Note: Descriptions are shown in the official language in which they were submitted.
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The invention pertains to a method and spray guns for
the intermittent spray coating of powder.
The methods conventionally used for the intermittent
coating of powder include electrostatic coating, screen
printing, roll coating, and parasprinkling, but all of them
suffer from the following drawbacks:
(1) the outline of the coated pattern is indistinct,
(2) the powder adheres to areas where coating is not
required,
(3) the use of masking is necessary and powder
adheres to the masking,
(4) low productivity, and
(5) complicated maintenance
Even the electrostatic coating method which is said
to be best among the above-mentioned methods, cannot avoid
indistinctly outlining coating patterns as mentioned in (1).
In particular, noncleancut peripheral lines of string- or band-
like intermittent coat:ing are serious problems in coated
products.
Summar~ oE the Invention
As described above, the number of intermittent spray
operations is limited and the boundary lines of the patterns
are indistinct in the discontinuous string- or band-patterns
applied by the conventional intermittent powder spraying
methods and guns.
The object of the invention is to increase the number
of intermittent spray operations and to provide a method and
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guns that can produce cleancut boundary lines in string- or band-like
intermittent powder spray coating.
Generally speaking, the present invention provides a method
for intermittently spraying solid particulate powder downward onto
products wherein, when the solid particulate powder is to be sprayed
from a spray nozzle of a gun body whereon the spray nozzle is mounted,
a mixture of the powder and air continuously and constantly supplied
by a powder pump travels through a first ejector path in the gun body
and the nozzle, and when spraying of the powder is to be interrupted,
the continuously and constantly supplied mixture is discharged out
of the gun body through a bypass within the gun body, which is in
close proximity to the spray nozzle branching off from the first ejector
path in the gun body and a second ejector path which is connected
thereto and in which an air ejector nozzle mounted in the gun body
is disposed, and by the air-ejector being intermittently operated,
intermittent spraying of the powder from the nozzle is effected.
The above method may be carried out by way of a gun Eor inter-
mittently spraying so:Lid particulate powder downward onto products,
comprising: a gun body; a first ejector path through the gun body
for passing therethrough a mixture of powder and air to be sprayed;
a second ejector path through the gun body having an air ejector
therein, which air ejector is mounted within the gun body; a bypass
within the gun body connecting the two paths, and a spray nozzle con-
nected to the first ejector path with the spray nozzle being mounted
on the gun body and in close proximity to the bypass, whereby the
air-ejector is intermittently operated to bypass the powder so that
intermittent spraying may be effected.
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13rief Descrip~i n_ f the Drawings
Figure I illustrates an intermittent ejection method accord-
ing to the invention and shows a front cross section of the basic
structure of a gun.
Figure 2 is a front cross section of modification No. 1
of the gun.
Figure 3A is a front cross section of modification No. 2
of tile gun and;
l~igure 313 is a side cross .section of Figure 3A.
~ igure 4 shows a cross section of a gun of the invention
to which an electrostatic coating noz%le according
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to a Practical New Device Patent applied for by the present
applicant is attached.
Figure 5 shows a front view of a multinozzle gun of
the invention.
Figure 6 shows a system diagram of the equipment using
a gun according to the invention.
Figure 7 shows a plane view of a discontinuous string-
like coating applied by a gun of the invention.
Figure 8 shows a plane view of a discontinuous band-
like coating applied by a flat nozzle gun according to theinvention.
Figure 9 shows plane views of two examples of
multistripe coating by a multigun according to the invention.
Figure 10 is a system diagram of an intermittent powder coating
device equipped with a conventional powder pump.
Figure 11 is a system diagram of an intermittent
powder coating device equipped with a conventional pinch valve.
Description of the Prior ~r_
The reason why the outline of a pattern becomes
indistinct is explained in the fol:Low:ing. The sequence of
intermittent powder coating equipment of the conventional
electrostatic type is outlined in Figure 10.
The powder transported by air from a powder pump 93
mounted on a tank 92, i.e. the powder supply source, reaches
the gun 81 through a transport pipe 94 and a distributor 95.
The powder is then ejected from a nozzle 85 on the said gun 81
and coated effectively on surface P of the material to be
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coated under the action of a corona pin 89. The coated
pattern, however, does not have clear peripheral lines
especially in intermittent spray coating, as described above.
