U.S. patent number 3,801,869 [Application Number 05/292,160] was granted by the patent office on 1974-04-02 for booth for electrostatic powder painting with contact type electric field curtain.
Invention is credited to Senichi Masuda.
United States Patent |
3,801,869 |
Masuda |
April 2, 1974 |
BOOTH FOR ELECTROSTATIC POWDER PAINTING WITH CONTACT TYPE ELECTRIC
FIELD CURTAIN
Abstract
A booth in which electrically charged particulate material is
sprayed onto a workpiece having an opposite charge, so that the
particles are electrostatically attracted to the workpiece, has all
of its walls that confront the workpiece made of electrical
insulating material. A grid-like arrangement of parallel, spaced
apart electrodes, insulated from each other, extends across the
entire area of every wall, parallel to a surface of the wall and in
intimate juxtaposition thereto. Each electrode is connected with
one terminal of an alternating high voltage source, every electrode
with a different terminal than each of the electrodes laterally
adjacent to it, to produce a constantly varying field that
electrodynamically repels particles from the wall.
Inventors: |
Masuda; Senichi (Nishigahara,
Kita-ku, Tokyo, JA) |
Family
ID: |
13662892 |
Appl.
No.: |
05/292,160 |
Filed: |
September 25, 1972 |
Foreign Application Priority Data
|
|
|
|
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Oct 6, 1971 [JA] |
|
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46-78470 |
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Current U.S.
Class: |
361/227; 134/1;
454/53; 55/DIG.46; 361/233; 96/54 |
Current CPC
Class: |
B05B
7/1454 (20130101); B05B 14/41 (20180201); B05B
14/412 (20180201); B05B 14/42 (20180201); B05B
5/088 (20130101); Y10S 55/46 (20130101) |
Current International
Class: |
B05B
5/08 (20060101); B05B 15/12 (20060101); B08b
007/00 () |
Field of
Search: |
;98/115SB ;15/1.5 ;134/1
;417/48,49 ;209/127,128,129,130,131 ;174/211 ;241/166 ;198/41
;117/93.41 ;118/628,DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
IBM Technical Disclosure Bulletin Vol. 7, No. 3-Aug. 1964, p. 181,
"Removing Impurities From Surfaces"..
|
Primary Examiner: Shoop, Jr.; William M.
Assistant Examiner: Moose, Jr.; Harry E.
Claims
What is claimed is:
1. A booth for electrostatic spray coating, having a zone at its
interior at which a workpiece can be located, said booth being
adapted for use with apparatus of the type comprising a nozzle that
is directed toward said zone and from which particulate material to
be coated onto the workpiece can issue, and means for impressing an
electrical charge of one polarity upon particles of said material
before they issue from the nozzle and for impressing upon the
workpiece an opposite charge that tends to attract the particles to
it electrostatically, said booth being characterized by:
A. substantially all walls of the booth that are in confronting
relation to said zone being of a material that is substantially an
electrical nonconductor;
B. a plurality of elongated electrodes distributed over
substantially the entire area of a surface of each of said walls,
said electrodes extending parallel to said surface and being in
intimate juxtaposition thereto, and being in electrically insulated
relation to one another, and substantial portions of the electrodes
being in closely spaced parallel relation to one another and
arranged alternately with one another in a regular sequence;
C. means for connecting each of said electrodes with only one of
the plural terminals of different polarity of a source of high
alternating voltage, each electrode being connected with a terminal
of said source that is different from the terminal to which each of
its adjacent electrodes is connected, so that the several
electrodes cooperate to produce a constantly varying electrical
field by which charged particles are repelled from the walls.
2. The spray booth of claim 1, further characterized by:
D. there being at least three of said electrodes distributed over
the area of the bottom wall portions of said booth and alternating
with one another in a regular sequence thereacross; and
E. said means for connecting each of the last mentioned electrodes
with a terminal of a high alternating voltage source providing for
such connection of said electrodes with a multi-phase high
alternating voltage source that there is a phase difference between
every electrode and its laterally adjacent electrodes, so that the
constantly varying electric field conjointly produced by all of
said last mentioned electrodes has a wave-like variation by which
charged particles are both repelled from the inner surface of said
bottom wall portions and urged along the wall in one direction
transverse to said parallel portions of said last mentioned
electrodes.
