US3791579A

US3791579A - Electrostatic paint spray system

Info

Publication number: US3791579A
Application number: US00228585A
Authority: US
Inventors: P Cowan
Original assignee: ELECTROGASDYNAMICS
Current assignee: ELECTROGASDYNAMICS; ELECTROGASDYNAMICS INC US
Priority date: 1968-12-31
Filing date: 1972-02-23
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12

Abstract

Electrostatic air atomized paint spray system and spray device wherein power of charging air atomized spray droplets and for maintaining electrostatic depositing field is obtained from selfcontained electrogasdynamic generator operatively responsive to the flow of seeded atomizing air therethrough.

Description

United States Patent Cowan Feb. 12, 1974 1 1 ELECTROSTATIC PAINT SPRAY SYSTEM [56] References Cited [75] Inventor: Philip L. Cowan, Morrisplains, NJ. UNlTED STATES PATENTS 3,048,498 8/1962 Juvinall et al 239/15 X [73] Assgnee' glictmgasdynam'cs Hanover 3,405,291 10/1968 Brandmaier 239/15 ux 3,474,266 10/1969 Koupal 310/5 22 i 23 1972 3,417,267 12/1968 Marks 310/11 X Appl. No.: 228,585

Related U.S. Application Data Division of Ser, No. 788,148, Dec. 31, 1968, Pat. No. 3,645,447.

U.S. Cl 239/3, 239/15, 117/934 R,

118/621,310/5 Int. Cl. B05b 5/00, B050 5/02 Field of Search 117/934 R; 118/621; 239/3,

Primary ExaminerR0be rt S. Ward, Jr.

[57] ABSTRACT Electrostatic air atomized paint spray system and spray device wherein power of charging air atomized spray droplets and for maintaining electrostatic depositing field is obtained from self-contained electrogasdynamic generator operatively responsive to the flow of seeded atomizing air therethrough.

18 Claims, 18 Drawing Figures PAIE'NTEDIFEBIZIW 3.791 579 v v I sum 1 or 7 PAIENIEDFEMZW 3.791.579

SHEEI 6 BF 7 CORONA CURRENT MICROANPERES 1 ELECTROSTATIC PAINT SPRAY SYSTEM This application is a division of my copending application Ser. No. 788,l48, filed Dec. 31, l968, now US. Pat. No. 3,645,447.

This invention relates to electrostatic spray coating systems and particularly to improved electrostatic spray coating methods and spraying apparatus employing air. as an atomizing medium for the liquid coating material.

Electrostatic spray coating systems employing air atomization of the coating liquid are widely utilized in paint spraying. Spray gun apparatus conventionally employed therein is generally constituted by an insulating barrel member having a grounded handle or mount disposed at one end thereof and a selectively sized and shaped high voltage electrode extending from the other end thereof disposed adjacent to the locus of atomization and usually charged to a potential in the neighborhood of from 50 to 85 kilovolts, and in certain installations as high as 150 kilovolts, to create a corona discharge condition and a concomitant electric field of appreciable magnitude. Under such conditions, the corona discharge current flowing from the high voltage electrode creates a region adjacent to the locus of atomization rich in unipolar ions that attach themselves to and charge the paint spray droplets. Alternatively, for conductive coating materials contact charging of the spray droplets will occur in the high field strength region around the fluid orifice. The charged droplets are then displaced, under the conjoint influence of their own inertial forces, the aerodynamic forces of the atomizing air and the electrostatic field extantin the spray region, toward a grounded workpiece. In the vicinity of the spray gun, the inertia and aerodynamic forces are usually dominant but as the particles recede therefrom and approach the grounded workpiece, the forces on the charged particles due to the electrostatic field extant between the charging electrode and the workpiece become more significant and operate to selectively drive the spray particles toward the workpiece to reduce undesired and wasteful blow-by of paint.

In accord with conventional practice, maximum paint savings are generally effected by maintaining the charging voltage as high as possible and of such magnitude as to produce an average depositing field strength of at least 5,000 volts/inch, and preferably as high as 10,000 volts/inch, between the gun and the workpiece. As a concomitant thereto, the spray velocity in the vicinity of the workpiece should be of minimal magnitude consistent withthe demands of adequate atomization and paint flow. Air flow rates above about 2,000 feet/minute in the vicinity of the workpiece are likely to result in operational override by the aerodynamic forces and in increased blow-by of paint. Conventionally employed electrostatic air atomized coating systems are generally characterized by a rapid fall-off in depositing efficiency as the fluid, i.e., paint, and atomizing air flow rates are increased. Such problems are accentuated when high air flow rates are necessarily utilized to effect a required very fine atomization of the coating material or to effect the required atomization of difficult to atomize materials. The requisite charging voltages are conventionally obtained through the utilization of standard electronic high voltage power supplies which are relatively large, heavy and expensive and are so constituted as to inherently function with essentially constant voltage type characteristics. In addition thereto and because of the magnitude of the potentials involved, the high voltage cable interconnecting such power supply with the spray gun is heavy, bulky and relatively inflexible, adding undesired weight to the gun assembly which, because of the concomitant high voltage insulation requirements is rendered unduly large, complex and, in most instances not field serviceable.

The utilization of such conventional power supplies has led to the inclusion of auxiliary, large magnitude resistive elements within the gun body to provide a limiting effect upon the current output. Such resistive elements function, as disclosed in US. Pat. No. 3,048,498,

in the nature of a voltage divider to suppress the tendency for arcs to occur when the gun to workpiece distance varies and thus provides a useful safety feature, both against the hazards of fire and for the protection of the operator should he inadvertently touch the high voltage electrode. Such resistance element additionally inherently functions to effectively vary the magnitude of the potential of the charging electrode in relation with the distance between the gun and workpiece to provide a more or less constant strength of depositing field. In such systems, however, and apart from the dangers that are always inherent in the event of failure of the limiting resistors, operations are always characterized by the drawing of inordinately high ionic currents from the charging electrodes, as for example, in the order of from to 200 microamperes whereas less than 10 microamperes are needed to effectively charge the paint. Such excess current normally flows in the form of ions to nearby objects resulting in an undesired charge buildup on all such objects that are not adequately grounded. As is well known, the hazard of sparking and consequent possible fire exists when the operator or some other grounded object is brought close to such a charged and poorly grounded object. The presence of such high currents also requires that the workpieces being coated are well grounded for the reasons set forth above.

This invention may, in its broad aspects, be briefly described as an improved construction for air atomized electrostatic spray devices in which the air supply to the device is utilized for the purposes of atomizing the liquid and shaping the spray of atomized material and also for operating a self-contained electrogasdynamic power generator for charging the atomized coating material and for maintaining an electrostatic depositing field having one terminus adjacent the locus of atomization. Also in such broad aspects, the subject invention includes the provision of a' diminutive electrogasdynamic power generator disposed within an air atomizing spray device that is operatively responsive to the flow of at least a portion of the seeded air supplied to the gun therethrough and has a voltage and current output of a magnitude dependent upon the. magnitude of the delivery rate of the atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of the electrostatic field engendered thereby and is characterized by field currents that are substantially independent of the potential gradient of the depositing field. In its more narrow aspects, the subject invention includes the provision of improved air atomized spray gun constructions utilizing cartridge type electrogasdynamic power generators removably mounted in the spray gun and electrically con- 3 nectable therewithin to ionizing electrode means constituting a portion of the atomizing spray nozzle assembly and associated external shielding means for the charging electrode to negate the influences of the grounded handle or mount portions thereof and permit utilization of field strengths markedly in excess of those usually employed and at minimal current flow levels.

