EP1362640A1 - Sprayer for electrostatic in-series coating of workpieces - Google Patents

Abstract

Sprayer unit for electrostatic serial coating of workpieces comprises an electrode array (10) which is integrated into the ring section (8) of an insulating material directly on the outer housing (1) of the unit.

Description

The invention relates to an atomizer according to the preamble of claim 1. In particular, it concerns high-speed rotary atomizers or possibly also air atomizers that are for the Series electrostatic coating of workpieces such as Vehicle bodies using the known Side and roof machines and painting robots are needed.

When the workpieces are coated with conductive material such as water-based paint electrostatic atomizers work as is well known in many cases with external charging, so the atomizer bells or other spray heads, which at the Direct or contact charging is at high voltage potential can be grounded and therefore not from the grounded Paint supply system must be isolated, for which the also generally known, relatively complex electrical isolation systems would be required. In other cases, the external charging also preferred for direct charging for other reasons or combined with it, for example around the as Ratio from the amount of that is deposited on the workpiece Define particles for the amount of sprayed particles Application efficiency to improve (DE 4105116).

In a high-speed rotary atomizer known from EP 0238031 of the genus mentioned at the beginning are the needle-shaped electrodes in a circular ring body made of insulating material, the atomizer's outer casing with considerable radial Distance should surround and for this purpose from the radial Protruding supports are held. This construction has in practice not proven because it is too bulky. In addition, efforts were made to Leakage current or surface path between the electrode tips by embedding the electrodes in protruding fingers To enlarge the pin (Fig. 3 of EP 0238031; EP 0283918). In Further training of this cone construction are general with the today usual atomizers for external charging Electrodes arranged in elongated insulators, the from an immediate to a rear part of the outer housing placed ring body axially towards the to be coated Project workpieces, here also the ionization ends of the electrodes at a considerable radial distance are arranged from the outside of the housing (Dürr / Behr, Technical manual, introduction to technology in car painting, 04/1999; EP 0767005; DE 19909369 etc.). apart assume that for constructive and other reasons such as e.g. only a small number of electrodes due to cleaning problems can also be distributed around the atomizer axis these usual electrode holder designs have the disadvantage that due to their bulky outer shape in coating systems with painting robots their movement and operating options restrict, for example because narrow angles or Inner areas of the workpieces are difficult or impossible to reach or because they are what is desired in some coating systems Replacing atomizers in automatic exchange stations hinder.

Another problem of the known atomizers of the considered But the main thing is that the radially far outside of the spray head arranged electrode tips for soiling in particular due to self-coating. This is not only because of the risk of contamination of the coating Workpieces due to later detaching Paint and other particles undesirable, but also because because the electrical field deteriorates due to the pollution becomes what a decrease in application efficiency and then even stronger self-coating results. Field weakening can also be caused by overspray particles become, i.e. sprayed past the workpiece and then "straying" Paint droplets on the tips of the electrodes of the atomizer moving through the overspray cloud can. Because of the field weakening more and more can Particles reach the electrodes until finally ionization the ambient air through the corona effect of the electrodes more or less breaks off. Pollution can also increase electrical flashovers and other faults. Out For these reasons, the electrodes must be placed regularly at short intervals are cleaned with the consequence of unwanted business interruptions. The cleaning is also undesirable required time, labor, equipment and material, being suitable for both manual and automatic Cleaning the mentioned cone-like electrode holder constructions to be a hindrance.

The invention is therefore based on the object, one for Coating systems with painting robots suitable if possible specify small electrostatic atomizer that is simple Way, in particular without frequent cleaning work enables a better application efficiency than before.

This object is solved by the features of the claims.

In contrast to the known atomizers mentioned are for the electrodes are therefore not finger-like projections, like cones projecting holder or spoke-like supports provided. Instead of the usual electrode holder, the charging electrodes are with no gap or outer distance between their ionization ends and the outside of the atomizer housing directly integrated in or on the housing.

