US3630441A - Electrostatic spraying apparatus - Google Patents

Abstract

A spray gun comprising a spray nozzle and a high-voltage generator consisting of a passage for conveying a gaseous fluid toward said nozzle, an electrode for imparting electric charges to said gaseous fluid, and a convergent-divergent portion in said passage downstream of said electrode for imparting a supersonic speed to the gaseous fluid carrying the electric charge. The gun comprises means for transmitting electric charges from the gaseous fluid to the nozzle.

Description

0 United States Patent 11113,630,441

[72] Inventors u 501 Field 01 Search 239/3, 15

nobleo zer Thololne, Celene; Fell! Gmch, [56] Reference CM GrenoblqnIolFrnnee UNITED STATES PATENTS 211 App]. No. 85,820 3,268,171 8/1966 Walbe 239/3 x 221 Filed 0a. 30, 1970 3,296,015 H1967 Juvinall et al..... 239/15 x [4 Patented 28, 1971 3,521,125 7 1970 Nelson 239/15 x 73 Assigne Tunzini-Snm s 3,558,052 1/1971 Dunn 239/3 Bumble FOREIGN PATENTSPmmy 5"" 1968 421,81 1 12/1934 Great Britain 239/3 [31] 5220 Primary Examiner-M. Henson Wood, Jr. Continuation of application Ser. No. Assistant Examiner-Thomas C. Culp, Jr. 797,995, Feb. 10, 1969, new nbnndoned. Attorney-Holcombe, Welherill & Brisebois This application on. 30, 1970, Ser. No. 85,820

[54] ELECTROSTATIC SPRAYING APPARATUS ABSTRACT: A spray gun comprising a spray nozzle and a high-voltage generator consisting of a passage for conveying a gaseous fluid toward said nozzle, an electrode for imparting 35 Chill, 18 Drawing Figs. electric charges to said gaseous fluid, and a convergent diver- [52] Us n 239/15 gent portion in said passage downstream of said electrode for 239/3 imparting a supersonic speed to the gaseous fluid carrying the I electric charge. The gun comprises means for transmitting [5u C 5,00 electric charges from the gaseous fluid to the nozzle.

Patented Dec. 28, 1971 7 13 Sheets-Sheet 1 in p I r w m I n m n m y v ow om mm omvm 13 Sheets-Sheet 3 ommwom S Patented Dec. 28, 1971 Patented 156C. 23, 1971 1 3,630,441

13 Sheets-Sheet 5 I Patented Dec. I 28, 1971 15 Sheets-Sheet 4= Eigl 1l I I J 13 Sheets-Sheet 5 Am no cm 00 vm mo mm mm Patented Dec. 28, 1971 13 Sheets-Sheet 6 l ""II"'AVI a: A; o; m; m: 2% L 09 5 m "lllflll baa/ .3m!

8w mww r ms EN; 5w E95E 6? @v v9 Patented Dec. 28, 1971 13 Sheets-Sheet 8 Patented Dec. 28, 1911 3,630,441

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Patented Dec. 28, 1971 13 Sheets-Sheet 1o fl w 05 mm? Xv on? mm? k \---K7A imur llwuw v v l a? =71 v I w? A is Viv/"1 M mt I L lr'l l v Ev 05 omv Patented Dc. 28, 1971 13 Sheets-Sheet 11 21 U LEI com Patntecl Dec. 28, 1971 15 Sheets-Sheet u 95mm wow wow wow EN tvow ovw wom Now mow NE \Q d J vow vvm mow mow oON vow mvow vow mvm ELECTROSTATIC SPRAYING APPARATUS This application is a continuation of Ser. No. 797,996, filed Feb. I0, l969,and now abandoned.

The present invention relates to electrostatic spraying apparatus of the type having an electric generator incorporated in the body of the sprayer.

It has been proposed to incorporate, in an electrostatic spray gun, the high-voltage generator which supplies the electric charge at high potential to the product to be sprayed. Up to now such proposals have not resulted in any practical use, mainly because the generators used are relatively heavy and cumbersome. However, the incorporation of the generator in the spray gun ofi'ers numerous advantages. Thus it eliminates the high-voltage connecting cable which is heavy to handle and which presents a great danger through the capacitive energy which it retains and which it releases in the case of an accidental earthing of the charge electrode, or of the product to be sprayed, at the outlet from the spray nozzle.

According to the invention a spray gun comprising a spray nonle incorporates a high-voltage generator consisting of a passage for conveying electric charges to a convergent-divergent nozzle for imparting a supersonic speed to a gaseous fluid carrying the said electric charge, and means for transmitting electric charges disposed in the region of the neck of the said convergent-divergent nozzle. Advantageously the fluid of the generator serves another function, either as a driving agent for a rotating spray head for example, or as a gaseous spray fluid for a liquid.

The invention will be further described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of one embodiment of a spray gun according to the invention,

FIG. 2 is a schematic view of a spraying installation,

FIGS. 3 to 5 are sections of other embodiments of the spray gun according to the invention,

FIG. 6 is a view along the line VIVI OF FIG. 7,

FIG. 7 shows a further embodiment of spray gun,

FIGS. 8 and 9 are sectional views of two further embodiments of a spray gun according to the invention,

FIG. 10 is an enlarged view of the cartridge-generator used in the spray gun of FIG. 9; and

FIGS. 11 to 18 are sections of other embodiments of spray gun.

