JPH09234395A - Method for rotary atomizing electrostatic coating and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coating adhesion efficiency. SOLUTION: Shaping air S1 is supplied from the back 38 of a bell cup 30, the second enclosing shaping air S2 is supplied from above a circumference with a diameter larger than the bell cup 30, and atomized coating material P1 discharged from the tip of the inner surface of the bell cup 30 is deflected to the substance. The flow velocity ratio between the shaping air S1 and S2 is made to be 0.4-1.6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary atomizing electrostatic coating method and a rotary atomizing electrostatic coating apparatus, and more particularly to shaping air for preventing paint scattering from the outer periphery of the shaping air (hereinafter, also referred to as a second envelope shaping air). The present invention relates to a rotary atomizing electrostatic coating method and a rotary atomizing electrostatic coating apparatus.

[0002]

2. Description of the Related Art A rotary atomizing electrostatic coating device using a bell cup has been known as a coating device for automobile bodies or automobile parts. In this type of rotary atomizing electrostatic coating device, a voltage of about -60 kV is applied and 35,000 r
When paint is supplied to the inner peripheral surface of the bell cup that rotates at a high speed of about pm, the paint reaches the tip of the inner peripheral surface of the bell cup due to centrifugal force, where it is atomized and charged, and outward in the radial direction of the bell cup. Shaping air is supplied from the back surface of the bell cup in order to concentrate the sprayed charged coating particles in the direction of the object to be coated to form an efficient ring-shaped coating pattern.

Here, the surface quality such as the coating surface and the clarity of the coated surface is improved as the particle diameter of the coating particles is smaller, that is, the atomization rate is higher, and the atomization rate is the number of revolutions of the bell cup. It is said that it is preferable to rotate the bell cup at a high speed in order to improve the surface quality of the coated surface because the higher the value, the better. However, when the bell cup is rotated at high speed, the center of the inner peripheral surface of the bell cup becomes negative pressure, the surrounding air is entrained, and this air is again pushed out to the tip of the inner peripheral surface of the cup by centrifugal force. Due to this air flow, the paint supplied to the nozzle has a strong tendency to fly outward in the radial direction of the bell cup. In this case, if the shaping air from the back surface of the bell cup is strengthened and the coating particles are deflected forward, the number of coating particles that bounce off the surface of the object to be coated increases. There was a problem of lowering.

Therefore, a coating device is proposed, in which paint splash prevention air is separately blown from a circumference having a diameter larger than that of the bell cup, and the coating particles that have jumped out radially outward of the bell cup are deflected forward again. (See, for example, Japanese Patent Laid-Open No. 58-104,656).

[0005]

However, even if the second outer envelope shaping air is provided separately from the shaping air, a turbulent flow occurs between the shaping air and the second outer envelope shaping air, and the radial direction of the bell cup is increased. It was observed that the coating particles that had jumped outward returned to the cancer side. Therefore, it has been a limit to improve the coating efficiency to 60% to 65%.

The present invention has been made in view of the above problems of the prior art, and it is an object of the present invention to provide a rotary atomizing electrostatic coating method and a rotary atomizing electrostatic coating apparatus which are excellent in coating efficiency. To aim.

[0007]

In order to achieve the above object, the rotary atomizing electrostatic coating method of the present invention according to claim 1 comprises:
The shaping air is supplied from the back surface of the bell cup, and the second envelope shaping air is supplied from the circumference having a diameter larger than that of the bell cup to cover the atomized paint discharged from the tip of the inner peripheral surface of the bell cup. In the rotary atomizing electrostatic coating method of deflecting to the coated surface, the flow velocity ratio of the shaping air to the second envelope shaping air is 0.4 or more and 1.6 or less.