The inclination of the atomizer is surprising by the invention reduced for self-coating of the electrode tips and accordingly both the application efficiency as well improves the service life of the atomizers in operation. On possible reason for this is the closer proximity of the ionization ends the electrodes to the spray edge of the atomizer bell a rotary atomizer (or to the nozzle mouth other Atomizer) with the result that the sprayed paint particles quickly and reliably in an area of high field line concentration and charged accordingly strongly ionized air before moving further away from the spray head. There the density of the field lines at sharp edges and tips at largest, the chargeability of the paint particles increases with increasing Distance from electrodes and spray head. In addition, the paint droplets will change according to their distance from the spray head increasingly drier, also due to the Spray jet steering from the atomizer onto the atomized coating material directed steering air, increasing the chargeability is reduced. According to the invention, however, it is possible the paint close to the spray head, so it’s still wet and therefore good rechargeable state with the highest possible field line concentration to supply.

A particular advantage of the invention is that good Application efficiency and low self-coating tendency due to a compact design without the usual housing protruding electrode holder can be reached. This compact External shape is especially useful for electrostatic support Robot painting of difficult to access workpiece areas and in front all of the workpiece interiors cheap and relieved addition, both a manual or automated cleaning of the Atomizer as well as automatic change of atomizer or of his spray head in a corresponding exchange station. Further is due to the compact design and the low mass of the Atomizer whose dynamic mobility on a robot and other coating machines improved. The invention is suitable for electrostatic high-speed rotary atomizers and for electrostatic supported air atomizer and still allows better than before a sensible alternative to the complex Potential burning systems for electrostatic coating with conductive coating material such. B. water-based paint.

Because of the arrangement of the charging electrodes directly on or their number in the housing can be significantly larger than that e.g. only six outer electrodes of today's rotary atomizers, the invention also results in a more uniform Spray pattern. At the same time increases with the possible number of charging electrodes because of the application efficiency Corona effect of many electrodes charged more air molecules who pass their charges on 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.

The invention is explained in more detail using the exemplary embodiments illustrated in the drawing. Show it

Figure 1 is a partial sectional view of an electrostatic rotary atomizer.

FIG. 2 shows an external view of an atomizer essentially corresponding to FIG. 1;

3 is an external view of another embodiment of a rotary atomizer;

4 shows a further embodiment of a rotary atomizer; and

Fig. 5 is a partial sectional view of an embodiment of the invention with two different electrode arrangements.

The high-speed rotary atomizer shown schematically in FIG. 1 contains in its outer housing body 1 of the shown, in essential hollow cylindrical shape in a known and Usually, a turbine 2 driven with compressed air whose hollow shaft 3 is in front of the front end of the housing body 1 rotating bell plate 4 is mounted. Through the hollow shaft 3 As is known, the line runs in a color tube construction 5 for the coating material to the bell plate 4.

On the rear end of the housing body 1 is a holding body 6 placed for a high voltage feeder, the the housing body 1 with its cylindrical ring part 61 concentrically encloses, and on its radially extending end wall 62 a high-voltage cable holder 63 in the axial direction outwards is scheduled.

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

Although the bell plate 4 of an atomizer shown Type for direct charging at an appropriate high voltage potential let us assume that this is from his rotating edge of radially sprayed coating material is initially uncharged and by an electric field outside of the atomizer to be charged. To this end is a ring in the ring body 8 from the axis of rotation a concentric circle with even angular distances surrounding needle electrodes 10 embedded in the illustrated Example with the front end of the atomizer and thus parallel to the workpieces to be coated lie to the axis of rotation. Instead, they could go against the direction of the axis of rotation is inclined or angled his.

The electrodes can expediently be embedded in such a way that the The ends of their tips are gapless (without sinking) flush with the it surrounding end face 82 or other surface of the insulating Ring part, so here are the ring body 8, so that the tips of the electrodes do not get dirty and the necessary ones Cleaning the surrounding surface areas of the ring body is not hindered. One way to do this is in the ring body or its surface in the area of Electrode tips z. B. made of ceramic or another material with similarly high strength properties and with the tightly inserted electrodes, what without significantly affecting the electrostatic that can be generated Field at the needle tips is possible. Another possibility is the arrangement of the needle tips in depressions surrounding insulating surface with an electrostatic Field not weakening mass poured out or possibly can be covered with a thin protective film.

