JPH05177155A - Electrostatic powder coating utilizing spray streams with pulse electrostatic field and spray pattern - Google Patents

Abstract

PURPOSE:To improve the uniformity of powder coating on an object with a non-uniform or uneven shape such as the inner surface of a container by dividing a pressurized gas/powder blend into individual electrostatically charged spray streams using an electrostatic powder coating gun so that high directional properties are ensured and lopsided alignment is minimized. CONSTITUTION:In an electrostatic powder coating gun 10, a pressurized gas/ powder blend is divided into individual electrostatically charged spray streams so that high directional properties are provided to the streams. The powder particles of the blend are electrostatically changed either using a DC electrostatic field or a friction force applied, while they are present in more than one chamber 24 of the gun. A flow path 26 through which the spray stream traverses is arranged in such a manner that a specific surface contour such as the inner surface of a container 30 can be coated with powder advantageously. Instead, the powder particle is electrostatically charged only by using electrodes 34 arranged on the outerior of the gun 10. Further, at least, one of the outer electrodes 34 is made to relate to each spray stream.

Description

Detailed Description of the Invention

[0001]

This invention relates to electrostatic powder coating or electrostatic powder coating or application. More particularly, this invention relates to improvements in electrostatic powder coatings that utilize multiple spray streams.

[0002]

2. Description of the Prior Art According to conventional powder coating methods and apparatus, a pressurized mixture of gas and powder particles is imparted with an electrostatic charge from a gun toward the object to be coated or painted. It is designed to be jetted or sprayed to the outside. The particles contained in the gas-powder mixture are generated inside the gun via an electrostatic field applied or by triboelectric charging, i.e. triboelectricity, or by external electrodes generated outside the gun. It is charged via the electric field. During electrostatic powder coating, the charged powder particles in the mixture repel one another as they move toward the object to be coated. During flight, the low potential of the coated object attracts particles with static electricity.

[0003]

In order to achieve coating uniformity with conventional coating guns, it is common to place a trumpet-shaped deflector in front of the gun nozzle. The deflector expands or widens the flow path of the mixture under pressure so that the powder covers a larger area. This method works reasonably well for roughly coating objects, but suffers from some limitations. First of all, over a relatively large cross-sectional area, the sprayed mixture produces a thick air cushion. This air cushion interferes with the subsequent flow of particles and repels a significant number of subsequently sprayed particles from the coating surface. as a result,
Powder coating by this method takes extra time to ensure a complete coating, and a significant amount of powder is lost by bounce.

Conventional powder coating methods and apparatus include
Further restrictions are placed on coating non-uniform or uneven surfaces such as the inner surface of cylindrical containers and metal pipes.
Using external electrodes to create an electrostatic field between the gun and the object results in the strongest line of electrostatic force being placed along a direct line of the site path to the closest part of the object, Also, the lines of electrostatic force directed to the recessed portion become significantly weaker. For example, the electrostatic field lines for the container are strongest between the gun and the top of the inner surface of the container and weakest between the gun and the bottom of the container.

When powder coating a large number of protrusions and / or cavities, ie objects or workpieces with uneven surfaces, the charged particles initially take the path of the strongest electrostatic field lines. Thereafter, the particles will try to continue along this same path, resulting in the accumulation of discontinuities in the object closest to the gun or in protrusions closer to the gun than the surrounding areas. As a result, the object is not uniformly coated. More specifically, workpieces or objects with protrusions and / or cavities are very unevenly coated. Often, the tops or edges of the protrusions are thickly coated, the bottoms of the cavities are thinly coated, and the corners of the cavities are barely coated. The tendency of particles to accumulate in the discontinuous surface area, rather than being uniformly accumulated over the entire surface, is called the Faraday cage effect.

Another problem associated with powder coating is
This is the point at which the powder particle mixture is not fully charged when triboelectric charging is used. In order to increase the charging rate when using triboelectric charging, it is necessary to increase the contact area of the mixture. However, this makes the flow path longer and more complex. As a result, if it is desired to change colors, it will take longer to change to a powder of another color.

With respect to the electrostatic field generated by the external electrodes, the charging efficiency may sometimes be increased by increasing the field strength. However, this increases the adverse effect produced by the Faraday cage effect. In addition, particles with a higher charge retain their charge after application, which repulses subsequent particles and interferes with the second coating.

Another problem associated with powder coating is
This is the point that the amount of powder particles sprayed per unit time changes. Generally, the amount of powder sprayed per unit time can be changed by increasing or decreasing the pump pressure.
However, the pressure change causes a change in the jet velocity from the spray gun, which results in another coating phenomenon such as soft landing or continuous jet stream impingement. In soft landing, the coating is affected via electrostatic attraction, and due to the Faraday cage effect,
The coating weight increases so that no additional coating is needed. In this case, no further coating is needed. With respect to jet stream collisions, the rebound is so severe that even the deposited powder particles are blown off the object.

Another limitation of conventional powder coating methods and apparatus is when coating relatively small objects. When low pressures, ie less than 1.5 kg / cm ^2, are used to accommodate the lower required volume, the spray pattern becomes unstable and results in a non-uniform coating.

It is an object of the present invention to improve the uniformity of powder particle (ie, granule) coatings on objects of non-uniform or irregular or irregular shape, such as the interior surface of a container. Another object of the invention is to reduce the amount of offset and rebounce that occurs during powder coating. Yet another object of the present invention is to provide a gas used for electrostatic powder coating without adversely affecting the subsequent coating.
Achieving a higher efficiency in charging the particles (ie powder) contained in the powder mixture. Yet another object of the present invention is to minimize the adverse coating results caused by the Faraday cage effect, especially when using powder coating apparatus with external electrodes. Yet another object of the present invention is to improve the efficiency of powder coating relatively small objects or objects having a relatively small volume.

