JPH0380957A - Rotary atomizing apparatus - Google Patents

Abstract

PURPOSE:To perform the pulverization of coating material, the defoaming of air bubbles contained in coating liquid and the mixing of the coating material and to prevent the precipitation of the solid in the coating liquid by using a large number of projections provided to the outer end edge part of the cone-shaped inner peripheral surface of a coating material atomizing member. CONSTITUTION:A coating material atomizing member 1 having a cone-shaped inner peripheral surface 2 and subjected to rotary driving is mounted and supplied coating liquid is guided to the outer end edge part 3 of the cone-shaped inner peripheral surface 2 along said surface 2 by centrifugal force based on rotation to be atomized. A large number of mutually independent projections 20, 20' are provided to the outer end edge part 3 of the inner peripheral surface so as to be arranged in one row at a predetermined interval over the entire periphery thereof and the adjacent projections of each row are arranged so as to be mutually shifted in the circumferential direction and the projections of the endmost row have a quarter globe shape wherein a vertical surface is formed along an end edge and the projections of other rows have a semispherical shape. As a result, the pulverization of coating material, the defoaming of air bubbles contained in coating liquid and the mixing of the coating material can be performed and, further, the precipitation of the solid in the coating liquid can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rotary atomizer, and more particularly to the structure of a member (hereinafter referred to as an atomizer head) that atomizes and releases liquid paint in the atomizer. Regarding.

[Prior Art and Problems to be Solved by the Invention] Conventionally, it is known to electrostatically paint articles by electrostatically atomizing liquid paint using a single-rotation atomizer.

Conventionally, the rotary atomizing head of such an atomizing device is a cup-shaped atomizing head, called a so-called mini-bell type rotary atomizing head, which is provided at the front end of a rotating shaft that can rotate once, and one end is annular. an atomizing head main body (bell rim) having a cone-shaped inner circumferential surface opened to the atomizing head main body, a liquid paint receiving part (bell hub) formed in the atomizing head main body, and a thin film of liquid paint on the cone-shaped inner circumferential surface. Those consisting of an outlet and an outlet for guiding are often used. For example, JP-A-53-147740, JP-A-55-47159, and JP-A-55-47160.

Utility Model Application Publication No. 55-49797, and Utility Model Application Publication No. 55-10
No. 7255, Japanese Patent Publication No. 55-41825, Japanese Patent Application Publication No. 141887-1987, Japanese Patent Application Publication No. 198-67388
All of the publications disclose the structure of a rotating atomizing head of a conventional atomizing device.

In the mini-bell type rotating atomizing head as mentioned above.

The paint supplied to the receiving part from the liquid paint supply nozzle is
The centrifugal force generated by the rotation of the atomizing head forms a thin film, which is discharged and supplied to the inner peripheral surface of the cone through the outlet.

However, in the conventional rotary atomizing head, the following problems occur in the process of supplying the liquid paint and the process of atomizing the paint. That is.

Bubbles may be included in the atomized droplets of liquid paint that adhere to the object to be coated. If the viscosity of the liquid paint is relatively low and the rotational speed of the rotating atomizing head is low, such as several hundred to several thousand revolutions per minute, or if the amount of paint atomized is relatively small, this foam will It is not included in the atomized droplets, and the atomized droplets show a satisfactory condition, but in cases where the viscosity of the liquid paint is relatively high, or in particular when the rotation speed of the rotating atomizing head is increased, the amount of atomized liquid paint may be reduced. This becomes noticeable when the amount of bubbles is increased, and a large number of bubbles are generated on the surface of the paint liquid film formed on the surface of the object to be coated.

There are problems in that not only does the quality of the coating deteriorate, but also that it cannot be used as a painted product when the generation of bubbles is excessive.

In order to prevent this, the tip of the mini-bell type rotary atomizing head is disclosed in the above-mentioned Japanese Patent Application Laid-open No. 147740/1983.

Japanese Patent Publication No. 55-41825 discloses providing a large number of grooves, and JP-A-58-67368 discloses providing a large number of notches. Further, the above-mentioned Japanese Patent Application Laid-Open No. 141887/1987 discloses providing a substantially vertical annular step.