The needle electrodes 10 can each be electrically connected via an in inserted the bore of the neck 81 of the ring body 8 Damping resistor 12 with a concentric to the axis of rotation circular ring conductor 14 are connected, the sits isolated in the holding body 6 and in turn over a or a plurality of further high-voltage conductors 15 arranged radially and an axial connector that one in the cable holder 63 located further resistor 16 may contain is connected to the high voltage cable 17. The ring leader 14 connects all electrodes 10 to cable 17.

The even distribution of a large number of charging electrodes increased with associated damping resistances et al Process reliability when the electrode arrangement is in operation approaches the earthed workpiece in an impermissible manner, so that flashovers or short circuits could occur, which are known Way of a control and regulating electronics of the high voltage generator should be prevented. Instead of every electrode to assign its own damping resistance, it is however, it is also possible to have two or more electrodes over one them common damping resistance to the high voltage supply device of the atomizer.

The usually consists of a compact cascade construction High voltage generator does not have to be external Cables like 17 are connected to the electrode arrangement, but can also be built directly into or attached to the atomizer his. It is also possible for each electrode or for individual electrode groups each have their own high-voltage generator to provide, for example in the bore of the approach 81 similar recesses near the electrodes.

The radial distance between the tips of the needle electrodes can be seen 10 from the axis of rotation of the atomizer and thus from the spray edge 4 'of the bell cup 4 is significantly smaller than with currently comparable atomizers. The radial one Distance of the electrode tips from the spray edge 4 ' smaller than their diameter in the example shown, in contrast e.g. to EP 0171042 and 0238031, after which it is larger should be as double the edge diameter. For outside charging working air atomizer applies accordingly provided that the radial distance around the longitudinal axis of the Atomizer, i.e. charging electrodes distributed around the central axis of the paint nozzle of the electrically conductive parts on the circumference of the spray head should be correspondingly low. Is essential further that the electrode tips in the axial direction with such Distance behind the spray edge 4 'of the bell cup 4 (or behind the electrically conductive parts of the spray head e.g. of an air atomizer) that the required Air insulation path between the earthed, if necessary Spray head and the electrode arrangement is observed and the ion current flowing between them through the charged air remains limited to permissible values. With regard to the Process security required control measures can a reliable grounding of the relevant components of the Atomizer may be important, these components such as the the coating material feeding the spray head and adjacent components expediently from bad electrical or non-conductive materials such as plastic or ceramic can.

In FIG. 2, the electrode arrangement is largely FIG. 1 corresponding atomizer with here, for example, twelve Electrode tips evenly distributed around the axis of rotation 102 in the end face 82 of the one placed on the housing body 1 ' Annular body 8 'spatially recognizable.

Furthermore, in Fig. 2 is in the front opening of the housing body 1 'used steering air ring 20 with a ring around concentrically the axis of rotation of distributed air nozzles 21 can be seen. The steering air ring has the well-known function of spraying into a desired one Bring shape and the sprayed coating material with an axial component in the direction of those to be coated Workpieces. The steering air can a reason in particular with the known atomizers be for poorer charging as they are the sprayed off Paint particles dry and thus their chargeability increases Distance from the spray edge reduced. According to the invention It also proves beneficial that the Paint droplets directly on the spray edge, i.e. still in the largely "wet" condition due to the radial proximity of the electrode arrangement get into an area of high field line density and accordingly well by the particularly strongly ionized there Air are rechargeable.

It may be appropriate to limit the ion flow through the electrode tips ionized air molecules by another too the axis of rotation concentric ring of nozzle-like (not illustrated) air holes in which the electrode tips containing ring part such. B. the ring body 8 preferably directly at or in the electrode tips Proximity, an additional component of movement in the direction to the spray head and thus to the paint particles sprayed there granted. This expediently like a cover over the surface of the outer housing, in Fig. 1 thus the outer housing body 1 directed air prevents in this area at the same time contamination of the outer housing and also serves as an additional Steering device for stray paint particles in axial direction to the workpiece. Instead of a wreath of Air holes can also be an annular nozzle-like Air gap may be provided.

