JP2007237089A - Spray gun for powder electrostatic coating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the coating efficiency by forming a spray pattern which shows that a sprayed powder coating has a proper spraying speed and the spread of spraying to a material to be coated and by providing a high charging efficiency to sprayed particles by charged electrodes in a spray gun for powder electrostatic coating. <P>SOLUTION: Adjusting air is sprayed and made to collide from both side surfaces to powdery particles sprayed from the spraying opening. The spraying opening dispersing the powdery particles is installed and a high-voltage charged electrode is arranged at the center of the powder spraying opening of the spray gun. The electrode is of a needle shape and the tip end is arranged at the collision and dispersion position of the sprayed air or immediately before that, that is, between the spray opening and a dispersion position. A cleaning air opening spraying the cleaning air is installed on the tip end part of the charged electrode protruding from the front side of the spraying opening. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a technique for improving the coating efficiency in a spray gun for powder coating in which a powder coating is sprayed and applied to an object to be coated by the action of static electricity.

Compared to the coating method using a liquid paint that uses a solvent and forms a coating film by drying, powder coating does not use a solvent, so it can save resources and prevent emissions of volatile organic compounds. There are also advantages such as excellent coating strength. Further, it is known as a coating method that can collect and reuse a paint that has not been applied to an object to be coated, and is excellent in effective use of resources.

On the other hand, among various powder coating methods, powder coating by a spray gun is widely used as a coating method that is highly versatile and can handle a wide range of objects to be coated. In addition, electrostatic coating, which utilizes the effect of high-voltage static electricity to increase the efficiency of sprayed paint and effectively uses resources, is expected to be widely used in the future as an effective coating method. Yes.

Since powder paint itself does not adhere to the object to be coated, a normal spray gun for powder coating attaches the sprayed powder paint to the object to be coated using high-voltage static electricity. It has a function to make it an electrostatic spray gun. Therefore, the powder paint is fed into the spray gun in a fluidized state by compressed air, sprayed from the spray port provided at the tip, and then charged in the ionization zone due to the discharge from the charging electrode, to the object to be coated. The electric field formed toward the surface effectively adheres to the object to be coated.

Since the supply of general powder paint is fed with a relatively large amount of air by an ejector-type pump, the spray port has a relatively large diameter to suppress the flow rate, and a baffle is placed in front of the spray port. The flow rate of the spray that goes straight forward is suppressed, and the effect of applying static electricity is not disturbed.

In order to perform efficient painting, the spray flow must be adjustable depending on the shape of the object to be coated. The spray flow speed is mainly taken up as a factor of the coating efficiency, the spray pattern shape is a factor for forming a uniform coating surface, and when performing efficient coating according to the size of the coating surface It is considered important. In other words, it is possible to obtain an average film thickness by spraying with a uniform pattern with a large spread over a large area, and the workability is also improved. These are also apparent in spray guns for liquid paints with a long history. It is said that.

On the other hand, powder coating that has not been applied to the object to be coated in powder coating is characterized by being collected and reused, but reused powder is inevitable to be contaminated with impurities and reused. Therefore, a large amount of money and time are required for the equipment to be collected and its maintenance work, and the industrial merit has been reduced when the cost is considered. Therefore, it is important to improve the coating efficiency with a new powder coating material, and it is directly linked to the improvement of workability by shortening the coating time and the coating process. Therefore, the improvement has been desired more than ever.

As mentioned above, powder spray guns have been supplied with powdered paint as well as compressed air, so the spray force of the carrier air is used as it is, and the above-mentioned baffle is typical for spray dispersion. Various shapes and sizes have been used depending on the size, shape, arrangement, and the like.

Needless to say, a narrow spread pattern is required for narrow gaps or narrow shapes in the object to be painted, and a large spread pattern is required for objects having a flat and wide painted surface. The pattern can be changed by using the technique described in Japanese Patent Application Laid-Open No. 54-24953, which obtains the spread of the pattern by colliding the spray flow from the two opposing spray ports, and the slit-shaped spray port. As a technique, a method disclosed in Japanese Patent Laid-Open No. 62-163758 has been proposed.

