Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~84271
ELECTROSTATIC ROTARY ATOMIZING
LIOUID SPRAY COATING APPARATUS
This invention relates to electrostatic spray
coating and more particularly to electrostatic liquid spray
coating apparatus utilizing rotary atomization.
Electrostatic spray coating apparatus incorporating
rotary atomizers have been available for many years.
Typically a conductive cup or disc maintained at high voltage
is rotated at very high speed causing liquid coating material
fed to the central part of the cup or disc to migrate
outwardly over the cup or disc surface under centrifugal
force, eventually leaving the cup or disc at the outer edge
thereof where it becomes atomized. Because the atomizing
edge of the cup or disc is sharp, the high voltage applied to
the conductive cup or disc causes ionization of the air in
the region of the atomizing edge, imparting electrostatic
charge to the atomized
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--2--
liquid coating particles in a manner well known in tne
field of electrostatic spray coating.
Over tne years tne nazards associated witn
tne use of conductive atomizing cups and discs main-
tained at nign voltage, wnicn take tne form of person-
nel snock and ignition wnen combustible coatings are
employed, nave become well publicized. In brief, tne
nazards exist by virtue of tne fact tnat substantial
electrical energy is stored in capacitive form by a
conductive cup or disc maintained at nign voltage
wnicn can rapidly discnarge if inadvertently grounded
or brougnt near a grounded object. To minimize tnese
nazards various solutions nave been proposed. For
example, it nas been proposed to make tne atomized cup
or disc of insulative material except for a conductive
skin or layer wnicn is provided on tne surface of tne
atomizing member to conduct nign voltage to tne
atomizina edge for tne purpose of creating ionization
tnereat. Anotner proposal involves making tne atomiz-
ing cup or disc of resistive material. Tnese and
otner proposals are contained in U.S. Patents:
Gautnier 2,926,106, Gautnier 2,989,241, Scnotland
2,955,565, Juvinall 3,009,441, Sedlacsik 3,010,428,
Gautnier 3,021,077, Juvinall et al 3,048,498, Point
3,063,642, Point et al 3,072,341, Gautnier 3,083,121,
Gautnier 3,128,C45, Point 3,178,114, Felici et al
3,279,429,Scnarfenberger et al 3,826,425, Point
1~:842~1
--3--
3,075,706, and Robiscn et al PC~ International Publi-
cation No. ~0 85/01455.
~ ne foregoing proposals have not been
entirely satisfactory for various reasons, one of
wnicn is tnat tne resulting transfer efficiency of tne
spray apparatus nas not been sufficient to satisfy
tnose desiring nign coating transfer efficiencies in
tne range of 90~ and above. ~y coating transfer
e ficiency is meant tne percentage or proportion of
coating material emitted from tne spray device wnicn
actually gets coated. Accordingly, it nas been an
objective of tnis invention to provide a safe electro-
static spray device of tne rotary atomizing type wnicn
affords nign coating transfer efficiency. Tnis
objective nas been accomplisned in accordance witn
certain of tne principles of tnis invention by provid-
ing an electrostatic spray coating device witn a
rotary atomizer of insulative material naving a first
surface over wnicn liquid coating can flow outwardly
to an atomizing edge tnereof wnen tne atomizer is
rotated about its axis of ro_ation and a second
surface separated from tne first surface by tne
atomizing edge. A circular ring-snaped cnarging
electrode is mounted on tne first surface, and an
electrical current-conducting element is mountefl on
tne second surface wnicn is electrically connected to
tne circular cnarging electrode. Plural stationary
electrical conductors, eacn naving a free end located
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in closely spaced proximity to tne circular electrical
current- -conductive element are provided. Tne
stationary electrodes facilitate transfer of electro-
static erergy to tne cup electrode wnen tne stationary
conductor is energized from a nign voltage source,
enabling contact cnarging of liquid coating supplied
to tne first surface wnen tne coating flows under
centrifugal force outwardly over tne first surface in
contact witn tne cnarging electrode toward tne
atomizing edge. By minimizing tne amount of con-
ductive material incorporated in tne rotating
atomizer, electrical energy stored in capacitive form
by tne atomizer is kept witnin safe limits, wnile
providing nign transfer efficiency due to tne arrange-
ment of tne plural stationar~ electrodes and tneirassociated circular moving current-conducting element
on tne rotating atomizer and tne contact cnarging
provided by tne conductive electrode embedded in tne
~urface of tne atomizer over wnicn tne coating flows
under centrifugal force as it migrates toward tne
atomizing edge.
In a preferred form of tne invention tne
safety of tne spray apparatus is even furtner ennanced
by fabricating of semiconductive material tne circular
contact-cnarging electrode and its associated circular
current-conducting element and tne connecting means
tnerebetween.
, . . .
1284271
-5-
Furtner according to tne invention and for
tne purpose of still furtner improving tne safety of
tne ~pray apparatus, tne free ends of tne electrodes
wnicn transfer electrical energy to tne contact
electrode located inside tne cup as well as tne
external ring electrode and tne exterior of tne cup
are protected from damage and inadvertent contact by
being located substantially witnin tne recess in wnicn
tne cup rotates.
In accordance witn certain otner features of
tne invention designed to promote compactness of tne
spraV coating apparatus, tne support body of tne spray
apparatus in wnicn tne drive means for tne rotary
atomizer is encased is provided witn a generally
cylindrical exterior snape in wnicn tne diameter of
tne intermediate section is substantially less tnan
tnat of tne forward and rear body sections, defining
an annular cavity tnerebetween in wnicn are located
tne liquid coating and cleansing solvent valves for
controlling tne flow of liquid coating and solvent to
tne rotary atomizer. Tnis enables tne liauid coating
and solvent valves to be located not only in close
proximitv to tne rotary atomizer, but also to be
located witnin tne overall envelope of tne support
body wnicn nouses tne rotary drive assembly for tne
atomizer.
To facilitate mounting of tne spray appa-
ratus to a post or tne like, a mounting bracket is
--5--
:~:28~
~6--
provided of desired design from wnicn project in a
forward direction several spaced parallel columns
wnicn at tneir forward end mount tne support body of
tne spray apparatus nousing tne various valves and tne
drive assembly for tne rotary atomizing element. In,a
preferred form, one of tne columns is nollow for
nousing an electrostatic energy-conducting core for
transporting nign voltage electrostatic energy between
a remote nign voltage source and tne stationary
electrode wnicn is located in close proximity to tne
circular conducting element on tne rotating atomizer
wnicn is connected to tne circular cnarging electrode.
