ELECTROSTATIC SPRAY NOZZLE

Abstract: An electrostatic nozzle assembly for coating row crops and other plants with electrostatically charged particles of pesticide including a nozzle body (12) formed with a passageway (22) to receive air and an earthed stream of waterborne pesticide for delivery through a nozzle tip (74) to an inductor ring (48) mounted between the nozzle body (12) and an air nozzle having a discharge orifice (32). As the stream of waterborne pesticide is projected from the nozzle tip (74), it is impacted with a swirling, spirally moving stream of air produced by a swirl plate (64) having a plurality of tapered air channels (86) oriented tangentially relative to the pesticide stream and communicating with the air passageway (22) in the nozzle body (12). The inductor ring (48) inductively charges the pesticide in the terminal end of the nozzle tip (74). The swirling air stream atomizes the charged pesticide stream expelled from the nozzle tip (74) into finely divided particles, and then imparts the swirling motion to the charged particles which fan radially outwardly in a wide spray pattern when ejected from the discharge orifice (32) in the air nozzle. An electrical standoff is also provided by forming the air nozzle with an irregularly-shaped outer surface which lengthens the electrical path which charged particles collected on the air nozzle would have to travel to migrate to an earthed support for the nozzle body or the nearest earthed point.

Description: The invention relates to an electrostatic nozzle assembly. In electrostatic spray coating a stream of coating material is atomized into finely divided particles which are electrostatically charged. The charged particles are then directed at a surface to be coated which is held at a different electrical potential to that of the particles. Due to the electrostatic attraction and the proximity of the charged particles to the surface to be coated, electrostatic forces move the particles onto the surface where they are deposited to form a coating or layer. Many electrostatic coating devices employ high voltages, e.g., 50 kilovolts or more, to create a corona discharge through which the particles pass to become electrostatically charged. One problem with employing high voltages in the application of electrostatic charges to waterborne pesticides for deposition onto trees or other crops, is that waterborne pesticides are highly conductive and the charge applied thereto is transferred back through the pesticide stream to its holding tank. The tank must therefore be electrically isolated from earth. When isolated, the tank becomes charged with the same high voltage as the electrical field, and must be electrically insulated and isolated from persons spraying the pesticide to avoid serious electrical hazards. Special insulation and mounting of the holding tank of a pesticide sprayer adds substantially to its costs, and therefore the use of corona electrostatic charging of waterborne pesticides has been traditionally cost prohibitive and dangerous. An electrostatic spraying device for agricultural applications which employs low voltage inductively to charge a stream of waterborne pesticides or similar treatment chemicals is shown, for example, in Patent Specification US-A-4,004,733 to Law. Electrostatic spray nozzles of this general kind comprise a nozzle body formed with a fluid passageway in which a stream of waterborne pesticide is atomized into finely divided droplets or particles. An electrode is mounted in the nozzle body, in axial alignment with the fluid passageway, and is operable electrostatically to charge the particles forming the atomized stream before they exit the nozzle body. The electrostatic charge is applied to the fluid stream at the point of atomization by induction using a voltage on about 2 kilovolts, as opposed to ionized field systems which typically employ voltages of 50 kilovolts to 100 kilovolts or higher. The charged particles which are entrained in the stream of air are then expelled through the fluid passageway in the nozzle body, which propels the charged particles onto the trees, grapevines or row crops to be coated. One limitation of spray devices such as disclosed in US-A-4,004,733 to Law, is that it produces a narrow spray pattern. Another limitation of electrostatic spray devices of the kind described in the Law patent involves the problem of earthing the electrode to the position at which the dielectric nozzle body is connected to earth potential. Charged particles emitted from the discharge orifice accumulate on the exterior surface of the nozzle body near the discharge orifice, and readily migrate along the nozzle body eventually reaching its connection to earth. Earthing of the electrode via the thin film of particles formed along the nozzle body and emitted from the discharge orifice reduces the charging efficiency of the electrode and limits the effectiveness of