EP1362640B1 - Sprayer for electrostatic in-series coating of workpieces - Google Patents

Description

The invention relates to a rotary atomizer according to the preamble of claim 1. In particular, it is high-rotation atomizer, which are needed for the electrostatic serial coating of workpieces such as vehicle bodies using the known side and roof machines and painting robots.

When the workpieces are to be coated with conductive material such as water-based paint, the electrostatic rotary atomizers are known to be externally charged in many cases, so that the atomizer bells that are at high voltage potential during direct or contact charging can be grounded and thus not isolated from the grounded paint supply system must, for which the well-known, relatively expensive potential separation systems would be required. In other cases, external charging may also be preferred or combined with direct charging for other reasons, for example to improve the application efficiency defined as the ratio of the amount of particles depositing on the workpiece to the amount of particles being sprayed ( DE 4105116 ).

At one of the EP 0238031 Known Hochrotationszerstäuber of the type mentioned sit the needle-shaped electrodes in a circular ring body made of insulating material, which is to surround the outer casing of the atomizer with considerable radial distance and is held for this purpose of radially projecting from the outer housing supports. This construction has not proven in practice, inter alia, because it is too bulky. In addition, efforts were made to creep or surface path between the electrode tips by embedding the electrodes in finger-like projecting pins ( Fig. 3 of the EP 0238031 ; EP 0283918 ). In a further development of this pin construction, the electrodes are arranged in elongated insulating bodies in the now commonplace atomizers for external charging, which protrude from a directly attached to a rear part of the outer housing annular body axially toward the workpieces to be coated, in which case the ionization ends of the electrodes in a considerable radial distance from the outside of the housing are arranged (Dürr / Behr, Technical Manual, Introduction to the technology in the car paint, 04/1999; EP 0767005 ; DE 19909369 etc.). Apart from the fact that for constructive and other reasons such as cleaning problems only a small number of electrodes can be distributed around the atomizer, these conventional electrode holder designs have the disadvantage that they due to their bulky outer shape in coating systems with painting robots whose movement and operation options Restrict, for example, because narrow angular or internal areas of the workpieces are difficult or impossible to reach, or because they impede the desired in some coating systems replacement of atomizers in automatic changing stations.

However, a further problem of the known atomizers of the type under consideration consists in the fact that the electrode tips arranged radially far outside of the bell cup are prone to fouling, in particular by self-coating. This is not only undesirable because of the risk of contamination of the workpieces to be coated by later detaching paint and other particles, but also because of the pollution, the electric field is deteriorated, resulting in a reduction of the application efficiency and then even stronger self-coating Episode has. Field weakening can also be caused by overspray particles are, ie sprayed on the workpiece and then "vagabond" paint droplets that can be reflected on the electrode tips of the moving through the overspray cloud atomizer. Because of the field weakening, more and more particles can reach the electrodes until finally the ionization of the ambient air is more or less interrupted by the corona effect of the electrodes. In addition, the pollution can lead to electrical flashovers and other disturbances. For these reasons, the electrodes must be regularly cleaned at short intervals with the result of unwanted interruptions. Undesirable is also required for the cleaning time, labor, equipment and material costs, which prove both manual and automatic cleaning the mentioned pin-like electrode holder designs as a hindrance.

The DE 197 09 786 A discloses an atomizer for the electrostatic series coating of workpieces with coating powder emerging from a nozzle of an insulating material housing. In the outer area in front of the nozzle, needle electrodes connected to a high-voltage device for the electrostatic charging of the sprayed coating powder are arranged. Similar spraying devices with electrodes arranged directly on the outside of the atomizer housing or at a small distance are also made US 5 686 149 respectively. US 5,928,731 known. These are not rotary atomizers.

On the other hand, the invention is based on the object of specifying a smallest possible electrostatic rotary atomizer which is also suitable for coating systems with painting robots, which enables a better application efficiency in a simple manner, that is to say in particular without frequent cleaning work.

This object is solved by the features of the claims.

In contrast to the mentioned known Rotationserstäubern so no finger-like projections, pin-like protruding holder or spoke-like supports are provided for the electrodes. Instead of the hitherto customary electrode holders, the charging electrodes are integrated directly into or on the housing without gap or external distance between their ionization ends and the outside of the atomizer housing.