In tne preferred embodiment, tne nollow column also
encases a gun resistor wnicn is in series witn tne
~5 stationary conductor.
In accordance witn certain additionzl
principles of tne invention, an annular air ring
provided witn a circular array of forwardly directed
air jet-defining ports is removably mounted to tne
front of tne support body. Tne air ring includes an
annular recess in tne rear wall tnereof, wnicn func-
tions as a circular air manifold for distributing air
to tne circular array of passages to establisn air
jets for snaping tne atomized liquid coating spray.
Tne air ring rear wall also includes an annular reces~
wnicn encloses a single circular conductor wnicn is
supplied witn nign voltage from tne remote electro-
static source. Tne circular conductor nas connected
1284~
--7--
to it tne plural stationary conductors wnicn transfer
electrostatic energy to tne cnarging electrode of tne
cup. In one preferred form tne stationary conductors
are located in sneatns wnicn are removably tnreaded
into suitably tnreaded bores in tne front surface of
tne air ring. Tne sneatns may also nouse cnarging
resistors in series circuit witn tne stationary
conductors. Tne foregoing construction naC been found
to be relatively simple to manufacture, assemble, and
maintain.
In an alternate embodiment of tne invention,
tne annular air ring takes tne form of a cap naving an
outer face whicn is aerodynamically contoured to nelp
avoid eddy currents generated by tne flow of air along
tne outside surface of tne rotary atomizer cup. Tnis
improves transfer efficiency and reduces fouling of
tne sprayer witn coating material by nelping to avoid
drawing tne spray pattern back toward tne sprayer.
Tne base of tne cap includes a groove wnicn encloses a
first circular conductor wnicn is supplied witn nign
voltage from tne remote electrostatic source wnile tne
outer face of tne cap includes a repulsion ring
recessed about its peripnery. $ne repulsion ring is
electrically connected to tne first circular conductor
as to be energized witn at tne same electrical
polaritv as tne cnarge imparted to tne atomized
droplets of coating material in order to furtner
ennance tran fer
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- 1284271
--8--
efficiencies and avoid tne buildup of coating material
on tne sprayer.
Instead of using sneatns tnreaded into an
air ring, tne alternate embodiment of tne invention
- 5 contemplates locating tne plural stationary conductors
and associated cnarging resistors imbedded witnin tne
cap. Tnis protects and stabilizes tne cnarging
resistors and associated leads and nelps snorten tne
overall lengtn of tne spray apparatus. Furtner
according to tne invention, tne cap preferably
includes a sligntly oversized recess in wnicn tne
atomizing cup is disposed to tnereby define a gap
between tne wall of tne recess and tne outer surface
of tne cap. ~o nelp prevent tne cnarging electrodes
from being accidentally contacted, tne free ends
tnereof ad tne circular conductor on tne outside of
tne atomizing cup are eacn located substantially
witnin tne gap.
Tnese and otnex features, advantages, and
objectives of tne invention will become more readily
apparent from a detailed description tnereof taken in
conjunction witn tne drawings wnicn: are described
briefly as follows and wnerein like numerals refer to
like items.
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1284271
,
_9_
BRIEF DESCRIP~ION OF THE DRAWINGS:
Figure 1 is a side elevational view, par-
tially in cross section, of tne rotary atomizing
liquid spray coating device of tnis invention.
Figure 2 ic a side elevational view, in
cross section, of tne front section of tne rotary
atomizing liquid spray coating device depicted in
Figure 1, snowing, among otner tnings, tne general
relationsnip of tne atomizing cup and its rotary
drive, air jets for snaping tne atomized coating
sprav, nign voltage circuit patns, and liquid coating
flow patn and associated valve.
Figure 3 is a cross-sectional view along
line 3-3 of Figure 2 snowing, among otner tnings,
portion5 of tne liquid coating and solvent flow patns
to tne rotary atomizing cup, as well as tne general
location of tneir respective valves, a portion of tne
air patn for snaping tne liquid coating spray pattern,
and tne electrical conductors wnicn transmit nign
voltage to tne ring-snaped liquid coating cnarging
electrode mounted inside tne atomizing cup.
Figure 4 is a cross-sectional view along
line 4-4 of Figure 3 snowing tne flow passages and
valving for solvent for cleansing tne exterior of tne
rotary atomizing cup.
Figure 5 is a cross-sectional view along
line 5-5 of Figure 3 snowing a portion of tne patn for
`` ~2842~
--10--
tne air for snaping tne atomized liquid spray coating
pattern.
Figure 6 is a cross-sectional view along
line 6-6 of Figure 1 snowing tne general relationsnip
of tne support columns between tne front and rear body
sections of tne spray device, tne nousing, and tne
dump valve.
Figure 7 is a cross-sectional view along
line 7-7 of Figure 1 snowing tne general relationsnip
of tne valves for tne liquid coating material and tne
solvent for cleansing tne interior and exterior of tne
rotary liquid atomizing cup.
Figure 8 is a cross-sectional view along
line 8-8 of Figure 3 snowing the flow passages and
lS valving for solvent for cleansing tne interior of tne
rotary atomizing cup.
Figure 9 is a cross-sectional view along
line 9-9 of Figure 1 snowing tne rear body section of
tne spray device, support columns, and various air and
solvent noses.
Figure 10 is a front view of an alternate
embodiment of tne discnarge nozzle of a rotary
atomizing spray coating apparatus.
Figure 11 is a partial cross-sectional view
taken on line 11-11 of Figure 10.
Witn reference to Figures 1 and 2, tne
rotary atomizing liquid spray coating device of tnis
invention is seen to include a support body 10 naving
--10--
-' ~Z8427i
a front or forward section 12 and a rearward section
14 between wnicn is positioned an intermediate section
16. Tne body sections 12, 14, and 16 are generally
cylindrically snaped. Tne diameter of tne forward and
rear body sections 12 and 14 are substantially tne
same. Tne diameter of tne intermediate body section
16 is substantially less tnan tnat of tne body
sections 12 and 14, defining tnerebetween an annular
cavity 18 witnin wnicn can be located and mounted, as
will be described in more detail nereafter, various
valves for controlling tne flow of liquid coating
material and solvent for cleansing tne interior and
exterior of tne rotary atomizing cup described
nereafter.