the spray device in completely coating the target trees or other crops. Yet another limitation of the prior art devices is that they do not comprise multiple component assemblies wherein the key components can be easily disassembled and reassembled for maintenance, repair and replacement of worn or defective parts. According to one aspect of the invention there is provided an electrostatic nozzle assembly for coating objects comprising: a nozzle body having an air passageway to receive a stream of air and a liquid passageway to receive a stream of liquid; and an air nozzle mounted on the nozzle body and formed with a discharge orifice; characterized by an inductor ring formed with an aperture and mounted between the nozzle body and the air nozzle so that the aperture axially aligns with the discharge orifice; charging means for applying an electrical potential to the inductor ring; means communicating with the liquid passageway for directing the stream of liquid into the aperture of the inductor ring; and means communicating with the air passageway for imparting a swirling, rotational motion to the stream of air, the swirling stream of air being directed into contact with the liquid stream to form finely divided particles within the aperture of the inductor ring, the particles becoming inductively charged by the inductor ring and entrained within the swirling stream of air for discharge onto the objects to be coated. Such a nozzle assembly can provide a wide spray pattern of electro­ statically charged particles for deposition of pesticides onto trees or other crops to be coated, and can avoid earthing of the electrode which imparts the electrostatic charge to the pesticide to maintain high charging efficiency. The swirling, substantially spiral motion of the air stream, and the charged particles entrained therein, can produce a wide spray pattern since the electrostatically charged particles tend to continue to rotate after they exit the discharge orifice and thus quickly fan radially outwardly in a wide pattern toward the objects to be coated. Preferably the outer surface of the nozzle assembly near the discharge orifice is formed with an irregular shape to lengthen the electrical path between electrostatically charged particles ejected from the discharge orifice, and the position at which the nozzle body of the spray device is connected to earth. The nozzle assembly can be a multiple component assembly wherein the components are releasably secured together and can be easily disassembled for maintenance and repair, or replacement of key components. Thus a stream of waterborne pesticide, held at or near earth potential, can be directed into the aperture of the inductor ring where it is atomized into finely divided particles by a swirling, substantially spirally moving stream of air. A flow path of the stream of waterborne pesticide to the inductor ring, and atomization of the stream thereat, is provided by a swirl plate which is disposed between the inductor ring and nozzle body. In a presently preferred embodiment the swirl plate is formed with a tapered central bore communicating with the liquid passageway formed in the nozzle body. The tapered central bore terminates at a nozzle tip having an outlet disposed approximately midway into the aperture of the inductor ring. Waterborne pesticide can thus be directed from the liquid passageway, to the tapered central bore and through the outlet in the nozzle tip into the aperture of the inductor ring. The swirl plate is also formed with a plurality of atomizing air channels which communicate with the air passageway and atomize the stream of waterborne pesticide discharged into the aperture of the inductor ring by the nozzle tip. In a presently preferred embodiment, the channels each extend radially outwardly from the nozzle tip of the central bore, substantially tangentially thereto, and terminate at an annular groove formed in the swirl plate which communicates with the air passageway. The channels preferably are tapered and decrease in cross section from the annular groove to the nozzle tip. Air introduced into the annular groove through the air passageway is directed by the channels along flow paths which are substantially tangential to the nozzle tip of the central bore and the stream of waterborne pesticide discharged therefrom. A swirling, spirally moving air stream is therefore created by the channels at the outlet of the nozzle tip which is accelerated by the tapered channels towards the nozzle tip and contacts the stream of waterborne pesticide at its highest velocity thereat to form finely divided droplets or particles. Preferably, the nozzle tip of the central bore is disposed within the aperture of the inductor ring so that the waterborne pesticide stream is atomized by the swirling air stream in the presence of the electrostatic field created by the inductor ring. An induced electrostatic charge is imparted