JP2001046926A - Rotary bell type electrostatic coating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coating efficiency by installing a metallic ring to be concentric with a rotary bell and to hold a space from a rotary bell coater body and applying high voltage equal to or above the voltage for the rotary bell to the metallic ring to effectively correct the flying direction of scattered particles of an unapplied coating material. SOLUTION: The metallic ring 11 is installed to be concentric with the rotary bell and to hold the space from the rotary bell coater body 12 and is electrically insulated from the rotary bell coater body 12. The high voltage equal to or above the voltage for the rotary bell is applied to the metallic ring 11. One similar to a high voltage generating device 17 for applying the high voltage to the rotary bell is used to the application of the high voltage to the metallic ring 11 and one high voltage generating device 11 is used in common for both. As a result, a spray pattern is effectively controlled and large sized particles apt to be scattered in centrifugal direction or coating material particles containing a metallic pigment having high specific gravity or the like is effectively deposited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic coating apparatus for atomizing a paint with a rotary bell and applying the atomized paint to a workpiece by shaping air and electrostatic force.

[0002]

2. Description of the Related Art A rotary bell type coating machine using a rotary bell has a good finish and high coating efficiency.
Industrial coating lines, such as automobile coating lines, are the mainstream of coating machines.

[0003] In a rotary bell type coating machine, 20,000 is usually used.
Is supplied to the bell which rotates at a high speed of 50,000 RPM, and the centrifugal force turns the paint into a thin film.
Droplets are atomized through string splitting. At this time, the atomized paint particles that have been atomized fly and spread in the direction of centrifugal force, and fly farther as the rotation speed is higher and the particle diameter is larger. Usually, the atomized particles are charged by a high voltage applied to the rotating bell, are subjected to the action of an electric field formed between the rotating bell and a grounded workpiece, and are applied to the workpiece by electrostatic force. To wear.

There is no problem in a line in which the object is placed in the direction of centrifugal force to be painted, but in a line in which the object is placed in the direction perpendicular to the direction of centrifugal force of the rotating bell, the object is painted.
Shaping air is required to correct the paint particles atomized by the rotating bell toward the workpiece. This shaping air discharges compressed air from a concentric slit near the bell edge of the rotating bell, and usually has a slit-shaped discharge port at a position several mm from the bell edge, and has a volume of about ² to 3 kg / cm ² . Compressed air at pressure is supplied. The effective spray pattern width is determined by the shaping air pressure, the paint discharge amount, and the number of rotations of the rotary bell.

In a rotary bell type coating machine for a metallic paint, a stronger shaping air is effectively supplied, for example, in a spiral shape, thereby increasing the straight-forward force of the atomized particles and improving the orientation of the metallic pigment. Improvements have been made, such as

[0006]

However, the rotary bell type electrostatic coating machine has the following disadvantages. Since the shaping air for forming the spray pattern is discharged in a thin air curtain shape from the discharge port which is a concentric slit near the bell edge of the rotating bell, relatively large atomized particles break through this air curtain and generate centrifugal force. Spatters in the direction. To some extent, it is possible to pull back and apply in the direction of the object with the electrostatic force, but the electric field formed by the bell head which is the applied electrode and the object to be grounded is concentrated in the area near the bell head, so the air curtain must be The atomized particles that break through and become scattered uncoated particles on the object to be coated, resulting in a problem that the coating efficiency is reduced. There is also a method of increasing the pressure of the shaping air to increase the straightness of the air curtain, but this not only increases the air consumption, but also the air that collides with the workpiece and rebounds, preventing the subsequent application of atomized particles. The problem of doing so occurs. Recently, there has been an increasing tendency to paint at short distances with an emphasis on the finish, but the above-mentioned impediment to the application of atomized particles was more remarkable under the condition that the coating distance of a rotary bell type coating machine was reduced. An object of the present invention is to provide a rotating bell type electrostatic coating apparatus capable of effectively correcting the flight direction of scattered particles, which has not been corrected with conventional shaping air or electric field and has become uncoated paint, and improving coating efficiency. To provide.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by a bell type coating machine having a metal ring to which a high voltage can be applied at a specific location. And completed the present invention.

That is, the present invention relates to "1. An electrostatic coating apparatus for atomizing paint by a rotating bell, wherein the metal ring is concentric with the rotating bell and holds the space with the rotating bell coating machine body. Wherein a high voltage equal to or higher than the voltage of the rotary bell is applied to the metal ring to perform electrostatic coating.

[0009] 2. The metal ring is porous and hollow, and by sending compressed air into the hollow part,
The rotary bell-type electrostatic coating device, wherein the compressed air is uniformly blown from the surface of the metal ring.

[0010] 3. The hollow metal ring, wherein thin tube nozzles are evenly arranged, and compressed air for spray pattern control can be ejected from the thin tube nozzle by sending compressed air to the hollow metal ring. 2. The rotary bell type electrostatic coating apparatus according to 2. ”.