In order to achieve the above object, the rotary atomizing electrostatic coating device of the present invention according to claim 2 has a rotatable bell cup to which paint is supplied to the inner peripheral surface, and the bell cup. A first air outlet group that is opened along the periphery of the rear surface and supplies shaping air from the rear surface to the front side, and a first air outlet group that is opened along a circumference having a diameter larger than that of the first air outlet group. And a second air outlet group that blows out a second envelope shaping air toward the surface of the bell cup, and the atomizing paint discharged from the tip of the inner peripheral surface of the bell cup is deflected to the surface of the object to be coated. In the coating apparatus, a flow velocity ratio of the shaping air to the second envelope shaping air is 0.4 or more and 1.6 or less.

When the paint is supplied to the inner peripheral surface of the bell cup by rotating the bell cup at a high speed, the paint reaches the tip while spreading on the inner peripheral surface of the bell cup in the form of a liquid film by the centrifugal force of rotation of the bell cup. Fine particles are formed at the tip of the inner peripheral surface of the bell cup, and the charged coating particles fly outward in the radial direction of the bell cup. At this time, the shaping air blown out from the first air outlet reaches the tip along the back surface of the bell cup and deflects the above-mentioned coating particles toward the object to be coated.

As described above, by the balance between the centrifugal force due to the rotation of the bell cup and the flow velocity of the shaping air,
Although the coating pattern of the coating particles is determined, in the present invention, the second outer packaging air is discharged from the second air outlet so as to wrap the shaping air.

The coating particles scattered from the shaping air to the outside can be deflected toward the object to be coated again by the second envelope shaping air. However, the present inventor has proposed that the shaping air and the second envelope shaping air be used. When the relationship was verified by focusing on the flow velocity ratio of
As shown in (3), the maximum value of the coating efficiency appears when the flow velocity ratio of both airs becomes almost 1. In particular, in the range where the flow velocity ratio of shaping air to the second envelope shaping air is 0.4 or more and 1.6 or less,
It was confirmed that the coating efficiency reached about 75% or more, and not only the coating cost reduction but also the environmental improvement such as the reduction of VOC (vaporized organic matter) can be realized.

The flow velocity ratio of these shaping airs is 0.
In the range of 4 or more and 1.6 or less, in other words, in the range of 1 ± 0.6, it means that the coating efficiency is improved, and it is the most preferable from the viewpoint of coating efficiency to make both shaping airs as equal as possible. Is. Since the difference in the flow velocities of both shaping air is small in this range, it is considered that the shaping air and the second envelope shaping air are flowing in a laminar state without turbulent flow or vortex flow therebetween. For this reason, if coating is performed while controlling both air in this range, the coating particles from the bell cup will be guided by the laminar flow to the surface of the object to be coated, which will significantly reduce the scattered coating particles and improve the coating efficiency. It is supposed to do.

As described above, in the rotary atomizing electrostatic coating method according to the first aspect of the present invention, it is considered that it is preferable that the flow velocities of the shaping air and the second envelope shaping air are equal to each other, but the shaping air and the second shaping air are equal to each other. This condition can be naturally satisfied by controlling the flow rate balance with the outer casing shaping air.

However, when the flow rate or the flow rate of the shaping air is increased, the coating particles ejected from the bell cup are affected by the shaping air to be atomized, and the coated surface quality is improved. In other words, in consideration of the quality of the coated surface, it is necessary to secure the flow rate or flow velocity of the shaping air at a certain value or more. Therefore,
In the rotary atomizing electrostatic coating method according to claim 1 and the rotary atomizing electrostatic coating device according to claim 2, it is possible to control the flow rates of both the shaping air and the second envelope shaping air. However, since the flow rate of shaping air is subject to a certain limit, it is better to control the flow rate of shaping air by fixing the flow rate of shaping air to an appropriate value and controlling the flow rate of the second envelope shaping air. preferable.

