JP3335937B2 - High voltage control method for electrostatic coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[OOO1]

BACKGROUND OF THE INVENTION The present invention mainly relates to a method of applying a metallic paint by an electrostatic hand air spray gun (hereinafter referred to as an electrostatic gun) when metallic particles dispersed in a paint are applied to a paint tube by a high voltage. The present invention relates to a high voltage control method for avoiding the problem that the high voltage charged to the electrodes of the electrostatic gun leaks to the nearest grounding grip portion, and the electrostatic painting cannot be substantially performed.

[OOO2]

2. Description of the Related Art In the field of automotive coating and the like, a metallic paint is often applied to improve the appearance of an external appearance. As shown in FIG. 4, a paint tube 54b is fixed to a grip 58 of an electrostatic gun. When the metallic paint is electrostatically applied with a general electrostatic gun such that the metallic paint is connected to the paint joint 53 almost linearly from the stay 56, the metallic particles dispersed in the paint are in the paint tube. And the high voltage charged in the electrode 52 of the electrostatic gun leaks through the stay 56 and the grip portion 58 which are the nearest grounding objects of the electrostatic gun, and the electrostatic coating is substantially performed. There is a problem that a so-called metal bridge phenomenon, such as the inability to perform, occurs. For this reason, in the automatic electrostatic spray gun, as a method of preventing high voltage leakage to the nearest ground object such as a color changer and a pump,
Various inventions such as a high-voltage block device and a high-voltage insulation device have been made. The present applicant also discloses a related invention in JP-A-8-173855. However, these methods cannot be applied to a hand-held type electrostatic gun because it is too large in terms of equipment and cost. Therefore, as a simpler method, as shown in FIG. A spiral tube made of resin having a high insulating property such as resin is used. The distance of the paint flow path to the electrode 52 of the electrostatic gun and the grip portion 58 which is the nearest grounding object is shown in FIG. It employs a method that is approximately five times that of a gun. However, even with this method, even though insulation was initially maintained depending on the type of metallic paint, paint flow rate, spraying time, spraying stop time, and the like, a metal bridge phenomenon occurred and high voltage was applied to the tube. It was not possible to prevent the metallic particles of the paint from being connected and to leak through the stay 56 and the grip portion 58 as the earth body.

[OOO3] For example, the metal bridge phenomenon does not occur when spraying is performed again at a level of several seconds after the previous spraying of the electrostatic gun is stopped, but the metal bridge phenomenon occurs when spraying is performed again several minutes later. Cheap. The cause is that the metallic particles are sufficiently dispersed in the paint that moves in the tube during spraying, but the paint is stopped when spraying is stopped, so the dispersion of the metallic particles in the paint gradually worsens and the partial In addition, the density of the metallic particles increases. As a result, high voltage charging is activated almost immediately when the needle valve of the electrostatic gun is opened when spraying again, so the high voltage increases the density inside the tube before the paint starts flowing and the metallic particles are sufficiently dispersed. This is because the metallic particles are connected and leaked. In particular, the metal bridge phenomenon tends to easily occur after the spraying of the electrostatic gun has been stopped for a long time, such as when the work is interrupted, lunch break, or the next morning after the work is completed. In another example, as in the case of painting a bumper part etc. in an automobile painting line, one painting is spraying time continuously with the trigger of the electrostatic gun being triggered, and the time to continue triggering is usually About 30 seconds compared to about 2-5 seconds
Even when the time is as long as 45 seconds, the metal bridge phenomenon easily occurs. In this case, at the beginning of spraying, the metallic particles in the paint flowing in the tube are sufficiently dispersed, but as time passes, the metallic particles in the tube start to be partially combined with each other by a high voltage, and for a certain time, This is because the metallic particles are connected at a stretch during the course of the process.