Referring to FIG. 1, an electrostatic paint spray gun comprises an insulating body 1 extending between aspray noule 2 and a rear part forming a handgrip. The insulating body 1 is provided with a passage 4 for the paint, connected by aunion 5 to aflexible pipe 6 leading to a paint source under pressure, or to a volumetric pump supplying the paint. As can be seen in the drawing, the paint passage 4 communicates at 4' with a chamber 7 located upstream of anozzle passage 8 which can be closed by a valve 9 operable by avalve rod 10 controlled by atrigger 11.

The insulating body 1 also contains anotherpassage 12, which communicates at its upstream end with a humidiftcation ordamping chamber 13 and also with a passage 14 for the admission of air under pressure. This passage is provided with avalve 15, also controlled by thetrigger 11.

In thepassage 12, on the upstream side in he direction of the air circulation, is provided a means for the transmission of electric charges, constituted by aneedle 16 axially placed at the center of aring 17 forming a convergent-divergent nozzle. Theneedle 16 is connected by aconductor stud 18 to a plug 19 in the end 0f a cable 20 joined to an excitation source of the order of. 2 to 5 kilovolts. Thering 17 forming a counterelectrode is itself connected by aspring 21 to aconductor cover 22 extending towards the rear part including the handgrip of the spray gun 3 and maintained at earth potential by metal braiding 23 of a cable cover covering both thepipe 6 for the admission of the paint and theexcitation cable 20,

The outlet at the downstream end of thepassage 12 is sealed by aball valve 24 subjected to the action of acompression spring 25, the while being located in achamber 26 communicating via passage 27 with anannular distribution chamber 28 disposed between the nozzle body 29 and anozzle cap 30. Thischamber 28 communicates in a normal way, for example by any means imparting a swirling effect to the air, with anannular passage 31 concentric with and surrounding the paint outlet,

One end of aporous wick 32 extends into thedamping chamber 13, its other end being located in atank 33 formed in the handgrip and filled with water.

In operation, pressure on the trigger ll opens the valve 9 to allow the ejection of the paint; and also opens thevalve 15 to allow the circulation of air in the passages l4, l2 and 31 (beyond which it pulverizes the paint). It may also cause the application of the voltage over theexcitation cable 20 to the extent where, by any appropriate means, the excitation is controlled by the circulation of the air so that theneedle 16 transmits electric charges into an air current circulating at high speed, at least partially supersonic, in thepassage 12, thevalve 24 being displaced towards the open position under the effect of repelling the air from thepassage 12. The electric charges transmitted by theneedle 16 are, due to the rapid circulation of air in thepassage 12 carried to a high potential and these charges are collected by theball 24, thespring 25 and from there, are transmitted to the conductive noule body 29. This allows a correct charge of the paint flowing through thepassage 8 and this paint is moreover pulverized by the air which has served to convey the electric charges. Thehumidification chamber 13 is particularly useful because it allows the air under pressure which arrives from the passage 14 to acquire a higher hygrometric value which is favorable to the formation, by condensation and/or elimination of liquid and/or solid particles making up the transporter of electric charges.

In the embodiment described, the humidifier consists of awater tank 33 closed by astopper 34 and is refilled from time to time, but it is obvious that a pipe could be used to supply water to thehumidification chamber 13.

Referring to FIG. 2, a spray gun 41 of the type described with reference to FIG. 1 is used, but which does not incorporate the humidification chamber. The humidification is effected by making the air under pressure pass into a saturated atmosphere of awater tank 42 with a porous wall 47, the air in thepipe 43 being thus sufficiently charged with water vapor to be able to transport electric charges. Thepaint pipe 44 andexcitation conductor 45 pass through thehandgrip 46.

By way of example, the air admitted upstream of thevalve 17 may have a pressure from 2 to 4 bars and a flow of 6 to 12 milh. into apassage 12 having a diameter of 3 mm. anda length of 5 cm.

Referring now to the embodiment of FIG. 3, aspray gun body 50 of insulating material comprises apassage 51 between aspray nozzle 52 and a rear part forming ahandgrip 53. Thepassage 51 is connected at its upstream end to a charge transmitter of the type previously described, having aneedle 55 in the center of aring 56 forming a counterelectrode and at its downstream end to thespray nozzle 52. Thepassage 51 is connected by apipe 57 to a source of air transporting the powder to be sprayed, while theneedle 55 is connected by acable 58 to an excitation source. Thecounterelectrode 56 is connected electrically to earth, that is to say to the potential of thehandgrip 53. In operation, the powder entrained by the air through thepipe 57 passes through the perforations of the needle-centeringdevice 59, passes at high speed in the area of thisionization needle 55. where the particles receive electric charges and whose potential is considerably increased by the circulation at high speed in thepassage 51, so that the particles emitted through thenozzle 52 are charged at a sufficiently high potential to ensure their electrostatic attraction on to the object to be sprayed, which is generally at earth potential.

FIG. 4 shows a modification of the embodiment in FIG. 3 wherein the air transporting he powder is conveyed through apipe 54 discharging between thenozzle 56 and thesupport 59 for theneedle 55, so that it is no longer necessary to perforate thesupport 59.

Referring to the embodiment of FIG. 5, anatomization nozzle 60 is made up of a plurality ofchannels 61 located in anatomization chamber 62. Thischamber 62 is fed by aliquid inlet passage 63 connected by aunion 64 and apipe 65 to a paint source (not shown). Opposite the outlet ofpassage 63 is disposed apassage 66 provided in an insulatingsupport 67. Thispassage 66 serves to transport the electric charges from an upstream zone where a transmitter ofelectric charges 68 is located to theatomization chamber 62. Thepassage 66 is connected, upstream of thecharge transmitter 68 to a source of air under pressure.

