JPH10151376A - Powder coating gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the effect of triboelectrification itself and the matchability between the triboelectrification and corona electrical charging, respectively, to uniformly and effectively improve the electrification quantity on a powder without causing an evil due to the generation of free ion, etc., and to remarkably ameliorate the coating efficiency and coating quality. SOLUTION: This gun is provided with a gun main body 3 and a nozzle hardware 6. The main body 3 has a paint passage communicating with a flow straightening chamber 19 through an agitated passage 13 for agitating and mixing powder and pressurized air in an inlet passage 12 communicating with a paint tank and passing the powder and pressurized air. The nozzle hardware 6 is provided with a plurality of small-diameter branch passages 27 with a nozzle port formed on their front end and forming a triboelectrification passage 29 with the flow straightening chamber 19. Further, an electrode needle for generating a corona discharge and corona-charging the powder is disposed in the triboelectrification passage 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can uniformly and effectively increase the charge of a powder coating while preventing the generation of free ions and the generation of an electric field between the coating material and the coating material. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating gun which greatly improves coating quality and enables use of, for example, a ceramic paint having poor triboelectricity (triboelectricity).

[0002]

2. Description of the Related Art In recent years, powder coatings in which powder coatings such as epoxy-based, polyester-based, and acrylic-based coatings are charged and the adhesion effect is enhanced by utilizing Coulomb force between the coatings and an object to be coated have been developed. It has been widely used from the viewpoints that it is easy to reuse, and that there is no occurrence of fire, pollution, etc. due to the use of an organic solvent, and that it has excellent safety.

In such powder coating, for example, FIG.
As shown in the figure, an electrode b connected to a high-voltage power supply is provided at the front end of an application gun a for discharging powder together with pressurized air, and the powder discharged from the nozzle port a1 is discharged by corona discharge e generated from the electrode b. A corona charging type for charging, or a coating agent flow path in an application gun is formed of a charging resin, and the powder is charged by friction with the charging resin when the powder flows with pressurized air. Tribo-charged type
Generally known.

[0004]

However, in the above-described corona charging type, the flow of powder from the nozzle port a1 is affected by the electric field f generated between the electrode b and the object g to be coated. For example, it is difficult to uniformly coat the object having a complicated shape, for example, it is difficult for the powder to enter the corner portion or the concave portion h of the object g. Also,
Since free ions are generated toward the object to be coated g, electrostatic repulsion is induced in the powder adhering layer, and there is a problem that coating quality is impaired, such as inducing pinholes and craters on the coated surface. In addition, in the case of corona discharge, in particular, about 70 km / h
Charging is not effectively performed on the powder discharged at the above high speed, and increasing the charging voltage in order to enhance the charging effect causes an increase in the generation of the electric field and free ions. Make it even bigger.

On the other hand, in the tribo-charging system, in order to obtain a required charging efficiency, it is necessary to flow powder at a relatively high speed and for a long distance. Painting workability is impaired. In addition, since the charge efficiency varies between powders, and the charge efficiency itself is affected by temperature, humidity, and the like, control and management thereof are difficult, and stability of coating quality is poor.

In order to solve the above-mentioned problems in the tribo-charging system, some composite systems in which an electrode for corona discharge is provided at the front end of a tribo-charging type coating gun have been proposed. However, this one requires a high-speed powder for tribocharging, so it is inferior in matching with corona charging, and has not yet achieved a sufficient improvement in charging effect. There is also a new problem that free ions and electric fields are generated.

Accordingly, the present invention provides a rectifying chamber for rectifying air mixed with powder, and a plurality of branch flow paths branched from the rectifying chamber to form a tribo-charging flow path, and the tribo-charging flow path is formed in the tribo-charging flow path. Based on the provision of an electrode needle for corona discharge, the charging effect of tribocharging itself, and the matching property between tribocharging and corona charging can be respectively increased, without causing adverse effects due to generation of free ions and the like. Aims to provide a powder coating gun that can uniformly and effectively improve the amount of charge on powder, greatly increase coating efficiency and coating quality, and also enable the use of powder coatings with poor triboelectricity, for example. And

[0008]

According to one aspect of the present invention, there is provided an inlet for communicating with a paint tank and allowing powder in the paint tank to flow with pressurized air. A plurality of nozzles formed at the front end of the gun body having a paint flow path leading to the rectifying chamber through a stirring flow path that generates mixed air in which powder is mixed by stirring and mixing the flow path, A nozzle fitting having a long and small diameter and a branch flow path that forms a tribocharging flow path together with the rectifying chamber is mounted, and an electrode needle that performs corona discharge and corona-charges mixed air powder in the tribocharging flow path. It is characterized by having provided.