[OOO4] When the metal bridge phenomenon occurs in this way, the current is detected by the current detection device, and the control device is abnormally controlled in an overcurrent state exceeding a preset regulation current value. As a conventional solution method at this time, (1) As shown in the flow chart of FIG. 5B, the reset button at the time of abnormal stop (stop of spraying and high-voltage charging) of the operation panel due to excessive current value is manually operated. Release,
(2) As shown in the flow chart of FIG. 5A, a method such as adoption of automatic stop release control by returning the trigger of the electrostatic gun when only high voltage charging is stopped due to overcurrent value is taken. Was. However, in these methods, every time the metal bridge phenomenon occurs, an operation for canceling the abnormal control is required, and there is a problem that the workability is poor. In the case of (2), it is necessary to continue the spraying for about one second after stopping only the high voltage charging, and to release the trigger of the electrostatic gun after the dispersion of the metal particles is recovered, which is troublesome for the operator. It was an operation. In addition, since the time lapse from the last stop of the spraying of the electrostatic gun to the next spraying is long, and when spraying again, the metal bridge phenomenon occurs almost at the same time as painting, so it is necessary to release the An operation for returning the trigger of the gun is required, which is very troublesome for an operator, and causes a decrease in workability.

[OOO5]

According to the present invention, as a means for preventing a metal bridge phenomenon in an electrostatic gun, a tube made of a resin having a high insulating property such as fluororesin is used as a paint tube, and the tube is formed in a spiral shape. Even if the paint flow path between the electrode charged with high voltage and the nearest grounding grip is lengthened, the painting work is interrupted each time the metal bridge phenomenon occurs depending on the situation. It is an object of the present invention to provide a high-voltage charge control method that does not require an operation for canceling abnormality.

[OOO6]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention relates to a method for coating an electrostatic spray gun which electrostatically applies a high voltage to atomized metallic paint by means of an electrode to apply a paint. The metal particles contained in the metallic paint in the paint tube for supplying paint to the paint passage of the electrostatic spray gun via the ground part of the electrostatic spray gun are connected in a chain, and When an overcurrent state in which the current flowing through the grip portion is detected and the current exceeds a preset regulation current value is temporarily stopped only the output of the high voltage is temporarily stopped, and the output of the high voltage is output after the set time. When controlling to restart automatically, if an overcurrent condition occurs more than a preset number of times within a certain period of time, the high voltage output will stop abnormally so that the high voltage output cannot be restarted automatically. To control the pressure. Further, in a method for coating an electrostatic spray gun in which a high voltage is charged to an atomized metallic paint by an electrode to electrostatically apply a coating, the electrostatic spray gun is connected to a ground portion of the electrostatic spray gun. The metal particles contained in the metallic paint in the paint tube supplying the paint to the paint passage are connected in a chain, and a current flowing from the electrode to the grip portion is detected, and the current is set to a predetermined regulated voltage. Controls to temporarily stop only high-voltage output and automatically restart high-voltage output after a set time in the event of an overcurrent condition that exceeds the current value. When the above overcurrent condition occurs, a control method for abnormally stopping the high voltage output so that it cannot be automatically restarted, and stopping the painting by stopping only the high voltage output and returning the trigger to stop the high voltage A switch is provided that can select a control method that can simultaneously restart pressure output and paint atomization, and a control method that stops high voltage output and paint atomization at the same time so that painting work cannot be performed unless an abnormal recovery operation is performed. Was. In addition, when the time elapsed since the previous coating work exceeds a preset time in the electrostatic spray gun coating method that applies high voltage to the atomized metallic paint by the electrode and electrostatically paints the coating. Is a device in which the output of high voltage is stopped at the start of painting by the electrostatic spray gun and only the atomization of paint is performed, and the output of high voltage is started after a set time.

[OO07]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a flowchart of the embodiment, and FIG. 3 is an external view of an electrostatic air spray gun of a metallic coating specification for performing high-voltage control of the present invention.

