Note: Descriptions are shown in the official language in which they were submitted.
L37
Rotary atomizer spray painting device
Background of the Invention
The present invention relates to rotary type atomizers
for applying paint and other materials in liquid atomizer
form, and more particularly relates to a rotary atomizer
adapted for electrostatic paint spraying.
The use of rotary atomizers for applying paint to
coating surfaces has been long known in the art. These
devices typically operate by rotating a disc or cup-shaped
bell at high speed, and by applying a metered flow of liquid
paint to the surface of the disc or bell as it is rotating.
Centrifugal forces cause the paint supplied to the surface
of the disc or bell to become hurled from its edge in drop-
lets, which droplets are then directed toward a surface to
be coated.
Rotary atomizers have also been used in conjunction
with electrostatic forces for the application of paint,
either by placing the rotary atomizer in a highly charged
electrostatic field so as to induce the atomized paint
particles to accept electrostatic charges and -thereby be-
come attracted to a grounded workpiece, or by directly
voltage charging the rotary atomizer and thereby causing
the paint droplets to become electrostatically charged
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as they are emitted from the edge of the rotating disc or
bell.
In applications where the atomizer itself is voltage
charged, the working voltages are typically in the range
of 50 - 150 kilovolts (kv), and therefore a high degree
of care must be taken to properly protect the charged com-
ponents from inadvertent contact with people or nearby
objects. Such systems are typica]ly shielded from any
possible contact by means of fences, booths, or other simi-
lar shielding contructions.
The hazards of prior art electrostatic rotary atomizershave limited the type and scope of applications in which
such systems may be used. For example, such systems can
only be used in applications wherein sufficient spatial
separation is available to provide for relative isolation
of the voltage charged rotary atomizer devices, and where
a high degree of control can be maintained over the spacing
between the atomizer device and articles moving past the
device on a conveyor line. Extreme care is required in
order to prevent accidental voltage discharges in solvent
or other volatile atmospheres. Since prior art atomizers
are constructed of metallic materials, or contain a high
percentage of metallic materials in their construction,
such atomizers inherently have a high value of electrical
capacitance. When charged to the voltages associated norm-
ally with electrostatic paint spraying, these atomizers
accumulate a very high amount of electrical energy in the
form of capacitance stored energy. Therefore, if conditions
occur wherein a voltage spark is generated, the capacitive
energy stored in the atomizer itself will immediately dis-
sipate through the spark, in sufficient energy quantities
so as to cause ignition of volatile solvents and the like.
Some prior art rotary atomizers attempt to minimize
this problem by applying a resistive coating to the surface
of the atomizer disc or bell. This approach is described
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in U.S. Patent No. 2,989,241, -the substance of which is to
incorporate an energy damping resistance between the high
capacitance components of the rotary atomizer and the work-
piece. This damping resistance effectively absorbs some of
the electrical energy which would otherwise be dissipated in
the form of a high energy spark, and thereby reduces the
hazard of fire or explosion.
Despite the foregoing and other disadvantages which
result from the use of prior art rotary atomizers, such
devices have found widespread use in industry, for they do
produce a finely atomized cloud or spray of paint and, as a
result, produce a high quality coating on a workpiece. There
is therfore a need to provide a rotary atomizer having the
inherent advantages of high quality painting, but without
the disadvantages associated with the various hazards.
It has been found that the quality of paint atomization
is directly related to the rotational speed of the rotary
atomizer, the higher the rotational speed the finer the
atomization. Therefore, it is not unusual to find rotary
atomizers which rotate in the range of 25,000 - 75,000
revolutions per minute (RPM?, which itself produces addi-
tional problems. Conventional bearings are difficult and
expensive to design to operate at high rotational speeds,
and therefore it has been the practice in the industry to
design rotary atomizers having various forms of air bearings
to suspend the rotating members. Such air bearings have
the advantage of providing long life of the rotating members,
and therefore it is desirable to incorporate them into any
rotary atomizer structure which is inherently less hazardous
than heretofore known in the art.
The concept of utilizing an energy damping resistance
between the capacitance charged components of an atomizer
and the workpiece is an advantage which is also well-known
in the art, at least in the form described hereinabove.
