US2923272A - Electrostatic coating apparatus with automatic self-wiping means - Google Patents

Description

Feb. 2, 1960 R. J. EMMERT 2,923,272

ELECTROSTATIC comma APPARATUS WITH AUTOMATIC SELF-WIPING MEANS Filed Nov. s, 1955 4 Sheets-Sheet 1 IN VENTOR.

xx BY j/ZZQ/Q AT TORNEV Feb. 2, 1960 R. J. EMMERT 7 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF--WIPING MEANS Filed Nov. 3, 1955 4 Sheets-Sheet 2 I INVENTQR acffmr zerf ATTORNEY Feb. 2, 1960 R. J. EMMERT 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF-WIPING MEANS Filed Nov. 3, 1955 4 Sheets-Sheet 3 I #61. M7 Q I aVfNfQ R 5; fi t/5W; 307/ A! 5 ATTORNEY A Feb. 2, 1960 R. J. EMMERT 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF-WIPING MEANS Filed Nov. 3, 1955 4 Sheets-Sheet 4 L? @5 200 w $52 465 i TIME/e 65 /2 swears INVENTOR.

supp" ATTORNEY United Sates Patent Of ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF-WIPING MEANS Rodger J. Emmert, Birmingham, Mich., assignor to General Motors Corporation, Detroit, Mich., of Delaware Application November 3, 1955, Serial No. 544,763 8 Claims. (Cl. 118- 4) This invention relates to improvements in electrostatic coating apparatus and to electrostatic atomizing devices therefor. More specifically, the invention is concerned with atomizing devices of the type in which paint or other liquid coating material is supplied at a controlled rate to the discharge orifice of an applicator device and is caused to flow and to be atomized therefrom by the cataphoric action of a high potential electrostatic field established between the applicator and an oppositely charged article to be coated.

Such electrostatic atomizing devices as have been proposed heretofore have proven to be impractical owing mainly to the clogging by paint, dirt and other particles of the very fine discharge orifice required to obtain atomization and to the difficulty of obtaining a satisfactory spray and article deposition pattern therefrom.

The present invention has among its general objects to provide improvements in electrostatic atomizing devices and coating apparatus of this character from the standpoint of facilitating their adjustment and cleaning, promoting uniformity of paint flow and improving the spray and article deposition pattern therefrom. Related objects are to improve the operating efliciency and to reduce the paint consumption of electrostatic coating apparatus of this character.

In the drawings:

"Fig. l is a cross-sectional, longitudinal view of a form of applicator device in accordance with the present invention;

Fig. 1A is a cross-sectional, longitudinal view of the applicator of Fig. 1 equipped with a drive mechanism for rotating a part thereof;

Fig. 2 is an enlarged cross-sectional view with parts broken away showing a modified part of the apparatus of Figs. 1 and 1A;

Fig. 3 is a diagrammatic illustration of a related form of applicator in accordance with another embodiment of the present invention;

Fig. 4 is a front view of another form of applicator in accordance with the present invention;

Fig. 4A is a modified form of the applicator of Fig. 4;

Fig. 5 is a cross-sectional, longitudinal view taken in the direction 5-5 of Fig. 4;

Fig. 5A is a cross-sectional view of a part shown in Fig. 5;

Fig. 6 is anenlarged, fragmentary portion of Fig. 4;

Fig. 7 is across-sectional, fragmentary view taken in the direction 7-7 of Fig. 6;

Fig. 8 is a view taken in the direction 88 of Fig. 5;

and

Fig. 9 is a diagrammatic illustration of an electrostatic spray painting installation and an electrical control system for a form. of applicator used therein in accordance with the present invention.

Referring to the drawings, Fig. 1 illustrates a form of applicator head or gun in which paint. or other liquid coating or film forming material may be finely atomized without the use of compressed air. The applicator 10 a corporation 2,923,272 Patented Feb. 2, 1960 comprises a generally spherical, outer body member 11 and a spool-shaped or piston-like inner member 12, which is received within a deep cylindrical'cavity 14 formed within the body member. The forward portion of the wall of the cavity forms 'with the outer surface of the body member a continuous lip 16 which is extended in a direction generally parallel to the axis of the applicator. The lip 16 may be of circular, or approximately circular, shape and has a thin discharge edge 18 which may be of knife-like sharpness.