In the above-mentioned case, intermittent spraying is
carried out by intermittent operation of the powder pump 93
attached to the above-mentioned tank. Accordingly, when
periodically interrupting the spraying, the powder pump 93 must
be stopped. Thus, air transport of the powder is also stopped,
and as a result, the powder sinks to the bottom of the
transport pipe 94. When the spraying of the powder from the
nozzle 85 is restarted in this state, the fresh powder is air-
transported from the tank by once again operating the said
powder pump 93. In this case, the aforementioned powder that
has settled in the transport pipe 94 is air-transported
together with the fresh powder, reaches the gun 81, and is
sprayed as ejected from the nozzle 85. Therefore, the density
of the powder being sprayed naturally increases and as a
result, the coated pattern changes. When stopping this
spraying, the aforementioned powder pump 93 (an air ejector is
generally used) is stopped again, but the spray stop response
is slow because oE the relatively long transport pipe (or hose)
between the powder pump and the nozzle, as seen in the said
figure; thus the maximum number of intermittent operations is
30 cycles/min and no cleancut outline can be produced, with the
end of the coated pattern tailing off. As described above,
peripheral lines in string-or band-like intermittent coating
become indistinct.
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Intermittent spraying can also be performed with the
use of a pinch valve in the conventional techniques. Refer to
Figure 11. A pinch valve 116 is provided on the air transport
pipe 114 immediately before the gun 101. A pinch valve 116 is
a device to press or release an elastic tube by means of
regulated air pressure applied on said elastic tube, and opens
or closes the route of the powder passing through said tube.
When closing said valve, a small amount of powder is trapped
inside because of its structural design. Accordingly, it is
difficult to close completely and therefore a small amount of
air may flow even when the valve is closed. When the operation
is started again, the trapped powder is pushed out together
with the following fresh powder and is sprayed as ejected from
the nozzle 105; thus the density increases. That is, the
coated pattern varies between intermittent sprayings and a
cleancut peripheral line is difficult to obtain.
As described above, it is difficult to precisely
switch on or off the air transportation of the powder by any
of the conventional techniques, and the response time for an
intermittent signal is also slow; thus it is impossible to
avoid indistinctness at the gap between coated patterns in
string- or band-like intermittent spraying.
Descri~tion of the Preferred Embodiment
The structure of the gun according to the invention
is shown in Figure 1. An ejection route 2 for a mixture PA of
a powder and a gas (hereinafter abbreviated as "mixture") is
provided inside the gun 1. A connector 8 with a feed hose (or
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pipe) is provided at the entrance of said route, and a nozzle
is provided at the other end of said route, as in
conventional guns. The difference from conventional guns is
that a branched bypass route 3 is provided on said ejection
route 2 and is connected with ejection route 4 provided on said
bypass route 3 and also inside the gun 1; and an air ejector
nozzle 6 is provided on said ejection route 4; and the nozzle
tip 6T of said air ejector is positioned approximately at the
intersection with said bypass route 3.
In Figure 1, ejection route 2 and ejection route 4 are
arranged in parallel with each other, with the directions of
ejection flow opposite to each other, but as shown in Figure
2, both routes can be arranged so that they are in parallel,
as mentioned above, but ejection flows assume the same
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direction (modification 1), or as sho~dn in Figures 3A and 3B, said two
routes may be arzanged with a certain angle "u" between them (modification 2)
instead of a parallel arrangement. In said figures, "~" is set at 90.
The nozzles of the above-mentioned guns may be provided with a corona pin
for electrostatic coating. Figure 4 shows a side cross section of a gun
attached to an electrostatic powder coating nozzle according to a Pract cal
~ew Device Patent ~pplication (applied for on Tanuar-J 31, 1930) bv the ?resent
applicant. Because the corona pin 28 in sa c nozzl2 is e~bedded in the body
of nozzle 27, the annihilation of the corona discharge current due to adhesion
of the powder to the corona pin 28, as seen in conventional nozzles, lessens.
The aforementioned nozzle 5 is a general type nozzle, i.e., a type with
a circular nozzle hole, even though a flat-type (slit-type) nozzle can also
be used.
Moreover, a numDer of the afore~entioned circular nozzles or flat nozzles
can be used to make a multipattern coating device in which a single row
or several rows of several nozzles are assembled in a frame in order to form
a multigun, as shown in Figure 5, and a signalling device to cause these nozzles
to eject powder independently is connected to each nozzle.
