Electrostatic coater

Abstract

An electrostatic coater capable of realizing high-level coating quality is provided. Shaping air SA, discharged from an air port, is directed radially outward. An elevation angle thereof preferably ranges from 10 to 20 degrees. Further, the shaping air SA is a flow in a state of being twisted in a direction opposite to the rotation direction R of a bell cup. The twisting angle about the axis O of the bell cup preferably ranges from 38 to 60 degrees. A liquid thread of paint extends radially outward from the outer peripheral edge of the bell cup, and the paint separated from the tip end thereof becomes a particle. It is preferable that the shaping air SA collides with the paint particle at a point P where the momentum of the paint particle is decreased of the paint particle is decreased.

Claims

1. An electrostatic coater comprising: a rotary atomizing head configured to rotate in a first direction and scatter paint radially outward to atomize the paint; and air ports positioned behind an outer peripheral edge of the rotary atomizing head, the air ports being configured to discharge shaping air to a front, wherein the air ports consist of only a plurality of air ports arranged at equal intervals on a single circumference coaxial with a rotational center axis of the rotary atomizing head; wherein the air ports direct the shaping air radially outward, the shaping air is directed such that part of secondary-dispersed air of the shaping air becomes air accompanying a liquid thread of paint extending from the rotary atomizing head, and that the shaping air collides with a paint particle separated from the liquid thread of the paint extending radially outward from the rotary atomizing head; wherein the shaping air collides with the paint particle at a point apart radially outward from a tip end of the liquid thread of paint; wherein the shaping air collides with the paint particle at a vertical separation distance between 5.6 mm and 43.2 mm from the outer peripheral edge of the rotary atomizing head; wherein the shaping air discharged from the air ports is twisted in a second direction opposite the first direction of the rotary atomizing head.

2. The electrostatic coater according to claim 1, wherein an elevation angle of the shaping air directed radially outward ranges from 10 to 20 degrees, and wherein the elevation angle is configured to direct the shaping air to collide with the paint particle after the paint particle separates from a liquid thread of paint.

3. The electrostatic coater according to claim 2, wherein a twisted angle of the shaping air about the rotational center axis of the rotary atomizing head ranges from 38 to 60 degrees.

4. The electrostatic coater according to claim 1, wherein the electrostatic coater is applicable to metallic coating.

5. The electrostatic coater according to claim 1, wherein the shaping air from neighboring air ports is configured to overlap while spraying.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view of a tip portion of an electrostatic coater of an embodiment;

(2) FIG. 2 is a perspective view of a shaping air ring and a rotary atomizing head constituting the tip portion of the electrostatic coater of the embodiment, when viewed from an obliquely rear side;

(3) FIG. 3 is a diagram for explaining an elevation angle of shaping air discharged from an air port of the electrostatic coater of the embodiment;

(4) FIG. 4 is a diagram for explaining an inclination angle of the air port for generating shaping air in a state of being twisted about the axis of a bell cup;

(5) FIG. 5 is a diagram for explaining a state where paint extends radially outward in a state of a liquid thread from the outer peripheral edge of the bell cup, and is separated from the tip end of the liquid thread to become a paint particle;

(6) FIG. 6 is a diagram for explaining a state where paint extends radially outward in a state of a liquid thread from the outer peripheral edge of the bell cup, and is separated from the tip end of the liquid thread to become a paint particle, and also explaining a region where the paint particle is decelerated due to the friction with the air;

(7) FIG. 7 is a diagram for explaining a state where paint extends radially outward in a state of a liquid thread from the outer peripheral edge of the bell cup, and is separated from the tip end of the liquid thread to become a paint particle, and also explaining a region where the paint particle is decelerated due to the friction with the air, similar to FIG. 6;

(8) FIG. 8 is a diagram for explaining distances of respective portions included in the electrostatic coater of the embodiment;

(9) FIG. 9 is a photograph showing a state of the paint when a metallic paint is deposited on a workpiece using a conventional electrostatic coater;

