JPH0510983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for electrostatically coating an object with a conductive material.

<Prior Art/Problems> In a known device suitable for painting car bodies, as disclosed in European Patent No. 0 032 391, a high voltage is applied to the atomizer head to generate an electric field, which The atomized paint particles are electrically charged between the atomizer head and the grounded workpiece. According to this, when relatively conductive coating materials such as so-called water-enamels are used, if the paint reservoir is at ground potential, the atomizer head can be connected to said paint reservoir. There is a problem in that the insulation resistance of the connecting line becomes too low.

This problem can be solved by isolating the entire reservoir from ground, but this method is undesirable because the reservoir requires multiple reservoir tanks to change colors. Apart from the very high cost required for this insulation, the capacitance of large-scale storage devices is very large and therefore the corresponding charging energy (1/
2CU ² ) can become very large and there is a possibility of explosive discharge at the atomizer head. Even with the use of almost solvent-free paints, this risk cannot be completely eliminated. Furthermore, it is not possible to fill a tank at a high potential without switching off the power unless an intermediate tank or a similar type of expensive separate device (German Patent No. 2900660) is provided. Additionally, many known devices require large power, high voltage power supplies that are expensive and uneconomical. Well-known devices of the type related to this invention (U.S. Pat.
No. 3,393,662), this known device has a grounded rotating atomizer and a plurality of external charging electrodes arranged around the atomizer device and connected to a high potential. However, in the case of a substantially radial atomizer arrangement, it is very difficult to prevent the atomizer arrangement and the charging electrodes arranged radially outside thereof from becoming rapidly contaminated by paint particles. . Not only are they harmful to the electric field, but they also have the disadvantage of contaminating the article to be painted when subsequently emitted after a color change. Another drawback is that the coating efficiency can be considerably lower than in conventional equipment in which the atomizer head is connected to a high voltage. These problems are caused by 4 radial installations that are relatively close to the metal part of the housing of the sprayer device, but set back axially a relatively large distance from the face of the spray end.
This problem cannot be solved with a known device having multiple charging electrodes.

SUMMARY OF THE INVENTION The object of the invention is to provide a device that is often used for highly conductive spray coating materials that can change color. The device described above requires little expense for insulation. Additionally, the paint delivery efficiency is very high, does not require excessively expensive (and therefore economically undesirable) high voltage sources, and significantly reduces contamination of the charging field-generating electrodes and atomizer equipment. be able to.

<Summary of the Invention> The object of the present invention is achieved by an apparatus as set forth in claim 1, and in particular by an apparatus having the following features.

The inventors have discovered that what is needed to solve the above-mentioned problems is to optimize not only the high-voltage external electrodes, but also the arrangement of these external electrodes, above all with respect to the external electric field.

The invention was achieved by finding an optimal compromise between good paint delivery efficiency (ratio between paint film and amount of material sprayed), relatively low operating current and minimal pollution. It was done. At the same time, the invention makes it possible to ensure that the electric field on the object to be coated has a uniform distribution, that is, uniform coating. Coating efficiency is improved by increasing the radial distance between the charging electrode and the axis of the atomizer head, while at the same time reducing the operating current.

The invention will be explained in more detail below by means of a preferred embodiment, which is shown to scale in the drawings.

<Description of Embodiments> The illustrated device is a well-known bell-shaped rotating atomizer 1.
It has a sprayer device of the type. The rotating atomizer 1 is preferably a high speed air turbine (e.g.
It has a bell plate 2 forming the atomizer head which is driven by 30000r.pm). For reasons of design and construction, the rotary atomizer drive and assembly unit are primarily made of metal.

A line 4 leading paint or other coating material from a reservoir (not shown) to the bell plate 2 extends along the axis of the atomizer arrangement. Due to the action of this line 4, made for example of a grounded metal tube, the water-based enamel or other similar electrically conductive coating material is at ground potential around the paint nozzle 5 and the spray end 6 of the bell plate 2. . Metal unit 3 is electrically connected to line 4.

The object to be painted, for example a part of the body of a motor vehicle placed on the axis in front of the bell plate 2, is kept at ground potential. The nebulizer device has a separate external housing 7 containing its metal drive and an assembly unit 3 made of an insulating plastic such as polyethylene terephthalate.
Equipped with: These are made as separate parts for ease of assembly. Adjacent parts 8
and 9 is provided with a groove 10 filled with an insulating compound. However, instead of this groove, the location indicated at 7 in the outer housing may be made of metal, for example aluminum, which results in a somewhat lower operating current.

The material of the outer housing 7 (metal or plastic) depends on the form of the atomizer device, i.e. whether a single rotary atomizer 1 is used or alternatively a plurality of atomizers arranged substantially next to each other in a common plane. The choice should depend on whether it is used in a group. If the distance between the axes of the atomizers is less than or equal to a predetermined minimum distance, e.g. less than 15 times the diameter of the atomizing end, then the said minimum distance must be such that the atomizer device or its charging electrode critical dimensions that pose a risk of contamination, and at least the front end of the housing 7 (e.g. extending axially to the radial stage of the housing as shown) must be made of an insulating plastic as described above. . Although the bell plate 2 can be made of plastic, for example acrylic glass, a conventional metal bell plate is preferred for large and low cases.

