JP2770079B2 - Spray gun type electrostatic coating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a spray gun type electrostatic coating apparatus particularly suitable for spraying water-based paints and metallic paints.

[Prior art] Generally, paints used for electrostatic coating are roughly classified into solvent-based paints (oil-based paints) having relatively large electric resistance and water-based paints (water-based paints) having relatively small electric resistance values. ,
Further, there are metallic paints in which a metal powder is dispersed in these solvent paints and water paints, and these metallic paints have relatively small electric resistance values like water paints. As described above, since the paint has a different resistance value depending on the kind of the paint, the method of applying the high voltage also differs depending on the kind of the paint.

In other words, paint supply lines, paint tanks, color change valve devices, etc. are used by connecting them to ground from the viewpoint of danger prevention. However, since solvent paints have relatively high resistance, the center of the spray gun main body is used. Even if a high voltage is applied directly to the electrodes, there is no danger that the spray gun body will be at ground potential via the paint supply line. Therefore, the electrostatic coating device used for the solvent-based paint is configured to apply a high voltage directly to the spray gun body and directly charge the paint particles.

On the other hand, since water-based paints and metallic paints have low electrical resistance, when a high voltage is applied directly to the center electrode of the spray gun body, the spray gun body is short-circuited to the ground potential via the paint in the paint supply pipe. As a result, the paint particles cannot be charged. Therefore, in the case of a water-based paint or a metallic paint, an external electrode is provided radially outside the spray gun body, a high voltage is applied to the external electrode, and the paint supply pipe of the spray gun body is grounded. Then, a corona discharge region is formed in front of the spray gun main body by the external electrode, and the paint particles sprayed from the spray gun main body are indirectly charged to perform coating on the object to be coated.

[Problems to be solved by the invention]

By the way, in the external electrode type spray gun type electrostatic coating apparatus according to the above-mentioned conventional technology, the spray paint atomized and sprayed by the air nozzle of the spray gun body forms a predetermined spray pattern. , Immediately after spraying, the dispersion density of paint particles is high,
The dispersion density is low in the vicinity of the object to be coated.

On the other hand, a high voltage applied from an external electrode is discharged toward paint particles forming the spray pattern,
At this time, more current flows to the air nozzle side where the dispersion density of the paint particles is high. Therefore, when the distance between the tip of the external electrode and the spray pattern is reduced, more current flows to the ground through the paint nozzle and paint supply pipe through the paint particles in the high-density area, causing a short circuit phenomenon and the continuation of electrostatic painting. Becomes impossible.

In order to solve this, in the related art, a method of reducing a high voltage applied to an external electrode, connecting a high resistance to the inside of the external electrode, and the like have been adopted. However, with these methods,
In order to prevent a short circuit phenomenon from occurring between the external electrode and the ground electrode, the limit of the current value flowing between the voltage application system and the ground system is usually about 180 μA, and the coating efficiency is significantly reduced. There is a problem.

The present invention has been made in view of such problems of the prior art, and the present invention suppresses a current from flowing to the ground via a paint nozzle and a paint supply pipe when a high voltage is applied to an external electrode. It is an object of the present invention to provide a spray gun type electrostatic coating apparatus which can maintain a high voltage and increase the coating efficiency within the range of the current value of the above.

[Means for solving the problem]

The configuration adopted by the present invention to solve the above-described problem is a spray gun main body, a paint nozzle provided on the tip side of the spray gun main body, which sprays paint from a paint spray port, and is held at a ground potential, A ground electrode provided on the spray gun main body such that a tip side protrudes from the paint nozzle, an electrode mounting bracket provided on an outer peripheral side of the spray gun main body, and mounted on the bracket;
At least one external electrode holding rod disposed so that a front end thereof projects forward from the ground electrode; and an external electrode provided on the external electrode holding rod so as to be exposed from the front end of the external electrode holding rod. An electrode, and a high-voltage generator connected to the external electrode via a high-voltage cable to apply a high voltage to the external electrode, and a tip of the external electrode holding rod faces a ground electrode. It is formed so that the inside is long and the outside is short.

