JP2006110448A - Electrostatic coating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an electrostatic coating apparatus based on an indirect charging system with an external electrode arranged closely to a spray head. <P>SOLUTION: The tip of the external electrode 3 has different shapes on the side 3a facing a work W and on the side 3b facing the rotating spray head 2: the side 3a facing the work W has such a shape as to facilitate concentration of the electric field, while the side 3b facing the rotating spray head 2 has such a shape as to soften the electric field. More specifically, the side 3a facing the work W has a shape sharpened toward the tip or an edge shape of an acute angle. The side 3b facing the rotating spray head 2 typically has a spherical-surface shape. When the side 3b facing the rotating spray head 2 is set to be flat, the edges of the flat surface are cut to form a curved surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an indirect charging type electrostatic coating apparatus provided with an external electrode.

  The electrostatic coating apparatus can be classified into a direct charging system and an indirect charging system. Both of these systems include a bell type having a spray head including a rotary atomizing head and a spray head including a spray nozzle. It is known as a gun type.

  A representative example of the indirect charging type electrostatic coating apparatus is an electrostatic coating apparatus including an external electrode. Patent document 1 is disclosing the typical example of the electrostatic coating apparatus provided with the external electrode. That is, this type of electrostatic coating apparatus has an external electrode around the spray head, applies a high voltage to the external electrode, and forms an electric field with the grounded object, thereby The paint particles discharged from the spray head are charged and applied to the object.

This external electrode type electrostatic coating apparatus is applied to a conductive paint such as a water-based paint, and the spray head is substantially maintained at a ground potential by the conductive paint flowing through the paint supply passage.
JP-A 61-78452

  The indirect charging type electrostatic coating apparatus has a problem that the diameter of the apparatus inevitably increases because an external electrode exists around the spray head. The diameter of the apparatus, that is, the separation distance between the spray head and the external electrode is substantially defined by the magnitude of the voltage applied to the external electrode. That is, the external electrode not only generates a discharge with the object to be coated, but also generates a discharge with the spray head, so if the separation distance between the external electrode and the spray head is too small, The possibility that abnormal electric discharge (streamer electric discharge) occurs between the spraying head and the electric field becomes unstable is increased. Of course, when an abnormal discharge occurs, the coating efficiency decreases, and the spray head and the like are contaminated.

  A conventional external electrode is composed of a thin metal wire having a tip of about 0.2 to 1.0 mm in diameter, and those skilled in the art call it a “discharge needle”. The relationship between the corona discharge area and the streamer discharge area relating to this discharge needle is shown in FIG. The horizontal axis in FIG. 1 is the separation distance between the discharge needle and the spray head, and the separation distance increases toward the right. The vertical axis in FIG. 1 is the needle tip voltage of the discharge needle, and the voltage increases as it goes upward. According to the data of FIG. 1, for example, when the tip voltage of the discharge needle is −80 kV, unless the distance between the discharge needle and the spray head is about 130 mm or more, the streamer discharge is generated between the discharge needle and the spray head. It turns out that will occur.

  Regardless of whether the electrostatic coating apparatus is a direct charging system or an indirect charging system, it is preferable that the electrostatic coating apparatus be small in size when coating a small object or an object having a complicated shape surface.

  An object of the present invention is to provide an electrostatic coating apparatus in which an external electrode can be disposed close to a spraying head even when the same voltage as that of the related art is applied to the external electrode.

  Another object of the present invention is to provide an indirect charging type electrostatic coating apparatus capable of improving the coating efficiency.

  The inventor of the present application has come up with the present invention by paying attention to the tip shape of the external electrode. FIG. 2 shows the experimental results showing the relationship between the corona discharge region and the streamer discharge region when the tip shape of the external electrode is made spherical or hemispherical and the curved surface faces the spray head. The horizontal axis in FIG. 2 is the separation distance between the external electrode and the spray head, and the separation distance increases toward the right as in FIG. The vertical axis in FIG. 2 is the tip voltage of the external electrode, and the voltage increases as it goes upward. As can be understood from comparison with FIG. 1 (conventional discharge needle) described above, when the tip of the external electrode is configured with a curved surface, the corona discharge region is enlarged. For example, when the spherical tip of the external electrode is −80 kV, It can be seen that even if the separation distance between the electrode and the spray head is 50 mm, for example, it does not enter the streamer discharge region.