The inner member has a threaded central stem or rod portion 22, which is coaxially received in a threaded body opening 24 that extends into the body cavity. The forward portion of the inner member is shaped to provide a continuous and substantially circular lip 26 also terminating in a thin knife-like discharge edge 28.

The discharge edge 28 of the inner member is spaced slightly from the outer member and forms therewith an annular opening or discharge orifice 30 for an annular passage 32, the curved walls of which are held to close limits of concentricity in order to obtain uniform flow of paint throughout the entire circumferentialclearance space between the outer and inner members forming the passage. The passage 32 communicates at its inner end with an annulus 34 formed by an annular groove in either the inner member or outer member or by a pair of annular grooves in the adjacent curved'surfaces of the outer member and the inner member, as shown. Paint or other liquid material is supplied under some pressure and at a uniform delivery rate to the annulus 34 from an external liquid supply line 35 (Fig. 9), which is suitably connected to the body member and communicates with an obliquely extending supply passage 38 leading to the annulus. An O-ring or other seal 40 located behind the annulus is provided in an annular groove in the inner member to prevent fluid leakage into the interior of the-applicator.

The outer end of the stem 22 of the inner member may be slotted,'or otherwise formed, as shown at 42, to receive an adjusting tool rearwardly insertable from the exterior of the applicator for axial adjustment of the inner member relative to theouter member without requiring system shutdown.. Either the outer lip or both the outer and'the inner lip may be tapered a few degrees, as shown, to permit of changing the gap spacing and the thickness of the liquid film supplied to the forward edge of the applicator by axial adjustment of the inner member relative to the outer member. By oppositely inclining or tapering the curved surfaces of the outer and inner members forming the rearwardly diverging paint passage 32, the width of the discharge orifice and, therefore, the paint flow may be increased by axial movement of the inner member in either the forward or rearward direction. Viewed as a nozzle, this construction may aid in shaping the spray pattern from the nozzle by reason of the different spray cone angles that can be obtained therefrom.

In order to reduce corona loss and electrical leakage, all corners and. edges of the applicator structure's described herein should be rounded except for their attenuated forward discharge edges which are of continuous extent transversely of the axis of the applicator. A

In operation, the applicator 10 is connected by a conbeen found to operate best when the paint is fed from the top when its axis is horizontal, so that the pressure difference in the annular passage 32 due to gravity head is counteracted by the pressure difference therein due to flow friction and turbulence.

With a potential difference of approximately 190 kilovolts or upwards between the grounded workpieces and the applicator, the thin liquid film supplied from the internal paint annulus to the forward edge of the applicator will become charged with electricity and will be caused by cataphoric action to flow from the ischarge edge in the form of an exceedingly line and dispersed liquid spray. The atomized spray particles will be charged to the potential polarity .of the electrified applicator and will be ,electrostatically attracted to and deposited on the oppositely charged workpiece. The

' atomization appears to take place from the terminus of the paint filmat the forward edge .of the applicator where there is formed a non disruptilvle, convective corona discharge or electric wind which is believed to cause the initial disintegration or rupture of the thin film into finely divided, charged particles.

In order to reduce the weight of the applicator and electrical leakage therefrom, either the outer member or inner member or both of these members may be .constructed of electrically non-conductive material, instead of from metal. The corona discharge necessary for atomization of the paint film can be'obtained from either of the knife-edged outer or inner members, from both of these members, or from the exposed terminus or edge of-the paint film itself. 7

To sharp circular discharge edges of the outer and inner members will induce the formation of cylindrical corona curtains which bound and may unduly tend to confine the spray from the atomizer where the outer and inner members are constructed of metal. Therefore, some improvement in the uniformity and spread of the annular spray pattern produced by the applicator may be obtained by constructing the inner member, at least, of electrically non-conductive material, thereby eliminating or reducing the intense corona discharge otherwise produced from the discharge edge of a metallic member. Since it may be desired occasionally to clean or flush the applicator with paint thinners or solvents, such parts of the applicator that may be formed of plastic should be formed of solvent resisting as ,well as of paint resisting materials. 7

The applicator devices of 'Figs. 1 and 1A also may be provided with an air born or manifold 52 surrounding and suitably attached to the outer member, as shown. Air or other gas may be supplied under pressure from a line 54 to .an air annulus 6 communicating with the i 'inner end of an annular air passage 58. Air from the outer end of the passage is supplied in an annular air sheath, which surrounds the .spray from the applicator and influences the pattern and the direction of the paint fog therefrom.