FIG. 3 shows an electrostatic gun used in the present embodiment. A gun body 50 has a needle valve / air valve (not shown) operated by a trigger 60 and compressed air from an air hose 57. A passage and the like are built in, and a transformer booster, a cockcroft circuit, etc. (not shown) for generating a high voltage by receiving a high frequency power from the low voltage cable 59 are built in. An air cap 51 and an electrode 52 are provided at the tip of the gun body 50, and a metal grip 58 is connected to the rear by a grounding body. The paint is supplied from a pump (not shown) by a paint hose (not shown) to a paint joint 55 fixed to a stay 56 attached to the lower end of the grip portion 58, and is passed through a tube 54b having a spiral portion 54a. It is sent from 53 to a paint flow path (not shown) at the tip of the gun body 50. With the above configuration, when the trigger 60 is operated with the hand holding the grip portion 58, the needle valve and the air valve are operated, the compressed air and the paint flow, and the paint is atomized by the air cap 51.
At the same time, a flow switch (not shown) is actuated by the flow of compressed air in the air hose 57 and a high-frequency circuit (not shown) of the control box is turned on by a signal from the flow switch.・ Sent to Cockcroft circuit and converted to high voltage. The generated high voltage applies an electric charge to the paint atomized by the air cap 51 by the electrode 52 and electrostatically applies the paint to the paint.

[OO09] Details of the control of the present invention are shown in FIG. 1 and FIG.
The flowchart will be described. At the time of painting, the worker is also charged with static electricity by the electric field of the static electricity. Therefore, for safety, the grip portion 11a is grounded by using the shielded wire 16c of the low voltage cable 16 which is a multi-core shielded cable or the core wire so as to release the static electricity. ing. When the coating is started, a high voltage is formed at the electrode 12 to form an electric field, and the atomized particles of the paint are charged. An attempt is made to leak to the part 11a. For this reason, the electrostatic gun 1
In, the spiral portion is provided so as to make the distance of the paint path between the electrode 12 and the stay 11 as long as possible. However, depending on conditions such as the kind of paint, paint flow rate, spraying time and spraying stop time, the metal bridge phenomenon may occur. That is what happens.

[OO10] In the present invention, according to the flowchart shown in FIG.
When the metal bridge phenomenon occurs, the high voltage output is turned off within a range where there is no problem in the painting work, and the metal bridge phenomenon is electrically controlled, so the metal bridge phenomenon occurred as in the conventional control method. Each time, it is not necessary to take trouble such as performing an abnormal release operation, so that the worker can work without being distracted by the metal bridge phenomenon. The electrostatic gun 1 has a paint container 7 as an earth body.
The paint is sent to the tip of the electrostatic gun 1 through the paint hose 9 and the tube 10 by the pump 8 to be atomized. Compressed air from the compressed air source 5 is sent to the electrostatic gun 1 by the air hose 17 via the pressure reducing valve 18 and the flow switch 19, and is used for atomizing paint. Further, the input power from the power supply 6 is a power supply circuit 22 and a high-frequency transmission circuit 2
The power is converted to a high-frequency power by the low-voltage cable 16 and sent to the transformer booster 15 and the Cockcroft circuit 14 inside the electrostatic gun 1 by the low-voltage cable 16 to be converted to a high voltage. This high voltage is sent from the high resistance 13 to the electrode 12 to form an electric field, which electrostatically charges the atomized paint particles and paints the paint grounded by the ground 4. Low voltage cable 16
Uses a multi-core shielded cable, and grounds the grip 11a and the stay 11 of the electrostatic gun 1 by means of a shielded wire 16c to release static electricity charged to an operator. One core wire is grounded by a ground wire 25 via a current detection circuit 24 as a current detection line 16b.

[OO11] With this configuration, when the operator triggers the electrostatic gun 1 (not shown), the paint and compressed air flow, and the paint is atomized at the tip of the electrostatic gun 1. When the high frequency transmission circuit 21 is turned on via the time delay circuit 20 by operating the flow switch 19 by the flow of the compressed air, the electrode 12 is charged with a high voltage. When the metal bridge phenomenon does not occur, XμA flows to the current detection circuit 24. However, when the metal bridge phenomenon occurs, metal particles in the paint of the tube 10 are connected, and the electrode 1
Current detection circuit 2 because a high voltage flows from
4, YμA flows. When the current value YμA exceeds the OCR set current value A1μA set in advance by the OCR circuit (current comparison circuit) 26, the atomization of the paint continues, but the OCR circuit 26 serving as the current comparison circuit judges that there is an abnormality and transmits a high frequency. Control is performed so that only the circuit 21 is turned off. In this way, even if the metal bridge phenomenon occurs while the paint is flowing, if only the high voltage charging is stopped for about 1 second, the connection of the metal particles connected by the high voltage is released, and the high voltage is charged again. However, since it has been experimentally confirmed that the metal bridge phenomenon does not occur immediately, the standby time circuit 23 automatically cancels the abnormality judgment of the OCR circuit 26 after the elapse of T3 seconds, and
1 is turned on so that electrostatic painting can be resumed.