to each particle by the inductor ring for deposition upon the article to be coated. The electrostatically charged particles become entrained within the swirling, spirally moving air stream which imparts that same motion to the charged particles. Once expelled from the discharge orifice of the air nozzle, the charged particles tend to continue to move with the same swirling, spiral motion and therefore fan radially outwardly from the discharge orifice to form a wide angle spray pattern for deposition onto trees, vines or row crops to be coated. It is contemplated that in some applications, fewer electrostatic nozzle assemblies according to the invention would be needed to achieve the same coverage of pesticide on the target trees or crops, as compared to prior art spray nozzles. In addition to the atomization of the pesticide stream and swirling motion imparted to the charged particles of pesticide which produces a desirably wide pattern, the air stream produced by the swirl plate can create an air barrier between the inductor ring and the waterborne pesticide. If the inductor ring became wetted with a film of the waterborne pesticide, a conductive path from the inductor ring to earth via the pesticide stream could be created which would cause the inductor ring to become earthed and ineffective in charging the atomized particle stream. The air barrier created by the swirling stream of air from the swirl plate is therefore important in maintaining the inductor ring and adjacent housing dry. An electrical standoff can be provided between the discharge orifice of the air nozzle and an earthed bracket which mounts the nozzle body by providing the air nozzle with an annular wall which extends outwardly from the discharge orifice forming a cavity into which the charged particle stream is discharged. The exterior of the annular wall includes grooves which form an irregular-shaped outer surface having a plurality of ridges and recesses. In normal operation of the nozzle assembly some of the charged particles emitted from the discharge orifice can collect on the wall of the air nozzle and will tend to migrate toward the earthed bracket. The ridges and recesses form an extended or lengthened path which impedes movement of the charged particles along the wall of the air nozzle to the bracket which earths the nozzle body. This extended or lengthened path mechanically impedes the flow of particles along the electric field lines, effectively lengthening the electrical standoff between the discharge orifice and earthed bracket without increasing the overall physical length of the air nozzle or nozzle body. Preferably, the wall of the air nozzle is also formed with an inner surface having a taper which increases in cross section as it extends outwardly from the discharge orifice. It has been found that such a tapered surface tends to collect charged particles emitted from the discharge orifice and causes them to drip off the air nozzle before the charged particles can migrate to the outer surface of the air nozzle wall. It is believed that this occurs because of the shape of the electric field lines produced by the charged particles emitted from the discharge orifice. According to another aspect of the invention there is provided an electrostatic nozzle assembly for coating objects comprising: a nozzle body having an air passageway to receive a stream of air, a liquid passageway to receive a stream of liquid; and an electrical passageway to receive an electrical conduit; characterized by a swirl plate positioned adjacent the nozzle body and having a central bore and a plurality of channels communicating with the air passageway to receive the stream of air therefrom, each of the channels extending radially outwardly from the central bore along an axis substantially tangential thereto, the channels imparting a swirling, rotational motion to the stream of air with respect to the axis of the central bore; a substantially disc-shaped inductor ring formed with an aperture and positioned adjacent the swirl plate; an air nozzle formed with a discharge orifice and positioned adjacent the inductor ring; charging means for applying an electrical potential through the electrical conduit means in the electrical passageway to the inductor ring; and releasable securing means for releasably securing the swirl plate adjacent the nozzle body, the inductor member adjacent the swirl plate, and the air nozzle adjacent the inductor member, with the central bore of the swirl plate, the aperture of the inductor ring, and the discharge orifice of the air nozzle in an aligned position. The invention is diagrammatically illustrated by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevational view in partial cross section of an electrostatic nozzle assembly according to the invention; Figure 2 is an enlarged view in partial cross section of a portion of the nozzle assembly shown in Figure 1; and Figure 