Fig. 2 illustrates a modification for the construction of the inner member 12, which maybe made of metal or of some flexible or expandible paint resisting material. The forward peripheral portion of the innermember may be'helically grooved or threaded or provided with forwardlyinclined serrations as shown at 60 for promoting I uniform paint flow whenthe inner member is rotated or oscillated about its axis or reciprocatedaxially of the structure by rotary, vibratory or other means.

..ma ne .in wh e rh inne mem 9 th ap l ernf may b ctat di er e amp e'iss pwn in .i is- 1A- The s em 2'2 .e t .in memh 'm v b ormed oftwo sections, including an integr 1. portion 22a, i hel is rotatable -with theinner member, and a statitonary threaded portion,22b, which is -;threadably ret e ed nih readed axial bodyopening :24. Suitable coupling means, -such asa split or flexible bearing62, "formed 'of nylon or other material, is provided to permit rotary movement of the inner member and axial adjustment thereof by adjustrnent of the stern portion 22b which fixes the axial position of the inner member. The inner member may have a ring gear formed internally thereof as shown at 64 meshing with a smaller drive pinion 66 secured to a drive shaft 63. Shaft 68 extends through an opening in the outer body member and may be rotated manually for occasional rotary adjustment. The shaft 68 could be driven continuously by either an air or electric drive motor, or it could be oscillatably indexed by the actuating mechanism of Figs; 5 and 8 to be described herein. Where the atomizing gap and the axial position of the inner member with respect to the outer member are fixed, a simple central drive can be employed.

Figs. 4 to 8 illustrate another form of applicator in accordance with the present invention in which the outer and inner members 71 and 72 are shown in Fig. 5 as a p f s x a ly ne ed, shal ew swamped me a elements each having a substantially circular lip 74 and 76, respectively, of approximately knife edge sharpness. The inner member is keyed to a shaft .78 that passes centrally through an axially extending stem or boss portion 8%, which is formed on the outer member and provides a bearing for the shaft. Keyed to the shaft and adjacent the boss portion 8t) is a rocker arm or lever 82, which is associated with an actuating mechanism, such as an air cylinder assembly 84, mounted on the back face of the outer member. The adjacent transverse faces of the outer and inner members are relieved as shown at 86 and are spaced apart axially by an Oilite type or other suitable thrust bearing 88 which provides a bearing surface between the faces of the two members.

A rounded jam nut 96 and a washer 92 are provided at the end ,of the shaft adjacent the inner member, and a spring94 coaxial with the shaft is provided between the lever 82 and a washer 96, .which is retained on the other end of the shaft by a cotter pin 98, to retain the outer and inner members in proper axial relation to each other. Screws, such as 100, may be provided in the inner member so as; to back the latter off from the outer member during disassembly of theldevice. A standard lubricator fitting 102 is threadably received in an opening in the back face of the outer member to supply lubricant to the shaft '78 through an inclined passage 104 and annular groove 106, as shown.

The outer member 71 may be provided with a rounded sheet metal cap or cover .110, which is suitably affixed thereto, as by flat head machine screws 112, and has a rod or handle 114 rearwardly projecting therefrom by means of which the applicator device may be mounted on an insulated support stand orfixture or through an insulating member to the support stand and connected to the power supply. The conductor rod 114 is fastened to the cover by a nut 116 and a dished washer 118 and is provided with asocket-like opening 12010 receive the high voltage conductor 44 from the power supply. The paint supply line 35 is shown extending through the cover 110 and is connected to the 'paint inlet side of an airoperated paint shut-01f valve 121 whose pain t outlet side is threadably received in a threaded opening in the back face of the outer member; An airline 122 is shown connected to the operating airinlet of the shut-off valve.

The shut-olf valve 121 is shown in Fig. 5A as having a .paint annulus shown formedbetween the opposed curved surfacesoftheouter andinner members. From the annulus 1 34, the paint is supplied through the annular passage 132 to the annular orifice 134-forrned-between the extended, knife-like discharge edges of the outer and lnner members. A removable drain plug 136, which is threadably received in a threaded radial opening 138 and commumcates with the paint annulus 134, may be provided to facilitate draining of the annulus during system shutdown. Another opening 140 extending between the faces of the inner member may be provided to drain any paint that may leak between the adjacent faces of the outer and inner members.