As can be understood from these prior arts, most of the powder coatings are based on electrostatic coating, and a charged electrode is provided in the vicinity of or included in the powder spray port. It has a configuration for charging. However, in the case of the conventional powder electrostatic spray gun, as described above, since the jet outlet jets with a large amount of carrier air, it has a relatively large opening area, and there is a situation where charging efficiency is not sufficient.

JP 62-163758 A JP 54-24953 A

In powder electrostatic coating, the charging effect on the powder greatly affects the coating efficiency, and it is necessary to improve the coating efficiency by charging. Previously, the electrode was placed in a spray with a wide opening, or the electrode was placed outside the spray. However, since the density of the powder is thin and the flow rate is high because of the carrier air, the effect is sufficient. In general, charging at a higher voltage value was necessary as compared with liquid coating.

The present invention relates to a spray gun for powder coating using static electricity, in which the sprayed powder coating forms a spray pattern having an appropriate spray speed and spread of spray on the object to be coated, and the spray particles It is intended to give a high charging effect by a charged electrode to improve the coating efficiency.

In powder coating in which air is mixed and conveyed in a fluidized state is sent to a spray port provided at the tip of a spray gun and sprayed onto the object to be coated from this spray port, powder coating is performed in the present invention, An injection port for dispersing the powder particles is provided by causing the adjustment air to be injected and collided from both sides with respect to the powder particles sprayed from the injection port. Further, a high voltage charged electrode is arranged at the center of the powder jet outlet of the spray gun, the electrode has a needle shape, and the tip is provided at or just before the collision dispersion position of the jet air, that is, within the range between the jet outlet and the dispersion position. Yes.

A cleaning air port is provided outside the jet port for jetting toward the tip portion of the charging electrode protruding forward of the jet port. The cleaning air port may also serve as an injection port for injecting the adjustment air.

According to the powder electrostatic coating spray gun of the present invention, the powder paint sprayed from the central nozzle is dispersed by the adjustment air sprayed from the side surface in a state of being mixed with the carrier airflow, and is appropriately dispersed. The spray pattern is formed and sprayed onto the object to be coated. A high voltage is discharged by being applied to the tip of the charged electrode located immediately before the dispersion position or dispersed, and the powder dispersed by the ionization sphere formed around the charged electrode has a high ionization sphere in a high density area. When passing through the area, it is charged with high efficiency and sprayed toward the object to be coated.

Since the charging effect is dispersed in the immediate vicinity of the electrode tip, charging is performed in a concentrated range, and the dispersion position is set at the point where the density of the electric field formed from the electrode tip toward the object is the highest. Therefore, it is performed with high efficiency. Accordingly, the coating efficiency of the object to be coated is improved, and an effect such as the application to the side surface of the object to be coated, which has been difficult to apply, can be obtained. As a result, the painting process can be shortened and workability can be improved.

In addition, the coating efficiency can be improved by reducing the cost required for recovery and regeneration at the time of reuse as well as when not reusing excess powder that is scattered. Resource utilization and economic effects can be expected.

Further, in the present invention, the spray powder adheres to the charged electrode due to the continuation of use, and this prevents the discharge from the electrode from being obstructed, and the charging effect is reduced by spraying the cleaning air, so that stable coating efficiency is achieved. The electrostatic powder coating can be used continuously.

FIG. 1 shows an example of a spray gun for powder coating in an embodiment of the present invention as an overall cross section. A gun body 1 is attached with a powder nozzle 3 constituting a spray device at the tip, and is concentric with the powder nozzle 3. An air cap 2 to be attached is detachably attached by a cover 4. The powder nozzle 3 is connected to a powder passage connected from a powder inlet 10 provided at the rear of the gun body 1 through a supply hose 8 to a powder inlet 7 near the tip. Although the air passage for adjusting the spray is not shown in detail, the adjustment air supply passage 11 opens at the tip of the gun body 1, and an air cap is provided between the powder nozzle 3 and the cover 4 as shown in FIG. The second adjustment air hole 32 is connected. Another auxiliary air supply path 12 is opened to an auxiliary air chamber 24 formed by attaching the powder nozzle 3.