[0011]

SUMMARY OF THE INVENTION The method and apparatus of the present invention accomplishes the above objectives by dividing a pressurized mixture of gas and powder particles (ie, particles) into a plurality of separate spray streams. To do. Dividing the mixture into multiple fine spray streams reduces the rebound effect and also allows relatively large or small surfaces with many channels arranged in selectable patterns dictated by the shape of the object to be coated. The area allows the operator to powder coat.

In a typical application, particles contained in many spray streams are electrostatically charged by many external electrodes associated with each of the spray streams, with at least one external electrode. With many fine spray streams associated with many external electrodes, a minimal air cushion can effectively charge the powder particles of the separate spray streams.

In addition, the present invention seeks to spray a gas and powder mixture from a gun in a pulsed manner to further reduce air cushioning and / or offset, and to more easily coat relatively smaller volumes. To do. By pulsing the powder particles from the gun,
More precise control over the amount of powder sprayed per unit time.

According to another aspect of the present invention, the DC power source supplied to the external electrodes that generate the electrostatic field to charge the particles is pulsed between "off" and "on" states during spraying. , Periodically pulsing the electrostatic field formed between the external electrode and the object to be coated. Pulsing the electrostatic field reduces the Faraday cage effect because particles flow unimpeded by the electric field along a flight path formed solely by aerodynamic forces when the field is "off". This provides a more uniform coating of areas such as the bottom of the container and irregularities, i.e. depressions on uneven surfaces.

For general powder coating applications, the present invention seeks to pulse an electrostatic field in connection with the pulsing of a powder stream. Furthermore, these two features are further linked to the use of many spray streams and many external electrodes.

The method and apparatus of the present invention are particularly suitable for powder coating the interior surface of a container. More specifically, the combination of many spray streams with powder charge inside the gun reduces the Faraday cage effect and also allows for a uniform coating inside the can. The present invention contemplates some additional features associated with particle charging inside the gun, utilizing multiple charge chambers connected in series or in parallel.

The present invention contemplates several other approaches for powder coating the interior surface of a container. More specifically, the invention also contemplates the association of many spray streams with many external electrodes in connection with the pulsing of the electrostatic field created by the electrodes. Further, the present invention seeks to pulse the powder sprayed from the spray gun with respect to a single spray stream or multiple spray streams. As yet another approach to coating the interior surface of the container, the present invention seeks to pulse the electrostatic field in combination with the pulsing of the powder jet.
These two features are further combined with the use of many spray streams and external electrodes.

Structurally, the present invention uses a multi-hole nozzle or multi-tube spray hole assembly that divides a pressurized gas-powder mixture into a plurality of fine spray streams. If a multi-hole nozzle is used, the nozzle connects to the front end of the gun and the multiple holes in the multi-hole nozzle form multiple openings in the interior chamber of the spray gun through which powder particles are sprayed. If a multi-tube spray hole assembly is used, the manifold of this assembly connects to the front end of the gun. The manifold holds a number of tubes in place at the forward end of the gun for fluid communication with the chamber. The opposite ends of the tubes are held in the desired arrangement by the holder. For a multi-tube spray hole assembly, the multiple tubes form multiple chamber openings.

With respect to either the multi-hole nozzle or the multi-tube spray hole assembly, the chamber openings are arranged in any desired pattern. The array of chamber openings defines a flow path that traverses when multiple spray streams are ejected from the gun. The openings may be aligned in a straight line, arranged around the circumference of a circle, or preferably arranged in many parallel rows, with each row staggered with respect to an adjacent row. The openings may also be beveled or angled to form angled channels.

Based on the shape and size of the object to be coated, the chamber openings are arranged to direct the flow path in the desired manner. This feature of the present invention is particularly important when powder-coating an object having many hollow portions, such as a heat radiation fin, a transformer, and a radiator. For objects of this type, it is usually preferred to use 6 to 24 separate spray streams. In the most common example, a range of about 2-8 mm is more preferred for the inner diameter of the chamber opening, i.e. the tube of a multi-tube spray hole assembly or the hole of a multi-hole nozzle. When using many chamber openings, it is preferred that the chamber openings be spaced apart by about 2-8 mm. The tubes and nozzles of the assembly are preferably made from plastics such as fluorine resin, nylon or polypropylene based on the polarity of charge and coefficient of friction.

One particular arrangement of chamber openings that has the advantage of coating uneven surfaces includes arranging the chamber openings around the circumference of the circle or orienting the chamber openings at an angle to the circle. I'm out. With this approach, if the chamber openings are directed outwards, a large number of spiral streams are created which are particularly suitable for coating the inside surface of containers and vipes. Instead, the chamber openings are oriented at a central axis through the circle to provide a circular shaped flow passage that first gathers at a point and then widens outward. Depending on the distance between the end of the gun and the object to be coated, this arrangement is used to coat large or small surface areas.

For any of these arrangements of chamber openings,
A gas-powder mixture pressurized by one or more external electrodes, or by a combination of internal and external charges,
Electrostatically charged inside the gun and outside the gun. For a particular commercial application of the invention, the most appropriate charge for the powder particles contained in the mixture is determined.

When one or more external electrodes are used for charging powder particles, it is sometimes necessary to pulse the electrostatic field generated by each electrode between the "on" and "off" states. It is said that. This pulsing of the electrostatic field is achieved by a pulse controller which provides a selectable interruption of the electrical connection between each external electrode and the DC power supply. Pulsing the electrostatic field will reduce the Faraday cage effect when using external electrodes. Pulsed electrostatic field is January 1, 1989.
It is disclosed in Japanese Patent Laid-Open Publication No. 1-11,669 published on 7th.

As noted above, another aspect of the invention relates to pulsing powder particles from a gun. Pulsing of the powder particles is accomplished by a powder pulse controller connected to the ejector to eject the mixture from the gun depending on the desired waveform. By cycling between the "on" and "off" states at a desired pressure, usually a uniform pressure, powder particles are sprayed from the gun end in successive pulses and the air cushion is reduced. Pulsing the powder particles reduces biasing and bouncing off of the object being coated. Since pulsing ensures that a uniform pressure is maintained during spraying, the controller ensures that the duration and amplitude of the pulse are carefully controlled and the amount of powder particles sprayed per unit time. Remains relatively uniform when coating small objects of relatively smaller volume. Powder pulsing, 1987 1
Published Japanese Patent Publication No. 62-11,57
No. 4 is disclosed.