Conventional automatic and manual spray guns utilize this
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same concept by placement of a physical resistance in a non-
conductive spray gun body, which resistance is placed proxi-
mate the front end of the spray gun to accomplish the re-
~uired electrical resistance damping. This approach in a
design of conventional spray guns has greatly reduced the
hazards associated with such guns, and it is desirable to
incorporate such a concept into a rotary atomizer. However,
prior art rotary atomizers which utilized such improvements
as air bearing assemblies were required to be constructed
of high precision metallic components, and such components
inherently prevented the use of nonconductive bodies. It
is therefore desirable to combine into a single rotary
atomizer structure all of the advantages heretofore known
with respect to conventional spray guns, air bearing tech-
nology, and rotary atomizer technology, so as to provide anew and improved rotary atomizer having all of the advan-
tages in each field of technology.
Summary of the Invention
The present invention comprises a rotary atomizer
constructed virtually entirely of nonconductive material,
thereby eliminating capacitive energy storage problems
and the inherent hazards which inevitably e~ist in an elec-
trostatic spray gun having metallic components. A noncon
ducting rotatable member is contained about a fixed axial
2~ nonconducting tubular member, having air bearing contacts
or nonconductive ball bearings therebetween. An outer
housing of nonconductive material partially encloses the
rotatable member, and an air bearing may be formed there-
between. A connecting shaft projects through the housing
from one end of the rotatable member, and a disc or cup-
shaped bell is contructed of nonconducting material and
connected to the shaft, so as to rotate therewith. A
portion of the rotatable member is formed into turbine
blades, and air passages are formed through the outer
housing so as to direct pressurized air against the turbine
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blades, and further air passages are formed through the
housing to provide a source of pressurized air intermediate
rotating and fixed members as an air bearing cushion. A
high voltage electrical path is provided through the hous-
ing, terminating in one or more needle electrodes whichproject e~ternal to the housing in the region proximate
the rotatable disc or bell. Further air passages may be
provided through the housing to direct a source of pres-
surized air forwardly past the rotatable disc or bell to
provide deflection and shaping air for atomized particles
which are emitted from the edge of the rotating disc or
bell.
Brief Description of the Drawings
A preferred embodiment of the invention is described
herein and with reference to the drawings, in which:
FIG. 1 shows an isometric view of an embodiment of
the invention; and
FIG. 2 shows a cross sectional view taken along the
lines 2-2 of FIG. l; and
FIG. 3 shows a cross sectional view taken along the
lines 3-3 of FIG. 2; and
FIG. 4 shows an alternative embodiment in cross
section; and
FIG. 5 shows a further alternative embodiment in cross
section; and
FIG. 6 shows an isometric view of the turbine member.
Description of the Preferred Embodiment
Referring first to FIG. 1, there is shown a rotar~
atomizer 10 constructed according to the teachings of the
present invention. Atomizer 10 has an outer housing 12
constructed from nonconductive material such as nylon or
plastic material. A disc or cupshaped bell 14 is connected
to a rotor shaft 16 which projects from the front of housing
12. The rear of housing 12 has a first air inlet 18 and a
second air inlet 22, both of which will be hereinafter
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described. A liquid inlet 19 is axially positioned relative
to housing 12 and rotor sha~t 16. An outer cover 28 is
circumferentially attached outside of housing 12. An an-
nular housing 24 surrounds housing 12 proximate its front
end, and housing 12 may be threadably attached to annular
housing 24. A nonconductive tube 26 is connected to an-
nular housing 24 near its top edge and a nonconductive tube
27 is connected to annular housing 24 near its bottom edge.
FIG. 2 shows an elevational cross-sectional view of
rotary atomizer 10. Shaft 16 is formed on one end of a
rotor 17, and both may be formed from a single piece con-
structed rom nonconductive material. Shaft 16 and rotor
17 are preferably constructed from a fiberglass or ceramic
material, chosen for its physical stability under widely
varying conditions of temperature, humidity, and other en-
vironmental effects. Rotor 17 is closely fitted within an
opening in housing 12, and has a turbine 30 constructed
proximate its rear end. Turbine 30 has a plurality of cir-
cumferential blades which will be described in more detail
hereinafter. Rotor 17 is concentrically mounted about a
fixed, nonconductive feed tube 20. Feed tube 20 is axially
positioned relative to rotor 17 and housing 12, and has a
center opening along its entire length. The rear end 19
of feed tube 20 is adapted for coupling to a source of
paint or other liquid, which is typically applied to feed
tube 20 under slight pressure so as to cause a forward
feed of the liquid to the front end of feed tube 20. The
front of feed tube 20 has an opening 29 to permit liquid
to be metered therethrough and to flow onto the forward
surface 15 of bell 14 through openings 13. Bell 14 is
fixedly attached to shaft 16 and rotates therewith.