In addition, the charging effect by corona discharge is enhanced,
In order to more reliably suppress the generation of free ions by reducing the voltage at the time of discharge, it is preferable to provide an electrode needle in each branch channel.

Further, in order to reduce the flow rate of the powder and enhance the charging effect by corona discharge, it is preferable that the sum of the cross-sectional areas of the branch flow paths is equal to or larger than the cross-sectional area of the inlet flow path.

It is preferable that the triboelectric charging channel and the sub-tribocharging channel have their flow walls formed of a Teflon material in order to maintain insulation and prevent leakage of electric charges to the outside.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3, a powder coating gun 1 includes a gun body 3 having a paint flow path 2 and a nozzle fitting 6 having a branch flow path 5 forming a triboelectric charging flow path 4 and attached to the gun body 3. I have.

The gun body 3 is provided with a handle 3B at the rear end of a body 3A having a blind hole 7 formed at the front end, for example, has a substantially L-shape, and a swirl member 9 is provided in the blind hole 7. On the other hand, a conduit 10 which is connected to the blind hole 7 and extends along the gun body 3 is disposed at the rear.

The conduit 10 has a front end opening concentrically with the blind hole 7 and opening at the bottom surface of the blind hole, and a rear end communicating with the paint tank 11 so that the powder in the paint tank 11 is compressed together with pressurized air. An inlet channel 12 to be passed is formed. The conduit 10 includes a main pipe section passing through the inside of the gun body 3 and an extension pipe section 1 extending from the main pipe section to the paint tank 11.
0B can be configured to be detachably connected.

As shown in FIG. 1, the paint tank 11 has a storage chamber 11A for storing the powder in a fluidized state,
An ejector 11B is connected to the storage chamber 11A via an on-off valve, and a high-pressure air source 11C communicates with the ejector 11B. Therefore, the paint tank 11
Sucks the powder in the storage chamber 11A by the negative pressure of the high-pressure air fed from the high-pressure air source 11C,
Through B, the powder can be supplied to the conduit 10 together with the high-pressure air. In addition, the paint tank 11 can freely switch between supplying and stopping supply of only high-pressure air.
This is performed by a trigger (not shown) provided on the handle 3B of the gun body 3.

The swirl member 9 has a stirring channel 13 for stirring the powder flowing from the conduit 10 and pressurized air to form a mixed air in which the powder is uniformly mixed. The paint channel 2 is formed by the channel 13 and the inlet channel 12. Further, in this example, the stirring channel 13 is a diffusion channel portion 13A that diffuses the powder from the conduit 10 together with pressurized air in a radially outward conical shape.
And a spiral flow path portion 13B for providing a spiral flow to the diffused powder flow. Each flow path portion 13A, 13B
It is formed from a diffusion ring piece 14 and a swirl piece 15.

The diffusion ring piece 14 has a ring shape arranged concentrically with the blind hole 7, and is provided with a cone which is inclined outward in the radial direction in front of a center hole 14 A connected to the inlet channel 12. A conical surface 14B is provided. The swirl piece 15 has a cylindrical base 16 concentric with the blind hole 7.
At the rear end of the base 16, on the axis I of the base 16,
A conical portion 16A substantially parallel to the cone surface 14B protrudes. Thus, a diffusion channel portion 13A is formed between the conical portion 16A and the cone surface 14B. The base 16 is located at a position radially outward from the conical portion 16A.
It has a plurality of, for example, six to sixteen, pores 17 arranged at substantially equal pitch intervals on the circumference thereof.
The spiral channel portion 13B is formed by penetrating the base portion 16 back and forth while being spirally twisted together around the axis I. The diffusion channel portion 13A ensures that the flow smoothly moves from the inlet channel 12 to the spiral channel portion 13B.

The flow surfaces of the inlet channel 12 and the agitating channel 13 have a negative side that is easily triboelectrically charged. In this example, the paint flow path 2 is formed as a sub tribo charge flow path 18.

Since the cross-sectional area of the inlet channel 12 of the sub-triboelectric charging channel 18 is relatively large and the flow velocity difference between the center side and the wall side is large, powder Tends to flow on the central side where the flow velocity is fast. as a result,
Since the chance of frictional contact with the flow wall surface is reduced, and the contact speed is reduced during frictional contact, the triboelectric charging effect is relatively small as before, and the charged powder and the non-charged powder are not charged. The body and the body are mixed unevenly.

