Rotary atomizing electrostatic applicator and shaping air ring for the same

Abstract

The present invention solves a problem of a trade-off between increases in paint discharge rate and maintenance of painting quality. A rotary atomizing electrostatic applicator includes a bell cup 10 whose back 10a is hit by atomization air SA-IN at an angle of 90 degrees or less; and first air holes 30 adapted to discharge the atomization air SA-IN directed at the back 10a of the bell cup, wherein the first air holes 30 are arranged at equal intervals on a circumference centered around a rotation axis of the bell cup 10, the first air holes 30 are oriented in a direction opposite to a rotation direction of the bell cup 10; and the atomization air SA-IN discharged through the first air holes 30 is twisted in the direction opposite to the rotation direction of the bell cup 10 at an angle of 50 degrees or more and less than 60 degrees.

Claims

1. A rotary atomizing electrostatic applicator comprising: a bell cup whose back is hit by atomization air, an angle of the back with respect to a plane of an outer circumferential edge of the bell is 90 degrees or less; first air holes adapted to discharge the atomization air directed at the back of the bell cup; and second air holes arranged on an outer circumferential side of the first air holes and configured to discharge a pattern air, wherein the first air holes are arranged at equal intervals on a circumference centered around a rotation axis of the bell cup, and the first air holes are oriented in a direction opposite to a rotation direction of the bell cup, wherein the bell cup is configured to rotate in a first direction about an axis of rotation thereof, wherein the atomization air discharged through the first air holes is twisted in a second direction opposite to the first direction at a twist angle, wherein the twist angle is the angle of atomization air discharged through the first air holes twisted in the second direction, and the twist angle of the atomization air is 50 degrees or more and less than 60 degrees, and wherein the pattern air discharged through the second air holes passes radially outward of an outer circumferential edge of the bell cup.

2. The rotary atomizing electrostatic applicator according to claim 1, wherein the twist angle of the atomization air is 56 degrees to 59 degrees.

3. The rotary atomizing electrostatic applicator according to claim 1, wherein the twist angle of the atomization air is 56 degrees to 58 degrees.

4. The rotary atomizing electrostatic applicator according to claim 1, wherein an air travel distance covered by the atomization air traveling from the first air holes to the back of the bell cup is equal to or smaller than 26.7 mm.

5. The rotary atomizing electrostatic applicator according to claim 1, wherein an air travel distance covered by the atomization air traveling from the first air holes to the back of the bell cup is 30 mm to 1 mm.

6. The rotary atomizing electrostatic applicator according to claim 1, wherein an air travel distance covered by the atomization air traveling from the first air holes to the back of the bell cup is 15 mm to 1 mm.

7. The rotary atomizing electrostatic applicator according to claim 1, wherein an air travel distance covered by the atomization air traveling from the first air holes to the back of the bell cup is 10 mm to 1 mm.

8. The rotary atomizing electrostatic applicator according to claim 1, wherein a discharge pressure of the atomization air discharged through the first air holes is 0.03 to 0.2 MPa.

9. The rotary atomizing electrostatic applicator according to claim 1, wherein a discharge pressure of the atomization air discharged through the first air holes is 0.03 to 0.15 MPa.

10. The rotary atomizing electrostatic applicator according to claim 8, wherein a discharge rate of the atomization air is 180 to 435 NL/min.

11. The rotary atomizing electrostatic applicator according to claim 1, wherein a maximum paint discharge rate is 1,000 cc/min to 300 cc/min.

12. The rotary atomizing electrostatic applicator according to claim 1, wherein the pattern air is twisted in the direction opposite to the rotation direction of the bell cup.

13. The rotary atomizing electrostatic applicator according to claim 12, wherein the first air holes are smaller in diameter than the second air holes.

14. The rotary atomizing electrostatic applicator according to claim 12, wherein the first air holes are larger in number than the second air holes.

15. The rotary atomizing electrostatic applicator according to claim 14, wherein the number of the first air holes is twice the number of the second air holes or more.

16. The rotary atomizing electrostatic applicator according to claim 1, wherein when the rotary atomizing electrostatic applicator is viewed from a side, the first air holes are positioned at positions close to the bell cup and the second air holes are positioned at positions away from the bell cup.

17. The rotary atomizing electrostatic applicator according to claim 1, wherein a rotational speed of the bell cup is 25,000 to 15,000 rpm.