Furthermore, regarding the prevention of bubbles that are thought to occur when liquid paint is supplied to the bell hub (liquid paint receiving part) of the atomizing head that rotates at high speed, Japanese Utility Model Publication No. 59-85783 and Japanese Patent Application Laid-Open No. 59-80380 There is a method in which liquid paint is supplied centering on a bell hub, as disclosed in .

However, according to the above-mentioned Japanese Patent Publication No. 55-41825, when the amount of liquid paint atomized per hour is relatively low, the formation of a liquid film extending outward beyond the discharge edge is suppressed. 2. If the amount of atomization is relatively large, there is a problem that the diameter of the atomized droplets becomes large or that air bubbles are likely to be trapped.

In addition, in the case of atomizing two-component liquid paint, in which individual liquid paints are supplied to a high-speed rotating atomizing head, and the amount of supply is relatively small, it is necessary to The flow rate of the flowing liquid paint is high, and sufficient mixing is not possible, which tends to cause problems such as deterioration of coating quality.

On the other hand, according to the above-mentioned Japanese Patent Application Laid-open No. 58-67388.

The above problem can be solved by a large number of regular notches extending radially at small intervals on the circumferential tip of the rotating atomizing head, and a smooth introduction surface formed on the inner peripheral surface of the rim inside the troughs of the notches. We are trying to find a solution.

However, the viscosity of liquid paints is relatively low.

Moreover, when the amount of atomization per hour is relatively small, the liquid paint is released and atomized only from the valley of the notch at the tip of the atomizing head, and is not released from the peak of the notch. . As a result, a solid/liquid/gas interface occurs at the notch,
Solids in liquid paint precipitate. Therefore, not only does this have an adverse effect on the atomization of the liquid paint, but in severe cases, the precipitated solid content is likely to be released and adhere to the object to be coated, resulting in a decrease in the quality of the coating.

In addition, in the case of atomization of two-component liquid paint, the above-mentioned Japanese Patent Publication No. 55
A problem similar to that which occurred in Publication No. 41825 occurs. Furthermore, according to the above-mentioned Japanese Unexamined Patent Publication No. 59-80360, a bush having a concave surface on one side is provided in the one-rotation atomizing head, and the bush is perpendicular to the surface formed by the outer peripheral edge of the concave surface. A method is disclosed in which the liquid paint is supplied to a central portion to prevent air bubbles occurring during the supply of the liquid paint, but when a relatively large amount of the liquid paint is atomized.

This poses a problem in that the diameter of the atomized droplets increases.

As mentioned above, a good quality paint film surface has been formed on the object to be coated regardless of the number of revolutions of the 1M head, the type of liquid paint used, the amount of supply per unit time, etc., and the quality of the two-component liquid paint has been There was a strong desire for a rotary atomizer capable of electrostatic coating.

Accordingly, one object of the present invention is to provide a novel rotary atomizer that solves the problems of the prior art. That is, to provide a rotary atomization device that is stable continuously for a long period of time, which does not contain air bubbles in the atomized droplets of atomized liquid paint, and which enables sufficient mixing in the case of atomization of two-component liquid paint. It is something.

[Means for Solving the Problems by the Invention] The rotary atomizing device of the present invention includes a paint atomizing member having a cone-shaped inner circumferential surface and being driven to rotate, and the supplied liquid paint is applied to the cone by centrifugal force based on the rotation. The rotary atomizer is of a type in which atomization is carried out along the inner circumferential surface of the rotary atomizer toward its outer edge.

It is characterized in that a large number of mutually independent protrusions are provided on the outer edge.

The projections are arranged in a line along the entire outer edge of the inner circumferential surface at predetermined intervals, and adjacent projections in each row are offset from each other in the circumferential direction.

It is preferable that the protrusions in the endmost row are ten-sphere-shaped protrusions with vertical surfaces along the edges, and the protrusions in the other rows are hemispherical-shaped protrusions.

