JPS6114871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for applying a powder coating to an object to be coated, such as a metal material. In recent years, due to environmental concerns, coatings using paints that do not contain solvents have been put into practical use in various forms. One of these is so-called powder coating, and electrostatic powder spraying has been most commonly used as a coating method.

In the electrostatic powder spraying method, powder paint is mixed with air to make it fluid, and then it is jetted out from the tip of a gun using compressed air. By charging the coating material with an electric charge, uniform coating can be efficiently applied to the grounded coating. The biggest advantage of this method is that it can be applied regardless of the shape of the object, and it is also easy to use because it is becoming popular.
However, there are many limitations as follows.

First, since the powder is sprayed using the force of compressed air, the powder that reaches the object still has some velocity, and a velocity component that differs from the direction of the electrostatic attraction force reduces the powder coating efficiency. In addition, the compressed air flow blows off the powder that has been applied to the object again, resulting in a decrease in the application efficiency. As a result, the primary coating efficiency by electrostatic powder spraying is only 80% at most, and it is difficult to apply thick films. Furthermore, when a large volume of coating is required, the number of electrostatic guns must be increased to increase the amount of spraying. An even bigger drawback is the increased amount of dust generated. The generated dust can be collected and collected, but if the size of the equipment or the reuse rate of the collected powder is taken into consideration, this will add an economic disadvantage to expensive powder coating.

The present inventors conducted various research into advantageous powder coating apparatuses with the intention of overcoming the above-mentioned disadvantages, and as a result, they came up with the present apparatus. The basic premise of the invention is that there is no necessity to use compressed air unless painting in all positions is required, and it is based on the idea that it is most natural to supply paint to the object to be coated in the direction of gravity.

That is, the gist of the present invention is that a grounded belt conveyor for conveying powder is arranged below a hopper for supplying powder, and the powder that falls from the hopper is moved between the two so that it forms a natural mountain of rest on the conveyor. A free space is provided between the two, and a powder conveyance amount adjusting plate is provided above the conveyor surface and below the hopper. Then, at the end of the conveyor, an AC high voltage is applied to vibrate and disperse the conveyed powder. The additional strip electrode is stretched horizontally and almost perpendicular to the direction of conveyor movement, and a DC high-voltage electrode for charging powder particles is placed at an intermediate position between the dispersed and falling powder and the object to be coated. There is provided a powder coating apparatus characterized by being provided with.

The apparatus of the present invention will be explained in detail below based on the drawings. FIG. 1 is a perspective view schematically showing one embodiment of the apparatus of the present invention, in which a hopper 1 for storing powder for coating has a lower part open above a belt conveyor 2 with an appropriate space in between. It is set up so that
Further, a comb plate 4 is provided below the hopper 1 so as to face the surface of the conveyor 2. The quantity adjusting plate may be a plate having a flat end so as to form a gap with the conveyor, but here a comb plate is used which is advantageous for maintaining the gap. Further, at the end of the conveyor 2, a strip-shaped AC voltage electrode 5 is stretched horizontally and substantially perpendicular to the direction in which the conveyor 2 moves. Furthermore, a DC high voltage electrode 8 is provided between the electrode 5 and the object 7 to be coated to charge the powder 6 that is dispersed and falls by the electrode 5. The reason for providing a free space under the hopper 1 is that if the falling powder from the hopper 1 is immediately connected to the combs of the comb plate 4, the narrow space at the bottom of the hopper 1 will not be blocked by the collection of powder. This causes unevenness in the flow of the powder and makes it difficult to stably adjust the quantity. Therefore, the powder is first allowed to fall without resistance to form a natural mountain 3 on the belt conveyor 2 according to the angle of repose of the powder. This is to enable stable amount adjustment by cutting out a certain amount of powder from the pile 3 in the direction of movement of the conveyor 2 using the combs of the comb plate 4. This method of adjusting the amount of powder conveyed using the comb size adjustment plate above the belt conveyor 2 is based on the cross-sectional area of the gap between the weight adjustment plate and the conveyor and the conveyor, regardless of the physical properties of the powder such as fluidity. This method has the advantage that the amount of powder to be cut out is determined only by the geometric quantity of the product of velocities. Next, at the end of the conveyor, an AC high voltage is applied to disperse the powder by vibrating the powder by an AC electric field formed between the AC high voltage electrode 5 and the grounded belt conveyor 2. , which applies the principle of applying a Coulomb repulsion force between powder unit particles to disperse them, and erasing the natural charging state of the powder group by the action of an AC electric field to facilitate the next high voltage DC charging. be.
Naturally, this electrode 5 acts as an electric doctor knife and can completely brush off the powder carried by the conveyor 2. Moreover, since air is not used, even if the powder is dispersed, no dust is scattered around. Although the AC voltage electrode 5 may not be coated for some purposes, it is safe and convenient to use a commercially available coated wire.