Thus, as has been explained previously, from the air circulating at great speed inpassage 66, the charges which this air acquires at the place of thecharge transmitter 68 are thus carried to a raised potential at the level of theatomization chamber 62. It is understood that the jet of liquid from thepassage 63 and the jet of gas from thepassage 66 meet in thechamber 62 which ensures, as is known, pneumatic atomization in the said chamber. But moreover, the electric charges transported by the air into thepassage 66 are transmitted to the pulverized liquid particles so that these liquid particles ejected from thechannels 61 of thenozzle 60, which can also be produced of insulating material, are charged electrically at a potential sufficient to ensure their attraction to an object at earth potential to be painted.

In the embodiment of FIGS. 6 and 7, a powder spray device comprises aspray nozzle 70 mounted at the end of and transversely of an insulatingsupport 71, having apassage 72 provided with anionizer 73. Thepassage 72 communicates with apassage 74 connected through avalve 75 to a gas source under pressure (not shown).

Thespray nozzle 70 comprises acylindrical cavity 76, into whichpassage 77 discharges axially, this passage being jointed to apipe 78 serving to feed the air transporting particles to be sprayed. Adeflector 79 faces the outlet from thepassage 77. As can be seen from FIG. 6, thepassage 72 discharges tangentially into thecavity 76 so that the air from thepassage 72 moves the particles from theconduit 77 in a whirling manner and imparts an electric charge to them. At the outlet from thenozzle 70 these particles create an electric field which extends to an object to be spray coated. The whirling effect produced by the tangential inlet of the air from the passage 72produces not only the electric charge of the particles but also in the chamber defined by the bottom of thecavity 76 and thedeflector 79, a centrifugal effect on the particles. This effect ensures the spreading of the jet at theoutlet nozzle 70 and a permanent sweeping of the nozzle, thus avoiding the risk of clogging by solid particles.

In the embodiment of FIG. 8, apowder spray 80 comprises a body of insulatingmaterial 81 in which is located an insulatingsleeve 82 carrying ametallic member 84 forming anannular counterelectrode 83, while theneedle 85 is connected by aresistance 86, a plug 95 and acontact 96 to a supply cable 87. Themember 84 is joined to an earth wire 88. The outlet from thesleeve 82 communicates with an annular chamber 89 of an atomization nozzle 90 entirely made of an insulating material. The powder to be sprayed is fed to the nozzle by a passage 91. Air under pressure is admitted into pipe 92 which discharges throughperforations 93 into themember 84 and from there into thepassage 82 in the vicinity of theionizer needle 85. In this embodiment the air admitted through the pipe 92 transports into thepassage 82 electric charges which are, as described previously, carried to a high potential at the outlet of thepassage 82. This air is used to spray the powder issuing from the nozzle 90. As the spraying is being carried out, the electric charges are transmitted to the powder particles to be sprayed which are thereby attracted by an object to be coated It will be noted that in this embodiment, thesleeve 82 transporting the electric charges is easily detachable and the unit can be detached and put back into place by simply releasing the nozzle 90 and alocknut 94.

Referring now to FIGS. 9 and 10, anelectrostatic spray device 100 comprises a barrel of an insulatingmaterial 101 with anatomization nozzle 102, the whole being made of an insulating material. The atomization nozzle is supplied with paint through achannel 103, while anannular chamber 104 communicates with the outlet of adetachable cartridge 106 constituting the voltage elevator; shown more clearly in H6. 10. Thiscartridge 106 is received in thepassage 107 of thebarrel 101, it abuts against a joint 108 and is retained in position by acap 110. The cartridge 106 (FIG. 10) is made up of a cartridge body in which is inserted atubular sleeve 111 with the means of ionization mounted in fixed positions; namely aneedle 112 supported by acrucifonn block 113, the needle being engaged axially in the interior of an annularmetallic ring 114 of convergent-divergent form. Theneedle 112 is connected within the cartridge to aresistance 115 whose other terminal is connected by aspring 116 to aconductor terminal 117 covered by an insulatingcap 118. The terminal 117 and thecounterelectrode 114 are in contact with asocket 127 and 119 respectively. As shown in FIG. 9, contact andspring assemblies 120, 123 and 121, 122 mounted in the body of the spray gun electrically connect theneedle 112 and thecounterelectrode 114 respectively to theexcitation cable 124 and to earth via conductingcover 125, which forms the handgrip.

In this embodiment, the air issuing from thesleeve 111 serves both for atomization and for direct transmission of the charge to the particles, given that the nozzle is entirely made of an insulating material. lt will be noted that the generator is mounted in a cartridge which is easily detachable and which can thus be replaced by a new cartridge in case of breakdown.

FIG. 11, shows an embodiment of paint spray gun for a fixed installation, comprising apaintsupply passage 131 feeding anatomization noule 132 consisting of an axially arrangedconductor nozzle 133 and anozzle cap 134 of an insulating material. Theaxial nozzle 133 can be sealed by an insulatingpin 135 controlled in position by apiston 136 movable in acylindrical body 137. The piston moves against the action of aspring 138 under the action of compressed air admitted throughinlet 139 to withdraw the pin from thenozzle 133. This compressed air can escape through apassage 140 discharging into the generator 141 composed, as previously, of aninsulating passage 142 and an ionization means 143. The downstreamend of'the passage 142 discharges into anannular chamber 144, then throughpassages 145 towards an outlet atomization orifice. A collectingelectrode 146 is positioned in thechamber 144, this electrode being connected to themetallic nozzle 133 through the insulating nozzle member.