Further, when the current value between the voltage application system including the external electrode, the high voltage cable and the high voltage generator and the earth system including the earth electrode becomes lower than a predetermined current value, the lowered current value becomes the predetermined current value. High voltage generation control means for increasing the generated high voltage so as to be a current value, and when the current value rises above a predetermined current value, reducing the generated high voltage so that the raised current value becomes a predetermined current value is provided. You may.

[Action]

With this configuration, when viewed from the ground electrode of the spray gun main body, the external electrode is concealed by the inner protruding portion of the external electrode holding rod, and apparently the insulation between the external electrode and the ground electrode. The distance can be lengthened, and even if the high voltage applied to the external electrode is increased, it is possible to prevent a current from being short-circuited to the ground via the paint particles forming the spray pattern, the paint nozzle, and the paint supply pipe.

Further, by controlling the generated high voltage by the high voltage generation control means, the value of the current flowing between the external electrode and the ground electrode can always be kept constant.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 5.

1 denotes a spray gun type coating machine, and the coating machine 1 is configured as shown in FIG. That is, reference numeral 2 denotes a spray gun main body 2, which is formed in a columnar shape, a paint nozzle 7 described later is fitted to the front end side, and a retainer ring 16 described later is screwed to the outer peripheral surface. The electrode mounting hole 3, the main body side paint passage 4, the main body side atomizing air passage 5, and the main body side pattern air passage 6 communicating with the tip of the mounting hole 3 are provided along the axis of the spray gun main body 2. Is formed.

Reference numeral 7 denotes a paint nozzle provided so as to be fitted to the front end side of the spray gun body 2, the paint nozzle 7 is formed of a resin material, and the paint nozzle 7 has a stepped cylindrical nozzle body portion 7A. A circumferential groove 7B formed at the rear side of the nozzle body 7A so as to communicate with the main body side atomizing air passage 5; and a nozzle forming section formed at the front side of the nozzle body 7A to have a small diameter. 7C and a circular flange 7D protruding in the radial direction from the axial center of the nozzle body 7A and disposed close to the inner peripheral surface of the retainer ring 16. A paint passage 8 is provided in the paint nozzle 7 in the axial direction.
Is formed, and a small-diameter paint spray port 9 is provided in the nozzle forming section 7C. The paint supplied from the paint spray port 9 through the main body-side paint passage 4 and the paint passage 8 is ejected. It has become. A number of atomizing air passages 10, 10,... Are formed in the nozzle body 7A in the axial direction so as to surround the paint passage 8. Furthermore, a large number of air passage grooves 11, 11, ... for pattern air circulation are formed in the outer peripheral surface of the flange portion 7D over the entire circumference.

Reference numeral 12 denotes an air nozzle provided on the front end side of the paint nozzle 7. The air nozzle 12 is formed so as to cover a concave portion 12A formed inside so as to surround the nozzle forming portion 7C and a front side of the concave portion 12A. Front wall portion 12B, and horn portions 12C, 12C formed so as to oppose the vertical position of the front wall portion 12B and protrude forward, and are pierced all around the outer peripheral surface,
It is roughly composed of a flange portion 12D locked to the retainer ring 16. A nozzle insertion hole 13 through which the nozzle forming portion 7C is inserted is formed in the front wall portion 12B of the air nozzle 12 on the axial center, and a number of atomized air jets are formed around the nozzle insertion hole 13. Are provided, and each horn portion 12C is provided with a pattern air ejection port 15, 15, which opens diagonally inward.

Reference numeral 16 denotes a retainer ring formed in a ring shape, an engagement protrusion 16A that engages with the flange portion 12D of the air nozzle 12 is formed inside the front end of the retainer ring 16, and a main body is provided on the inner periphery at the rear end side. The paint nozzle 7 and the air nozzle 12 are fixed by screwing to the outer peripheral surface 2.

Thus, the paint nozzle 7,
When the air nozzle 12 is fixed, the atomizing air chamber 17 is defined in the recess 12A of the air nozzle 12, and the pattern air chambers 18, 19 are defined before and after the collar 7D of the paint nozzle 7. Is done. Then, one pattern air chamber 18 is supplied with pattern air from the main body side pattern air passage 6,
The other pattern air chamber 19 communicates with the pattern air in the other pattern air chamber 19 through a pattern air passage formed by each air passage groove 11 and the inner peripheral surface of the retainer ring 16. It is designed to spout from the spout 15.