3. The spray booth of claim 2 wherein all of said bottom wall
portions are inclined to the horizontal and slope downwardly in
said one direction so that the force of gravity tends to supplement
the effect of the constantly varying electric field in transporting
the particles in said one direction, further characterized by:
F. collecting means having an inlet adjacent to the lowest edge
portions of said wall portions and into which particles can fall
after being transported along said wall portions, to be available
for re-use.
4. The spray booth of claim 3, wherein bottom wall portions of the
spray booth are porous, further characterized by:
G. means for directing a flow of pressurized gas upwardly through
said porous bottom wall portions and into the interior of the spray
booth;
H. filter means external to the spray booth, for filtering
particles of said material out of gas in which they are entrained;
and
I. passage defining means having an inlet communicated with the
interior of the spray booth near the top thereof and having an
outlet opening to said filter means, for conducting to the filter
means gas that has flowed upwardly through the spray booth from
said porous bottom wall portions, together with particles entrained
in such gas.
Description
This invention relates to a booth for electrostatic powder painting
having a device for removing powder particles from the wall of the
booth with a contact type electric field curtain.
Hitherto in the actual practice of electrostatic painting with
powder, various methods have been employed. For example, powder for
painting is dispersedly discharge into the space in front of the
object to be painted and is electrically charged by means of a gun
supplied with a d.c. high voltage and electrostatic force drives
the powder onto the surface of the object to be adhered thereon,
after which for example, by heating, said powder is adhesively
attached to said surface. In this instance, since a part of the
powder particles dispersed in the space do not attach to the object
to be painted, a booth is provided to surround the space in which
the painting operation is performed and in which the object to be
painted is placed, and the floating particles that are not arrested
to the object are carried by air through a hood arranged in the
booth are collected in a suitable dust collector such as a cyclone
or bag filter.
However, in this instance, the floating powder particles, having
been electrified, tend to become attached to the inner wall of the
booth due to the influence of an electric image; and further, since
such particles are of a substance such as plastic, resin or the
like having high electric resistance, once attached to the wall,
they tend to hold an electric charge for a long time. Consequently,
as the painting operation proceeds, it has been usual that powder
particles accumulate on the inner wall of the booth, the inner wall
of the hood, and, in some cases, the inner wall of a duct leading
from said hood to the dust collector, and on the inner wall of a
hopper beneath the hood. In such cases it is difficult to strip off
powder particles accumulatingly deposited on the walls merely by
mechanical hammering.
Therefore when kind or color of powder particles has been changed
in the course of a painting operation, such particles of different
kinds or colors are mixedly deposited on said inner walls; and as
these mixed powders are collected in a mass, it becomes difficult
to separately sort and collect them. This spoils the utility value
of the powder resulting in considerable economic loss.
The object of the present invention is to eliminate such
difficulties by preventing painting powder from settling on said
inner walls of the booth, hood, hopper, cyclone or bag filter. This
is done by continually or intermittently removing whatever sort of
painting powder attaches to the walls using electrical means
whereby any powder clinging to the inner wall of the booth is
completely swept off. If kind or color of powder has been changed
in the course of a painting operation, the present invention
nevertheless makes it possible to separately sort and collect the
different powder particles.
The object of the present invention is achieved by providing
contacting type electric field curtain apparatus having a powerful
electrodynamic function for driving deposited powder off the inner
wall of the booth, hood, duct, hopper and various dust collectors
and removers.
The contact type electric field curtain apparatus just referred to
is a device that functions to drive off whatever sort of powder is
settled on the wall by producing a constantly changing electric
field that employs an electrodynamic principle.
The basic construction and operation of that apparatus will become
more apparent as the description proceeds with reference to the
accompanying drawings, in which:
FIG. 1 is a diagrammatic view of stationary wave contact type
electric field curtain apparatus according to the present
invention.
FIG. 2 is a similar view of traveling wave contact type electric
field curtain apparatus.