In this embodiment, the electric charges are thus picked up by theelectrode 146 and finally transferred tonozzle 133. It can be seen that a resistance for stabilizing thedischarge 147 is fixed in theaxial plug 148 of aconnector 149, thisaxial plug 148 being connected to earth and to thecounterelectrode 150 of the ionization device by awire 151.

The embodiment of FIG. 12, has the same general arrangement as that in FIG. 11, with the difference that thenozzle 152 is also made of an insulating material like thecap 134 and aconnection 153 is established from the outlet of thepassage 142 to penetrate into the internal cavity of thenozzle 152 so as to establish an electric link picking up the charges at the outlet of thepassage 142 and conveying them to the interior of the liquid destined to be sprayed, within thenozzle 152, slightly upstream of the discharge from this nozzle. Here, thedischarge stabilization resistance 154 is no longer in series with theneedle 143, but with theionization counterelectrode 150 in the insulatingbody 155 of the spray gun. In this embodiment, thepin 156 for sealing the nozzle is controlled by apiston 157 acted on by the air admitted throughconnection 158, while the air admitted into the passage generating the high-voltage current is fed throughconnection 159.

In FIG. 13, a paint spray gun comprises an insulating body with apassage 151 for the generation of electrical charges at a raised potential discharging into anannular chamber 152 and particles at raised potential communciates these charges to the conductingnozzle 154, which then applies a potential to the jet of paint which circulates within thisnozzle member 154.

Referring supported the embodiment of FIG. 14, a powder spray gun comprises an insulatingbody 160 with achannel 161 supplied with fluidized powder and apassage 162 for the generation of particles at high potential. Thislatter passage 162 discharges into anannular chamber 163 which communicates with the interior of ametallic nozzle 164 throughtangential conduits 165. Adeflector 166 is positioned in the end of theconduit 161 at some distance from its outlet. Thenozzle 164 is supported by a conductor means 167 which serves for collecting the electric charges transmitted by conductivity to the discharge edgel68 of thenozzle 164.

In the embodiment of FIG. 15, an electrostaticpaint spray device 170 of the with with hydrostatic pulverization comprises an insulatingbody 171 withametallic noule 172 of very fine section, generally in the form of a slot, placed on an insulatingsupport 173 located in acover 174. Thesupport 173 abuts amember 175 forming the seat for an insulatingpin 176. Achannel 177 for paint under high pressure communicates by appropriate sealed joints with achamber 178. Atube 179 for generating particles at raised potential is arranged in thecover body 171 of the sprayer and its end leads into anannular chamber 180 with forwardly directedorifices 181. Arigid wire 182 is mounted in thecover 174 and extends from the interior of thechamber 180 to a small distance from the jet of paint sprayed an atomized by hydrostatic action.

In this embodiment, the air coming from thepassage 179 generating the particles at raised potential escapes through theopenings 181 so as to form a series of air jets protecting the paint against any return towards the rear of the pulverized particles. The air, before leaving thechamber 180, is freed from the electric particles which are picked up by theelectrodes 182 whose other end serves to change by discharge the parti cles from the atomized paint spray.

Referring to the embodiment of FIG. 16, a hydrostaticpressure spray gun 190 comprises apaint supply pipe 191 discharging into achamber 192 having apin valve 193 and communicating with anozzle 194 through apassage 195. Thepassage 196 for generating particles at high potential discharges into achamber 197. All the components of this nozzle are made of an insulating material, with the exception of a threadedrod 198 which penetrates into thechamber 197, and which at its other end holds anaxial discharge needle 199 in position which protrudes beyond the nozzle in the middle of the atomized spray jet. In this embodiment, it can be seen that the paint is atomized by the jet of air issuing from thepassage 196 and from theannular chamber 200, which communicates with theexchange chamber 197 for the electric charges in which the charges are collected by therod 198.

Referring now to FIG. 17, a portable paint spray gun comprises ametal handgrip 201 connected to earth to which is fixed an insulatingbarrel 202 at the end of which is positioned apneumatic spray nozzle 203.

Within the insulatingbarrel 202 is arranged a passage forming anozzle 204 supplied through achamber 25 itself joined through apipe 206 to a source of compressed airnot shown. Thenozzle 204 comprises, in the longitudinal direction, first of all a part 204a of a convergent-divergent shape immediately adjacent to thechamber 205, followed by adivergent part 204b, while the rest of the nozzle 2040 is cylindrical.

In this way a nozzle of the Laval type is produced, that is tosay a convergent-divergent nozzle creating in the cylindrical part a flow at supersonic speed presenting the character of regularity and parallelism of streams of air peculiar to this type of flow.

As can be seen, this cylindrical part is followed by amain part 204d following the arc of a circle and discharging into the atmosphere at a lateral position from the spray. Aspray passage 204e feeds thespray nozzle 203, which can be of thezle 204, in the region of the convergent-divergent part 204a, 204b, a means of ionization is provided consisting of apointed electrode 207 connected by acable 208 to a DC source of medium voltage, not shown, the saidelectrode 207 being situated axially in the center of acounterelectrode 209 connected to earth by aconductor 210 of annular form and delimiting the convergentdivergent part 2040, 204b, of thenozzle 204. At a position spaced from the ionization means 207, 209 and as near as possible to thenozzle 203 is placed in the nozzle 204 a charge-collecting member, for example, in the form of a tensionedwire 11. This extends across thepart 204d of the nozzle and is directly connected to ametal nozzle part 212 of thenozzle 203, while the remainder of the nozzle member is insulating.