Instead of air, the explained nozzle arrangements can also be fed with another suitable steering gas. About that In addition, it can be useful to increase electrical Conductivity of the air molecules in the vicinity of the electrode tips from the described nozzle arrangement z. B. air increased Moisture or a gas that increases conductivity blow and / or the escaping air to increase the conductivity Add gas. Also the use of corona ionization increasing gases is conceivable.

A conductive paint particle layer on the outside of the atomizer housing could lead bridges between the electrodes and grounded parts of the atomizer. Similar to an air or gas envelope surrounding the atomizer housing contamination of the housing can also be avoided by that the housing and preferably the entire outer surface of the Atomizer from a shell made of a porous air permeable Material is surrounded (cf. also the EP already mentioned at the beginning 0283918). Another possible measure against pollution or Self-coating of the outside of the atomizer exists therein, the surfaces of the housing and / or others therefor vulnerable outer parts from a material that the Has particularly low wettability property and / or static electrical charge in the sense of a low tendency to contamination affected. Among others from interface chemistry known materials or coatings prove for this purpose in particular with water-soluble colored lacquer z. B. materials with the known "lotus effect" accordingly microstructured surfaces as suitable (which also with PTFE can be realized).

Instead of the needle electrodes of the exemplary embodiments described here it is also conceivable to insulate in the relevant Ring part one concentric to the atomizer axis circular electrode ring with a sharply defined knife edge use.

3 shows an embodiment modified from FIG. 2, in which the outer housing 30 with one at its front end axially projecting, e.g. B. integrally molded end ring 31st umbrella-like up to a rear part of the spray head extends, here the bell plate 34. Through the end ring 31 is the bell plate 34, which, as usual, made of metal or other electrically conductive material can exist, so be shielded so that it does not directly touch the electrode tips 103 and an area facing the highest field line density. The end ring 31 is therefore in the direct (straight line) connection path between the bell cup and the electrode tips. This measure makes it possible to remove the electrode tips to be arranged axially closer to the bell cup or spray head. Moreover Fig. 3 shows that even an even greater number of electrode tips 103 is possible than in FIG. 2.

In 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 contain trough-like shape, in which on its rear Each end of the tip of one around the axis of rotation distributed needle electrodes 104 is exposed. The trough shape the recesses should be as easy to clean as possible. The with their tips in these recesses 42 recessed electrodes 104 can, for example, in a separate ring body as in Fig. 1 or instead directly into the outer housing 40 be embedded yourself. The ring body or the outer housing form the radially extending, surrounding the electrode tips, So facing the workpieces to be coated End face regions 84 which define the trough-like recesses 42 limit at the end. Similar to Fig. 3 is also used here the bell plate 44 itself (in contrast to the sprayed Paint particles) from an axially projecting end ring 41 against shielded field line concentration too high.

Another embodiment shown in FIG Atomizer of the invention corresponds in the rear part of the Atomizer and especially with regard to the high voltage supply device the embodiment of Fig. 1. The needle electrodes However, 10 'does not sit in a separate manner as in FIG. 1 Ring body, but in a ring body 8 similar molded part 8 'of the outer housing body 1' itself as in Fig. 1 a rounded and stepless in the front peripheral part the end face 82 'of the housing body 1' forms.

In a further development of the invention, the one in FIG illustrated embodiment in addition to the electrodes 10 'a second arrangement of concentric with them similar equal mutual angular distances around the axis of rotation distributed needle electrodes 105 are provided. The needle electrodes 105 and / or the electrodes 10 'can, as shown, be axially parallel lie or an appropriate angle with the longitudinal direction form. The needle electrodes 105, like that Electrodes 10 'as shown in a the peripheral wall of the Housing body 1 'self-forming ring part 8' 'or instead in a separate one placed on the housing body Ring body to be embedded. The ionization ends of these additional The electrode arrangement is preferably radial Plane axially offset against the ends of the electrodes 10 ' lies between this and the bell plate 54, and her radial distance from the axis of rotation can, as shown be smaller than that of the ionization ends of the rear Electrodes 10 '. The electrodes 105 are similar to the electrodes 10 'via damping resistors 56 to one in the ring part 8 '' ring conductor concentric with the axis of rotation 57 connected, which in turn in not shown Way is connected to a high voltage device.