18. A shaping air ring applied to the rotary atomizing electrostatic applicator according to claim 1, comprising the first air holes.

19. A shaping air ring applied to the rotary atomizing electrostatic applicator according to claim 1, comprising the first air holes and the second air holes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a tip portion of a prototype electrostatic applicator, where the illustrated electrostatic applicator is equipped with a bell cup with a back angle of 60 degrees.

(2) FIG. 2 shows a tip portion of a prototype electrostatic applicator, where the illustrated electrostatic applicator is equipped with a bell cup with a back angle of 75 degrees.

(3) FIG. 3 shows a tip portion of a prototype electrostatic applicator, where the illustrated electrostatic applicator is equipped with a bell cup with a back angle of 90 degrees.

(4) FIG. 4 illustrates, as a comparative example, an incident angle at which shaping air hits the back of a bell cup when a twist angle of the shaping air is zero, where FIG. 4(I) is a side view of the bell cup and FIG. 4(II) is a sectional view taken along line 4(II)-4(II) in FIG. 4(I).

(5) FIG. 5 illustrates how an incident angle at which shaping air hits the back of a bell cup becomes relatively small when the shaping air has a twist angle, where FIG. 5(I) is a side view of the bell cup and FIG. 5(II) is a sectional view taken along line 5(II)-5(II) in FIG. 5(I).

(6) FIG. 6 shows a relationship between a twist angle of shaping air SA-IN and atomization of paint particles.

(7) FIG. 7 shows a relationship between the twist angle of the shaping air SA-IN and coating efficiency.

(8) FIG. 8 is a diagram created to check whether a prototype applicator can achieve a high coating efficiency in a low-rpm region.

(9) FIG. 9 shows a tip portion of a rotary atomizing electrostatic applicator according to a comparative example, where an air travel distance is L.sub.0=26.7 mm.

(10) FIG. 10 shows a tip portion of a rotary atomizing electrostatic applicator with an air travel distance L of 8.63 mm.

(11) FIG. 11 shows a tip portion of an electrostatic applicator according to an embodiment of the present invention.

(12) FIG. 12 is a front view of a shaping air ring included in the applicator of FIG. 11.

(13) FIG. 13 shows painting pattern control capacity of the applicator according to the embodiment (a paint discharge rate is 600 cc/min).

(14) FIG. 14 shows painting pattern control capacity of the applicator according to the embodiment when the paint discharge rate is set to 200 cc/min and only discharge pressure of atomization air (first shaping air SA-IN) is varied.

(15) FIG. 15 shows painting pattern control capacity of the applicator according to the embodiment when the paint discharge rate is set to 200 cc/min and only discharge pressure of pattern air (second shaping air SA-OUT) is varied.

(16) FIG. 16 shows how the applicator according to the embodiment can change the paint discharge rate greatly between 600 cc/min and 200 cc/min and vary a painting pattern width.

(17) FIG. 17 shows a film thickness distribution of a paint film produced when painting was done by the applicator according to the embodiment.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(18) [Embodiment]

(19) A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

(20) Rotary Atomizing Electrostatic Applicator According to the Embodiment (FIGS. 11 to 17):

(21) FIG. 11 is a side view of a tip portion of the rotary atomizing electrostatic applicator according to the embodiment. The electrostatic applicator 20 illustrated in FIG. 11 includes a bell cup 22 and a shaping air ring 24. Diameter of the bell cup 22 is 77 mm. A back angle of a back 22a of the bell cup is 60 degrees.

(22) The shaping air ring 24 is positioned forward compared to a conventional one. FIG. 12 is a front view of the shaping air ring 24. The shaping air ring 24 has a first air discharge hole group 26 located on a first circumference (with a radius of 35.95 mm) centered around a rotation axis Ax of the bell cup 22 and a second air discharge hole group 28 located on a second circumference (with a radius of 46.1 mm) on an outer circumferential side thereof.

(23) The first air discharge hole group 26 is made up of plural first air discharge holes 30 arranged at equal intervals. Air discharged through the first air discharge holes 30 is the shaping air SA-IN described earlier. The first air discharge holes 30 are referred to as atomization air holes. The atomization air holes 30 are 0.5 mm in diameter. The number of atomization air holes 30 is 90.