When the diameter of the part 204a is small (lower than 3 or 4 mm.) a resistance of 10 to 50 megohms is inserted in the ionization circuit so as to stabilize the outlet charge and to avoid the discharge of the junction cable, in series with thepint 207 of the counterelectrode 204a. The member 204a can also be produced in a semiconducting material.

The arrival of paint at thenozzle 212 is affected by a passage shown schematically in 213, this passage being fed from a tank under pressure, or a pump.

In the usual way, the spray gun is provided ,with a control device or trigger 214 controlling the opening and closing of thecompressed air pipe 206, and also possibly the admission of paint and the feeding of the low voltage to theionizer 207, 209. These latter can alternatively be controlled by the airflow in thepipe 206.

In this embodiment thenozzle 204 between the discharge means 207, 209 and thecollector 211 has a length of 5 to 8 centimeters while the diameter in the cylindrical part 2040 is about 6 mm.

Experience has shown that by using a source of compress air of 4 bars, a supersonic flow speed of about450 meters per second was obtained, with a DC excitation voltage on theionizer 207, 209 of 5 kilovolts and a series resistance with thepoint 207 of 20 megohms, which provides at the nozzle 212 a DC voltage of 40 kilovolts at a current of 30 microamperes.

As can be easily shown, these results show that the spray gun in question is completely suitable to be used as a portable electrostatic spray gun, since it does not comprise any element of weightadditional with respect to the spray guns used at present with a separate high-voltage source.

In the embodiment described and shown, the presence of air under pressure is employed in order to derive by means of thenozzle 204e, the .quantity of air sufiicient to supply thepneumatic spraying nozzle 203. In certain cases, there is not an overabundance of air and theshunt 204d to the atmosphere can be suppressed.

Referring finally to FIG. 18, a spray gun is arranged so its its rear part (handle 221 and body 222) are similar to those described in FIG. 17, but here the atomization head is represented in the form of acap 223 mounted to rotate continuously on a pivot 224 constituted by an inlet head 225, comprising thepaint feed channel 226 communicating with the radialchannels 227 discharging opposite one face of thecap 223. Thecap 223 is provided at the rear with a driving device 228 of the blade type opposite which the compressed airpipe 229 discharges, forming the terminal part of the electrostatic generator described in the previous figure.

In this embodiment, when thecap 223 is metal or semiconducting, it is not necessary to provide a charge collector in the pipe 229, the role of the latter being played by the blades 228 of the motor member. However, it is obvious that if an insulating cap is used with a metal or resistive electrode, within or adjacent the edge of this cap, it is then necessary as in the previous embodiment, to arrange a charge collector in the pipe 229 connected electrically to the said electrode.

type creating a whirling action of the air. Upstream of the nozthe generation of high-voltage electricity with the aid of a noncombustible gas such as (nitrogen, carbon dioxide, argon, etc.) or with the aid of a gas and/or. chemically active particles with a sprayed product. The invention also applies to flock spraying as well as to the spraying of agricultural products and to the spraying of powdered metals.

What is claimed is:

l. Electrostatic spraying apparatus including a spray nozzle and a high-voltage generator, said generator comprising a passage for transporting a gaseous fluid to said spray nozzle, said passage having a convergent-divergent portion for imparting a supersonic speed to at least part of said gaseous fluid, and electrode means adjacent-said convergent-divergent portion for transmitting electric charges to said gaseous fluid.

2. Apparatus according to claim 1, including means for injecting solid particles into the passage upstream of the the electrode means.

3. Apparatus according toclaim 2, including means for injecting a volatile liquid into said passage upstream of the electrode means.

4. Apparatus according to claim 1, wherein the outlet of the passage for the gaseous fluid transporting the electric charges is adjacent to the outlet of said spray nozzle, in a position such that the gaseous fluid contributes to the atomization of a liquid sprayed out of the nozzle.

5. Apparatus according to claim 1, including means for injecting particles of a product to be sprayed close to the electrode means.

6. Apparatus according to claim 1, including a chamber into which a passage transporting the product to be sprayed discharges, as well as the passage for the gas transporting the electric charges, and a further passage leading from said chamber towards said spray nozzle.

7. Apparatus according to claim 1, wherein the nozzle is made of an insulating material and the passage for the gas transporting the electric charges discharges into the atmosphere adjacent and coaxially to the periphery of a passage transporting the product to be sprayed.

8. Apparatus according to claim 1, including means for picking up electric charges situated in the passage for the gas transporting the electric charges downstream of said electrode means and convergent-divergent portion, and electric conductor means electrically connecting said pickup means to a passage for transporting the product to be sprayed.

9. Apparatus according toclaim 8, wherein the conductor means is in contact with the product to be sprayed.

10. Apparatus according to claim 9, wherein the conductor means and the pickup means comprises at least one wall of the spray nozzle.

11. Apparatus according toclaim 8, wherein the conductor means tenninates in an ionizing electrode protruding beyond the spray nozzle.

12. Apparatus according to claim 1, wherein the highwoltage generator is constructed as a detachable cartridge.

13. Apparatus according to claim 3, ,wherein the means for injecting the volatile liquid is a wick immersed in a tank and discharging into the passage.

