US 3645447 A
Electrostatic air atomized paint spray system and spray device wherein power for 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.
Claims available in
Description (OCR text may contain errors)
Fraser ..239/15 o 1 limited States Patent 1151 mmmm (Iowan I1 Welt, 29, W72
 ELECTRQSTATKQ PAINT SPRA 3,351,285 11/1967 SYfi'lllEM 3,405,291 10/1968 3,417,267 12/1968  Inventor: Philip L. Cowan, Basking Ridge, NJ. 3471'039 10/1969 '73 A El 1 11 11 H ,N.J. 3473735 10/1969 ssignee ec rogas ynamrcs, nc anover 3,474,266 10/1969  Filed: Dec. 311, 1968 Primary Examiner-Lloyd L. King ] Appl' 788148 Attorney-Albert C. Johnston, Robert E, lsner, Lewis H.
Eslinger and Alvin Sinderbrand  US. Cl ..239/l5 [5 llut. Cl ....B05l1 5/00, F23d 11/28  ABSTRACT [58) Field of Search 15; 310/5 I Electrostatic air atomized paint spray system and spray device wherein power for charging air atomized spray droplets and  References Cited for maintaining electrostatic depositing field is obtained from UMTED STATES PATENTS self-contained electrogasdynamic generator operatively responsive to the flow of seeded atomizing air therethrough. 3,048,498 8/1962. Juvinall et a1. ..239/l5 X 117 Qlaims, 18 Drawing Figures Patented Feb. 29, 1972 7 Sheets-Sheet 1 INVENTOR. PH! LIP L, COWAN ATTORNEY 7 Sheets-Sheet 7;
PHIUP L, COWAN ATTORNEY 7 Sheets-Sheet 3 PHILIP L. COWAN ATTORNEY Patented Feb. 29, 1972 3,645,447
7 Sheets-Sheet 4.
cowAw BY Q4 vie I II F- 5 I! I'llmmmm I INVENT PHI UP L.
ATTORNEY E n g n 3 3 V 1 I lll l 'lll Patented Feb. 29, 1972 CURRENT MICROAMPERES 7 Sheets-Sheet I q J o.2 0.3 036 031 0 F2 114 His is SPARK GAP SPACING INS. Mi 180 I :40 a 120 E 100 7 2 so g CONVENTIONAL ELECTROSTATIC HANDGUN WITH 5 k KV ELECTRONIC POWER SUPPLY SIMILAR HANDGUN WITH EGD SUPPLY IN THE PLASTIC BODY 20 l V 7.... V *7". O ..l. l+, V7.7. l V. n
.2 .4 .6 .8 1.0 l2 1.4 L6 INVENTOR.
SPARK GAP SPACING INS. PHILIP L. COWAN H W fl Aim ATTORNEY Patented Feb. 29, 1972 3,,e45,447
- 7 Sheets-Sheet 6 F1 cg/xJ/ g W|TH SHIELD E 5 6 i- E Q E g-- WITHOUT SHIELD 2: Z L? 0 a i 3 6 9 l2 l5 I8 2| 24 "S" DETECTOR GUN SPACING INCHES ATTORNEY Patented Feb. 29, 1972 3,,645'5447 7 Sheets-Sheet 7 CORONA CURRENT NICROAMPERES INVENTOR.
PHILIP L. COWAN 34 I72 ATTORNEY HELIECTROSTATHC fAlINT SPRAY SYSTEM 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 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 instal' lations 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 extant in the spray region, toward a grounded workpiece. In the vicinity of the spray gun, the iner tia 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 blowby 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 with the demands of adequate atomization and paint flow. Airflow 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 blowby of paint. Conventionally employed electrostatic air atomized coating systems are generally characterized by a rapid falloff in depositing efficiency as the fluid, i.e., paint, and atomizing airflow rates are increased. Such problems are accentuated when high airflow 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 supplied 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 U.S. Pat. No. 3,048,498, in the nature ofa 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 elements additionally inherently function 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 sparkling and consequent possible fire exists when the operator ro 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 selfcontained 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 connectable 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 operations of charging potentials and at effective 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 field serviceable, lightweight, diminutively sized and readily manipulatable 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 operablly 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 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 for electric 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 p.s.i.g. to I00 p.s.i.g., 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 mag nitude 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 accordance with the mandates of the patent statutes, the principles of the invention as embodied in a presently preferred construction of an electrostatic spray painting system and air atomization-type spray gun assembly for use therein.