The invention surprisingly reduces the tendency of the atomizer to self-coat the electrode tips and, accordingly, both the application efficiency and the useful life of the atomizers in operation are improved. One possible reason for this is the greater proximity of the ionization ends of the electrodes to the sprayer atomizer spray tip of a rotary atomizer, with the result that the radially sprayed paint particles are rapidly and reliably charged in a region of high field line concentration and correspondingly highly ionized air before moving farther from the atomizer Remove spray head. Since the density of the field lines is greatest at sharp edges and tips, the chargeability of the paint particles decreases with increasing distance from the electrodes and the bell cup. In addition, the paint droplets become increasingly drier according to their distance from the bell cup, also by the spray jet directed from the atomizer to the atomized coating material directing air, whereby the chargeability is reduced. According to the invention, however, it is possible to supply the paint close to the bell cup, ie in the still wet and therefore easily chargeable state with the highest possible field line concentration.

A particular advantage of the invention is that good application efficiency and low self-coating tendency are achieved by a compact design without the usual electrode holder projecting from the housing. This compact outer shape is favorable especially in the electrostatically assisted robot painting hard to reach workpiece areas and especially of workpiece interiors and also facilitates both manual or automated cleaning of the atomizer and automatic change of the atomizer or its spray head in a corresponding change station. Furthermore, the compact design and low mass of the atomizer improves its dynamic mobility on a robot and other coating machines. The invention is suitable for electrostatic high-speed rotary atomizers and even better than before a meaningful alternative to the complex potential separation systems in the electrostatic coating with conductive coating material such. B. water-based paint.

Because of the arrangement of the charging electrodes directly on or in the housing, their number may be substantially greater than that of e.g. only six outer electrodes of today conventional rotary atomizer, resulting from the invention also has a more uniform spray pattern. At the same time, the application efficiency increases with the possible number of charging electrodes, since the corona effect of many electrodes charges more air molecules, which transfer their charges to the coating material.

• Fig. 1 die Teilschnittansicht eines elektrostatischen Rotationszerstäubers;
• Fig. 2. eine Außenansicht eines im wesentlichen Fig. 1 entsprechenden Zerstäubers;
• Fig. 3 eine Außenansicht einer anderen Ausführungsform eines Rotationszerstäubers;
• Fig. 4 eine weitere Ausführungsform eines Rotationszerstäubers; und
• Fig. 5 die Teilschnittansicht eines Ausführungsbeispiels der Erfindung mit zwei verschiedenen Elektrodenanordnungen.

In the embodiments illustrated in the drawings, the invention is explained in detail. Show it

• Fig. 1 the partial sectional view of an electrostatic rotary atomizer;
• Fig. 2 , an exterior view of a substantially Fig. 1 corresponding atomizer;
• Fig. 3 an external view of another embodiment of a rotary atomizer;
• Fig. 4 another embodiment of a rotary atomizer; and
• Fig. 5 the partial sectional view of an embodiment of the invention with two different electrode arrangements.

The in Fig. 1 schematically shown Hochrotationszerstäuber contains in its outer housing body 1 of the illustrated, in essential hollow cylindrical shape in a conventional and conventional manner a driven with compressed air turbine 2, on the hollow shaft 3 of the front end of the housing body 1 rotating bell cup 4 is mounted. Through the hollow shaft 3 is known to extend in a paint tube construction 5, the line for the coating material to the bell cup 4th

On the rear end of the housing body 1, a holding body 6 is placed for a high-voltage supply, concentrically enclosing the housing body 1 with its cylindrical ring member 61, and at the radially extending end wall 62 in the axial direction outwardly a high voltage cable holder 63 is attached.

On the side facing the bell cup 4 of the housing body 1 sits on the peripheral surface adjacent to the holding body 6, an annular body 8, at its rear end a projection 81 is formed with evenly distributed around the axis of rotation of the atomizer bores, which extends axially parallel in the holding body 6 , The outer surfaces of the annular body 8 and the holding body 6 form a step and gapless transition. The housing body 1, the annular body 8 and the holding body 6 are made of insulating material, in particular the body 1 and 6, but also the annular body 8 may consist of PTFE, which is particularly prone to contamination due to its surface properties.

Although the bell cup 4 of an atomizer of the type illustrated could operate at a convenient high voltage potential for direct charging, it is here assumed that the coating material radially sprayed from its rotating edge is initially uncharged and is to be charged by an electric field outside the atomizer. For this purpose, in the annular body 8, a ring of the rotation axis on a concentric circle with uniform angular intervals surrounding needle electrodes 10 which lie in the illustrated example with the front end of the atomizer and thus the workpieces to be coated facing peaks parallel to the axis of rotation. Instead, they could also be inclined or angled against the direction of the axis of rotation.