Since the atomizer device and the object to be painted are held at ground potential, the electric field necessary to charge the coating material must be generated by an external high voltage charging device 20. As shown, each of these external electrodes is attached to an axially projecting outer leg 22 of a right-angled plastic electrode holder 21, and the other leg 23 is attached to an integral part of the holder 21. Preferably it extends at right angles from said outer housing 7 which is secured by a plastic support ring 29. As explained later,
In the illustrated embodiment, three electrode holders are provided, which are distributed equidistantly around the nebulizer device. The electrode 20 itself is an axially disposed metal needle, preferably made of hardened steel with a diameter of about 1.2 mm, the tip of which is at least approximately flush with the axial front end of the retaining portion 24. leg 2 so that it is located at
It is inserted into the holding portion 24 separately provided at the tip of the holder 2. This minimizes the possibility of contamination of the electrode 20. In the illustrated example, only the leading edge of the needle electrode 20 is exposed in a small recess in the holding portion 22.

As an alternative to the arrangement shown, there are other ways of holding the charging electrode in the required position relative to the bell plate 2.

At least two and at most three electrodes 20 can be provided. If only one electrode is used, the electric field and coating will be highly asymmetric, the bell plate 2 will be contaminated, and the coating efficiency will be low, but these drawbacks can be overcome by using two electrodes. I can't say that, but it's a significant improvement.
In the above example of using one nebulizer device alone, the optimum effect is obtained using three electrodes. Providing more electrodes only increases the operating current. If a closed metal ring is used as the external electrode instead of the electrode used in the embodiment according to the invention, the paint delivery efficiency will be very low and, moreover, not only said metal ring but also the atomizing bell plate will be seriously contaminated. Ru.

However, if the atomizer device is configured in a plurality of atomizer groups or arrays arranged side by side with their respective axis distances separated from each other by a distance less than the previously mentioned minimum distance, there is a risk of cross-contamination. However, an optimal device can be constructed with only two electrodes for each nebulizer device. Furthermore, as already mentioned, the distance between the charging electrode 20 and the bell plate 2,
The optimum radial distance from the atomizing tip 6 is thus important; it must be significantly larger than the diameter of the atomizing tip. In the illustrated embodiment, 2 to 4 times the diameter of the atomizing tip is preferred, and approximately 3 times that diameter is optimal. Using a common atomizing bell plate with a spray end diameter of 66 mm and an emissivity of around ¹²⁰ cm3 per minute, the radial distance between the electrode and the axis of the bell plate is, for example, about 225 mm (i.e. 192mm from end 6). If this distance is too close,
The electric field near the object to be painted becomes undesirably weak,
On the other hand, if the radial distance is too large, the electrode or nebulizer head will become contaminated.

In order to obtain a satisfactory electric field distribution, it is desirable that the tip of the charging electrode 20 be disposed not in front of the plane of the spray end, but at least within this plane, preferably at a position further back from the plane. The retreat distance is electrode 2
0 and the spray end 6 should not be greater than 1/2. Preferably it should be less than 1/5 of the above radial distance. In the example above,
The above retraction distance is 10mm to 20mm, or the maximum
1/10 of the radial distance between the electrode 20 and the spray end 6
It is. As the retraction distance increases, the operating current will be somewhat smaller, but the paint delivery efficiency will be significantly reduced.

Each charging electrode 20 is connected to a high voltage cable 26 in series with a high impedance damping resistor (eg, 50 megohms). The high-voltage cable 26 is led outside the housing 7 through the electrode holder 21 without any circuit breakers or connection points, so that if necessary it can be connected via a power distribution device to supply the other electrodes 20. high voltage power supply (not shown)
It is connected to the. As in general, the potential of a high-voltage source can be negative or positive, and can take a normal value, e.g.
It is 75KV. Resistor 25 prevents rapid changes in current without appreciably reducing charging efficiency and can reduce operating current by about 10%.

Three cables 26 led from the electrodes 20 are each attached to the retaining ring 2 at the base of the associated holder 21.
9 and are connected to each other at a certain distance.
However, it is preferable to lead the three cables next to each other in an annular channel (not shown) in a retaining ring 29 that at least partially surrounds the periphery of the housing, and to route them in said annular channel or preferably in a feed tube of the retaining ring. They can also be connected to each other either on the outside. in this case,
The location of the connection is embedded in the casting compound.

Separate deflection devices are required to prevent contamination. This imparts an additional axial movement component to the sprayed paint material in the direction of the object to be painted. In the illustrated example, this deflection device is first applied to the surface of the axially recessed portion of the outer housing 7, which is located outwardly from the bell plate 2 from the surface facing the surface of the object to be painted. It consists of deflection air ducts 27 that open radially. As is well known, the axis of the duct 27 is 8° or
They are arranged concentrically with the atomizer at angular intervals of 20°. Secondly, on the front side of the housing 7 there is provided a second group of deflecting air ducts 27', which likewise have their axes arranged concentrically with respect to the atomizer. The diameter of the circle in which this air duct 27' is arranged, unlike that of the duct 27, is smaller than the diameter of the atomizing end 6. A third group of deflection air ducts (not shown) may be provided near the tip of the housing 7. The diameter of this third group of circles is larger than the diameter of the spray tip. Any combination of these three groups of air ducts can be used. The risk of contamination of the deflection air can actually be significantly reduced even when using groups or arrays of multiple atomizers as described above.