[Preferred embodiments and effects] The protrusions preferably have a hemispherical shape, but other shapes are also possible as long as the protrusions formed on the outer edge are regularly arranged under certain conditions. For example, 1 cylindrical shape,
It can take many shapes such as a cylinder with a spherical upper part, a square prism, a cone, and a square pyramid.

Further, it is preferable that the distance between the centers of each protrusion is larger than the diameter of the protrusion and smaller than twice the diameter.

These protrusions perform a decelerating and mixing action on the liquid paint. In other words, when the liquid paint passes through the outer edge, since the adjacent protrusions in each row are offset from each other in the circumferential direction, it collides with the protrusions in the next row located outward between the protrusions, creating resistance. The flow rate is reduced and the direction of the flow is changed, thereby dividing and mixing.

Due to this deceleration, the air bubbles contained in the liquid paint have a longer residence time at the outer edge, and due to the centrifugal force caused by nine rotations, they float onto the protrusions, are separated from the paint, and are broken.

Furthermore, as the speed decreases, the liquid film at the outer edge becomes thicker. As a result, only a small portion of the paint gets over the protrusions, thereby preventing the solid content in the liquid paint from precipitating.

Furthermore, in the case of atomization of two-component liquid paint, these protrusions
By repeatedly dividing and mixing the paint, sufficient mixing is achieved and deterioration in coating quality is prevented.

Furthermore, the liquid paint is applied to a small interval (0.1 to 0.00 mm) formed between the protrusions in the most extreme row (ten-spherical protrusions in this example).
5+u), the paint can be atomized.

The degree of atomization, that is, the size of the droplets of the liquid paint that is atomized and discharged, can be adjusted by optimally selecting the distance and shape between the protrusions depending on the viscosity and supply amount of the liquid paint used. be.

Furthermore, the extent to which the liquid paint introduced to the outer edge changes its direction of flow or is separated is influenced by the diameter a and center-to-center distance ad of the outer edge protrusions. For example, if the center-to-center distance #1d is large and the diameter a is small, the degree to which the direction of paint flow changes or the degree to which the paint is separated is low.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

The atomizing head main body 1 is a cup-shaped hollow member and consists of a cylindrical part 21 and a cone part 22 integrally formed on one end side of the cylindrical part 21. The cone part has an inner peripheral surface 2 shaped like a cone. The outer end edge 3 of the inner circumferential surface thereof is opened in an annular shape. A bushing 4 is provided concentrically within the cylindrical portion 21 of the atomizing head main body 1, and the bushing 4 and the atomizing head main body 1 are integrated. This bushing 4 has a cylindrical shape that is short in the axial direction, and has a conical concave surface 4a formed on one end surface thereof. The tip of the paint supply nozzle 8 fits into the internal space 7 formed by the concave surface 4a and the inner peripheral surface of the cylindrical portion 21, and the tip fits slightly into the concave surface 4a.
The tip end axis is located at or very close to the center of the conical concave surface 4a.

The nozzle 8 passes through a hollow shaft 10 provided in an air bearing type air motor 9, and its rear end is connected to a paint supply device (not shown).

An annular gap 11 is formed between the inner circumferential surface of the cylindrical portion 21 of the atomizing head body 1 and the outer circumferential surface of the bushing 4, one end of which communicates with the internal space 7, and the other end communicating with the atomizing head. Main body 1
It communicates with a cylindrical peripheral wall surface 18 that is continuous with the cone-shaped inner peripheral surface 2 of. Inside this annular gap 11, support columns 13 having a streamlined shape with a number of vi (four in this embodiment) are arranged in the direction in which the liquid paint flows out.
is positioned in the radial direction and has a screw 5 inside the cylindrical part 21.
Fixed by

A flange 14 is integrally formed on the shaft IO, and a flange 23 is integrally formed on the other end side of the cylindrical portion 21, and an uneven fitting surface is formed between these flanges. It is positioned in the radial direction and is concentrically attached to the shaft lO by screws 6. The rotation of the air motor 9 is output to a shaft 10 and further transmitted from the shaft 10 to the atomizing head main body 1, so that the atomizing head 1 is rotationally driven.

