JP7177468B2 - Spray gun for electrostatic painting - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to electrostatic spray guns.

For example, electrostatic coating is one of coating methods for automobile bodies. Electrostatic coating is a method of coating an object to be coated by causing the paint sprayed from an electrostatic coating spray gun (hereinafter simply referred to as a spray gun) to adhere to the object to be coated, such as a vehicle body, by electrostatic attraction. is. Generally, in electrostatic coating, the object to be coated is set as an anode, the spray gun is set as a cathode, and a high voltage is applied between the object to be coated and the spray gun to form an electrostatic field. Then, the paint, that is, the paint particles are sprayed from the spray gun while being charged to a negative high voltage (see, for example, Patent Document 1). As a result, it is possible to obtain advantages such as improved coating efficiency and cost reduction compared to air spray.

By the way, the object to be coated does not necessarily have a flat surface. However, when the object to be coated has such an uneven shape, the so-called Faraday cage effect concentrates the electric field on the deep corners and the like, causing more paint to adhere to the surface and corners close to the spray gun. The film thickness of the paint in the deep part of the recess becomes thin, or there arises a problem that the paint does not adhere. It is desirable that the surface of an object to be coated having such an uneven shape be coated with a uniform film thickness.

JP-A-2015-73948

Conventionally, in the object to be coated having the uneven shape as described above, as a countermeasure against the nonuniformity of the film thickness of the coating film, the application of the high voltage to the spray gun is turned off. Alternatively, by lowering the voltage, concentration of the paint on a part is suppressed, or touch-up is performed in a post-process of electrostatic painting. However, all of these countermeasures lead to an increase in the amount of paint used, making it impossible to obtain the merits of electrostatic painting.

Therefore, even if the surface of the object to be coated has an uneven shape, it is possible to achieve high-quality coating with a uniform coating film thickness, and to enjoy the benefits of electrostatic coating. We provide spray guns for

An electrostatic coating spray gun according to an embodiment includes a gun body having a nozzle for spraying a coating material at its tip, a discharge electrode provided in the gun body for charging the coating material sprayed from the nozzle, and the and a second electrode to which a high voltage is applied separately from the discharge electrode, which is arranged annularly on the outer peripheral side of the nozzle, and the second electrode has a diameter of 50 mm or more and 100 mm or less centered on the nozzle. are arranged in a ring shape.

1 is a perspective view of a spray gun for electrostatic painting, showing one embodiment; A schematic perspective view showing a state in which painting work is being performed Schematic plan view showing electric lines of force assumed during painting work A diagram showing the results of a test that investigated the relationship between the presence or absence of a ring electrode and the transfer efficiency. Schematic plan view showing electric lines of force when the ring electrode is far Schematic plan view showing electric lines of force when ring electrodes are close A diagram showing the test results of investigating the relationship between the position of the ring electrode and the transfer efficiency. Schematic plan view showing electric lines of force when the diameter of the ring electrode is large Schematic plan view showing electric lines of force when the diameter of the ring electrode is small A diagram showing the test results of investigating the relationship between the diameter of the ring electrode and the transfer efficiency.

Hereinafter, an electrostatic coating spray gun according to one embodiment will be described with reference to the drawings. FIG. 1 shows an external configuration of an electrostatic coating spray gun 1 (hereinafter simply referred to as "spray gun 1"). A spray gun 1 according to this embodiment includes a gun body 2 made of an insulating material and having a cylindrical shape extending in the front-rear direction, and a ring electrode as a second electrode annularly arranged on the outer periphery of the tip of the gun body 2. 3.

The gun body 2 is constructed as follows. That is, the tip of the gun body 2 is provided with a nozzle 4 for spraying paint. The nozzle 4 has a paint discharge port and a pin-like discharge electrode 6 for electrifying the paint passing through the paint ejection port 5 . An air cap 7 having an air ejection port for atomizing paint is provided on the outer periphery of the nozzle 4 . Although not shown in detail, the gun body 2 is provided with a paint passage for guiding the powder or liquid paint supplied from the paint supply source to the paint discharge port. A needle valve is provided for opening and closing. An air passage is also provided in the gun body 2 for guiding compressed air supplied from an air supply source to the air ejection port.