A rotarv atomizing cup 20 extends forwardly
from tne front surface 22 of tne forward body section
12. ~.emovably secured to tne front surface 22 of tne
forward section 12 of tne body 10 in any suitable
manner, sucn as by bolts, tnreaded engagement, or tne
like, is an annular ring 24. Tne ring 24 includes a
circular air passage or manifold 26 formed in tne rear
surface tnereof from wnicn extend forwardly a
plurality of circularly arranged air ports 28 for
establisning a circular array of air iets for snaping
tne atomized liquid coating spray pattern 29 formed at
tne forward edge or rim 42 of tne atomizing cup 20.
As noted, extending forwardly from tne
forward section 12 of tne body 10 is tne rotary
atomizing cup 20. Cup 20 is dri~ingly mounted on a
--11--
. .
~28~
-12-
snaft 23 for rotation about its axis. Tne cup drive
snaft 23 extends tnrougn a bore 12b in forward body
section 12 and an air or ball bearing 25 of a conven-
tional commercially available type located witnin a
suitably configured bearing cavity or bore 27 in
intermediate body section 16. Snaft 23 is driven at
it rear (left as viewed in Figure 2) by a rotary
actuator 31, sucn as an air-driven turbine, also of a
conventional commercially available type wnicn is
located rearwardly of tne bearing 25 in a turbine
cavity or bore 31a in rear body section 14. A liquid
coating control valve 33 mounted to tne rear surface
of tne flange-defining portion of tne forward section
12 of tne body 10 controls tne flow of liquid coating
material to a coating nozzle 30 via a passage 32
formed in tne forward section 12 of tne body 10.
~ia,uid coating under slignt pressure exiting nozzle 30
enters an annular cavity 34 formed in tne rear section
of tne cup 20. Under centrifugal orce due to tne
rotation of cup 20 by drive snaft 23, tne liquid
coating material in tne annual cavity 34 passes
radially outwardly and forwardly tnrougn a series of
coating passages 36 in radial cup wall 20c to a
forward cup cavity 38. Once in tne forward cup cavity
38 tne liquid coating moves radially and forwardly
along a first surface defined by interior cup wall 40
toward tne forward atomizing edge 42 of tne cup 20
wnereat it is atomized under centrifugal force to form
-12-
--` 12~4271
-13-
the atomized spray pattern 29. A flat circular
ring-snaped cnarging electrode 46 imbedded in tne
irterior wall 40, wnicn is connected to a conventional
nign voltage electrostatic supply (not snown) in a
manner to be described, cnarges tne liquid coating
material by contact as it passes tnereover in its
movement from passages 36 in wall 20c to tne forward
atomizing edge 42 of tne cup wnereat tne liquid is
centrifugally atomized to form spray pattern 29.
Disposed rear~ardly of tne body 10 and
spaced tnerefrom is a mounting bracket 50. Bracket 50
consists of a circular plate 52 and a rearward]y
extending collar 54. Tne plate 52 and collar 54 are
provided witn a tnrougn bore into wnicn can be posi-
tioned a circular post 56 supported in any suitable
manner by a spray reciprocating device, stationary
pedestal, or tne like. A locking screw 58 tnreaded
radially into tne wall of collar 54 is provided for
locking tne bracket 50 on tne post 56.
Extending between tne circular plate 52 ar.d
tne rear surface 60 of tne rear section 14 of tne body
10 are several mounting posts or columns 62, 64, and
66. Columns 64 and 66 can be fastened in any suitable
manner to tne plate 52 and tne rear wall 60 of tne
rear section 14 of tne body 10. For example, columns
64 and 66 can be tnreaded at tneir forward ends and
screwed into suitably provided tnreaded bores in tne
rear wall 60 of tne rear section 14 of tne bodv 10.
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2 ~ ~L
-14-
Tne column~ 64 and 66 at tneir rearward ends may be
provided witn reduced diameter portions wnicn extends
tnrcugn suitably provided bores in tne plate 52 sucn
tnat tney project rearwardly (leftwardly as viewed in
Figure 1) of rear surface 55 of tne plate 5 By
providing tnreads on tne reduced diameter portion of
tne rear ends of tne columns 64 and 66 wnicn project
rearwardly of tne plate surface 55, nuts can be used
to secure tne rearward ends of tne columns 64 and 66
to tne plate 52, as is done witn tne rear end of
column 6' in a manner to be described.
Tne support column 62 at its r~ar or left
end nas a reduced diameter portion 62c wnicn passes
tnrougn a suitable bore in plate 52, extending rear-
wardly of surface 55 tnereof. A nut 62d tnreadedly
engages tne column end portion 62c to secure column 62
to plate 52. Tne support column 62 at its forward end
passes tnrougn a suitably provided bore 70 in tne rear
section 14 of body 10 and extends forwardly to tne
rear wall 12a of tne forward body sectlon 12. Tne
forwardmost portion 62a of tne column 62 is of reduced
diameter and tnreaded sucn tnat it will tnreadably
engage a suitable tnreaded bore 72 formed in tne rear
surface 12a of tne forward body section 12.
Tne column 62 is provided witn an axial
internal bore 62b witnin wnicn is positioned a nign
voltage insulated cable 74 connected at its rearward
end to a nign voltage electrostatic supply (not
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~`
-15-
snown). Tne cable 74 at its forward end 74a connects
to a gun resistor 76. An electrical conductor 78
extends between tne forward end of tne gun resistor
for energizing tne electrode 46 in a manner to be
described in more detail nereafter.
As snown in Figure 1, a dump valve 80
mounted to tne forward wall 57 of tne plate 52
connects to tne liquid coating valve 33 via a flexible
conduit 82 and to a wafite receptacle 86 via a conduit
88. Dump valve 80 diverts cleansing solvent from
coating valve 33 during color cnange operations in a
manner well known, in tne art.