Referring to the drawings:
FIG. 1 is a schematic representation of the components of an electrostatic paint spray system incorporating the principles of this invention;
FIG. 2 is a vertical section through an air atomized spray gun constructed in accord with the principles of this invention and constituting a presently preferred embodiment thereof;
FIG. 2A is a sectional view as taken on the line 2A2A of FIG. 2;
FIG. 2B is a sectional view as taken on the line 2B2B of FIG. 2;
FIG. 2C is a sectional view as taken on the line 2C-2C of FIG. 2;
FIG. 3 is a front elevation ofthe 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;
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 nozzle-charging 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 of FIG. 11;
FIG. 13A is a vertical section illustrating a presently preferred configuration for a charging electrode.
FIG. 13B is a section taken on the line 13B-l3B of FIG. 13A.
Referring to the drawings and initially to FIG. I there is generally illustrated the components of a hand-manipulable type of air atomized electrostatic paint spraying system embodying the principles of this invention. 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 p.s.i.g. or greater and capable of supplying the requisite flow rates, that serves to conjointly supply fluid paint delivery pressure through a T- type fitting l2 and associated regulator and gauge assembly 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 the flow rate of the air conveyed to the air atomized paint spraying device, generally designated 28 and suitably constituting a hand manipulatable 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 to 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 follows, 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 utilized for effecting atomization of the liquid coating material either by direct interaction therewith or indirectly 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 is the seeded atomizing air supply hose 30, with the latter desirably containing a metallic conductor element, suitably in the form of a sheath or strand, which serves to ground the conducting handle portion 32 of the air atomized spray device 28 through the grounded vapor seed pot assembly 26.
The workpiece or object 42 to be coated is suspended, in a manner conventional in electrostatic spray painting systems, from a grounded support assembly 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.
As will be apparent to those skilled in this art the airatomized spray device 2% may be of varying character in which the seeded atomizing air may directly or indirectly effect atomization as pointed out above. As schematically illustrated in FlG. l, the spray gun device 28 may suitably comprise a hand manipulatable 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 designated 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 33 thereof via a lead 40, suitably comprising an unshielded conductor wire fastened directly to or contained within the seeded atomizing air supply line 30.
As clearly delineated in FIG. 1, a spray gun 2d 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 34) and, as noted earlier, a lightweight unshielded wire 40 for the electrogasdynamic power generator excitation voltage and which may be conveniently fastened to or disposed within the 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 form 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 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 atomizing 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 44), 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 p.s.i.g. or even higher. The composite seeded atomizing air-ex citation 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 so surrounding a spring'biased electrical contact receptacle-type assembly comprising a displaceable receptacle-type contact member 432 connected to one end of an internally disposed insulated excitation voltage lead be that leads to the electrogasdynamic voltage generator as will be described in detail hereinafter. Biasing of the contact member as is effected by the spring member o4 having its remote end fixedly positioned by the insulating plug 65. The connector assembly 56 generally comprises a selectively shaped elongate sleeve assembly 64 incorporating a plurality of atomizing air escape apertures 74) adjacent its midlength and upwardly terminating in a guide portion 72 sized and shaped to coaxially 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 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 5%. Suitable O-ring seals '78 and iii) are disposed in the walls of the sleeve member 68 on either side of the seeded atomizing air escape apertures 7i} 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 134 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 setscrew 42.
When the connector assembly 56 is properly positioned as described above, the seeded atomizing air escape apertures are disposed in gaseous communication through the aperture 84 with an elongate bore 9b 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 911% is disposed in fluid communication with a transverse bore generally designated )4, 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 93 having a base portion fixedly mounted in the open end of the bore 94 and an extension Nib shaped to open end provide an annular seat W4 and a plurality of apertures liilii disposed adjacent thereto in gaseous communication with the bore M2. Associated therewith is displaceable valve plug member tilt) that is normally biased, as by the spring 102, into hermetically sealed relation with the valve seat. Displacement of the valve plug member W0 is effected by the pushrod 103 that extends through the valve body member and associated plug and packing 8d and is longitudinally displaceable in response to rotative displacement of the trigger as. Thus, rotative displacement of the trigger in the clockwise direction as illustrated in FllG. 2 effects a rearward displacement of the pushrod MP8 against the action of the biasing spring 102 and lifts valve plug Mill out of sealing engagement with the seat 1104. Such lifting of the plug 10ft off the seat MP4 pennits a flow of seeded atomizing air from the bore through the apertures llllfi and into the bore M2. The bore 112 is disposed in gaseous communication with the entry portion 114 of the electrogasdynamic power generator 5% and thus serves to effeet the introduction of seeded atomizing air therein.