Among the advantages of the subject invention is the provision of a field serviceable, light weight, diminutively sized and readily manipulable air atomized spray gun construction for use in electrostatic spray coating systems that dispenses with the conventional large and bulky high voltage power supplies and associated heavy insulated cables and the like and derives its electric power from self-contained electrogasdynamic power generator means that is operably responsive to the gun air supply and functions to provide very high voltages at low current levels by direct conversion of the kinetic energy of portions of the moving atomizing air supply into electrical power. Still other advantages include the provision of an air atomized electrostatic spray gun system capable of operating at charging potentials as high as 150 kilovolts and with inherently current limited characteristics wherein high currents cannot be drawn even under short circuit conditions. Further advantages include the provision of a system wherein the kinetic energy of the air utilized for paint atomization is utilized forelectric power generation to thereby dispense with auxiliary high voltage cables and auxiliary air lines; wherein the electrogasdynamic power generating means operates efficiently over a relatively wide pressure range, as for example from 20 psig to 100 psig, with a small pressure drop so as to be fully compatible with normally available compressed air pressures and delivery rates; wherein the electrogasdynamic power generator operates essentially dry and requires only reduced quantities of conventional and inexpensive paint solvent seed materials that are compatible with the emitted atomized paint sprays and which are introduceable into the systems in a simple and inexpensive manner; wherein the magnitude of the average depositing field strength is proportionally related to the delivery rate of the atomizing air and wherein the actual output capacitance of the electrogasdynamic power supply is so low that no additional precautions need be taken, other than when highly conducting paints are being utilized, to limit the maximum spark energy drawable from the charging electrode to minimal values irrespective of the rates of approach thereof to grounded objects.

Other objects and advantages of the subject invention will become apparent from the following portions of this specification and from the appended drawings which illustrate, in accord with the mandates of the patent statutes, the principles of the invention as embod- FIG. 2A is a sectional view taken on the line 2A-2A of FIG. 2; 7

FIG. 2B is a sectional view as taken on the line 28-28 of FIG. 2;

FIG. 2C is a sectional view as taken on the line 2C2C of FIG. 2;

FIG. 3 is a front elevation of the spray gun illustrated in FIG. 2;

FIG. 4 is a vertical section of an alternative construction for an electrogasdynamic power generator cartridge;

FIG. 4A is a sectional view of certain constructional details of an alternate configuration for the transition section configuration for an electrogasdynamic power generator;

FIG. 5 is a generalized graphical representation of the current-voltage characteristics of an electrogasdynamic powered spray gun assembly constructed in accord with the principles of this invention;

FIG. 6 is a schematic representation of the test apparatus employed in obtaining the data for the plot of FIG. 5;

FIG. 7 is a generalized graphical representation of the output characteristics of an electrogasdynamically powered spray gun constructed in accord with the principles of this invention as compared with those of a commercially available electrostatic type air atomized hand gun of generally conventional construction; 7

FIG. 8 is a generalized graphical representation illustrating the magnitude of the corona currents drawable from a spray gun constructed in accord with the principles of this invention for various pressures of atomizing air;

FIG. 9 is a schematic representation of the test apparatus employed in obtaining the data for the plot of FIG. 8;

FIG. 10 is a sectional view illustrating the incorporation of a shielding electrode in the atomizing nozzlecharging electrode assembly;

FIG. 11 is a generalized graphical representation showing the effects of inclusion of a shielding electrode in the atomizing nozzle-charging electrode assembly on the strength of the electrostatic depositing field;

FIG. 12 is a schematic representation of the test apparatus. employed in obtaining the data for the plot if FIG. 1 1;

FIG. 13A is a vertical section illustrating a presently preferred configuration fora charging electrode;

FIG. 13B is a section taken on the line 13B-l3B of FIG. 13A.

Referring to the drawings and initially to FIG. 1, there is generally illustrated the components of handmanipulable type of air atomized electrostatic paint spraying system embodying the principles of this inven tion. As there shown, such system conventionally includes a compressed air supply hose l0 connectable to a remote source of compressed air (not shown) suitably of a pressure of about 20 psig or greater and capable of supplying the requisite flow rates, that serves to conjointly supply fluid paint delivery pressure through a T-type fitting 12 and associated regulator and gaugeassembly 14 to a paint supply pot l6 and to supply the necessary air alternately utilizable for atomization and electric power generation through line 18 to a vapor seed pot assembly 26. The line 18 is desirably provided with an independent regulator and gauge assembly, generally designated 20, to provide discrete and independent operational control over the pressure and the flow rate of the air conveyed to the air atomized paint spraying device, generally designated 28 and suitably constituting a hand manipulable air atomized spray gun, as hereinafter described. The paint supply pot 16, which is also of conventional character, is desirably supported on an insulating stand 22 and fluid paint is conveyed therefrom to the insulated barrel portion of the spray gun 28 through an insulated paint supply hose 24 so as to insure when conducting paints are being utilized against possible shorting of the voltage carrying spray gun components to ground through the above described components of the paint supply system.

As noted above, a common supply of air is introduced into the vapor seed pot assembly 26 wherein small quantities of seed material, here suitably an inexpensive and conventionally employed paint solvent of a character compatible with the fluid paint being employed, is selectively introduced thereinto in the form of vapor. Upon exiting from the vapor seed pot assembly the now seeded air is transported via the single supply hose 30 to the air atomized spray device 28 for utilization therein for the conjoint purposes of effecting atomization of the liquid coating material, shaping of the spray of atomized material if desired and for the generation of electric power for effecting electrostatic deposition of the atomized liquid. For the purposes of this application, the seeded air conveyed via the common supply line 30 from the locus of seed material introduction to the spray device will be hereinafter termed as the seeded atomizing air irrespective of the particular utilization or disposition thereof that is made or effected after its introduction into the spray device. As will become more apparent from what hereinafter fol lows, some or all of said seeded atomizing air" is, in accord with the principles of this invention, passed through the electrogasdynamic power generator to generate the power required for electrostatic deposition of the atomized material in addition to being uti lized for effecting atomization of the liquid coating material either by direct interaction therewith or indi rectly by powering a mechanical device such as a high speed turbine that drives an atomizing device as well as being utilizable as fan air emittable from orifices adjacent the locus of atomization for the purposes of shaping the spray of atomized liquid coating material.

