Electrostatic coating apparatus

This is a 371 national phase application of PCT/JP2008/069550 filed 28 Oct. 2008, claiming priority to Japanese Patent Application No. 2007-286795 filed 2 Nov. 2007, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an electrostatic coating apparatus.

BACKGROUND ART

In the rotary atomizing electrostatic coating apparatus, when the paint adheres around the nozzle for spraying the paint, the paint scatters around with forced by the centrifugal force generated by high-speed rotation of the bell cup or by the air blown out from the shaping air ring, which is called a spit. When the paint adheres to the painted surface, the poor paint quality occurs. Thus, in the rotary atomizing electrostatic coating apparatus, in order to keep good paint quality, required is the technique of preventing the paint (blot) from adhering to the periphery of the nozzle.

In the conventional technique, needle electrodes are provided around the nozzle to form electrostatic fields around the electrodes so that the electrostatic repulsion is acted on the paint mist floating around the electrodes, keeping it away from the nozzle, thereby preventing the paint from adhering to the nozzle.

JP 2006-82064 A discloses the rotary atomizing electrostatic coating apparatus, which includes the needle electrodes radiating from the ring electrode, arranged at the periphery thereof to form uniform electrostatic field around the nozzle.

Referring FIGS. 7 to 10, the conventional blot preventing device 51 is explained below.

As shown in FIG. 7, the device 51 has an electrode part 54 including a ring electrode 52 and multiple (ten) needle electrodes 53 (53a, 53b, 53c, 53d, 53e, 53f, 53g, 53h, 53i, 53j) radiating from the ring electrode 52 each of which is spaced at the substantially equal distance, and the electrode part 54 is connected with a high voltage generator 56.

As shown in FIG. 8, in the actual using, the electrode part 54 is fixed to a coating gun 55. In detail, the electrode part 54 is arranged at the periphery of a shaping air ring 55b located backside of a bell cup 55a.

As shown in FIG. 8, the high voltage generator 56 is built in the coating gun 55, electrically connected to a built-in air motor 55c and to a built-in wire 56a.

The high voltage generator 56 is supplied with 24 V from the external source, in which the voltage is raised to about 90 kV. The high voltage generated in the generator 56 is applied to the air motor 55c.

The air motor 55c is composed of conducting members and contacts the shaping air ring 55b which is also composed of conducting members. Thus, the air motor 55c and the shaping air ring 55b are electrically connected. The voltage applied to the air motor 55c is also applied to the bell cup 55a.

The electrode part 54 is fixed to the ring 55b, so that they are electrically connected. The voltage applied to the ring 55b is applied to the electrode part 54.

As described above, the electrode part 54 is electrically connected to the high voltage generator 56 built in the gun 55, to which high voltage applied.

As shown in FIG. 9, the high voltage generated by the generator 56 is applied to the electrode part 54, whereby the needle electrodes 53 form the high-intensity electrostatic field (electric barrier) toward a grounded body 57. The paint mist discharged from the bell cup 55a of the gun 55 is controlled with the electrostatic repulsion, keeping the paint away from the gun 55, thereby preventing the paint from adhering to the gun 55 (especially to proximate portions to the bell cup 55a, shaping air ring 55b).

As shown in FIG. 9, when the electrode part 54 is apart from the grounded body 57 by the normal distance (in the normal state), the needle electrodes 53 foam the electrostatic field toward the grounded body 57 and the corona discharge occurs in which the slight current about a few μA flows from the electrodes 53 to the grounded body 57.

Unfortunately, as shown in FIG. 10, when the needle electrodes 53 come closer to the grounded body 57 beyond the proper range (namely, the distance between them becomes not more than the distance L1), the electric discharge amount increases and the discharge energy becomes higher, so that the discharge phase is shifted to the spark discharge from the corona discharge.

