JPH0556191B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an improvement in a powder coating booth for carrying out electrostatic powder coating, in which most of the oversprayed powder forms the bottom surface of the booth. Powder paint is collected on a conductive belt conveyor and collected by an ion shower blow type static eliminator and a paint recovery device, which increases the efficiency of powder paint usage.
This relates to a powder coating booth that allows color changes in a short time.

BACKGROUND TECHNOLOGY Electrostatic powder coating has extremely advantageous features in terms of excellent coating performance, pollution prevention measures, resource saving, etc., and its importance has been increasingly recognized in recent years.
However, in conventional electrostatic powder coating, most of the so-called overspray that is not applied to the object to be coated among the electrically charged powder paint discharged from the paint gun is absorbed together with the booth exhaust gas. The dust is separated and collected by a large exhaust dust collector, and the remaining part is deposited on the bottom and sides of the booth.

In another method, the bottom surface of the booth is formed by a permeable belt conveyor, the air is passed through the conveyor to perform exhaust, and the overspray collected on the inner surface of the booth is collected at the end of the conveyor.

Problems to be Solved by the Invention Among powder coating booths according to the prior art, in a system in which overspray is collected by a booth exhaust dust collector, the exhaust dust collector for overspray collection is large, and there is an electrical charge inside it. Since the paint powder adheres to the paint, it takes a lot of time to clean the exhaust dust collector in order to avoid color mixing when changing the paint color, and the down time of the painting line increases.

As a countermeasure to this problem, there is a method of preparing dedicated dust collectors for each color and switching between them, but in this case, not only does the equipment cost become large, but the space occupied by the dust collectors prepared for each color is too large. This makes plant layout difficult and causes various inconveniences in operation management, which is not desirable.

In addition, as a solution to the above problem, a preliminary dust collector is installed in addition to the main dust collector for color changes, and one dust collector is cleaned while the other is in operation, so that when the color is changed, the other dust collector is cleaned immediately. There is a way to shorten the downtime by using switching, but if the booth has a large exhaust volume, the manufacturing time will be excessive, and even if the booth is small, it will be impossible to implement if the number of color changes is large. .

Next, the adhering paint powder on the inside of the booth must be cleaned every time the color is changed, but this also takes a lot of time, shortens the effective operating time, and causes adhesion to accumulate over a long period of time. Deteriorated paint often falls and is collected, causing paint defects. In addition, the falling and collapsing of adhering paint powder temporarily generates a gas powder mixture that exceeds the explosive limit, which poses a serious safety problem. In a system where the bottom of the booth is constructed of an air-permeable conveyor, usually a filter cloth,
The permeation rate in the conveyor becomes excessive, making it difficult to collect the fine powder, and it is often difficult to completely remove the overspray collected on the conveyor, so it is necessary to replace the conveyor when changing colors, which costs a lot of money. It takes time to change the color, which is not practical as a color change booth.

Means and Effects for Solving the Problems In the powder coating booth according to the present invention, the side walls are made of an insulating material so that the side walls of the booth are charged up by the ion current coming from the electrostatic powder gun. By maintaining a high potential with the same polarity as the gun, it prevents overspray powder from adhering to the gun, and even if it does, the adhesion force is weakened, reducing the amount of time it takes to clean the inside of the boom when changing colors. A favorable effect is obtained. A similar effect can also be obtained by constructing the side wall of the booth with a high-resistance semiconductor and connecting a power source to this to maintain a high potential of the same polarity as the gun. This also has the advantage of improving gun deposition efficiency since the electric field from the gun toward the booth sidewalls is eliminated. Furthermore, by placing the exhaust part of the booth close to the bottom of the booth and supplying air from the ceiling, a weak downward airflow is always created inside the booth, thereby preventing overspray from adhering to the ceiling. This, in combination with the construction of the bottom of the booth with a grounded conductive belt, removes most of the overspray paint powder by the synergistic effect of the electric field directed from the gun to the belt. By forcibly depositing the paint on the belt and reducing the proportion of paint discharged along with the booth exhaust, even if the paint in the booth exhaust is disposable, there will be no significant decrease in paint usage efficiency. Therefore, there is no need to change the color of the large booth exhaust dust collector, which is an extremely desirable effect. Overspray powder paint collected by the grounded conductive belt that forms the bottom of the booth is removed by a small device, usually under the belt head pulley, by an AC ion shower airflow type static eliminator. Since the belt can be collected and reused with less entrained air, and at the same time the belt can be constantly cleaned automatically, there is no need to clean the belt when changing colors, and long-term continuous operation is also possible. In addition, the belt-based paint recovery device, which is centered around this static eliminator, has a simple structure, is small, and is inexpensive, so it is easily detachable and can be prepared in multiple pieces or for each color, which also makes it easier to change colors. The time can be significantly reduced.

Specific embodiments of the present invention will become clear from the following figures and their descriptions.