On the other hand, in the stirring channel 13, the mixing of the charged / uncharged powder is made uniform by stirring. Also multiple (N
When the total cross-sectional area is equal to that before dispersion, the total area of the N flow walls increases N times. Moreover, in each of the pores 17, the flow velocity difference between the center side and the wall side becomes small, and the distance between the center side and the wall side also becomes short, so that the chance of frictional contact between the powder and the flow wall becomes large. In addition, since the flow velocity on the flow wall side, that is, the contact velocity is high, triboelectric charging can be performed uniformly and effectively. In particular, in the spiral channel portion 13B, since each powder receives a large contact pressure from the flow wall surface, higher charge can be generated more uniformly. In this example, the spiral flow path portion 13B
Is substantially equal to the cross-sectional area of the inlet channel 12.

In the front end of the swirl piece 15 and in the blind hole 7, a rectifying chamber 19 is formed in which the mixed air from each of the spiral flow passages 13B is merged to rectify the air into one stable spiral flow. The rectifying chamber 19 includes an outer ring 20 sandwiched between the swirl piece 15 and the nozzle fitting 6 and disposed in the blind hole 7, and an inner shaft 21 concentric with the axis I. It is formed in a cylindrical shape between the ring 20 and the inner shaft 21.

The nozzle fitting 6 comprises a base 22 which is hermetically attached to the front end of the body 3A of the gun body 3, and a base 22
And 6 to 16 nozzle tubes 23, for example, having a nozzle port 23A at the front end and extending forward. The nozzle fitting 6 is not formed of a metal material as the name implies, and in this example, together with the gun body 3,
It is mainly formed of an insulating material such as a synthetic resin.

The base 22 has a cylindrical shape attached via a connection nut 25 screwed to the front end of the body 3A. The base 22 has a small-diameter connection which penetrates back and forth and has a nozzle tube 23 attached to the front end. A hole 26 is formed. The connection hole 26 is formed in an opening 26 opening in the rectifying chamber 19.
A are arranged on the circumference around the inner shaft 21 at substantially equal pitch intervals, and each of the connection holes 26 has a conical shape centered on the axis I, that is, faces forward from the opening 26A. To extend radially outward. The rectification chamber 19
By rectifying into one stable spiral flow,
The subsequent branching of the flow to the plurality of branch channels 27 is facilitated.

The nozzle tube 23 is a long, small-diameter, and relatively flexible tube attached to the front end of each connection hole 26. In this embodiment, each nozzle tube 23 is, as shown in FIG. The nozzle openings 23A are arranged on a straight line and fixed to the frame F. In this example, the frame F is supported by the nozzle fitting 6 using a screw shaft 28 which is integral with the inner shaft 21 and penetrates the base 22 and protrudes from the front end thereof.

Accordingly, the nozzle fitting 6 forms a branch channel 27 by the connection hole 26 and the inner hole of the nozzle tube 23, and the flow wall between the branch channel 27 and the rectifying chamber 19 is formed by The branch flow path 27 and the rectification chamber 1 are formed by using a chargeable resin, in this example, Teflon.
9 form a triboelectric charging channel 29.

The tribo-charging flow path 29, like the spiral flow path section 13B, can be divided into a plurality of sections to increase the total area of the flow wall surface, and furthermore, the flow velocity difference between the center side and the wall side becomes small, Further, since the distance from the wall surface side is shortened, the chance of frictional contact of the powder is greatly increased, and further, the triboelectric charging can be uniformly and effectively performed because the flow speed on the wall surface side, that is, the contact speed is high. In addition, the fact that the flow velocity difference between the center side and the wall side is small has an effect of substantially reducing the flow velocity as compared with the center side of the inlet flow path 12, and therefore, there is an effect that the charging by the corona discharge described later is not performed. Matching can be improved. In this example, the sum of the cross-sectional areas of the branch flow paths 27 is equal to or larger than the cross-sectional area of the inlet flow path 12, thereby further guaranteeing the deceleration of the powder in the branch flow path 27.

The length of each of the plurality of branched nozzle tubes 23 can be arbitrarily set according to the shape of the object to be coated. It can be set freely, which helps to improve coating quality.

The powder coating gun 1 is provided with an electrode needle 30 for corona discharging and corona charging the mixed air powder in the tribocharging flow path 29, in this example, in each of the branch flow paths 27. ing.