Further, reference numeral 20 denotes an earth electrode cable inserted into the electrode mounting hole 3 of the spray gun body 2, reference numeral 21 denotes an electrode support rod provided in the paint passage 8 of the paint nozzle 7 and connected to the earth electrode cable 20, 22. Reference numeral denotes an earth electrode provided at the tip of the electrode support rod 21, inserted into the paint spray port 9, and protruding outside the paint spray port 9.

Next, 23 is an electrode mounting bracket provided on the outer periphery of the spray gun body 2, 24 is a cable housing supported by the bracket 23, 25 is an external electrode holding rod mounted on the cable housing 24, 26 is an external electrode The external electrode holding rod 25 extends so as to protrude forward of the coating machine 1, and the external electrode 26 is exposed from the tip of the external electrode holding rod 25 as described later.

Here, the shapes of the external electrode 26 and the external electrode holding rod 25 will be described with reference to FIGS. That is, the external electrode holding rod 25 is formed of an insulating resin (for example, Teflon), and the tip surface is formed as an inclined surface 25A that is inclined outward, and the tip portion of the inclined surface 25A becomes a concealing projection 25B. 25B is formed such that, when viewed from the ground electrode 22 of the coating machine 1, the inside facing the ground electrode 22 becomes longer, and the outside remote from the ground electrode 22 becomes shorter. The external electrode 26 is provided so as to be slightly exposed from the inclined surface 25A, and is concealed by the concealing projection 25B of the external electrode holding rod 25 so that the external electrode 26 is not directly visible from the ground electrode 22. . Then, the external electrode 26
Is a high-voltage generator 33 to be described later via the high-voltage cable 27.
It is connected to the.

The spray gun type coating machine 1 thus configured is the first type.
As shown in the figure, the spray gun body 2 is attached to a reciprocator or the like (not shown) via an insulation support 28.

The paint particles sprayed from the coating machine 1 are conveyed.
The object to be coated 30 suspended from the container 29 is sprayed. The conveyor 29 and the object to be coated 30 are grounded via an earth 31.

Next, a high voltage generator applied to the external electrode 26 via a high voltage cable 27 will be described.

Reference numeral 32 denotes a voltage setting device for setting an output voltage value of a high voltage to be generated by a high voltage generator 33 described later.
Numeral 32 sets an optimum high voltage value according to the type of the paint.

Reference numeral 33 denotes a high voltage generator. The high voltage generator 33 includes a high voltage generator 34 and a control circuit 35. The high voltage generator 34 is connected to the external electrode 26 of the coating machine 1 via a high voltage cable 27. The control circuit unit 35 is supplied with a power supply voltage from a commercial power supply 36 of, for example, 100 V AC.

Here, the high voltage generator 34 has a step-up transformer therein,
A multiplying voltage circuit (cockcroft circuit) or the like is provided to generate a high-voltage output voltage corresponding to an input voltage from a high-voltage generation control circuit 41 (described later) constituting the control circuit unit 35. Grounded. In addition,
The high voltage generator 34 itself is conventionally known.

The control circuit section 35 includes a current-voltage control circuit 37, an overcurrent safety circuit 38, a minimum voltage protection circuit 39, a power supply conversion circuit 40, a high-voltage generation control circuit 41, and the like.
37, the input side of the overcurrent safety circuit 38 is an overcurrent detection signal line 42
And the input side of the minimum voltage protection circuit 39 is connected to the high voltage generator 34 via the high voltage detection signal line 43, respectively. On the other hand, the output side of the current / voltage control circuit 37 is connected via a voltage rise / fall command signal line 44 to the overcurrent safety circuit.
38, the output side of the minimum voltage protection circuit 39 is a signal line 45 for abnormal command
Are connected to the input side of the high-voltage generation control circuit 41 through the respective terminals. Further, the high voltage generation control circuit 41 is connected to the power line 4
6, while being connected to the commercial power supply 36 via the power supply conversion circuit 40, the output side thereof is connected to the input side of the high voltage generator 34 via the high voltage generation control power supply line 47, and It is connected to the voltage setting device 32 via a signal line 48. In addition,
49 and 50 are external signal lines for abnormality command.
Outputs an abnormal command signal from the overcurrent safety circuit 38 and the minimum voltage protection circuit 39 to an external buzzer, lamp, or the like.