Mounted to tne rear surface 12a of tne
flange-defining portion of forward body section 12, in
addition to tne coating control valve 33, are solvent
valves 90 and 92 wnicn control tne flow of solvent, in
A manner to be described, to tne exterior of tne
rotary atomizing cup 20 and tne interior of tne rotary
atomizing cup, respectively, as snown in Figures 3, 4,
7, and 8. Valves 90 and 92 are located in tne ~nnular
cavity 18.
Tne rotary atomizing cup 20, as best seen in
Figure 2, includes a frusto-conical tubular section
20a and a nub 20b wnicn are interconnected by radial
wall 20c wnicn collectively define tne rear annular
cavity 34 and tne forward cavity 38. Tne nonuniform
cross section of tne tubular section 20 increases
along tne axis tnereof in tne direction of tne
-15-
.: ' . ' . .
,
-
128~ 7~
-16-
atomizing edge 42. Tne nub 20b is provided witn a
tapered bore 20f wnicn snugly engages a similarly
tapered portion 23a of tne drive snaft 23. Tne
forward end 23b of tne drive snaft 23 is tnreaded for
tnreadedly receiving a retaining nut lO0 wnicn locks
tne nub 20b of tne cup 20 in place on tne drive snaft
23. Imbedded in tne outer surface 20d of tne frusto-
conical section 20a of cup 20 is a circular current-
conducting flat ring element 102, pre.ferably of
semiconductive material. Ring element 102 is elec-
trically connected to tne flat electrode 46, wnicn is
also preferably fabricated of semiconductive material,
via a series of conducting means in tne form of pins
104 seated in suitably provided bores in tne cup
section 20a. Tne pins 104, wnicn are preferably of
semiconductive material, at tneir opposite ends are in
electrical contact witn tne confronting surfaces of
tne ring 102 and electrode 46. Tne cup 20 is prefer-
ably made of insulative material, as is tne nut 100,
snaft 23, bearing 25, annular ring 24, body 10, rotary
actuator 31, valves 33, 80, 90, and 92, and associated
fluid conduits, mounting bracket 50, and mounting
columns 62, 64, and 66 for tne purpose of minimizing
tne storage of electrical energy in capacitive form in
tne spray coating device. A preferred type of insu-
lating material for tne cup 20 is PEEK (polyetner-
~ ~ etnerketone) available from I.C.I. of America, and for
A tne remaining insulative elements is ERTALYTE~r
-16-
r~c,~ ~rk
.. .... ~ .....
~284271
-17-
~polyester) available from Erta Incorporated, Malvern,
Pennsylvania.
Surrounding tne bracket 50 and body 10, as
well as tne various valves, is a tubular nousing, as
best snown in Figure 1, for enclosing tne various
operating components of tne spray device. Tne nousing
is preferably fahricated of insulative material.
Tne liquid coating valve 33, wnicn may be of
any conventional type, preferably includes a valve
body 120 naving a stepped diameter bore 122. Located
in tne forward end of tne bore 12~ is a valve seat
insert mount 12~ naving a bore 126 witnin wnicn is
positioned a valve seat insert 128 naving an axial
passage 128a wnicn is normally blocked by a ball valve
element 130 formed at tne forward end of a recipro-
cable rod 132 wnicn is normally forwardly biased to
close tne valve hy a spring-biased air-operated piston
134 secured to tne rear end 132a of tne snaft 132. A
spring 135 normally biases tne piston 134 in a forward
direction (rigntwardly afi viewed in Figure 2). An air
cnamber 136 connects to a source of pressurized air
via a passage 138 in tne wall of tne rear portion of
tne valve body 120. wnen pressurized air is admitted
into tne cnamber 136 via passage 138 under control of
means not snown, tne piston 134 is urged rearwardly
(leftwardly) to unseat tne ball valve element 130
relative to tne seat of tne seat insert 128, inter-
connecting passage 128a witn a liquid coating cnamber
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''
128~7~
-18-
142. Cnamber 142 communicates witn a source of
pressurized liquid coating (not snown) via a passage
144 formed in tne wall of tne valve body 120 wnicn
connects to a coating supply conduit 145.
Tnus, wnen pressurized air is admitted into
cavity 136 via passage 138 urging tne piston 134
rearwardly and unseating tne valve ball element 130,
pressurized liquid coating in cnamber 142 passes
tnrougn passage- way 128a into tne passageway 32 of
tne forward body section 12 wnereupon it exits under
pressure from tne nozzle 30 into tne rear cavity 34 of
tne rotary cup 20. In a manner described neretofore,
tne liquid coating material in rear cavity 34 flows
tnrougn passages 36 along interior wall 40 of tne
forward cavity 38 over flat ring electrode 46 wnereat
tne coating material is electrostatically cnarged.
Eventually tne cnarged electrostatic coating is
atomized at tne forward edge 42 of tne cup 20 to form
spray pattern 29.
Air cavity 136 and coating cavity 142 are
separated by suitable seals 150 wnicn permit axial
reciprocation of tne rod 132. Tne cavity 142 of tne
valve 33 connects via passage 152 formed in tne wall
of tne valve body 120 to tne conduit 82, ultimately
being passed to a waste receptacle 86 via tne dump
valve 80 and tne conduit 88. The dump valve 80 is
substantially identical to tne valve 33, except it
nas, in addition to a single inlet passage, only one
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-- ~28~2~
--19--
outlet passage for tne flow of liquid coating
material. Tne dump valve 80, like tne valve 33, is
air-operated and for tnis purpose nas a controlled
source of pressurized air (not snown) connected to it
via an air nose 80a.
Snaping of tne atomized liquid coating spray
pattern 29 emanating from tne forward edge 42 of tne
rotary atomiæing cup 20, as previously noted, is
provided by a circular air passage 26 formed in tne
annular ring 24 wnicn feeds a plurality of circularly
arranged axially extending ports 28 wnicn establisn
~orwaraly projecting air jets. To provide pressurized
air to tne circular air passage 26 formed in annular
ring 24, tne forward body section 12 is provided witn
a passage 160 wnicn at its forward end communicates
witn tne circular air passage 26 and at its rearward
end connects to a suitable source of pressurized air
(not snown) via a nose 162. Control means, also not
snown, regulate tne flow of air in tne nose 162 in a
conventional manner. Wnen pressurized air is provided
to tne nose 162, air is emitted under pressure from
tne circularly arranged ports 28 in a forwardly
direction, snaping tne electrostatically cnarged
atomized liquid coating particle spray pattern 29, as
desired.