(10) FIG. 10 is a photograph showing a state of the paint when a metallic paint is deposited on a workpiece using the electrostatic coater of an example;

(11) FIG. 11 is a diagram for explaining a dual pattern which is a problem in a conventional electrostatic coater;

(12) FIG. 12 is a diagram for explaining that there is a relatively large secondary dispersion region in the vicinity of a collision point where shaping air discharged radially outward from the air port collides with paint particles in the electrostatic coater of the embodiment; and

(13) FIG. 13 is a diagram for explaining that at a collision point where shaping air collides with paint particles, the shaping air in a state of being twisted in a direction opposite to a rotation direction of a bell cup generates an air curtain continuing in a circumferential direction, in the electrostatic coater of the embodiment.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Embodiments

(14) Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a sectional view of a tip end portion of an electrostatic coater of a rotary atomization type, according to an embodiment. FIG. 2 is a perspective view when a bell cup is viewed from a shaping air ring side. Reference numeral 10 denotes a rotary atomizing head. The rotary atomizing head 10 is called a bell cup. The bell cup 10 rotates in a single direction about the axis O thereof. The bell cup 10 has a front surface 10a in a recessed shape that is open toward the front. At the time of coating, paint is supplied to the center portion of the front surface 10a of the rotating bell cup 10. The paint extends radially outward along the recessed front surface 10a by the centrifugal force, and then the paint is scattered radially outward from an outer peripheral edge 10b of the bell cup 10. Air ports 12, which discharge shaping air SA are positioned behind the outer peripheral edge 10b of the bell cup 10. More specifically, the air ports 12 are formed on a front end surface of a shaping air ring 14.

(15) Referring to FIG. 3, a plurality of air ports 12 are arranged at equal intervals on a circumference coaxial with the axis O of the bell cup 10. A configuration of forming the plurality of air ports 12 on a circumference coaxial with the axis O of the bell cup 10 has been well known, as it is understood from Patent Literatures 1 to 5. As such, the detailed description thereof is omitted. The shaping air SA discharged from the air port 12 is directed radially outward. A radially outward elevation angle of the shaping air SA directed radially outward, that is, an inclination angle relative to the axis O of the bell cup 10, preferably ranges from 10 to 20.

(16) Referring to FIG. 4, the shaping air SA discharged from the air port 12 is a flow in a state of being twisted about the axis O of the bell cup 10. The twisted direction is opposite to a rotation direction R of the bell cup 10. The twisted angle preferably ranges from 38 to 60. Now, as the shaping air SA in a state of being twisted about the axis O of the bell cup 10 is described in detail in Patent Literatures 3 to 5, the description thereof is omitted by incorporating the entire description of Patent Literatures 3 to 5 herein by reference.

(17) As means for causing the shaping air SA to be in a twisted state, it is acceptable to adopt a configuration of tilting a shaping 16 communicating to the air ports 12 in a direction opposite to the rotation direction R of the bell cup 10 about the axis O of the bell cup 10 (FIG. 4), or adopt an air guide arranged adjacent to the air port 12 as disclosed in Patent Literature 3.

(18) Referring to FIGS. 5 to 8, the paint extends as a liquid thread 20 from the outer peripheral edge 10b of the rotating bell cup 10, and then becomes paint particles 22. In the electrostatic coater of the embodiment, the radially outward elevation angle of the air port 12 is set such that the shaping air SA directed radially outward is applied to the paint particles 22, rather than the liquid thread 20 (FIG. 3). As described above, it is preferable that the outward elevation ranges from 10 to 20. The most preferable elevation is set as described below.