The compressed air supply hose 10, the paint supply hose 24 and the atomizing air supply hose 18 are suitably constructed of electrically insulating material, as

7 generally designated 44 and which may comprise a conveyor device or the like to sequentially present successive articles to be coated in predetermined spaced relation with the path of the emitted spray 46 from the spray device 28. i

As will be apparent to those skilled in this art the air atomized spray device 28 may be of varying character in which the seeded atomizing air may directly of indirectly effect atomization as pointed out above. As schematically illustrated in FIG. 1, the spray gun device 28 may suitably comprise a hand manipulable unit in the nature of a spray gun having a generally cylindrical barrel portion 34 with a'conducting pistol grip type handle portion 32 mounted at one end thereof and an atomizing nozzle-charging electrode assembly, generally des- .ignated 36, disposed at the other end thereof. Although one specific construction will be hereinafter described in detail, the spray gun 28 may broadly include other conventional fluid paint delivery systems and atomizing nozzle assemblies in conjunction with a self-contained cartridge type electrogasdynamic power generating device disposed in the flow path of at least a portion of the seeded atomizing air and having its excitation voltage supplied from a remote source 38 thereof via a lead 40, suitably comprising an unshielded conductor wire fastenecl directly to or contained within the seeded atomizing air supply line 30.

As clearly delineated in FIG. l, a spray gun 28 constructed in accordance with the principles of this invention differs in one aspect from those conventionally employed in air atomized electrostatic spray coating systems in that it has connected thereto only the paint supply line 24, the seeded atomizing air supply line 30 and, as noted earlier, a lightweight unshielded wire 46 for the electrogasdynamic power generator excitation voltage and which may be conveniently fastened to or disposed withinthe seeded atomizing air supply line 30. The subject construction thus completely dispenses with the heretofore required large and heavy floor supported power supply unit and the associated heavy and relatively inflexible insulated cable inherently required to transmit the charging potentials from the power supply to the spray gun.

By way of specific example, FIG. 2 illustrates the constructional details of an electrostatic air atomized type of spray gun that incorporates the principles of this invention and constitutes a presently preferred embodiment thereof. As previously noted the subject gun includes, in its broad aspects, a selectively configured insulating barrel portion 34 having a pistol grip type of conducting handle portion 32 mounted at one end thereof and an atomizing and charging assembly, generally designated 36, disposed at the other end thereof. included therewithin and located in the lower portion of the barrel 34 is a fluid paint delivery system, generally designated 46, a seeded atomizing air conveying system extending through the handle and barrel portions; an electrogasdynamic power generator, generally designated 50 and operably responsive to the flow of seeded atomizing air therethrough, disposed within the insulating barrel member 34 together with provision for introducing the necessary excitation voltages thereto through the handle member 32; and an atomizing nozzle and charging electrode assembly, generally designated 36, mounted at the terminal end of the barrel 34 wherein atomization of the fluid paint by the direct interaction with the seeded atomizing air and charging of the atomized spray particles is effected.

in order to desirably reduce the number of connecting conduits to two and thereby markedly add to the ease of manipulation of the subject gun, the seeded at-.

omizing air and the electrogasdynamic power generator excitation voltages are conjointly supplied to the gun via a composite conduit and specialized entry fitting and connector unit. More specifically the external exciter voltage supply lead 40., suitably in the form of an insulated wire, is disposed within the seeded atomizing air supply line 30 which carries seeded atomizing air, suitably under pressures in the range of from 20 to 75 psig or even higher. The composite seeded atomizing air-excitation voltage supply conduit terminates in a selectively shaped connector assembly generally designated 56 that is removably insertable through an aperture in the base of the handle 32 into a bore 58 longitudinally disposed therein. Disposed within the upper reaches of the bore 58 is an elongate insulating sleeve 60 surrounding a spring biased electrical contact receptacle type assembly comprising a displaceable receptacle type contact member 62 connected to one end of an internally disposed insulated excitation voltage lead 66 that leads to the electrogasdynamic voltage generator 50 as will be described in detail hereinafter. Biasing of the contact member 62 is effected by the spring member 64 having its remote end fixedly positioned by the insulating plug 65. The connector assembly 56 generally comprises a selectively shaped elongate sleeve assembly 68 incorporating a plurality of atomizing air escape apertures 70 adjacent its mid-length and upwardly terminating in a guide portion 72 sized and shaped to co-axially position the extending end portion 74 of the insulated electrogasdynamic power generator excitation lead 40. Said end portion 74 of the lead 40 is encased in a rigid insulating sleeve 75 that is sized to be removably contained within the sleeve 60 and dependently terminating in an electrical contact element 76 that is adapted to be disposed in firm electrical contact with the spring biased receptacle type contact member 62 when the connector assembly 56 is properly located within the bore 58. Suitable O-

ring seals

78 and 80 are disposed in the walls of the sleeve member 68 on either side of the seeded atomizing air escape apertures 70 for disposition in sealing relation'with the walls of the bore 58 to prevent leakage of the compressed seeded atomizing air therepast and to direct such seeded atomizing air through aperture 84 into bore 90.

As will be now apparent, insertion of the connector 56 into the bore 58 serves to automatically effect proper interconnection of the gun to both the requisite supply of seeded atomizing air and to the requisite source of excitation voltage for the electrogasdynamic power generator. The desired proper positioning of the connector within the bore is maintained by the set screw 82.

When the connector assembly 56 is properly positioned as described above, the seeded atomizing air escape apertures 70 are disposed in gaseous communication through the aperture 84 with an elongate bore 90 that longitudinally traverses the handle portion 32 and is adapted to be closed at its dependent end by a threaded plug member 92. The upper end of the seeded atomizing air transmitting bore is disposed in fluid communication with a transverse bore generally designated 94, adapted to contain a valve assembly responsive to manual actuation of a trigger member 96 to control the admission of seeded atomizing air into the electrogasdynamic power generator and its ultimate transmission to the locus of atomization. Suitably included in the valve assembly is a valve body member 98 having a base portion fixedly mounted in the open end of the bore 94 and an extension 106 shaped to provide an annular seat 104 anda plurality of apertures 110 disposed adjacent thereto in gaseous communication with the bore 112. Associated therewith is displaceable valve plug member 100 that is normally biased, as by the spring 102, into hermetically sealed relation with the valve seat. Displacement of the valve plug member 100 is effected by the push rod 108 that extends through the valve body member and associated plug and packing 88 and is longitudinally displaceable in response to rotative displacement of the trigger 96. Thus, rotative displacement of the trigger 96 in the clockwise direction as illustrated in FIG. 2 effects a rearward displacement of the push rod 108 against the action of the biasing spring 102 and lifts valve plug out of sealing engagement with the seal 104. Such lifting of the plug 100 off of the seat 104 permits a flow of seeded atomizing air from the bore 90 through the aperture 1 10 and into the bore 112. The bore 112 is disposed in gaseous communication with the entry portion 114 of the electrogasdynamic power generator 50 and thus serves to effect the introduction of seeded atomizing air therein.

As will be apparent from the foregoing, the above described structure operates to introduce both the seeded aotomizing air and the excitation voltage to the electrogasdynamic power generator 50. Preparatory however to describing the structure andoperation of the electrogasdynamic power generator 50 and the remainder of the seeded atomizing air conduit system, clarity and brevity will be served. by digressing and describing the nature of the fluid paint delivery system components included in the subject gun.