Wnen it is desired to cnange tne color of
tne liquid coating material being sprayed from tne
device of tnis invention, solvent is introduced into
--19--
. .
~:84273,
-20-
tne port 144 of tne valve 33, in a manner well known
in tne art, and tne valve 80 opened. Tne solvent
flows tnrougn and flusnes tne valve 33, tne passage
32, and nczzle 30, as well as tnrougn passage 152 and
nose 82 to tne dump valve 80, allowing tne solvent to
pass tnrougn tne dump valve into tne waste receptacle
86 via nose 88. Cleansing of tne exterior surface 20d
of li~uid coating material witn solvent as an incident
to color cnange is provided by means of a solvent
nozzle 170 tnreaded into a suitably provided bore 172
in tne front surface 22 of tne forward body section
12. Tne passage 172 at its rear end connects to tne
output port 90a of tne solvent valve 90. Connected to
tne input port 90b of tne solvent valve 90 is a
solver' nose 174 supplied rom a suitable source of
pressurized solvent (not snown). Tne valve 90 is
constructed substantially identical to dump valve 80
and, like dump valve 80, is provided witn an air-
operated ball valve element 90c at tne forward end of
a rod 90d controllea by a spring-biased air-actuated
piston 90e. A controlled source of pressurized air is
connected to tne valve 90 via a suitable air nose 176
to actuate tne valve, as desired.
To cleanse t~e rearward cup cavity 34,
passages 36, and forward cup cavity 38 of coating
material as an incident to color cnanging, a solvent
nozzle 94 and valve 92 snown in Figure 8 is provided,
tne valve being substantially identical to tnat snown
-2n-
--` 128~
-21-
in Figure 4 for cleansing tne exterior surface of tne
atomizing cup 20. Tne only difference between tne
solvent cleansing nozzle 94 and valve assembly 92 for
cleansing tne interior of tne cup 20 and tne nozzle
170 and valve 90 for cleansing tne exterior of tne cup
is tnat tne nozzle 94 for cleansing tne interior of
tne cup projects from tne forward surface section 22a
of tne forward body section 12 into tne rear cavity 34
of tne cup 20. Tne coordination of tne various valves
to effect color cnange and tne flusning of tne valves,
nozzles, associated passages, noses, and tne like and
cleansing tne interior and exterior of tne atomizing
cup is accomplisned in accordance witn procedures well
known in tne art, and tnerefore are not further
aiscussed herein.
A source of pressurized solvent 180 feeds a
nose 182 wnicn is bifurcated to supply tne nose 174
wnicn provides solvent to tne valve 90 for controlling
tne flow of solvent for cleaning tne exterior of tne
cup 20 and to supply a nose 175 wnicn supplies solvent
to tne valve 42 wnicn controls tne flow of cleansing
solvent to tne interior cavity 34 of tne atomizing cup
20.
A source of pressurized air 185 connects to
nose6 186 and 188 wnicn are input to tne air turbine
31 for driving and braking tne turbine rotor, respec-
tively, and in turn, driving and braking,
respectively, tne snaft 23 and ultimately tne
atomizing cup 20. A
-21-
-22-
nose 190 vents exnaust air from tne turbine 31. Py
selectively controlling tne pressure and flow of air
in noses 186 and 188, tne speed of tne air turbine 31,
and nence of tne output snaft 23 and ultimately tne
rotary atomizinq cup 20, can be controlled in a manner
well known to tnose skilled in tne art.
An air nose 192 connected to a selectively
operable source of pressurized air controls tne
solvent valve 92 for cleansing tne interior of tne
rotary atomizing cup 20. Air nose 192 functions witn
respect to solvent valve 92 in a manner analogous to
air nose 176 wnicn is connected to solvent valve 90
for controlling its operation and air nose 138 wnicn
connects to the paint valve 33 for controlling its
operation.
To minimize tne accumulation of coating
material on tne surface of tne snaft 23, air purge
means are provided to supply a positive air flow along
tne snaft toward tne rotary atomizing mem~er 20. In a
preferred form tne air purge means includes, as snown
in Figure 2, a port 300 provided in tne back wall 12a
of tne forward body section 12 for connection to an
air supply line (not shown). Tne air line will supply
air tnrougn a passage 302 to a discnarge port 304 into
tne space 308 between tne bore 12b of tne forward body
support section 12 and tne snaft 23. Tnis air
supplies a positive air purge along tne snaft 23
towards tne
-2~-
1284i~71
-23-
cup 20 to prevent coating from migrating back along
tne snaft into tne bearing 25.
Hign voltage electrostatic energy is coupled
from tne electrode 78 at tne output of tne gun
resistor 76 to tne semiconductive ring 102 ~and
ultimately to tne semiconductive electrode 46 via tne
semiconductive pins 104~ via a patn wnicn includes an
electrically conductive spring contact 200 located in
tne forward end of tne bore 72 formed in tne forward
body section 12, an electrical conductor 202 snugly
fitting in a bore formed in tne forward body section,
an electrode ring 204 imbedded in an annular recess
formed in tne rear wall 206 of tne annular ring 24,
and several parallel circuit patns connected between
tne ring conductor 204 and tne semiconductive ring
102. ~ne series circuit patns between rings 204 and
102 include a resistor 210 disposed between a? an
electrical conductor 212 wnicn is connected between
tne resistor 210 and tne ring 204 and b) a conductor
214 extending from tne forward end of tne resistor 210
toward and in close proximity to tne semiconductive
ring 102. An insulative sneatn 216 tnreaded at its
inner or rear end into a suitably tnreaded bore in tne
annular ring 24 encases tne resistor 210, conductor
212, and conductor 214, witn conductor 214 projecting
from tne forward end of tne sneatn. Insulative
sneatns 218 and 220, identical to sneatn 216, mounted
in circumferentiallv spaced relation around tne
annular ring 24 120
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~ ~ .