(24) The second air discharge hole group 28 is made up of plural second air discharge holes 32 arranged at equal intervals. The second air discharge holes 32 are referred to as pattern air holes. The pattern air holes 32 are 0.8 mm in diameter, larger than the atomization air holes 30. The number of pattern air holes 32 is 40, fewer than half the atomization air holes 30.

(25) Air is fed to the atomization air holes 30 and pattern air holes 32 through independent channels. Therefore, the discharge pressure and flow rate of the first shaping air SA-IN discharged through the atomization air holes 30 and the discharge pressure and flow rate of the second shaping air SA-OUT discharged through the pattern air holes 32 can be controlled independently of each other.

(26) Both first shaping air SA-IN and second shaping air SA-OUT have respectively a twist angle in the direction opposite to the rotation direction of the bell cup 22. That is, both atomization air holes 30 and pattern air holes 32 are configured to be holes inclined in the direction opposite to the rotation direction of the bell cup 22.

(27) The first shaping air SA-IN discharged through the atomization air holes 30 is referred to as atomization air. The atomization air SA-IN is oriented toward the back 22a of the bell cup 22. An axial distance between discharge ends of the atomization air holes 30 and collision points P.sub.1 at which the atomization air SA-IN hits the back 22a of the bell cup is 3.1 mm. An axial distance between the collision points P.sub.1 and an outer circumferential edge of the bell cup is 5 mm. The collision points P.sub.1 of the atomization air SA-IN discharged through the respective atomization air holes 30 are set at equal intervals on a same circumference on the back 22a of the bell cup 22. The twist angle of the atomization air (shaping air SA-IN) is 57 degrees.

(28) The second shaping air SA-OUT discharged through the pattern air holes 32 is referred to as pattern air. The pattern air SA-OUT is oriented toward points P.sub.2 7.5 mm away from an outer circumferential edge of the bell cup 22. That is, the pattern air SA-OUT is directed at the points P.sub.2 7.5 mm away from the outer circumferential edge of the bell cup 22 on a plane including the outer circumferential edge of the bell cup 22.

(29) An axial distance between discharge ends of the pattern air holes 32 and the points P.sub.2 reached by the pattern air on the plane including the outer circumferential edge of the bell cup 22 is 12.4 mm. The points P.sub.2 reached by the pattern air discharged through the pattern air holes 32 are set at equal intervals on a same circumference on the plane including the outer circumferential edge of the bell cup 22. A twist angle of the pattern air SA-OUT is 15 degrees.

(30) An axial distance between the air discharge ends of the atomization air holes 30 and the plane including the outer circumferential edge of the bell cup 22 is 8.1 mm. An axial distance between the air discharge ends of the pattern air holes 32 and the plane including the outer circumferential edge of the bell cup 22 is 12.4 mm. A front face of the shaping air ring 24 is configured as a stepped face. That is, the front face of the shaping air ring 24 is shaped to protrude forward on an inner circumferential side. The atomization air holes 30 open in an inner circumferential portion protruding forward. An axial distance between the inner circumferential portion protruding forward and the plane including the outer circumferential edge of the bell cup 22 is 8.1 mm. On the other hand, the pattern air holes 32 open in an outer circumferential portion located relatively rearward of the inner circumferential portion. An axial distance between the outer circumferential portion and the plane including the outer circumferential edge of the bell cup 22 is 12.4 mm.

(31) Data of the rotary atomizing electrostatic applicator equipped with the bell cup 22 and shaping air ring 24 illustrated in FIG. 11 is shown in Table 17 below.

(32) Painting conditions were as follows.

(33) (1) High voltage: 80 kV

(34) (2) Paint discharge rate: 600 cc/min

(35) (3) Rotational speed of bell cup: 20,000 rpm

(36) (4) Painting speed (gun speed): 350 mm/sec

(37) (5) Painting distance (gun distance): 200 mm

(38) TABLE-US-00017 TABLE 17 particle particle particle sauter diameter diameter diameter mean SA-IN SA-OUT of paint of paint of paint diameter air SA-IN air SA-OUT particle particle particle of paint coating pressure flow rate pressure flow rate in d10 in d50 in d90 particle efficiency (MPa) (NL/min) (MPa) (NL/min) (m) (m) (m) (m) (%) 0.12 375 0.01 150 7.9 24.4 51.1 16.4 90.2 0.15 425 0.01 150 7.4 23.6 51.0 15.8 90.3 0.12 375 0.02 175 8.0 24.8 51.5 16.6 0.15 425 0.02 175 7.5 23.9 51.4 15.9 0.12 375 0.03 210 7.9 24.9 51.7 16.6 0.15 425 0.03 210 7.5 24.3 52.0 16.0

(39) The following test was conducted to verify the performance of the rotary atomizing electrostatic applicator 20 according to the embodiment.

