Note: Descriptions are shown in the official language in which they were submitted.
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ROTARY ELECTROSTATIC ATOMIZER
FIELD OF THE INVENTION
[0001] The present invention relates to a rotary electrostatic atomizer.
BACKGROUND OF THE INVENTION
[0002] Electrostatic coating is a technology for bringing atomized and
electrically
charged paint particles into adhesion onto a work. One of known devices for
such
coating is a rotary electrostatic atomizer having a rotary head (normally
called a "bell
cup"). This kind of electrostatic atomizer is used with a powder paint,
electrically
insulating liquid paint (such as oil paint) and electrically conducting paint
(such as
waterborne paint). Electrostatic atomizers used with an insulating paint are
typically
configured to electrically charge the paint with a high voltage applied to a
rotary head.
Most of electrostatic atomizers used with an electrically conducting paint are
configured
to electrically charge the paint with a high voltage applied across external
electrodes
provided outside the atomizer.
[0003] Rotary electrostatic atomizers use shaping air to direct the paint
toward
an intended work. Patent Document 1 (Japanese Patent Laid-open Publication No.
H03(1991)-101858) points out the problem that the width of the coating pattern
becomes narrower with an increase of the quantity of the shaping air, and
proposes to
improve this problem by inclining the emitting or discharging direction of the
shaping
air about the rotation axis line of the rotary head. By noting this prior
Patent Document
1, detailed explanation of this proposal is omitted here. In short, such a
decrease of the
width or area of the coating pattern with an increase of the quantity of the
shaping air
is caused by a negative pressure produced in a forward region of the rotary
head. That
is, the negative pressure acts to pull in the shaping air inward, and this
results in
reducing the width (or area) of the coating pattern.
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[0004] The proposal of Patent Document 1, namely, emitting the shaping air in
inclined directions about the rotation axis line of the rotary head thereby
makes a
spiral flow of shaping air to make use of the centrifugal force of the spiral
flow to
alleviate or cancel the influence from the reduced or negative pressure and
thereby increase the coating pattern width (or area).
[0005] This proposal of Patent Document 1 is useful for increasing the
quantity
of shaping air to enhance the finished quality (brightness) of coating by a
rotary
electrostatic atomizer when a metallic paint containing aluminum or mica
particles
is used.
[0006] Patent Document 2 (Japanese Patent Laid-open Publication No.
H07(1995)-24367) points out that rotary electrostatic atomizers of the type
disclosed in Patent Document 1 is fixed in width of the coating pattern, and
therefore involves the problem of overspray when coating thin works such as
vehicle pillars, and proposes a countermeasure.
[0007] More specifically, Patent Document 2 proposes to reduce the coating
pattern width by emitting shaping air (first shaping air) in inclined
directions about
the rotation axis line of the rotary head like Patent Document 1, and emitting
second shaping air outside the first shaping air, such that the both air flows
get
into collision.
[0008] Patent Document 3 (USP 6,991,178) is different from Patent Documents
1 and 2 in not inclining the emitting direction of shaping air about the
rotation axis
line of the rotary head. Patent Document 3 rather proposes to narrow the
coating pattern width by emitting shaping air toward a conical outer
peripheral
surface of the rotary head and also emitting pattern control air radially
outwardly
adjacent to the shaping air to bring the both air flows into collision.
[0009]
[Patent Document] JP Laid-open Publication No. H03(1991)-101858
[Patent Document] JP Laid-open Publication No. H07(1995)-24367
[Patent Document] USP 6,991,178
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SUMMARY OF THE INVENTION
[0010] The present invention seeks to solve the problem that the coating
pattern
width is fixed invariably when shaping air is emitted or discharged in
directions
inclined around a rotation axis line of a rotary head as disclosed in Patent
Document
1.
[0011] A further aspect of the present invention is to provide a rotary
electrostatic atomizer capable of changing the coating pattern width.