In accordance with another aspect of the invention, the holes of a multi-hole nozzle or the tubes of a multi-tube spray hole assembly further comprise a small scale nozzle having either many smaller holes or a single elongated slit. I have it. Small scale nozzles of this kind separate the mixture into a finer spray stream.

Based on the type of powder particles used and the size, shape and composition of the object to be coated, the above features may be used in various combinations to achieve a uniform powder coating. These and other features of the present invention will be readily understood by the following detailed description and drawings.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows an electrostatic powder spray coating apparatus 10 according to an embodiment of the present invention. This device 1
0 includes a powder feed hopper 12 in which the powder particles are mixed with air which takes in the powder particles therein. The ejector or pump 14 stores the gas-powder mixture in the tank 12
To the inside of the gun body 18 via the transport pipe 16. The air compressor 20 drives the pump 14 and maintains a pressure high enough to suspend the powder particles in the air from the hopper 12. In the gun body 18, the mixture is tube 1
Exit 6 and enter chamber 22. From the chamber 22, the mixture exits through a plurality of chamber openings 24 formed in a perforated nozzle 25 at the front end of the gun 18.

During operation, the gas-powder mixture flows through the flow path 26.
Sprayed from the chamber 22 through the chamber openings 24 and they are sprayed toward the surface 28 of the article 30 to be coated to form a plurality of discrete, fine spray streams across.

During spray coating, the particles contained within the gas-powder mixture are electrostatically charged so that they are attracted to the low electrostatic potential of surface 28 shown in FIG. 1 as ground potential. FIG. 1 shows a high voltage generator 32 that provides a DC voltage to generate one or more electrostatic fields to electrostatically charge (ie, charge) particles in a gas-powder mixture. The conductive cable 33 connects the voltage source 32 to the gun 1
The electrodes 34 are connected to a plurality of electrodes 34 protruding outward from the front end of the electrode 8. Each electrode is associated with each chamber opening 24 to maximize electrostatic charging of particles within the gas-powder mixture across each flow path 26.

All embodiments of the present invention using one or more external electrodes involve an electrical circuit having a resistance (not shown) in the range of about 10 ⁵ to 10 ⁹ ohms,
This is desirable to prevent sparking when the gun 18 is in close proximity to the object 30 to be coated. In a preferred embodiment, the outer electrode is made of silicon carbide and has a resistance of about 10 ⁶ ohm centimeters.

If desired, to further enhance the efficiency of electrostatic charging of the particles contained within the gas-powder mixture,
The cable 33 supplies a high voltage to a DC electrode 36 located in the chamber 22 of the gun 18. The electrode rod 36, in cooperation with the internal ground terminal 37, forms an electrostatic field within the gun 18 and electrostatically charges the particles contained within the gas-powder mixture while flowing through the chamber 22. To occur. Room 2
Due to the relatively high pressure and flow velocity of the particles contained in the gas-powder mixture while at 2, most of the charged particles contained therein will move through the ground terminal 37, even if some are present at the ground terminal 37. Even if the charged particles are attracted and deposited, they are sprayed from the nozzle 25.

FIG. 2 is a cross-sectional view of the front or spray end of nozzle 25. According to this embodiment, the multi-hole nozzle 2
5 generates a spray flow through each of the flow paths 26a, 26b, 26c, 26d and external electrodes 34a, 34b, 34.
chamber opening 24 electrostatically charged by c, 34d, 34e
It has a, 24b, 24c and 24d. Thus,
In this embodiment, each flow path 2 generated by each chamber opening is
6 extends between the pair of external electrodes 34. this is,
Maximize the number of particles in the gas-powder mixture that are electrostatically charged during spraying.

FIG. 3 shows the chamber opening 24 on the way to the surface 28.
The individual channels 26a, 26b, 26c, 26d due to the spray flow formed by a, 24b, 24c, 24d are shown in cross section. FIG. 4 shows a composite spray pattern 38 formed on the surface 28 by the four separate spray streams depicted in FIG. As shown in FIG. 4, the flow path 26 is traversed by separate spray streams.
Are enlarged and join together on the way to the surface 28.
The final spray pattern 38 formed on the surface 28 is
It depends on the distance between the front end of the gun 18 and the surface 28.

FIG. 5 shows a second embodiment of the present invention which is a modification of the electrostatic powder spray coating apparatus 10 depicted in FIG. According to this modification, the multi-hole nozzle 25
Is replaced by a multi-hole nozzle 125 having a tapered or converging chamber opening 124. These chamber openings 124 are narrower and darker than the spray pattern 38 depicted in FIG. 4 through the flow path 126 to produce a spray pattern 138 as shown in FIG. Generate a close flow.

FIG. 7 depicts another variation of the perforated nozzles 25, 125 used in the first two embodiments. More specifically, the device 10 comprises a multi-hole nozzle 225 having a plurality of chamber openings 224 arranged around a circle. For this nozzle 225, a single external electrode 2
34 is located in the center of the chamber opening 224.

FIG. 8 shows a plurality of circularly arranged spray streams produced by the multi-hole nozzle 225 immediately after injection from the gun 18. Because the chamber openings 224 are arranged around a circle, the flow path 226 through which the spray flow passes.
Are further arranged in a circular pattern. FIG. 9 shows the same spray stream as depicted in FIG. 8, but the spray streams merge to form a single annulus shaped flow path.

FIG. 10 shows the same spray flow as that depicted in FIGS. 8 and 9, but after application onto surface 28. The deposition spray stream forms a disc-shaped pattern 238. Compared to FIG. 9, FIG.
FIG. 10 shows particles from within the gas-powder mixture flowing toward the center so as to eliminate the central opening shown in FIGS. 8 and 9.