~284271
-24-
on eitner side of tne sneatn 216 contain resistors
218a (Figure 3) and 220a wnicn are identical to
resistor 210. Resistor 218a is connected between
a) an outer electrical conductor 218b wnicn extends
from tne forward end of its associated sneatn toward
and in close proximity to tne semiconductive ring 102
and b) an electrical conductor 218c wnicn is connected
to tne conductive ring 204 for transmitting electro-
static voltage to tne resistor 218a. Resistor 220a is
connected between a) an electrical conductor 220b
wnicn extends from tne forward end of its associated
sneath toward and in close proximity to tne semi-
conductive ring 102 and b) an electrical conductor
220c wnicn is connected between tne resistor and tne
electrically conductive ring 204. Tne forwardly
projecting ends of tne electrical conductors 214
218b and 220b are spaced very sligntly from tne
exterior surface of tne fiemiconductive ring 102 sucn
tnat wnen nign voltage is transmitted tnereto ~ia tne
insulated cable 74, gun resistor 76, conductor 78,
spring 200, conductor 202, ring conductor 204 and
conductor/resistor pairs 210/212, 218a/218c, and
220a/220c, electrostatic energy is transmitted across
tne gap to tne semiconductive ring 102 and ultimately
to tne ring electrode 46 via pins 104 for contact
cnarging of liquid coating material wnicn flows
radially outwardly and forwardly along inner wall 40
over tne surface of tne fiemiconductive electrode 46.
-24-
1284Z71
It has been discovered that the coating transfer
efficiency is enhanced by the use of three circumferentially-
spaced conductors 212, 218c and 220c in comparison to that
achieved when only a single conductor is used. Thus, plural
conductors provide improved results and are clearly preferred
where high transfer efficiency is desired.
Gun resistor 76 can have a resistance which varies
depending upon the operating range of the electrostatic power
supply which energizes the cable 74. Preferably, for
electrostatic supplies operating in the range of 50Kv-125Kv,
the gun resistor has a resistance of 75 megohms. The
resi~tors 210, 218a, and 220a can also have varying
resistance~, although preferably each such resistor has a
resistance of approximately 12 megohms.
The insulated cable 74 may take a variety of forms,
although the preferred cable is one in which the conductive
core 74b is fabricated of silicon carbide fiber in accordance
with the disclosure and claims of Hastings et al. U.S. Patent
4,576,827, granted March 18, 1986, assigned to the assignee
of the present application. The semiconductive ring 102,
pins 104, and electrode 4Ç are also preferably fabricated of
RYTON (trade mark for polyphenylene sulfide tPPS~), available
from Phillips 66, although other semiconductive materials may
be used. In
11548/LCM:
~' ~
1284Z71
-26-
addition, and altnougn not preferred, tne ring 102,
pins 104, and/or electrode 46 can be fabricated of
conductive material. ~owever, wnen fabricated of
conductive material, tne capability of tne rotating
atomizing cup 20 to capacitively store electrical
energy is increased over tnat wnicn exists wnen tne
ring 102, pins 104, and electrode 46 are fabricated of
semiconductive material. If desired, tne conductive
elements 78, 200, 202, 204, 212, 214, 218b and 218c,
~C and 220b and 220c can be fabricated of semiconductive
material ratner tnan conductive material.
Accordingly, and for tne purpose of minimizing ~ne
electrical energy stored capacitively in tne spray
device of tnis invention, all elements of tne spray
device are preferably fabricated of insulative
material, except for tnose wnicn are fabricated of
semiconductive and/or electrically conductive material
for tne purpose of transporting electrostatic energy
a~ nign voltage from a remote source ~not snown) to
tne coating cnarging electrode 46 in tne rotary
atomizing cup 20.
In tne preferred embodiment, tne rotating
atomizing cup 20 nas been described as being frusto-
conical in snape. As tnose skilled in tne art will
understand, otner snapes can be utilized witnout
departing from tne spirit and scope of tnis invention.
Tne valves 33, 80, 90, and 92 are generally
constructed in accordance with tne teacnings of
-26-
- .
.
~ ~2~
27
Hastings et al. U.S. Patent 3,870,233, assigned to the
assignee of this application.
ALTERNATE EMBODIMENT
Other aspects of the present invention will now be
described with reference to the alternate embodiment shown in
Figs. 10 and li to which we now refer. Except for the
differences to be described, the alternate embodiment is
substantially the same as the first embodiment discussed
above, with like parts having been assigned like reference
numerals.
The alternate embodiment of the rotary atomizing
liquld spray coatlng device of this invention iB seen to
in¢lude a support body 10 having a front or forward section
12. AB w$th the first embodiment, an annular cavity 18 is
located rearwardly of the forward section 12. Within cavity
18 are located, as will be described in more detail
hereafter, various valves for controlling the flow of liguid
coating material and solvent for cleansing the interior and
exterior of the rotary atomizing cup 20.
Rotary atomizing cup 20 extends forwardly from the
~ront surface 22 of the forward body section 12. Removably
secured to the front surface 22 of the forward section 12 of
the body 10 in any suitable manner, such as by bolts,
threaded engagement, or the like, is a cap 400 having a
generally convex outer face 402 and a centrally disposed,
inwardly tapering
11548/LCM:~q
'' ~,i:"l~
~,.
. .
-- 128~Z~l
-28-
recess 404 inside wnicn, at least a portion of
atomizing cup 20 may be located. Cap 400 includes a
base 406 naving a generally circular air passage or
manifold 26 formed tnerein. A gasket 408 naving
suitably sized and positioned apertures is interposed
between cap 400 and tne front surface 22 of tne
forward section 12 of body 10 to provide a suitable
seal for air and solvent passages, to be described
later, wnicn communicate between forward section 12
and cap 400. Similar to tne annular ring 24 of tne
first embodiment, cap 400 includes a plurality of
circularly arrangcd air ports 28 for establisning a
circular array of air jets surrounding rotary
atomiz~ng cup 20 for snaping tne atomized liquid
coating spray pattern 29 formed at tne forward edge or
rim 42 of tne atomizing cup 20 and projecting it
toward a workpiece to be coated in tne manner
previously described.
As noted, extending forwardly from tne
forward section 12 of tne body 10 is tne rotary
atomizing cup 20. Cup 20 is drivingly mounted for
rotation on a snaft 23 of a rotary actuator ~rot
snown). Tne cup drive snaft 23 extends tnrougn a bore
'2b in forward body section 12. As in tne first
embodiment, a liquid coat~ng control valve 33 is
mounted to tne rear surface of tne forward section 12
and controls tne flow of liquid coating material to
tne coating nozzle 30. Liquid coating under slignt
pressure exiting nozzle 30 enters tne cup 20 and
-28-
128427~ -
-29-
passes tneretnrougn tnere as previously described witn
reference to tne first embodiment.