The fluid paint delivery components of the illustrated spray gun serve to effect-the controlled delivery of a flow of liquid coating material to the locus of atomization and are essentially of conventional character. The liquid coating material is adapted to be introduced into the gun from the paint supply line 24 through a suitable fitting 122 disposed on the underside of the barrel portion 34. The fitting 122 is in fluid communication with a short bore 126 which in turn communicates with an elongate bore 128 running longitudinally of the barrel 34. Mounted at one end of the bore 128 is a fluid tip nozzle member 130 having a conically shaped end portion terminating in a short cylindrical section that defines a liquid paint emitting aperture. As best shown in FIG. 2 the fluid tip nozzle member is formed of electrically conducting material and includes an extending flange portion 131 disposed in abutting engagement with the front end 163 of the barrel member 34. Disposed in coaxial alignment with the liquid paint emitting aperture defined by the cylindrical section 120 and adapted to control the effective cross-sectional area thereof is a displaceable needle valve member 132. The needle valve member 132 is mounted at one end of an elongatefluid flow control shaft member 134 having a bellows type sealing assembly 136 disposed in encircling relation about the portion thereof disposed within the front or forward section of the bore 128 to limit the disposition of liquid paint under pressure to said front section of the bore 128. The fluid flow control shaft 134 extends rearwardly through a reduced intermediate section 144 of the bore 128 and into a rear enlarged section 146 thereof. The rear end of the fluid flow control shaft 134 is supported in an insulated coupling member 138 sized to be closely contained within the bore 146. The coupling member 138 is in turn connected to a shaft included as a part of a spring biased and trigger displaceable actuating assembly generally designated 140. Such assembly includes a sleeve type adjusting stop screw 142 disposed about a biasing spring 148 for limiting the degree of displacement of shaft 135 and for controlling the amount of biasing force applied by such spring to the shaft 135 to maintain the fluid flow needle member 132 in sealing engagement with the fluid emitting aperture in the fluid tip nozzle member 130. In operation of the above described structure, displacement of the trigger 96 in a clockwise direction effects a rearward displacement of the shaft 135, coupling member 138 and fluid flow control. shaft 134 against the opposition of the biasing spring 148. Such retraction of the shaft 134 removes the needle valve member 132 from sealing relation within the fluid emitting aperture to permit the emis sion of a stream of liquid paint therefrom.

The upper portion of the insulating barrel 34 contains a relatively large elongate bore 156 which is adapted to removably receive an electrogasdynamic power generator assembly, generally designated 50, in which the electric power necessary to charge the atomized paint spray particles and to create the electrostatic depositing field is derived from the direct conversion of the kinetic energy of the moving stream of seeded atomizing air. In the illustrated unit, the seeded atomizing air under pressure is introduced, in response to actuation of the trigger 96, through the bore 112 into an annularly shaped entry section 114 of the electrogasdynamic power generator which is of relatively large cross-sectional area so as to produce a relatively low flow velocity and minimal pressure drop therewithin. Disposed within the entry section 114 is the extending portion of an insulated mounting sleeve assembly 190 which serves to coaxially position an elongate ionizer needle electrode 124 relative to a surrounding converging transition section 192 and an annular attractor electrode 194. Such sleeve assembly 190 also serves to provide a receiving support for the end of the excitation supply voltage lead 66 which, in the illustrated embodiment, is connected to the said ionizer needle electrode 124. The ionizer electrode needle 124 extends axially downstream within the transition section 192 to the attractor electrode ring 194 which operatively effects a marked decrease in the cross-sectional flow area for the moving seeded atomizing air stream and serves to increase the speed thereof as it approaches the attractor ring. After passage through the attractor ring electrode 194, the atomizing air stream passes through an elongate channel 158 of relatively small, and preferably slightly increasing in the direction of flow, crosssectional area suitably sized so that, within which and under the pressure conditions extant, the flow velocity of the seeded atomizing air will be markedly higher than that extant in the entry section 114 and which, for good performance, should preferably be in the vicinity of the sonic velocity. After exiting from the channel 158 the seeded atomizing air stream impinges against the adjacent axially disposed collector needle electrode 198 mounted in a plug 196 and expands into the bore l56.and flows therewithin at reduced velocities toward the exit conduit 160 therefrom. As shown, the collector electrode 198 is directly connected, as by a conducting metallic lead 200, to the fluid tip nozzle member 130 which latter serves as the charging electrode.

As best shown in FIGS. 2b and 2c the exit conduit 160 is disposed in gaseous communication with a discrete atomizing air transfer conduit 162 and a discrete fan air transfer conduit 164 running longitudinally of a barrel portion 34 and terminating at the forward end 163 thereof. The atomizing air and

fan air conduits

162 and 164 respectively are of reduced cross-sectional area and are selectively sized so as to permit delivery of the seeded atomizing air at the rates requisite to effect desired atomization under the range of ambient pressures available within the gun. Associated with the exit conduit is a screw type plug member 166 that is effectively longitudinally displaceable in response to rotative displacement thereof into selective overlying or closing relation with the end of the fan air transfer conduit 164 to thereby permit manual control of the amount of the seeded atomizing air stream diverted into the fan air transfer conduit 164. As will now be apparent, the atomizing air transfer conduit 162 and the fan air transfer conduit 164 terminate at'spaced locations on the front end of the barrel portion 34 of the gun radially outward of the flange portion 131 of the fluid tip nozzle member 130 disposed in overlying relation therewith and removably secured in desired position by a threaded retaining ring 172 is a selectively configured air cap member formed of insulating material. As is conventional, the air cap 170 is shaped to provide a first set of internal conduits, generally designated 174, disposed in fluid communication with the end of the fan air transfer conduit 164 atv the end 63 of the barrel portion of the gun and having the other ends thereof selectively terminating at one or more predesired locations downstream of the fluid tip nozzle member 1130 and with a positional location and angular disposition that serves to selectively direct the emission of jets of fan air to modify the shape of the spray of atomized material. In addition thereto the surface of the air cap 170 disposed in abutting facing relation with the end portion 163 of the barrel is contoured to provide for the transfer of atomizing air emanating from the transfer conduit 162 to one or more apertures disposed in surrounding relation to the extending cylindrical section of the fluid tip nozzle 130 to effect, by direct interaction, atomization of the liquid paint stream being emitted therefrom.