Embodiment FIG. 1 schematically shows an embodiment of a powder coating booth according to the present invention. Fig. 2 is a vertical sectional view taken along line BB in Fig. 3 showing the details of the booth bottom of the embodiment, and Fig. 3 is A in Fig. 2 of the booth bottom.
-A is a horizontal sectional view. In FIG. 1, the booth side wall 1 is made of an insulating material such as plastic or a high-resistance semiconductor, and the ceiling is an air supply box 2.
The supply air blown through the supply air duct 5 by the supply fan 4 passes through the supply air filter 3 forming the lower surface of the supply box to form a uniform downward airflow. There is. The booth bottom is formed by an electrically conductive belt conveyor 13 held at a predetermined potential, usually ground. An air supply hood 6 is provided at the lower part of the booth side wall 1 near the top surface 13 of the belt conveyor, and the booth is evacuated as shown by the arrow. In this way, a downward airflow is always formed inside the booth from the ceiling to the lower part of the side wall.
Powder is discharged from the electrostatic powder gun 17, which sprays charged powder by applying a high voltage while making a reciprocating motion toward the object to be coated (not shown). Body paint overspray is always transferred toward the bottom of the booth and never ends up on the ceiling. Although the workpiece is not shown, the electrostatic powder gun 17 passes through the hanger slit 15 and is suspended from the hanger conveyor (not shown) and passes through the workpiece entrance 14 and into the booth. According to
Powder coating is applied electrostatically. Since the booth side wall 1 is usually made of an insulating material, it is charged up by the electrostatic powder gun 17 during operation and is held at a high potential with the same polarity as the electrostatic powder gun 17. Almost no overspray powder paint, which is charged to the same polarity as the side wall, sticks to the wall, and even if it does stick, it can be easily removed in a short time by blowing or scraping when changing colors. As a result, in the booth according to the present invention, the time required for color change cleaning of the ceiling and side walls is significantly shortened. The booth side wall 1 may be made of a high-resistance semiconductor and, as shown in FIG. 2, may be applied with a desired high voltage by a power source 23 to achieve the same purpose as the side wall made of an insulator. In consideration of this, the inner surface of the booth side wall may be made of semiconductor, and the outer surface may be made of insulating material. The bottom surface of the powder coating booth according to the present invention has a second
As shown in the figure, most of the electric field formed by the electrostatic powder gun 17 is directed toward the object to be coated because it is held at a potential opposite to that of the gun by the power supply 24 or grounded. The rest of the electric field is formed towards the belt at the bottom of the booth, so
The charged powder discharged from the electrostatic powder gun 17 is efficiently applied to the object to be coated, and the overspray is caused not only by the downward airflow formed inside the booth but also by the action of the electric field, and the overspray is caused by the bottom surface of the booth. The main feature is that the proportion of overspray powder paint that is strongly collected towards the conductive belt and entrained in the exhaust air is significantly lower than that of a normal powder coating booth. For this reason, even if the powder paint collected by the dust collector for exhausting the booth is discarded, the paint usage efficiency will not be reduced, so there is no need for cleaning when changing colors, which is a significant advantage of the present invention.
The charged overspray powder paint 30 collected on the grounded conductive belt 13 as described above is removed by the static eliminator 8 built in the collection hopper 10 provided on the belt pulley 29. Then, the static electricity is removed and the liquid falls onto the perforated plate 20 at the bottom of the hopper, where it is collected in a fluidized bed and recovered as shown by arrow 11. Of course, the method for collecting the recovered paint may be other than the fluidized bed, such as air current or small cyclone. Reference numeral 9 denotes a power supply (alternating current) for driving the static eliminator 8, which supplies a large amount of positive and negative ions alternately generated to the lower side of the head pulley 29 of the belt 13 through the blower 7. The charged overspray powder paint is sufficiently neutralized and removed, and the belt is cleaned to a sufficient degree for color change every rotation of the belt. The arrow 21 indicates the air for fluidizing the recovered paint at the bottom of the hopper, and the arrow 19 indicates the recovery hopper exhaust to prevent the supply air 28 and 21 from blowing out from the hopper 10. Depending on the selection, the hopper 10 is evacuated so that the recovered paint can be collected in a state containing almost no air. Therefore, the amount of air contained in the recovered paint 11 can be minimized, and the separation device for removing this air can be extremely small. 1st
An example of a detailed internal structure of the static eliminator 8 schematically shown in the figure is as shown in FIG. An AC high voltage is applied by an AC power source 9 via a protective impedance (a capacitor in FIG. 2) to a large number of needle electrodes arranged perpendicularly to the plane of the paper, facing the small holes 27 or slits 27. As a result, an alternating current corona discharge is formed from the tip of the needle 26 through the gap 27, and a large amount of positive and negative ions are generated alternately, which is indicated by the arrow 28.
Since the static electricity of the overspray powder paint 30 that is blown onto the belt and collected on the belt by the supplied air shown by is removed, it is cleanly peeled off from the belt and forms a fluidized layer on the perforated plate 20. The recovered belt is highly cleaned with each revolution, sufficient for color change. An example in which the bottom of a powder coating booth is constructed with a belt is already known, but overspray powder paint removal and recovery equipment using air currents, rotating brush scraping equipment, etc. cannot completely remove adhering fine powder due to static electricity. However, the ability to handle color changes is insufficient, and at the same time, it is not possible to prevent the paint from sticking during long-term operation, and it is also difficult to prevent the occurrence of defective paint due to peeling of the paint. The overspray paint powder recovery system, which is mainly composed of the recovery hopper 10 and the static eliminator 8 incorporated therein, is a simple, compact, and inexpensive device, so it can be configured to be detachable from the belt, and multiple pieces or more can be used as needed. Since there is no problem in preparing each color, by doing so, color changes can be handled very easily and in a short time, and the paint usage efficiency can be kept sufficiently high for practical use. In order to prevent overspray from adhering to the side walls of the booth by forming a downward airflow inside the booth, and at the same time to reduce the rate of overspray mixing into the booth exhaust, the booth exhaust intake should be
As shown in FIG. 3, a plurality of ducts 22 having narrow downward air supply holes are provided close to the belt 13 and are formed of an insulating material or a high-resistance semiconductor. By forming the conductive belt 13 at a potential of the same polarity as that of the electrostatic powder gun, it may be possible to improve the efficiency of collecting overspray paint powder on the conductive belt 13.