[0012] In a broad aspect, the invention provides a method of spraying a paint
using a rotary electrostatic atomizer having a rotary head for centrifugally
forwarding
and spraying the paint expelled from a front perimeter of the rotary head
toward a work
with the aid of shaping air comprising:
emitting the shaping air from the rotary head front perimeter in a shaping air
inclined direction around a rotation axis line of the rotary head,
emitting pattern control air from the rotary head front perimeter in a control
air
inclined direction around the rotation axis line of the rotary head front
perimeter, the
pattern control air being emitted radially outwardly alongside the shaping air
in the
same direction as that of the shaping air, and
an angle of the control air inclined direction of the pattern control air is
larger
in absolute value than an angle of the shaping air inclined direction of the
shaping
air.
[0012A] A further aspect of the invention comprehends a rotary electrostatic
atomizer comprising:
a rotary head for centrifugally forwarding a paint;
a plurality of shaping air outlets aligned on a first circle concentric with a
rotation axis line of the rotary head to emit shaping air which directs the
paint emitted
from a front perimeter of the rotary head toward a work; and
a plurality of pattern control air outlets aligned on a second circle
concentric
with and having a larger diameter than the first circle to emit pattern
control air
alongside the shaping air. A shaping air adjusting means is provided for
adjusting the
quantity of the shaping air emitted from the shaping air outlets, and a
pattern control
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air adjusting means is provided for adjusting the quantity of the pattern
control air
emitted from the pattern control air outlets. A control means controls the
shaping air
adjusting means and the pattern control air adjusting means. The shaping air
outlets
and the pattern control air outlets are oriented in inclined directions around
the rotation
axis line of the rotary head, and the inclined direction of the shaping air
outlets and that
of the pattern control air outlets are in the same direction. An angle 13 of
the inclined
direction of the pattern control air outlets is larger in absolute value than
an angle cC.
of the inclined direction of the shaping air outlets.
[0013] FIG. 1 shows a general concept of the present invention. In FIG. 1,
reference letter L denotes a rotation axis line of a rotary head. Shaping air
outlets 1 are
a plurality of holes aligned on a first circle 2 having its center on the
rotation axis line
L of the rotary head. Radially outward of the first circle 2, pattern control
air outlets
3 are provided. The pattern control air outlets 3 are a plurality of holes
aligned on a
second circle 4 concentric with and larger than the first circle 2. Arrow A in
FIG. 1
indicates the rotating direction of the rotary head.
[0014] Shaping air 5 emitted in inclined directions around the rotation axis
line
L from the shaping air outlets 1 is shown by broken lines in Fig. 1. The
shaping air
makes a first spiral air flow. Outside the spiral air flow of the shaping air
5,
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the pattern control air 6 emitted from the pattern control air outlets 3 makes
a
spiral air flow.
[0015] As explained in the chapter of background art with reference to Patent
Document 1, the coating pattern width tends to be reduced by a negative
pressure
produced in a forward region of the rotary head as the quantity of the shaping
air
increases. However, the spiral air flow of the shaping air 5 can generate a
centrifugal force large enough to reduce the influence of the negative
pressure or
overcome the negative pressure, and can thereby increase the coating pattern
width. Further, another spiral air flow of the pattern control air 6 is made
radially
outward of the spiral air flow of the shaping air 5 to whirl in the same
direction.
Setting the angle 13 of inclination of the pattern control air outlets 3
larger in
absolute value than the angle a of inclination of the shaping air 5 makes it
possible to increase the swirling rate of the pattern control air 6 and
thereby
enhance the centrifugal force of the shaping air 5, which further increases
the
coating pattern width. In addition, by changing the quantity of the pattern
control
air 6 relative to the quantity of the shaping air, the coating pattern width
can b e
controlled variously. It is also possible to change the coating pattern width
by
increasing or decreasing the quantity of the shaping air 5. Therefore, the
present invention can control the coating pattern width variously by
controlling the
quantity of the shaping air 5 or quantity of the pattern control air 6, or by
controlling the relative quantity of the pattern control air with respect to
the
quantity of the shaping air 5.
