JP4584291B2 - Rotating atomizing electrostatic coating machine and rotating atomizing coating method - Google Patents

Description

  The present invention relates to a rotary atomizing electrostatic coating machine and a rotary atomizing coating method for atomizing a paint by rotating a rotary atomizing head at high speed.

  As a rotary atomizing electrostatic coating machine, paint is supplied from a paint feed tube to the inner bottom of a bell cup-shaped rotary atomizing head that is rotated at a high speed by applying a high voltage, and the paint is applied to the cup of the rotary atomizing head. There is a structure that flows along a surface (coating passage surface) and discharges in a mist form from the tip (see, for example, Patent Document 1). In electrostatic coating using such a coating machine, the particles atomized by the rotary atomizing head are negatively charged and fly to the object to be coated. It adheres well. In order to prevent spraying of the atomized particles around the rotating atomizing head (radial direction) and to adjust the coating pattern for the object to be coated, usually shaping air is blown forward from behind the rotating atomizing head. I try to put it on.

  By the way, in a painting line such as an automobile body, the painting robot described above is held in a painting robot, a plurality of painting robots are installed along the painting line, and the automobile body is conveyed at a predetermined speed on the painting line. In general, a plurality of coating robots are used for overcoating. In such a painting line, in order to reduce the painting cost, it is effective to reduce the number of painting robots and the number of painting robots installed, and to increase the conveyance speed and shorten the painting time. Is also premised on increasing the amount of paint discharged from the rotary atomizing head.

  However, the atomization mechanism of the paint by the rotary atomizing electrostatic coating machine is based on the liquid discharged through the V groove 2 formed at the opening end (paint discharge end) of the rotary atomizing head 1 as shown in FIG. The thread | yarn 3 is parted and atomization (atomization) advances. For this reason, if the amount of paint discharged from the rotary atomizing head 1 is simply increased, the liquid yarn 3 becomes thicker and it becomes difficult to atomize, resulting in deterioration of the coating film quality.

  Therefore, when increasing the amount of paint discharged, it is necessary to increase the rotational speed of the rotary atomizing head at the same time to increase the discharge speed of the paint. However, if the rotational speed of the rotary atomizing head is increased, the liquid yarn 3 A large turbulence occurs, and the dispersion of the particle size distribution of the atomized coating grains increases. In other words, the particle size distribution spreads from the extremely fine particle region with a very small particle size to the coarse particle region with a large particle size, and when there are many particles in the very fine particle region, the coating efficiency decreases, and there are many particles in the coarse particle region. In such a case, the coating quality is deteriorated. Also, if the rotational speed of the rotary atomizing head is increased, the amount of atomized paint particles scattered around the periphery increases, so the pressure of the shaping air must be increased. The amount of rebound increases and the coating efficiency is further reduced.

In addition, for example, in the one described in Patent Document 2, an annular weir (dam part) is provided on the inner surface of a bell cup (rotating atomizing head), the paint is once accumulated therein, and the paint overflows from the annular weir. Is allowed to flow as a uniform thick liquid film to the paint discharge end so that it can be atomized even when the amount of paint supplied is large. However, even in this case, since the liquid yarn 3 (FIG. 4) becomes thicker as the paint supply amount increases, it is necessary to take measures to increase the rotational speed of the rotary atomizing head. , It does not lead to a fundamental solution.
Japanese Patent Laid-Open No. 11-123349 JP 2007-7506 A

  The present invention has been made in view of the above-described technical background, and the problem is that it is possible to increase the amount of paint discharged without causing a decrease in coating efficiency or deterioration in coating film quality, Accordingly, it is an object of the present invention to provide a rotary atomizing electrostatic coating machine and a rotary atomizing electrostatic coating method that greatly contribute to the reduction of coating cost.

  In order to solve the above-described problems, the present invention provides a rotary atomizing electrostatic coating machine and a rotary atomizing electrostatic coating method, in which a rotary atomizing head is rotated at high speed to atomize a paint. An annular paint reservoir is provided on the passage surface, the paint is once accumulated therein, and the paint is discharged from a large number of paint discharge passages provided in the paint reservoir.