Figure 6 shows one e~ample of a system diagram for intermittent powder
spray coating where the aforementioned gun of the invention is used. The
powder feed tank 62 is a fluidized-type (suspension-type) tank and is equippea
with a vibrator 78. An air ejector 63 is provided as the powder pump, and an
air heater 76 is provided on the air supply pipe 75 for the air ejector. The
air-Cransport pipe 6~ for the powder is connected to the gun 51 through a
distributor 65. Al air generator 73 for air to be supplied to the air ejector
which is installed in said gun and an intermittent switching valve 72 for said
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air to be supplied are provided. Said valve is connected to a timer 7~. The
discharging side of said air ejector is connected to a back filter 77 via a
transport pipe 75. The nozzle 53 of the above-mentioned gun is provided with
a corona pin 59 for electrostatic coating, and a high-potential generator oO
is connected to the corona pin.
Actions
First, the ac~ion of the gun is described. Refer to Figure l. r~hen a
mi~ture P.4 of a powder and a gas is fed into the e,ection route 2 in the gun 1
in order to eject the powder intermittently, said mixture PA travels through
the above-mentioned route 2 and is sprayed (PAI) from a nozzle 5 mounted on
the end of said route. Then, when air A is fed through the air generator 73
provided outside the said gun into the said gun 1 by opening an intermittent
air switching valve 72, air is e,ected (A') from the air ejec~or nozzle 6.
Because the tip 6T of said air ejector is positioned appro~imately at the
intersection with the bypass route 3 from the above-mentioned ejection route 2,
the gas around the tip is sucked by the action of the air ejector and sent in
the direction of ejection. This suction action also e~tends to the said bypass
route 3 and the powder ejection route 2, and as a result, the mi~ture P.4~ of
powder and gas travelling through the ejection roùte 2 is all suc'~ed in and
discharged from the gun 1. That is, the ejection of powder from ehe nozzle 5
is interrupted. Then,when the supply of air A to the above-mentioned air ejector
is suspended by closing the above-mentioned intermittent air switching valve
72, the suction action of said air ejector stops, and thus the aforementioned
original ejection of powder is resumed, the powder being ejected through the
nozzle 5. That is, the ejection of powder from the nozzle 5 can be stopped
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or started by the inter~ittent sup?ly of air to the air ejector.
When the nozzle S to be mounced on the above-mentioned gun ' is of the
general circular type, its discontinuous string-like coated pat.erns are as
shown in "C" and "D" of Figure 7.
Figure 8 shows discontinuous band-like patterns that can be obtained bv
using a flat (slit) nozzle. As can be seen in said figure, the discontinuous
patterns e~`nibit cleancut peri?he;al lines.
When multinozzles are used, various pat.erns can be produced by operating
each nozzle independently, as shown in "G" and "H" of Figure 9.
10Next, the operation of an intermittent powder spray coating system with
a gun of the invention to which various types of nozzles can be attached is
explained. Refer to Figure 6. The powder tank 62 is a suspension-.ype tank
and the uniform disDersion of powder is promoted with a vibrator 7~. The air
supplied to the powder pump 63 wnich is mounted on said tank, an air ejector
in this figure, is hot-air heated by an air heater 76, A mixture of a powder
and a gas conveyed under air pressure by the above-mentioned powder pump 63
is fed continuously and constantly into the gun 51 of the invention through
an air transport pipe 64 and then a distributor 65, and is sprayed from a
nozzle 55. ~hen periodically lnterrupting said spraying, an intermittent air-
~0 switching valve 72 for the air ejector, used to supply air to the gun 5i, is
opened in order to feed air into said air ejector in the gun, and the powder-
gas mi~xture passing through the said gun 51 is sucked in by the ejector's action,
discharged away from the gun 51, and conveyed to an air back filter 77 through
an air transport pipe 75. Thus, the powder can be sprayed intermittently from
the gun by intermittent operation of the intermittent air-switching valve for
the air ejector in the above-mentioned gun.
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Experimental data for the above-mentioned system are
as follows.
Powder used: nylon 12 and polyethylene, epoxy resin
Powder pump: air ejector
Air pressure of pump: 0.3 kg/cm2
Transport pipe: powder hose 3/16
Length between distributor and gun: 2.000 mm
Gun nozzle diameter: 2.4 mm~
Air pressure of gun air ejector: 0.7 kg/cm2
Electrostatic voltage applied: 17 kV
Conveyor speed: 50 m/min
No. of intermittent spray operations: 1,500
cycles/min.
(Note) The number of intermittent spray operations
by conventional powder pump (air ejector) at the powder tank
was 30 cycles/min at maximum.
Effects of the Invention
According to the method and gun of the invention,
discontinuous string- or band-like powder coatings with
cleancut and uniform outlines can be obtained during high-speed
intermittent coating of 30-1,500 cycles/min in an intermittent
powder spray coating operation, and powder coatings of band-
like clear geometrical patterns can be obtained with a
multinozzle gun.
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