Here, the current-voltage control circuit 37 has high-voltage control means, and the high-voltage control means sets a high-voltage current value generated from the high-voltage generator 34. Inside is a normal maximum current value, for example, 200 μA
Is stored as a predetermined current value (hereinafter, referred to as a set current value i ₀ ), and a program or a processing circuit according to the processing operation shown in FIG. 5 is stored. Further, the current-voltage control circuit 37 is connected to the high-voltage generator via the overcurrent detection signal line 42.
The detected current value i inputted from a current detector (not shown) provided at 34 is compared with the set current value i _0.
Is exceeded, a voltage drop command signal is output to the high voltage generation control circuit 41 in order to reduce the current value.
Is lower than the set current value i ₀ , a voltage increase command signal is output to the high voltage generation control circuit 41 to increase the current value.

Further, the overcurrent safety circuit 38 stores, for example, 280 μA as an abnormal overcurrent value, and rapidly detects the detected current value i input via the overcurrent detection signal line 42 so as to exceed the abnormal overcurrent value. If it has increased, an abnormal stop command signal is output to the high voltage generation control circuit 41. The minimum voltage protection circuit 39 internally stores, for example, -48 kV as the minimum voltage value during normal operation, and the high voltage value input via the high voltage detection signal line 43 has become equal to or less than the minimum voltage value. If
An abnormal stop command signal is output to the high voltage generation control circuit 41.

On the other hand, the power supply conversion circuit 40 includes a high-voltage transformer and an A / D converter, and converts the power of 100 V AC supplied from the commercial power supply 36 via the power supply line 46 to 24 V DC.

Furthermore, the high voltage generation control circuit 41 is a regulator, NPN
The high voltage generation control circuit 41 controls the input voltage applied to the input side of the high voltage generator 34, and thereby varies the high voltage generated by the high voltage generator 34. It is. The input side of the high-voltage generation control circuit 34 is connected to a voltage setting device 32, a current-voltage control circuit 37, an overcurrent safety circuit 38, and a minimum voltage protection circuit 39, and the high voltage set by the voltage setting device 32. When a voltage drop command signal or a voltage rise command signal is input from the current / voltage control circuit 37, the base voltage is lowered / increased step by step in each program cycle, thereby setting the voltage by the voltage setting unit 32. Regardless of the value, the function to step down / up the input voltage to the high voltage generator 34 and drop / up the output high voltage, and the abnormal stop command signal from the overcurrent safety circuit 38 and the minimum voltage protection circuit 39 are input And a function to stop the generation of the high voltage when it is performed.

Reference numeral 51 denotes a paint pipe connected to the main body paint passage 4 of the coating machine 1 and a paint supply device (not shown) for supplying paints of various colors, and 52 denotes an atomizing air passage to the main body side atomizing air passage 5. Numeral 53 denotes a pattern air pipe for supplying pattern air to the main body pattern air passage 6. Further, the joints 54 and 5 of the atomizing air pipe 52 and the pattern air pipe 53 are provided.
Numeral 5 is connected to the earth 31 so that the coating machine 1 is set to the earth potential. Further, reference numeral 56 denotes an earth cable. The earth cable 56 connects the earth electrode 22 to the earth 31 via the earth electrode cable 20.

The present embodiment is configured as described above, and its operation will be described below.

 First, paint spraying of the coating machine 1 will be described.

The coating machine 1 is grounded to the ground 31 via the ground electrode 22, the ground electrode cable 20, and the ground cable 56, thereby preventing the paint system from floating with respect to the ground 31.
A high voltage is applied to the external electrodes 23 from a high voltage generator 34 via a high voltage cable 27.

In this state, by opening a paint valve (not shown) of the paint supply device, the paint in the paint passage 4 on the main body side is ejected from the paint outlet 9 through the electrode mounting hole 3 and the paint passage 8. Can be

The atomizing air supplied from the main body side atomizing air passage 5 is ejected from the atomizing air jet port 14 through the peripheral groove 7B of the paint nozzle 7, the atomizing air passage 10, and the atomizing air chamber 17. You. The sprayed atomizing air promotes atomization of the paint sprayed from the paint spray port 9 and atomizes the paint particles.