Further, although not shown, a high voltage generator (cascade) for generating a DC high voltage is provided in the gun body 2 and its output terminal is connected to the discharge electrode 6 . The high voltage generator includes a booster circuit and a rectifier circuit, and is supplied with an AC voltage of a predetermined voltage (for example, 12 to 20 V) from an external first power supply device 8 . Then, a DC voltage proportional to the AC voltage is generated, and a negative high voltage (eg, -75 kV) is applied to the discharge electrode 6 . At this time, the AC voltage supplied by the first power supply device 8 is configured to be adjustable.

On the other hand, the ring electrode 3 is provided while being supported by the second high voltage generator 9 . The ring electrode 3 has a ring shape centered on the nozzle 4 (discharge electrode 6) and is electrically and mechanically connected to an output terminal 9a protruding from the tip of the second high voltage generator 9. ing. The diameter of the ring electrode 3 is in the range of 50 mm or more and 200 mm or less, for example 100 mm. , and three needle-like electrodes 10 are provided.

The second high-voltage generator 9 includes a booster circuit and a rectifier circuit in a body made of an insulating material. supplied. A DC voltage proportional to the AC voltage is generated, and a negative high voltage (eg, -75 kV) is applied to the output terminal 9a and the ring electrode 3. FIG. For example, the second high voltage generator 9 is provided above the gun body 2 via a holder 12 made of an insulating material so as to extend in the front-rear direction. At this time, the second high-voltage generator 9 and thus the ring electrode 3 are configured so that the mounting position in the front-rear direction with respect to the holder 12 , that is, the gun body 2 can be adjusted. However, instead of using the holder 12, for example, the second high voltage generator 9 may be provided integrally with the gun body 2. FIG.

The spray gun 1 configured as described above is fixedly provided, for example, in a coating line (not shown). 1 is provided with a conveying device for conveying at a constant speed. Alternatively, the spray gun 1 is provided at the tip of a reciprocator or a robot arm, and configured to coat an object to be coated 21 held in a grounded state while moving. In either case, the coating line is provided with a control device including a computer to control the operation of the coating line and automatically perform the coating work.

Next, the operation of the spray gun 1 having the above configuration will be described with reference to FIGS. 2 to 10 as well. When the spray gun 1 is used to coat an object 21 to be coated, paint such as powder paint is supplied to the paint passage of the gun body 2 and compressed air is supplied to the air passage. Furthermore, a negative high voltage generated by the high voltage generator is applied to the discharge electrode 6 and a negative high voltage generated by the second high voltage generator 9 is applied to the ring electrode 3 . As a result, the paint ejected from the paint ejection port is atomized by the air ejected from the air ejection port, charged to a negative high voltage by the discharge electrode 6 and sprayed forward from the nozzle 4 .

Along with this, the surface of the object to be coated 21 and the nozzle 4 (discharge electrode 6) are placed between the object to be coated 21 and the spray gun 1, which are at ground potential, as shown in FIGS. An electric field (lines of electric force) is generated so as to connect them, and an electric field (lines of electric force) is generated so as to connect the surface of the object 21 to be coated and the ring electrode 3 . The negatively charged paint particles ejected from the nozzle 6 fly along the lines of electric force as if being pulled by the electrostatic force against the surface of the object 21 to be coated, which is at ground potential. is applied to the surface of As a result, the object 21 to be coated is electrostatically coated.

The inventors conducted several tests to confirm the performance of the spray gun 1 of the above embodiment. First, as shown in FIGS. 2 to 4, a test was conducted to examine the efficiency of coating with respect to the depths of recesses when the object 21 to be coated has an uneven shape. In this test, the spray gun 1 of the embodiment was compared with a conventional spray gun, ie without a ring electrode. That is, as shown in FIG. 2, the object 21 to be coated has a plate-like shape and has a U-shaped concave portion 21a in the middle thereof. In this case, the recess 21 is provided with a depth of 100 mm and a width of 100 mm, for example. The test was conducted under the conditions that the coating distance from the nozzle 4 of the spray gun 1 to the object 21 to be coated was 200 mm, and the feed speed of the object 21 in the horizontal direction was 3 m/min.