(19) The paint extends out as the liquid thread 20 from the outer peripheral edge 10b of the rotating bell cup 10. Then, the paint 22 separate from the tip end of the liquid thread 20. The paint particles 22, separated from the liquid thread 20, fly radially outward by the centrifugal force, but starts decelerating by the friction with the air. That is, the momentum of the paint particle 22 is decreased. Reference character A in FIGS. 6 and 7 indicates a region where the momentum of the paint is relatively large by the rotating bell cup 10. Further, reference character B in FIGS. 6 and 7 indicates a region where the momentum of the paint particle 22 is decreased by the friction with the air.

(20) In the electrostatic coater of the embodiment, the momentum of the paint 22 start decreasing at the starting point of the region B (FIGS. 6 and 7), and the momentum decreases to some extent in the vicinity of the starting point of the region B. It is preferable to set a collision point P such that the shaping air SA collides with the paint 22 at the starting point of the region B or the vicinity thereof. Of course, the shaping air SA discharged from the air port 12 is directed to the collision point P.

(21) In order to confirm the effect of the present invention, an experiment was carried out under the following conditions:

(22) (1) Diameter of the bell cup 10: 77 mm

(23) (2) Horizontal separation distance L(b, a) between the collision point P and the air port 12: 19.42 mm (FIG. 8)

(24) (3) Vertical separation distance Hsa between the point P where the shaping air SA collides with the paint particle 22, and the air port 12: 14.16 mm (FIG. 8)

(25) (4) Horizontal separation distance Lh between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 9.42 mm (FIG. 8)

(26) (5) Vertical separation distance Lv between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 17 mm (FIG. 8)

(27) (6) Outward elevation of the shaping air SA (FIG. 3): 15

(28) (7) Twisted angle of the shaping air SA (FIG. 4): 55

(29) (8) Pitch between adjacent air ports 12 and 12: 8.5 mm when converted into a linear distance.

(30) Here, the diameter of the air port 12 is 0.8 mm and the number of air ports 12 is thirty (30).

(31) It should be noted that a virtual line in FIG. 8 shows a spread of the paint scattered radially outward from the outer peripheral edge 10b of the bell cup 10 when there is no shaping air SA.

(32) As a comparative example, experimental results were collected using a conventional electrostatic coater of a rotary atomization type. The coating conditions using a conventional electrostatic coater were as follows:

(33) (1) Diameter of a bell cup: 77 mm;

(34) (2) Horizontal separation distance L(b, a) between the outer peripheral edge of the bell cup and an air port: 11 mm;

(35) (3) Shaping air was a flow parallel to the axis of the bell cup when viewed laterally;

(36) (4) Shaping air was directed to a point which is 2 mm radially outward from the outer peripheral edge of the bell cup;

(37) (5) Shaping air was a flow in a twisted state in a direction opposite to the rotation direction of the bell cup about the axis of the bell cup;

(38) (6) Twisted angle of the shaping air: 40.

(39) Metallic coating was carried out using the conventional electrostatic coater and the electrostatic coater of the embodiment. The experimental results were as shown below.

(40) TABLE-US-00001 TABLE 1 Metallic coating Separation distance Rotating Paint Flow rate between speed of discharge of shaping workpiece Coating bell cup amount air (Nl/ and coater efficiency (rpm) (cc/min.) min.) (mm) (%) Conven- 40,000 150 600 250 86.10 tional example embodiment 40,000 150 400 200 89.70

(41) From the above-described experimental results, it was found that the coating efficiency of the embodiment was improved. Further, regarding the coating NV value (%), a good result was obtained that it was 33.5% in the case of using the electrostatic coater of the embodiment, while it was 25.8% in the case of using the conventional electrostatic coater. Regarding evaluation of the coating NV value (%), Patent Literature 6 should be referred to.

(42) FIGS. 9 and 10 are photographs of paint deposited on workpieces. FIG. 9 shows a coated surface in the case of using a conventional electrostatic coater. FIG. 10 shows a coated surface in the case of using the electrostatic coater of the embodiment. In FIGS. 9 and 10, white portions are aluminum chips. As is well understood from a comparison between FIG. 9 (conventional example) and FIG. 10 (embodiment), a larger number of aluminum chips are exposed on the coated surface in the embodiment than in the conventional example.