As shown in FIG. 4, the electrode needles 30 are made of a conductive metal having a plurality of electrode needles 30 extending forward on the front surface of an annular ring base 31 embedded at the rear end of the base 22. Each electrode needle 3 is formed as an electrode unit 32.
Numeral 0 passes through the inside of the base 22 and has its tip exposed in the branch channel 27. The body 3 of the gun body 3
A connection terminal 3 which contacts the ring base 31 at the front end
3 is provided, and the connection terminal 33 is connected to a corona discharge generator 40 provided in the gun body 3 via a lead wire 34.

The corona discharge generator 40 applies a high voltage to each of the electrode needles 30 to create a high positive corona discharge electric field around the electrode needles 30 to further apply powder to the powder in the tribocharging flow path 29. Causes corona charging.

At this time, since corona discharge is generated in the narrow tribocharging flow path 29, all the powder passing through this flow path can be charged, and the powder in this flow path is decelerated. The corona charging effect can be further improved. In addition, when passing through the elongated nozzle tube 23, the charge of ions adheres to the powder, so that the release of free ions from the nozzle port 23A can be effectively suppressed. Further, since corona discharge occurs in the tribocharging flow path 29, No electric field is generated between the substrate and the object. Therefore, it is possible to apply a uniform thickness to an object having a complicated shape without unevenness, and it is possible to prevent the occurrence of pinholes or the like on the painted surface, thereby improving the coating quality.

As described above, the powder coating gun 1 enhances the tribocharging efficiency itself, and at the same time, the corona discharge is adapted to this tribocharging structure, so that the corona charging effect can be improved, and the amount of charge on the powder can be improved. And uniformly and effectively increase the use of, for example, a ceramic powder coating having poor triboelectricity. Further, since the corona discharge can be freely controlled by the corona discharge generator 40, it is possible to cover defects in tribo-charging such as temperature, humidity, the amount of charge being affected by the lot of powder, etc. Can be guaranteed.

In the present application, the stirring flow path 13 and the entrance flow path 12 are formed as the auxiliary triboelectric charging flow path 18, but one or both of the stirring flow path 13 and the entrance flow path 12 have low charging. It is also possible to use a conductive resin and thereby form a normal paint flow path that is not triboelectrically charged. Further, in the present embodiment, the tip of the electrode needle 30 is provided at a position deviated from the center line of the branch channel 27, but may be provided on the center line.

[0034]

Since the present invention is configured as described above,
The charging effect of tribocharging itself and the matching property between tribocharging and corona charging can each be improved, and the amount of charge on the powder can be uniformly and effectively improved without causing any adverse effects due to generation of free ions and the like. The coating efficiency and quality can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a side view showing a powder coating gun according to one embodiment of the present invention.

FIG. 2 is an enlarged sectional view showing a main part thereof.

FIG. 3 is an exploded perspective view thereof.

FIG. 4 is an exploded perspective view illustrating an electrode unit.

FIG. 5 is a diagram illustrating a conventional technique.

[Explanation of symbols]

 2 paint flow path 3 gun body 6 nozzle fitting 11 paint tank 12 inlet flow path 13 stirring flow path 18 tribo charging flow path 19 rectifying chamber 23A nozzle port 27 branch flow path 29 tribo charging flow path 30 electrode needle

Claims (5)

[Claims] 1. An agitating flow path, which communicates with a paint tank and in which the powder in the paint tank flows with pressurized air is stirred and mixed to generate mixed air in which the powder is mixed. Then, a nozzle body having a plurality of long and small diameter nozzles formed at the front end and having a branch flow path that forms a tribocharging flow path together with the flow rectification chamber is attached to a gun body having a paint flow path leading to the flow control chamber. Further, an electrode needle for corona-charging the powder of mixed air by corona discharge is provided in the tribocharging flow path. 2. The powder coating gun according to claim 1, wherein said electrode needle is provided in each of said branch flow paths. 3. The powder coating gun according to claim 1, wherein said triboelectric charging passage has a flow wall formed by using a Teflon material. 4. The powder coating gun according to claim 1, wherein the sum of the cross-sectional areas of the branch flow paths is equal to or larger than the cross-sectional area of the inlet flow path. 5. The inlet channel and the stirring channel whose flow wall surfaces are formed using Teflon material, whereby the inlet channel and the stirring channel form a sub-tribocharging channel. The powder coating gun according to claim 1, wherein