In operation of the described unit, application of excitation voltage, suitably in the order of 5,000 volts, to

the ionizer needle electrode 124 will initiate a corona discharge condition and cause a corona current to flow in the gap between the point .of the ionizer needle electrode 124 and the adjacent ring electrode 194. Concurrently therewith, the seeded atomizing air moving through the gun in the path described above will travel from the bore 112 and entry section 114 into the converging inlet or transition section 192 and the attractor electrode ring-194 and through the corona discharge area with progressively increasing velocity. Under corona discharge conditions as described above, the passage of the seeded atomizing air therepast at progressively increasing speeds with result in condensation of at least a portion of the seed vapor therein in the form of extremely small particles or droplets around the unipolar ions present in the .corona discharge area. The ions in the region where the seed material condenses are thereby degraded in mobility, become fixed or nearly so in the stream of moving atomizing air and are swept out of the corona discharge area, past the attractor ring electrode 194 and down the elongate insulating channel 158 at high velocity, as for example at speeds in the vicinity of the sonic velocity. The ions in the moving gas stream will then be collected at the collector electrode 198 and will raise the potential thereof to extremely high values, which such potential being applied by the conductor 200 to the fluid tip nozzle member 130.

As will now be apparent, in operation of the described device, clockwisedisplacement of the trigger 96 will conjointly effect emission of liquid paint through the aperture defined by the cylindrical nozzle portion 120 of the fluid tip nozzle member 131) and a flow of seeded atomizing air through the bore 90, the electrogasdynamic power generator 50, the atomizing air and fan

air transfer conduits

162 and 164 respectively and through the various conduits of air cap 170 to effect atomization of the emitted liquid paint and to selectively shape the spray patterns of the atomized fluid. As noted above, the passage of the stream of seeded atomizing air through the electrogasdynamic power generator 50 results in the generation of high d.c. voltages at. the collector electrode 198 and in the direct application thereof, through conductor 200, to the fluid tip nozzle member 130, which thereby per forms the dual function of serving as the charging electrode for the electrostatic deposition system. The application of such potentials to the fluid tip nozzle member 130 will create a corona discharge condition adjacent the terminus thereof and an area rich in unipolar ions closely adjacent to the locus of atomization, which ions attach themselves to the atomized paint particles and selectively charge the same. Under such conditions the fluid tip nozzle member 130, which charged in the manner described, will also serve as one terminus of an electrostatic depositing field with the other terminus thereof being constituted by the grounded object to be coated.

As pointed out earlier, the utilization of a selfcontained electrogasdynamic power generator as the source of the necessary high potential not only eliminates the heretofore required large and bulky floor supported high voltage power supplies and associated heavy and inflexible cables necessary to the transmittal of such high voltages to the charging electrode on the gun, but also provides advantageous operating characteristics that where heretofore unobtainable with conventional equipment. An understanding and appreciation of such advantageous operating characteristics requires a more detailed disclosure of the nature of the electrogasdynamic power generators and particularly of an improved character of generator that is preferably utilized herein.

ln electrogasdynamic power generators of the general type described, the initiation of the requisite corona discharge at the entrance to channel 158 requires the application of only relatively low excitation voltages, as for example in theorder of 5,000 volts, in order to effect the generation of very high voltage at the collector electrode 198. The load current and voltage can be much higher than that of the excitation supply, since the electrical power generated is derived from the kinetic energy of the moving gas stream which does the necessary work in driving the ions along the channel 158 from the attractor ring electrode 194 to the collector electrode 198 against the opposing electrical field. It should be noted that although convenience has here dictated application of the excitation voltage to the ionizer needle 124 and having the attractor ring electrode 194 grounded, such can be readily reversed and operations effected with a grounded needle electrode and a charged attractor electrode with the necessary construct-ional modification relative to insulation and the like. In the electrogasdynamic power generator, the maximum output voltage thereof is essentially determined by the voltage at which electric breakdown will occur between the collector electrode and ground, and in the unit shown in FIG. 2 such breakdown will most likely occur between the collector and attractor electrodes along the walls of the channel 158. As such, the length of the insulating channel 158 employed provides a convenient control of the magnitude of the maximum voltage obtainable from the system and different generator cartridges can be made available in accord with the exigencies of the desired use thereof.

FIG. 4 illustrates certain improvements in construction of an electrogasdynamic power generator which provides, in a diminutive size unit adapted for cartridge type utilization and employing velocities in the vicinity of the sonic velocity in the generator channel, high performance characteristics over a wide range of operating pressures and mass flow rates. As previously described in conjunction with FIG. 2, the subject generator includes an ionizer needle 124 coaxially disposed relative to the axis of the channel 158 formed by the insulating sleeve 212 by a mounting member and sized to extend through a converging inlet or transition section to the attractor ring electrode 194 as defined by the conically bored insulating member 192. Preferably all such units are-preassembled and permanently secured in desired position so as to facilitate unit replacement of the generator assembly when desired, thus making the spray gun readily field serviceable in the event of failure or deterioration. In this illustrated embodiment, the excitation voltage is connected to the attractor ring electrode 194 as an alternative to the previously described construction and the needle electrode 124 is operated at ground potential. With proper design almost all of the current flowing from the ionizer needle 124 can be caused to move with the atomizing air downstream to the collector electrode 198 which operates to effectively minimize the excitation power re quired since under such condition the current flowing in the excitation circuit approaches zero in value. As noted earlier, the subject electrogasdynamic power generator is proportioned so that the flow of atomizing air in the elongate channel 158 is near sonic in character which provides high performance at low pressure drops of a magnitude that are essentially compatible with commercially available compressor delivery characteristics. In addition thereto, the portions of the generator disposed immediately adjacent to the attractor ring electrode 194 are selectively shaped to provide one or more relatively sharp edged surface discontinuities in the walls' defining the atomizing air flow path. One suitable means for introducing such a surface discontinuity is to make the diameter of the downstream end of the converging inlet section 192 appreciably larger than the diameter of the attractor ring electrode 194 to effectively provide an annular shoulder extending at right angles to the longitudinal axis of the flow path. A second means isto incorporate an annular recess 220 intermediate the attractor ring electrode 194 and the downstream end of the transition member 192. A third means is to incorporate a second annular recess 216 intermediate the attractor ring electrode 194 and the channel 158 which is of a transverse diameter effectively greater than the air passage defined by the ring and channel. A fourth means is to make the internal diameter of the channel 158 slightly larger than the diameter of the attractor ring electrode 194. Additionally the channel 158 diverges slightly in cross-sectional extent in the direction of air flow to insure maintenance of near sonic velocities in the vicinity of the attractor electrode 194.

All of the above means are desirably incorporated in the generator disclosed in FIG. 2. While the reasons for the improved performance obtained by the incorporation of such type of structure is not clearly understood, it is believed that the discontinuities in the defining walls of the system function to introduce a high degree of turbulence into the flow through the attractor ring electrode 194 and the channel 158 and serves to minimize, if not prevent, 'build up of a relatively slow moving gas layer along the wall portions within the attractor ring electrode 194 and within the channel 158.

FIG. 4A illustrates an alternative means whereby surface discontinuities may be introduced into the defining walls of the generator adjacent the attractor ring electrode 194. In this embodiment, the converging inlet or transition section 192 is shaped to provide a series of steps or shoulders facing the flow of seeded air that serve to introduce a plurality of sharp-edged surface discontinuities therein.

