CA1284271C - Electrostatic rotary atomizing liquid spray coating apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Electrostatic liquid spray coating apparatus including a frusto-conical rotary atomizing cup of insulative material driven by an air turbine, is provided with a ring-shaped semi-conductive charging electrode for contact charging liquid coating material supplied to the rear of the cup as it contacts the electrode prior to atomization at the forward edge of the cup. An insulative support body, housing a turbine and its associated air bearing and cup drive shaft, has a reduced diameter intermediate section which provides an annular cavity in which are located liquid coating and solvent flow control valves. The support body is mounted to a rear bracket by several parallel spaced apart insulative columns, one of which is hollow to accommodate a high voltage insulated cable for energizing the charging electrode via a stationary conductor. A semi-conductive ring on the cup exterior is electrically connected to the ring-shaped charging electrode on the cup interior via a series of semi-conductive pins extending through the wall of the cup between the ring-shaped conductor and charging electrode. A dump valve is mounted on the bracket between the columns.

Description

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 11548/LCM~

~28~271 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 3,075,706, 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 28~7~

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.

, . . .

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 :~: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~

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 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.

, _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~

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 -' ~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 . .

~28~

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 --` 12~4271 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.

2 ~ ~L

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 ~`

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 .: ' . ' . .

, -128~ 7~

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 r~c,~ ~rk .. .... ~ .....

~284271 ~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 '' 128~7~

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 -- ~28~2~

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 . .

~:84273, 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~

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

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 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 ~ ~ .

~284271 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.

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:

~' ~

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 - .

.

~ ~2~

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 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 128427~ -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 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 8~

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

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 ~Z1~42~

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 i284~7~

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 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 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 . .

28~

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:

,,~ .,.. ,, :, , .

Claims (41)

1. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a support body of insulative material having forward, intermediate, and rear sections, a rotary atomizer of insulative material having an axis of rotation, a first surface over which liquid coating can flow outwardly to an atomizing edge thereof when said atomizer is rotated about said axis of rotation, and a second surface separated from said first surface by said atomizing edge, a circular ring-shaped charging electrode mounted on said first surface encircling said axis of rotation, a circular electrical current-conducting element mounted on said second surface encircling said axis of rotation, means mounted to said rotary atomizer for electrically connecting said circular electrode and said electrical current-conducting element, drive means incorporated in said support body drivingly mounting said rotary atomizer to said forward section of said support body for rotating said rotary atomizer about said axis of rotation, means fabricated of insulative material for supplying liquid coating to said first surface of said rotary atomizer when said atomizer is rotating about its rotational axis, and plural circumferentially-spaced electrical conductors stationarily mounted to said forward section of said support body, said conductors having a free end located in closely spaced proximity to said circular electrical current-conducting element for transferring electrostatic energy thereto when said stationary electrical conductors are energized from a high voltage source for facilitating contact charging of liquid coating supplied to said first surface when said coating flows outwardly over said first surface in contact with said charging electrode toward said atomizing edge.

2. The apparatus of claim 1 wherein said circular electrode is semi-conductive.

3. The apparatus of claim 2 wherein said electrical current-conducting element and said elec-trical connecting means are semiconductive.

4. The apparatus of claim 1 further including first and second solvent spray nozzles stationarily mounted to said forward section of said support body proximate said first and second surfaces, respectively, for directing solvent thereat to cleanse said surfaces, solvent valve means mounted proximate said forward section of said support body, and solvent conduit means interconnecting said solvent valve means and said solvent nozzles for transporting solvent to said solvent nozzles under control of said solvent valve means to cleanse said first and second surfaces.

5. The apparatus of claim 1 wherein said liquid coating supply means includes a liquid coating nozzle mounted on said forward section of said support body in proximity to said rotary atomizer, a liquid coating valve mounted proximate said forward section of said support body, and a liquid coating conduit interconnecting said liquid coating valve and said liquid coating nozzle for transporting liquid coating to said liquid coating nozzle under control of said liquid coating valve.

6. The apparatus of claim 4 wherein said liquid coating supply means includes a liquid coating nozzle mounted on said forward section of said support body in proximity to said rotary atomizer, a liquid coating valve mounted proximate said forward section of said support body, and a liquid coating conduit interconnecting said liquid coating valve and said liquid coating nozzle for transporting liquid coating to said liquid coating nozzle under control of said liquid coating valve.