Uses water-based enamel and deflection air is 120KPa
= 1.2 bar, when painting a grounded metal pipe placed 300 mm in front of the spray end, the paint delivery efficiency was , at high voltage,
The same efficiency as a conventional bell atomizer with a bell plate and paint source of corresponding dielectric strength was obtained. Only a slightly higher current was required to obtain the gain that could reduce this isolation. Further, neither the electrode nor the spray device was substantially contaminated by the paint. This also applies to electrode holders in a retracted position in areas of low field strength.

As a modification of the device of the above-described embodiment, the legs 23 of the electrode holder 21 may be tilted forward by 2° to 3° from the vertical direction. However, in this case the electric field strength at the spray end was somewhat lower, while the electric field in the region between the electrode holder and the bell plate was larger than when the legs 23 were vertical. Particles of paint reaching this area are therefore deflected by a corresponding magnitude towards the electrode holder.

[Brief explanation of drawings]

The figure is a side view showing a schematic structure of an embodiment of an electrostatic coating sprayer device according to the present invention. 1...Rotating atomizer, 2...Atomizer head,
4... Paint supply path, 6... Spraying end, 7... External housing, 20... Charging electrode, 21... Electrode holder, 22, 23... Legs, 26... High voltage cable, 27, 27' ...Duct, 29...Support ring.

Claims (1)

Claims: 1. An atomizing device, preferably consisting of a rotating atomizer, imparting a substantially radial component of movement to the atomized material; an outer housing enclosing a passageway for supplying coating material to the spray end and electrically grounding said passageway and coating material supplied thereby to said sprayer head; electrodes arranged radially around the atomizer head and connected to a high voltage source for generating an electric field for charging the coating material; and at least one electrode arranged around the axis of the atomizer. an independent deflection device consisting of a group of deflection gas ducts arranged in an annular configuration and imparting another component of axial movement to the atomized coating material towards the object to be coated; The radial distance between the charging electrode and the spray end is at least twice the diameter of the spray end,
An electrostatic coating sprayer device for electrostatically coating an object with a conductive coating material that is 4 times or less. 2. The tip of the charging electrode shall be set back in the axial direction from the surface of the spray end by a distance not greater than 1/2 of the radial distance between this electrode and the spray end. Claim 1 characterized by
The electrostatic coating sprayer device described. 3. The electrostatic coating spray device according to claim 1 or 2, characterized in that only three charging electrodes are provided. 4 A plurality of atomizer devices arranged side by side substantially in a common plane, the axes of which are spaced apart from each other by a distance of not more than 15 times the diameter of the atomizing end, each atomizer device having only two electrically charged 3. The electrostatic coating spray device according to claim 1, further comprising an electrode for electrostatic coating. 5. Each charging electrode is arranged axially set back from the charging electrode, and includes a plastic electrode holder having a portion extending substantially radially from the outer housing and a portion projecting forwardly along the axis. An electrostatic coating sprayer device according to any one of claims 1 to 4, characterized in that the device is attached to an electrostatic coating sprayer device. 6. An electrostatic coating sprayer device according to claim 5, characterized in that the electrode holder is connected to a support ring configured to fit in a sliding manner in the housing. 7. The charging electrode consists of an axially arranged needle inserted into an electrode holder made of insulating material;
7. The electrostatic coating spray device according to claim 1, wherein the tip of the needle is located at least substantially in the same plane as the tip of the electrode holder in the axial direction. 8. A high-voltage cable is led to each charging electrode, and the cable extends to the outside through an electrode holder and a support ring without being interrupted. Sprayer device for electrostatic painting. 9. The electrostatic coating spray device according to claims 1 to 8, characterized in that each charging electrode is connected to a high impedance damping resistor. 10. Electrostatic coating according to claims 1 to 9, characterized in that the outer housing of the unit holding the atomizer head, at least its front end portion extending axially close to the electrode holder, is made of an insulating material. sprayer device for. 11. Claim 1, characterized in that the axis of the annularly arranged group of deflecting gas ducts lies on a circumference having a diameter larger than the diameter of the spray end.
11. The electrostatic coating spray device according to any one of 10 to 10. 12 (a) An annularly arranged deflection gas tube having a diameter greater than the diameter of the atomizing end, located at the front end of the outer housing facing the atomizer head;
(b) a group of deflecting gas ducts arranged in an annular manner in the axially recessed part of the outer housing and having a diameter greater than the diameter of the spray end; (c)
at least two of the annularly arranged deflection gas ducts having a diameter smaller than the diameter of the spray end;
12. An electrostatic coating sprayer device according to claim 11, characterized in that there are provided groups of deflecting gas ducts.