As depicted in FIG. 10, for example, when the distance between the needle electrode 53d and the grounded body 57 becomes the distance L2 (L2<L1, which is not more than the normal distance), the current concentrates on the electrode 53d, thereby increasing the electric energy in the electrode 53d and unfortunately generating the spark from the electrode 53d to the grounded body 57.

The conventional device 51 having the needle electrodes 53 is controlled to prevent the spark discharge. For instance, the discharge current is monitored and when the higher current than the predetermined value is detected, the power supply to the high voltage generator 56 is stopped or lowered.

In other case, when the electrode 53d come closer to the grounded body 57 beyond the proper range, the current concentrates on the electrode 53d, thereby dropping the voltages applied to the other electrodes (apart from the electrode 53d). Mentioned to the electrodes 53c and 53e, the distances from the grounded body 57 are the distance L3, which is in the proper range, however, the voltages dropped caused by the electrode 53d, whereby the electrostatic fields generated therefrom become less than the proper intensity. Moreover, the similar situation occurs in the other electrodes. As a result, the performance of the device 51 (blot preventing performance) is lowered.

The conventional device 51 can be applied to the case that the distance between the coating object and the gun 55 is easily kept in the proper range, for example when coating the exterior of the vehicle body. However, when coating the inside of the complex configuration such as the interior of the vehicle body, the gun 55 easily moves close to the coating object (flame or the like) beyond the proper range. In the close situation, the spark discharge or the voltage drop may occur, so that the measure is needed such as to stop the power supply to the electrodes 53. In such situation, the coating operation is interrupted, and the performance of the device 51 may fail to be kept properly.

DISCLOSURE OF INVENTION
Problems to be Solved by the Invention

The objective of the present invention is to provide an unexpected electrostatic coating apparatus including a blot preventing device provided with multiple needle electrodes enabled to prevent the spark discharge if the electrodes approach the grounded body and to keep the electrostatic field proper intensity.

Means of Solving the Problems

The first aspect of the present invention is an electrostatic coating apparatus, including a blot preventing device which contains a ring electrode provided with multiple needle electrodes radiating from a ring base and a high voltage generator applying high voltage to the ring electrode, in which the needle electrodes are parallelly connected to the high voltage generator through resistors.

Due to the above structure, when the current concentrates on any needle electrode, the voltage applied to the electrode is dropped largely, thereby preventing the spark discharge. Moreover, in the other electrodes, the voltages applied thereto are not dropped largely, so that the intensities of the electrostatic fields are maintained. Therefore, the blot preventing performance of the other electrodes is provided properly.

In the advantageous embodiment of the present invention, the electric resistances of the resistors are more than 1 MΩ.

Thus, the necessary voltage-drop amount is obtained for preventing the spark discharge on a needle electrode. In the other electrodes, the necessary voltage-drop amount is obtained for keeping the proper electrostatic fields.

In the preferable embodiment of the present invention, the needle electrodes are parallelly connected to the high voltage generator through individual resistors.

Preferably, in the embodiment of the present invention, the electric resistances of the individual resistors are more than 1 MΩ.

In the other embodiment of the present invention, the needle electrodes are divided into multiple blocks and in the each block the needle electrodes are connected parallelly to the high voltage generator through block-by-block resistors.

Preferably in the preferable embodiment of the present invention, the electric resistances of the block-by-block resistors are more than 1 MΩ.

The second aspect of the present invention is an electrostatic coating apparatus, in which the high voltage generator is composed of multiple generators, the needle electrodes are divided into the same number of blocks, and the needle electrodes in each block are connected to the each generator.

Due to the above structure, the voltage fluctuation occurred in a needle electrode does not influence on the other electrodes.

Effect of the Invention

According to the present invention, if the any electrodes approach to the grounded body, the spark discharge is prevented and the other electrodes keep the electrostatic fields proper intensities.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a first embodiment showing a blot preventing device according to the present invention.

FIG. 2 is a plan view and a side view illustrating a blot preventing ring according to the present invention.

FIG. 3 is a side sectional view illustrating an electrostatic coating apparatus including the blot preventing device.