Air inlet 22 is connected to a passage 23 inside of
housing 12. Passage 23 connects to an annular groove 32
about the inner surface of the opening in housing 12, and
serves to distribute pressurized air evenly about rotor 17.
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Pressurized air from annular groove 32 is distributed evenly
over the intergap region between rotor 17 and the opening
in housing 12, flowing between the respective surfaces and
exhausting at either end of rotor 17. This air flow serves
as an air bearing cushion between rotating rotor 17 and
fixed housing 12.
A further passage 33 passes khrough rotor 17 to an
annular groove 21 about feed tube 20. The pressurized air
which is fed into annular groove 21 serves a similar purpose;
namely, to provide a flow of air between rotor 17 and feed
tube 20. In the preferred embodiment, the gap between the
inner opening of rotor 17 and feed tube 20 may be larger
than the gap between rotor 17 and housing 12. Pressurized
air distributed via annular groove 21 is also provided for
the purpose of maintaining a positive pressure about feed
tube 20, thereby to purge foreign materials from accumu-
lating within this region.
An air bearing surface is also created about turbine
member 30, by virtue of the air flow paths described here-
in. The outer edge 35 of turbine 30 receives pressurizedair from inlet 22, and this pressurized air creates an
air cushion film between turbine member 30 and housing 12.
Likewise, an air cushion film is maintained between turbine
edge 37 and housing 12, so that edges 35 and 37 serve as
a thrust bearing member to continue the forward and rear-
ward movement of rotor 17 within housing 12.
Air inlet 18 is coupled to a passage 34 in housing
12, and passage 34 communicates with turbine chamber 36.
Turbine chamber 36 is an annular chamber extending about
turbine 30 to provide a source of pressurized air for
driving turbine 30 in a rotating direction. A plurality
of nozzles 38 are directed toward the blades on turbine 30,
and open into turbine chamber 36. These nozzles provide
a plurality of air jets for injecting pressurized air
against the turbine blades and thereby to rotate the
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turbine. Turbine 30 is fixedly attached to rotor 17, and
rotor 17 therefore rotates with turbine 30. One or more
exhaust ports 40 open into the region surrounding turbine
30, and serve to exhaust pressurized air from turbine 30
into a muffler ehamber 42. Muffler chamber 42 extends
annularly about the exterior surface of housing 12, and
may be filled with a sound insulating material to diminish
the exhaust noise of pressurized air escaping from the
muffler. A plurality of exterior openings 43 are drilled
through the exterior wall of muf~ler chamber 42 in order
to exhaust the air therein into the atmosphere.
Annular housing 24 is either formed as a part of
housing 12 or is fixedly attached about housing 12, proxi-
mate the front end of housing 12. Annular housing 24 is
eonneeted to noneonductive tube 27, and tube 27 is adapted
for eonnection to a further source of pressurized air.
Housing 24 has an annular passage 25 extending about its
interior, and a plurality of air jet openings 44 extend
about housing 24 in air flow contact with passage 25. Air
jets 44 are ~orwardly directed, and may be as many in
number as thirty to ninety, and serve to provide a forwardly
directed plurality of ~ets of air for shaping the atomized
paint pattern as it develops from bell 14.
Annular housing 24 also has connected thereto a non-
conductive tube 26. Nonconductive tube 26 contains the
eleetrieal eircuits for electrostatically energiziny the
apparatus. The rear end of noneonduetive tube 26 is adapted
for eonneetion to an eleetrieal eable 47, which eable may
provide high voltage to the apparatus. A large resistor
45 is loeated inside of tube 26, resistor 45 serving the
funetion of damping out any capacitively stored energy
whieh may exist in the supply cable 47. Resistor 45 is
conductively eoupled ~o an electrical eontact 46 in housing
24. Contact 46 may extend annularly about housing 24, or
it may be a single eontact point, depending upon the par-
ticular design desired for the apparatus. A smaller
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g
resistor 48 is conductively coupled to contact 46, and the
forward end of resistor 48 i6 connected to an electrode 50.