As will be apparent from the foregoing, the above-described structure operates to introduce both the seeded atomizing air and the excitation voltage to the electrogasdynamic power generator 54). Preparatory however to describing the structure and operation 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 pain 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 a elongate bore 1213 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 120 that defines a liquid paint emitting aperture. As best shown in FIG. 2 the fluid tip nozzle member 130 is formed ofelectrically 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 elongate fluid 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 rearvvardly 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 135 included as a part of a spring biased and trigger displaceable actuating assembly generally designated 140. Such assembly includes a sleevetype adjusting stop screw 142 disposed about a biasing string 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 permi the emission ofa 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, which in 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 elctrogasdynamic 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 airstream and serves to increase the speed thereof as it approaches the attractor ring. After passage through the attractor ring electrode 194, the atomizing airstream passes through an elongate channel 158 of relatively small, and preferably slightly increasing in the direction of flow, cross-sectional 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 airstream impinges against the adjacent axially disposed collector needle electrode 198 mounted in a plug 196 and expands into the bore 156 and flows therewithin at reduced velocities toward the exit conduit 160 therefrom. As shown, the collector electrode 198 is directly connected, as by the lead 200, to a conducting metallic fluid tip nozzle member which latter serves as the charging electrode.
As best shown in FIGS. 2b and 2c the exit conduit is disposed in gaseous communication with a discrete fan air transfer conduit 164 running longitudinally of the 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 160 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 airstream 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 10, disposed in overlying relation therewith and removably secured in desired position by a threaded and removably secured in desired by a threaded retaining ring 172 is a selectively configured air cap member formed 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 at the end 163 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 130 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 30 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 fro 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 will 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 w l and down the elongated 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 lldtl and will raise the potential thereof to extremely high values, which such potential being applied by the conductor Illllll to the fluid tip nozzle member llfltl.
As will now be apparent, in operation of the described device, clockwise displacement of the trigger as will conjointly effect emission of liquid paint through the aperture defined by the cylindrical nozzle portion lllltl of the fluid tip nozzle member 130 and a flow of seeded atomizing air through the bore 90, the electrogasdynamic power generator 50, the atomizing air and fan air transfer conduits M52 and M4 respectively and through the various conduits of the air cap l'ltl 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 "5'0 results in the generation of high lDC voltages at the collector electrode W8 and in the direct application thereof, through conductor 2%, to the fluid tip nozzle member 1130, which thereby performs 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 lldtl 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 lldtl, 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 self-contained 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 advantages 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.
In electrogasdynamic power generators of the general type described, the initiation of the requisite corona discharge at the entrance to channel 151% requires the application of only relatively low excitation voltages, as for example in the order of 5,000 volts, in order to effect the generation of very high voltage at the collector electrode N23. 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 l5?) from the attractor ring electrode 1% to the collector electrode 198 against the opposing electrical field. llt should be noted that although convenience has here dictated application of the excitation voltage to the ionizer needle 12d and having the attractor ring electrode PM grounded, such can be readily reversed and operations effected with a grounded needle electrode and a charged attractor electrode with the necessary constructional 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 MG. 2 such llll breakdown will most likely occur between the collector and attractor e ectrodes along the walls of the channel 2158. As such, the length of the insulating channel llfid 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.
H6. t 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 coaxially disposed relative to the axis of the channel llfill formed by the insulating sleeve 2112. by a mounting member 1% and sized to extend through a converging inlet or transition section to the attractor ring electrode 1% as defined by the conically bored insulating member i923. 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. ln this illustrated embodiment, the excitation voltage is connected to the attractor ring electrode 19d as an alternative to the previously described construction and the needle electrode M4 is operated at ground potential. With proper design almost all of the current flowing from the ionizer needle can be caused to move with the atomizing air downstream to the collector electrode llfilfl which operates to effectively minimize the excitation power required 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 58 is near sonic in character which provides high performance at lowpressure drops of a magnitude that are essentially compatible with commercially available compressor delivery characteristics. ln 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 he atomizrng airflow path. Une suitable means for introducing such the surface discontinuity is to make the diameter of the downstream end of the converging :inlet section l92 appreciably larger tan the diameter of the attractor ring electrode lid l to effectively provide an annular shoulder extending at right angles to the longitudinal axis of the flow path. A second means is to incorporate an annular recess 2% intermediate the attractor ring electrode ls d and the downstream end of the transition member W2. A third means is to incor porate a second annular recess Zllld intermediate the attractor ring electrode lldd and the channel lSll 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 1% slightly larger than the diameter of the attractor ring electrode t ll ll. Additionally the channel 15ft diverges slightly in cross-sectional extent in the direction of airflow to insure maintenance of near sonic velocities in the vicinity of the attractor electrode W4.