The powder 6 dispersed as described above falls in the direction of gravity, and during the fall passes around the electrode 8 to which a high DC voltage is applied. The air around this electrode 8
The powder 6 is ionized by the corona discharge between the powder 6 and the grounded workpiece 7, and as a result, the powder 6 passing around the electrode receives an electric charge from the air and is charged to a high voltage according to the polarity of the electrode 8. At this time, in the device of the present invention, since the powder is dispersed and de-energized by AC high voltage in advance, charging by DC is effectively realized, and as a result, the fallen and charged powder 6 is removed from the grounded coating material. It is strongly attracted to the object 7 and enables uniform and gap-free powder coating. Note that the DC high voltage electrode 8 preferably has a shape with a sharp tip, such as a needle, in order to ensure corona discharge. The number of electrodes 8 is appropriately set according to the coating width, but one electrode is sufficient for widths up to 300 mm.

Further, it goes without saying that the apparatus of the present invention can be applied to the object 7 to be coated whether or not it is heated.

The various parts and mechanisms constituting the present invention are as described above, and by organically combining these parts, the present invention has made it possible to perform powder coating with extremely high efficiency and with little dust generation. , the effects brought about are as follows.

First of all, the quality of powder coating depends on whether the powder can be transported uniformly without gathering or clogging, and in this regard, the device of the present invention has a free space between the hopper and the conveyor. I solved this problem. In addition, since the device of the present invention employs a pure geometric mechanism as a means of quantifying the amount of powder conveyed, the quantification is not indirect, as is the case with conventional methods (vibration method, ejector method, etc.). Since it can be defined by the product of the cross-sectional area of the gap between the adjustment plate and the conveyor and the conveyor speed, it is possible to accurately design coating equipment for various scales, regardless of the type or physical properties of the powder. Furthermore, although it has not been previously possible to attach an AC high voltage dispersion mechanism to the end of the conveyor as in the present invention, experiments have shown that such a combination is the most effective combination of powder conveyance and dispersion. It became clearer.

As described above, the present invention is a completely new coating device in which various considerations have been made to the combination of various mechanisms, and powder coating is extremely advantageous in the technology of coating objects installed below the coating machine. This can be expanded to.

Next, in order to show the effects of the present invention more specifically,
Examples are given below.

Example According to Figure 1, a belt conveyor made of thin stainless steel plate (200 mm width x 100 mm projected length) was arranged with a free space of 10 mm below 60 powder supply hoppers (lower opening is 160 mm width x 50 mm length). Then, a comb plate (total cross-sectional area of the comb gap with a pitch of 1.5 mm) is placed below the hopper.
100mm ² ). When epoxy powder coating with an average particle size of 30 μm was placed in the hopper and the conveyor was moved at 5 m/min, the amount of powder cut out from the comb plate gaps was 600 g/min. This value is 14 from the calculated value.
It is only % lower.

Next, a polyethylene-coated copper wire (core wire 2 mmφ, coating thickness 1 mm) is stretched horizontally at right angles to the direction of movement of the conveyor at the end of the conveyor, and a hot terminal of a 60 Hz, 5 KV AC power source is connected to this, and the other terminal of the AC power source is connected to the wire. was grounded. After grounding the conveyor belt,
When an AC voltage was applied to the above copper wire, the powder that reached the end of the conveyor was approximately 200mm wide in the width direction of the conveyor.
The particles were evenly distributed and fell in a pattern of 50 to 100 mm in the thickness direction of the falling flow.

Object to be coated: diameter 200mm, wall thickness 5.8mm, length 1m
Prepare a steel pipe of
It was advanced in the axial direction at n. When the above pipe was exposed to powder falling from the end of the conveyor, the film thickness was approximately 250.
A coating film of μ was obtained. Calculating this coating efficiency
80%, and there were three pinholes in the paint film. However, in order to implement the present invention, one needle-shaped electrode was installed 150 mm above the steel pipe toward the steel pipe, a terminal of a 50KV DC power supply was connected to this, the side was grounded, and the steel pipe was also grounded. When DC high pressure was applied, a coating film with a thickness of 300 to 310μ and no pinholes was obtained. The coating efficiency of this is calculated to be 97%, which is very good.

Throughout the above examples, no troubles related to powder transportation occurred. These are all effects obtained by the novel configuration of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the device of the present invention. 1...hopper, 2...belt conveyor, 3...
...Natural haven of powder coating, 4...Comb board, 5...
AC high voltage electrode, 6...Falling powder, 7...Object to be coated, 8...DC high voltage electrode.

Claims (1)

[Claims] 1. A grounded belt conveyor for conveying powder is arranged below the hopper for supplying powder, and a free space is provided between the two so that the powder falling from the hopper forms a natural mountain of rest on the conveyor. A powder conveyance amount adjustment plate is provided above the conveyor surface and below the hopper, and at the end of the conveyor, a strip electrode to which an AC high voltage is applied is installed in the direction of conveyor movement to vibrate and disperse the conveyed powder. A powder that is stretched at right angles and horizontally, and has a DC high voltage electrode for charging powder particles at an intermediate position before the powder that is dispersed and falls reaches the object to be coated. Body painting equipment.