FIG. 11 illustrates an apparatus 10 of the present invention in which a multi-tubular spray hole assembly 325 is provided in place of the perforated nozzles 25, 125, 225 depicted in FIGS. 1, 5 and 7, respectively. Yet another embodiment is shown. The multi-tube spray hole assembly 325 includes a manifold 327 connected to the front end of the gun 18, a plurality of tubes 329 connected to the manifold 327 for fluid communication with the chamber 22, and a front end of the tubes 329 in a predetermined arrangement. And a holder 331 for holding. Like the holes of those embodiments of the present invention that use a multi-hole nozzle, the tubes of the embodiments that use a multi-tube spray hole assembly form a plurality of chamber openings.

The conductive cable 333 has a first end connected to a DC power source (not shown) and a plurality of external electrodes 33.
And a second end connected to 4. The electrode 334 extends forward from the holder 331. Multi-hole nozzle 25,
Like 225, the multi-tube spray hole assembly 325 divides the gas-powder mixture into a plurality of fine spray streams through a plurality of channels 326 toward the surface 28. In this example, six channels 326a, 326b ,. ． ． 326f
(See FIG. 13) are present and particles entering the spray stream moving through these flow paths are trapped by the external electrodes 336a, 336.
b, 336c ,. ． ． Each of them is electrostatically charged by 336f. See FIG.

FIG. 12 shows linear chamber openings 324a and 324.
b ,. ． ． The front view of the holder 331 in which the front end of the pipe 329 is linearly arranged so as to arrange 324f is shown.
FIG. 13 shows a cross section of the spray formed by the multi-tube spray hole assembly 325 immediately after injection. At some distance the spray streams are separate and distinct,
It takes the form of a disk that is arranged in six straight lines. Figure 1
4 shows the same spray stream at a certain distance thereafter, where the spray streams merge to form a single elongated spray pattern 338.

FIGS. 15, 16 and 17 show that the chamber openings 24 of a multi-hole nozzle or a multi-tube nozzle are arranged in a straight line, and that electrostatic charging of particles in a gas-powder mixture serves as an electrode. 9 shows a variant of the invention achieved via a wire 42 of a book. The wire 42 is parallel to the chamber opening 24 aligned just before the opening or offset to one side. A variation of this single wire electrode of the present invention is
It is understood that it is equally suitable for either the multi-hole nozzle embodiment or the multi-tube spray hole assembly embodiment of the present invention. Object to be coated (not shown)
Is installed on the other side of the wire 42 from the chamber opening 24.

FIG. 15 shows the wire electrode exposed over its entire length with the insulating cover 43 removed at the end of the wire 42 beyond the chamber opening 24. Instead, the insulation cover 43 extends along the entire length of the wire 42, except for a plurality of spaced-apart selected regions 44 corresponding to each chamber opening 24 in which the wire 42 is exposed.

According to another alternative shown in FIGS. 17 and 18, the insulating cover 43 comprises a bottom portion 4 which serves as an electrode.
4 is removed from the V-shaped area 47 at the bottom of the wire 42 of FIGS. 17 and 18 opposite the object to be coated.

FIG. 19 shows another multi-tube spray hole assembly 425 which is a fifth embodiment of the present invention. Multi-tube assembly 425 includes a plurality of tubes 429 having a manifold 427 similar to manifold 327, a first end communicating with chamber 22 and an opposite end defining a plurality of chamber openings 424.
And have. These opposite ends of the tube 429 are connected to the chamber openings 4 in two separate groups of three in a linear array.
It is held in a holder 431 pointing 24.

In use, the multi-tube spray hole assembly 42
5 produces two separate groups of spray streams, each group containing three spray streams. As a result, FIG.
The assembly 425, as shown in FIG.
a top region 438a and channels 426d, 426e, 4 formed by the spray flow through a, 426b, 426c.
Lower region 4 formed by spray flow through 26f
38b is generated to generate a spray pattern 438.
The conductive cable 433 connects a power source (not shown) to the plurality of external electrodes 434 extending forward from the holder 431. The cable 433 and the external electrode 434 are shown in FIG.
The cable 333 and the external electrode 334 shown in FIG.

FIG. 21 shows another multi-tube spray hole assembly 525 which is the sixth embodiment of the present invention. The multi-tube spray hole assembly 525 has a plurality of tubes 529 having a manifold 527, a first end communicating with the manifold 527, and a second end held by the holder 531 in a predetermined shape.
And have. The conductive cable 433 is connected to a power source (not shown) and extends along the holder 531 and is connected to a plurality of external electrodes 534 extending forward from the holder 531.

As in the first, second, fourth and fifth embodiments, the sixth embodiment preferably has at least one outer electrode 534 associated with each chamber opening 524.
As shown in FIG. 22, the front end of the tube 524 is oriented such that the chamber openings 524a are aligned in a first row parallel to the second row of chamber openings 524b, and the first and second The rows of openings are staggered with respect to each other. The chamber openings 524c form a third row parallel to the first two rows and staggered with respect to the second row and aligned with the first row.

FIG. 23 shows a multi-tube spray hole assembly 525 formed with chamber openings 524a, 524b, 524c.
3 shows a spray pattern 538 of three separate coating lines 538a, 538b, 538c corresponding to the first, second, and third columns, respectively.

FIG. 24 shows an application example of the electrostatic spray coating apparatus 10 of the present invention. FIG. 24 shows an object 50 including a bottom horizontal member 51 and a plurality of parallel vertical members 52, each of which forms a bottom parallel surface 53 and a sidewall 54.
3 shows a multi-tube spray hole assembly 325 used for spray coating the. Due to the straight orientation of the front end of the tube 329 in the holder 331, the spray flow is to coat the side wall 54 and the bottom 53 of one slot at a time, as shown in FIGS. 24 and 25. It is aimed at the object 50. If necessary, the assembly 325 is extended downward into the slot during spray coating.