3 is a cross sectional view taken generally along line 3-3 of Figure 1 showing the bottom surface of a swirl plate. Referring to the drawings, an electrostatic nozzle assembly 10 includes a nozzle body 12 having a yoke 14 at its upper end which receives a mounting bracket 16 connected thereto by a pin 18. The bracket 16 is earthed as indicated at 20. The nozzle body 12 can be pivoted with respect to the bracket 16 due to the pin 18 and yoke 14 connection. The nozzle body 12 is formed of dielectric material and includes an air passageway 22, a liquid passageway 24 and an electrical passageway 26 all of which extend longitudinally, that is to say in the direction from the base 13 of nozzle body 12 towards the yoke 14. Suitable hoses (not shown) connect sources of air, and liquid in the form of waterborne pesticide, to the air and liquid passageways 22, 24, respectively. An electrical cable 25 from a source of relatively low voltage 27 is connected to the nozzle body 12 at the electrical passageway 26. Mounted at the base 13 of the nozzle body 12 is an air nozzle 28 formed of dielectric material. The air nozzle 28 is secured in place by a nozzle nut 30, also formed of dielectric material, having a radial flange 31 and internal threads which engage external threads formed on the outer surface 15 of the nozzle body 12. In the illustrated embodiment, the air nozzle 28 is formed with a conical-shaped discharge orifice 32 which terminates within a cavity 34 defined by an annular wall 36. The annular wall 36 has an inner surface 38 formed in a generally frusto-conical shape which increases in cross section from the discharge orifice 32 outwardly relative to the axis of the discharge orifice 32. The exterior of the annular wall 36 is formed with grooves 40 forming an outer surface 42 of irregular shape having a plurality of recesses and ridges. An electrode in the form of an inductor ring 48 having a central aperture 50 rests atop the air nozzle 28 so that the aperture 50 is axially aligned with the discharge orifice 32 in the air nozzle 28. The inductor ring 48 is preferably formed of an electrically conductive material which does not corrode in the presence of liquid pesticide or similar chemicals. A relatively low voltage, preferably of about 1,000 volts, is applied to the inductor ring 48 to create an electrostatic field across its aperture 50. Electrical potential is applied to the inductor plate 48 through the electrical passageway 26 which contains a pin 52 disposed at the base of the electrical passageway 26 and having a tip 54 mounted to the inductor plate 48. The upper end of the pin 52 is formed with a contact 58 which engages a spring-biased plunger 60 within the passageway 26 and commercially available from Jurgens, Inc. of Cleveland, Ohio under Part No. 27226. The plunger 60 is disposed between the pin 52 and a slug 62 mounted within the uppermost portion of the electrical passageway 26. The slug 62 is a section of electrically conductive material which is connected directly to the electrical cable 25 from the source 27 of electrical potential. The slug 62, the plunger 60 and the pin 52 together provide an electrical path from the source 27 to the inductor plate 48. The spring-biased plunger 60 maintains the elements in electrical contact with one another to ensure that the inductor plate 48 is constantly charged. The electrostatic nozzle assembly 10 is operable to atomize a stream of waterborne pesticide into finely divided particles, electrostatically charge the particles and propel the charged particles onto plants or crops to be coated through the discharge orifice 32 of the air nozzle 28. The liquid stream is directed to the inductor ring 48, charged, atomized and then carried away by a stream of swirling air formed by a swirl plate 64. The swirl plate 64 is made of dielectric material and is positioned directly atop the inductor plate 48 and is separated from the base 13 of the nozzle body 12 by a gasket 66 formed of a flexible, dielectric material. Both the swirl plate 64 and the gasket 66 are formed with a throughbore to receive the pin 52 connected to the inductor plate 48. Considering first the delivery of waterborne pesticide to the inductor ring 48, a central bore 68 is formed in the swirl plate 64 in axial alignment with the liquid passageway 24 which tapers radially inwardly from a top surface 70 of the swirl plate 64 to a bottom surface 72 thereof. The central bore 68 terminates at a nozzle tip 74 having an outlet 75 which extends outwardly from the bottom surface 72 of the swirl plate 64 and approximately midway into the depth of the aperture 50 of the inductor plate 48 beneath. Waterborne pesticide introduced into the liquid passageway 24 flows through a strainer 76 having a check valve (not shown), into the central bore 68 of the swirl plate 64 and then through the outlet 75 in the nozzle tip 74 into the aperture 50 of the inductor plate 