14. Apparatus according to claim 1, in which said nozzle is rotatable and driven in rotation by said gaseous fluid.

l5. Electrostatic spraying apparatus comprising a body carrying a spray nozzle, a passage in said body leading to the region of said nozzle a convergent-divergent portion located upstream of said passage, an electrode arranged adjacent said convergent-divergent portion, means for applying a voltage to said electrode, means for feeding a gaseous fluid to said convergent-divergent portion so as to impart a supersonic speed to at least part of said fluid, as said fluid passes along said passage carrying an electric charge to the region of said spray nozzle.

16. In electrostatic spraying apparatus, a high-voltage generator comprising a passage, a convergent-divergent portion communicating with said passage, electrode means adjacent said convergent-divergent portion, means for applying a voltage to said electrode means, and means for feeding a gaseous fluid to pick up electric charges from said electrode means and so that said charged fluid flows down said passage at least partially at supersonic speed.

17. Electrostatic spraying apparatus including a spray nozzle and a high-voltage generator, said generator comprising a barrel made of insulating material and defining a passage adapted to carry a pressurized gaseous fluid from a source of such fluid to said nozzle, and electrode means in said passage for transmitting electrical charges to said fluid, said passage having a convergent-divergent portion adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid.

18. Electrostatic spraying apparatus as claimed inclaim 17 comprising a counterelecrode in said passage adjacent said electrode and adapted to be connected to ground.

19. Electrostatic spraying apparatus as claimed inclaim 18 in which said counterelectrode defines said convergent-divergent portion.

20. Electrostatic spraying apparatus as claimed inclaim 18 in which a barrel defines a second passage for conducting a material to be sprayed from a source of such material to said nozzle, and said nozzle comprises means for causing said gaseous fluid to impinge on said material to be sprayed, and thereby transmit thereto electrical charges transmitted to said fluid by said electrode.

21. Electrostatic spraying apparatus as claimed inclaim 18 in which said barrel defines a second passage for conducting material to be sprayed to said nozzle and said nozzle comprises electrically conductive means positioned adjacent the ends of said passages to contact both said gaseous fluid and said I material to be sprayed, and thereby transmit to said material to be sprayed electrical charges acquired by said fluid from said electrode.

22. Electrostatic spraying apparatus as claimed inclaim 18 comprising means for introducing a material to be sprayed into said passage upstream of said convergent-divergent portion.

23. Electrostatic spraying apparatus as claimed inclaim 18 comprising means for introducing a material to be sprayed .into said passage upstream ofsaid electrode.

24. Electrostatic spraying apparatus as claimed inclaim 18 in which said barrel defines a chamber connecting said passage to said nozzle and comprising an additional passage for material to be sprayed which terminates in said chamber.

25. Electrostatic spraying apparatus as claimed inclaim 18 in whichsaid electrode is upstream of said convergent-divergent portion and comprising means for introducing a material to be sprayed into-said passageway upstream of said convergent-divergent portion but downstream of said electrode.

26. Electrostatic spraying apparatus as claimed inclaim 21 in which said nozzle comprises a head of insulating material defining a separate opening aligned with each passage, and said electrically conductive means is a conductor extending into both openings.

27. Electrostatic spraying apparatus as claimed inclaim 21 in which said nozzle comprises an electrically conductive part defining an opening aligned with said second passage, and

positioned to be contacted by fluid emerging from the passage having said convergent-divergent portion.

28. Electrostatic spraying apparatus as claimed inclaim 21 in which said nozzle is electrically conductive, and the passage containing said electrode reaches said nozzle through a conductive collector ring electrically connected to the walls of said nozzle, said nozzle being provided with a deflector positioned to deflect said material to be sprayed against the wall of said nozzle, whereby electrical charges imparted to said gaseous fluid by said-electrode are conducted from said gaseous fluid by said collector to said nozzle and imparted by said nozzle to said material to be sprayed.

29., Electrostatic electrical conductor apparatus as claimed inclaim 18 in which said nozzle comprises an electrically conductive part at the end of said second passage, the passage having said convergent-divergent portion being divided into two branches downstream of said convergent-divergent portion, with one of said branches leading to said nozzle so as to conduct to said nozzle particles of gaseous fluid charged by said electrode, and the other bypassing said nozzle and leading to the ambient atmosphere, and said apparatus further comprising an electrical conductor athwart said other branch and leading to the electrically conductive part of said nozzle.

30. Electrostatic spraying apparatus as claimed inclaim 18 in which said nozzle comprises a stationary electrically conductive part at the outlet of said second passage, and a rotatable charge collector made of electrically conductive material, said charge collector being positioned in electrical contact with said stationary electrically conductive part and comprising blades athwart the nozzle end of the passage having said convergent-divergent portion, whereby said gaseous fluid acquires an electrical charge from said electrode, is accelerated by said convergent-divergent portion, rotates said charge collector by impinging on said blades, and transmits to said charge collector, and through said charge collector to said stationary nozzle portion the electrical charge acquired from said electrode.

31. Electrostatic apparatus as claimed inclaim 18 comprising valve means for controlling the flow of fluid in said passage.

32. Electrostatic apparatus as claimed inclaim 21 comprising valve means for controlling flow through each passage, and single actuating means for simultaneously actuating both valves.