The appliczaor devices of Figs. 4 and 4A feature the use of a novel cleaning arrangement that effectively removes trapped paint, dirt and other particles that may clog the annular paint passage and discharge orifice and mterfere with the paint flow and spray pattern therefrom. {\s shown in the embodiment of Fig. 4, the outer and mner members are provided with a number of uniformly spaced, narrow wiper elements 146, 148 which wipe the walls of the annular paint passage 132 when the inner member 72 is oscillatably indexed and rotated. The wipers may be carbide or other metal inserts, which are pressed and cemented into uniformly spaced slots in the paint film carrying surfaces of the outer and inner members. They also could be formed as integral risers by selectively plating selected portions of the opposed curved surfaces of the outer and inner members. manner of attaching or forming the metal wipers may be equally satisfactory.

As indicated in Fig. 7, the wipers extend from the paint annulus 130 to the discharge edges of the inner and outer members and across the annular passage 132 between the lips of the outer and inner members. After installation in the outer and inner members, the wipers are ground to conform to the attenuated and curved lip contours of the outer and inner members, and their wiping surfaces are honed sufliciently to permit movement of the inner member with respect to the outer member. In order to provide complete Wiping action of substantially the entire annular paint passage, the inner member is rotatably indexed an amount approximately equal to the arcuate distance between adjacent wipers of the inner or outer member.

The air cylinder actuating mechanism 84, by means of which the inner member may be oscillated relative to the outer member, includes a cylinder body portion 152, which is securely mounted on the back face of the outer member, and an internal piston 154, which is loosely coupled to the end of one arm of the rock lever 82 by a link pin 156, as shown. An air line 150 connected to the cylinder body is adapted to supply compressed air from a suitable air source 162 to actuate the air piston. The piston displaces the lever 82, which is connected with the inner member to the dotted position shown in Fig. 8. The lever is displaced against a button stop 166, which prevents damage to the wipers and is mounted on the back face of the outer member. The lever is returned against another button stop 168 by a spring 170 that is connected to the lever 82 and a post 172 on the back of the outer member. In lieu of the return spring, the cylinder may be adapted to have air selectively admitted to either side of a double-ended piston to obtain the forward and return strokes thereof.

The inner member of the applicator need be only intermittently indexed. In operation it has been found suflicient to index the inner member but once over intervals of from 3 to 20 minutes, but this may vary depending upon the type of paint employed and the job. Since paint in the annular passage 132 maybe ejected therefrom in a stream when the inner member is rotatably indexed, the inner member is indexed preferably only when the applicator is between parts on the conveyor.

A suitable control installation, which permits the applicator to be indexed between parts on a conveyor and after a predetermined number of parts have passed the applicator, is shown in Fig. 9. The installation includes a conventional counter or timer device 184 that is adapted to close a set of normally-open contacts 186 after a. pre- Any other determined time or after a predeterminednuuiber of parts 46 have been conveyed past the applicator 10. The contacts 186 are connected in series in the energizing circuit of a conventional solenoid valve shown at 188, together with an additional set of normally-open contacts 190 of a photo-electrically operated relay 192. The relay 192 forms a part of a photo-electric control system which includes a lamp 194 that is located on one side of the conveyor 50 anda light sensitive cell 196, which is located on the other side thereof. The cell 196 may be a selenium cell or other photo-electric device andis connected in controlling relation with an amplifier 198 that includes the relay 192. The lamp and cell are so located relative to the applicator that when the latter is between parts on the conveyor, the lamp, and cell also'will be located between a pair of adjacent parts on the conveyor.