Further, the pattern air from the main body side pattern air passage 6 passes through one of the pattern air chambers 18, the air passage groove 11 on the outer periphery of the flange 7D, and the other pattern air chamber 19 through the upper and lower pattern air outlets. Ejected from 15. With this pattern air, the paint pattern sprayed in a circular shape is formed into a flat shape in the vertical direction. And painting machine 1
The patterned paint is charged by a corona discharge region formed by an external electrode 26 provided in front of the object, and is applied to an object 30 grounded to the earth 31.

Next, the generated high voltage control processing in the current / voltage control circuit 37 will be described with reference to FIG.

In step 1, a high voltage is applied to form a corona discharge region in front of the external electrode 26. In step 2, it is determined whether or not painting is in progress. If "YES" is determined, step 3
And returns to step 1 if determined to be “NO”. In step 3, the detected current value i is read from the current detector provided in the high voltage generator 34, and in step 4, it is determined whether or not the current value i is equal to or more than the set current value i ₀ (for example, 200 μA). If "YES" is determined, the current value i is high, and a short circuit phenomenon is likely to occur between the external electrode 26 and the ground electrode 22. The applied voltage is reduced to prevent the occurrence of a short circuit phenomenon, and the program returns in step 7 to repeat this program. On the other hand, in step 4
When it is determined to be "O", the current value i is low, so that the corona discharge region by the external electrode 26 is small, and the paint cannot be charged efficiently, and the coating efficiency on the object 30 is reduced. Therefore, in step 6, a voltage increase command signal is output to the high voltage generation control circuit 41 in order to increase the applied voltage from the high voltage generator 34. Then, the process returns in step 7.

Thus, in this embodiment, the coating machine 1 is completely grounded by the ground electrode 22 of the coating machine 1, and safety can be ensured. In addition, the external electrode 26 is connected to the concealing projection of the external electrode rod 25.
With 25B, the insulation distance between the external electrode 26 and the ground electrode 22 can be increased. Furthermore, the current-voltage control
By controlling the high voltage applied to the external electrode 26 by the 37, even if the paint sprayed during the coating becomes a resistance and the current value i decreases, the application from the high voltage generator 34 The voltage is controlled by the current-voltage control circuit 37 so that the current value i is always the set current value i ₀ (20
0 μA), so that the coating efficiency can be reliably improved as compared with the prior art.

Further, as described above, the external electrode 26 is
The concealing protruding portion 25B makes it possible to increase the insulation distance between the external electrode 26 and the earth electrode 22 as viewed from the ground electrode 22, thereby preventing the occurrence of a short circuit phenomenon. In this regard, in the prior art, in order to prevent the short circuit phenomenon, the generated high voltage and the set current value are also limited, and the current value flowing between the external electrode and the ground electrode is limited to 180 μA. However, according to the present embodiment, as described above, the concealing protrusion 25B of the external electrode holding rod 25 is used.
As a result, the insulation distance between the external electrode 26 and the ground electrode 22 can be increased, so that the generated high voltage can be increased by -5 kV or more as compared with the related art, and as a result, the processing in the current-voltage control circuit 37 can be performed. Set the operation current value i ₀ to 200
It is also possible to set it to μA or more, and it is possible to remarkably improve the efficiency of coating the object 30 to be coated.

Furthermore, since the paint sprayed from the coating machine 1 has a higher straightness than the rotary atomizing gun, the external electrode 26 is connected to the ground electrode 22.
Can be reliably prevented from staining the external electrode 26, and the external electrode 26 can sufficiently charge the paint particles even with only one external electrode 26.

Furthermore, since the external electrode 26 is provided in front, the distance to the object 30 can be shortened, and a strong magnetic field can be obtained between the external electrode 26 and the object 30 to improve the coating efficiency. Has the effect of

Note that the external electrode holding rod 25 of the external electrode 26 of the above-described embodiment forms the inclined surface 25A on the distal end side, so that the distal end side is a concealing protruding portion 25B, so that the insulation distance from the ground electrode 22 is increased. However, as shown in FIGS. 6 and 7, the tip of the external electrode holding rod 25 'is formed on a stepped inclined surface 25A', and the left and right sides of the inclined surface 25A 'are concealed on both sides. By forming the portion 25B 'so as to cover the external electrode 26, the same effect as in the above embodiment can be obtained.