Suitably, the electrodes may be embedded so that the ends of their tips are gap-free (without recess) flush with the surrounding end face 82 or other surface of the insulating ring member, so here the ring body 8, so that the electrode tips do not pollute and possibly necessary Cleaning the surrounding surface areas of the ring body is not hindered. One possibility for this is the ring body or its surface in the region of the electrode tips z. B. ceramic or other material with similar high strength properties and to grind with the densely inserted electrodes, which is possible without significantly affecting the producible electrostatic field at the needle tips. Another possibility is the arrangement of the needle tips in depressions of the surrounding insulating surface, which can be filled with a non-weakening the electrostatic field mass or possibly covered with a thin protective film.

The needle electrodes 10 can be electrically connected in each case via a damping resistor 12 inserted into the bore of the projection 81 of the annular body 8 with a circular ring conductor 14 concentric with the axis of rotation, which is seated in the holding body 6 in isolation and in turn via one or more radially arranged further high-voltage conductors 15 and an axial connection means which may include a further resistor 16 located in the cable holder 63 is connected to the high voltage cable 17. The ring conductor 14 connects all electrodes 10 to the cable 17.

The uniform distribution of a larger number of charging electrodes, each with associated damping resistances u.a. the process reliability, when in operation, the electrode assembly inappropriately approaches the grounded workpiece, so that it could cause flashovers or short circuits, which should be prevented in a known manner by a control and regulating electronics of the high voltage generator. However, instead of assigning each electrode its own damping resistor, it is also possible to connect two or more electrodes via a common damping resistor to the high-voltage supply device of the atomizer.

The high-voltage generator usually consisting of a compact cascade construction does not have to be connected to the electrode arrangement via an external cable such as 17, but can also be installed directly in or on the atomizer. It is also possible to provide for each electrode or individual electrode groups each have their own high voltage generator, for example, in the bore of the approach 81 similar recesses in the vicinity of the electrodes.

As can be seen, the radial distance of the tips of the needle electrodes 10 from the axis of rotation of the atomizer and thus of the spray edge 4 'of the bell cup 4 is substantially smaller than in the currently conventional comparable atomizers. The radial distance of the electrode tips from the spray-off edge 4 'is smaller in the illustrated example than the diameter thereof, in contrast to, for example, the EP 0171042 and 0238031 according to which it should be larger than twice the edge diameter. For working with external charging air atomizer applies with the proviso that the radial distance of the distributed around the longitudinal axis of the atomizer, ie the central axis of the ink nozzle charging electrodes of the electrically conductive parts on the circumference of the spray head should be correspondingly low. It is essential Further, that the electrode tips in the axial direction at such a distance behind the spray edge 4 'of the bell cup 4 (or behind the electrically conductive parts of the spray head eg an air atomizer) are reset, that the required air insulation distance between the possibly grounded spray head and the electrode assembly complied and the ion current flowing between them through the charged air remains limited to acceptable levels. In view of the control and regulatory measures required for process safety, a reliable grounding of the respective components of the atomizer may be important, these components such as the coating material supplying the spray head and adjacent components expedient from electrically poor or non-conductive materials such as plastic or ceramic can exist.

In Fig. 2 is the electrode arrangement of a large extent Fig. 1 corresponding atomizer with here, for example, twelve evenly distributed around the axis of rotation electrode tips 102 in the end face 82 of the on the housing body 1 'patch ring body 8' spatially recognizable.

Furthermore, in Fig. 2 an inserted in the front opening of the housing body 1 'shaping air ring 20 with a ring concentrically around the axis of rotation distributed air nozzles 21 recognizable. The directing air ring has the known function of bringing the spray into a desired shape and to apply the sprayed coating material with an axial component in the direction of the workpieces to be coated. The shaping air can be a cause of deteriorated charging in particular in the known atomizers per se, since it dries the sprayed paint particles and thereby reduces their chargeability with increasing distance from the spray-off. Therefore, according to the invention, it proves to be advantageous for the paint droplets to be located directly on the spray-off edge, ie still in the largely "wet" state, due to the radial proximity of the electrode assembly reach in a range of high field line density and are correspondingly well chargeable by the particularly highly ionized air there.

