JPS6051858B2 - High-speed rotating atomizer for electrostatic painting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-speed rotary atomizing device for electrostatic coating, and more particularly, the present invention relates to a high-speed rotary atomizing device for electrostatic coating, and more specifically, the present invention relates to a high-speed rotary atomizing device for electrostatic coating, and more particularly, when a high-viscosity liquid coating is atomized at a high discharge speed, it is possible to reduce electrostatic atomization of paint. The present invention relates to an atomizing device for electrostatic coating, which enables atomization of fine particles without entrapping air bubbles.

Conventionally, as a method of electrostatically atomizing liquid paint, liquid paint is supplied in a thin film along the inner peripheral surface of a rotating body, and the liquid paint is supplied in a thin film form along the inner circumferential surface of the rotating body from a knife-shaped tip provided on the circumferential edge of the rotating body. A method of atomizing and discharging paint is known.

In this electrostatic atomization means, when the viscosity of the liquid paint is relatively low and the rotational speed of the rotating body is low, such as several hundred to several thousand revolutions per minute, the amount of paint discharged is relatively small. In some cases, even if the formed paint mist is satisfactory, if the viscosity of the liquid paint is relatively high or if the rotational speed of the rotating body is increased to increase the amount of paint discharged, The paint tends to leave the knife tip in an irregular film, the resulting paint mist contains air, and the film that forms on the object is free of bubbles. This has the disadvantage that it is included.

On the other hand, reducing the amount of solvent in liquid paint and using it in a form with as high a viscosity as possible has the potential to reduce solvent costs, reduce paint film baking costs, prevent air pollution, speed up the painting process, etc. This is highly desirable from this point of view. Conventionally, proposals have already been made to solve the problem of air bubbles being trapped when a high viscosity liquid paint is used and the rotational speed of the atomizing rotor is increased; for example, Japanese Patent Publication No. 55-41825
The publication discloses that when a liquid paint is supplied as a thin film-like flow toward an annular discharge edge having a knife-edge cross section of a rotary atomizer, a peripheral portion of the paint-guiding surface of the rotary atomizer is supplied. By providing a large number of shallow concave grooves extending in the direction of flow and whose outer ends reach the edge, the paint can be divided into a number of branched flows and supplied to the annular discharge edge. Disclosed.

According to this known method, even if the formation of a liquid film extending outwardly beyond the discharge edge is suppressed, if the hourly discharge rate of the paint liquid is relatively low, this discharge rate is relatively low. If it is large, the problem arises that the particle size of the mist droplets becomes large or that air bubbles are likely to be trapped.

Therefore, an object of the present invention is to make it possible to atomize the paint with fine particle size and without trapping air bubbles, etc. even when a highly viscous liquid paint is atomized at a high discharge rate per unit time. The present invention provides a high-speed rotating atomizer for electrostatic coating.

Another object of the present invention is to atomize paint to a significantly finer particle size than a conventional atomizer at the same discharge rate, and to atomize the paint to the same particle size. Accordingly, it is an object of the present invention to provide a rotary atomizer for electrostatic coating that can significantly increase the amount of liquid paint discharged.

Still another object of the present invention is to provide a rotor along the inner circumferential surface of the rotating body.

A discharge edge that converts a flow of paint flowing approximately axially obliquely forward into a plurality of divided flows radially outward at a non-knife-edged uneven discharge edge of the rotating body and atomizes the paint. By increasing the effective dimensions of
Air entrapment with fine particle size! To provide a high-speed rotary atomizing device for electrostatic coating, which enables atomization of paint without any turbidity. According to the present invention, the paint atomizing cup 4 is provided with an inner circumferential surface for guiding liquid paint in the form of a thin film toward the tip and a circumferential tip for atomizing and discharging the paint, The circumferential tip of the paint atomizer has an annular surface substantially perpendicular to the rotation axis of the paint atomizer, and the annular surface has regularly repeated recesses and ridges in the radial direction. An electrostatic coating characterized in that the ridge lines are formed to be inclined relative to each other, and the ridge lines overlap each other when projected in the radial direction, or are arranged so as to be connected at small intervals. A high speed rotary atomization device is provided.

The invention will be described in detail below with reference to the accompanying drawings.