FIG. 4 depicts an approaching state of needle electrodes and a grounded body.

FIG. 5 depicts a voltage drop of the blot preventing device.

FIG. 6 depicts a second embodiment showing a blot preventing device according to the present invention.

FIG. 7 depicts a conventional blot preventing device.

FIG. 8 is a side sectional view illustrating an electrostatic coating apparatus including the conventional blot preventing device.

FIG. 9 depicts an electrostatic field formed by the blot preventing device.

FIG. 10 depicts an approaching state of the conventional needle electrodes and grounded body.

FIG. 11 depicts a voltage drop pf the conventional blot preventing device.

THE BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment

The best mode for carrying out the present invention, or a blot preventing device 1, is described below.

As shown in FIG. 1, the device 1 includes a ring electrode part 4 provided with multiple (ten) needle electrodes 3 (3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j) radiating from a ring base 2, each of which is arranged at spacing same distance from the adjacent electrodes.

As shown in FIGS. 1, 2, the base 2 is composed of an insulator and foamed in the ring shape, which supports the electrodes 3 radiately and at the same spacing. Note that the base 2 does not function as the electrode.

The base 2 has wires and multiple resistors (individual resistors 9, block-by-block resistors 10).

As shown in FIGS. 1, 2, one ends of the wires built in the base 2 are connected to an input terminal 12. The other ends of the wires are connected to the electrodes 3a to 3j. As depicted in FIG. 2, the input terminal 12 is a conducting material configured in the ring shape to engage in the ring base 2, and a thread portion 12a is formed in the inside of the input terminal 12.

As shown in FIG. 3, a coating gun 5 as the electrostatic coating device includes a bell cup 5a, a shaping air ring 5b, an air motor 5c, and a high voltage generator 6. The outside of the shaping air ring 5b is formed with a thread portion 5d threadably attached to the thread portion 12a, whereby the electrode part 4 is fixed and electrically connected to the shaping air ring 5b.

To the shaping air ring 5b, high voltage (about 60 to 90 kV) is applied by the generator 6 and the base 2 touches the ring 5b, whereby the input terminal 12 becomes a contact point, so that the needle electrodes 3 connected to the terminal 12 via the resistors 9, 10 are applied by the high voltage generated in the generator 6.

The internal structure of the electrode part 4 is explained below.

As shown in FIGS. 1, 2, the electrode part 4 has five blocks (Br1, Br2, Br3, Br4, Br5) dividing the wires in the base 2, and two electrodes 3 are arranged in one block. The blocks Br1 to Br5 are connected in a parallel manner to the terminal 12 via the resistors 10 (10a, 10b, 10c, 10d, 10e). The resistors 10 have high electric resistances, 1 MΩ or more.

The electrodes 3a to 3j are divided into blocks Br1 to Br5 including the same number of (two) electrodes 3, in which the electrodes are connected to the generator 6 through the resistors 10a to 10e in a parallel manner.

The structure containing the resistors 10 provides that when the current concentrates on one electrode, the voltage drop in the electrode is increased, thereby preventing the spark discharge. Further, in the other electrodes, the voltage-drops are small, preventing the electrostatic fields from lowering, thereby enabled to maintain the blot preventing performance.

In the embodiment, the electrode part 4 is divided into five blocks, however, the dividing number is not limited and adjusted in accordance with the number of the needle electrodes, the size of the coating gun or the like.

In the inner wires of the blocks Br1 to Br5, the electrodes 3a to 3j are parallelly connected to the resistors 10a to 10e through the resistors 9 (9a, 9b, 9c, 9d, 9e, 9f, 9g, 9h, 9i, 9j). The resistors 9a to 9j have high electric resistances, 1 MΩ or more.

In other words, the needle electrodes 3a to 3j are connected to the contact point (input terminal 12) to the high voltage generator 6 through the individual resistors 9a to 9j, respectively.