According to a third aspect of the present invention, there is provided the rotary atomizing electrostatic coating device according to the present invention, wherein the bell cup is rotated in the rotational direction between the first air outlet group and the second air outlet group. It is characterized in that an annular space is formed along it. In the rotary atomizing electrostatic coating device according to the third aspect of the present invention, since the annular space is formed along the rotation direction of the bell cup between the first air outlet group and the second air outlet group, Turbulent flow generated between the shaping air and the second envelope shaping air can be suppressed in the annular space. Therefore, the shaping air and the second envelope shaping air are in a more preferable laminar flow state, and further improvement in coating efficiency can be expected.

[0016]

According to the rotary atomizing electrostatic coating method of the first aspect and the rotary atomizing electrostatic coating apparatus of the present invention of the second aspect, a coating efficiency of 75% or more, which has hitherto been unachievable, is realized. As a result, not only the cost of the paint is reduced and the post-treatment work of the scattered paint is reduced, but also the improvement of the environment is achieved.

Further, according to the rotary atomizing electrostatic coating device of the third aspect, the turbulent flow generated between the shaping air and the second outer envelope shaping air can be suppressed in the annular space. The combined air of the second outer envelope shaping air and the second outer envelope shaping air is in a more preferable laminar flow state, and further improvement in coating efficiency can be expected. As a result, the cost of the coating material is reduced, the post-treatment work of the scattered coating material is reduced, and the environmental performance is further improved.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a rotary atomizing electrostatic coating apparatus of the present invention, FIG. 2 is a graph showing a relationship between a flow velocity ratio of shaping air with respect to a second envelope shaping air and a coating efficiency, and FIG. FIG. 4 is a graph showing the relationship between the shaping air flow velocity and the coating particle diameter, FIG. 4 is a graph showing the relationship between the coating particle diameter and the coating film sharpness value, and FIG. 5 is a sectional view for explaining the action of the annular space.

As shown in FIG. 1, the rotary atomizing electrostatic coating apparatus 100 of this embodiment has a rotating shaft 20 inside a housing 10.
Is rotatably supported by a motor (not shown), and a bell cup 30 is fixed to a tip of the rotary shaft 20 by a nut 22 at a bell hub portion 34. Bell cup 3
0 is rotated at a high speed of about 35,000 rpm during coating.

An annular plate 12 is fixed between the housing 10 and the bell cup 30, and an annular air passage 14 is provided in the vicinity of the bell cup side of the annular plate 12.
Are formed. A shaping air inlet 18 is formed in the air passage 14, and the bell cup 30 has a surface facing the rear surface 38.
A plurality of first air outlets 16 are provided along the circumference of the back surface 38 of the.

Therefore, the compressed air introduced from the inlet 18 passes through the annular air passage 14 and then a plurality of first air flows.
The air is discharged as shaping air S ₁ from the first air outlet group consisting of the air outlets 16 toward the rear surface 38 of the bell cup 30.

A plurality of paint holes 36 are formed in the gap between the inner peripheral surface 32 of the bell cup 30 and the bell hub portion 34, and the paint nozzle 50 fixed to the annular plate 12 is provided.
The paint supplied to the back surface of the bell hub portion 34 from this is guided to the inner peripheral surface 32 of the bell cup 30 through these paint holes 36. Although illustration is omitted, fine irregularities are formed at the tip of the inner peripheral surface 32 of the bell cup 30 for atomizing the coating material P _t that spreads in a liquid film shape along the inner peripheral surface 32. ing. The applied voltage circuit is the rotary shaft 20.
And a DC voltage of, for example, about −60 kV is applied to the bell cup 30 via the rotary shaft 20.

A plurality of second air outlets 40 are provided on the outer circumference of the bell cup 30 on a circumference having a diameter larger than this.
The air flow rate is controlled by a control circuit different from the shaping air S ₁ described above. The plurality of second air outlets 40 constitutes a second air outlet group, and the second envelope shaping air S ₂ discharged from the second air outlets 40 is the shaping air described above. A so-called air curtain is formed to wrap S ₁ from the outside.