7. The apparatus of claim 6 wherein said drive means includes an air turbine mounted to said rear section of said support body, a drive shaft interconnecting said turbine and said rotary atomizer, and an air bearing mounted to said intermediate section of said support body, said liquid coating valve and solvent valve means are located radially outwardly of said bearing.

8. The apparatus of claim 7 further com-prising a mounting bracket, and insulative column means fixedly interconnecting said bracket and said support body for mounting said bracket and rear section of said support body in spaced apart relation to establish a space tnerebetween.

9. The apparatus of claim 8 further com-prising a dump valve mounted in said space between said bracket and said rear section of said support body, and conduit means interconnected between said dump valve and said liquid coating valve.

10. The apparatus of claim 9 further comprising a tubular housing extending between said bracket and forward section of said support body for enclosing said dump valve, liquid coating valve and solvent valve means and said conduit interconnecting said dump valve and said liquid coating valve.

11. The apparatus of claim 1 wherein said rotary atomizer includes a tubular section having an inner surface which includes said first surface and an outer surface which includes said second surface, said tubular section terminating forwardly at said atomizing edge and having a nonuniform cross section which increases in the direction of said atomizing edge, and wherein said electrical connecting means extends radially through said tubular section.

12. The apparatus of claim 1 comprising at least three said electrical conductors stationarily mounted to said forward section of said body support at substantially equally spaced circumferential intervals, each said conductor having a free end located in closely spaced proximity to said circular electrical current-conducting element for transferring electrostatic energy thereto when energized from a high voltage source.

13. The apparatus of claim 12 further including separate insulative sleeves having forward and rear ends encasing each of said three electrical conductors, with the free ends of said electrical conductors projecting from the forward ends of their respectively associated insulative sleeve, separate resistors encased within each of said sleeves in series circuit with their respectively associated electrical conductors, said rear ends of said sleeves each being mounted to said forward section of said support body at circumferentially spaced locations.

14. The apparatus of claim 7 wherein said rear section of said support body includes a turbine cavity within which is located said turbine, said intermediate section of said support body includes a bearing cavity within which said bearing is located, and said forward section of said support body includes a bore through which said shaft extends, whereby said support body substantially encases said turbine, bearing and shaft.

15. The apparatus of claim 14 wherein said forward section of said support body includes a flange extending radially outwardly of said intermediate body section to define a rear-facing surface, and wherein said liquid coating valve and said solvent valve means are mounted to said rear-facing surface of said flange adjacent said intermediate body section.

16. The apparatus of claim 8 wherein said column means includes at least two spaced-apart columns, with one of said columns having an axial bore along its length for housing an electrostatic energy-conducting core for transporting high voltage electro-static energy between said stationary conductor which is in closely spaced proximity to said circular electrical current-conducting element and a high voltage source located remote therefrom.

17. The apparatus of claim 16 further including a gun resistor located in said axial bore of said one column in series circuit with said circular electrical current-conducting element.

18. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a generally cylindrically shaped support body having forward and rear sections disposed on opposite sides of an intermediate section, said intermediate section having a diameter substantially less than that of said forward and rear body sections to define an annular cavity therebetween, a frusto-conically shaped tubular rotary atomizer of insulative material having an inner surface and an outer surface extending between a rear edge and a forward atomizing edge, with the diameter of the forward edge exceeding the diameter of the rear edge, said atomizer having an axis of rotation, a circular charging electrode mounted on said inner surface encircling said axis of rotation, a circular current-conducting element mounted on said outer surface encircling said axis of rotation, means mounted to said rotary atomizer for electrically connecting said circular electrode and said circular element, drive means or rotating said rotary atomizer about its axis of rotation, said drive mean including a) an air turbine located within a cavity in said rear body support section, b) a drive shaft connected between said turbine and said rotary atomizer and extending through a bore in said forward body support section, and c) an air bearing located in a cavity in said intermediate body support section for rotatably supporting said shaft, means for supplying liquid coating to said inner surface of said rotary atomizer when said atomizer is rotating about its rotational axis, said means including a) a liquid coating valve mounted in said annular cavity proximate said forward section of said support body, and b) a liquid coating nozzle mounted on said forward body support section in proximity to said inner surface of said rotary atomizer, and c) a liquid coating conduit inter-connecting said liquid coating valve and said liquid coating nozzle for transporting liquid coating to said liquid coating nozzle under control of said liquid coating valve, plural electrical conductors stationarily mounted to said forward body support section at circumferentially spaced intervals, each said con-ductor having a free end located in closely spaced proximity to said circular conducting element for transferring electrostatic energy thereto when said stationary electrical conductors are energized from a high voltage source for facilitating contact charging of liquid coating supplied to said inner surface of said rotary atomizer when said coating flows forwardly and outwardly over said inner surface in contact with said charging electrode toward said atomizing edge under centrifugal force produced by rotation of said rotary atomizer.