(40) When the paint discharge rate was great (600 cc/min), the ability to control a painting pattern width (diameter of a pattern) was tested, and good results were obtained as shown in Table 18 below and FIG. 13.

(41) Painting conditions were as follows.

(42) (1) High voltage: 80 kV

(43) (2) Paint discharge rate: 600 cc/min

(44) (3) Rotational speed of bell cup: 20,000 rpm

(45) (4) Painting speed (gun speed): 350 mm/sec

(46) (5) Painting distance (gun distance): 200 mm

(47) TABLE-US-00018 TABLE 18 (1) (2) (3) (4) paint flow rate 600 600 600 600 (cc/min) air pressure at 0 0.01 0.02 0.03 pattern air hole 32 (MPa) air flow rate at 0 150 175 210 pattern air hole 32 (NL/min) air pressure at 0.12 0.12 0.12 0.12 atomization air hole 30 (MPa) air flow rate at 375 375 375 375 atomization air hole 30 (NL/min) painting pattern width 700 450 350 300 (diameter: mm) rotational speed of 20,000 20,000 20,000 20,000 bell cup 22 (rpm) coating efficiency (%) 90.2

(48) Next, by setting a maximum paint discharge rate at 750 cc/min to 300 cc/min, the capacity to control the paint discharge rate was tested with the painting pattern width kept constant and results are shown in Table 19 below.

(49) TABLE-US-00019 TABLE 19 painting pattern width 450 450 450 450 (diameter: mm) paint discharged rate 750 600 450 300 (cc/min) air pressure at 0.01 0.01 0.01 0.01 pattern air hole 32 (MPa) air flow rate at 150 150 150 150 pattern air hole 32 (NL/min) air pressure at 0.12 0.1 0.08 0.05 atomization air hole 30 (MPa) air flow rate at 375 330 290 225 atomization air hole 30 (NL/min) rotational speed of 20,000 20,000 20,000 20,000 bell cup 22 (rpm)

(50) Next, when the paint discharge rate was relatively small (200 cc/min), the ability to control the painting pattern width (diameter of a pattern) was tested, and good results were obtained as shown in Table 20 below.

(51) TABLE-US-00020 TABLE 20 paint discharged rate 200 200 200 200 (flow rate: cc/min) air pressure at 0.08 0.1 0.12 0.15 pattern air hole 32 (MPa) air flow rate at 420 465 510 575 pattern air hole 32 (NL/min) air pressure at 0.05 0.05 0.05 0.05 atomization air hole 30 (MPa) air flow rate at 225 225 225 225 atomization air hole 30 (NL/min) pattern width 300 250 220 200 (diameter: mm) rotational speed of 20,000 20,000 20,000 20,000 bell cup 22 (rpm) coating efficiency (%) 90.9 90.2

(52) FIG. 14 shows how controllability of the painting pattern width is checked by changing only the air discharge pressure (MPa) at the atomization air holes 30 with the paint discharge rate (flow rate) set at 200 cc/min. Part (1) of FIG. 14 shows a state of spray produced when the air discharge pressure at the atomization air holes 30 is 0.01 MPa. Part (2) of FIG. 14 shows a state of spray produced when the air discharge pressure at the atomization air holes 30 is 0.03 MPa. Part (3) of FIG. 14 shows a state of spray produced when the air discharge pressure at the atomization air holes 30 is 0.05 MPa. Part (4) of FIG. 14 shows a state of spray produced when the air discharge pressure at the atomization air holes 30 is 0.07 MPa.