All of the above means are desirably incorporated in the generator disclosed in Fit}. 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 i9 4 and the channel 15d 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 W4 and within the channel llfitl.
FlG. d-A illustrates an alternative means whereby surface discontinuities may be introduced into the defining walls of the generator adjacent the attractor ring electrode lldd. in this Atomizing Air delivery pressures of from 20 I p.s.i.g. Attractor ring electrode (I94) 01 I6" ID by 0177" long Converging or transition section (192) 0.260" ID at entry 0.]50" ID at exit and 0.410" long Recess (220) 0.035" deep by 0,300" diameter Recess (216) 0.320" diameter by 0.060" deep Channel (I58) 0120" ID by 30" long with 0008"!" 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 mounting 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 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 voltage-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 of 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 abovedescribed electrogasdynamic power generator means with the output characteristics of an air atomized electrostatic-type handgun manufactured by the Eclipse Equipment Company of Fairfield, N.J., utilizing a conventional 65 kilovolt electronic power supply and incorporating a limiting resistor as taught by US. Pat. No. 3,048,498.
As is readily apparent from FIG. 7, the short circuit current of the handgun 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" type characteristics inherent in the conventionally employed electronic power supplies in association with a se- -ries 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-com tained electrogasdynamic power generator having a magnitude that varies in accord with the rate of flow of seeded atomizing air which functions to minimize the dropoff in depositing efficiency characteristic in conventional systems as the liquid paint and airflow 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 handgun of the type illustrated and described herein is placed in close proximity with an insulated 6 inch diameter sphere 254 and the corona currents delivered to a grounded probe 256, specifically a square cut brass rod 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 airstream is increased. FIG. 8 also shows, by curve 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 generating purposes. Thus the stream of seeded atomizing air may be preliminarily subdivided into atomizing and fan airstreams 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 llEl conventionally employed for the purposes 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 opera tor, 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. lltl (and also FIGS. 13a and tllb) schematically illustrates the incorporation of such a shield electrode to the atomizing nozzlecharging electrode assembly of the spray gun of H6. 2.. As
there shown, the shield electrode suitably comprises an annular ring of conducting material Mil mounted on the surface of the air cap ll'ltl surrounding the cylindrically shaped terminal portion ilitl of the fluid tip nozzle member ll3tl serving as the charging electrode. Such shield electrode Mil is electrically floating," in that it is neither connected electrically to the charging electrode or to ground, and will thereby collect cur rent 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. illi. FlG. it 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, NY.) connected intermediate a probe 24% and ground and a spray gun Mo constructed in accord with the principles of this invention and of the type described above. The two curves shown on FM]. llll 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 point in this specification the fluid tip nozzle member Kit and particularly the cylindrically shaped terminal sleeve portion 135i) 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 electrogasdynamic 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 l-iGS. 113A and lid 13B. As there shown the dependent end of the sleeve portion 1% of the fluid tip nozzle member 1% is sharpened into a V configuration to provide a plurality of relatively sharp edged surface discontinuities 2% at the terminal portion thereof. A shielding electrode Mil is again disposed in encircling relationship around the charging electrode.
While l have shown and described certain presently preferred embodiments incorporating the principles 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.
l. A spray device for use in an electrostatic spray coating system wherein grounded articles are coated by having charged atomized spray particles electrostatically attracted toward and deposited thereon while still in the liquid state, comprising a source of pressurized air,
means for selectively introducing seed material into the pressurized air,
electrogasdynamic power generating means,
first conduit means for directing at least a portion of the pressurized seeded air to said electrogasdynamic power generating means for passage therethrough for charging the atomized spray particles and for maintaining an electrostatic depositing field having one terminus adjacent the locus of atomization,
means for atomizing liquid coating material by interaction with a high velocity gaseous stream and for projecting the atomized coating material as a. spray of fine coating material particles, and
second conduit means for directing at least a portion of the seeded air discharged from said electrogasdynamic power generating means to said atomizing means.