The energizing circuits for the solenoid valve 188, the lamp 194, and photo-electric system together with the input circuit of the high voltage power supply 45 are connected for energization through a master switch 20.0 from local supply mains 202, 204. With the switch 200 closed, the counter or timer 184 will close its contacts 186 after a predetermined time or after a predetermined number of parts have been conveyed past the applicator. The solenoid valve, however, will not be energized to permit compressed air to be supplied from the air source 162 of the air motor until the applicator is located between parts on the conveyor. The light beam from the lamp will then impinge upon the photocell and cause the relay amplifier to close the contacts 190 and complete the energizing circuit for the solenoid valve. I

The above-described photo-electric system may be employed with another solenoid valve 208 to operate the paint valve 121, as shown in Fig. 5A, so that paint is supplied to the-applicator only while a part is in the spraying region, thereby preventing loss of paint when the applicator is between adjacent parts on the conveyor. The solenoid valve 208 supplies compressed air from the air source 162 to line 122 to the paint valve when the contacts 186 of the photo-electric control system close to complete the energizing circuit of this solenoid. The

paint shut-off valve 121 is located preferably within the applicator, as shown in Fig. 5, and as close to the paint annulus therein so that there will be a minimum volume of paint in the applicator gun when the paint supply is shut off. By indexing the wiping mechanism of the applicator each time the applicator is between parts, a single solenoid valve and photocell control system can be employed to operate both the indexing air motor and the paint shut-off valve.

The DC. power supply 45 may be either of the high voltage transformer-rectifier variety or of the RF. oscillator-rectifier variety and should be able to supply voltages up to and, in some cases, in excess of 150 kilovolts. In the spraying of heavy pigmented material, such as may be used for the prime coating of automobile bodies, for example, satisfactory operation may be obtained with a spacing of around 18 inches between the applicator and the articles, an atomizing gap of around 0.004 inch and a potential difierence of from to kv. between the applicator and the articles on the grounded conveyor. Satisfactory atomization has been obtained with various paint compositions employed in the applicators described herein with atomizing gaps between the limits of 0.0017 and 0.006 inch. The degree of atomization has been found to vary with the articleapplicator spacing, the atomizing gap spacing, the composition and viscosity of the liquid coating material and the applied voltage, all of which variables need to be taken into account in any particular installation. The paint is supplied to the top of the atomizer in sufiicient quantity and at a uniform delivery rate to replenish the paint atomized from the edge of the applicator.

The above described applicator devices will produce an annular spray and deposition pattern upon the surface of an article intercepting the path of the annular spray. The outer portionso'fthe band of coating material which is produced as theart'icle is moved past the applicator will have a thicker deposit of coating material than portions intermediate the ends of the band. To aid inthe promotion of a more uniform coating thickness, the applicator of Fig. 4 may be slightly modified, as shown in Fig. 4A, to include a pair of enlarged, diametrically opposed wiper elements 146a in the outer member 71 and a corresponding pair of enlarged wipers 148a in the inner member 72 of the applicator assembly. The elements 146a, 148a are shown located immediately adjacent and disposed on opposite sides of the vertical center line of the applicator. Each of the wide elements replaces an adjacent pair of narrow wipers carried by the individual outerand inner members and is of the same width or arcuate length as'the arcuate distance spanned by a pair of adjacent narrow wipers 146and 148 in the outer or inner members. Conceivably, the narrow wipers 146, 148 between the "wideset'sof wipers at the top and bottomof the applicator could be eliminated and the wide wipers made to wipe the unobstructed portions of the gap or passage 132.

The wipers 146a and 148a will obstruct the top and bottom portions of the discharge orifice so that the spray and deposition pattern produced by the applicator on a stationary workpiece will be a pair of slightly curved, spaced or separated bands elongated in a generally vertical direction. Such an arrangement eliminates the curved top and bottom portions ofthe annular deposition pattern that otherwise would be obtained with an uninterrupted or substantially continuous annular spray pattern. A more uniform thickness of deposited coating material will thus be obtained when "the vertically disposed workpiece is moved past the applicator in a horizontal direction, as in Fig. 9. If the vertically disposed workpiece were moved in a vertical direction, the wide wipers should be adjacent the horizontal center line of the applicator. With respect to the direction of movement of the plane of the workpiece, the wipers 146a, 148a should be arranged so that the direction of elongation of the spaced bands produced by the applicator will be normal to the direction of movement of'the plane of the workpiece so that the workpiece will intercept first one band and then the other and will be successively sprayed thereby.