19. The apparatus of claim 18 wherein said circular electrode and circular element are semi-conductive.

20. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a support body of insulative material having forward, intermediate, and rear sections, said forward section having a front surface, a rotary atomizer of insulative material having an axis of rotation, and a surface over which liquid coating can flow outwardly to an atomizing edge thereof when said atomizer is rotated about said axis of rotation, said rotary atomizer including means for charging liquid coating material, drive means incorporated in said support body drivingly mounting said rotary atomizer to said forward section of said support body for rotating said rotary atomizer about said axis of rotation, means fabricated of insulative material for supplying liquid coating to said surface of said rotary atomizer when said atomizer is rotating about its rotational axis, an annular ring detachably mounted to said forward section of said support body and having a rear surface in contact with said front surface of said forward section of said support body and a front surface provided with a circular array of air passages, said rear surface of said annular ring having a first annular recess communicating with said circular array of air passages for supplying air thereto to establish a circular array of air jets for shaping the pattern of atomized liquid coating, said rear surface of said annular ring having a second annular recess, a circular conductor mounted in said second annular recess, and plural circumferentially-spaced electrical conductors stationarily mounted to said annular air ring, said conductors each having a rear end connected to said circular conductor and a forward free end located in closely spaced proximity to said rotary atomizer charging means for transferring electrostatic energy thereto when said stationary electrical conduc-tors are energized from a high voltage source connected to said circular conductor for facilitating charging of liquid coating supplied to said rotary atomizer surface when said coating flows outwardly over said surface toward said atomizing edge in charging relationship to said rotary atomizer charging means.

21. The apparatus of claim 20 further comprising:
plural insulative sheaths respectively encasing said plural electrical conductors, each said sheath having a rear end detachably secured to said air ring from which the rear end of its respectively associated conductor extends and a forward end from which the forward end of its respectively associated conductor projects.

22. The apparatus of claim 21 wherein said air ring includes plural threaded bores extending between said front surface and second annular recess of said air ring, and wherein said rear ends of said sheaths are threadedly secured in said threaded bores of said air ring with the rear ends of said conductors electrically connected to said circular conductor in said second annular recess of said air ring.

23. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a generally cylindrically shaped support body having forward and rear sections disposed on opposite sides of an intermediate section, said intermediate section having a diameter substantially less than that of said forward and rear body sections to define an annular cavity therebetween, a rotary atomizer of insulative material having an axis of rotation and a first surface over which liquid coating can flow outwardly to an atomizing edge thereof when said atomizer is rotated about said axis of rotation, and a second surface separated from said first surface by said atomizing edge, a circular ring-shaped charging electrode mounted on said first surface encircling said axis of rotation, a circular electrical current-conducting element mounted on said second surface encircling said axis of rotation, means mounted to said rotary atomizer for electrically connecting said circular electrode and said electrical current-conducting element, drive means for rotating said rotary atomizer about its axis of rotation, said drive means including:
a) an air turbine located within a cavity in said rear body support section, (b) a drive shaft connected between said (claim 23 continued) turbine and said rotary atomizer and extending through a bore in said forward body support section, and (c) a bearing located in a cavity in said intermediate body support section for rotatably supporting said shaft, means for supplying liquid coating to said surface of said rotary atomizer when said atomizer is rotating about its rotational axis, said means including:
a) a liquid coating valve mounted in said annular cavity proximate said forward section of said support body, and b) a liquid coating nozzle mounted on said forward body support section in proximity to said surface of said rotary atomizer, and c) a liquid coating conduit interconnecting said liquid coating valve and said liquid coating nozzle for transporting liquid coating to said liquid coating nozzle under control of said liquid coating valve, and an electrical conductor stationarily mounted to said forward body support section, said conductor having a free end located in closely spaced proximity to said circular conducting element for transferring electrostatic energy thereto when said stationary electrical conductor is energized from a high voltage (claim 23 continued) source for facilitating charging of liquid coating supplied to said first surface of said rotary atomizer when said coating flows outwardly over said first surface in contact with said charging electrode toward said atomizing edge under centrifugal force produced by rotation of said rotary atomizer.