Electrode 50 projects forwardly to serve as the source of
electrostatic energy for accomplishing electrostatic paint
S distribution. It should be apprecia~ed that a plurality
of electrodes 50 may be dispersed about housing 24, if more
than one electrode discharge point is desired. For example,
in the preferred embodiment of the present invention it
has been found to operate satisfactorily with four electrodes
50 positioned at approximately 90 angles about housing 24.
In this case, contact 46 is extended about the interior of
housing 24, and an individual resistor 48 is provided be-
tween contact 46 and electrode 50 at each of the four
connection points.
FIG. 3 shows a cross sectional view taken along the
lines 3-3 of FIG. 2, wherein the structure of the turbine
assembly may be noted. Turbine blades 31 are distributed
equally about the outer surface of turbine 30. Turbine
blades 31 are shaped so as to provide a maximum effective
area for receiving pressurized air from nozzles 38. As air
is used to cause rotational motion to turbine 30 it develops
a positive pressure in the region around turbine 30, and
must be exhausted into muffler chamber 42, and thereafter
to the atmosphere. In addition, pressurized air used as
an air bearing cushion 51 between rotor 17 and housing 12
is also exhausted into the atmosphere via the same path
as air supplied to turbine 30.
FIG. 4 shows an alternative embodiment of the invention
in cross section. This embodiment functions generally the
same as the embodiment shown in FIG. 2, although certain
constructional differences are present. A significant
constructional difference is rela~ed to rotor 117, and in
par~icular its air bearing system relative to housing 112.
Rotor 117 is formed of two generally cone-shaped sections,
having a narrowed center portion and extending to larger
diameter end portions. Pressurized air entering air inlet
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port 122 is coupled through passage 123 to an annular
chamber 132. Chamber 132 provides a source of pressurized
air for uniformly distributing air over the external sur-
face of rotor 117 in both directions from its narrowed
center region. This film of air is flowed outwardly to-
ward both ends from the center, and serves to provide an
air bearing cushion for rotor 117. The inherent design
of rotor 117 as shown in FIG. 4 eliminates the need for
a thrust bearing in the apparatus, since axial thrust
forces are inherently balanced by the shape of rotor 117.
Pressurized air is provided at inlet port 118, and
fed through passage 134 to turbine chamber 136. From
turbine chamber 136 the pressurized air passes through a
plurality of nozzles 138, which inject the air against
the surfaces of blades on turbine 1~0. This pressurized
air causes turbine 130 to rotate, and thereby causes rotor
117 to rotate therewith, generating the necessary rota-
tional motion for the apparatus. Exhaust air is collected
and routed out of the turbine region via exhaust ports
140 into muffler chamber 142. From muffler chamber 142
the air is exhausted into the atmosphere through openings
143.
The function of nonconductive tube 127, and annular
housing 124, and nonconductive tube 126 is essentia].ly
similar to the corresponding positioned elements described
with reference to FIG. 2. For example, a plurality of
forwardly directed air jets 144 may be provided in annular
housing 124 for the purpose of shaping and assisting in
the control of the atomization pattern from bell 114.
Likewise, a plurality of electrodes 150 may be arranged
about the forward surface of annular housing 124 to provide
necessary electrostatic voltages for electrostatic operation.
As an alternative embodiment to the electrical circuit
described herein, it is contemplated that a cascade voltage
multiplier circuit may be enclosed within a conductive tube
126 or equivalent, and may thereby provide high voltage
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multiplication directly within the apparatus itself. In this
case, the high voltage multiplier circuit need only have
supplied to it a relatively low input voltage, the cascade
multiplier providing the necessary voltage magnification for
driving electrode 150 or equivalent. The design of appro-
priate cascade multiplier ci~cuits is well-known in the art,
and technology in recent years has enabled the design of
such devices to be accomplished within a relatively small
volume, which volume would be suitable for operation with the
present invention.