Fig. 3 is a diagrammatic illustration of arelated form of electrostatic atomizer in which the novel wiping and cleaning feature'of the present invention may be included. The applicator comprises a pair of flat, circular disk elements including an upper disk element 211 and lower disk element 212, each'of which has an extended, attenuated discharge edge 213, 214 which may be of knife-edge sharpness. The outer disk 211 is provided with a shaft 216 which is coaxially received in a hollow shaft 218 of the inner member. The adjacent faces of the upper and lower member may be relieved from the edge of the disks to a point inwardly thereof to form a paint supply passage 220 which extends continuously around thedisks. Paint is supplied to the passage 220 through a suitable opening 222 in the lower member and flows from the passage 220 in a thin film to the discharge orifices 224 formed between the relieved portions of the disks. With the atomizer spaced from and mounted with its axis parallel to the article surface to be coated, the

atomizer will produce a generally flat, 360 degree spray pattern therefrom.

' Cleaning of the passage 22 is efiected by the wipers 226 and 22$; which are carried by and maybe provided uniformly around the paint carrying surfaces of the upper and, lower members in the manner suggested herein. The upper member may be -o'scillatably indexed with respect to the lower member by mechanism similar to that already described, such as an air cylinder 230 the pistonr od 232 of'which may be loosely coupled to a lever element 234. The element 234 is shown connected to the shaft 216 and entends through an elongated, transverse slot inthe hollow shaft 218 of the lower member substantially as sl own. 7 I

As in the case of the embodiment of Fig. 4A, one or more pairsof-enlarged wiper elements can be employed in the applicator of Fig. 3 to obstruct any portion of the circular discharge orifice and thereby interrupt any desired portion of the flat, 360 degree spray pattern otherwise obtained therefrom.

It is apparent that the novel cleaning and wiping arrangements described herein can be embodied in various other forms and shapes of electrostatic atomizing applicator devices having a fine discharge orifice and that various arrangements and forms of movable wipers in the extended passage conveying liquid to the discharge orifice can 'be employed, all within the province of the present invention.

What is claimed is:

1. An electrostatic coating system comprising in combination a conveyor for conveying a succession of articles to be coated into a coating zone, an atomizer in said zone spaced from said articles on said conveyor and comprising a pair of coaxially nested members defining an annular passage therebetween and including an outer member and an inner member, each having an attenuated forward discharge edge, fluid supply means extending through one of said members and communicating with said annular passage, said fluid supply means being adapted to supply liquid material in a thin film to the forward discharge edge of the atomizer for electrostatic atomization therefrom, the opposed surfaces of the outer and inner members forming the opposite walls of said annular passage, a plurality of rigid wipers mounted in spaced relationship on said opposed surface of each of said outer and inner members,'said wipers being spaced around said annular passage adjacent said forward discharge edge, and each wiper being mounted on one of said walls and projecting across said annular passage into wiping engagement with the opposite wall 'of said annular passage to provide a wiping action when one of v said outer and inner members is rotatably displaced relative to the other member, the wipers on the inner member being equally spaced from each other and the wipers on the outer member being equally spaced from each other and angularly displaced from the wipers on the inner member, actuating means on the atomizer for moving one of said outer and inner members relative to the other, and control means operable when said atomizer is located between articles on said conveyor to energize said actuating means for relative movement of said members onlywhen the atomizer is between articles on the conveyor.

2. An electrostatic atomizer device of the character described, comprising a pair of coaitially nested members defining an annular passage therebetween and including an outer member and an inner member, each having an attenuated forward discharge edge, the edges-being spaced from each other and defining the forward edge" of said annular passage, fluid supply means extending through one of said members and communicating with said annular passage, said fluid supply means being adapted to supply liquid material in a thin film to the forward discharge edge of the atomizer for electrostatic atomization therefrom, the opposed surfaces of the outer and inner members forming'the opposite walls of said annular passage, and a plurality of rigid wipers mounted in spaced and inner members is rotatably displaced relative to the other member.

3. Apparatus of the character claimed in claim 2, wherein the wipers on the inner member are equally spaced from each other and the wipers on the outer member are equally spaced from each other and are angularly displaced from the wipers on the inner member.