Mounted witnin cavity 18 and on tne rear
surface of tne forward body section 12, in addition to
tne coating control valve 33, is a single solvent
valve 412 wnicn, in lieu of tne dual interior and
exterior solvent valves 90, 92 of tne first embodi-
ment. Valve 412 controls tne flow of solvent, in a
manner to be described, to botn tne interior and
exterior of tne rotary atomizing cup 20.
Tne diameter of frusto-conical rotary
atomizing cup 20 increases along tne axis of tne cup
in tne direction of tne atomizing edge 42. Imbedded
in tne outer surface 20d of tne frusto-conical cup 20
is a circular current-conducting flat ring element
102, preferably of semi-conductive material.
P.ccording to one aspect of tne invention, ring element
102 is recessed substantially entirely witnin tne
recess 404 in wnicn cup 20 is disposed tnereby
decreasing tne likelinood tnat personnel or objects
can contact element 102 creating a snock nazard. As
witn tne firct embodiment, ring element 102 is
electrically connected to tne cnarging flat electrode
located on tne interior surface of cup 20 in tne
manner previously described. A nousing 416 is used to
enclose all tne operating components and tne various
conduits for coating material solvent and waste as
well as tne nign voltage electrical cable are
preferably routed
-29-
-30-
rearwardly tnrougn appropriate apertures (not snown)
in tne rear mounting bracket ratner tnan tnrougn tne
side walls as snown in Fig. '. Tnis locates tne
conduits and cable as far as possible from tne spray
pattern 29 emanating from tne edge of atomizing cup 20
to nelp prevent tne accumulation of coating material
on tnem. It also provides a sleek, attractive
uncluttered appearance.
~nen it is desired to cnange tne color of
tne liquid coating material being sprayed from tne
device of tnis invention, coating valve 33 is flusned
witn solvent by way of dump valve in tne manner
previously described. According to tne alternate
embodiment of tne invention, interior and exterior
cleansing of atomizer cup 20 of liquid coat;ng
material witn solvent as an incident to color cnange
is performed using single solvent valve 412. To tnis
end, valve 412 communicates witn a bore 420 in body
section 12. Tne bore 420 nas a pair of brancn bores
422, 424. Brancn bore 422 connects witn nozzle 32 to
cleanse tne interior of cup 20 in tne manner
previously described. Tne otner brancn bore 424,
exits tnrougn a suitable aperture in gasket 408 and
connects witn a bore 426 in cap 400. Tnis bore 426
nas an exit port 428 at tne wall of inwardly tapering
recess 404 directed to cleanse tne exterior 20d of cup
20. Valve 412 is constructed substantially
identically to dump valve 30 as previously described
and is actuated by a
-30-
8~
-31-
controlled source of pressurized air to simultaneously
flusn the interior and exterior of cup 20 witn solvent
prior to a color cnange or for periodic cleaning.
In tne first embodiment, purge air was
provided to minimize tne accumulation of coating
material on tne surface of tne snaft 23. According to
tne alternate embodiment, bearing 25 is selected to be
an air bearing. Tnis eliminates a separate purging
air passage sucn as passage 302 previously deccribed
witn reference to tne first embodiment, since tne
normal air leakage of tne air bearing (not snown) to
flow along snaft 23 as a air purge means in tne space
308. Tnis flow of leakage air supplies a positive air
purge along tne snaft 23 towards tne cup 20 to prevent
coating from migrating back along tne snaft into tne
bearing ~not snown).
Tne patn for conducting nign voltage
electrostatic energy from gun resistor 76 to tne
cnarging electrode 102 imbedded in tne interior wall
20d of atomizing cup 20 according to tne alternate
embodiment will now be described in furtner detail.
An annular conductor 430 wnicn substantially encircles
cap 400 is disposed in an annular stepped groove 432
cut in base or rear face 434 of cap 400. Cohductor
430 is captured witnin groove 432 by an insulating
ring 436 wnicn is sealed in tne larger step of groove
432 using a suitable adnesive sealant sucn as an
epoxy. Tne conductor 430 is connected by soldering,
brazing or -31-
8 ~ ~L
-32-
otner suitable means to a conductive disk 438, wnicn
is preferably of brass or otner electrically conduc-
tive corrosion resistant material. Disk 438 nests
witnin a recess 440 of an electrically insulating
busning 442 wnicn, in turn nests partially inside tne
front end 62a of tne support column 62 wnicn nouses
gun resistor 76. Tne opposite end of busning 442
nests in a pocket in tne ring 436. Busning 442
includes an axial bore 444 wnicn receives a cylindri-
cal projecting portior. a46 of column 62. Column end62a and projection 446 include a bore 448 wnicn
communicates witn gun resistor 76. Received witnin
bore 448 is tne nollow tubular body portion 450 of
electrically conductive spring contact assembly 452.
Body portior. 448 contains a spring 454 whicn is
compressively biased by a plunger 456 naving a nead
458 wnicn abuts disk 438 as tne base of body portion
; 450 abuts gun resistor 76 tnereby providing good
electrical contact between gun resistor 76 and disk
438 wnicn is in turn connected to annular conductor
430.
Electrostatic energy is transferred from
conductor 430 to cnarginq electrode 102 by way of
tnree cnarging resistors 210 of identical nominal
resistance connected electrically in parallel between
cnarging electrode 102 and conductor 430. According
to tne alternate embodiment, tne cnarging resistors
210 are pnysically mounted witnin cap 400 in evenly
-32-
~Z1~42~
-33-
circumferentially spaced relation to one anotner.
Resistors 210 all fit snugly witnin bores 460 wnicn
communicate witn conductor 430, and wnicn are disposed
witn tne recess 404 of cap 400 wnerein atomizer cup 20
is located. Bores 460 eacn intersect recess 404 at a
location opposite tne ring element 102 of atomizer cup
20 so tnat tne free ends 462 of tne cnarging resistors
act as electrodes wnicn terminate in closely spaced
proximity to semi-conductive ring element 102. By
imbedding cnarging resistors 210 witnin cap 400 tne
invention affords substantial protection against tneir
being damaged or misaligned due accidental impact.