FIG. 25 shows a pulse controller 339 connected to a cable 333 which supplies DC power to the electrode 334. The pulse controller 339 performs switching for connecting and disconnecting DC power to the electrode 334 in a desired sequence. This pulses the electrostatic field formed by the electrode 334 between the "on" and "off" states.

FIG. 25A illustrates one method of pulsing the electrostatic field during spraying. With a spray gun that sprays continuously, the pulse controller 339 cycles the electrostatic field every 60 ms, ie, the field is "on" for 20 ms, as shown by the top waveform.
And "off" for 40 ms. Furthermore, the pulsing of the electrostatic field is indicated by the lower waveform. The relative time of "on" and "off" can be varied according to the desired sequence, according to the time of the entire cycle. Electrostatic field pulsing may be utilized in combination with other powder coating features disclosed herein, such as pulsing powder flow, to uniformly coat non-uniform surfaces such as the interior surface of a container. can do.

FIG. 26 shows another multi-hole nozzle according to the seventh embodiment of the present invention. The multi-hole nozzle 625 fits on the end of the gun 18 of FIG.
It includes a plurality of chamber openings 624 arranged around a circle coaxial with the longitudinal axis of the gun 18, the openings 624 being formed obliquely with respect to the central axis 628 of the multi-hole nozzle 625 and directed outward. There is. FIG. 27 shows the orientation and shape of the chamber opening 624 more clearly, with the outer electrodes 634 arranged along the axis 628 or in the center of the circle formed by the chamber opening 624.

In FIG. 28, a plurality of spray streams are provided in the chamber opening 62.
4 shows a multi-use perforated nozzle 625 exiting 4 and across a flow path 626. The spray stream exiting the multi-hole nozzle 625 forms a spray pattern that includes six distinct disc-shaped regions arranged around a large circle.

FIG. 29 shows an application example in which the apparatus 10 of the present invention utilizes the multi-hole nozzle 625 depicted in FIGS. 26 and 27, and particularly the seventh embodiment of the present invention is well suited.
This application includes powder spray coating on the inner surface of hollow container 55. Depending on the orientation of the chamber opening 624,
The flow path 626 for the spray stream is angled. When sprayed inside the container 55 or any other hollow cylindrical object such as a pipe, the spray stream will be
5 continues to flow along a channel 626 that twists and twists down from the inner surface 58 of the No. 5, resulting in less air cushion in the container and more uniform coating of the inner surface 58. FIG. 29
And FIG. 30 includes directional arrows 59 indicating the twisting or spiraling effect that occurs as the spray stream travels away from the inner surface 58 of the container 55 toward the opposite or closed end. An air cushion within the container that attempts to prevent suitable powder coatings from entering the container is provided by pulsing the pump 14 of FIG. 1, as described below in connection with FIGS. 37 and 38. It is further reduced. Further, reduction of the Faraday cage effect within container 55 is achieved by pulsing the power supply to electrode 634 in a manner similar to that described with respect to Figures 25 and 25A.

FIG. 31 depicts an eighth embodiment of the present invention in which the perforated nozzles 725 are arranged around a circle and are diagonally formed, similar to that of the perforated nozzle 625, but with a circle. Has a plurality of chamber openings 724 directed inward toward a centerline passing through. This perforated nozzle 725
Thus, the flow path 737 through which the spray flow passes converges toward the centerline 737 and then diverges outwardly therefrom as shown in FIG.

FIG. 32 shows the spray pattern 738 formed by the multi-hole nozzle 725. The spray pattern 738 includes six distinct areas arranged around a large circle, which areas are slightly elliptical to the circle and are radially elongated. The pattern formed by the spray stream generated by the multi-hole nozzle 725 is sometimes referred to as Japanese hand held drum. With this array of channels 726, the surface area of the coating can be made very small to very large by adjusting the distance between the end of the multi-hole nozzle 725 and the object to be coated.

FIG. 33 shows a ninth embodiment of the present invention, a multi-tube spray hole assembly 825 designed to produce the same spray pattern as the multi-hole nozzle 625. The multi-tube spray hole assembly 825 includes a manifold 827,
It has a plurality of tubes 829 extending from the manifold 827 and held by a holder 831 in a predetermined arrangement. As shown most clearly in FIG. 34, tube 829
The chamber openings 824 formed by are arranged around the circle and are directed obliquely and inward with respect to the center line passing through the circle. Single electrode (not shown) if required
Can be extended forward from the holder 831.

FIG. 35 depicts a small scale multi-hole nozzle 60 connected to, for example, one tube 29 of the multi-tube assembly of FIG. 11, for example, in fluid communication with each chamber opening 324. .. The small scale multi-hole nozzle 60 has a frustoconical outwardly extending passage 62 terminating in a plurality of small scale holes 64 arranged around a circle 65. The use of small scale holes 64 produces a smaller spray stream, which enhances the directional control of the spray stream used in powder coating.

As shown in FIG. 36, for example, a small scale slit nozzle 70 is attached to the tube 29 of, for example, the multi-tube assembly of FIG. 11 in fluid communication with each chamber opening 324. The small scale slit nozzle 70
It has an elongated, hollow portion 72 that terminates in an elongated slit 74.

A small scale perforated nozzle 60 and a small scale slit nozzle 70 are shown attached to the ends of the tubes 29 of the multi-tube assembly and are further illustrated in the embodiment of the invention for the perforated nozzle 25. It will be appreciated that the principles apply.

FIG. 37 and FIG. 38 show the gas from the gun 18
Figure 2 illustrates another aspect of the invention in which a powder mixture is sprayed in pulses. According to this aspect of the invention, a pulse generator 7 is applied to the solenoid valve SV that controls the air flow from the compressor 20 to force the gas-powder mixture out of the hopper 12 through the gun 18 and in series pulses therefrom.
6 is electrically connected via a lead wire 77. Regarding the pulse operation of the electrostatic powder coating apparatus, the patent publication JP-A-62 (1987) -mentioned earlier in this application.
No. 11,574.