[0016] FIG. 1 shows a preferable mode in which the shaping air 5 and the
pattern control air 6 as swirling in the same direction that is opposite from
the
rotating direction A of the rotary head, i.e. a trailing direction behind the
rotating
direction A of the rotary head. However, the whirling direction of the shaping
air
5 and the pattern control air 6 may be the same as the rotating direction A of
the
rotary head.
[0017] The rotary electrostatic atomizer summarized above is typically
assembled to or in a coating robot widely used for coating vehicle bodies, and
used to coat works under automatic control. In this case, useless paint caused
by its overspray can be reduced by changing the coating pattern width in
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accordance with the width of one portion to another of the work. The rotary
electrostatic atomizer according to the invention is applicable to
electrostatic
atomizers of various types for liquid paints, powder paints, electrically
insulating
paints, or electrically conductive paints. Needless to say, the atomizer is
also
suitable for use with metallic liquid paints for which an increase of the
quantity of
the shaping air is especially desirable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a diagram showing a basic concept of the present invention.
FIG. 2 is a perspective view of a front end portion of an electrostatic
atomizer according to a first embodiment, taken from a front diagonal
direction.
FIG. 3 is side elevation of a front end portion of the electrostatic
atomizer according to the first embodiment.
FIG. 4 is a sectional view of a front end portion of the electrostatic
atomizer according to the first embodiment of the invention.
FIG. 5 is a sectional view corresponding to FIG. 4, for explaining a first
modification.
FIG. 6 is a sectional view corresponding to FIG. 4, for explaining a
second modification.
FIG. 7 is a sectional view corresponding to FIG. 4, for explaining a third
modification.
FIG. 8 is a sectional view corresponding to FIG. 4, for explaining a
fourth modification.
FIG. 9 is a sectional view corresponding to FIG. 4, for explaining a fifth
modification.
FIG. 10 is a sectional view corresponding to FIG. 4, for explaining a
second embodiment.
KEY TO REFERENCE NUMERALS AND SYMBOLS
[0019] L Rotation axis of the rotary head
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A Rotating direction of the rotary head
1 Shaping air outlets
2 First circle with alignment of shaping air outlets
3 Pattern control air outlets
4 Second circle with alignment of pattern control air outlets
Shaping air
6 Pattern control air
BEST MODES FOR CARRYING OUT THE INVENTION
[0020] Some preferred embodiments of the invention are explained below with
reference to the drawings.
[0021] First Embodiment (FIGS. 2-4)
A rotary electrostatic atomizer 10 shown in FIGS. 2 to 4 include a rotary
head 12, often called a bell cup 12, having a conical wall surface and rotated
by
an air motor housed in an atomizer main body 11 to forward and disperse a
paint
under a centrifugal force, similarly to existing atomizers of this type. A
paint is
supplied to a central part of the bell cup 12, and after moving radially
outwardly
along the inner surface of the bell cup 12, the paint is expelled from the
front
(downstream) perimeter 12a of the bell cup 12. Reference letter L in the
drawings denotes the rotation axis line of the bell cup 12, and an arrow A
indicates the rotating direction of the bell cup 12.
[0022] The shaping air outlets 1 and the pattern control air outlets 3 are
located behind the front perimeter 12a of the bell cup 12. In FIG. 4,
reference
numeral 13 denotes a ring-shaped space for the shaping air, and 14 denotes a
ring-shaped space for the pattern control air. The ring-shaped space 13 for
the
shaping air and the ring-shaped space 14 for the pattern control air are
provided
at the distal end (front end, i.e. downstream end) of the atomizer main body
11.
The ring-shaped space 13 for the shaping air is supplied with compressed air
from
a first air source 16 via a first air supply path 15. The ring-shaped space 14
for
the pattern control air is supplied with compressed air from a second air
source 18
through a second air supply path 17. As explained later with reference to a
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modification, the first air source 16 and the second air source 18 may be a
single
common air source 22 (see FIG. 5, for example).
[0023] A first control valve 19 and a second control valve 20 are provided
respectively in the first air supply path 15 and the second air supply path
17.