By way of specific example, markedly improved performance has been obtained with a spray gun incorporating an electrogasdynamic power generator of the type illustrated in FIGS. 2 and 4 having the following dimensions and operating with an air flow velocity in the vicinity of the sonic velocity in the channel 158 under the following operating parameters:

Atomizing Air delivery pressures of from20 100 psig Attractor ring electrode (194)0.ll6 inch ID by .177 inch long Converging or transition section (l92)0.260 inch ID at entry 0.l50 inch Id at exit and 0.4l inch long Recess (220).035 inch deep by .300 inch diameter Recess (216)0.320 inch diameter by 0.060 inch deep Channel (158)-.l20 inch ID by 3.0 inches long with .008 inch/inch divergence In general the materials of construction do not appear to be of prime importance although the insulating portion thereof, i.e., the transition section 192 and the channel 158 and'amounting member 190 (when the ionizer needle is subjected to the excitation voltage) should be formed of insulating material of high dielectric strength.

Such a generator configuration provides high voltage performance over a wide pressure range and readily delivers a current of up to about 60 microamperes. The approximate current-voltage relationship for such a generator has been determined experimentally using a spark gap as a load by means of the apparatus illustrated in FIG. 6. As there shown, the fluid tip nozzle 130 of a spray gun generally designated 28 having a self-contained electrogasdynamic power generator as described above incorporated therein was placed in close physical proximity with an isolated 3 inch diameter sphere 230 having a grounded 3 inch diameter sphere 230 having a grounded 3 inch diameter sphere 232 disposed in contact therewith. The grounded sphere 232 was then slowly moved away from the sphere 230. As the two spheres are separated a spark forms in the gap therebetween and a meter 234 in the line connecting the sphere 232 to ground measures the current flowing across the gap. A capacitor 236 is desirably connected in parallel with the meter to smooth out the current surges and to prevent damage to the meter movement. Thus by measuring the magnitude of the current as a function of the spark gap length an approximate voItage-current curve as illustrated in FIG. 5 was obtained for the subject generator. As reference thereto clearly shows, the current, which is quite small even at maximum value, drops off relatively slowly with increasing voltage, as the latter is measured by the spark gap spacing. FIG. 7 serves to compare the output characteristics of a spray gun incorporating the above described electrogasdynamic power generator means with the output characteristics of an air'atomized electrostatic type handgun manufactured by the Eclipse Equipment Company of Fairfield, New Jersey, utilizing a conventional kilovolt electronic power supply and incorporating a limiting resistor as taught by U.S. Pat. No. 3,048,498.

As is readily apparent from FIG. 7, the short circuit current of the hand gun constructed in accord with the principles of this invention is markedly lower than the short circuit current for the conventionally employed unit and, the open circuit voltage (as again measured by spark gap spacing is markedly higher for the device of this invention than that for the conventionally employed unit. FIG. 7 also clearly shows that the incorporation of an electrogasdynamic power generator operatively responsive to the flow of seeded atomizing air functions as an essentially constant current" type of power source in direct contradistinction to the essentially constant voltage typ'e characteristics inherent in the conventionally employed electronic power supplies in association with a series connected limiting resistor in the order of several megohms per kilovolt in the output thereof. Thus in the practice of this invention, the output current is limited by the inherent characteristics of the electrogasdynamic power generator and the actual output capacitance thereof is also so low that no additional specialized precautions or constructions need be taken to limit the maximum spark energy drawable from the charging electrode as the gun is brought close'to a grounded object and irrespective of the rate of approach thereof as are characteristically required in conventional constructions.

One of the highly advantageous operating characteristics of spray devices incorporating the principles of this invention is the provision of a voltage and current output of the self-contained electrogasdynamic power generator having a magnitude that varies in accord with the rate of flow of seeded atomizing air which functions to minimize the drop-off in depositing efficiency characteristic in conventional systems as the liquid paint and air flow rates are increased. Thus in the spray gun devices of this invention, an increase in the rate of flow of the seeded atomizing air effects an increased flow through the generator and production of increased current and voltage output therefrom and a corresponding increase in the magnitude of the average depositing field strength of the electrostatic field engendered thereby. FIG. 8 graphically demonstrates the variation in measured corona currents at various gap spacings for various rates of flow of seeded atomizing air as evidenced by data obtained from the test arrangement illustrated in FIG. 9. As shown in FIG. 9, the fluid tip nozzle member of a hand gun of the type illustrated and described herein is placed in close proximity with an insulated 6 inch diametersphere 254 and the corona currents delivered to a grounded probe 256, specifically a square cut brass roa of .048 inch diameter, over a gap of known geometry was measured by a suitable meter 258. As clearly shown in FIG. 8, the device of the subject invention provides increasing outputs, as evidenced by the increased corona currents at all spacings as the supply pressure of the seeded atomizing air stream is increased. FIG. 8 also shows, by curve at 260, the current drawn from the Eclipse air atomized electrostatic type spray gun referred to earlier under similar test conditions. Such current is markedly higher at the smaller gap spacings but drops appreciably below that of the device of this invention at higher gap spacings, thus confirming the higher voltage capabilities of the subject construction.

It should be here noted that while the presently preferred construction illustrated in FIG. 2 and described above passes all of the seeded atomizing air through the electrogasdynamic power generator, practice of the invention also includes utilization, of portions of such seeded atomizing air for power generation purposes. Thus the stream of seeded atomizing air may be preliminarily subdivided into atomizing and fan air streams and the electrogasdynamic power generator selectively disposed in either of said streams. Likewise operation can be effected by preliminarily diverting a portion of the seeded atomizing air through an electrogasdynamic power generator that exhausts into the atmosphere at a location remote from the locus of atomization, as for example, to create a forwardly moving sheath of air over the gun barrel to prevent or minimize wrap-back of slowly moving charged particles to the handle.

In each of these instances however the power output of the generator will have a magnitude dependent upon the delivery rate of the incoming seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of an electrostatic field engendered thereby and will provide the other desirable characteristics described above.

In addition to the foregoing advantageous characteristics, practice of the subject invention also effectively dispenses with the need for any counter electrode" function oftentimes conventionally employed for the purpose of maintaining higher. field strengths in the region of the paint charging electrode with lower charging potentials and particularly when the charging electrode is spaced at a relatively large distance from the workpiece. While the functioning of such counter electrode systems may have some degree of utility in hand guns powered by conventional electronic power supplies and wherein the maximum practicably useable voltages are not much in excess of 60 kilovolts, its utilization in the electrogasdynamically powered handgun of the subject invention with its higher voltage capability and lower current capacity is distinctly disadvantageous. Such counter electrode may be constituted by a grounded handle for the spray gun and since the subject spray gun described above desirably includes a grounded handle for the purpose of protection of the operator, charging electrode shielding means are desirably included to minimize, if not negate, the possible deleterious effects of the presence thereof. It has been found that the utilization of such a shield electrode permits operation of a compact electrogasdynamically powered hand or automatic gun incorporating the principles of this invention at voltages that are appreciably higher than those conventionally employed. FIG. 10 (and also FIGS. 13 and 13b) schematically illustrates the incorporation of such a shield electrode to the atomizing nozzle-charging electrode assembly of the spray gun of FIG. 2. As there shown, the shield electrode suitably comprises an annular ring of conducting material 240 mounted on the surface of the air cap 170 surrounding the cylindrically shaped terminal portion of the fluid tip nozzle member serving as the charging electrode. Such shield electrode 240 is electrically floating, in that it is neither connected electrically to the charging electrode or to ground, and will thereby collect current from the charging electrode when the latter is at high potential and rise to a potential that is slightly below that of the charging electrode. As the shield electrode rises in potential it tends to extinguish the corona discharge around the charging electrode, but since the system herein disclosed is essentially possessed of constant-current characteristics, the shielding electrode acts to cause the voltage on the charging electrode to increase to maintain the same current flow.