The plurality of second air outlets 4 are also provided.
0 and the second air outlet 16 between the annular space 6
0 is formed to prevent turbulent flow due to interference between the shaping air S ₁ from the first air outlet 16 and the second external shaping air S ₂ from the second air outlet 40. To do.

That is, for example, as in the rotary atomizing electrostatic coating apparatus described in Japanese Patent Application Laid-Open No. 58-104,656 cited as a conventional example, the first air outlet 16 and the second air outlet 40 are provided. , Which are connected by a large-diameter disk, as shown by a dotted arrow in FIG. 5, a turbulent flow (vortex flow) is generated between the shaping air S ₁ and the second envelope shaping air S _2.
Occurs and a part of the air flows back to the gun side. As a result, the coating particles riding on the backflow air also return to the gun side, and as a result, the improvement of the coating efficiency is suppressed.

However, as in this embodiment, the second
If an annular space 60 is formed between the air outlet 40 and the first air outlet 16 of the shaping air S ₁
If so interfering object in the vicinity of the second discharge port of the outer cover shaping air S ₂ is not present, without the vortex flow is generated, is blown to the object to be coated side becomes appropriate laminar flow. The specific structure of the annular space 60 is not particularly limited as long as it is a recess or a space that can prevent turbulent flow such as vortex flow.

Next, the operation will be described. In this embodiment, the bell cup 30 is rotated to remove the paint P _t from the paint nozzle 50.
From the bell hub portion 34 to the back surface of the bell hub portion 34,
By the rotational centrifugal force of 0, the paint P _t passes through the paint hole 36 and reaches the tip while spreading the inner peripheral surface 32 of the bell cup 30 in the form of a liquid film. Then, the charged coating particles are atomized by the fine irregularities formed on the tip of the inner peripheral surface of the bell cup 30 and fly outward in the radial direction of the bell cup 30. At this time, the shaping air S ₁ blown out from the first air outlet 16 reaches the tip along the back surface 38 of the bell cup 30 and deflects the above-mentioned coating particles toward the object to be coated.

As described above, the coating pattern of the coating particles is determined by the balance between the rotational centrifugal force of the bell cup 30 and the flow velocity of the shaping air S _{1. In} the present embodiment, the second pattern is formed so as to wrap the shaping air S ₁ . The outer casing shaping air S ₂ is discharged from the second air outlet 40.

In particular, the second envelope shaping air S ₂
The flow rate of the second envelope shaping air S ₂ is controlled so that the flow rate ratio of the shaping air S _{1 to} the flow rate is 0.4 or more and 1.6 or less. In other words, the second envelope shaping air S ₂ not only deflects the coating particles scattered outward from the shaping air S ₁ to the object side again, but also balances the flow rates of these airs S ₁ and S _2. FIG. 2 shows the relationship between the flow rate ratio of both air S ₁ and S ₂ and the coating efficiency, which is believed by the present inventor to make the flying state of the particles smoother and thus to improve the coating efficiency. As described above, it was found that the coating efficiency was highest when the flow velocity ratio of both air S ₁ and S ₂ was close to 1. In particular, it was confirmed that when the flow velocity ratio of both air S ₁ and S ₂ is controlled in the range of 0.4 or more and 1.6 or less, coating can be performed with a coating efficiency of 75% or more, which could not be achieved conventionally. This means not only reduction of paint cost and improvement of post-treatment of waste paint,
It will also lead to the improvement of environmental friendliness by reducing VOD.

The second envelope shaping air S ₂
The reason for controlling the flow rate of the _second envelope shaping air S ₂ so that the flow rate ratio of the shaping air S _{1 to} the flow rate is 0.4 or more and 1.6 or less is as follows. That is, when the flow rate or the flow velocity of the shaping air S ₁ is increased, the coating particles ejected from the tip of the inner peripheral surface of the bell cup 30 are affected by the shaping air S ₁ , and the atomization proceeds as shown in FIG. Thereby, as shown in FIG. 4, the clearness value of the coating film, which is an index of the quality of the coated surface, becomes good.
Therefore, to be set to a predetermined value or more in the flow rate or flow rate of shaping air S ₁ Speaking the relationship between the coated surface quality and shaping air S _1, it is not obtained coated surface quality of interest.