The first and second control valves 19, 20 are controlled by a signal from a
control panel 21 to adjust the quantity of air supplied to the ring-shaped
space 13
for the shaping air and the ring-shaped space 14 for the pattern control air.
[0024] The shaping air outlets 1 provided at the front end surface of the
atomizer main body 11 and the pattern control air outlets 3 around the outlets
1
are configured to incline their discharge directions around the rotation axis
line L
of the bell cup 12, as explained before with reference to FIG. 1 (angles a and
13 in
FIG. 1). The shaping air outlets 1 are a plurality of bores aligned on a
circle
(designated by reference numeral 2 in FIG. 1) having its center on the
rotation
axis line L of the bell cup 12. In the illustrated atomizer, these bores are
in form
of a number of minute pores. The pattern control air outlets 3 are a plurality
of
bores aligned on a circle (designated by reference numeral 4 in FIG. 1) that
is
concentric with and larger than the circle 2 of the shaping air outlets 1. The
pattern control air outlets 3 are also illustrated in this embodiment as being
a
number of minute pores.
[0025] The direction of inclination of the shaping air outlets 1 and the
pattern
control air outlets 3 may be equal to the rotating direction A of the bell cup
12.
However, it is preferable that the direction of inclination is opposite from
the
rotating direction A of the bell cup 12, i.e. a trailing direction behind the
rotating
direction A of the bell cup 12, as shown in FIG. 1. In addition, as already
explained with reference to FIG. 1, the inclination angle a of the shaping air
outlets 1 is smaller than the inclination angle [3 of the pattern control air
outlets 3
in absolute value. In other words, absolute value of the inclination angle [3
of the
pattern control air outlets 3 is larger than absolute value a of the shaping
air
outlets 1 >
[0026] In the first embodiment, both the orientation of the shaping air
outlets 1
and the orientation of the pattern control air outlets 3 are parallel to the
rotating
axis line L of the bell cup 12, and the shaping air outlets 1 is directed
toward the
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front (downstream) perimeter 12a of the bell cup 12, as best shown in FIG. 4.
As
a result, shaping air emitted from the shaping air outlets 1 acts to spray the
paint
toward a work (not shown) located downstream (forward) of the bell cup 12.
That is, the shaping air not only acts to direct the paint toward the work,
but also
functions to atomize the liquid paint expelled from the front perimeter 12a of
the
bell cup 12.
[0027] The rotary electrostatic atomizer 10 according to the first embodiment
is
optimum for use with a liquid paint, such as a metallic paint, i.e. a liquid
paint
containing metal powder or particulates, especially for vehicle bodies. In the
course of coating a vehicle body, control of the first and second control
valves 19,
20 is performed to adjust the spread width of the atomized paint and make a
coating pattern width suitable for a relatively wide coating target such as a
roof of
a vehicle body, or a relatively narrow coating target such as pillars of a
vehicle
body. This is particularly effective to reduce overspray upon coating
relatively
narrow portions such as pillars.
[0028] First Modification (FIG. 5)
The above-explained rotary electrostatic atomizer 10 according to the
first embodiment may be modified as shown in FIG. 5. More specifically,
although the rotary electrostatic atomizer 10 according to the first
embodiment is
configured to supply compressed air to the ring-shaped space 13 for the
shaping
air and the ring-shaped space 14 for the pattern control air from independent
first
and second air sources 16, 18, the rotary electrostatic atomizer 30 shown in
FIG.
is configured to supply compressed air to the ring-shaped space 13 for the
shaping air and the ring-shaped space 14 for the pattern control air from a
common air source 22.
[0029] The rotary electrostatic atomizer 30 according to the first
modification
is identical to the first embodiment in the feature that the angle 6 of
inclination of
the pattern control air outlets 3 is larger in absolute value than the angle a
of
inclination of the shaping air outlets 1 and in the feature that the
orientation of the
pattern control air outlets 3 is parallel to the orientation of the shaping
air 1.
However, the atomizer 30 according to the first modification is different from
the
atomizer 10 according to the first embodiment in that the shaping air outlets
1
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direct toward the conical outer surface 12b of the bell cup 12 instead of its
front
(downstream) perimeter 12a.