4. An electrostatic atomizer device comprising a pair of coaxially nested members defining an annular passage therebetween and including an outer member and an inner member, each member having an attenuated forward discharge edge, the inner member being in sliding engagement throughout a substantial portion of its length with the outer member, the outer wall of said annular passage provided by said outer member being slightly inclined to the inner wall thereof provided by said inner member to permit of changing the width of said passage, fluid supply means extending through one of said members and communicating with said annular passage for supplying liquid material as a thin film to the forward edge of the atomizer for electrostatic atomization therefrom, means for adjusting the inner member axially with reference to the outer member, said outer member having an opening therein located behind said annular pas-. sage through which an adjusting tool may be inserted to engage and displace the inner member axially of the outer member and change the thickness of the film of liquid supplied to the forward edge of the atomizer, and means for rotating the inner member with reference to the outer member.

5. An electrostatic atomizer device comprising a pair of coaxially nested members defining an annular passage therebetween and including an outer member and an inner member, each member having an attenuated forward discharge edge, the inner member being in sliding engagement throughout a substantial portion of its length with the outer member, the outer wall of said annular passage provided by said outer member being slightly inclined to the inner wall thereof provided by said in ner member to permit of changing the width of said passage so that the passage is most restricted when the forward edges of said members lie in a common plane, fluid supply means extending through one of said members and communicating with said annular passage for supplying liquid material as a thin film to the forward edge of the atomizer for electrostatic atomization therefrom, means for adjusting the inner member axially with reference to the outer member, said outer member having an opening therein located behind said annular passage through which an adjusting tool may be inserted to engage and displace the inner member axially of the outer member and change the thickness of the film of liquid supplied to the forward edge of the atomizer, and means for rotating the inner member with reference to the outer member.

6. An electrostatic atomizer device comprising a pair of coaxially nested members formed of dielectric material defining an annular passage therebetween and including an outer member of approximate spherical configuration and an inner member each having an attenuated forward discharge edge, the inner member being in sliding engagement throughout a substantial portion of its length with the outer member, the outer wall of said annular passage provided by said outer member being slightly inclined to the inner wall thereof provided by said inner member to permit of changing the width of said passage so that the passage is most restricted when the forward edges of said members lie in a common plane, and fluid supply means extending through one of said members and communicating with said annular passage near said discharge edges for supplying liquid material as a thin film to the forward edge of the atomizer for electrostatic atomization therefrom, said outer member having a rearwardly facing opening therein located behind said annular passage through which an adjusting tool may be inserted to engage and displace the inner member axially of the outer member and change the film thickness of the liquid supplied to the forward edge of the atomizer.

7. An electrostatic atomizer device comprising a pair of coaxially nested members defining an annular passage therebetween and including an outer member and an inner member each having an attenuated forward discharge edge, the outer wall of said annular passage provided by said outer member being slightly inclined to the inner wall thereof provided by said inner member to permit of changing the width of said passage so that the passage is most restricted when the forward edges of said members lie in a common plane, and fluid supply means extending through one of said members and communicating with said annular passage for supplying liquid material as a thin film to the forward edge of the atomizer for electrostatic atomization therefrom, said outer member having an opening therein located behind said annular passage through which an adjusting tool may be inserted to engage and displace the inner member axially of the outer member and change thefilm thickness of the liquid supplied to the forward edge of the atomizer.

8. An electrostatic atomizer device of the character described comprising a pair of coaxially nested members defining an annular passage therebetween including an outer member and an inner member each having a forward discharge edge of approximately knife-edge sharpness, said outer member having a cylindrical cavity therein coaxially receiving said inner member, and fluid supply means extending through one of said members and communicating with said annular passage for supplying liquid material to the forward edge of the atomizer for electrostatic atomization therefrom, said inner member being movable axially of said outer member, the walls of the annular passage defined by said members being oppositely inclined and diverging rearwardly from the forward edge of said atomizer to permit of increasing fluid flow and changing the cone angle of the spray produced therefrom upon axial adjustment of the inner member in either direction from the outer member.

References Cited in the file of this patent UNITED STATES PATENTS 442,865 Kinder Dec. 16, 1890 1,832,096 Chaflee et al. Nov. 17, 1931 1,861,475 Hopkins et al. June 7, 1932 2,283,768 Schueler May 19, 1942 2,536,946 Larson Jan. 2, 1951 2,728,606 Smart et al Dec. 27, 1955 2,759,763 Juvinall Aug. 21, 1956 2,803,496 Ransburg Aug. 20, 1957 FOREIGN PATENTS 710,852 Great Britain June 23, 1954

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