Due to the above-explained structure provided with the individual resistors 9 with respect to the needle electrodes 3, when the current flows concentrating on one electrode, the voltage-drop in the electrode is increased, thereby preventing the spark discharge. Further, in the other electrodes, the voltage-drops are small, preventing the electrostatic fields from lowering, thereby enabled to maintain the blot preventing performance.

Moreover, in the inner wires of the needle electrodes 3a to 3j, the electrodes have the built-in resistors 11 (11a, 11b, 11c, 11d, 11e, 11f, 11g, 11h, 11i, 11j), respectively, and these resistors 11 are connected in a parallel manner to the input terminal 12. The resistors 11 have high electric resistance more than 1 MΩ.

As described above, the gun 5 has the generator 6, the electrode part 4 connected to the generator 6 and provided with the electrodes 3a to 3j each of which radiates from the base 2 to the radiately outward and is arranged in such manner that the electrode is spaced out with respect to the adjacent electrodes, and the device 1. The electrodes 3a to 3j are connected in a parallel manner to the generator 6 via the resistors 11a to 11j built in the electrodes, respectively.

Thus, when the current concentrates into one needle electrode, the voltage thereof is highly dropped, so that the spark discharge is prevented from occurring. Further, in the other electrodes, the voltage-drops occur in a small amount, so that the electrostatic fields formed by the electrodes are not weakened, and the performances of the blot preventing in the other electrodes are maintained properly.

As shown in FIG. 4, for example, the electrode 3d in the block Br2 is connected to the generator 6 through the three resistors; the block-by-block resistor 10b, the individual resistor 9d, and the built-in resistor 11d. In this case, the resistors 9d, 10b, 11d have higher electric resistance than 1 MΩ.

The above structure provides that when the electrode 3d approaches to the grounded body 7 and the discharge current concentrates on the electrode 3d, the voltage-drops occurred in the resistors 9d, 10b, 11d make the applied voltage to the electrode 3d is lowered according to the amount of discharge current. Here, as to the electrode 3c in the same block Br2, the voltage drop of the resistor 10b acts thereon, so that the applied voltage lowers.

The electrode 3c is approached to the grounded body 7 in response to the approach of the electrode 3d, so that it is advantageous to lower the applied voltage to the electrode 3c, in this respect, there is a merit to divide the electrodes 3 into multiple blocks.

The division of the electrodes 3 into multiple blocks lowers the influence of the voltage drop occurred in one block (e.g. block Br2) on the different blocks. In the electrodes 3a, 3b, 3e to 3j belong to the blocks Br1, Br3 to Br5 apart from the block Br2 including the electrode 3d, which approaches to the grounded body 7, they keep the proper electrostatic fields, thereby keeping the blot preventing performance of the device 1. In this respect, the division of the electrodes 3 into multiple blocks also gives a merit.

Referring FIGS. 5, 11, the effects given by the embodiment are explained in which the needle electrodes 3 and the high voltage generator 6 are connected via the resistors 12 having the high electric resistance (which is defined as 1 MΩ or more resistance).

FIG. 5 depicts the structure of the electrode part 4 schematically; the electrodes 3 are connected to the generator 6 via the resistors 13 having 50 MΩ resistance. FIG. 11 depicts the structure of the conventional electrode part 54 schematically, in which the electrodes 53 are directly connected to the generator 56.

The example shown in FIG. 5, in which the electrodes 3 are connected to the generator 6 generating 90000 V and 1 μA current flows between the electrodes 3 and the grounded body 7, is compared with the example shown in FIG. 11, in which the electrodes 53 are connected to the generator 6 generating 90000 V and 1 μA current flows between the electrodes 53 and the grounded body 57.

As shown in FIG. 11(a), in the electrode part 54, there are no resistors between the generator 6 and the electrodes 53. In the state where there exists the proper distance between the electrodes 53 and the grounded body 57, the electrodes 53 are applied the high voltage (90000 V) by the generator 56. Thus, in the proper state, the electrodes 53 form the electrostatic fields toward the grounded body 57, and corona discharge occurs to flow slight current GRA current).