(43) Considering the grounds thereof, it can be said as follows when the conventional example and the embodiment are compared. FIG. 11 is a diagram for explaining a problem when the conventional electrostatic coater is used. Referring to FIG. 11, as a paint particle 22b having a relatively large particle diameter has large momentum, it penetrates the shaping air and jumps radially outward. Due to this phenomenon, the inner peripheral portion of the spraying pattern is configured of relatively small paint particles 22s, and the outer peripheral portion thereof is configured of relatively large paint particles 22b. As such, the spraying pattern is a dual pattern.

(44) As is well known, coating is performed while moving the electrostatic coater. The moving direction is shown by the arrows in FIG. 11. The relatively large paint particles 22b, penetrating the shaping air radially outward, cover the small paint particles 22s deposited on the workpiece. Consequently, a large number of relatively large paint particles 22b are positioned on the coated surface.

(45) As metallic chips (aluminum flakes) in the metallic paint have larger mass than that of a resin component, a collision speed of the metallic chip to the workpiece surface is relatively fast. On the workpiece surface, the surfaces around aluminum flakes are covered with the relatively large paint particles 22b due to the phenomenon described with reference to FIG. 11, so that the surroundings of the aluminum flakes tend to be swelled. This is also known from the photograph of FIG. 9 showing the conventional example.

(46) FIGS. 12 and 13 are diagrams for explaining effects of the electrostatic coater according to the present invention. With reference to FIG. 12, each of the air ports 12 is directed radially outward, and the collision point P is set in a region where the physical quantity of the paint particle 22, separated from the tip end of the liquid thread 20, is decreased. As such, a linear distance from the air port 12 to the collision point P is relatively large. Accordingly, at the collision point P, the shaping air SA discharged from the air port 12 is in a state of being dispersed radially from the axis of the shaping air SA. This means that regarding the shaping air SA discharged from the air port 12, a region of secondary dispersion thereof is relatively large in the vicinity of the collision point P. FIG. 12 shows the secondary dispersion of the shaping air SA with oblique lines.

(47) The airflow of the secondary-dispersed shaping air SA becomes a state accompanying the liquid thread 20 extending radially outward from the outer peripheral edge 10b of the bell cup 10. It can be expected that the airflow of the secondary-dispersed shaping air SA acts on the liquid thread 20 extending radially outward so as to allow the liquid thread 20 to further extend radially outward. As the length of the liquid thread 20 becomes longer, the cross-sectional area of the tip end portion thereof becomes smaller. Consequently, the paint particle 22, generated by separating from the tip end of the liquid thread 20, becomes smaller. This means that further micronization of the paint is realized by the airflow of the secondary-dispersed shaping air SA.

(48) Referring to FIG. 13, at the collision point P, the shaping air SA is in a state of being dispersed in a radial direction from the axis of the shaping air SA. As such, the collision point P is in a state where a region in which one adjacent shaping air SA is secondary dispersed and a region in which the other shaping air SA is secondary dispersed overlap with each other. This means that at the collision point P, an air curtain continuing in a circumferential direction is formed. Then, as the momentum of the paint 22 is relatively small at the collision point P, it is less likely that the paint 22 penetrate the air curtain. Thereby, it is possible to restrain a spraying pattern from becoming a dual pattern which has been a problem.

(49) This is also clear from the photograph of FIG. 10 showing the coated surface by the embodiment. It can be said that the coated surface is in an ideal state where a large number of aluminum flakes are exposed relatively, and relatively small paint particles 22s fill in the gaps between the large number of aluminum flakes.

(50) As other embodiments, modifications of the above-described embodiment were experimentally produced and tested. As a result, substantially the same effects as those of the above-described embodiment could be obtained. The specifications of the other embodiment s are as described below.