According to the present invention, in order to achieve the above-mentioned problem,
An electrostatic coating device provided with external electrodes around the spray head,
Provided is an electrostatic coating apparatus characterized in that the tip shape of the external electrode is formed into a shape in which the side facing the work is likely to concentrate an electric field, and the side facing the spray head is formed into a shape in which the electric field is easily relaxed. The

  According to this, as the tip shape of the external electrode, the side facing the spray head is formed in a shape that is easy to relax the electric field, so the corona discharge between the spray head and the spray head is relatively weak compared to the conventional one. Since the external electrode can be installed close to the spray head, the indirect charging type electrostatic coating apparatus can be downsized.

  Further, since the value of the current flowing between the external electrode and the spray head between the two is smaller than that in the prior art, the voltage at the tip of the external electrode increases accordingly. In addition, the tip of the external electrode is shaped so that the electric field is concentrated on the side facing the workpiece, so that a strong electric field can be created between the external electrode and the workpiece, thereby increasing the coating particle application efficiency. Can be increased.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 3 shows an electrostatic coating apparatus provided with the external electrode of the embodiment. The illustrated electrostatic coating apparatus 1 is a bell-type coating apparatus as an example, but may be a gun-type coating apparatus. The electrostatic coating apparatus 1 has a plurality of external electrodes 3 disposed around a rotary atomizing head 2 that rotates at a high speed, and a high voltage is supplied to the external electrodes 3 from a high voltage generator 4. The tip of the external electrode 3 has a different shape on the side 3a facing the workpiece W and the side 3b facing the rotary atomizing head 2, and the side 3a facing the workpiece W is formed in a shape that easily concentrates the electric field. On the other hand, the side 3b facing the rotary atomizing head 2 is formed in a shape that can easily relax the electric field.

  FIG. 4 shows an example of the tip shape of the external electrode 3. In the example of FIG. 4, the side 3a facing the workpiece W is made of a sharp metal tapering toward the workpiece W or a thin metal wire having a diameter of about 0.2 to 1.0 mm as in the conventional case. The side 3b facing is made in a curved surface shape. A typical example of the curved surface shape on the side 3b facing the rotary atomizing head 2 is a spherical surface.

  FIG. 5 shows another example of the tip shape of the external electrode 3. In the example of FIG. 5, the side 3a facing the workpiece W is formed in an acute angular shape, and the side 3b facing the rotary atomizing head 2 is constituted by a plane, and each edge of this plane has an edge. It consists of a curved surface that is rounded down.

  In this way, the tip shape of the external electrode 3 is made different between the side 3a facing the work W and the side 3b facing the rotary atomizing head 2, and the side 3a facing the work W is formed into a shape that easily concentrates the electric field. By forming the side 3b facing the rotary atomizing head 2 into a shape in which the electric field is difficult to concentrate, in other words, a shape in which the electric field is easily relaxed, the rotary atomizing head 2 It is possible to dispose the external electrode 3 with the external electrode 3 close to the rotary atomizing head 2 by making it difficult for electric discharge to occur between the

  That is, conventionally, as described above, the separation distance between the spray head and the external electrode is substantially defined by the voltage applied to the external electrode. However, as in the present invention, the tip shape of the external electrode 3 is defined. As a result, the distance between the rotary atomizing head 2 and the external electrode is determined not only by the voltage applied to the external electrode but also by the shape of the side 3b facing the rotary atomizing head 2 as another factor. In addition, by making the shape of the side 3b facing the rotary atomizing head 2 into a shape that can easily relax the electric field, the distance between the rotary atomizing head 2 and the external electrode can be set smaller than the conventional distance. . Of course, the extent to which the external electrode 3 can be brought closer to the rotary atomizing head 2 must satisfy the condition that an appropriate corona discharge is generated between the external electrode 3 and the rotary atomizing head 2. Needless to say, it must be determined by experiment.

  FIG. 6 shows a conventional electrostatic coating apparatus 10 for comparison. The configuration of this conventional electrostatic coating apparatus 10 uses a discharge needle 11 as an external electrode, and the other configuration is the same as that of the electrostatic coating apparatus 1 of the embodiment of FIG.