Further, in the embodiment, the case of the water-based paint or the metallic paint has been described, but the ground electrode 22 is not connected to the ground 31, but is connected to the high voltage generator 31, and the external electrode 26 is connected to the ground 31. The spray gun type electrostatic coating device can also be used for a solvent-based coating material having a high resistance, and in this case, the coating efficiency can be improved by the control processing in the current / voltage control device 37.

Furthermore, the spray gun type spraying machine 1 according to the present embodiment has been described by taking as an example an atomizing air type spray gun using atomizing air, but a hydraulic atomizing type sprayer using a lip-shaped nozzle tip as a coating nozzle. It may be applied to a gun, in which case it is atomized by discharging high-pressure paint from a nozzle tip.

Furthermore, although it has been described that only one external electrode holding rod 25 and one external electrode 26 are provided, a plurality of these may be provided.

〔The invention's effect〕

The spray gun-type electrostatic coating device according to the present invention is as described in detail above. The ground electrode of the spray gun main body is maintained at the ground potential, the external electrode is provided forward of the spray gun main body, and the external Since the electrode holding rod is formed so that the inside facing the ground electrode is long and the outside is short, the insulation distance from the external electrode as viewed from the ground electrode is extended by the external electrode holding rod, and the high voltage applied to the external electrode is increased. Can be prevented, and a higher current value can be passed between the voltage application system and the ground system than in the prior art. As a result, even when a high voltage is applied to the external electrode, a short circuit phenomenon between the ground electrode and the external electrode can be effectively prevented, and safety can be ensured.

Also, since high voltage control means for controlling the current value between the voltage application system applied to the external electrode and the earth system to a predetermined current value is provided, the high voltage control means applies the voltage to the external electrode. High voltage is controlled so as to be a predetermined current value for preventing a short circuit phenomenon, and it is possible to surely improve the coating efficiency with respect to an object to be coated, improve coating quality, and reduce the occurrence rate of defective products. Can be reduced.

Furthermore, since the paint sprayed from the paint nozzle has high straightness, various excellent effects such as the fact that the external electrode can be reliably prevented from being stained even when the external electrode is provided in front of the ground electrode are exhibited.

[Brief description of the drawings]

1 is an overall configuration diagram showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of a main part of a spray gun type coating machine, FIG. 3 is a side view of external electrodes, external electrode holding rods and the like, and FIG. 3 is a plan view of FIG. 3, FIG. 5 is a flow chart showing a high voltage control process, FIGS. 6 and 7 show a modification of the embodiment, FIG.
FIG. 7 is a side view of the external electrode holding rod and the like, and FIG. 7 is a plan view of FIG. 1. Spray gun coating machine, 2. Spray gun body, 7.
Paint nozzle 9, 9 paint spray port, 22 earth electrode, 23 electrode mounting bracket, 25 external electrode holding rod, 25B concealing projection, 26 external electrode, 33 high voltage generator.

Claims (2)

(57) [Claims] 1. A spray gun main body, a paint nozzle provided at a tip side of the spray gun body and ejecting paint from a paint spray port, and a paint nozzle maintained at a ground potential and having a tip end projecting from the paint nozzle. A ground electrode provided on the spray gun main body, an electrode mounting bracket provided on the outer peripheral side of the spray gun main body, and mounted on the bracket, and disposed such that a distal end side projects forward from the ground electrode. At least one external electrode holding rod;
An external electrode provided on the external electrode holding rod so as to be exposed from a tip side of the external electrode holding rod, and connected to the external electrode via a high voltage cable to apply a high voltage to the external electrode. A spray gun type electrostatic coating apparatus comprising: a high voltage generator; and wherein the tip of the external electrode holding rod is formed so that the inside facing the ground electrode is long and the outside is short. 2. When a current value between a voltage application system including the external electrode, the high-voltage cable, and a high-voltage generator and an earth system including an earth electrode drops below a predetermined current value.
The generated high voltage is increased so that the reduced current value becomes a predetermined current value, and when the current value rises above a predetermined current value, the generated high voltage is reduced so that the increased current value becomes a predetermined current value. The spray gun type electrostatic coating apparatus according to claim 1, further comprising high voltage generation control means.