Second Embodiment

(51) (1) Diameter of the bell cup 10: 50 mm

(52) (2) Horizontal separation distance L(b, a) between the collision point P and the air port 12: 15.1 mm

(53) (3) Vertical separation distance Hsa between the point P where the shaping air SA collides with the paint particle 22, and the air port 12: 2.7 mm

(54) (4) Horizontal separation distance Lh between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 5.1 mm

(55) (5) Vertical separation distance Lv between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 5.6 mm

(56) (6) Outward elevation of the shaping air SA: 5

(57) (7) Twisted angle of the shaping air SA: 45

(58) (8) Pitch between adjacent air ports 12 and 12: 3.8 mm when converted into a linear distance

(59) Here, the diameter of the air port 12 is 0.8 mm and the number of air ports 12 is forty five (45).

Third Embodiment

(60) (1) Diameter of the bell cup 10: 40 mm

(61) (2) Horizontal separation distance L(b, a) between the collision point P and the air port 12: 37 mm

(62) (3) Vertical separation distance Hsa between the point P where the shaping air SA collides with the paint particle 22, and the air port 12: 40.5 mm

(63) (4) Horizontal separation distance Lh between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 26 mm

(64) (5) Vertical separation distance Lv between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 42.2 mm

(65) (6) Outward elevation of the shaping air SA: 15

(66) (7) Twisted angle of the shaping air SA: 55

(67) (8) Pitch between adjacent air ports 12 and 12: 3.8 mm when converted into a linear distance

(68) Here, the diameter of the air port 12 is 1 mm and the number of air ports 12 is thirty six (36).

Fourth Embodiment

(69) (1) Diameter of the bell cup 10: 40 mm

(70) (2) Horizontal separation distance L(b, a) between the collision point P and the air port 12: 37.3 mm

(71) (3) Vertical separation distance Hsa between the point P where the shaping air SA collides with the paint particle 22, and the air port 12: 40.7 mm

(72) (4) Horizontal separation distance Lh between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 26.3 mm

(73) (5) Vertical separation distance Lv between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 42.7 mm

(74) (6) Outward elevation of the shaping air SA: 15

(75) (7) Twisted angle of the shaping air SA: 55

(76) (8) Pitch between adjacent air ports 12 and 12: 3.8 mm when converted into a linear distance

(77) Here, the diameter of the air port 12 is 1 mm and the number of air ports 12 is thirty six (36).

Fifth Embodiment

(78) (1) Diameter of the bell cup 10: 40 mm

(79) (2) Horizontal separation distance L(b, a) between the collision point P and the air port 12: 37.6 mm

(80) (3) Vertical separation distance Hsa between the point P where the shaping air SA collides with the paint particle 22, and the air port 12: 40.7 mm

(81) (4) Horizontal separation distance Lh between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 26.6 mm

(82) (5) Vertical separation distance Lv between the outer peripheral edge 10b of the bell cup 10 and the collision point P: 43.2 mm

(83) (6) Outward elevation of the shaping air SA: 15

(84) (7) Twisted angle of the shaping air SA: 55

(85) (8) Pitch between adjacent air ports 12 and 12: 3.9 mm when converted into a linear distance

(86) Here, the diameter of the air port 12 is 1 mm and the number of air ports 12 is thirty six (36).

REFERENCE SIGNS LIST

(87) 10 Rotary atomizing head included in coater of embodiment (bell cup) O Axis of bell cup 10a Recessed front surface of bell cup 10b Outer peripheral edge of bell cup 12 Air port which discharges shaping air SA Shaping air Radially outward elevation angle of shaping air Twisted angle of shaping air P Point where shaping air collides with paint particles L(b, a) Horizontal separation distance (between collision point P and air port) Hsa Vertical separation distance between air port and collision point Lh Horizontal separation distance between outer peripheral edge of bell cup and collision point Lv Vertical separation distance between outer peripheral edge of bell cup and collision point 20 Liquid thread of paint 22 Paint particle