FIG. 38 shows two example waveforms 78, 79 used to control the pulsing of the spray flow out of the gun 18. By selecting the number of pulses per unit time, as shown in the above patent publication, the amplitude and duration of the pulses and the amount of powder sprayed out of the gun 18 are easily adjusted and accurate. Controlled by. Perhaps most importantly, the air pressure to the pump 14 is increased to ensure a constant injection volume and velocity per unit time. This ensures better uniformity in the coating. In addition, pulsing the spray stream makes spray coating easier when thin coating thickness is required.

39-42 show the electrostatic charging of particles within the gas-powder mixture within the gun 18 of FIG. FIG. 1 shows that the internal charge is used to supplement the external charge via the external electrode 34. Instead, the internal charge would be the only means for electrostatically charging the particles in the gas-powder mixture. Internal charging is particularly advantageous for coating the inner surface of metal containers, where the use of external electrodes tends to create a Faraday cage effect, as explained in the technical background.

FIG. 39 depicts an internal electrode 80 charged by a power source (not shown) and a ground terminal 81 for generating an electrostatic field inside the gun 18. When electrostatically charging the particles of the gas-powder mixture in the gun, it is important to prevent the particles of powder from adhering to either the electrode 80 or the ground terminal 81. FIG. 39 shows compressed air inlet 82 in communication with conduit 83 through hole 84 in the gun. Conduit 8
3 blows air around the electrode 80 to surround the electrode 80 and prevent charged particles from accumulating on it. Another air inlet 85 supplies compressed air into a hollow hood 86 surrounding the outside of the gun. Compressed air from the bar 86 flows radially inward into the gun through a plurality of holes 87 spaced around the gun. The air flow directed inward in the radial direction from the hole 87 hinders the accumulation of charged particles on the ground terminal 81.

FIG. 40 shows an alternative structure for this same aspect of the invention. The inlet 85 is aligned with a single hole 89 in the outer wall of the gun. The hole 89 communicates with an annular hollow space 88 that surrounds the gun along its inner surface. The annular hollow space 88 is formed of a tubular conductive sintered metal 90 connected to electrical ground (not shown). The porosity of the sintered metal 90 allows the air supplied to the inlet 85 to escape from the gun, thereby impeding the accumulation of particles thereon.

As indicated above, electrostatic charging within the gun is used by itself or in combination with external charging. When used alone, it is desirable to use multiple charging chambers to increase or maximize the number of charged particles in a gas-powder mixture. For example, FIG.
a, 80b and ground terminals 81a, 81b installed therein
Shows an alternative embodiment of the present invention including two charging chambers 22a, 22b each connected in series with each other. Multi-hole nozzle 2
5 is arranged at the downstream end of the second chamber 22.

Alternatively, many chambers 22 are connected in parallel to eliminate the pressure loss associated with series connection. The use of parallel connected chambers when not increasing the charge on the powder will increase the flow rate of the powder sprayed from the gun.

FIG. 42 shows another modification of the present invention including a large number of charging chambers. According to this embodiment, the upstream chamber 22a utilizes triboelectric charging rather than an applied DC electrostatic field. The tribo or triboelectric charge is then a serpentine plastic or Teflon tube 92 which preferably contacts the inner surface of the chamber 22 which is then connected to a ground terminal 93.
It is generated by passing powder particles through. The powder particles are triboelectrically charged by making many frictional contacts with the tube 92. For this embodiment, it is important to ensure that the second charging chamber 226 charges the powder with the same polarity as the triboelectric charging chamber 22a.

From the above general description of the invention and the above detailed description of the preferred embodiments, those skilled in the art will readily appreciate the various modifications that are susceptible to the invention. Therefore, we wish to be limited only by the scope of the appended claims and their equivalents.

[Brief description of drawings]

FIG. 1 is a schematic view showing an electrostatic powder spray coating apparatus according to an embodiment of the present invention in a longitudinal cross section.

2 is a cross-sectional view taken along line 2-2 of FIG.

3 is a cross-sectional view along line 3-3 of FIG. 1 showing four separate spray streams of gas-powder mixture as they progress toward the object to be coated.

FIG. 4 is a sectional view taken along line 4-4 of FIG. 1, which is also shown.

5 is a schematic view showing a second embodiment of the electrostatic powder spray coating apparatus depicted in FIG. 1 in a longitudinal cross section.

6 is a cross-sectional view taken along line 6-6 of FIG. 5, showing the coating pattern produced by the four spray streams of the gas-powder mixture shown in FIG.

FIG. 7 shows a third embodiment of the electrostatic powder spray coating device depicted in FIG. 1, in which the device is equipped with a central electrode and a multi-hole nozzle with holes arranged around the circle,
FIG. 3 is the same cross section as in FIG. 2.

FIG. 8 illustrates a spray pattern produced by the nozzle shown in FIG. 7 as the spray stream travels progressively further away from the nozzle as it travels toward the object to be coated.

FIG. 9 also shows a farther spray pattern.

FIG. 10 also shows an even further distant spray pattern.

11 shows a fourth embodiment of the electrostatic powder spray coating apparatus of the present invention having a multi-tube spray hole assembly, and is the same schematic longitudinal view as FIG.

12 is a cross-sectional view taken along line 12-12 of FIG.

FIG. 13 illustrates multiple spray streams of a gas-powder mixture produced by the multi-tube spray hole assembly shown in FIG. 11 as the spray streams travel toward an object to be coated. 13 is a cross-sectional view taken along line 13-13 of FIG.

FIG. 14 is a sectional view taken along line 14-14 of FIG.

FIG. 15 is an enlarged cross-sectional schematic view of another alternative embodiment of the electrostatic powder spray coating apparatus of the present invention in which a wire is used to create an electric field that charges static electricity to the particles.

16 shows a variation of the embodiment shown in FIG. 15 in which the wire is insulated along its length except for a plurality of spaced uncovered regions, FIG. 2 is an enlarged cross-sectional view similar to FIG.