FIG. 3 is a front view of one example of stationary wave contact
type electric field curtain apparatus that can be use, in the
present invention.
FIG. 4 is a section view taken on the plane of the line IV--IV in
FIG. 3.
FIG. 5 is a front view of another example of stationary wave
contact type electric field curtain apparatus that can be used in
the present invention.
FIG. 6 is a section view taken on the plane of the line VI--VI in
FIG. 5.
FIG. 7 is a front view of an example of a traveling wave contact
type electric field curtain apparatus.
FIG. 8 is a section view taken on the plane of the line VIII--VIII
in FIG. 7.
FIG. 9 is a front view of still another example of electric field
curtain apparatus.
FIG. 10 is a section view taken on the plane of the line X--X in
FIG. 9.
FIG. 11 is a diagrammatic view of one example of a novel booth for
electrostatic powder painting according to the present
invention.
In FIG. 1, numeral 1 designates an insulator or semiconductor body
1 (referred to as an exciter) placed in close or contacting
relation to a number of electrodes 2, 3, 2', 3' ..... that are
arranged in parallel and insulated relation to one another, these
electrodes being alternately connected to conductors 4 and 5,
respectively in two groups, and said leads 4 and 5 being further
connected through leads 6, 7 respectively to the secondary
terminals A, B of a single-phase transformer 8. When an a.c.
voltage is applied thereto, there is produced between adjacent
electrodes a series of stationary wave constantly varying
alternating electric fields 10 having electric force lines 9 as
shown by dotted lines 9. Some of the lines of force, as indicated
at 11, penetrate through the exciter and enter into the space 12 at
the side of the exciter remote from the electrodes. Now if powder
14 of any kind deposits on the surface 13 of the exciter, that is
remote from the electrodes, then, because of contact
electrification between the powder and the exciter either one is
positively charged and the other is negatively charged.
Hence the stationary wave constantly varying electric field curtain
generally exerts a strong electrodynamical repulsive action upon
the charged powder particles, whether they be positively or
negatively charged, to drive in the direction of arrow 15, that is
in the direction away from the series of electrodes 2, 3, 2', 3'
..... and thus said power particles 14 are repelled in the
direction 15 by action of the constantly varying alternating
electric field curtain penetrated into said area 12 whereby the
particles are removed from the surface 13 of the exciter and fall
down by gravity in the direction of arrow 16.
Thus there is provided a combination of an exciter to create a
contact charge by contact with object powders and a constantly
varying alternating electric curtain functioning to repel the
charged powders. The inventor named the apparatus that has
repelling and driving action to powders as a contact type electric
field curtain, and also named apparatus based on this as contact
type electric field curtain apparatus. Addition to the stationary
wave constantly varying alternating electric field curtain produced
by applying a single-phase alternating voltage as shown in FIG. 1
it is also possible to produce a traveling wave constantly varying
electric curtain field formed by applying a poly-phase alternating
voltage in phase order to the corresponding electrodes. In the
latter case, besides electrodynamic repulsion there is generated an
electrodynamic propelling action that to forcibly transports powder
particles, whether they be positively or negatively charged, in the
direction that the traveling wave is oriented.
FIG. 2 shows one example of such travelling wave apparatus with
three-phase alternating voltage used as an electric source.
An exciter 1 is placed in close or contacting relation to a number
of electrodes 17, 18, 19, 17', 18', 19' ...., arranged in parallel
and in insulated relation to one another. The electrodes are
divided into three groups by connecting every third electrode to
one of the conductors 20, 21, 22 said conductors are further
connected respectively in phase order to the corresponding
secondary terminals U,V,W of three-phase transformer 26, in either
the primary or the secondary side thereof, the neutral point of Y
connection being earthed, whereby between adjacent electrodes 17,
18, 19, 17', 18', 19' ....., there is produced a traveling
constantly varying alternating electric field 29 represented by
electric force lines 28 which field advances along the electrodes
in a direction 27 a part of the lines of force pass through the
exciter 1 and come into the area 12 at the side of the exciter
remote from the electrodes. In contacting the surface 13 of the
exciter 1, deposited charged powder particles 14 are strongly
repelled with electrodynamic force in the direction of arrow 15 and
are concurrently driven in the direction of arrow 27. As a result,
the deposit of powder particles 14 is forcibly driven off from the
surface 13 of the exciter 1 and is transported in the direction of
arrow 27. Of the contact type electric field curtains, utilizing
the traveling wave constantly alternating electric field is called
as traveling wave contact type constantly varying electric field
curtain.