33. In combination, electrostatic spraying apparatus as claimed inclaim 18, a source of gaseous fluid under a pressure of several atmospheres connected to said passage, and a source of electric power connected to supply to said electrode an excitation voltage of several kilovolts.

34. Electrostatic spraying apparatus for use with a source of gaseous fluid under a pressure of several atmospheres and a source of direct voltage adapted to supply a voltage of several kilovolts, said spraying apparatus including a spray nozzle and a high-voltage generator, and said generator comprising a barrel made of insulating material, said barrel defining a passage for connecting said gaseous fluid source to said nozzle, an electrode in said passageway adapted to transmit electric charges from said voltage source to the gaseous fluid in said passage and a counterelectrode in said passageway adapted to be connected to ground, said passage having a convergentdivergent portion therein adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid, thereby increasing the voltage of the electrical charges transitted thereto, and means for introducing a fluent material to be sprayed into said passage so that at least some of said electrical charges are transferred from said gaseous fluid to said material.

35. Electrostatic spraying apparatus for use with a source of gaseous fluid under a pressure of several atmospheres and a source of direct voltage adapted to supply a voltage of several kilovolts, said spraying apparatus including a spray nozzle and a high-voltage generator, and said generator comprising a barrel made of insulating material, said barrel defining a passage for connecting said gaseous fluid source to said nozzle, an electrode in said passageway adapted to transmit electric charges from said voltage source to the gaseous fluid in said passage and a counterelectrode in said passageway adapted to be connected to ground, said passage having a convergentdivergent portion therein adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid, thereby increasing the voltage of the electrical charges transmitted thereto, said barrel defining an additional passage adapted to lead a fluent material to be sprayed to said nozzle, and electrically conductive means positioned to conduct electric charges from said gaseous fluid to said fluent material to be sprayed.

Claims (35)

1. Electrostatic spraying apparatus including a spray nozzle and a high-voltage generator, said generator comprising a passage for transporting a gaseous fluid to said spray nozzle, said passage having a convergent-divergent portion for imparting a supersonic speed to at least part of said gaseous fluid, and electrode means adjacent said convergent-divergent portion for transmitting electric charges to said gaseous fluid.

2. Apparatus according to claim 1, including means for injecting solid particles into the passage upstream of the the electrode means.

3. Apparatus according to claim 2, including means for injecting a volatile liquid into said passage upstream of the electrode means.

4. Apparatus according to clAim 1, wherein the outlet of the passage for the gaseous fluid transporting the electric charges is adjacent to the outlet of said spray nozzle, in a position such that the gaseous fluid contributes to the atomization of a liquid sprayed out of the nozzle.

5. Apparatus according to claim 1, including means for injecting particles of a product to be sprayed close to the electrode means.

6. Apparatus according to claim 1, including a chamber into which a passage transporting the product to be sprayed discharges, as well as the passage for the gas transporting the electric charges, and a further passage leading from said chamber towards said spray nozzle.

7. Apparatus according to claim 1, wherein the nozzle is made of an insulating material and the passage for the gas transporting the electric charges discharges into the atmosphere adjacent and coaxially to the periphery of a passage transporting the product to be sprayed.

8. Apparatus according to claim 1, including means for picking up electric charges situated in the passage for the gas transporting the electric charges downstream of said electrode means and convergent-divergent portion, and electric conductor means electrically connecting said pickup means to a passage for transporting the product to be sprayed.

9. Apparatus according to claim 8, wherein the conductor means is in contact with the product to be sprayed.

10. Apparatus according to claim 9, wherein the conductor means and the pickup means comprises at least one wall of the spray nozzle.

11. Apparatus according to claim 8, wherein the conductor means terminates in an ionizing electrode protruding beyond the spray nozzle.

12. Apparatus according to claim 1, wherein the high-voltage generator is constructed as a detachable cartridge.

13. Apparatus according to claim 3, wherein the means for injecting the volatile liquid is a wick immersed in a tank and discharging into the passage.

14. Apparatus according to claim 1, in which said nozzle is rotatable and driven in rotation by said gaseous fluid.

15. Electrostatic spraying apparatus comprising a body carrying a spray nozzle, a passage in said body leading to the region of said nozzle, a convergent-divergent portion located upstream of said passage, an electrode arranged adjacent said convergent-divergent portion, means for applying a voltage to said electrode, means for feeding a gaseous fluid to said convergent-divergent portion so as to impart a supersonic speed to at least part of said fluid, as said fluid passes along said passage carrying an electric charge to the region of said spray nozzle.

16. In electrostatic spraying apparatus, a high-voltage generator comprising a passage, a convergent-divergent portion communicating with said passage, electrode means adjacent said convergent-divergent portion, means for applying a voltage to said electrode means, and means for feeding a gaseous fluid to pick up electric charges from said electrode means and so that said charged fluid flows down said passage at least partially at supersonic speed.

17. Electrostatic spraying apparatus including a spray nozzle and a high-voltage generator, said generator comprising a barrel made of insulating material and defining a passage adapted to carry a pressurized gaseous fluid from a source of such fluid to said nozzle, and electrode means in said passage for transmitting electrical charges to said fluid, said passage having a convergent-divergent portion adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid.

18. Electrostatic spraying apparatus as claimed in claim 17 comprising a counterelecrode in said passage adjacent said electrode and adapted to be connected to ground.

19. Electrostatic spraying apparatus as claimed in claim 18 in which said counterelectrode defines said convergent-divergent portion.