It may be expedient, the ion flow of the ionized by the electrode tips air molecules by another concentric to the axis of rotation ring of nozzle-like (not shown) air holes, which in the electrode tips containing ring member such. B. the ring body 8 are preferably located directly on the electrode tips or in the vicinity, to grant an additional component of movement in the direction of the spray head and thus to sprayed there paint particles. This expediently like a shell over the surface of the outer housing, in Fig. 1 Thus, the outer casing body 1 directed air prevented in this area at the same time a contamination of the outer housing and also serves as an additional steering device for vaping paint particles in the axial direction to the workpiece. Instead of a ring of air holes and an annular nozzle-like air gap can be provided.

Instead of air, the illustrated nozzle arrangements can also be fed with another suitable steering gas. In addition, it may be useful to increase the electrical conductivity of the air molecules in the vicinity of the electrode tips from the nozzle arrangement described z. As air of increased humidity or a conductivity-increasing gas to blow and / or the exiting air to add a conductivity-increasing gas. The use of corona ionization increasing gases is conceivable.

A conductive paint particle layer on the outside of the nebulizer housing could form lead bridges between the electrodes and grounded parts of the nebulizer. Similar to an air or gas envelope laying around the atomizer housing can also be avoided by contaminating the housing by enclosing the housing and preferably the entire outer surface of the atomiser by a shell made of a porous, air-permeable material (see also the already mentioned above EP 0283918 ). Another possible measure against contamination or self-coating of the outside of the atomizer is to produce the surfaces of the housing and / or other vulnerable outer parts of a material having the property of particularly low wettability and / or the static electrical charge in the sense of low tendency to fouling affected. In addition to other materials or coatings known from interface chemistry, for this purpose, in particular in the case of water-soluble colored lacquer, z. B. materials with the well-known "lotus effect" according to microstructured surfaces suitable (which can be realized even with PTFE).

Instead of the needle electrodes of the embodiments described here, it is also conceivable to use a circular electrode ring concentric with the atomizer axis with a sharply delimited knife edge in the relevant insulating ring part.

Fig. 3 shows one against Fig. 2 modified embodiment in which the outer housing 30 with an axially projecting at its front end, z. B. integrally molded end ring 31 extends like a umbrella over a rear part of the spray head, here so the bell cup 34. By the end ring 31 of the bell cup 34, which may consist of metal or other electrically conductive material as usual, so that it is shielded not directly facing the electrode tips 103 and a region of highest field line density. The end ring 31 thus lies in the direct (straight line) connection path between the bell cup and the electrode tips. By this measure, it is possible to arrange the electrode tips axially closer to the bell cup or spray head. Also shows Fig. 3 in that an even greater number of electrode tips 103 are possible than in Fig. 2 ,

In a further development of the invention and the embodiment according to Fig. 3 can according to Fig. 4 the outer housing 40 of the atomizer in its circumference axially elongated recesses 42 of the illustrated trough-like form contain, in which at its rear end in each case the tip of one of the distributed about the axis of rotation needle electrodes 104 is exposed. The trough shape of the recesses should be as easy as possible to clean. The sunk with their tips in these recesses 42 electrodes 104 may be in a separate annular body, for example, as in Fig. 1 or instead be directly embedded in the outer housing 40 itself. The annular body or the outer housing form the electrode tips surrounding radially extending, so the workpieces to be coated facing end surface regions 84, which limit the trough-like recesses 42 at the end. Similar to in Fig. 3 Here, too, the bell cup 44 itself (in contrast to the sprayed paint particles) is shielded by an axially projecting end ring 41 against excessive field line concentration.

An in Fig. 5 illustrated further embodiment of a nebulizer of the invention corresponds in the rear part of the nebulizer and in particular with respect to the high voltage supply device according to the embodiment Fig. 1 , However, the needle electrodes 10 'are not seated as in FIG Fig. 1 in a separate annular body, but in a similar to the annular body 8 molded part 8 'of the outer housing body 1' itself, as in Fig. 1 a rounded and continuous in the front peripheral portion of the housing body 1 'merging end face 82' forms.