[OO12] Further, if this metal bridge phenomenon occurs frequently, it is determined that metal particles adhere and deposit inside the tube 10 so strongly that cleaning and tube replacement are necessary. For this purpose, a counter circuit 27 is provided, and when the number of times that the OCR circuit 26 determines that there is an abnormality has occurred N times or more within the preset cumulative time T4 of the painting work, an alarm output 28 is output. The output is completely turned off so that the high-frequency transmission circuit 21 cannot be automatically released, and an abnormal lamp display (not shown) and an abnormal output (not shown) are displayed. Further, in this configuration, the current value YμA is set in advance by the OCR due to a cause other than the metal bridge phenomenon.
If the set current value A1 μA is exceeded, for example, an abnormal approach of a grounded object such as a painted object to the electrode 12 or the cockcroft circuit 1
In the case of an abnormality such as 4, an alarm output 28 is similarly output to completely turn off the high-frequency transmission circuit 21 so that it cannot be automatically restored, and an abnormal lamp is displayed and an abnormal signal is output. It is also possible to detect.

[OO13] Apart from the metal bridge phenomenon that occurs during the spraying operation described above, there is a metal bridge phenomenon that occurs when spraying is performed again because the stop time after the previous spraying of the electrostatic gun is long and the spraying is performed again. In this case, since the flow of the paint in the tube 10 is stopped while the spraying is stopped, the dispersion of the metallic particles in the paint gradually deteriorates, and the density of the metallic particles partially increases, so that the spraying is performed again. When the needle valve of the electrostatic gun opens when the
Because the high voltage is charged, before the paint starts to flow and the metallic particles are sufficiently dispersed, the high voltage connects the metallic particles with a high density inside the tube and causes a leak. is there. In particular, it tends to occur after the spraying of the electrostatic gun is stopped for a long time, such as when the work is interrupted, during lunch, or the next morning after the work is completed. In order to solve this problem, the configuration of the present invention employs a flow switch 1
The time delay circuit 20 conditions the operation of the high frequency transmission circuit 21 by turning on the high frequency transmission circuit 21. That is, if the stop time t after the previous spraying of the electrostatic gun exceeds the preset time T1, the spraying of the paint is performed when the triggering of the electrostatic gun is started and the spraying is started. The ON of the circuit 21, that is, the output of the high voltage
Two delays. As a result, even if the spraying is restarted after the spraying of the electrostatic gun is stopped for a long time, the high-frequency oscillation circuit 21
The paint in the tube flows during the time T2 is turned ON for the time T2, and the density of the metal particles becomes uniform. Therefore, even if a high voltage is output, the metal bridge phenomenon does not occur and the painting work is performed smoothly. Can be performed.

[OO14] In addition to the method of the present invention, two types of methods have been conventionally used for canceling the metal bridge phenomenon, and these three types can be selected depending on the type of coating work and the working environment. Although not shown, three types of control methods for canceling the metal bridge phenomenon can be selected in the control device 2 (not shown). The three types of methods are as follows: (1) As shown in the flowchart of FIG. 2, when control is performed such that only high-voltage output is temporarily stopped and high-voltage output is automatically restarted after a set time. ,
A control method for abnormally stopping the motor so that the high voltage output cannot be automatically restarted when an overcurrent state occurs more than a predetermined number of times in a certain time. (2) As shown in the flowchart of FIG. (3) A control method capable of simultaneously restarting the output of the high voltage and the atomization of the paint when the output is stopped and the trigger is returned to stop the coating, and (3) the output of the high voltage and the paint as shown in the flowchart of FIG. This is a control method in which the spraying operation cannot be performed unless the atomization is stopped at the same time and the abnormal stop is released.