In the rotary atomizing electrostatic coating machine and the rotary atomizing electrostatic coating method configured as described above, the centrifugal force acts on the paint accumulated in the paint reservoir, and thus hydraulic pressure is generated in the paint in the paint reservoir, This liquid pressure causes the paint to be discharged from the paint discharge passage at high speed, and the discharge speed of the paint released from the tip of the rotary atomizing head also increases. Therefore, even if the paint discharge amount is increased, it is possible to prevent the liquid yarn discharged from the tip of the rotary atomizing head from becoming thick.
In the following, some aspects of the present invention will be illustrated and described.

(1) Supplying paint from the paint feed tube to the inner bottom of a bell cup-shaped rotary atomizing head rotating at high speed by applying a high voltage, and causing the paint to flow along the inner surface of the cup of the rotary atomizing head In the rotary atomizing electrostatic coating machine that discharges in the form of a mist from its tip, the inner surface of the cup of the rotary atomizing head is composed of an annular wall body that matches the wall surface with a surface orthogonal to the axis of the rotary atomizing head, The rotary atomizing electrostatic system is characterized in that an annular dam portion for collecting paint toward the tip of the rotary atomizing head is provided, and a large number of paint discharge passages are provided in the circumferential direction in the dam portion. Painting machine.

  In the rotary atomizing electrostatic coating machine described in the item (1), liquid pressure is generated in the paint in the dam by the centrifugal force acting on the paint accumulated in the dam, and the paint is discharged from the paint discharge passage by this liquid pressure. The speed of the paint discharged at high speed and discharged from the tip of the rotary atomizing head increases. Therefore, even if the amount of paint discharged is increased, the liquid yarn discharged from the tip of the rotary atomizing head can be set to an appropriate thickness. As a result, atomization proceeds smoothly and a desired coating film quality can be obtained. It becomes like this. In this case, since the rotation speed of the rotary atomizing head is not increased, the dispersion of the particle size distribution of the atomized coating grains can be suppressed, and the coating efficiency is deteriorated because it is not necessary to increase the pressure of the shaping air. Nor.

In addition, since the dam part is made of an annular wall body whose wall surface coincides with the surface perpendicular to the axis of the rotary atomizing head, the overflow of the paint from the dam part is suppressed, and the paint is concentrated on the dam part. Can be stored.

( 2 ) The rotary atomizing electrostatic coating machine according to ( 1 ), characterized in that a paint discharge passage is provided at a connecting portion between the annular wall body and the cup inner surface of the rotary atomizing head.

In the rotary atomizing electrostatic coating machine described in the item (2), the paint is applied to the connection part between the annular wall body and the inner surface of the cup of the rotary atomization head, that is, the part corresponding to the bottom of the dam part and where the centrifugal force acts most. Since the discharge passage is provided, the paint is pushed out from the paint discharge passage at a high pressure, and the discharge speed of the paint is sufficiently increased.

( 3 ) The ratio S / D between the total effective sectional area S of the paint discharge passages provided in the dam part and the diameter D of the pitch circle in which the paint discharge passages are arranged is set to 0.3 or less. The rotary atomizing electrostatic coating machine according to (1) or (2) .

In the present invention, the diameter and number of the paint discharge passages provided in the dam portion are arbitrary, but the ratio S / D between the total effective sectional area S and the pitch circle diameter D is 0.3 as described in ( 3 ). When set to the following, the speed of the paint discharged from the paint discharge passage becomes sufficiently large, and the atomization of the paint is surely promoted.

( 4 ) A paint is supplied from a paint feed tube to the inner bottom of a bell cup-shaped rotary atomizing head rotating at a high speed by applying a high voltage, and the paint flows along the inner surface of the cup of the rotary atomizing head. In the rotary atomizing electrostatic coating method in which the tip is discharged in the form of a mist, an annular dam portion is provided on the inner surface of the cup of the rotary atomizer head, and the coating toward the tip of the rotary atomizer head is temporarily stored in the dam portion. A rotating mist characterized by generating a hydraulic pressure by centrifugal force in the paint accumulated in the dam part and discharging the paint from a large number of paint discharge passages provided in the circumferential direction in the dam part. Electrostatic coating method.