20. Electrostatic spraying apparatus as claimed in claim 18 in which a barrel defines a second passage for conducting a material to be sprAyed from a source of such material to said nozzle, and said nozzle comprises means for causing said gaseous fluid to impinge on said material to be sprayed, and thereby transmit thereto electrical charges transmitted to said fluid by said electrode.

21. Electrostatic spraying apparatus as claimed in claim 18 in which said barrel defines a second passage for conducting material to be sprayed to said nozzle and said nozzle comprises electrically conductive means positioned adjacent the ends of said passages to contact both said gaseous fluid and said material to be sprayed, and thereby transmit to said material to be sprayed electrical charges acquired by said fluid from said electrode.

22. Electrostatic spraying apparatus as claimed in claim 18 comprising means for introducing a material to be sprayed into said passage upstream of said convergent-divergent portion.

23. Electrostatic spraying apparatus as claimed in claim 18 comprising means for introducing a material to be sprayed into said passage upstream of said electrode.

24. Electrostatic spraying apparatus as claimed in claim 18 in which said barrel defines a chamber connecting said passage to said nozzle and comprising an additional passage for material to be sprayed which terminates in said chamber.

25. Electrostatic spraying apparatus as claimed in claim 18 in which said electrode is upstream of said convergent-divergent portion and comprising means for introducing a material to be sprayed into said passageway upstream of said convergent-divergent portion but downstream of said electrode.

26. Electrostatic spraying apparatus as claimed in claim 21 in which said nozzle comprises a head of insulating material defining a separate opening aligned with each passage, and said electrically conductive means is a conductor extending into both openings.

27. Electrostatic spraying apparatus as claimed in claim 21 in which said nozzle comprises an electrically conductive part defining an opening aligned with said second passage, and positioned to be contacted by fluid emerging from the passage having said convergent-divergent portion.

28. Electrostatic spraying apparatus as claimed in claim 21 in which said nozzle is electrically conductive, and the passage containing said electrode reaches said nozzle through a conductive collector ring electrically connected to the walls of said nozzle, said nozzle being provided with a deflector positioned to deflect said material to be sprayed against the wall of said nozzle, whereby electrical charges imparted to said gaseous fluid by said electrode are conducted from said gaseous fluid by said collector to said nozzle and imparted by said nozzle to said material to be sprayed.

29. Electrostatic spraying apparatus as claimed in claim 18 in which said nozzle comprises an electrically conductive part at the end of said second passage, the passage having said convergent-divergent portion being divided into two branches downstream of said convergent-divergent portion, with one of said branches leading to said nozzle so as to conduct to said nozzle particles of gaseous fluid charged by said electrode, and the other bypassing said nozzle and leading to the ambient atmosphere, and said apparatus further comprising an electrical conductor athwart said other branch and leading to the electrically conductive part of said nozzle.

30. Electrostatic spraying apparatus as claimed in claim 18 in which said nozzle comprises a stationary electrically conductive part at the outlet of said second passage, and a rotatable charge collector made of electrically conductive material, said charge collector being positioned in electrical contact with said stationary electrically conductive part and comprising blades athwart the nozzle end of the passage having said convergent-divergent portion, whereby said gaseous fluid acquires an electrical charge from said electrode, is accelerated by said convergent-divergent portion, rotates said charge collector by impinging on said blades, and transmits to said charge collector, and through said charge collector to said stationary nozzle portion the electrical charge acquired from said electrode.

31. Electrostatic apparatus as claimed in claim 18 comprising valve means for controlling the flow of fluid in said passage.

32. Electrostatic apparatus as claimed in claim 21 comprising valve means for controlling the flow through each passage, and single actuating means for simultaneously actuating both valves.

33. In combination, electrostatic spraying apparatus as claimed in claim 18, a source of gaseous fluid under a pressure of several atmospheres connected to said passage, and a source of electric power connected to supply to said electrode an excitation voltage of several kilovolts.

34. Electrostatic spraying apparatus for use with a source of gaseous fluid under a pressure of several atmospheres and a source of direct voltage adapted to supply a voltage of several kilovolts, said spraying apparatus including a spray nozzle and a high-voltage generator, and said generator comprising a barrel made of insulating material, said barrel defining a passage for connecting said gaseous fluid source to said nozzle, an electrode in said passageway adapted to transmit electric charges from said voltage source to the gaseous fluid in said passage and a counterelectrode in said passageway adapted to be connected to ground, said passage having a convergent-divergent portion therein adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid, thereby increasing the voltage of the electrical charges transitted thereto, and means for introducing a fluent material to be sprayed into said passage so that at least some of said electrical charges are transferred from said gaseous fluid to said material.

35. Electrostatic spraying apparatus for use with a source of gaseous fluid under a pressure of several atmospheres and a source of direct voltage adapted to supply a voltage of several kilovolts, said spraying apparatus including a spray nozzle and a high-voltage generator, and said generator comprising a barrel made of insulating material, said barrel defining a passage for connecting said gaseous fluid source to said nozzle, an electrode in said passageway adapted to transmit electric charges from said voltage source to the gaseous fluid in said passage and a counterelectrode in said passageway adapted to be connected to ground, said passage having a convergent-divergent portion therein adjacent said electrode which imparts a supersonic speed to at least part of said gaseous fluid, thereby increasing the voltage of the electrical charges transmitted thereto, said barrel defining an additional passage adapted to lead a fluent material to be sprayed to said nozzle, and electrically conductive means positioned to conduct electric charges from said gaseous fluid to said fluent material to be sprayed.

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