[0030] Second Modification (FIG. 6)
A rotary electrostatic atomizer 40 as a second modification shown in FIG.
6 is different from the electrostatic atomizer 30 according to the first
modification
(FIG. 5) in orientation of the pattern control air outlets 3. In the second
modification, orientation of the pattern control air outlets 3 is determined
such that
the shaping air 5 emitted from the shaping air outlets 1 flows in parallel to
the
center line of the shaping air 5 deflected by the front (downstream) perimeter
12a
of the bell cup 12.
[0031] Third Modification (FIG. 7)
A rotary electrostatic atomizer according to a third modification show in
FIG. 7 is common to the first embodiment shown in FIG. 4 in that the shaping
air
outlets 1 are directed to the front (downstream) perimeter 12a of the bell cup
12.
However, the direction of the shaping air outlets 1 pointing the front
(downstream)
perimeter 12a of the bell cup 12 is not parallel to the rotation axis line L.
Instead,
the direction of the shaping air outlets 1 is angled with an elevation angle
(+0)
relative to an imaginary line L' drawn from the center of the front end of
each
shaping air outlet 1 in parallel to the rotation axis line L of the bell cup
12, for
example, by changing the diameter of the first circle 2 of the shaping air
outlets
relative to the outermost diameter of the bell cup 12.
[0032] Fourth Modification (FIG. 8)
A rotary electrostatic atomizer 60 according to the fourth modification
shown in FIG. 8 is contrary to the atomizer 50 according to the third
modification
shown in FIG. 7 in that the direction of the shaping air outlets 1 is angled
by a
depression angle (-8) relative to an imaginary line L' drawn from the center
of the
front end of each shaping air outlet 1 in parallel to the rotation axis line L
of the
bell cup 12.
[0033] Fifth Modification (FIG. 9)
Although the first embodiment (FIG. 4), third modification (FIG. 7) and
fourth modification (F(G. 8) propose to direct the orientation of the shaping
air
outlets 1 toward the front (downstream) perimeter 12a of the bell cup 12, the
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rotary electrostatic atomizer 70 according to the fifth modification orients
the
direction of the shaping air outlets 1 toward a proximity of the front
(downstream)
perimeter of the bell cup, that is, toward an imaginary concentric circle
slightly
larger than the front (downstream) perimeter 12a of the bell cup 12.
[0034] Second Embodiment (FIG. 10)
The first embodiment and its modifications have been explained with
reference to FIGS. 2 through 9 as the shaping air 5 acting to spray the paint
expelled from the front (downstream) perimeter 12a of the bell cup 12 toward a
work and to atomize the paint just after expelled from the front perimeter 12a
of
the bell cup 12. In a rotary electrostatic atomizer 80 according to the second
embodiment shown in FIG. 10, however, the shaping air 5 does not function to
atomize the paint expelled from the front perimeter 12a of the bell cup 12.
Instead,
the shaping air 5 only acts to direct the paint toward the work. Also in the
electrostatic atomizer 80 according to the second embodiment, the shaping air
outlets 1 and the pattern control air outlets 3 may incline in the same
direction as
the rotating direction A of the bell cup 12. Preferably, however, these
outlets 1
and 3 had better incline in the opposite direction from the rotating direction
A of
the bell cup 12, i.e. a trailing direction behind the rotating direction A of
the bell
cup 12. Here again, as already explained with reference to FIG. 1, the angle
13 of
inclination of the pattern control air outlets is larger in absolute value
than the
angle a of inclination of the shaping air outlets 1 (1131 > lal).
[0035] Also in the rotary electrostatic atomizer 80 according to the second
embodiment, similarly to the first embodiment, the coating pattern width can
be
controlled variously by supplying the pattern control air 6 to envelope the
swirling
shaping air 5 from outside and to swirl in the same direction, and by
controlling
the quantity of the pattern control air 6 relative to the shaping air 5 or
controlling
the quantity of the shaping air 5.