However, as shown in FIG. 11(b), the electrode 53x that is one of the electrodes 53 approaches to the grounded body 57 beyond the proper range, and the corona discharge (e.g. around 300 μA) occurs from the electrode 53x to the grounded body 57. Thus, if the discharge current becomes higher, the discharge may be switched to the spark discharge from the corona discharge. Therefore, when detecting the high current, the measure for safety is adopted such as the breaker of the power supply.

Furthermore, when the high current flows in the electrode 53x, whereby the other electrodes 53 are influenced because there are no resistors in the system, so that the voltages applied to the other electrodes 53 are lowered and they do not keep the proper electrostatic fields.

In other words, as to the conventional blot preventing device 51 including the electrode part 54, the blot preventing performance is kept in the case that the electrodes 53 are properly apart from the grounded body 57, however, if the electrodes 53 approach to the grounded body 57 beyond the proper distance, it is necessary to stop the operation when the electrodes 53 come close to the grounded body 57, thereby preventing the smooth operation.

Contrastingly, as shown in FIG. 5(a), as to the electrode part 4, the resistors 13 are arranged between the generator 6 and the electrodes 3. When the electrodes 3 keep the proper distance from the grounded body 7, the corona discharge occurs from the electrodes 3 to the grounded body 7, so that the slight (1 μA) current flows and the electrostatic fields are fowled from the electrodes 3 toward the grounded body 7. Here, in the resistors 13 having 250 MΩ resistance, and the voltage drops by 250 V, so that the electrodes 3 are applied by the voltage (89750 V) subtracted by the voltage drop (250 V) in the resistors 13 from the applied voltage (90000 V) by the generator 6. Thus, in the electrodes 3, the voltage-drops occur in the proper using state and the applied voltage to the each electrode 3 is lower than the conventional one, however, the sufficient voltage is maintained to form the electrostatic field.

Furthermore, as shown in FIG. 5(b), the electrode 3x that is one of the electrodes 3 approaches to the grounded body 7 beyond the proper range, and the corona discharge (e.g. 300 μA) occurs from the electrode 3x to the grounded body 7. In the resistor 13x connected with the electrode 3x, the voltage-drop increase with respect to the current, and the drop amount becomes 75000 V, as a result, the applied voltage to the electrode 3x becomes 15000 V. In such case, if the discharge current becomes higher, the applied voltage to the electrode 3x is lowered to avoid the increase of the discharge energy, thereby preventing the spark discharge from occurring.

As explained above, the more the discharge current increases, the higher the voltage-drop in the resistor 13 becomes, and the voltage applied to the electrodes 3 is lowered to prevent the spark discharge, so that if the electrodes 3 approach to the grounded body 7 beyond the proper range, the discharge state is not switched form the corona discharge to the spark discharge, therefore, it is not necessary to break the power supply.

Note that in order to increase the voltage-drops in the resistors 13 sufficiently, the electric resistances of the resistors 13 should be set as the high values. In the embodiment, referring to the example in which the resistors 13 have the 250 MΩ resistance, the blot preventing device 1 has the resistors 9, 10, 11 each of which has the 1 MΩ or more resistance so that the combined resistance of them satisfies sufficiently high value.

Moreover, even if the huge current flows in the electrode 3x, every electrode 3 is connected to the resistor 13 and the other electrodes 3 are not influenced, whereby the voltages applied to the other electrodes 3 are kept from lowering and the proper electrostatic fields are maintained.

Therefore, in the electrode 3x, the voltage-drop is obtained to the certain extent that the spark discharge is prevented from occurring. Further, the voltage-drops of the other electrodes 3 are in the range where the blot preventing performance is maintained.