2. A spray device according to claim ll further comprising body means for carrying said electrogasdynamic power generating means.
3. A spray device according to claim 2 wherein said body means includes a forward portion formed substantially ofinsulating material.
4. t spray device according to claim 2 wherein said body means includes a bore and said generating means is selectively dimensioned for removable disposition within said bore.
5. A spray device as set forth in claim l wherein said electrogasdynamic power generating means has a voltage and current output of a magnitude dependent upon the magnitude of the delivery rate ofsaid seeded atomizing air for effecting proportional variations in the magnitude of the average depositing field strength of said electrostatic depositing field engendered thereby.
d. A spray gun as set forth in claim 5, wherein said electrogasdynamic power generating means generates direct current and voltage.
7. A device as set forth in claim 3 including spray charging discharge electrode means mounted at one end of said forward body portion and comprising at least a portion of said atomizing means electrically connected to the output of said electrogasdynarnic power generating means for maintaining said ionized atmosphere in proximity to said atomized coating material.
ii. The device as set forth in claim 7 including electrically isolated shielding electrode means disposed in spaced relation to said spray charging discharge electrode means for increasing the operating potential of the latter.
9. The device as set forth in claim 7 wherein said spray including charging discharge electrode means is selectively contoured to provide at least one corona inducing projection at the terminus thereof.
iltl. The device as set forth in claim 7 wherein said spray charging discharge electrode means is selectively contoured to provide at least one corona inducing projection at the ter minus thereof and including electrically isolated shielding electrode means disposed in spaced relation thereto for increasing operating potential thereof.
11. The device as set forth in claim 8 wherein said shielding electrode means comprises a sleeve of conducting material disposed in surrounding spaced relation with said discharge electrode and having its forwardly directed end extending beyond the forward terminus of said discharge electrode.
12. The device as set forth in claim 10 wherein said shielding electrode means comprises a sleeve of conducting material disposed in surrounding spaced relation with said discharge electrode and having its forwardly directed end extending beyond the forward terminus of said discharge electrode.
13. The device as set forth in claim 7 wherein said spray charging discharge electrode means comprises liquid emitting nozzle portions of said atomizing means selectively contoured to provide at least one corona inducing surface discontinuity at the terminus thereof.
14. The device as set forth in claim 3 comprising an elongate needlelike member extending forwardly of said atomizing means.
15. The device as set forth in claim 14 including electrically isolated shielding electrode means disposed in spaced relation to said spray charging discharge electrode means for increasing the operating potential of the latter.
16. A device as set forth in claim 2 wherein said electrogasdynamic power generating means comprises a removably insertable cartridge.
17. The device as set forth in claim 2 including manually graspable support means mounted on the end of said body portion formed of conductive material and adapted to be grounded during operation of said electrogasdynamic voltage generating means.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 11 545 447 Dated February 29 1972 Inven r( Philip L. Cowan It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
IN THE SPECIFICATION Column 1, line 67, "supplied" should read supplies Column 2, line 15, "re" should read or Column 4-, line 19, after "designated" should be inserted I 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 d i d Column S, line 46, after "is" should be inserted a Column 6, line 48, "open" (second occurance) should be deleted Column 6, line 49, "end" should be deleted Column 7, line 3 "pain" should read paint Column 7, line ll, "a" should read an FORM PO-IOSO (10-69) USCOMM-DC 50376-5 69 \LS. GOVERNMENT PRINTING OFFICE 1 I969 0-366-334 UNITED STATES PATENT OEFTCE CERTIFICATE OE COREECTTON Patent No. q 54=5 447 Dated Februarv 29. 1972 Inventor(s) L C an It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 7, line 51, "perm" should read permit olumn 8, line 40, "10, disposed" should read 130.
Disposed Column 8, lines 41, 42, "and...threaded" should be deleted Column 8, line 43, after "formed" should be inserted Column 8, line 69, "fro" should read from Column 10, line 43 "he" should read the Column 10, line 47, "tan" should read than Column ll, line 54, "of" should read off Column 13, line 65, "130" should read lZO Signed and sealed this 10th day of October 1972.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Atte sting Officer Commissioner of Patents FORM PO-lOSO (10-69) USCOMM-DC 60376-P69 Q U.S, GOVERNMENT PRINTING OFFICE: 1969 O366-334