[0011]

According to the rotating bell type electrostatic coating apparatus of the present invention, when the paint is atomized by centrifugal force by the rotating bell which is the first application electrode, the paint is charged by contact charging, Most of the atomized particles fly in the direction of the object to be coated by electrostatic force, being controlled by shaping air, which is compressed air from concentric slits, near the bell edge of the rotating bell, which is a conventional mechanism, and is applied by electrostatic force. The atomized particles of the part penetrate the first air curtain by the shaping air. The penetrated atomized particles can be applied by electrostatic force by an electric field formed by the metal ring serving as the second application electrode and the grounded object.

This metal ring is installed concentrically with the rotary bell while maintaining the space with the rotary bell coating machine main body, and the metal ring is electrically insulated from the rotary bell coating machine main body. A high voltage equal to or higher than the voltage of the rotating bell can be applied to the metal ring. For applying a voltage to the metal ring, the same high voltage generator that applies a high voltage to the rotating bell can be used, and one high voltage generator can be shared.

The metal ring can be changed in diameter or number according to the desired spray pattern shape. For example, the spray pattern width can be up to 30 cm.
If you want to control the diameter of the metal ring is usually 30c
m. The effective range of the electric field due to the metal ring is about ± 10 cm around the ring diameter at a normal coating distance of 25 cm to 35 cm, and the effective range of the electric field formed by the rotating bell is about +10 cm of the bell diameter. No electric field can be formed.

Further, by making the metal ring porous and hollow and purging the interior with compressed air under pressure, it is possible to prevent paint from adhering to the surface of the metal ring.

Further, by hollowing the metal ring, uniformly disposing the thin tube nozzles in the metal ring, and sending compressed air into the hollow metal ring, the spray nozzle for controlling the spray pattern is formed from the thin tube nozzles arranged in a ring shape. Compressed air may be ejected. Further, a ring-shaped slit is provided outside the thin-tube nozzle arranged in a ring shape, and compressed air discharged from the thin-tube nozzle is discharged from the slit, whereby more uniform shaping air can be formed. Compressed air ejected from a thin tube nozzle or a ring-shaped slit provided on a metal ring entrains a surrounding airflow to form a second air curtain, and the second air curtain usually includes the first air. It has a thickness several times that of the curtain, and can reliably control the flight path of the atomized particles blown in the direction of centrifugal force from the rotating bell toward the object to be coated.

It is also possible to combine a porous metal ring with a capillary nozzle. In this case, it is easier to control the compressed air supply path and the pressure purge air supply path to the capillary nozzle.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a rotary bell type electrostatic coating apparatus according to an embodiment of the present invention.

Comparative Example 1 FIG. 1 is an explanatory view of the flow of compressed air and associated airflow from a shaping air discharge port and lines of electric force due to an electric field in a conventional rotary bell type electrostatic coating machine. The shaping air 1 is discharged from the concentric slit 3 so as to flow along the outer end surface of the bell head 2. The accompanying airflow is divided into an airflow 4 flowing into the outer end surface of the bell head and an airflow 5 flowing from the inside of the bellhead to the inner end surface. In this case, the thickness of the airflow formed by the shaping air on the end face of the bell head is 1
The spray pattern is about 2 cm, and the spray pattern is controlled by shaping air. A relatively small paint particle group 6 (only part of which is shown) and a relatively large paint particle group 7 (one (Only the portion shown). It is difficult to control the paint particle group 7 by the electrostatic force due to the electric field formed by the electric force lines 8.

Embodiment 1 FIGS. 2 and 3 are explanatory views of a first embodiment of a rotary bell type electrostatic coating apparatus according to the present invention. First, an alkyd / melamine resin-based white paint “Amirac White” (trade name) manufactured by Kansai Paint Co., Ltd. supplied from the gear pump 9 was supplied to a bell head (bell diameter: 50 mmφ), and the paint discharge amount 2
00cc / min, bell head rotation speed 30,000rpm
The paint was atomized under the following conditions. The coating distance was set to approximately 30 cm from the bell head to the flat coated object. The average particle size of the atomized paint particles at this time is about 30 μm (measured with a Malvern Particle Sizer), and the maximum particle size is about 1 μm.
It was 20 μm. When a metal ring is not used, the spray pattern width is 2 kg / cm ² shaping air pressure.
Is about 50 cm, and the applied voltage of the bell head is -60 kv.
The coating efficiency was about 80%.