  According to the rotary atomizing electrostatic coating machine and the rotary atomizing electrostatic coating method according to the present invention, it is not necessary to increase the rotational speed of the rotary atomizing head or increase the pressure of the shaping air even if the paint discharge amount is increased. Therefore, desired coating efficiency and coating film quality can be ensured. In addition, since the amount of paint discharged can be increased, the number of painting robots installed in the painting line can be reduced or the conveying speed can be increased, which greatly contributes to the reduction of painting cost.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
1 and 2 show the main structure of a rotary atomizing electrostatic coating machine according to the present invention. The rotary atomizing electrostatic coating machine includes a bell cup-shaped rotary atomizing head 10, a motor 11 that rotationally drives the rotary atomizing head 10, a paint feed tube 12 that supplies paint to the rotary atomizing head 10, and And a high voltage generator (not shown) for generating a high voltage to be applied to the motor 11, and the motor 11, the paint feed tube 12 and the high voltage generator have an attachment portion for the coating robot at the rear end. It is stored in the insulating coating machine main body 14 in a lump. The rotary atomizing electrostatic coating machine also includes a ring member 15 having a plurality of air discharge ports 15a for discharging shaping air from the back of the rotary atomizing head 10 toward the periphery thereof. , Coupled to the front end of the coating machine main body 14.

  Here, the motor 11 is an air motor, and a hollow rotating shaft 16 that is an output shaft thereof is drawn forward from the motor casing 11a. A female screw is formed at the tip of the hollow rotary shaft 16, and the rotary atomizing head 10 is screwed into the tip of the rotary shaft 16. The motor casing 11a is made of metal, and an electrostatic high voltage (as an example, -90 kV) is supplied to the motor casing 11a through an internal cable from the high voltage generator. The paint feed tube 12 is extended through the hollow rotating shaft 16 of the motor 11, and the nozzle portion 12 a at the tip thereof is inserted into the inner bottom portion of the rotary atomizing head 10.

  The inner bottom portion of the rotary atomizing head 10 is partitioned by a disk-shaped hub 20, and the nozzle portion 12 a of the paint feed tube 12 is introduced into a chamber 21 partitioned by the hub 20. The hub 20 includes a center cone 22 that faces the nozzle portion 12a in the center of the back surface thereof, and includes a large number of paint supply passages 23 that are equally distributed in a circumferential direction at a portion connected to the inner surface of the rotary atomizing head 10. ing. The coating material 24 (FIG. 2) supplied from the coating material feed tube 12 to the rotary atomizing head 10 collides with the center cone 22 on the back surface of the hub 20 and diffuses to the periphery, passes through the coating material supply passage 23 and rotates. It is supplied to the cup inner surface (paint passage surface) 25 on the front side of the chemical head 10. At this time, when the rotary atomizing head 10 rotates at a high speed, centrifugal force acts on the paint 24 supplied to the cup inner surface 25, and the paint 24 moves along the cup inner surface 25 to the tip of the rotary atomizing head 10 (paint). It flows toward the discharge end) 26. As described above, a large number of V grooves 2 (FIG. 4) are formed at the paint discharge end 26 of the rotary atomizing head 10, and the paint 24 is discharged through the V grooves 2.

  A dam portion 27 is provided on the cup inner surface 25 of the rotary atomizing head 10 to collect the paint 24 flowing along the cup inner surface 25. Here, the dam portion 27 is composed of an annular wall body 28 whose wall surface coincides with a surface orthogonal to the axis of the rotary atomizing head 10, and the outer periphery of the annular wall body 28 is the inner surface of the cup of the rotary atomizing head 10. 25 is connected. Thus, a large number of paint discharge passages 29 are provided at equal intervals in the circumferential direction at the connection portion of the annular wall 28 with the cup inner surface 25 of the rotary atomizing head 10. As the rotary atomizing head 10 rotates at a high speed, a centrifugal force acts on the paint 24 accumulated in the dam portion 27, and a hydraulic pressure is generated in the paint 24 in the dam 27 by this centrifugal force. The liquid pressure causes the paint 24 to be discharged from the paint discharge passage 29 at a high speed, and the high speed is maintained as it is toward the paint discharge end 26.

  The type of the motor 11 that rotates the rotary atomizing head 10 is arbitrary, and a hydraulic motor, an electric motor, or the like can be used instead of the above-described air motor.

  When performing electrostatic coating using the rotary atomizing electrostatic coating machine, the motor 11 rotates and atomizes while applying an electrostatic high voltage generated by a high voltage generator (not shown) to the casing 11a of the motor 11. The head 10 is rotated at a high speed, and the paint is fed to the rotary atomizing head 10 from the paint supply source through the paint feed tube 12. Then, the paint 24 flows out from the back side of the hub 20 through the paint supply passage 23 to the cup inner surface 25 of the rotary atomizing head 10 and flows along the cup inner surface 25 toward the paint discharge end 26.

  Since the dam part 27 is provided in the middle of the cup inner surface 25, the paint flowing toward the paint discharge end 26 temporarily accumulates in the dam part 27. In this case, since the dam portion 27 is composed of the annular wall body 28 whose wall surface coincides with the surface orthogonal to the axis of the rotary atomizing head 10, the overflow of the paint 24 from the dam portion 27 is suppressed, and the paint 24 accumulates in the dam part 27 intensively. Centrifugal force due to the high-speed rotation of the rotary atomizing head 10 acts on the paint 24 accumulated in the dam part 27, thereby generating a hydraulic pressure in the paint 24 in the dam part 27, and this paint pressure causes the paint to be discharged. The paint 24 is discharged from the passage 29 at a high speed. In this case, since the paint discharge passage 29 is provided at the site where the annular wall 28 and the cup inner surface 25 of the rotary atomizing head 10 are connected, that is, the portion corresponding to the bottom of the dam portion 27 and where the centrifugal force acts most. The coating material 24 is extruded from the coating material discharge passage at a high pressure, the coating material is efficiently accelerated, and the coating material discharge speed becomes sufficiently large. Then, the paint 24 discharged from the paint discharge passage 29 is maintained at a high speed as it is, toward the paint discharge end 26, and discharged at a high speed from the V groove 2 formed in the paint discharge end 26.

  The paint 24 released from the V-groove 2 of the paint discharge end 26 is released in the state of the liquid yarn 3 as shown in FIG. 4, and then divided and atomized (atomized). In the embodiment, since the coating material 24 is discharged from the coating material discharge end 26 at a high speed, the liquid yarn 3 is discharged in a thin state. In other words, even if the amount of paint discharged from the rotary atomizing head 10 is increased, it is possible to suppress the liquid yarn 3 from becoming thick. As a result, the atomization of the paint proceeds smoothly, and the desired coating film quality is obtained. It will be obtained. Further, since there is no need to increase the rotational speed of the rotary atomizing head 10, variation in the particle size distribution of the atomized coating grains is suppressed, and it is not necessary to increase the pressure of the shaping air from the ring member 15, Good coating quality and coating efficiency can be obtained.

  Here, the thickness (diameter) of the liquid yarn 3 necessary to obtain an ideal particle size distribution is roughly determined (as an example, about 30 μm). Further, the amount of paint discharged from the rotary atomizing head 10 is determined by the diameter of the liquid yarn 3 and the paint discharge speed. Therefore, if the target paint discharge amount is determined, it is necessary to obtain the liquid yarn 3 having an ideal thickness. You can see the speed of paint release. On the other hand, the coating material release speed depends on the fluid pressure generated in the coating material 24 accumulated in the dam portion 27. Therefore, by appropriately controlling the fluid pressure, the size of the fluid yarn 3 can be maintained while maintaining the ideal size. A paint discharge amount can be obtained. In this case, the hydraulic pressure generated in the coating material 24 in the dam portion 27 is determined by the mass of the coating material 24 accumulated in the dam portion 27 if the rotational speed of the rotary atomizing head 10 and the diameter of the dam portion 27 are constant. If the height of the dam portion 27 (annular wall 28) is set according to the target paint discharge amount, the paint discharge amount can be increased while ensuring the desired coating film quality and coating efficiency. become.

  In the rotary atomizing electrostatic coating machine shown in FIG. 1, the installation site of the dam part 27 and the number of paint discharge passages 29 provided on the cup inner surface 25 of the rotary atomizing head 10 are changed as shown in Table 1, A rotary atomizing head (outer diameter 70 mm) according to the present invention 1 and the present invention 2 was manufactured. And the atomization experiment which atomizes a coating material by setting the rotation speed of the said rotation atomization head to 25000 rpm was performed, the particle size of the atomization coating grain was measured with the particle size measuring device, and the particle size distribution was calculated | required. For comparison, the same atomization experiment was performed for Comparative Example 1 which is an existing rotary atomizing head in which the dam portion 27 does not exist in the rotary atomizing head 10 shown in FIG.

  Here, Table 1 shows the paint obtained from the diameter and number of paint passages (the paint discharge passage 29 provided in the dam portion 27 in the present inventions 1 and 2 and the paint supply passage 23 provided in the hub 20 in the comparative example 1). The total effective cross-sectional area S (S = caliber × number) of the passage is written together, and the total effective cross-sectional area S and the pitch circle diameter D in which the paint passages are arranged (here, the diameter of the dam portion 27 and the diameter of the hub 20) The ratio (S / D ratio) is also shown. For reference, the corresponding numerical values are also shown as reference examples 1 and 2 for general rotary atomizing heads that are often used for painting automobile bodies.

  Referring to Table 1, the S / D ratios of the present inventions 1 and 2 are 0.3 or less, whereas the S / D ratios of the conventional Comparative Example 1 and Reference Examples 1 and 2 are 1.0 or more. Thus, it can be said that there is a large difference in the S / D ratio between the rotary atomizing head according to the present invention and the conventional rotary atomizing head.

  FIG. 3 shows the results of the atomization experiment described above. In the figure, SMD represents the average particle diameter, and D10, D50, and D90 represent the particle diameters of 10%, 50%, and 90% of the volume cumulative distribution, respectively. From this, in the average particle size SMD and the volume cumulative distributions D10 and D50, although there is not much difference in the particle size between the present inventions 1 and 2 and the comparative example 1, it is clear from the particle size of the volume cumulative distribution D90. In addition, the present invention is smaller than the comparative example. This means that when the rotary atomizing head of the present invention is used, there is less coating in a large particle size region (coarse particle region), and the effect of providing the dam portion 17 is effective. it is obvious. In this case, the structural difference between the present invention and the comparative example is remarkably expressed in the S / D ratio shown in Table 1 above. Therefore, this S / D ratio is 0.5 or less, preferably 0.8. It can be seen that it is desirable to set the diameter, number, and pitch circle diameter of the paint passage so as to be 3 or less.

It is sectional drawing which shows the principal part structure of the rotary atomization electrostatic coating machine which concerns on this invention. It is sectional drawing which shows the detailed structure of the dam part in this rotary atomization electrostatic coating machine. It is a graph which shows the result of the atomization experiment which is an Example of this invention in contrast with a comparative example. The atomization mechanism of the coating material by a rotary atomization electrostatic coating machine is typically shown, (A) is a cross-sectional view, and (B) is a front view showing the front end of the rotary atomization head in an expanded state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Rotating atomizing head 11 Motor 12 Paint feed tube 16 Hollow rotating shaft 20 Hub 23 Paint supply passage around hub 24 Paint 25 Inner cup inner surface of rotating atomizing head 26 Paint discharge end (tip of rotating atomizing head)
27 Dam part 28 Annular wall 29 Paint discharge passage

Claims (4)

A paint is supplied from a paint feed tube to the inner bottom of a bell cup-shaped rotary atomizing head that is rotated at a high speed by applying a high voltage, and the paint flows along the inner surface of the cup of the rotary atomizing head from the tip. In the rotary atomizing electrostatic coating machine for discharging in the form of a mist, the inner surface of the cup of the rotary atomizing head is composed of an annular wall body having a wall surface aligned with a surface orthogonal to the axis of the rotary atomizing head, and the rotary fog A rotary atomizing electrostatic coating machine characterized in that an annular dam portion for collecting paint toward the tip of the chemical head is provided, and a large number of paint discharge passages are provided in the circumferential direction in the dam portion. Paint discharge passages, rotary atomizing electrostatic coating machine according to claim 1, characterized in that provided in the connecting portion between the annular wall body and the cup inner surface of the rotary atomizing head. The ratio S / D between the total effective sectional area S of the paint discharge passages provided in the dam part and the diameter D of the pitch circle in which the paint discharge passages are arranged is set to 0.3 or less. Item 3. The rotary atomizing electrostatic coating machine according to Item 1 or 2 . A paint is supplied from a paint feed tube to the inner bottom of a bell cup-shaped rotary atomizing head that is rotated at a high speed by applying a high voltage, and the paint flows along the inner surface of the cup of the rotary atomizing head from the tip. In the rotary atomizing electrostatic coating method for discharging in the form of a mist, an annular dam portion comprising an annular wall body in which a wall surface coincides with a surface perpendicular to the axis of the rotary atomizing head on the cup inner surface of the rotary atomizing head The paint toward the tip of the rotary atomizing head is temporarily accumulated in the dam part, and hydraulic pressure is generated by centrifugal force on the paint accumulated in the dam part, and the dam part is equally distributed in the circumferential direction. A rotary atomizing electrostatic coating method characterized by discharging paint from a number of paint discharge passages provided.

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