  In the conventional example shown in FIG. 6, the discharge needle 11 and the edge of the rotary atomizing head 2 and the separation distance L1 are set to 85 mm, and a high voltage of −80 kV is supplied to the discharge needle 11 from the high voltage generator 4. Suppose that 240 μA flows toward the rotary atomizing head 2 due to corona discharge between the discharge needle 11 and the rotary atomizing head 2. This current is substantially grounded through the paint supply passage 6 for supplying paint to the rotary atomizing head 2. Therefore, the voltage at the tip of the discharge needle 11 is substantially close to −80 kV.

  On the other hand, in the electrostatic coating machine 1 of the embodiment of FIG. 3, the side 3b facing the rotary atomizing head 2 of the external electrode 3 is formed in a shape that is easy to relax the electric field. When the separation distance L2 from the atomizing head 2 is set to be the same as the separation distance L1 between the discharge needle 11 and the rotary atomizing head 2 described above, corona discharge between the external electrode 3 and the rotary atomizing head 2 is performed. Therefore, the current flowing between the external electrode 3 and the rotary atomizing head 2 has a slight current value of, for example, about 80 μA, and the voltage at the tip of the external electrode 3 increases accordingly. On the other hand, since the side 3a of the external electrode 3 facing the workpiece W is formed in a shape that easily concentrates the electric field, a strong corona discharge occurs between the external electrode 3 and the external electrode 3 between the external electrode 3 and the workpiece W. The electric field becomes stronger, and this increases the charging effect on the paint particles, thereby increasing the coating efficiency.

  If the corona discharge between the external electrode 3 and the rotary atomizing head 2 is weakened, from a different point of view, the possibility of abnormal discharge between the two becomes low. Since the diameter of the electrostatic coating apparatus 1 can be reduced by being placed close to the chemical head 2, the electrostatic coating apparatus 1 can be downsized.

  The above description has been given by taking a bell-type electrostatic coating apparatus having a rotary atomizing head as an example, but the same applies to a gun-type electrostatic coating apparatus having a spray head including a spray. Needless to say, the application has substantially the same effect as the bell type.

It is a figure for demonstrating the relationship between the corona discharge area | region and the streamer discharge area | region in the conventional electrostatic coating apparatus of the indirect charging system which uses a discharge needle as an external electrode. It is a figure for demonstrating the relationship between the corona discharge area and the streamer discharge area in the electrostatic coating apparatus of the indirect charging system of this invention. It is a schematic block diagram of the electrostatic coating apparatus of this invention. It is a figure which shows an example of the front-end | tip shape of an external electrode. It is a figure which shows the other example of the front-end | tip shape of an external electrode. It is a figure for demonstrating the structure and the effect | action of the conventional electrostatic coating apparatus of an indirect charging system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Indirect charging type electrostatic coating apparatus 2 Rotating atomizing head 3 External electrode 3a Side facing external electrode workpiece 3b Side facing external atomizing rotary atomizing head 4 High voltage generator W Workpiece

Claims (7)

An electrostatic coating device provided with external electrodes around the spray head,
The electrostatic electrode having an external electrode, wherein the tip of the external electrode is formed in a shape in which the side facing the workpiece is likely to concentrate an electric field, and the side facing the spray head is formed in a shape in which the electric field is easily relaxed. Painting equipment. The electrostatic coating apparatus according to claim 1, wherein the spray head includes a rotary atomizing head. The electrostatic coating apparatus according to claim 1, wherein the spray head includes a spray nozzle. The electrostatic coating apparatus according to any one of claims 1 to 3, wherein a side of the external electrode facing the workpiece is shaped into a shape including an acute edge. The electrostatic coating apparatus according to any one of claims 1 to 3, wherein a side of the external electrode facing the workpiece in a tip shape is formed in a shape that is tapered toward the tip. The electrostatic coating apparatus according to claim 4 or 5, wherein a side of the external electrode facing the spray head in a tip shape is formed in a curved surface shape. 6. The electrostatic coating apparatus according to claim 4, wherein a side of the external electrode facing the spray head having a tip shape is a flat surface, and each edge of the flat surface is formed in a rounded shape.

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