the insulating shell 7 covers the outlet opening 5 against the inlet opening 6 of the intermediate container B. For additional insulation, the insulating shell 9 is located above the inlet opening 6.

Before the intermediate container A is then emptied into the intermediate container B, it is connected to high voltage, and its inlet opening 4 is covered by the insulating shell 7 against the earthed outlet pipe 1, while the opening 8 of the insulating shell 7 now clears the way below the outlet opening 5 ( as indicated by dashed lines in the drawing). At the same time, the insulating shell 9 is turned away from the inlet opening 6 (as is also indicated by dashed lines). These processes are repeated cyclically according to the material consumption.

The cyclical switching between filling and emptying the containers is not time-critical. The containers and / or insulating shells can be rotated quickly and easily, even while the coating material is being sprayed, without having to rely on coating breaks. This also results in the possibility of a single common intermediate container arrangement (per color) for all connected atomizers, e.g. to be used for all "levels" consisting of several atomizers in one spray booth.

The embodiment of FIG. 2 differs from that of FIG. 1 only in that the intermediate container A is rotatable and has only one opening 14, which is designed as a valve and serves alternately as an inlet opening and outlet opening, and in that the insulating shell 17 of the intermediate container A is similarly partially cylindrical is like the insulating shell 9 of the intermediate container B. When the intermediate container A is filled through the opening 14, the insulating shell 17 is rotated here by 180 ° to the lower end of the intermediate container A, where it lies between the two containers as well as the insulating shell 9. Zum Will drain the intermediate container A is then rotated by 180 ° so that its opening 14 is aligned with the inlet opening 6 of the intermediate container B, while the insulating shells 17 and 9 are rotated into the positions shown in broken lines, in which the insulating shell 17 interrupts the rollover distance to the outlet pipe 1 and the insulating shell 9 clears the way to the inlet opening 6.

Rotatable intermediate containers have the additional advantage that they can be moved continuously or periodically during operation and also during breaks in operation, in order to prevent paint from settling on the inside of the containers. This eliminates the need to prevent sedimentation, for example by pumping, as was previously the case with comparable systems.

With the exception of their openings for the inlet and outlet of the coating material (and possibly of air), the intermediate containers A and B are preferably completely closed insulating cylinders. However, they do not have to be circular-cylindrical as in the previously described exemplary embodiments, but they can also have expedient other cross-sectional shapes. In the embodiment shown in Fig. 3, a rotatable intermediate container A is approximately pear-shaped in cross-section, that is higher than wide, the widest part being when the container is filled and the height dimension along the axis of the outlet pipe 1 and an opening 18 which runs as Valve is formed and as in Fig. 2 alternately serves as an inlet and outlet. The cross-sectional shape shown increases the insulation distances without taking up a lot of space.

3 differs from those of FIGS. 1 and 2 in that there are no separately rotatable insulating shells. Instead is just an attached to the intermediate container A, the round bottom surrounding insulating shell 19 is provided. When the intermediate container A is filled, the insulating shell 19 thus covers the inlet opening 6 of the lower intermediate container B, while covering the mouth of the outlet tube 1 when the intermediate container A is emptied.

FIG. 4 shows the shape and arrangement of intermediate containers A and B essentially in accordance with FIG. 3 in an oblique representation, the separate insulating shells 19 being omitted for simplification. In the other exemplary embodiments, too, the separate insulating shells are not always absolutely necessary. As can be seen from Fig. 4, except for the openings 18 and 6 completely closed containers A and B are elongated cylinders with a circular, pear-shaped or other cross-section, which are horizontally spaced one above the other in a common frame structure below the outlet pipes 1 for the various Colors are stored. Since the intermediate container B is always at high voltage potential, the bearing structure 20 is designed to be insulating.

Instead of an intermediate container in the form of an elongated cylinder with intermediate walls, cylindrical individual containers can also be provided for the different colors, which can be arranged vertically parallel to one another and firmly connected to one another.

The second intermediate container B for the spraying device can be emptied in a manner known per se, not shown, using gear pumps, paint pressure regulators, piston pumps, etc.

5, there is also the possibility of emptying by applying compressed air to the intermediate container B.

In this case the intermediate container is separated by e.g. horizontally lying partition 22 divided into two chambers B1, B2, which are connected by a valve 23. The upper chamber B1 has an inlet opening 26 in the form of a valve, while the lower chamber B2 has an outlet opening 27 in the form of a valve which is connected to the spray device 29 via a line 28. A compressed air line 30 or 31 with a valve is connected to each of the two chambers.

First, when the compressed air valves are closed, both chambers B1 and B2 can be filled through the inlet opening 26 and the valve 23. It is also possible to fill chamber B1 first and then empty it into chamber B2 using compressed air. The chamber B2 is emptied through the compressed air line 31 when the valve 23 is closed. The supply in the chamber B2 can be continuously supplemented in accordance with the consumption.

A return line 32 leading from the line 28 back into the chamber B1 is expediently provided with a valve 33, as a result of which the settling and drying of paint can be avoided. A vent line 34 with a valve 35 is also provided.

The illustrated embodiments can be modified in various respects, and in particular individual features of the different exemplary embodiments can be combined with one another.

The arrangement described with small distances between the intermediate container A and the outlet pipe 1 of the supply system on the one hand and the intermediate container B on the other hand has the advantage of small "fall distances", so that no significant foaming of the coating material is to be feared.

However, there is also the possibility of installing suitable detachable line couplings between the various openings and / or, for example, of designing the outlet pipe 1 in such a way that it can be immersed through the inlet opening for filling the intermediate container A.