The liquid paint supplied from the axial liquid supply nozzle 8 is applied to the concave surface 4.
It changes direction while being guided by a, and spreads radially outward in a thin film form due to the action of centrifugal force generated by rotation.

It is desirable that the conical angle θ of the concave surface 4a formed on the bushing 4 to change the direction of the liquid paint, that is, to spread it in a thin film, is at least 30 degrees, preferably at least 60 degrees. If it is less than 30 degrees, change direction and move to the concave surface 4a.
This is not preferable in terms of the structure of the atomizing head main body 1 and the bushing 4 because the atomizing head body 1 and the bushing 4 become thin and widen << and the concave slope becomes steep.

Note that the effect of the present invention can be further enhanced if the space 7 is made to have a slightly large volume so that the liquid film can stay therein. This is due to the centrifugal effect during the residence period.
This is because even if the liquid film formed on the concave surface 4a contains microbubbles, a defoaming effect can be expected.

For high-quality electrostatic coating, it is necessary to make the liquid film formed on the outer edge 3 thinner. This can be achieved by

Next, the annular outer end edge 3 of the rotary atomizing head will be explained.

3 to 6, the outer edge 3 is provided with a large number of mutually separated and independent protrusions 20, and these protrusions have a hemispherical shape and are regularly arranged. Furthermore, protrusions 20' are provided in a row in the circumferential direction at the most distal end of the outer edge, and these protrusions form a plane 20' perpendicular to the inner circumferential surface 2B of the edge.
It has a hemispherical shape with a flat surface 20'a along an edge 25.

Width A of the outer edge 3 where these protrusions 20, 20' are formed
is 0, 25 +u to 8■1. Especially from 0.51m to 5
The width 1 is preferably determined by the viscosity of the liquid paint used, the substance contained therein, the amount supplied, etc.

Further, the protrusions 20, 20' are arranged in several rows in the circumferential direction with a diameter a and a center-to-center distance d, and are arranged so that the center of the protrusions in the adjacent row is located at the center between the protrusions in each row.

This diameter a is between 0.1 mm and 0.8++ m, especially 0.2
A range of 0.51 m to 0.51 m is preferable.

In addition, the center distance d is 0.2 mm to 1.2 mm, especially 0
．． The thickness is preferably 3 sm to 0.75 mm, but can be determined appropriately depending on the amount of paint supplied. The diameter of atomized droplets can be determined by the size of this d.

The height h of these protrusions 20 and 20' is 0.
05 speed to 0.4+m, especially 0.1m+e to 0.25+
A range of ++s is preferred.

Further, the angle α at which the lines connecting the centers of the protrusions intersect is preferably from 30 degrees to 120 degrees, particularly preferably from 45 degrees to 90 degrees.

The annular tip 19 has an annular tip surface 24 that projects further radially outward from the tip 25 of the outer edge 3 and has an inclination angle β. The width S of the annular tip surface 24 is b/cos
It is denoted by β.

Here, the vertical distance between the annular tip 19 and the edge inner peripheral surface 2B is 0.1 mm to 3+u, especially 0.2 m to 2III
11 is preferred.

Also, the angle β affects the direction in which the paint is atomized and discharged, and the angle β is between 3 degrees and 60 degrees, particularly between 5 degrees and 45 degrees, depending on the inclination angle of the cone-shaped inner circumferential surface 2. preferable.

[Operation of the embodiment] While a high voltage is applied to, for example, an air bearing type air motor 9 through a conductive wire (not shown) and the atomizing head main body 1 is rotating at high speed, the liquid paint is supplied to the paint (not shown). The paint is supplied from the device through the paint supply nozzle 8 to the center or very close to the center of the four conical surfaces 4a that function as paint receivers. The paint on the concave surface 4a spreads radially outward in the form of a thin film due to the centrifugal force generated by the rotation of the atomizing head main body 1, and is discharged onto the inner wall surface 17 of the inner space 7. At this time, even if the atomizing head main body 1 is rotating at a high speed, the center of the two conical four faces 4a and the vicinity thereof have a relatively slow circumferential speed, so the paint supply nozzle 8 is applied to the concave surface 4a. Air is entrained in the liquid paint that collides with the center and very close to it.
＜The flow of liquid paint is less likely to be disturbed, so the generation of bubbles can be prevented.