As a result of this test, as shown in FIG. 4, in the case of the conventional spray gun without the ring electrode, the coating efficiency to the deep part of the concave portion 21a was 11.4%. In the gun 1, the coating efficiency for the deep part of the concave portion 21a was 16.3%, which was an improvement of about 5 points in comparison with the conventional gun. There was a difference of about 10 μm in the thickness of the coating film between the conventional method and the present embodiment. The reason is that, as shown in FIG. 3, in the spray gun 1 of the embodiment, in addition to the electric field generated by the nozzle 4 (discharge electrode 6), an electric field is also generated between the ring electrode 3 and the object 21 to be coated. Therefore, it is considered that the lines of electric force directed toward the inner part of the concave portion 21a can be relatively increased, and a sufficient amount of paint can be applied to the inside of the concave portion 21a.

Next, as shown in Figs. A test was conducted to investigate the relationship between the transfer efficiency and the In this test, as shown in FIGS. 5 and 6, with the coating distance from the nozzle 4 to the object 21 to be coated fixed at 200 mm, the distance between the ring electrode 3 and the object 21 to be coated was set to 270 mm (Fig. 5), 200 mm (not shown), and 160 mm (see FIG. 6). The results of this test are shown in FIG.

From this result, even when the separation distance between the ring electrode 3 and the object 21 to be coated was changed to 160 mm, 200 mm, and 270 mm, there was almost no change in the coating efficiency with respect to the deep portion of the concave portion 21a. However, the closer the distance between the ring electrode 3 and the object 21 to be coated, the higher the electric field intensity. , there is a possibility that electric lines of force which do not go to the object 21 to be coated, that is, lines of electric force which go from the ring electrode 3 to the discharge electrode 6 are generated. Therefore, it is desirable to keep the discharge electrode 6 and the ring electrode 3 at the same potential.

8 to 10, the inventors conducted tests to examine the relationship between the diameter of the ring electrode 3 and the coating efficiency with respect to the deep portion of the recess 21a. In this test, as shown in FIGS. 8 and 9, with the coating distance from the nozzle 4 to the object 21 to be coated fixed at 200 mm, the diameter of the ring electrode 3 was 200 mm (see FIG. 8), 100 mm (not shown) and 50 mm (see FIG. 9). The results of this test are shown in FIG. FIG. 10 also shows the result of examining the coating efficiency of a conventional spray gun (not having a ring electrode).

From this result, the transfer efficiency was highest when the ring electrode 3 had a diameter of 50 mm, and the transfer efficiency decreased in the order of 100 mm and 200 mm. However, even when the diameter of the ring electrode 3 was set to 200 mm, it was possible to obtain a coating efficiency that was sufficiently superior to that of the conventional spray gun. Therefore, the second electrode 3 is preferably arranged in a ring shape with a diameter of 50 mm or more and 200 mm or less with the nozzle 4 at the center. I was able to It is more preferable to set the diameter of the ring electrode 3 to 50 mm or more and 100 mm or less, so that a higher coating efficiency can be obtained.

According to the spray gun 1 of this embodiment, the following functions and effects can be obtained. That is, in this embodiment, the ring electrode 3 as the second electrode is provided on the outer peripheral side of the nozzle 4 . With this configuration, in addition to the electric field between the nozzle 4 (discharge electrode 6) and the object 21 to be coated, an electric field is also generated between the ring electrode 3 and the object 21 to be coated, and the electric field is controlled by the ring electrode 3. can control the field strength and range as a whole. At this time, the ring electrode 3 was arranged around the nozzle 4 in a ring shape having a diameter of 50 mm or more and 200 mm or less.