(53) FIG. 15 shows how controllability of the painting pattern width is checked by changing only the air discharge pressure at the pattern air holes 32 with the paint discharge rate (flow rate) set at 200 cc/min. Part (1) of FIG. 15 shows a state of spray produced when the air discharge pressure at the pattern air holes 32 is 0 (zero) MPa. Part (2) of FIG. 15 shows a state of spray produced when the air discharge pressure at the pattern air holes 32 is 0.10 MPa. Part (3) of FIG. 15 shows a state of spray produced when the air discharge pressure at the pattern air holes 32 is 0.15 MPa.

(54) As can be seen when FIG. 14 and FIG. 15 are compared, the atomization air SA-IN discharged through the atomization air holes 30 plays a minor role in controlling the painting pattern width. The pattern air SA-OUT discharged through the pattern air holes 32 contributes greatly to controlling the painting pattern width.

(55) Next, by setting the paint discharge rate to a low level (low flow rate) (150 cc/min to 250 cc/min), the capacity to control the paint discharge rate was tested with the painting pattern width kept constant and results are shown in Table 21 below.

(56) TABLE-US-00021 TABLE 21 pattern width 220 220 220 (diameter: mm) paint discharged rate (flow rate) 150 200 250 (cc/min) air pressure at 0.12 0.12 0.12 pattern air hole 32 (MPa) air flow rate at 510 510 510 pattern air hole 32 (NL/min) air pressure at 0.03 0.05 0.08 atomization air hole 30 (MPa) air flow rate at atomization 150 235 290 air hole 30 (NL/min) rotational speed of bell cup 22 20,000 20,000 20,000 (rpm)

(57) FIG. 16 shows results obtained by changing the paint discharge rate (flow rate) greatly between 600 cc/min and 200 cc/min and varying the painting pattern width. Painting conditions in Part (1) of FIG. 16 were as follows.

(58) (i) Paint discharge rate (flow rate): 600 cc/min;

(59) (ii) Rotational speed of bell cup 22: 20,000 rpm;

(60) (iii) Discharge pressure at atomization air holes 30: 0.12 MPa (flow rate: 375 NL/min);

(61) (iv) Discharge pressure at pattern air holes 32: 0.01 MPa (flow rate: 150 NL/min).

(62) The painting pattern width (pattern diameter) at a paint discharge rate of 600 cc/min in Part (1) of FIG. 16 was 470 mm. Also, the average particle diameter of paint particles was 19.9 m.

(63) Painting conditions in Part (2) of FIG. 16 were as follows.

(64) (i) Paint discharge rate (flow rate): 200 cc/min;

(65) (ii) Rotational speed of bell cup 22: 20,000 rpm;

(66) (iii) Discharge pressure at atomization air holes 30: 0.05 MPa (flow rate: 225 NL/min);

(67) (iv) Discharge pressure at pattern air holes 32: 0.15 MPa (flow rate: 575 NL/min).

(68) The painting pattern width (pattern diameter) at a paint discharge rate of 200 cc/min in Part (2) of FIG. 16 was 220 mm. Also, the average particle diameter of paint particles was 16.6 m.

(69) FIG. 17 shows a film thickness distribution of a paint film produced when painting was done by the applicator 20 according to the embodiment (maximum film thickness: 40 m). Painting conditions were as follows.

(70) (i) Paint discharge rate (flow rate): 200 cc/min;

(71) (ii) Rotational speed of bell cup (Bell revolution) 22: 20,000 rpm;

(72) (iii) Discharge pressure at atomization air holes 30: 0.01 MPa (flow rate: 110 NL/min);

(73) (iv) Discharge pressure at pattern air holes 32: 0.15 MPa (flow rate: 575 NL/min);

(74) (v) Applied voltage to bell cup 22: 80 kV.

(75) Referring to FIG. 17, a range (d) in which the film thickness was 20 m or more had a diameter of 200 mm. A range (d) in which the film thickness was 10 m or more had a diameter of 330 mm. A base expansion ratio is (d/d)=330/200=1.6. The value 1.6 is an extremely good value compared with conventional ones. Incidentally, with conventional applicators, generally the base expansion ratio is (d/d)=3.2.

REFERENCE SIGNS LIST

(76) 20 Rotary atomizing electrostatic applicator according to embodiment 10, 22 Bell cup 10a, 22a Back of bell cup 24 Shaping air ring 30 First air discharge hole (atomization air hole) 32 Second air discharge hole (pattern air hole) SA-IN Shaping air (atomization air) SA-OUT Pattern air P Point at which shaping air SA-IN hits back of bell cup