Due to the electrode part 4 of the present invention, it is not necessary to stop the operation at the time that the electrodes 3 approach to the grounded body 7, because the spark discharge does not occur even if the electrodes 3 come close to the grounded body 7 and the other electrodes 3 keep the proper performance of blot preventing. Therefore, the blot preventing device 1 of the present invention solves the problems in coating the interior of the vehicle body, and the coating gun 5 including the device 1 can be utilized to paint the inner parts of the vehicle body or the like.

In the embodiment, the electrodes 3 are connected via three types of resistors, however the structure of the resistors is not limited and the other configurations may be employed, for example, the resistors combining the individual resistors 9 and the built-in resistors 11 and having the total resistance of the individual resistor 9 and the built-in resistor 11, or the more resistors connected to the electrodes 3.

Second Embodiment

Below, a blot preventing device 21 as the second embodiment of the present invention is explained.

As shown in FIG. 6, the device 21 includes a ring electrode part 24 provided with multiple needle electrodes 23 radiating from a ring base 22, each of which is arranged at spacing same distance from the adjacent electrodes.

The base 22 contains wires, and as shown in FIG. 6, one ends of the wires are connected to a high voltage generator 26, which has multiple (five) groups (26a, 26b, 26c, 26d, 26e, 26f). In this respect, the blot preventing device 21 of the second embodiment is different from the blot preventing device 1 of the first embodiment.

The other ends of the wires are connected to the electrodes 23 (23a, 23b, 23c, 23d, 23e, 23f, 23g, 23h, 23i, 23j).

In the electrode part 24, the inner wires arranged in the base 22 are divided into five blocks (blocks Br1, Br2, Br3, Br4, Br5 as depicted in FIG. 6), the each block (Br1 to Br5) has two electrodes 23. The blocks Br1 to Br5 are connected in a parallel manner to the generators 26a to 26e, respectively.

In the embodiment, the electrode part 24 is divided into five blocks, however, the dividing number is not limited and adjusted in accordance with the number of the needle electrodes, the size of the coating gun or the like.

In the inner wires in the blocks Br1 to Br5, the electrodes 23a to 23j are connected to the generators 26a to 26e through individual resistors 29 (29a, 29b, 29c, 29d, 29e, 29f, 29g, 29h, 29i, 29j), respectively.

In the inner wires of the electrodes 23a to 23j, the electrodes 23a to 23j have built-in resistors 31 (31a, 31b, 31c, 31d, 31e, 31f, 31g, 31h, 31i, 31j).

Thus, the individual control for the applied voltages is obtained, so that when the electrode 23a approaches to the grounded body 27 and high current flows therein, the output voltage of the generator 26a in the block Br1 where the electrode 23a belongs is adjusted to prevent the spark discharge without influencing on the other electrodes.

The generators 26b to 26e connected to the other electrodes 23b to 23j have separated wires, so that there are no influences on the applied voltages to the other electrodes 23b to 23j apart from the electrode 23a; as a result, the electrostatic fields formed by the electrodes 23b to 23j are maintained properly, thereby preventing the blot preventing performance from lowering.

Furthermore, it is possible to identify which electrode 23 approaches to the grounded body 27.

As explained above, in the electrode part 24 of the device 21, the generator 26 is composed of five generators 26a to 26e, and the electrodes 23a to 23j are divided into five (the same number as the generators 26) blocks Br1 to Br5 including two electrodes 23, each of the blocks Br1 to Br5 is connected to the generator 26a to 26j, respectively.

Thus, the voltage fluctuation occurred in a needle electrode does not influence on the other electrodes.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an electrostatic coating apparatus including the blot preventing device in which the multiple needle electrodes are configured in the ring shape.

Number	Name	Date	Kind
4887770	Wacker et al.	Dec 1989	A
5947377	Hansinger et al.	Sep 1999	A
20080178802	Sakakibara et al.	Jul 2008	A1

Number	Date	Country
64-11661	Jan 1989	JP
2006-82064	Mar 2006	JP
2006-110449	Apr 2006	JP
2007-69136	Mar 2007	JP
WO 2006030991	Mar 2006	WO

Electrostatic coating apparatus

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