The influence of the shielding electrode on the strength of the depositing field between the gun and the workpiece can be readily observed from FIG. 11. FIG. 11 presents measured values of depositing field strengths at various gun-target spacings as determined by an electrostatic field meter 242 (manufactured by Munroe Electronics Co. of Middleport, New York) connected intermediate a probe 244 and ground and a spray gun 246 constructed in accord with the principles of this invention and of the type described above. The two curves shown on FIG. 11 clearly show the marked increase in operating voltage and hence field strength when a shield electrode is employed. Variations in size shape and location of the shield electrode may be made to effect even greater increases in the strength of the depositing field. In general, the configuration of such electrode is largely determined by the configuration of the charging electrode and by the geometry of the system adjacent to the locus of atomization with limitation thereof being dictated by practical considerations such as avoidance of interference with the flow of fan or atomizing air or with the emitted spray pattern.

As described in detail at an earlier pointin this specification the fluid tip nozzle member 130 and particu-' larly the cylindrically shaped terminal sleeve portion 120 constituting the paint emitting aperture therein serves as the charging electrode. Other configurations of charging electrodes well known in the art as, for example, elongate needle members or the like, may be employed. As well as the direct application of the output of the electrogasdynami c power generator to the liquid paint prior to its discharge through a nozzle member. A particularly simple and effective electrode configuration for providing a high charge to the atomized spray particles and which at the same time provides the proper loading for the electrogasdynamic power generator is shown in FIGS. 13A and 133. As there shown the dependent end of the sleeve portion 120 of the fluid tip nozzle member 130 is sharpened into a V configuration to provide a plurality of relatively sharp edged surface discontinuities 250 at the terminal portion thereof. A shielding electrode 240 is 17 again disposed in encircling relationship around the charging electrode.

While I have shown and described certain presently preferred embodiments incorporating the principle of my invention, it should be understood that the same is capable of modification. Changes, therefore, in both constructions may be made without departure from the spirit and scope of the invention as disclosed in the appended claims.

I claim: 1. In an electrostatic spray coating system wherein high velocity atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state,

means for selectively introducing such material into a stream of pressurized atomizing air, and

an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization and operatively responsive to at least a portion of the fiow of said seeded atomizing air therethrough at a velocity in the vicinity of the sonic velocity and having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby. 2. In an electrostatic spray coating system wherein high velocity atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state,

means for selectively introducing seed material into a stream of pressurized atomizing air, and

an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization and operatively responsive to at least a portion of the flow of said seeded atomizing air therethrough having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby,

said electrogasdynamic power generating means comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto, ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on the downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

3. The combination as set forth in claim 2 wherein said converging conduit section is constituted by a plurality of coaxial bores of progressively decreasing internal diameter in the direction of air flow therethrough thereby presenting a plurality of annular shoulders in substantially perpendicular relation to the approaching air flow.

4. In an air atomized electrostatic spray coating device wherein a high velocity stream of seeded atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state,

an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization therein and operatively responsive to the flow of at least a portion of said stream of seeded atomizing air therethrough having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said first air stream to effect proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby;

said electrogasdynamic power generating means comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto,,ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on the downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

5. The combination as set forth in claim 2 wherein said ionizing electrode means and attractor electrode means are selectively electrically connected intermediate an excitation potential and ground.

6. In an electrostatic spray coating gun wherein an emitted spray of atomized liquid coating material is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state,

an insulating body member containing a cartridge receiving bore and having liquid coating material atomizing means disposed at one end thereof and a groundable conducting base member disposed at the other end thereof,

an electrogasdynamic power generating cartridge member removably disposed within said cartridge receiving bore and operatively responsive to the flow of a stream of seeded airtherethrough and having a voltage and current output of a magnitude dependent upon the volumetric magnitude of said seeded air stream therethrough to effect proportional variations 'in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby,

said electrogasdynamic power generating: cartridge member comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto, ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on the downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

7. The combination as set forth in claim 6 wherein said ionizing electrode means and attractor electrode means are selectively electrically connected intermediate an excitation potential and ground.

8. The combination as set forth in claim 6 wherein said cartridge member includes a conducting sleeve member for mounting said ionizing electrode means in predetermined spatial relation with said attractor electrode means and for electrically connecting the latter with the groundable conducting base member of said gun when said cartridge is operatively disposed in said cartridge receiving bore.

9. The combination as set forth in claim 6 including a collector electrode element mounted in said body member and extending into said cartridge receiving bore in coaxial spaced relation with the end of said elongate channel member disposable therein.

10. The combination as set forth in claim 9 wherein said cartridge member includes a mounting sleeve adjacent said conduit section thereof threadedly engageable with a complemental coaxial bore surface in said groundable base member for fixedly locating said cartridge member in said cartridge receiving bore with said elongate channel member disposed in predetermined spaced relation with said collector electrode element.

11. The combination as set forth in claim 8 wherein said conducting sleeve member is threadedly engageable with a complemental coaxial bore surface in said groundable conducting base member for fixedly locating said cartridge member within said cartridge receiving bore in said body member,

12. The combination as set forth in claim 6 wherein said seeded air is introduced into said electrogasdynamic power generating cartridge member from a remotely located pressurized supply thereof through a hose means connected to said groundable base member and wherein said base member is connectable to ground through conducting means associated with said hose member.

13. The combination as set forth in claim 9 wherein said cartridge receiving bore is of greater internal diameter than the external diameter of the elongate channel section of the electrogasdynamic power generating cartridge member disposed therewithin for providing an annulus for an exiting flow of seeded air moving countercurrent to the flow through said cartridge member and in a direction away from said collector electrode element and toward said groundable base member. I

14. The combination as set forth in claim 13 including valve means for directing the exiting flow of said air disposed remote from said collector electrode means and in close proximity to said groundable base member.

15. The combination as set forth in claim 6 wherein said seeded air, the excitation potential for maintaining a corona current flow intermediate said ionizing electrode means and said attractor electrode means, and a conductor for connecting said base member to ground are associated with a common conduit member connectable to said base member.