FIG. 5 shows a further alternative embodiment of the
invention. A nonconductive housing 212 surrounds a rotatable
rotor 217, and rotor 217 is contained by nonconductive ball
bearings 260 and 261 which support rotor 217 and permit rota-
tion thereof relative to housing 212. Rotor 217 is construc-
ted from nonconductive material, terminating at its forward
end in a projecting shaft section 216. Shaft section 216
is threadably attached to a bell or disc 214 as has been
described hereinbefore. An annular nonconductive housing
224 is threadably attached proximate the forward end of
housing 212, and annular housing 224 supports the electrical
components including one or more electrodes 250, resistors
248, and electrical circuits 245. Annular housing 224 also
includes a plurality of air jets 244 which are forwardly pro-
jecting to direct the pattern of spray paxticles emitted
from bell 214. Turbine member 230 is fixedly attached to
rotor 217, for rotation therewith, and pressurized air is
deflected to rotate turbine member 230 via nozzles 238.
Nozzles 238 are in flow communication with a ~urbine chamber
236, which in turn is coupled via passage 234 to air inlet
218. The pressurized air is exhausted from the device via
exhaust ports 240 which pass the exhaust air into muffler
chamber 242 and into the atmosphere via openings 243. A
nonconductive spacer 263 is inserted be-tween bearings 260
and 261, to position and hold the bearings in place.
FIG. 6 shows an isometric view of turbine member 30,
or the other similar turbine members described herein. The
turbine blades 31 of turbine member 30 are curved so as to
receive pressurized air proximate the center of the turbine
member, and to deflect the air outwardly to both sides as
the air is used to drive the turbine member in a rokatable
fashion. The exhaust air is deflected outwardly along
either turbine edge, and is conveyed to the atmosphere as
has been described hereinbefore.
It should be noted that all of the components illus-
trated in the figures are constructed from nonconductive
materials, with the exception of certain electrical connec-
tions. Because of the almost exclusive use of nonconductive
materials there is no capacitive energy storage caused by
the accumuIation of voltage charges on metallic members, and
therefore there is no possibility for a spark discharge to
occur from this device as a result of excess capacitive
energy. Therefore the use of nonconductive materials pro-
vides for an almost completely safe apparatus, and the
further use of suitably sized resistors as shown in the
figures provides an additional margin of safety. The only
capacitively stored energy which may be identified in con-
nection with the invention would be that energy stored in
the voltage delivery cables, and the use of resistors down-
stream from these voltage cables suitably protects againstexcessive discharge currents.
It should also be appreciated that the invention
contemplates utilizing independently controlled air pressure
sources for driving the respective air inlets shown and
described herein. For example, the pressurized air used to
provide the air bearing cushion for the turbine rotor may be
provided from a different air pressure regulator than the
pressurized air used to drive the turbines. Likewise, the
pressurized air for use in shaping the atomized pattern may
be independently controllable.
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In operation, the apparatus is placed in proximity
to a painting zone, preferably adjacent a conveyor line
adapted for conveying articles to be coated. The respective
air pressures are adjusted to provide an optimum atomization
pattern from the rotating bell, which may occur at rotational
speeds in the range of 20,000 - 80,000 revolutions per minute
(RPM). The pressurized air utilized to drive the turbine and
the pressurized air utilized to provide the air bearing
cushion may be balanced for optimum operation of the rotor
at the desired RPM. Likewise, the pressurized air utilized
to provide air shaping is set to provide the desired amount
of control over the atomized pattern, consistent with the
liquid delivery rate into the apparatus. The high voltage
circuits are adjusted to provide electrostatic forces suit-
able for optimum paint spraying and all of these parametersmay be adjusted to optimize the overall operating conditions.
The apparatus may be used in conjunction with other similar
devices in an automatic painting system, wherein atomizers
are controllable in synchronization with articles conveyed
along a conveyor line to provide a wide coating area. In
this manner, large articles such as automobile bodies may be
effectively coated without danger of electrical discharge.
The present invention may be embodied in other specific
forms without departing from the spirit or essential attri-
butes thereof, and it is therefore desired that the presentembodiment be considered in all respects as illustrative
and not restrictive, reference being made to the appended
claims rather than to the foregoing description to indicate
the scope of the invention.