As a result, in the case of the object to be coated 21 having the concave portion 21a, it is possible to apply a sufficient amount of paint to the concave portion 21a by relatively increasing the lines of electric force directed toward the deep portion of the concave portion 21a. , the film thickness of the coating film can be made uniform. Of course, even a flat surface can be coated with a uniform film thickness over a wide area. In addition, high coating efficiency, which is an advantage of electrostatic coating, can be obtained, and cost reduction and the like can be achieved. At this time, by setting the diameter of the ring electrode 3 to 50 mm or more and 200 mm or less, more preferably 50 mm or more and 100 mm or less, it was possible to obtain a sufficiently high coating efficiency for the deep portion of the recess 21a.

In this embodiment, the ring electrode 3 is attached to the gun body 2 so that the position can be adjusted within a predetermined range from the front to the rear in the spray direction of the nozzle 4, so the electric field (electric line of force) is adjusted. becomes possible. However, it is not preferable that the voltage fluctuates depending on the position of the ring electrode 3, and it is preferable that the potential be the same as that of the discharge electrode 6 regardless of the position of the ring electrode 3 in the front-rear direction. As a result, the lines of electric force directed toward the object to be coated 21 can be maintained in good condition.

Further, in this embodiment, the potentials of the discharge electrode 6 and the ring electrode 3 are configured to be individually controllable. As a result, it is possible to satisfactorily control the electric field strength and range as a whole. Furthermore, in this embodiment, the ring electrode 3 is provided with a plurality of needle electrodes 10 . As a result, when the voltage at the ring electrode 3 is interrupted, the needle electrode 10 self-discharges and the charge accumulated in the ring electrode 3 can be discharged immediately. can increase safety.

In the above embodiment, it was explained that the discharge electrode 6 and the ring electrode 3 are preferably at the same potential. A single (shared) configuration is also possible. In the above embodiment, the ring electrode 3 is arranged so that the position thereof can be adjusted in the front-rear direction. Further, in the above embodiment, the ring electrode 3 is provided with three needle-like electrodes 10, but the number and positions of the needle-like electrodes can be changed in various ways, and the needle-like electrodes 10 are not provided. It may be a configuration. The spray gun is not limited to an automatic gun, and may be a so-called hand gun that is held by the user himself during work. The specific numbers such as the voltage of each electrode and the distance to the object to be coated, which have been described in the above embodiments, are merely examples, and various modifications are possible.

The above embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and its equivalents.

In the drawings, 1 is an electrostatic coating spray gun, 2 is a gun body, 3 is a ring electrode (second electrode), 4 is a nozzle, 6 is a discharge electrode, 8 is a first power supply device, 9 is a second A high voltage generator, 10 a needle electrode, 11 a second power supply device, 12 a holder, and 21 an object to be coated.

Claims (5)

a gun body having a nozzle for spraying paint at the tip;
a discharge electrode provided on the gun body for charging the paint sprayed from the nozzle;
a second electrode, which is annularly arranged on the outer peripheral side of the nozzle of the gun body and to which a high voltage is applied separately from the discharge electrode,
The spray gun for electrostatic coating, wherein the second electrode is arranged in a ring shape with a diameter of 50 mm or more and 100 mm or less centered on the nozzle. a gun body having a nozzle for spraying paint at the tip;
a discharge electrode provided on the gun body for charging the paint sprayed from the nozzle;
a second electrode, which is annularly arranged on the outer peripheral side of the nozzle of the gun body and to which a high voltage is applied separately from the discharge electrode,
The second electrode is arranged in a ring shape with a diameter of 50 mm or more and 200 mm or less centering on the nozzle,
A spray gun for electrostatic coating, wherein the position of the second electrode can be adjusted within a predetermined range from the front to the rear in the spray direction of the nozzle with respect to the gun body. 3. A spray gun for electrostatic painting according to claim 1, wherein the potential of said discharge electrode and the potential of said second electrode are individually controllable. The electrostatic coating spray gun according to any one of claims 1 to 3, wherein the potential of the discharge electrode and the potential of the second electrode are the same. The spray gun for electrostatic coating according to any one of claims 1 to 4, wherein the second electrode is configured with a plurality of needle electrodes.

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