In a further development of the invention is further in the in Fig. 5 illustrated embodiment, in addition to the electrodes 10 'a similar second arrangement of concentric with equal mutual angular intervals distributed around the axis of rotation needle electrodes 105 is provided. As shown, the needle electrodes 105 and / or the electrodes 10 'can lie parallel to the axis or form a suitable angle with the longitudinal direction. The needle electrodes 105, as well as the electrodes 10 'as shown, can be embedded in a ring part 8 "itself forming the peripheral wall of the housing body 1' or instead in a separate ring body placed on the housing body. The ionization ends of this additional electrode assembly are preferably in a radial plane axially offset from the ends of the electrodes 10 'between them and the bell cup 54, and their radial distance from the axis of rotation may be smaller than that of the ionization ends of the back electrodes 10'. , The electrodes 105 are similar to the electrodes 10 'connected via damping resistors 56 to a ring in the part 8''located, concentric with the axis of rotation ring conductor 57, which in turn is connected in a manner not shown with a high voltage device.

An improved control behavior can be achieved with the two electrode arrangements spaced from one another in the manner described, since the operating current (flowing largely into the grounded bell cup) is better divided. In addition, in principle similar to the known combined internal and external charging ( DE 4105116 ), but preferably with a grounded bell cup, wherein the front electrode ring with the needle electrodes 105 mainly for charging the coating material and the rear and outer electrode ring is also to serve for guiding and shielding the spray jet. Preferably, the two (or more) separate electrode arrangements become The described type each connected to their own high voltage generator and placed on different potentials, wherein the electrodes closer to the spray head are usually at a lower potential. But it is also possible to connect the two electrode assemblies to a common high voltage generator.

Claims (14)

1. A rotary atomiser for the serial electrostatic coating of workpieces including a rotating bell plate (4), from whose edge (4') the coating material is sprayed radially, an outer housing (1) of insulating material, which supports the bell plate (4) of the atomiser and through which a conduit (5) for the coating material extends along the rotary axis of the atomiser to the bell plate (4), and an electrode arrangement (10), which is connected to a high voltage supply device (14) and is adapted to externally charge the atomised and radially sprayed coating material by ionisation of the air surrounding the outer housing (1) and which concentrically surrounds the rotary axis of the atomiser and is embedded at the outwardly exposed ionisation end in an annular member (8) of insulating material, which is set back with an axial spacing behind the bell plate (4), characterised in that the electrode arrangement (10) is arranged in the annular member (8) of insulating material directly on the outer surface of the outer housing (1).
2. An atomiser as claimed in claim 1, characterised in that the annular member (8,8',8") is positioned on the outer surface of the outer housing (1,1') or constitutes a portion of the wall of the outer housing.
3. An atomiser as claimed in claim 1 or 2, characterised in that the electrode arrangement consists of a plurality of needle-shaped electrodes (10,105).
4. An atomiser as claimed in claim 3, characterised in that the electrodes (10,105) are connected to an annular conductor (14,17), which is concentric with the rotary axis and is common to them.
5. An atomiser as claimed in one of the preceding claims, characterised in that at least two annular electrode arrangements (10,105) concentric with the rotary axis are provided, the ionisation ends of which are spaced from one another axially and/or radially.
6. An atomiser as claimed in one of the preceding claims, characterised in that the ionisation ends of the electrodes (104) are arranged recessed in trough-like recesses (42) formed in the outer surface of the outer housing (40).
7. An atomiser as claimed in one of the preceding claims, characterised in that a ring of axially opening gas openings (21), which concentrically surround the rotary axis, is provided, which openings are connected to a pressurised gas conduit in the atomiser.
8. An atomiser as claimed in claim 7, characterised in that the gas openings are located in the annular member including the electrode arrangement in the vicinity of the ionisation end.
9. An atomiser as claimed in one of the preceding claims, characterised in that the ionisation ends (102) of the electrodes (10) are embedded in the surface regions (82,84) of the annular member adjoining one another without gaps at the surface regions.
10. An atomiser as claimed in one of the preceding claims, characterised in that the ionisation ends of the electrodes (10,104,105) are embedded in end surfaces (82,82',82",84) of the outer housing or annular member extending transversely to the rotary axis of the atomiser.
11. An atomiser as claimed in one of the preceding claims, characterised in that the outer housing (300 defines a shield ring (31), which projects axially beyond at least a portion of the bell plate (34).
12. An atomiser as claimed in one of the preceding claims, characterised in that the outer housing (1,1') and/or the annular member (8) containing the electrode arrangement consist of PTFE.
13. An atomiser as claimed in one of the preceding claims, characterised in that at least one high voltage generator constituting the high voltage supply device is arranged in the atomiser.
14. An atomiser as claimed in one of the preceding claims, characterised in that a respective individual high voltage generator is provided for each electrode or for individual electrode groups.

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