Therefore, as long as the shaping air S ₁ is within a range in which a coated surface of the desired quality can be obtained, both the shaping air S ₁ and the second external shaping air S ₂ S ₁ , S 2 are formed. It is also possible to control the flow rate of ₂ . However, shaping air S
_Since the flow rate of ₁ is subject to a certain limit, in this embodiment,
The flow rate of the shaping air S ₁ is fixed to an appropriate value,
The flow rate or flow velocity of the _second envelope shaping air S ₂ is controlled. Accordingly, it is sufficient to control the flow rate of the _second envelope shaping air S ₂ with respect to the flow rate of the shaping air S ₁ that is fixed, so that the control is extremely simple.

As described above, according to the present embodiment, it is possible to suppress the turbulent flow and the eddy flow generated between the shaping air S ₁ and the second outer envelope shaping air S _{2 due} to the existence of the annular space 60. Both airs are in the most preferable laminar flow state. As a result, it is possible to achieve a coating efficiency of 75% or more, which has not been achieved so far, and not only the cost of the coating and the post-treatment of the scattered coating are reduced, but also the improvement of the environment is achieved. Further, since the shaping air is fixed and controlled by the second envelope shaping air, it is possible to simplify the control circuit, reduce the facility cost, and improve the workability of maintenance work.

The embodiments described above are described for facilitating the understanding of the present invention and not for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a rotary atomizing electrostatic coating device of the present invention.

FIG. 2 is a graph showing a relationship between an air flow rate ratio and a coating efficiency.

FIG. 3 is a graph showing the relationship between the shaping air flow rate and the coating particle size.

FIG. 4 is a graph showing the relationship between the coating particle size and the coating film clarity value.

FIG. 5 is a sectional view for explaining the action of the annular space according to the present invention.

[Explanation of symbols]

100 ... Rotating atomizing electrostatic coating device 10 ... Housing 12 ... Annular plate 14 ... Air passage 16 ... First air outlet 18 ... Air inlet 20 ... Rotating shaft 30 ... Bell cup 32 ... Inner peripheral surface 36 ... Paint hole 38 Back surface 40 Second air outlet 50 Paint nozzle 60 Annular space S ₁ Shaping air S ₂ Second outer shaping air P _t Paint

Claims (3)

[Claims] 1. The shaping air is supplied from the back surface of the bell cup, and the second envelope shaping air is supplied from the circumference of a diameter larger than that of the bell cup, and is discharged from the tip of the inner peripheral surface of the bell cup. In the rotary atomizing electrostatic coating method for deflecting atomized paint to the surface of an object to be coated, the flow velocity ratio of the shaping air to the second outer envelope shaping air is 0.4 or more and 1.6 or less. Rotating atomization electrostatic coating method. 2. A rotatable bell cup to which paint is supplied to the inner peripheral surface, and a first air blower which is opened along the periphery of the back surface of the bell cup and supplies shaping air from the back surface to the front. An outlet group; and a second air outlet group that is opened along a circumference having a diameter larger than that of the first air outlet group and blows out a second envelope shaping air toward the front. In the rotary atomizing electrostatic coating device for deflecting the atomized paint discharged from the tip of the inner peripheral surface of the object to the surface of the object to be coated, the flow velocity ratio of the shaping air to the second outer envelope shaping air is 0.4 or more and 1 or more. A rotary atomizing electrostatic coating device characterized by having a value of 6 or less. 3. An annular space is formed between the first group of air outlets and the second group of air outlets along the direction of rotation of the bell cup. Rotary atomizing electrostatic coating device.