Next, a metal ring 11 having an outer diameter of 30 cm and an inner diameter of 27 cm was attached to the above-mentioned coating machine to perform coating. In the metal ring 11, a large number of thin stainless steel nozzles 10 (nozzle length 15 mm) having an outer diameter of 1.5 mm in the spray direction are arranged in a ring shape (only a part is shown).
Therefore, the discharge of the compressed air from the metal ring 11 is considered to be uniform. The metal ring 11 is mounted on a rotating bell type coating machine main body 12 with a support 13. The mounting position of the metal ring 11 was 2 cm behind the edge position of the bell head of the rotating bell. The outer diameter of the coating machine body (Ransburg's μ microbell) is about 12c
m, so there is approximately 7.5 between the metal ring and the coating machine body.
cm space will be formed. The metal ring 11 is hollow, and compressed air supplied from the air supply port 14 is discharged from the hollow portion of the metal ring through the narrow nozzle 10. The discharged compressed air is amplified together with air from the rear of the metal ring and is blown out in the painting direction. The thickness of the airflow of the shaping air 15 formed by the thin tube nozzle disposed on the metal ring is such that the pressure of the supplied compressed air is 1
It was about 5 to 6 cm in kg / cm ² . Then, a voltage of −60 kv was applied to the metal ring, and the grounded flat-plate coated object 16 was coated under the above-mentioned coating conditions. as a result,
The spray pattern width was controlled at the target of about 30 cm, and the coating efficiency was improved to about 90%. Furthermore, when a voltage of -90 kv was applied to the metal ring, the coating efficiency could be increased to about 94% without substantially changing the spray pattern width. In this case, a high voltage cable is connected from the high voltage generator 17 to the metal ring and a resistor 18 (100M) is connected.
Ω) to the bell head. The electric field formed at this time is formed by combining the electric lines of force 19 formed by the bell head as the first applied electrode and the electric lines of force 20 formed by the metal ring as the second applied electrode, and almost all of the atomized particles in the spray pattern are formed. Was able to be applied. In each case where the above metal ring was used, the applied voltage of the bell head was -60 kv.

Embodiment 2 FIGS. 4 and 5 are explanatory views of a rotary bell type electrostatic coating apparatus according to a second embodiment of the present invention. A metal ring 21 having an outer diameter of 40 cm and an inner diameter of 37 cm is mounted on a rotating bell type coating machine main body by a support 22. Metal ring 2
Numeral 1 is made of a sintered metal and has a hollow inside, and compressed air from an air supply port blows out from the inside of the metal ring to the surface. Bellhead applied voltage is -60 kv
Then, a voltage of -90 kv was applied to the metal ring 21, and at the same time, 1 kg / cm ² of compressed air was supplied into the metal ring to perform coating under the same atomization conditions as in the first embodiment. As a result, the spray pattern width was controlled to about 40 cm, and the coating efficiency was able to secure about 90%. Further, contamination of the metal ring was at a practical level with almost no problem.

[0022]

The coating apparatus of the present invention can be obtained by using a conventional rotary bell type coating machine and installing a metal ring on the coating machine. The coating apparatus of the present invention can increase the electric field strength without requiring a special high-pressure generator, so that the spray pattern can be effectively controlled, and the spray pattern can be scattered in the direction of centrifugal force. Large particles and paint particles containing a metallic pigment having a large specific gravity can be effectively applied, so that the application efficiency can be improved.

Further, since the spray pattern can be controlled to be smaller than before, the overspray portion can be reduced in automatic painting using a reciprocating or painting robot, and paint loss can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a shaping air flow and lines of electric force of a conventional bell type electrostatic coating machine.

FIG. 2 is an explanatory diagram of a first embodiment of the present invention.

FIG. 3 is an explanatory view of a metal ring according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a second embodiment of the present invention.

FIG. 5 is an explanatory view of a metal ring according to a second embodiment of the present invention.

[Explanation of symbols]

 1 ... shaping air 2 ... bell head 3 ... slit 4 5 ... accompanying airflow 6, 7 ...・ Paint particle group 8 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Line of electric force 9 ・ ・ ・ ・ ・ ・ ・ ・ ・ Gear pump 10 ・ ・ ・ ・ ・ ・ ・ ・ ・ Narrow tube nozzle 11, 21 ・ ・ ・ ・ ・ ・ Metal ring 12 ・ ・ ・ ・ ・ ・... Coating machine body 13,22 ... Support 14 ... Air supply port 15 ... Shaping air 16 ... Plate coated object 17 ... ······ High voltage generator 18 ····· Resistors 19 and 20 ···

Claims (3)

[Claims] 1. An electrostatic coating apparatus for atomizing paint by a rotating bell, comprising a metal ring concentric with the rotating bell and holding a space with the rotating bell coating machine main body. A rotating bell type electrostatic coating apparatus characterized in that electrostatic coating can be performed by applying a high voltage equal to or higher than the voltage of the rotating bell to the metal ring. 2. The metal ring is porous and hollow, and compressed air is blown out from the surface of the metal ring by sending compressed air into the hollow portion. Item 2. A rotary bell type electrostatic coating apparatus according to Item 1. 3. The hollow metal ring is formed by uniformly disposing thin tube nozzles. By sending compressed air into the hollow metal ring, compressed air for controlling a spray pattern can be ejected from the thin tube nozzle. The rotary bell type electrostatic coating device according to claim 1 or 2, wherein: