JP2008136965A - Atomizing head for rotary atomization type coating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an atomizing head which can effectively utilize groove rows in the inside end part even at high-velocity revolution with a peripheral velocity of ≥0.5 Mach to achieve uniform atomization. <P>SOLUTION: The atomizing head 13 is used for a rotary atomization type coating apparatus, and a plurality of grooves 37 are circumferentially formed at a constant pitch P in the end part 32 of a coating diffusing surface 31 inside of the atomizing head. The length L of the grooves 37 is equal to or less than the pitch P of the grooves 37. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an atomizing head (also referred to as a bell cup) of a rotary atomizing coating apparatus, and in particular, air entrainment is prevented even at a high speed rotation with a peripheral speed of Mach 0.5 or more, and uniform atomization is achieved. It can be related to the atomizing head.

  Rotating atomizing electrostatic coating equipment used in automobile painting, etc. supplies paint liquid to the inner surface of the atomizing head that rotates at high speed, and uses the centrifugal force to apply the paint liquid at the end of the atomizing head. Atomized atomized particles are transported in the direction of the object to be coated by the shaping air supplied from the back of the atomizing head, and the paint particles are attached to the object by static electricity applied to a high voltage. . Such an atomizing head has been put into practical use in various cross-sectional shapes, but on the other hand, it has also been proposed to provide a large number of grooves at its end (see Patent Document 1 and Patent Document 2).

The main purpose of this type of groove row is to prevent air entrainment when the paint released in the form of a film in an intermediate or clear paint having a high paint viscosity is broken into fine particles. Although its structure and action are detailed in the above-mentioned patent document 1, the main focus was on suppressing the generation of hollow paint particles entrained with air mainly by shaping air supplied from the back of the atomizing head. . That is, when an atomizing head having no groove row is used at a relatively low rotational speed, the coating liquid is discharged from the atomizing head in a film form, so that air entrainment tends to occur. Since the paint is discharged in the form of a liquid thread, the entrainment of air is prevented when the liquid thread paint is divided into fine particles.

Although such a groove array is effective in preventing air entrainment, it does not guarantee the uniformity of atomized paint particles. Therefore, the present inventors paid attention to the paint liquid film flow on the paint diffusion surface for the purpose of improving the uniformity of the paint particles, and provided a convex shape on the paint diffusion surface of the rotary atomizing head or a large number on the diffusion surface. (Patent Document 3), and it has been found that this makes it possible to atomize more uniformly than the conventional atomizing head. This is a significant improvement in atomization performance compared to the atomized head having a concave shape that had been put to practical use before that, but with regard to the function of preventing the entrainment of air, a groove row should be formed at the inner edge. Was still effective.

However, in recent years, it has been found that water-based paints, which have begun to be used in automobile coatings, have several problems with respect to uniform atomization and the function of preventing air entrainment.

That is, since the paint viscosity of the water-based base paint is higher than that of the organic solvent-based clear paint or the organic solvent-based intermediate paint, it is naturally expected that the air entrainment effect is suppressed. However, in a rotary atomizing coating apparatus that rotates at a much higher speed than in the past, the actual condition is that an atomizing head that does not have groove rows at the inner surface end is employed. This is because the groove row at the inner surface edge has a problem that the air entrainment prevention function is not effective and the cleaning property of the atomizing head deteriorates due to the groove row.

Here, whether or not it is rotating at high speed is determined based on the boundary between the “peripheral speed”, which is the product of the “circumferential length” of the atomizing head and the “rotational speed per second”, approximately Mach 0.5 (= 170 m / s). can do. That is, even if the peripheral speed of the conventional rotary atomizing coater is fast, it is about Mach 0.4 (about 52000 rpm for an atomizing head having a diameter of 50 mm). It is considered to be effective.

On the other hand, in a high-speed rotation region of Mach 0.5 or more, air is hardly trapped even if a groove row is not provided at the inner surface edge. This is presumably because the paint is discharged from the end of the atomizing head in the form of a liquid rather than in the form of a liquid film, but the reason is not clearly understood.

Disadvantages of atomizing heads that do not have groove rows at the inner surface edge are that, at low speed rotation of about Mach 0.4 or less, atomization becomes extremely worse and air entrainment occurs, and the resulting fine particles There is a problem that the diameter distribution is relatively wide, and the only way to improve this is to increase the rotational speed.

That is, the fine particles generated by high-speed rotation have many fine components, and there is a drawback that the coating efficiency decreases when the shaping air is strengthened. This is the same tendency as the conventional organic solvent-based paint. For this reason, when atomizing by high-speed rotation, generally, the shaping air is often used with weakening, and the pattern width tends to be widened, which has a drawback that it becomes a limitation of the coating method.

Japanese Patent Publication No.55-41825 Japanese Patent Publication No. 4-37743 JP-A-10-52658

The problem to be solved by the present invention is that the atomization head capable of effectively utilizing the groove row at the inner surface end portion and achieving uniform atomization even at high speed rotation with a peripheral speed of Mach 0.5 or more. Is to provide.

In order to achieve the above object, the atomizing head of the rotary atomizing coating apparatus of the present invention is used in the rotary atomizing coating apparatus, and a plurality of grooves are circular at the end of the paint diffusion surface on the inner surface of the atomizing head. An atomizing head formed at a constant pitch in the circumferential direction, wherein the length of the groove is equal to or less than the pitch of the groove.

By setting the length of the groove formed at the end of the paint diffusion surface on the inner surface of the atomizing head to be equal to or less than the pitch of the groove, the resistance component of the groove is reduced, and the flow of the coating liquid film is not hindered by the groove. As a result, air entrainment can be prevented and uniform atomization can be achieved.

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

<< First Embodiment >>
FIG. 1 is a cross-sectional view showing a structure of a tip portion of a rotary atomizing coating apparatus 10 to which an atomizing head according to a first embodiment of the present invention is applied, and FIG. 2 relates to the first embodiment of the present invention. FIG. 3 is a half sectional view showing the atomizing head 13 in an enlarged manner, and FIG. 3 is a half sectional view showing the inner peripheral end portion of the atomizing head 13 in accordance with the first embodiment of the present invention.

An example of a rotary atomizing electrostatic coating apparatus will be described with reference to FIG. 1. A rotary atomizing electrostatic coating apparatus 10 shown in FIG. 1 is rotated by an air motor (not shown) provided in a housing 11. The hollow shaft 12 is screwed to the distal end side of the hollow shaft 12 and is rotationally driven, and the atomizing head (bell cup) 13 that sprays the paint is disposed on the rotational center in the center hole 12a of the hollow shaft 12. And a non-rotating feed tube 14 for supplying paint to the atomizing head 13. The outer periphery of the housing 11 is covered with a housing 16 made of an electrically insulating material.

The electrostatic coating apparatus 10 causes paint particles charged by application from a high-voltage power source (not shown) to fly along an electrostatic field formed between the objects and to be applied to the object. The high voltage application is either an internal application type in which a high voltage power source is provided in the housing and applied to the atomizing head, or an external voltage application type in which a high voltage power source is provided around the atomizing head and applied to the particles ejected from the atomizing head. Can also be adopted.

Further, an air flow called shaping air is discharged from the back side of the atomizing head 13 from the air discharge port 17, and the paint particles atomized by the atomizing head 13 are placed in front of the atomizing head 13. Deflection in the direction toward the paint. The paint particles are imparted with the momentum necessary to reach the object even by the shaping air. Reference numeral 18 denotes an air guide that guides the shaping air discharged from the air discharge port 17 toward the atomizing head 13. The air discharge port 17 is formed in an annular shape between the first air ring 41 and the second air ring 42, and the air guide 18 is formed by the outer peripheral surface of the first air ring 41. The first air ring 41 is attached to the distal end portion of the housing 16. An annular air passage is formed between the housing 11 and the housing 16, and an air introduction hole 43 that connects the air discharge port 17 and the air passage is formed in the first air ring 41. Then, the air supplied to the air passage via an air pipe (not shown) passes through the air introduction hole 43 and is ejected as shaping air from the air discharge port 17.

The feed tube 14 is composed of a double pipe including an inner pipe 20 and an outer pipe 21 through which the inner pipe 20 is inserted. The inner pipe 20 is supplied with a paint, and the outer pipe 21 is an automatic cleaning thinner. (For organic solvent-based paints) or automatic cleaning water (for water-based paints) is supplied. The distal end of the feed tube 14 is exposed from the distal end of the hollow shaft 12 and extends toward the inside of the atomizing head 13. A paint valve is provided on the base end side of the feed tube 14, and this paint valve communicates with a paint tank (both not shown) via a paint pipe.

The atomizing head 13 has a substantially cup shape and is made of a conductive material such as metal. The cup-shaped outer surface 30, the inner-surface paint diffusing surface 31, and the end where the paint located at the inner-surface tip is discharged. 32. In the atomizing head 13, a paint inflow chamber 34 is defined by a bell hub portion 33, and the tip opening of the feed tube 14 communicates with the paint inflow chamber 34. The bell hub portion 33 is formed with a central opening 35 located at the central portion and a plurality of paint outlet holes 36 located at the peripheral portion, and the plurality of paint outlet holes 36 are arranged circumferentially at predetermined intervals. Has been. The atomizing head 13 rotates at an ultra high speed of, for example, a peripheral speed Mach 0.5 or more during painting.

In particular, a fine groove 37 for atomizing the paint spreading in the form of a liquid film along the paint diffusion surface 31 is formed at the end 32 of the inner surface of the atomizing head 13 of the present embodiment. The groove 37 is shown enlarged in FIG.

The groove 37 of this example is formed at the boundary between the inner surface 31 and the end portion 32 of the atomizing head 13, and is formed side by side in the circumferential direction of the end portion 32 at a constant pitch P. The length L of the groove 37 along the radial direction of the atomizing head 13 is equal to or shorter than the pitch P between the adjacent grooves 37 (that is, L ≦ P).

The absolute length L of the groove 37 is 0.3 mm or less, preferably 0.1 to 0.2 mm in an atomizing head having a diameter of 30 to 50 mm. Moreover, it is preferable that the pitch P of the groove | channel 37 is 0.05 mm-0.3 mm, after satisfy | filling the conditions (L <= P) that it is more than the length L of the groove | channel 37. FIG. If the length L of the groove 37 is shorter than 0.1 mm, the time for processing and forming the groove 37 becomes longer and the cost is increased, and if the length L of the groove 37 is short, the depth of the groove is inevitably shallow. This is because the effect of the groove 37 cannot be expected. On the contrary, when the length L of the groove 37 is longer than 0.3 mm, the above-described problems of the conventional example cannot be solved.

If the length L of the grooves 37 is shorter than the pitch P of the grooves 37 as in this example, the grooves 337 can be formed by knurling or the like without using conventional mechanical grinding with a wheel cutter or the like. Therefore, the processing time can be shortened and the cost can be reduced.

Next, the operation will be described.

The hollow shaft 12 and the atomizing head 13 are rotated at high speed by an air motor. The paint is guided to the paint inflow chamber 34 through the feed tube 14 and supplied to the front surface of the atomizing head 13 from the central opening 35 and the paint outlet hole 36. The paint supplied to the front surface of the atomizing head 13 is thinly stretched along the paint diffusing surface 31 by the centrifugal force generated by the rotation of the atomizing head 13, passes through the plurality of grooves 37, and then forms a mist from the end portion 32. To be atomized and released.

The discharged paint particles try to jump out radially outward by centrifugal force. However, the discharged paint particles are controlled or shaped into a desired pattern so as to be squeezed forward by the shaping air ejected from the air discharge port 17, and are carried toward the object to be coated.

At the same time, since the paint particles are charged, the paint particles fly toward the object connected to the ground, and efficiently adhere to the surface of the object by the Coulomb force.

  Here, the effect of the groove 37 of this example will be considered.

As shown in FIG. 2 of the above-mentioned Patent Document 1, the length of the groove formed on the inner surface end of the conventional atomizing head is generally more than twice the groove pitch. The inventors of the present invention can obtain stable atomization performance by forming a groove having a length of 5 to 10 times the groove pitch at the inner end of the organic solvent-based paint to be applied at a relatively low rotation. I have confirmed that.

However, for example, when an ultra-high speed rotation type atomizing head having a peripheral speed of Mach 0.5 or more is applied to the water-based base paint, these groove rows hardly function and the groove rows are not formed. However, there is a problem that the atomization performance is slightly deteriorated. As a result of detailed investigations by the present inventors, it was found that the cause is that there is a large angle difference between the direction in which the grooves are formed and the flow direction of the coating liquid film, and the present invention has been completed.

That is, the conventional groove is generally processed into a linear groove in a radial direction from the center of the rotation axis. However, the paint on the paint diffusion surface of the atomizing head that rotates at high speed tends to slide greatly backward in the direction of rotation, and the direction in which the paint / liquid film flows is less than 90 ° with respect to the end of the atomizing head. It becomes the angle of. Such a tendency was also observed in organic solvent-based paints applied at a relatively low rotation, but the angle difference was usually within 5 °, which was hardly a problem.

However, it has been found that in an ultra-high-speed rotation type atomizing head, a large angle difference occurs between the liquid film flow direction of the paint and the extension direction of the groove, and the groove impedes the flow of the paint. That is, the coating liquid flowing on the coating material diffusing surface 31 is distributed to each groove 37 and then behaves so as to be temporarily accumulated in the groove 37. The accumulated coating material is irregularly formed on the atomizing head. Since it will be discharged | emitted from the edge part 32, a stable paint flow will no longer be formed by the groove | channel 37 on the contrary.

In the present invention, the direction of the paint liquid film flow thinly spread on the paint diffusion surface 31 forms a flow that is greatly inclined to the side opposite to the rotation direction because the atomizing head 13 is rotating at an ultra-high speed. In addition, since this angle changes depending on the discharge amount of the paint and the size of the selected rotation speed, the groove 37 having a normal length functions only with a specific discharge amount and a specific rotation speed that can be handled. On the other hand, it has been found that the groove 37 functions effectively in a wider range by making the length L of the groove 37 shorter than the pitch P of the groove 37.

  In the present invention, since the length L of the groove 37 is shortened as a result, the function of accumulating the paint in the groove 37 is weak, and the paint supplied to the start of the groove row (center side of the atomizing head 13). Will be released almost immediately from the end 32 of the atomizing head 13. That is, the resistance component of the groove 37 decreases, and the groove 37 flows smoothly.

  Therefore, even when the atomizing head 13 rotates at an ultra-high speed of the peripheral speed Mach 0.5 or more, the flow of the coating liquid film is not inhibited by the groove 37, and as a result, the entrainment of air is prevented. At the same time, uniform atomization (small atomization distribution width) can be achieved.

  FIG. 6 shows the measurement of the average particle diameter of the coating grains when the atomizing head 13 is rotated so that the peripheral speed is Mach 0.3 to 0.8. The diameter of the atomizing head 13 having a diameter of 40 mm is measured. The length of the atomizing head according to Example 1 in which grooves 37 having a length L of 0.2 mm are formed in the inner surface end portion 32 at a pitch of 0.2 mm, and the inner surface end portion 32 of the atomizing head 13 having a diameter of 40 mm. The results of Comparative Example 1 in which grooves 37 having L of 2 mm are formed at a pitch of 0.3 mm and Comparative Example 2 in which grooves 37 are not formed in the inner surface end 32 of the atomizing head 13 having a diameter of 40 mm are shown.

  According to Comparative Example 1 and Comparative Example 2 among the results shown in the figure, in the ultra-high speed rotation region where the peripheral speed is Mach 0.5 or more, the atomization can be achieved regardless of whether or not the inner surface end portion 32 has the groove 37. There is no significant difference in degree. However, according to Example 1 which concerns on this invention, it understands that atomization is accelerated | stimulated in this super-high-speed rotation area.

<< Second Embodiment >>
FIG. 4 is an enlarged half sectional view showing an end portion of an atomizing head according to the second embodiment of the present invention.

  In the first embodiment described above, the extending direction of the groove 37 formed in the inner surface end portion 32 of the atomizing head 13 is matched with the radial direction of the atomizing head 13 (α = 0 ° in FIG. 4). In the example, as shown in FIG. 4, the inclination angle α of the groove 37 with respect to the straight line in the radial direction from the center of the atomizing head 13 is 5 ° to 35 °, more preferably 20 ° ± toward the rear side in the rotation direction. It is set to 5 °. For example, when the atomizing head 13 rotates counterclockwise, the tip side of the groove 37 is set to the right and the base end side is set to the left side when the atomizing head 13 rotates counterclockwise. Say to tilt. If the inclination angle α is smaller than 5 °, the effect of the inclination cannot be expected. Conversely, if the inclination angle α is larger than 35 °, the number of grooves 37 that can be formed is inevitably reduced, or the pitch P of the grooves 37 is reduced. There are disadvantages.

  By inclining the groove 37 toward the rear side in the rotation direction in this manner, the direction of the coating liquid film flow that is thinly spread on the coating material diffusion surface 31 is more closely matched. As a result, the flow is not further inhibited, and as a result, the entrainment of air can be prevented and uniform atomization (the atomization distribution width can be reduced) can be achieved.

<< Third Embodiment >>
FIG. 5 is an enlarged half sectional view showing an atomizing head according to the third embodiment of the present invention.

In the atomizing head 13 according to the first and second embodiments described above, the coating material diffusion surface 31 which is the inner surface thereof is a concave curved surface, and the inner surface end portion 32 is formed with a plurality of grooves 37 as described above. Although the paint diffusing surface 31 is a smooth surface, in the atomizing head 13 of this example, the paint diffusing surface 31 is convex toward the rotation axis of the atomizing head 13. In other words, the inclination of the cross-sectional tangent to the rotation axis of the atomizing head 13 is larger on the outer edge side than on the center side of the atomizing head 13.

On such a convex paint diffusing surface 31, the paint behaves differently from the atomizing head 13 according to the first and second embodiments, and the liquid film thickness of the paint on the paint diffusing surface 31 is uniformly thin. The effect of refining the paint can be promoted by the surface shape in addition to the action of the second groove 38 described later.

  That is, the paint supplied from the paint outlet hole 36 located at the center of the atomizing head 13 faces outward and reaches the paint diffusing surface 31 due to the centrifugal force generated by the high speed rotation of the atomizing head 13. However, since the angle formed between the starting portion of the paint diffusing surface 31 (that is, the end portion on the rotating shaft side) and the rotating shaft of the atomizing head 13 is small, most of the centrifugal force is in the circumferential direction of the liquid surface of the supplied paint liquid. Work to spread. On the other hand, since there is a slight component force in the radial direction, the atomizing head 13 is also pushed outward in the radial direction (outer edge direction). At this time, the coating liquid level is substantially uniform in the circumferential direction, and the effect of uniformizing the coating liquid supply amount over the entire circumferential direction can be obtained without extremely increasing the working accuracy of the coating material outlet hole 36. Next, the coating liquid is split by a second groove 38 to be described later at the inflection portion, and is further transported to the end portion 32 side by centrifugal force. From this, the end portion 32 side is inclined with respect to the rotation axis of the coating material diffusion surface 31. Is larger than the inclination on the center side, the coating material supplied in the form of a large number of threads is stretched abruptly, and as the end portion 32 is approached, the coating liquid becomes thinner. For this reason, at the same rotation speed, the effect that the atomization head 13 according to the present example has higher refining capability than the atomization head 13 according to the first and second embodiments is obtained.

A plurality of second grooves 38 having a center line in the radial direction of the atomizing head 13 are formed at a constant pitch in the circumferential direction in the convex top region of the paint diffusing surface 31. The number of the second grooves 38 is preferably larger than the number of the paint outlet holes 36 that supply the paint onto the inner surface of the atomizing head 13 in order to divide the paint flow more effectively. That is, although it depends on the arrangement position of the second groove 38 and cannot be defined unconditionally, it is, for example, 2 to 50 times, more preferably about 5 to 10 times the number of the paint outlet holes 36.

  Further, the length of the second groove 38 in the extending direction may be at least about 1 mm, and the longer the length, the better the effect can be expected from the viewpoint of atomization of the paint. However, when the groove 38 is extremely long, the formation process thereof becomes difficult, and a problem that a vehicle component such as a pigment or a metal piece contained in the paint is clogged in the groove 38 tends to occur. . For this reason, it is usually about 1 to 5 mm, more preferably within 1.5 to 3 mm.

  Further, although the width of the second groove 38 depends on the arrangement position of the groove row, it is usually desirable that the width is equal to or smaller than the opening diameter of the paint outlet hole 36. The opening diameter of the outlet hole 36 is 1/2 to 1/20 times, more preferably about 1/3 to 1/5 times. More specifically, the groove width is, for example, about 0.5 to 0.05 mm, more preferably about 0.3 to 0.2 mm.

  Further, the depth of the second groove 38 is not particularly limited, but it is usually desirable to be, for example, 0.05 to 3 mm, more preferably about 0.1 to 0.2 mm.

According to the atomizing head 13 of the present example configured as described above, the groove 37 formed in the inner surface end portion 32 has the same function and effect as those of the first and second embodiments described above. By forming the paint diffusing surface 31 in a convex shape and providing the second groove 38 therein, atomization of the coating grains can be further promoted.

Incidentally, in the present example, the groove 37 formed at the inner surface end can adopt either the form shown in FIG. 3 or the form shown in FIG. 4.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

It is sectional drawing which shows the structure of the front-end | tip part of the rotary atomization type coating apparatus with which the atomization head which concerns on embodiment of this invention is applied. It is a half sectional view expanding and showing the atomization head concerning a 1st embodiment of the present invention. It is a half sectional view which expands further and shows the inner peripheral end part of the atomization head concerning a 1st embodiment of the present invention. It is a half sectional view which expands and shows the end of the atomization head concerning a 2nd embodiment of the present invention. It is a half sectional view expanding and showing the atomization head concerning a 3rd embodiment of the present invention. It is a graph which shows the relationship between the peripheral speed when rotating the atomization head so that the peripheral speed may be Mach 0.3-0.8, and the average particle diameter of a coating grain.

Explanation of symbols

13 ... Atomizing head 31 ... Paint diffusing surface 32 ... End 37 ... Groove L ... Groove length P ... Groove pitch α ... Groove inclination angle 38 ... Second groove

Claims (7)

The atomizing head is used in a rotary atomizing coating apparatus, and a plurality of grooves are formed at a constant pitch in the circumferential direction at the end of the paint diffusion surface on the inner surface of the atomizing head, and the length of the grooves is An atomizing head having a pitch equal to or less than the pitch of the groove. The atomizing head according to claim 1, wherein the atomizing head is rotated at a peripheral speed of 0.5 or more by Mach by the rotary atomizing type coating device. The atomizing head according to claim 1 or 2, wherein the groove has a length of 0.1 mm to 0.3 mm. The atomization head according to any one of claims 1 to 3, wherein a pitch of the groove is 0.05 mm to 0.3 mm. The mist according to any one of claims 1 to 4, wherein an inclination angle of the groove with respect to a straight line in the radial direction from the center of the atomizing head is 5 ° to 35 ° toward the rear side in the rotation direction. Head. The coating material diffusion surface is formed in a convex shape toward the rotation axis of the atomizing head, and a plurality of second grooves having a center line in the radial direction of the atomizing head are formed on the coating material diffusion surface at a constant pitch in the circumferential direction. The atomizing head according to any one of claims 1 to 5, wherein The atomizing head according to any one of claims 1 to 6, means for rotationally driving the atomizing head, means for supplying paint to the atomizing head, and voltage applied to the paint supplied to the atomizing head And a rotary atomizing electrostatic coating apparatus.

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