In addition, there is the possibility of pivoting separate insulating shells not around the container axis, but around its own, different axis into the section to be insulated, or to push them linearly into this section.

If the second intermediate container can be pressurized, there is also the possibility, during breaks in operation, of the line connected to it and leading to the coating device, e.g. to apply a periodically changing container pressure to the line 28 in FIG. 5 in order to keep the coating material in the line uniformly viscous and to prevent it from settling.

Claims (16)

1. Method of serially electrostatically coating workpieces with electrically conductive coating material in which the coating material flows firstly from a supply system at low potential or earth potential into a first intermediate container (A) insulated from the supply system, then flows out of the first intermediate container (A) into a second intermediate container (B) which is insulated from it and from the supply system and is finally supplied from the second intermediate container (B) to a spraying device at a high voltage potential, the content of the second intermediate container (B) being continuously electrically connected with the spraying device and the content of the first intermediate container (A) being subjected to the high voltage potential when discharged into the second intermediate container (B) but, on the other hand, when being introduced by the supply system is at the potential thereof and the content of the first intermediate container (A) being electrically insulated from an inlet opening of the second intermediate container (B) during filling of the first intermediate container (A) and from an outlet opening of the supply system during filling of the second intermediate container (B), characterised in that at least one of the intermediate containers (A,B) is filled through an opening (4,6,8,14,18) or recess in an insulating shell (2,7,9,17,19) which constitutes the container or at least partially surrounds it and which after filling is so moved for the purpose of insulating that a closed portion of the insulating shell is situated in the pathway through which the coating material is supplied.
2. Method as claimed in claim 1, characterised in that the insulating shell (2,7,etc.) is rotated about an axis for the purpose of insulating.
3. Method as claimed in claim 1 or 2, characterised in that an opening (8) in an insulating shell (7) completely surrounding the first intermediate container (A) is situated, during filling of the first intermediate container, between an inlet opening (4) of the first intermediate container and the outlet opening (1) of the supply system and, after the rotation of the insulating shell (7), is situated between an outlet opening (5) of the first intermediate container (A) and an inlet opening (6) of the second intermediate container (B).
4. Method as claimed in one of the preceding claims, characterised in that an inlet opening (6) of the intermediate container (A,B) is covered after it has been filled by an insulating shell (9) of the container.
5. Method as claimed in one of the preceding claims, characterised in that at least the first intermediate container (A) is rotated for the purpose of insulating.
6. Method as claimed in claim 5, characterised in that the intermediate container (A) is rotated through 180°.
7. Method as claimed in one of the preceding claims, characterised in that the second intermediate container (B) is emptied by compressed air.
8. Installation for carrying out the method of serially electrostatically coating workpieces with electrically conductive coating material as claimed in one of the preceding claims, including a supply system at low potential or earth potential, a first intermediate container (A) disposed insulated from the supply system and having an opening (4,14,18) through which the coating material may be supplied to it from an outlet opening (1) of the supply system, a second intermediate container (B) disposed insulated from the first intermediate container (A) and from the supply system and having an opening (6) through which the coating material may be supplied to it from an opening (5,14,18) in the first intermediate container (A), and a spraying device (29) which is connected to a high voltage and to which the coating material may be supplied from the second intermediate container (B), characterised in that the spacing of the content of the first intermediate container (A) from the outlet opening (1) of the supply system and/or from the content of the second intermediate container (B) is equal to the flashover distance of the applied high voltage or is smaller than it and remains at a constant small value during filling and emptying of the two intermediate containers (A,B) and that at least one insulating shell (7,9,2) is provided which defines or at least partially surrounds the container and which is movable into the flashover path between the first intermediate container (A) and the outlet opening (1) of the supply system and/or an inlet opening (6) in the second intermediate container (B).
9. Installation as claimed in claim 8, charcterised in that the insulating shell is constituted by the wall (2) of the intermediate container (A).
10. Installation as claimed in claim 8 or 9, characterised in that an insulating shell (7,9,17) is provided which is movable around the intermediate container (A,B).
11. Installation as claimed in one of claims 8 to 10, characterised in that the insulating shell (7,9,17,2) is rotatable about a horizontal axis.
12. Installation as claimed in one of claims 8 to 11, characterised in that the first and/or second intermediate container (A,B) is of cylindrical or near cylindrical shape and the insulating shell (7,9,17,19) is of at least part-cylindrical shape.
13. Installation as claimed in one of claims 8 to 12, characterised in that at least one of the intermediate containers (A) is higher than it is broad in cross-section (Fig. 3).
14. Installation as claimed in one of claims 8 to 13, characterised in that the second intermediate container (B) is divided by a partition wall (22), which includes a connecting valve (23), into two chambers (B1,B2), of which the one chamber (B1) has an inlet opening (26) and the other chamber (B2) has an outlet opening (27) connected to the spraying device (29) and that a respective compressed air line (30,31) is connected to the two chambers (B1,B2).
15. Installation as claimed in one of claims 8 to 14 for a plurality of selectable coating materials of differing colour, characterised in that each intermediate container (A,B) comprises a plurality of component containers which are associated with a respective colour, are separated from one another by partition walls and constitute a constructional unit and the two intermediate containers (A,B) are arranged parallel to one another and to a series of correspondingly many outlet openings (1) of the supply system.
16. Installation as claimed in one of claims 8 to 15, characterised in that one or both intermediate containers (A,B) are completely closed cylinder-like containers of insulating material with the exception of the inlet and/or outlet openings (4,5,6).

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