With the two spaced apart in the manner described Electrode arrangements can be improved control behavior reach because the (for the most part in the grounded Bell dish flowing) operating current is better divided. In addition, it can in principle be similar to the known one combined internal and external charging (DE 4105116) the charging be improved, but preferably with grounded Bell plate, the front electrode ring with the needle electrodes 105 mainly for charging the coating material and the rear and outer electrode ring also for Steering and shielding of the spray jet should serve. Preferably become the two (or more) separate electrode assemblies of the type described each to its own high voltage generator connected and placed on different potentials, whereby usually the electrodes closer to the spray head lower potential. But it is also possible that two electrode arrangements to a common high voltage generator to join.

Claims (14)

Atomizer for the electrostatic series coating of workpieces
with an outer housing (1) made of insulating material holding the spray head (4) of the atomizer, through which a line (5) for the coating material leads to the spray head along a longitudinal axis of the atomizer,
and with an electrode arrangement (10), which is connected to a high-voltage supply device (14) and is suitable for externally charging the atomized coating material by ionizing the air surrounding the outer housing (1), concentrically surrounding the longitudinal axis of the atomizer and at the ionizing end, which is exposed to the outside, in a ring part (8) is embedded from insulating material, which is set back axially behind the spray head,
characterized in that the electrode arrangement (10) is arranged in the ring part (8) made of insulating material directly on the outside of the outer housing (1). Atomizer according to claim 1, characterized in that the ring part (8, 8 ', 8'') is placed on the outside of the outer housing (1, 1') or forms part of the wall of the outer housing. Atomizer according to claim 1 or 2, characterized in that the electrode arrangement consists of a plurality of needle-shaped electrodes (10, 105). Atomizer according to claim 3, characterized in that the electrodes (10, 105) are connected to an annular conductor (14, 57) which is common to them and concentric with the longitudinal axis. Atomizer according to one of the preceding claims, characterized in that at least two annular electrode arrangements (10 ', 105) concentric to the longitudinal axis are provided, the ionization ends of which are axially and / or radially spaced apart. Atomizer according to one of the preceding claims, characterized in that the ionization ends of the electrodes (104) are arranged recessed in trough-like recesses (42) formed on the outside of the outer housing (40). Atomizer according to one of the preceding claims, characterized in that a ring of axially opening gas openings (21) concentrically surrounding the longitudinal axis is provided, which are connected to a compressed gas line of the atomizer. Atomizer according to claim 7, characterized in that the gas openings are in the ring part containing the electrode arrangement in the vicinity of the ionization end. Atomizer according to one of the preceding claims, characterized in that the ionization ends (102) of the electrodes (10) are embedded in the ring part adjacent to the surface regions (82, 84) surrounding them without gaps. Atomizer according to one of the preceding claims, characterized in that the ionization ends of the electrodes (10, 104, 105) are embedded in end faces (82, 82 ', 82'', 84) of the outer housing or ring part running transversely to the longitudinal axis of the atomizer. Atomizer according to one of the preceding claims, characterized in that the outer housing (30) forms a shielding ring (31) projecting axially over at least part of the spray head (34). Atomizer according to one of the preceding claims, characterized in that the outer housing (1, 1 ') and / or the ring part (8) containing the electrode arrangement consist of PTFE. Atomizer according to one of the preceding claims, characterized in that at least one high-voltage generator forming the high-voltage supply device is arranged in the atomizer. Atomizer according to one of the preceding claims, characterized in that a separate high-voltage generator is provided for each electrode or for individual electrode groups.

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