In general all devices that produce the stationary wave or
traveling wave contact type electric field curtain can be regarded
as electric field curtain apparatus. Therefore, here the contact
type electric field curtain apparatus can be incorporated in a
variety of devices having (for ex. a bag filter air-permeable
contact type electric field curtain apparatus applied to its cloth,
an air slide conveyor having an air-permeable plate is comprising
such a said unit, unit, or a duct or chute constituted with a
cylinder shaped contact type electric field curtain) In these
instances, if deposited powder particles have already been
sufficiently electrified by a previous charging that adapts them to
be used for painting, the operation of such contact type electric
field curtain apparatus will have a strange electrodynamic
effect.
Accordingly when such stationary wave or traveling wave contact
type electric field curtain apparatus is arranged to the inside
wall of a booth, hood, duct, hopper or any kind of dust collector
or dust removing device on which spreading power settles, the
powder can be continually or intermittently removed therefrom
solely by electrical means and without need for mechanical removal
apparatus.
In this connection, the electrodes in FIG. 1 and FIG. 2 not need be
of metal but instead any electrically conductive painting film,
plastic, fiber, carbonic fiber or any other conductive material may
be used. Also the electrodes can be in the shape of a bar, panel,
plate, net or any other suitable shape. Further, the electrodes may
be placed not only in close or contacting relation to one side of
the exciter, as shown in FIG. 1 and FIG. 2, but could also be
placed on the opposite sides of the exciter or could be embedded in
the exciter.
The exciter can be of any organic material such as plastic,
bakelite, or ebonite, or of any inorganic material such as glass,
cement, asbestos. In this instance, as for fire protection,
incombustible or noninflammable material is preferably used for the
exciter. Needless to say, the exciter may be in the form of a
plate, sheet, filament, net, cloth, fiberous layer, porous plate,
thread, tape or tube or any other suitable shape.
As applicable voltage, either single-phase or poly-phase
alternating voltage may be used and as the case may be, a d.c.
voltage may be superposed or an impulse voltage may be applied or
superposed. Also as it may be necessary to remove an electric
charge from the stripped powder layer and to prevent its particles
from resettling, any unelectrifying device utilizing a.c. or d.c.
corona discharge, or unelectrifying device utilizing radiation or
any other suitable means, may be arranged in the booth, hood, duct,
dust collector, hopper or in any other suitable location to
function in cooperation with a contact type electric field
curtain.
Now a contact type electric field curtain apparatus to be used for
a novel booth according to the present invention will be
specifically described with reference to the drawings.
FIG. 3 is a front view of a unit of contact type electric field
curtain apparatus to be used in a novel booth according to the
present invention in which a number of sheet electrodes are
embedded in a plate exciter made of incombustible synthetic resin
such as teflon, vinyliden fluoride, or vinyl fluoride, to produce a
stationary wave contact type electric field curtain as illustrated
in FIG. 1. In FIG. 3 and FIG. 4, in a plate exciter 1 of about 4mm
thick, there are embedded a number of aluminum sheet electrodes 2,
3, 2', 3'....., each of about 10mm wide and 0.1mm thick and
arranged in parallel to one another with equal spaces of 10mm
between them to produce a stationary wave electric field
curtain.
The electrodes are alternately connected to conductors 3,4 likewise
embedded, and via terminals 31, 32 and 31', 32', are connected in
series or parallel to an adjacent similar unit and further
connected to a single-phase a.c. power source (not shown). Thus, on
the opposite sides of the exciter 1 there is formed a stationary
wave contact type electric field curtain like that shown in FIG.
1.