16. In an electrostatic spray coating gun wherein an emitted spray of atomized liquid coating material is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state,

an electrogasdynamic power generating cartridge member removably disposed within said cartridge receiving bore and operatively responsive to the flow of a stream of seeded air therethrough and having a voltage and current output of a magnitude dependent upon the volumetric magnitude of said seeded air stream therethrough to effect proportional variations in the magnitude of the average depositing field strengthof an electrostatic depositing field engendered thereby,

a liquid coating material delivering bore disposed within said body member in fluid communication with said atomizing means disposed at the end thereof, an externally actuatable valve stem assembly displaceably mounted within said liquid delivering bore for regulating the flow of liquid therethrough to said atomizing means, said valve stem assembly including telescopic sleeve means disposed within said bore to increase the length of available surface paths to ground from said liquid coating material disposed therein.

17. In a method of electrostatically depositing a coating material on an article wherein liquid coating material is emitted in an atomized spray pattern into an electrostatic depositing field by action of high velocity air delivered from a remote supply thereon in proximity to an electrostatically induced ionized atmosphere, the step of passing at least a portion of the air delivered from said remote supply through an electrogasdynamic power generator at an average speed in the vicinity of the sonic velocity to maintain said electrostatically induced ionized atmosphere and said depositing field at an average field strength of a magnitude proportional to the rate of flow of said air that interacts with said liquid coating material.

18. In a method for electrostatically depositing a coating meterial on an article wherein liquid coating material is emitted in an atomized spray pattern into an electrostatic depositing field by the action of high velocity air in proximity to an electrostatically induced ionized atmosphere the steps of,

introducing seed material into said air at a location remote from the locus of atomization of said liquid coating material,

passing at least'a portion of said seeded air through an electrogasdynamic power generator at an average speed in the vicinity of the sonic velocity to maintain said electrostaticallyinduced ionized atmosphere and said electrostatic depositing field at an average field strength of a magnitude proportional to the rate of flow of said air.

Patent 5,791,579 Dated February 12, 1974 Philip L. Cowan Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4,1ine 1, azEter "View" insert as Column 8, line 13, seal." should fead seat Column 10, line 56, "with" should re d H brillf-fl Columu 15, line 66,- "230" should read 23 2 lines 66(Q6 -7, delete having a grounded 3 inch' diameter sphere 2325 Co1umr1"20', 'line 46', "material" shouldv readg material H Signed and sealed this 19th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. 7 c. MARSHALL DANN I Attesting Officer v Commissioner of Patents FORM PC4050 (10.69) USCOMM-DC 60376-P6D U.54 GOVERNMENT PRIIGYING OFFICE: 869. 930

Patent No. 7 Dated February 12 1974 Philip L Cowan Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Column 4, line 1, after "View" insert as Column 8, line 13, "seal" should lead seat Column 10, line 56, "with" should read H will- Column 13, line 66, "230" should read 232 lines 66Q67, delete having a grounded 3 inch diameter sphere 232 E Column 210', line 46, "material" should read material Signed and sealed this 19th day of November 1974a (SEAL) Attest:

c. MARSHALL DANN 4 Attesting Officer USCOMM-DC 60376-0 69 u.s, GOVERNMENT PRINTING orncz: 930

FORM PO-IOSO (10-69)

Claims

1. In an electrostatic spray coating system wherein high velocity atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state, means for selectively introducing such material into a stream of pressurized atomizing air, and an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization and operatively responsive to at least a portion of the flow of said seeded atomizing air therethrough at a velocity in the vicinity of the sonic velocity and having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby.

2. In an electrostatic spray coating system wherein high velocity atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state, means for selectively introducing seed material into a stream of pressurized atomizing air, and an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization and operatively responsive to at least a portion of the flow of said seeded atomizing air therethrough having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby, said electrogasdynamic power generating means comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto, ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on The downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

4. In an air atomized electrostatic spray coating device wherein a high velocity stream of seeded atomizing air is employed to generate a spray of atomized liquid coating material which is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state, an electrogasdynamic power generating means disposed integrally adjacent the locus of atomization therein and operatively responsive to the flow of at least a portion of said stream of seeded atomizing air therethrough having a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate of said first air stream to effect proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby; said electrogasdynamic power generating means comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto, ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on the downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

6. In an electrostatic spray coating gun wherein an emitted spray of atomized liquid coating material is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state, an insulating body member containing a cartridge receiving bore and having liquid coating material atomizing means disposed at one end thereof and a groundable conducting base member disposed at the other end thereof, an electrogasdynamic power generating cartridge member removably disposed within said cartridge receiving bore and operatively responsive to the flow of a stream of seeded air therethrough and having a voltage and current output of a magnitude dependent upon the volumetric magnitude of said seeded air stream therethrough to effect proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby, said electrogasdynamic power generating cartridge member comprising an elongate channel having an attractor electrode means shaped to define a passage for the flow of said seeded atomizing air therethrough, a converging conduit section disposed on the upstream side of said attractor electrode to accelerate the flow of seeded atomizing air thereto, ionizing electrode means positioned within said conduit section to provide a discharge current flow path to said attractor electrode and an elongate channel section disposed on the downstream side of said attractor electrode means for conveying said atomizing air stream therefrom at an average speed in the vicinity of the sonic velocity.

11. The combination as set forth in claim 8 wherein said conducting sleeve member is threadedly engageable with a complemental coaxial bore surface in said groundable conducting base member for fixedly locating said cartridge member within said cartridge receiving bore in said body member.

13. The combination as set forth in claim 9 wherein said cartridge receiving bore is of greater internal diameter than the external diameter of the elongate channel section of the electrogasdynamic power generating cartridge member disposed therewithin for providing an annulus for an exiting flow of seeded air moving countercurrent to the flow through said cartridge member and in a direction away from said collector electrode element and toward said groundable base member.

16. In an electrostatic spray coating gun wherein an emitted spray of atomized liquid coating material is electrostatically attracted toward and deposited upon a grounded article while still in a liquid state, an insulating body member containing a cartridge receiving bore and having liquid coating material atomizing means disposed at one end thereof and a groundable conducting base member disposed at the other end thereof, an electrogasdynamic power generating cartridge member removably disposed within said cartridge receiving bore and operatively responsive to the flow of a stream of seeded air therethrough and having a voltage and current output of a magnitude dependent upon the volumetric magnitude of said seeded air stream therethrough to effect proportional variations in the magnitude of the average depositing field strength of an electrostatic depositing field engendered thereby, a liquid coating material delivering bore disposed within said body member in fluid communication with said atomizing means disposed at the end thereof, an externally actuatable valve stem assembly displaceably mounted within said liquid delivering bore for regulating the flow of liquid therethrough to said atomizing means, said valve stem assembly including telescopic sleeve means Disposed within said bore to increase the length of available surface paths to ground from said liquid coating material disposed therein.

18. In a method for electrostatically depositing a coating meterial on an article wherein liquid coating material is emitted in an atomized spray pattern into an electrostatic depositing field by the action of high velocity air in proximity to an electrostatically induced ionized atmosphere the steps of, introducing seed material into said air at a location remote from the locus of atomization of said liquid coating material, passing at least a portion of said seeded air through an electrogasdynamic power generator at an average speed in the vicinity of the sonic velocity to maintain said electrostatically induced ionized atmosphere and said electrostatic depositing field at an average field strength of a magnitude proportional to the rate of flow of said air.