In the case of the present embodiment, the high voltage generator 5 is built in the gun body, and the high voltage output is connected from the high voltage terminal 6 to the charging electrode 9 disposed at the center of the powder nozzle 3. It has become.

The details of the spraying apparatus will be described with reference to FIG. A jet port 22 connected by a caliber is formed. An auxiliary air port 23 is formed on the circumference between the center port 21 and the jet port 22, and the air from the auxiliary air chamber 24 is ejected through the auxiliary air passage 25 of the powder nozzle 3. In this embodiment, eight auxiliary air ports 23 are formed on the circumference.
In another embodiment, an auxiliary air port is formed by an annular slit 26 on the outer periphery of the jet port 22 as shown in FIG.

The air cap 2 is configured to be concentrically mounted by a taper sheet that is in contact with the powder nozzle 3 and forms a pair, and the powder nozzle 3 has an opening at the front side of the injection port, and a corner portion opposed to both front sides thereof. 33 is provided with an adjustment air port 31 for spraying toward the spray flow from the center. The size, the injection angle, the number, and the like of the adjustment air port 31 are selected according to the spray adjustment balance. In the embodiment, two each are provided.

The supply of compressed air to the auxiliary air port 23 and the adjustment air port 31 is supplied from the auxiliary air supply path 12 and the adjustment air supply path 11, respectively. Although not shown, these air amounts can be adjusted independently through adjusting means such as each adjusting valve device.

In another embodiment, as shown in FIG. 4, it is possible to change the pattern direction by providing two pairs of adjustment air ports 31A and 31B in a perpendicular direction and ejecting only one opposite side. It can easily be used as an automatic spray control for coating objects and used for automatic painting by painting robots.

The spray gun for performing powder electrostatic coating is made of an insulating resin as a whole, including the gun body, and has a charged electrode at the tip, as in the configuration of other spray guns for electrostatic coating. In the case of this example, an electrode terminal 91 provided at the rear end of the charging electrode 9 attached to the gun main body 1 is provided at a height built in the gun main body 1 so that the tip protrudes several millimeters at the center of the jet nozzle. The voltage generator 5 is configured to be electrically connected to a high voltage terminal 6 that is connected to the high voltage output side and extends.

The powder paint to be sprayed is fed into the powder inlet 10 of the powder spray gun in a state of being fluidized together with compressed air by a supply pump. In the case of the present embodiment, the supply pump is a pump that feeds powder that has been fluidized by air, and the amount of air when transported to the powder spray gun is as small as 1/10 that of a conventional injector pump. The pump which is is used.

In order to effectively use the present invention, a positive displacement pump using a cylinder / piston is used as a preferred example. As an example of this type of pump, powder is sucked into the cylinder by repeated pressurization and decompression by the movement of a piston that reciprocates in a cylindrical cylinder, and discharged together with a small amount of air fed into the cylinder for fluidization. A pump is used to supply the powder spray gun through the supply hose. The amount of powder supplied is about 50 to 300 g per minute, which is often used as powder coating.

With the supply pump according to the embodiment, stable supply is possible with an air amount of 8 to 10 liters per minute for conveying and supplying the powder, whereas the injector pump requires 60 to 100 liters per minute. Reduction. The spray nozzle 22 of the spray gun has conventionally required a minimum of several tens of millimeters for stable conveyance at low speed, but it is smaller than that, preferably about 5 to 7 mm, and there is no clogging. The speed of ejection from there can be reduced to about 1/2 of the conventional speed, or about 1/4 on average.