FIG. 5 is a front view of another contact type electric field
curtain apparatus unit that can be used for a novel booth. Therein,
on the surface of a plate exciter, electric wires sheathed with
incombustible resin are arranged. In FIG. 5 and FIG. 6, the plate
exciter 1 which is about 3 mm thick, has in its opposite sides
recesses 33, 34, 33', 34' ....., and 35, 36, 35', 36' ..... of
which alternate recesses differ in depth. On the face of the
exciter, two sheathed wires 37, 38, each having 3mm outer diameter,
are arranged in 15mm spaced apart relation to each other the
respective recesses and have their opposite ends connected to
adjacent similar units (not shown) respectively through terminals
31, 32 and 31', 32' leading to a single-phase a.c. power source
(not shown) whereby a stationary wave contact type electric field
as in FIG. 1 is formed on the surface of the exciter 1.
FIG. 7 is a front view of a unit generally like that of FIG. 3 and
FIG. 4 but adapted to create a traveling wave contact type electric
field curtain as shown in FIG. 2 in the opposite sides of the
exciter, by reason of the application of a three-phase a.c. voltage
instead of single-phase a.c. voltage. Every third one of the sheet
aluminum electrodes 17, 18, 19, 17', 18', 19' ..... enbedded in the
exciter is connected to one of the conductors 20, 21, 22 which are
likewise embedded and which are connected through terminals 39, 40,
41, 39', 40', 41' to an adjacent unit and are further connected
respectively in phase order to corresponding output terminals U, V,
W of a three-phase a.c. current source (not shown) whereby there is
formed a downwardly traveling wave contact type electric field
curtain on the opposite sides of the exciter 1.
FIG. 9 is a front view of a unit in which a traveling wave contact
type electric field curtain like that shown in FIG. 2 is formed on
the opposite sides of an exciter by applying three-phase a.c.
voltage. The plate exciter 1 like that in FIG. 5 and FIG. 6, has in
its opposite sides recesses 42, 43, 44, 42', 43', 44' ..... and 45,
46, 47, 45', 46', 47' ..... three progressively different depths.
As shown, three sheathed wires 48, 49, 50 extend in parallel and
equally spaced relation to one another on the surface of the
exciter 1 and through corresponding recesses; and at their opposite
ends they are connected to terminals 39, 40, 41 and 39', 40', 41'
respectively for connection to adjacent units and to be further
connected to output terminals of a three-phase a.c. power source
(not shown). There is thus produced on the surface of the exciter a
traveling wave contact type electric field curtain which advances
downwardly.
FIG. 11 is an example of a novel booth for effecting electrostatic
painting with powder, incorporating a stationary wave or traveling
wave contact type electric field curtain apparatus unit as shown in
FIG. 3 to FIG. 10.
The booth 52 has an opening 51 through which a powder spray nozzle
or gun 61 can be directed towards a workpiece 58 in the booth. In
the upper interior 53 of the booth, an earthed rail 54 is provided,
in the grooves 55 of which a pair of rollers 56 are slidable. The
workpiece 58 to be painted is suspended with a metal suspender 57
from said rollers. As the workpiece moves along the rails, painting
is effected with powder particles 62 blown from the nozzle 61 and
charged with negative high voltage from a d.c. negative high
voltage source 59 through a cable 60 connected to the nozzle. Then
the dispersingly discharged powder particles 63 are drawn by air
from the inside 53 of booth 63 through hood 64 and duct 65 to a
cyclone 67 that is provided with a suction fan 66. In the cyclone
the particles are collected and separated from the air. Clean air
is discharged upward through duct 68. The collected powder
particles for painting are delivered through an air-tight valve 69
onto an air-slide conveyor 70 are transported by it to a collector
pipe 71. Then by means of a selector valve 72, the particles are
sorted (in this case, it is assumed they are of two kinds) and they
are returned to respective tanks 73, 74 from which they can be
withdrawn and fed to the nozzle 61 for re-use. Also particles
slipping down from the deposit on the inner wall of the booth 52
and particles 96 settling by gravity directly from the interior of
the booth 52 are together carried by another air slide conveyor 97
and are returned through collector pipe 71 to the powder tank 73 or
74.
The returned powder particles in the tanks are supplied through
another selector valve 75 and outlet pipe 76 to an ejector 77. Then
by action of pressure air supplied from piping 78, the particles
are delivered through a flexible pipe 79 to the gun 61 and are
again ejected therefrom, electrically charged.