Also, since tne electrode leads 462 are located witnin
recess 404 tnere is less likelinood tney can be
contacted by personnel or objects tnereby reducing tne
risk o4 electrical snock or mecnanical damage. Tne
opposite leads 464 of tne cnarging resistors 210 pass
tnrougn reduced diameter portions of bores 460 wnicn
intersect groove 432, at wnicn point leads 464 are
connected to conductor 430 by ~oldering or otner
suitable means.
Tnus, nign voltage electrostatic energy is
transmitted by way o' nign voltage cable 74 as previ-
ously described to gun resistor 76. It i8 tnen
carried to conductor 430 by way of spring contact 452
and disk 438. From conductor 430, electrostatic
energy is carried to cnarging electrode 102 of
atomizing cup 20 by way of tne tnree cnarging
-33-
i284~7~
-34-
resistors 210 connected electrically in parallel
between conductor 430 and tne gap between tne elec-
trodes or free ends 462 of said resistors and tne ring
element 102 on tne outside of atomizing cup 20.
Electrostatic energy is tnen transmitted across tne
gap between eacn said electrodes 462 and semi-
conductive ring element 102. From ring element 102,
tne electrostatic energy is utilized in tne manner of
tne first embodiment to impart a cnarge to tne coating
material.
Tne resistances of gun resistor 76 and
cnarging resistors 210 are selected as previously
described. As witn tne embodiments previously
described, and for tne purpose of minimizing tne
electrical energy Etored capacitively in tne spray
device of tnis invention, all elements of tne sprav
device are preferably fabricated of insulative
material, except _or tnose wnicn are fabricated of
semi-conductive ar.d/or electrically conductive
material for tne purpose of transportina electrostatic
energy at nign voltage from a remote source (not
snown) to tne coating cnarging electrode 102 in tne
rotary atomizing cup 20.
Tne alternate embodiment of tne rotary
~5 atomizing liquid spray system of tne invention
includes several features wnicn nelp to project tne
spray pattern 29 forwardly toward tne work piece to be
coated and avoid tne accumulation of coating material
-34-
1284271 _35_
on tne sprayer itself tnereby increasing transferefficiency and decreasing fouling of tne sprayer. One
sucn feature, namely tne provision of a plurality of
air ports 28 for establisning an array of forwardly
directed air jets surrounding atomizing cup 20 for
snaping and projecting spray pattern 29 toward tne
workpiece to be coated nas already been described.
Furtrler according to tne invention, tne sprayer of
tnis embodiment also preferably includes at least one
of tne additional features wnicn will now be
described.
Atomizer cup 20 is surrounded by electro-
static repulsion means wnicn preferably takes tne form
of a substantially continuous conductive, or more
preferably, semi-conductive ring 470. Ping 470 is
imbedded in a groove 472 cut in tne outer face 402 of
cap 400 as to lie substantially flusn tnerewitn as not
to interfere significantly witn its contour for
reasons wnicn will later become apparent. Ring 470 is
electrically connected directly to conductor 430 by
way of a conductive pin 474 so tnat ring 470 i8
energized witn a nign voltage cnarge of tne same
polarity as tne cnarge carried by tne coating drop-
lets. Tnis nelps to promote tne migration of spray
pattern away from tne spray apparatus and toward tne
workpiece to be coated.
Anotner important aspect of tne present
invention wnicn nas been found to nelp increase
transfer efficiency by avoiding air flow eddys wnicn
-35-
-36-
tend to innibit tne forward migration of spray pattern
29 and to be useful in avoiding tne accumulation of
coating material on tne spray apparatus is tne provi-
sion of a curved, aerodynamically contoured outer face
402 on cap 400 as snown. Tne forward portion of cap
400 defines a circular dome naving a contoured outer
face 402 and a central recess 404 in wnicn frusto-
conical atomizing cup 20 is recessed. For tne purpose
of avoiding reverse air flow eddys, tne degree to
wnicn cup 20 is recessed witnin cap 400 is not
believed to be critical. In fact, recess 404 may be
eliminated 80 ~ nat outer face 402 lie~ substantially
entirely benind cup 20. However, so tnat conductive
ring 102 and electrodes 462 may be protected as
previously described, cup 20 ifi preferably recessed
witnin cap 400 from to approximately one-nalf to
two-tnirds of its overall lengtn. Recess 404 tapers
inwardly at a sligntly greater rate tnan tne wall of
cup 20 so tnat tne gap between cup 20 and recess 404
is ~ligntlv narrower at its base tnan at is moutn.
Tne transition edge between tapered recess 404 and
curved outer face 402 is not snarp but ratner is
provided witn a generoùs radius afi snown in tne
drawings. This aspect of tne invention will become
furtner apparent in lignt of its tneorv of operation
wnicn is believed to be as follows.
As atomizer cup 20 rotates at an angular
speed sufficient to atomize coating material, usuallv
in tne range of ln,000 to 40,000 R.P.M., its atomizing
-36-
. .
28~
-37-
edge 42, wnicn is a larger diameter tnan its base 480,
rotates at a greater surface speed tnan its base.
Since tne air surrounding cup 20 will tend to move
witn tne surface of tne cup 20 due to drag, tnere will
be a pressure gradient along tne outside wall 20d of
cup 20 tending to cause a flow of air along tne
outside wall 20d in a direction generally parallel to
wall 20d and oriented from base 480 toward edge 42.
Since tne aforementioned air flow would tend to
partially evacuate tne region near tne base of tne
cup, it is believed tnat a make-up air flow takes
place along outer face 20d inwardly toward tne base
4P0 of cup 20 along tne wall of recess 404. Tne snape
of cap 400, particularly tne snape of its outer face
402 ic selected sucn tnat under conditions of normal
operation, tne flow of make-up air acrosæ its surface
will be in a substantially laminar flo~r regime. Tnis
is believed to nelp avoid tne generation of eddy
currents in tne vicinity of cup 20 wnicn would otner-
wise tend to draw coating material back toward tne~pray apparatus ratner tnan permit it to be directed
toward tne workpiece as de~ired.
what is claimed is:
-37-
,,~ .,.. ,, :,
,
.