24. The apparatus of claim 23 further including a solvent spray nozzle stationarily mounted to said forward section of said support body proximate said surface of said rotary atomizer for directing solvent thereat to cleanse said surface, a solvent valve mounted in said annular cavity proximate said forward section of said support body, and solvent conduit means interconnecting said solvent valve and said solvent nozzle for transporting solvent to said solvent nozzle under control of said solvent valve to cleanse said surface of said rotary atomizer.

25. The apparatus of claim 24 wherein said solvent and liquid coating valves are fabricated substantially of insulative material.

26. The apparatus of claim 1, further comprising, a cap on the forward section of said support body generally surrounding said rotary atomizer, said cap having an outer face whose shape is adapted to provide a substantially laminar flow of air there-across as said rotary atomizer rotates about said rotational axis during normal operation.

27. The apparatus of claim 26 wherein said cap includes a recess in which said rotary atomizer is at least partially disposed to define a gap between said cap and said second surface of said rotary atomizer, said free ends of said conductors and said circular current conducting element each being dis-posed substantially within said gap whereby said free ends and said element are afforded substantial protec-tion against inadvertent contact.

28. The apparatus of claim 26, further comprising, an array of air passages surrounding said rotary atomizer, and means for supplying air under pressure to said passages to establish an array of air jets for projecting and shaping a pattern of atomized liquid coating material.

29. The apparatus of claim 1, further com-prising, electrostatic repulsion means affixed to said apparatus to repel charged, atomized liquid coating therefrom.

30. The apparatus of claim 1, further com-prising, a cap on the forward section of said support body generally surrounding said rotary atomizer, said cap having an outer face whose shape is adapted to provide a substantially laminar flow of air there-across as said rotary atomizer rotates about said rotational axis during normal operation;
an array of air passages in said cap surrounding said rotary atomizer;
means for supplying air under pressure to said passages to establish an array of air jets for projecting and shaping a pattern of liquid coating material atomized by said rotary atomizer, and a repulsion ring on said cap to electro-statically repel charged liquid coating material atomized by said rotary atomizers.

31. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a support body of insulative material having forward, intermediate, and rear sections;
a cap on the forward section of said support body, said cap having a recess;
a rotary atomizer of insulative material having an axis of rotation, a first surface over which liquid coating can flow outwardly to an atomizing edge thereof when said atomizer is rotated about said axis of rotation, and a second surface separated from said first surface by said atomizing edge, said rotary atomizer being at least partially disposed within said recess to define a gap between said cap and said second surface;
a circular ring-shaped charging electrode mounted on said first surface encircling said axis of rotation;
a circular electrical current-conducting element mounted on said second surface encircling said axis of rotation;
means mounted to said rotary atomizer for electrically connecting said circular electrode and said electrical current-conducting element;
drive means incorporated in said support body drivingly mounting said rotary atomizer to said forward section of said support body for rotating said rotary atomizer about said axis of rotation;

means fabricated substantially of insulative material for supplying liquid coating to said first surface of said rotary atomizer when said atomizer is rotating about its rotational axis, and plural circumferentially-spaced electrical conductors stationarily mounted to said cap, said each of said conductors having a free end located within said gap in closely spaced proximity to said circular electrical current-conducting element for transferring electrostatic energy thereto when said stationary electrical conductors are energized from a high voltage source for facilitating contact charging of liquid coating supplied to said first surface when said coating flows outwardly over said first surface in contact With said charging electrode toward said atomizing edge.

32. The apparatus of claim 31 wherein said circular electrical current-conducting element is located recessed within said cap.

33. The apparatus of claim 32 further comprising, a charging resistor connected electrically in series with each of said plural circumferentially spaced electrical conductors, each of said charging resistors being at least partially imbedded within said cap.

34. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a generally cylindrically shaped support body having forward and rear sections disposed on opposite sides of an intermediate section, said intermediate section having a diameter substantially less than that of said forward and rear body sections to define an annular cavity tnerebetween, a frusto-conically shaped tubular rotary atomizer of insulative material having an inner surface and an outer surface extending between a rear edge and a forward atomizing edge, with the diameter of the forward edge exceeding the diameter of the rear edge, said atomizer having an axis of rotation, a circular charging electrode mounted on said inner surface encircling said axis of rotation, a circular current-conducting element mounted on said outer surface encircling said axis of rotation, a cap on the forward section of said support body, said cap having an outer face whose shape is adapted to provide a substantially laminar flow of air thereacross as said rotary atomizer rotates about said axis of rotation during normal operation, means mounted to said rotary atomizer for electrically connecting said circular electrode and said circular element, drive means for rotating said rotary atomizer about its axis of rotation, said drive means including a) an air turbine located within a cavity in said rear body support section, b) a drive shaft connected between said turbine and said rotary atomizer and extending through a bore in said forward body support section, and c) an air bearing located in a cavity in said intermediate body support section for rotatably supporting said shaft, means for supplying liquid coating to said inner surface of said rotary atomizer when said atomizer is rotating about its rotational axis, said means including a) a liquid coating valve mounted in said annular cavity proximate said forward section of said support body, and b) a liquid coating nozzle mounted on said forward body support section in proximity to said inner surface of said rotary atomizer, and c) a liquid coating conduit interconnecting said liquid coating valve and said liquid coating nozzle for transporting liquid coating to said liquid coating nozzle under control of said liquid coating valve, plural electrical conductors stationarily extending from said cap at circumferentially spaced intervals, each said conductor having a free end located in closely spaced proximity to said circular conducting element for transferring electrostatic energy thereto when said stationary electrical con-ductors are energized from a high voltage source for facilitating contact charging of liquid coating supplied to said inner surface of said rotary atomizer when said coating flows forwardly and outwardly over said inner surface in contact with said charging electrode toward said atomizing edge under centrifugal force produced by rotation of said rotary atomizer.

35. The apparatus of claim 34 wherein said cap further comprises, air flow means for establishing a generally forwardly directed flow of air, and a repulsion ring to electrostatically repel charged liquid coating material atomized by said rotary atomizer.

36. The apparatus of claim 35 wherein said air flow means comprises, at least one air passage located rearwardly of said atomizing edge, and means for supplying air under pressure to said passages.

37. The apparatus of claim 36 wherein said passages are disposed in an array surrounding said rotary atomizer to establish a corresponding array of air jets for shaping and generally forwardly projecting said spray pattern.

38. Electrostatic rotary atomizing liquid spray coating apparatus comprising:
a support body, a frusto-conically shaped tubular rotary atomizer of insulative material supported by said support body, said atomizer cup having an inner surface and an outer surface extending between a rear edge and a forward atomizing edge, with the diameter of the forward edge exceeding the diameter of the rear edge, said atomizer having an axis of rotation, means for supplying liquid coating material to said atomizer cup to form an atomized spray pattern of coating material, electrostatic charging means for imparting an electrostatic charge to said coating material, a cap included on the forward section of said support body, said cap including a generally convex outer face along at least a portion thereof, said outer face being adapted to provide a substantially laminar flow of air thereacross as said rotary atomizer rotates about said axis of rotation during normal operation, air flow means located rearward of said atomizing edge for establishing a generally forwardly directed flow of air, and a repulsion ring adapted to be energized to a polarity the same as the polarity of said electrostatic charge imparted to said coating material, whereby said outer face of said cap, said air flow means and said repulsion ring cooperate to urge said spray pattern generally forwardly of said rotary atomizer.

39. The apparatus of claim 38 wherein said cap further includes a recess, said rotary atomizer being at least partially disposed within said recess.

40. The apparatus of claim 38 wherein said air flow means comprises, at least one air passage located rearwardly of said atomizing edge, and means for supplying air under pressure to said passage.

41. The apparatus of claim 40 wherein said passages are disposed in an array surrounding said rotary atomizer to establish a corresponding array of air lets for shaping and generally forwardly projecting said spray pattern.