In Figures 1 and 2 showing the overall arrangement of the electrostatic coating device, the coating device main body 1 is located at the tip of an electrically insulating support rod 2 that is movable up and down by a suitable lifting device (not shown). It is rotatably provided around a fulcrum 4 by a bracket 3. The coating device main body 1 is equipped with an air motor 6 housed inside a housing 5, and a cup-shaped atomizing rotating body (cup) 8 is attached to a nut 9 at the tip of a rotating shaft 7 of the air motor 6. It is fixed by fastening means such as.

The coating apparatus main body 1 is also provided with an air supply port 10 for driving and rotating the air motor 6 at high speed, and an exhaust port 11 for discharging this air. Further, the coating device main body 1 is provided with a liquid paint supply port 12, and the liquid paint is supplied to the paint supply vibrator 1 extending from the supply port 12 through the interior of the main body 1 to the atomization cup 8.
3 into the atomizing cup 8. Furthermore, the coating apparatus main body 1 is provided with a high voltage cable connection terminal 14, and although not shown, the high voltage from the high voltage generator passes through the cable to the coating apparatus main body 1, and is therefore atomized. The voltage is applied to cup 8. On the side of the housing 5 on which the rotating body is attached, a large number of jet holes 15 for shaving air, that is, pattern adjustment air, are arranged in an annular manner and are connected to an air supply port 16 . In FIGS. 3 and 4 showing enlarged views of the atomizing cup 8, the cup 8 has the shape of a rotating body consisting of a metal outer body 17 and a metal inner body 18 that are fitted together. , an inner circumferential surface 19 for guiding liquid paint in the form of a thin film toward the tip, and a circumferential tip 20 for atomizing and discharging the paint.

Furthermore, this rotary body 8 is provided with the aforementioned paint supply vibrator 13.
An annular paint reservoir 21 for temporarily storing the paint supplied from and uniformly supplying the paint over the entire circumference of the inner circumferential surface 19.
is formed, and this paint reservoir 21 and the inner peripheral surface 19
The outer body 17 and the inner body 18 are in communication with each other via a small annular slit 22 between the outer body 17 and the inner body 18 . A high voltage is applied to the atomization cup 8 via the cable connection terminal 14,
The air motor 6 is driven by the air supplied through the air supply port 10, and the atomizing cup 8 is driven and rotated at a high speed of, for example, 8,000 to 30,000 r''Pm. The paint is supplied to the paint reservoir 21 in the cup 8 through the paint supply port 12 and the paint supply vibrator 13, and further through the annular slit 22 in the form of a uniform thin film over the entire inner peripheral surface 19 of the rotating body. Inner peripheral surface 1
The paint on 9 flows approximately axially forward of the rotating body, and is atomized and discharged from the aforementioned circumferential tip 20. In the present invention, the circumferential tip 20 of the cup 8 is shown in FIGS. 3 and 4 and in FIGS. 5 and 6 which are enlarged views of the tip.
is an annular surface 23 substantially perpendicular to the axis of the cup, and this annular surface 23 has regularly repeated recesses 24 and ridges 25.
are arranged so that the recess 24 and the ridge line 25 are inclined with respect to the radial direction, and when the ridge line is projected in the radial direction, they overlap each other or are connected at a small interval.

That is, in the present invention, by adopting this configuration, as shown in the explanatory diagrams of FIGS. This divided flow 27 is exchanged into a large number of radially outward branched flows 27 along regularly repeating recesses 24.
are atomized and released into the air from the recess 24 of the annular surface 23 through the ridge line 25.

In this case, the conversion from a generally axially forward flow to a radially outward flow at the circumferential tip 20 is effected by centrifugal force generated by rotating the rotating body, i.e. the cup, at a very high speed; This division into a number of radially outward flows at the tip 20 is achieved by providing a number of regularly repeating depressions 24 in the annular surface 23.