[OO15] Although the control method described above has been described with reference to the electrostatic hand spray gun, the control method can be similarly applied to the electrostatic automatic spray gun. In addition, airless electrostatic gun (automatic
Hand) and air assist electrostatic gun (automatic / hand)
Can also be summarized.

[OO16]

As described above, the high-voltage charge control method of the present invention has the following effects. (1) Even if a metal bridge phenomenon occurs during the electrostatic coating work, there is no need to take trouble such as performing an abnormal release operation with the control device every time the metal bridge phenomenon occurs, and the worker is not distracted by the metal bridge phenomenon. Can paint. (2) If the frequency of occurrence of the metal bridge phenomenon is high during the electrostatic coating work, an abnormal signal is output, so that the tube can be replaced or the tube can be washed, and measures to prevent the recurrence of the metal bridge phenomenon can be taken. I can do it. (3) With the same circuit configuration, it is possible to detect an abnormal approach of a grounded object such as a coating object to the electrode, and an abnormality of the cockcroft booster. (4) The metal bridge phenomenon which occurs when the spraying is restarted due to a long stopping time after spraying can be prevented, and the painting work can be performed smoothly. (5) Since three types of methods for canceling the metal bridge phenomenon can be selected, they can be properly used depending on the type of painting work and work environment.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a flowchart of an embodiment.

FIG. 3 is an external view of an electrostatic air spray gun of a metallic coating specification for performing high voltage control according to the present invention.

FIG. 4 is an external view of a general electrostatic air spray gun.

5A is a control flowchart of a conventional example, and FIG. 5A is a flowchart of a control method for stopping only high-voltage output, and FIG. 5B is a flowchart of a control method for simultaneously stopping high-voltage output and paint atomization.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrostatic hand spray gun 3 Painted object 10 Paint tube 11a Grip part 12 Electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B05D 1/04 B05B 5/025 B05B 5/053

Claims (3)

(57) [Claims] 1. A method of coating an electrostatic spray gun, wherein a high voltage is charged to an atomized metallic paint by an electrode to electrostatically apply a coating, and the electrostatic spray gun is grounded via a ground portion of the electrostatic spray gun. The metal particles contained in the metallic paint in the paint tube that supplies paint to the paint passage of the electrospray gun are connected in a chain, and the current flowing from the electrode to the grip is detected and the current is set in advance. If the overcurrent state exceeds the regulated current value, only the high-voltage output is temporarily stopped and the high-voltage output is automatically restarted after the set time. A high-voltage control method for electrostatic coating, characterized in that when an overcurrent state occurs more than a preset number of times, abnormal output is stopped so that high-voltage output cannot be automatically restarted. 2. A coating method for an electrostatic spray gun in which a high voltage is charged on an atomized metallic paint by an electrode to electrostatically apply a coating material, wherein the electrostatic spray gun is grounded via a ground portion of the electrostatic spray gun. The metal particles contained in the metallic paint in the paint tube that supplies paint to the paint passage of the electrospray gun are connected in a chain, and the current flowing from the electrode to the grip is detected and the current is set in advance. In the event of an overcurrent condition that exceeds the regulated current value, only the high-voltage output is temporarily stopped, and the control is performed so that the high-voltage output is automatically restarted after the set time. A control method that abnormally stops the high voltage output so that it cannot be automatically restarted when an overcurrent state occurs more than the specified number of times, and stops the painting by stopping only the high voltage output and returning the trigger A switch that can select a control method that can restart high voltage output and paint atomization at the same time, and a control method that stops high voltage output and paint atomization at the same time so that painting work cannot be performed unless an abnormal return operation is performed A high voltage control method for electrostatic coating, characterized in that it is provided. 3. A coating method for an electrostatic spray gun in which a high voltage is charged to an atomized metallic paint by an electrode to electrostatically apply a coating material, the elapsed time after a previous coating operation is set to a predetermined time. When it exceeds, at the start of painting of the electrostatic spray gun, the high voltage output is stopped and only the paint is atomized, and after a set time, the high voltage output is started. .