As the static eliminator used to remove the charged overspray from the belt, any static eliminator shown in the examples can be applied as long as it can neutralize the charged powder paint and remove it from the conductive belt. be able to.

Effects of the Invention According to the present invention, it is possible to obtain a powder coating booth that can reliably change colors in a short time with a small and inexpensive device, and to improve paint utilization efficiency and gun application efficiency. I can do it. Furthermore, the number of personnel and costs for operating and maintaining the equipment can be reduced, making a major contribution to the development of powder coating.

Since this invention has a bottom section consisting of a conductive belt conveyor exclusively for overspray powder, overspray powder that does not adhere to the object to be coated is forced to be electrostatically adhered to the conveyor.

In addition, since the ion shower type static electricity removal device is equipped with a blowing means for blowing gas toward the surface of the belt conveyor, and a discharge electrode provided in a flow path of the blowing means, The ions are blown toward the surface of the conveyor by the blown gas to eliminate static electricity from the overspray powder on the surface, and also blow off the static neutralized overspray powder to expose the non-static overspray powder layer. Therefore, the overspray powder layer can be efficiently neutralized.

Further, since this blown gas always flows while washing the discharge electrode, the discharge electrode is always cleaned and maintained in a clean state. Therefore, discharge as designed can be maintained.

Furthermore, since the recovery device is provided with the recovery hopper exhaust means, the blown gas is sucked and exhausted from the opening of the recovery hopper without being spouted out. Therefore,
Overspray powder can be collected and the belt surface can be cleaned. Furthermore, since the entrance and exit of the hanger conveyor are provided as openings in the front and rear walls of the booth, the objects to be coated are electrostatically coated while moving within the booth, and most of the overspray powder falls and adheres to the belt conveyor. Furthermore, since the object to be coated is transported while suspended using a hanger conveyor,
After assembly, both sides of a three-dimensional object or a flat object can be easily coated.

In addition, since it has side walls made of insulators or semiconductors and a ceiling with a downward air supply function, it is possible to prevent overspray powder from adhering to the ceiling, and it is also possible to prevent overspray powder from adhering to the ceiling. By charging up the side walls of the booth and maintaining a high voltage of the same polarity as the gun, overspray powder can be prevented from adhering to the side walls.

[Brief explanation of drawings]

Fig. 1 is a perspective view of the entire powder coating booth according to the present invention, Figs. 2 and 3 are mainly for explaining the structural details of the bottom of the booth in Fig. 1, and Fig. 2 is a perspective view of the entire powder coating booth according to the present invention. BB vertical sectional view, and FIG. 3 is an AA horizontal sectional view in FIG. 1...Booth side wall, 2...Air supply box, 3...
... Air supply filter, 6 ... Suction hood, 8 ... Static eliminator, 10 ... Collection hopper, 12 ... Booth exhaust, 13 ... Belt, 17 ... Electrostatic powder gun.

Claims (1)

[Scope of Claims] 1. A bottom section consisting of a conductive belt conveyor dedicated to overspray powder; an ion shower blow type static eliminator installed near the booth exit of the belt conveyor; openings in the front and rear walls of the booth that form the entrance and exit of the hanger conveyor; a side wall made of an insulator or semiconductor; an electrostatic powder gun provided on the side wall; The powder coating booth has a ceiling having an air supply function; and the ion shower blow type static eliminator includes a spraying means for spouting gas toward the surface of a belt conveyor, and a flow rate of the spraying means. A powder coating booth, comprising: a discharge electrode provided in the path; and a collection hopper exhaust means provided in the collection device. 2. The powder coating booth according to claim 1, wherein the ion shower type static electricity removal device is provided in a recovery hopper of a recovery device. 3. The powder coating booth according to claim 1, wherein the inner surface of the insulator is formed of a semiconductor.