The powder sprayed from the central jet port 22 is dispersed and flattened in a state where the whole is crushed by the adjustment air ejected from the adjustment air ports 31 provided on both side surfaces. This spread increases as the flow rate of the compressed air increases, and is selected according to the coating width of the object to be coated. Naturally, the amount of adjustment air that adjusts the spray pattern depends on the amount of powder sprayed. In one example, the amount of air is about 50 liters per minute for a discharge amount of 200 g per minute, and about 300 mm at a position 200 mm away. The above pattern width could be obtained.

The charging electrode 9 for obtaining the electrostatic effect is located between the position where the adjustment air collides with the spray flow and the jet outlet, and discharges toward the counter electrode when charged with a high voltage, and a high ionization zone at the tip of the electrode. Is formed. When the powder particles passing through the ionized sphere are charged and approach the object to be coated which is the counter electrode, the powder particles are adsorbed to the object by electrostatic effect.

The ionized sphere region is charged one after another by the powder that is dispersed by the collision of the adjustment air so that it is caused to flow forward by the spray flow that is jetted. Therefore, the ionization area of the charged electrode can be formed so as to overlap the position where the powder is dispersed, and it is provided outside the spray dispersed so far, or in the spray flow already dispersed with a large amount of air flow. As a result, a higher electrostatic effect can be obtained.

The charged electrode 9 of the present invention has a tip in front of the jet port 22 and is located in a region where adjustment air for forming the pattern is ejected. Therefore, although it is an electrode to which a powder coating material tends to adhere, compressed air is always sprayed and adhesion of a coating material is prevented. For this reason, since clean air is always blown as compared with the case where it is simply placed in the spray flow or in the vicinity where it is off the center of the spray, the charging effect of the charging electrode 9 always exhibits stable performance. be able to. In addition to spraying, a separate cleaning air port may be provided for the purpose of cleaning the paint adhering to the electrode tip.

FIG. 5 is an example showing the effect of application by actual painting, but shows a comparison of application efficiency when applied to flat plates and round pipes. In any case, when spraying powder from a supply device with a small amount of carrier air using a spray gun that sprays with an open shape from an existing spray nozzle (A), a large amount of carrier air is used using an injector pump. In comparison with the case of spraying the powder supplied in (B), the case of the present invention (C) shows high efficiency.

Further, FIG. 6 is a graph showing the coating state of the front, back and side surfaces of the spray when a round pipe is painted, but according to the present invention, average coating is also seen on the side surface which is difficult to be applied. It was possible to improve the overall coating efficiency and average the coating thickness.

1 is an overall cross-sectional view of a spray gun for electrostatic powder coating according to the present invention. It is sectional drawing which expanded and showed the spray apparatus and charge electrode part of FIG. It is the front view which looked at the spraying apparatus part of FIG. 2 from the left. It is the front view which looked at the spraying apparatus part in another Example from the same direction as FIG. The graph which compared the coating efficiency of this invention and the conventional electrostatic spray gun. The graph which compared the throwing-around situation at the time of painting on a pipe with this invention and the conventional electrostatic spray gun.

Explanation of symbols

1 Gun body 2 Air cap 3 Powder nozzle 5 High voltage generator 7 Powder inlet
9 Charging electrode 11 Adjustment air supply path 12 Auxiliary air supply path 21 Central port 22 Spout 23 Auxiliary air port 24 Auxiliary air chamber 25 Auxiliary air passage 31 Adjustment air port

Claims (2)

In powder coating in which powder is mixed by air and conveyed in a fluidized state to a spray port provided at the tip of a spray gun, and sprayed onto the object to be coated from this spray port, the spray port A jet of adjusting air is jetted and collided from both sides to the powder particles sprayed from the nozzle, and an injection port for dispersing the powder particles is provided, and a high voltage charged electrode is arranged at the center of the jet port, A spray gun for electrostatic powder coating, which is needle-shaped and has a tip provided in a collision dispersion position of the spray air or in a range between the ejection outlet and the dispersion position. The spray gun for powder electrostatic coating according to claim 1, wherein a cleaning air port for spraying toward a tip portion of the charging electrode protruding forward of the jet port is provided outside the jet port.

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