As already stated, to remove charged powder particles deposited on
the wall, by means of the electrodynamic driving action of the
contact type electric field curtain, a suitable contact type
electric field curtain apparatus unit as shown in FIG. 3 to FIG. 10
or any other contact type electric field curtain may be used. In
the embodiment shown in FIG. 11, there are traveling wave contact
type electric field curtain apparatus units 80, 81, 82 as shown in
FIG. 9 and FIG. 10.
Also, units 83, 84 of the same type are arranged on the inner wall
of the hood 64.
The units are connected, through assigned triple terminals, in
phase order to secondary terminals U, V, W of a three-phase
transformer 26 similar to that shown in FIG. 2, with a switch 85 on
its primary side. Thereby on the surface of each unit 80 - 84, a
traveling contact type electric field curtain is formed whereby as
stated before, the inner wall of the booth and hood are kept
completely clear of deposits of powder particles. Switch 85 may be
either kept closed or intermittently closed. In this case, with the
provision of a d.c. source, the secondary neutral point 86 of
three-phase transformer 26 is given a negative voltage against
earth whereby each electrode of the contact type electric curtain
apparatus units 80 - 84 is kept to a high negative voltage, that
is, maintained at the same polarity as the nozzle 61 relative to
the d.c. earthed workpiece 58. As a result negatively charged
particles 63 floating in the interior 53 of the booth are
influenced by an electric force that drives them from the surface
of the booth wall to the workpiece 58, thus further preventing
deposits of the powder particles on the wall surface. On the inner
wall of duct 65, stationary wave contact type electric field
curtain apparatus units 88, 89, of the type shown in FIG. 3 and
FIG. 4, are arranged, each being connected through two terminals to
the secondary terminals X, Y of the three-phase transformer 26 thus
to form a stationary wave contact type electric field curtain
whereby deposition of powder particles on the inner wall of the
duct is completely prevented.
In this instance, needless to say that instead of arranging the
contact type electric field curtain units 88, 89 at the local
positions, it is possible to form the duct 65 as a cylindrical
stationary or traveling wave contact type electric field curtain
unit.
Pressure air is forced from tubes 90, 91 the respective air slide
system conveyors 70, 97 into their lower chambers 92, 93
respectively, and thereabove are fiber layers or porous plates 94,
95 made of suitable insulating material which serve as exciters and
in each of which three sets of plate electrodes like those shown in
FIG. 6 and FIG. 7 are embedded. Those electrodes are connected
through a corresponding three terminals in phase order to the
respective secondary terminals U, V, W of the three-phase
transformer, whereby above the respective plates 94, 95 there is
produced a traveling wave contact type electric field curtain
oriented to the right which transports electrically charged powder
particles without depositing them on said conveyors 70 97.
In this connection, instead of the air slide system conveyor, a
chute, screw conveyor, chain conveyor or any other transportation
device may be used. And said contact type electric field curtain
apparatus unit may comprise the dust depositing face of the
conveyor or the conveyor casing itself may be made as a cylindrical
or other suitably shaped stationary wave or traveling wave contact
type electric field curtain apparatus. Also the inner wall of the
cyclone 67 may be lined with a suitably shaped contact type
electric field curtain, or instead of the cyclone 67, a bag filter
may be used comprised of air-permeable cloth or having a fiber
layer which itself constitutes an exciter of a contact type
electric field curtain apparatus.
As specifically described above, the novel device of the present
invention is enabled to effectively prevent painting powders from
settling on the inner wall of the booth, hood, duct, conveyor and
dust collector with solely electrical means and without the need
for any mechanical means. Therefore when it is necessary to change
the kind or color of powder, it is possible at any time to remove
and collect previously used powder so that there will not be any
mixture of power in painting.
A booth according to the present invention may be used not only in
electrostatic powder painting but also for electrostatic powder
coating on the inside of pipe, electrostatic printing,
electrostatic coloring, electrostatic pile planting and for any
other operation that involves imparting an electrostatic charge to
any powdery or fiberous object.
* * * * *