Furthermore, the atomization discharge through the ridge line 25 of the annular surface 23 is achieved by providing the recess 24 and the ridge line 25 at an angle with respect to the radial direction,
This is conveniently done by ensuring that any radial line passing through the annular surface almost certainly abuts one ridge line 25. That is, in contrast to the conventional method in which the paint is supplied to the knife-edge tip of the cup in the form of many divided streams, in the present invention, the paint is supplied in the form of a continuous thin film up to the circumferential tip 20. However, at this circumferential tip 20,
This thin film-like flow flowing approximately axially forward of the rotating body 8 is converted into a large number of divided radially outward flows 27, and each of the divided flows 27 is tilted toward the annular surface. The liquid is atomized and discharged through a convex portion, that is, a ridge line 25 provided at the top.

That is, in the present invention, each of the ridge lines 25 provided in large numbers at an angle to the annular surface acts as a unique discharge edge for the divided paint flow. This feature therefore achieves very significant advantages in the present invention over the prior art methods described above. One of its advantages is that
This means that the length of the contact edge between the paint atomizer (cup) and the air, that is, the length of the paint discharge edge, can be significantly increased. Now, in FIG. 6, when the pitch of the uneven portions 24 and 25 is P1, the radial width of the annular surface 23 is DN, and the inclination angle with respect to the radial direction is α, the length 1 of the discharge end edge 25 of the cup is The length of the circumferential knife-like edge of is 1.

, the ratio is expressed by the following formula. For example, even if the width d of the annular surface 23 and the pitch p of the uneven portions 24 and 25 are equal, if the inclination angle α is 60 degrees, the emission edge 2
5 is twice the length of the discharge edge of a conventional cup. Of course, if the width of the annular surface 23 is doubled compared to this pitch p, the length of the discharge edge 25 will be four times the length of the discharge edge of the conventional cup. Thus, according to the present invention, since the length of the discharge edge is large, when compared assuming that the supply amount of paint per unit time is constant, it is different from the case of a normal knife-edge-shaped circumferential seven tips. This makes it possible to significantly reduce the average coating film thickness d1 at the edge in contact with air, thereby making it possible to significantly reduce the atomized particle size of the paint. Conversely, when atomizing into droplets with the same particle size as the conventional method, the present invention increases the amount of paint supplied per unit time compared to the conventional method. This means that entrapment of air bubbles during atomization is also effectively prevented. Moreover, in the present invention, since unique atomization discharge ridge lines are provided corresponding to each divided flow, the divided individual flows merge at the discharge edge into the air. This conventional inconvenience is also effectively resolved.

Further, in the paint atomizing device (cup) of the present invention, due to the feature of the electrode structure that the annular surface 23 is provided with a large number of ridges 25, atomization is performed in the form of fine particles. The atomized particles of paint become highly charged,
It also has the advantage of improving coating efficiency.

In the present invention, it is preferable that the valleys and ridges 25 of the recess 24 are aligned so that they are each located in a plane substantially perpendicular to the axis of the rotating body 8.

Furthermore, it is desirable that the inner circumferential surface 19 of the rotating body forms a smooth surface inside the recess 24 of the annular surface 23.
In the specific example shown in FIGS. 3 to 6, the recess 24 and the ridge line 25 are provided in the form of sawtooth notches in the annular surface 23, and the sawtooth notches are formed by applying paint at the tip of the rotating body. It is particularly suitable for the purpose of effectively splitting the membrane-like flow of the pipe, and for providing a large number of recesses and corresponding discharge ridges in the annular surface for the split flow.

The pitch p of this sawtooth notch is 0.1 to 1.5 Tfr
1n, especially in the range of 0.2 to 0.8TI0fL,
Further, it is preferable for the above-mentioned purpose of the present invention that the angle β of the teeth is in the range of 30 to 120 degrees, particularly 45 to 90 degrees.

Further, the radial dimension d of the annular surface 23 is generally 0.5 to 5.
7WL1 Especially in the range of 1 to 3T$l. However, it is preferable from the viewpoint of the mechanical strength of the rotating body, keeping the discharge current within an appropriate range, or enabling finer atomization. In the specific example shown in FIG. 6, the ridge line 25 is provided with an inclination 3 of an angle α in the same direction as the rotational direction of the cup with respect to the radial direction. line 2
5 may be inclined at an angle α in the direction opposite to the direction of rotation of the cup with respect to the radial direction.