FIG. 17 is another variation of the embodiment shown in FIG. 15 with angled slits exposing a plurality of spaced uncovered areas toward the wire coated product. FIG. 17 is an enlarged cross-sectional view shown and similar to FIGS. 15 and 16.

18 is a cross-sectional view taken along line 18-18 of FIG.

FIG. 19 shows a fifth embodiment of the invention of another variation of the multi-tube assembly, and is the same longitudinal schematic view as in FIG. 11.

FIG. 20 depicts two spray patterns formed by the multi-tube assembly shown in FIG.
FIG. 20 is a cross-sectional view taken along line 20-20 of 9.

FIG. 21 shows a fifth embodiment of the present invention in yet another modification of the multi-tube assembly, and is a schematic longitudinal view similar to FIGS. 11 and 19.

22 is a cross-sectional view taken along line 22-22 of FIG.

FIG. 23 depicts a spray pattern formed by the multi-tube assembly shown in FIGS. 21 and 22.

FIG. 24 is a perspective view depicting an application of the present invention in which the tubes of a multi-tube assembly are arranged in a straight line.

25 is an elevational or side view of FIG. 24 taken along the direction indicated by arrow 25 in FIG. 24. A shows two graphs illustrating another embodiment of the invention in which an electrostatic field is pulsed during the spraying of powder particles.

FIG. 26 is a seventh embodiment of the present invention which is a further modified example of the multi-hole nozzle in which the spray holes are arranged around the circle, are formed obliquely with respect to the center line of the circle, and are directed outward. It is a longitudinal schematic diagram showing an example.

27 is a cross-sectional view taken along line 27-27 of FIG.

28 is a perspective view showing the powder spray flow and deposition pattern produced by the nozzle shown in FIGS. 26 and 27. FIG.

29 is a longitudinal cross-sectional schematic view showing another embodiment of the present invention, spray coating the inner surface of a can using the nozzle shown in FIGS. 26 and 27. FIG.

30 is a cross-sectional view taken along the line 30-30 of FIG.

FIG. 31 is formed when the spray holes are oriented more circumferentially with respect to the centerline of the circle and are angled, but the perforated nozzle shown in FIGS. 26 and 27 is changed to be oriented inward. Figure 3 shows a perspective view of the spray flow and the deposition pattern applied.

32 shows a spray pattern formed by the multi-hole nozzle shown in FIG. 31, taken along line 32-32 of FIG.

FIG. 33 shows an eighth embodiment of the present invention, which is a further variation of the multi-tube assembly, in which the tubes are arranged circumferentially about the center line of the circle, formed obliquely and oriented inward. FIG. 3 is an enlarged longitudinal schematic view showing FIG.

34 is a cross-sectional view taken along the line 34-34 of FIG. 33.

FIG. 35 is a perspective view of a small scale multi-hole nozzle attached to the spray holes of either the multi-hole nozzle or the multi-tube assembly.

FIG. 36 is a perspective view of a small scale slit nozzle attached to a spray hole of a multi-hole nozzle or multi-tube assembly.

FIG. 37 shows an electrostatic powder spray coating apparatus according to the present invention in which the apparatus is equipped with a pulse generator for pulsing the gas-powder mixture flow from the gun.

FIG. 38 shows pulse waveforms used to control the operation of the electrostatic powder spray coating apparatus shown in FIG.

FIG. 39 is a schematic longitudinal view showing an electrostatic powder spray coating apparatus according to the present invention in which particles in a gas-powder mixture are electrostatically charged in a gun chamber.

40 shows another variant of the electrostatic powder spray coating device according to the invention, in which the particles are electrostatically charged in the gun, and is a longitudinal schematic view similar to FIG. 39.

FIG. 41 is a schematic longitudinal cross-section showing an electrostatic powder spray coating apparatus according to the present invention, in which the apparatus includes two chambers connected in series.

42 shows another variation of the embodiment shown in FIG. 41 and is a schematic longitudinal cross-section similar to FIG. 41.

[Explanation of symbols]

 10 Electrostatic powder spray coating equipment

Continuation of the front page (72) Inventor Isao Yabuuchi 108 Idogani Nakamachi, Minami-ku, Yokohama-shi, Kanagawa Sanheim Idogaya 101

Claims (35)