The liquid paint in the internal space 7 becomes a uniform thin film on the circumferential wall surface 17 due to centrifugal force, passes through the annular gap 11, becomes a uniform thin film on the cylindrical inner circumferential surface 18, and forms a continuous cone-shaped inner circumferential surface. 2.

Since the surface area of the cone-shaped inner circumferential surface 2 rapidly increases, the liquid paint guided to the cone-shaped inner circumferential surface 2 forms a thinner liquid film as it approaches the outer edge 3. Here, the liquid paint that has been uniformly formed into a thin film reaches the outer edge 3 and is atomized and discharged from the two-ringed tip 19.

The liquid paint on the outer edge 3 is applied by the multiple protrusions 20.

The resistance reduces the flow rate of the paint, increases the residence time, and changes the direction of the flow while simultaneously separating the separated paints, which are then mixed. By repeating this phenomenon, the liquid paint reaches the tip of the outer edge 3, and
It is atomized and discharged through between the protrusions 20' provided there.

If air bubbles exist in the paint whose flow velocity is reduced at the outer edge 3, the air bubbles float up and separate due to the longer retention time of the paint and the centrifugal force caused by the high speed rotation of the rotating atomizing head, and are further broken. Ru.

[Effects of the Invention] As described above, the rotary atomizer of the present invention has a large number of protrusions provided on the outer edge of the cone-shaped inner peripheral surface of the paint atomizing member to atomize the paint and reduce the amount of particles contained in the liquid paint. It is possible to eliminate bubbles caused by the liquid paint, mix the paint, and prevent precipitation of solids in the liquid paint.

A rotary atomizer using the paint atomizing member of the present invention has the following features:
．． 000 to 50.00 Or, p, +g, especially 10,0
00 to 30.000 r, p, 11. This is particularly useful for high-speed rotations such as Furthermore, most of the paints conventionally used for this type of electrostatic paint can be used, but paints that do not contain organic solvents, such as water-based paints, are more advantageous than paints that contain high-boiling point solvents.

The properties of the atomized droplets vary considerably depending on the shape and arrangement of the protrusions.1 For example, when using an atomizing head with an outer diameter of about 70 mm at the leading edge, using a water-based paint, and using a water-based paint at a rate of 20 cc/min.
Bubble-free fine droplets are obtained even when atomized over a wide range of volumes, c/min. the result.

By using this rotary atomizer for electrostatic coating, it is possible to obtain consistently good coating quality for a long period of time.

Furthermore, in the case of atomization of a two-part liquid paint, it can be assumed that fine and fine droplets are sufficiently mixed, judging from the quality of the resulting coating.

[Brief explanation of drawings]

FIG. 1 is a front view of a rotating atomizing head showing an embodiment of the present invention;
2 is a sectional view taken along line A-A in FIG. 1, FIG. 3 is an enlarged partial plan view of the outer edge, FIG. 4 is a partial plan view of the outer edge, and FIG. B-line sectional view. FIG. 6 is a partial front view of the outer edge. 1... Atomization head body 2... Cone-shaped inner peripheral surface 3.
... Outer edge of atomizing head 4 ... Bush 8 ... Liquid paint supply nozzle

Claims (2)

[Claims] (1) A paint atomizing member having a cone-shaped inner peripheral surface and driven to rotate, the supplied liquid paint being guided along the cone-shaped inner peripheral surface to its outer edge by centrifugal force based on the rotation. What is claimed is: 1. A rotary atomizer of a type in which atomization is performed, characterized in that a large number of mutually independent protrusions are provided on the outer end edge. (2) The protrusions are arranged in a line along the entire outer edge of the inner circumferential surface at predetermined intervals, adjacent protrusions in each row are offset from each other in the circumferential direction, and the protrusions in the endmost row are 2. The rotary atomizer according to claim 1, wherein the ten-sphere-shaped protrusions have vertical surfaces along the edges, and the protrusions in the other rows are hemispherical-shaped protrusions.