In the former case, the ridge line 25a that comes next to the recess 24 becomes the discharge edge of the paint flow passing through this recess 24, and in the latter case, the ridge line 25b that precedes the recess 24 becomes the discharge edge of the paint flow passing through this recess 24.
serves as the discharge edge for the paint flow through. This inclination angle α is generally ±10 to ±70 degrees with respect to the radial direction, particularly ±2
It is best to select within the range of 0 to ±60 degrees, especially when a large number of ridge lines are projected in the radial direction, the outer edge (or inner edge) of the preceding ridge line will become the next ridge line. It is best to provide the ridge line so that it exactly overlaps the inner circumferential side end (or outer circumferential side end).

Further, although the ridge line 25 shown in FIGS. 5 to 7 is provided as a single line, it may be formed and provided so as to be divided into two or more lines as shown in FIG. You can leave it there.

In that case, each of the divided ridges independently acts as a discharge edge for discharging the liquid paint in finer divided streams. In the present invention, the shape of the notches may be any number of shapes other than sawtooth, as long as a large number of the notches are regularly and repeatedly provided on the edge 7, for example, rectangular wave shape, The shape can be a trapezoidal wave, a U-shaped notch, a V-shaped notch, or the like.

In the electrostatic coating method of the present invention, the rotating body is
0r'Pml is particularly useful for applications in which painting is performed by rotating at high speeds such as 8,000 to 30,000r''Pm,
Further, the voltage applied to the rotating body can be appropriately selected from the range of 20 to 160 kV, especially 40 to 120 kV.

The paint to be used may be any of those conventionally used for this type of electrostatic coating, such as organic solvent paints such as epoxy paints, phenol paints, melamine paints, and acrylic paints, or water-based paints, especially solvents. It can be advantageously applied to high viscosity paints in which a small amount of is used, for example, high viscosity paints with a viscosity of 3@ or more (75 centipoise or more) based on a #4 food cup. The amount of paint discharged, that is, the amount of paint to be processed, varies considerably depending on the diameter of the open edge of the rotating body, the dimensions of the notch, etc., but according to the present invention, the paint having the above-mentioned viscosity is used, and the outside diameter of the edge is It is possible to form a beautiful coating film with no coating defects by electrostatic coating using a rotating body with a rotation rate of 60 TTm at a rate of up to 500 cc/min.

In this embodiment, the paint atomizing device is described only in the form of a cup, but the present invention is also suitable even if the shape of the paint atomizing device is a flat disk-like shape or a disk-like shape. It should be understood that this can be done in any way.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional plan view of the entire electrostatic coating device, FIG. 2 is a side sectional view of the device shown in FIG. 1, FIG. 3 is a side sectional view of the cup-shaped paint atomizing device, and FIG. The figure is a front view of the atomization device shown in FIG. 3, FIG. ■
7 and 8 are enlarged front views of a part of the circumferential edge of the paint atomizing device. 1 is the main body of the painting device, 6 is the motor, 8 is the cup-shaped paint atomizer, 13 is the paint supply vibrator, 14 is the high voltage cable connection terminal, 19 is the inner peripheral surface, 20 is the circumferential tip, and 23 is the annular surface. , 24 are concave portions, 25, 25a, and 25b are ridge lines, and α is the angle at which the concave degree and the ridge line are inclined with respect to the radial direction of the (rotary) paint atomizing device, respectively.

Claims (1)

[Scope of Claims] 1. A paint atomizing device comprising an inner circumferential surface for guiding liquid paint toward the tip in the form of a thin film and a circumferential tip for atomizing and discharging the paint, comprising: The circumferential tip of the paint atomizer has an annular surface substantially perpendicular to the axis of rotation of the paint atomizer, the annular surface having regularly repeating recesses and ridges in the radial direction. for electrostatic coating, characterized in that the ridges are formed so as to be inclined relative to each other, and the ridges are arranged so as to overlap each other or to be connected at small intervals when projected in the radial direction. High speed rotating atomizer. 2. The atomization device according to claim 1, wherein the recess and the ridge line are provided in the annular surface in the form of sawtooth wave-like notches. 3. The atomizing device according to claims 1 and 2, wherein the paint atomizing device has a so-called cup-like shape. 4. Claims 1 to 2, wherein the paint atomizing device has a so-called flat circular dish shape or disk shape.
Atomization device as described in section.