[Claims] 1. Spraying a pressurized mixture of gas and powder particles from a spray gun with a plurality of separate spray streams, wherein the powder particles contained in the spray stream are disposed on a plurality of exterior surfaces of the gun. An electrostatic powder coating method comprising the steps of applying static electricity through electrodes. 2. The method of claim 1, further comprising the step of causing the plurality of spray streams to be sprayed in pulses. 3. The method of claim 1, wherein at least one external electrode is associated with the spray stream. 4. The electrodes generate an electrostatic field when operably connected to a power source, and the step of applying the electric charge further comprises the step of pulsing the electrostatic field during the spraying step. The method of claim 1. 5. The method of claim 4, further comprising the step of pulsing in a predetermined timing sequence, thereby producing a desired coating effect. 6. Spraying a pressurized mixture of gas and powder particles from a spray gun with a plurality of separate spray streams, wherein the particles contained in the mixture are connected to a DC power source during the spraying process. Electrostatic powder is applied through an electrostatic field formed by the electrodes, and the electrostatic field is pulsed during the spraying step. 7. The step of applying a charge is performed through a plurality of electrodes located outside the gun, and the spraying step further comprises dividing the mixture into a plurality of separate spray streams. 7. The method of claim 6 configured. 8. A plurality of separate spray streams spray outwardly a pressurized mixture of gas and powder particles from a spray gun to impart static electricity to the particles contained in the mixture within the interior of the gun. An electrostatic powder coating method for an inner surface of a container, which comprises: each step of generating a plurality of spray streams to which static electricity is applied so as to uniformly coat the inner surface of the container. 9. A plurality of separate spray streams spray outwardly a pressurized mixture of gas and powder particles from a spray gun, wherein the powder particles in the spray stream are located outside the gun. Electrostatic powder coating on the inner surface of the container, wherein the electrostatic powder is applied through a plurality of electrodes, and the electrostatic field associated with each of the electrodes is pulsed during the spraying process. Method. 10. A pressurized mixture of gas and powder particles is outwardly sprayed along a flow path from a spray gun toward the inner surface of the container with a plurality of separate spray streams, and said inner surface is directed toward said inner surface. Inner surface of the container, characterized in that it comprises the steps of allowing the mixture to be sprayed in a pulsed state, thereby coating the inner surface more evenly with minimal offset inside the container. Electrostatic powder coating method. 11. The method of claim 10 wherein said spraying step further comprises the step of dividing said mixture into a plurality of separate spray streams across a plurality of corresponding flow paths. 12. A pressurized mixture of gas and powder particles is sprayed outward from a spray gun, and the particles contained in the mixture are electrostatically charged when connected to a power source during the spraying process. A method for coating electrostatic powder on the inner surface of a container, which comprises each step of applying static electricity by an electrode for generating the electric field and pulsing the electrostatic field during the spraying step. 13. The step of imparting electric charge is accomplished with a plurality of electrodes disposed external to the gun, and the spraying step is further divided into a plurality of separate spray streams across corresponding flow paths. 13. The method of claim 12, comprising dividing the mixture. 14. A plurality of separate spray streams spraying a pressurized mixture of gas and powder particles outward from a spray gun to impart static electricity to the particles contained in the mixture to generate static electricity. It consists of steps to generate a given plurality of spray streams, where the spray streams are arranged around a circumference of a circle coaxial with the front end of the gun, the spray streams being oblique to the circle. A method for electrostatic powder coating of an inner surface of a container, characterized in that the inner surface of the container is uniformly coated by a flow path that is directed to the outside and is guided outward from a central axis line passing through the center of the circle. 15. The method of claim 14 further comprising the step of causing the spray stream to be sprayed from the gun in a pulsed state. 16. A gun having at least one internal chamber having a plurality of chamber openings open to the atmosphere, and introducing a pressurized mixture of gas and powder particles into the chamber and providing a plurality of separate chambers. Means for spraying the mixture outwardly from the gun through the opening in a spray stream, and means for imparting static electricity to the particles contained in the spray stream including a plurality of electrodes disposed outside the gun. An electrostatic powder coating device comprising: 17. The apparatus of claim 16 wherein the gun further comprises a multi-hole nozzle having a plurality of holes defining a plurality of chamber openings. 18. The apparatus of claim 16 wherein the gun further comprises a multi-tube spray hole assembly having a tube defining a plurality of chamber openings. 19. The apparatus of claim 16, wherein at least one electrode is associated with each of said spray streams. 20. The device of claim 16, wherein the electrode comprises silicon carbide and has a resistance of about 10 ⁶ ohm centimeters. 21. The plurality of chamber openings are arranged in a straight line, and the means for imparting charge is further arranged outside the gun and oriented parallel to the arranged chamber openings. 18. The device of claim 16, wherein the device acts as an electrode. 22. The chamber openings are further arranged in a straight line, and the means for imparting charge further covers the wire partially and at least one selected portion. 17. The device of claim 16, wherein the device comprises an insulating layer that is left untouched, the at least one selected portion acting as an electrode. 23. The apparatus of claim 16, wherein the chamber openings are arranged in a plurality of parallel staggered rows. 24. The apparatus of claim 16 further comprising means for pulsing the mixture to be sprayed outward from the gun. 25. Means for connecting a power supply to the electrode to generate an electrostatic field for imparting static electricity to the particles contained in the spray stream; and the electrostatic field during spraying. 17. The apparatus of claim 16 comprising means for pulsing the. 26. A gun having at least one internal chamber having at least one chamber opening to the atmosphere, and introducing a pressurized mixture of gas and powder particles into the chamber, and Means for spraying the mixture outwardly from the gun through the chamber opening; means for imparting static electricity to the particles contained in the mixture by electrodes that generate an electrostatic field when connected to a power supply; An electrostatic powder coating device comprising means for causing the mixture to be sprayed from a gun and means for pulsing the electrostatic field while the mixture is being sprayed. .. 27. The means for imparting electrostatic charge further comprises a plurality of electrodes external to the gun, and the means for introducing and spraying further comprises: admixing the mixture into a plurality of separate spray streams. 17. The apparatus of claim 16, comprising splitting means, each of said streams being associated with at least one of said outer electrodes. 28. A gun arranged around a circumference of a circle coaxial with the gun and having at least one internal chamber having a plurality of chamber openings open to the atmosphere, and a pressurized gas and powder particles. Means for introducing the mixture into the chamber and spraying the mixture from the gun through the chamber opening outward in multiple spray streams, and having electrodes on the outside of the gun for the particles in the spray stream. An electrostatic powder coating apparatus comprising a means for applying static electricity. 29. The chamber opening is directed obliquely and is guided outward with respect to a central axis passing through the circle.
Equipment. 30. The apparatus of claim 28, wherein the aperture is oriented diagonally and is directed inward with respect to a central axis passing through the circle. 31. The apparatus of claim 28, further comprising means for causing the mixture to be sprayed from the gun in pulses. 32. A gun, at least one of which has at least two internal chambers with at least two chamber openings open to the atmosphere, and a pressurized gas and powder particles. Introduced mixture into the room,
And means for spraying the mixture outwardly from the gun through the at least two chamber openings, and means disposed in each of the internal chambers for imparting static electricity to the particles contained in the mixture. An electrostatic powder coating device characterized in that 33. The apparatus of claim 32, wherein the at least two interior chambers are connected in series. 34. The means for applying static electricity further comprises at least one electrode disposed in the room and means for applying static electricity by friction disposed in at least one of the rooms. 33. The apparatus of claim 32 which is 35. The apparatus of claim 32, further comprising means for causing the mixture to be sprayed from the gun in pulses.