48. The strainer 76 is commercially available from Spraying Systems Company of Wheaton, Illinois under Part No. 4193A. In order to control the flow of waterborne pesticides supplied through the liquid passageway 24, an orifice plate 78 having a metering orifice 80 is positioned between the strainer 76 and the nozzle tip 74 atop an annular shoulder 82 formed in the central bore 68. The orifice plate 78 functions to meter the flow of waterborne pesticide from the liquid passageway 24, and directs a stream of waterborne pesticide toward the nozzle tip 74. A turbulence pin 84 is mounted to the walls of the swirl plate 64 within the central bore 68, substantially transverse to the orifice 80 in the orifice plate 78, to deflect the waterborne pesticide stream emitted through the orifice 80. The pin 84 helps reduce the velocity of the stream and induces turbulence in the stream so that it can be properly atomized and electro­ statically charged as described in detail below. The orifice plate 78 is commercially available from Spraying Systems Company under Part No. 4916-16. Preferably, the atomization takes place within the aperture 50 of the inductor plate 48 where the stream is discharged from the outlet 75 of the nozzle tip 74. Referring to Figure 3, atomization of the waterborne pesticide stream is achieved by a plurality of channels 86 formed in the swirl plate 64. The channels 86 extend along the bottom surface 72 of the swirl plate 64 and taper downwardly from an annular groove 88 formed in the upper portion 70 of the swirl plate 64 to the central bore 68. The annular groove 88 communicates with the air passageway 22. Each tapered channel 86 decreases in cross section from the annular groove 88 to the central bore 68. Preferably, the channels 86 have longitudinal axes which are substantially tangential to the central bore 68 and the outlet 75 of the nozzle tip 74. Each of the channels 86 therefore defines a flow path for the air supplied by the air passageway 22 which is substantially tangential to the outlet 75 of the nozzle tip 74. The channels 86 thus produce a swirling, essentially spiral-shaped flow of air which is accelerated from the annular groove 88 toward the nozzle tip 74, due to the tapered shape of the channels 86. This accelerating flow of air reaches the point of maximum geometric constriction, and therefore maximum velocity in the space between the nozzle tip 74 and the wall of the aperture 50 of inductor ring 48. With the accelerating swirling air stream reaching maximum velocity of the outlet end 75 of the nozzle tip 74, atomization of the waterborne stream of pesticide as it is ejected from the outlet end 75 is optimally achieved to form discrete, finely divided droplets or particles. The air streams from the channels 86 impart the same swirling, substantially spiral motion to the atomized particle stream. Charging of the waterborne pesticide stream occurs within the aperture 50 of the inductor ring 48. It is believed that the leading end of the waterborne pesticide stream ejected from the nozzle tip 74 is subjected to the electrostatic field created by the inductor ring 48 which has a sufficiently intense negative charge to drive the electrons in the stream back through the stream to earth. This process is enabled by the fact that the pesticide stream is conductive and is itself earthed through the pesticide column leading back to the earthed supply tank (not shown). With the free electrons driven back towards earth and away from the terminal end of the pesticide stream in the nozzle tip 74, the leading end of the stream has an overall positive charge. The leading end of the waterborne pesticide stream is then atomized by the swirling air stream from the channels 86 forming finely divided particles having a positive charge, or, of a polarity opposite to that of the inductor ring 48. The charged particles are then discharged through the discharge orifice 32 of the air nozzle 28 for deposition upon row crop or other plants to be coated with pesticide. Because the charged particle stream of pesticide is entrained within a swirling stream of air, it tends to continue the spiral or swirling motion after discharge from the discharge orifice 32. This swirling motion causes the particle stream quickly to fan radially outwardly from the discharge orifice 32 to form a wide spray pattern 90 which ensures coverage of the plants to be coated. See Figure 2. The air stream produced by the channels 86 of the swirl plate 64 forms a high velocity air barrier between the inductor plate 48 and the stream of waterborne pesticide. This is important, because the inductor ring 48 must be maintained at its full electrical potential efficiently to impart an electrostatic charge to the particles. If the stream of waterborne pesticide, which is held at earth potential, was permitted to wet the surface of the inductor ring 48, a conductive path from the inductor ring 48 to earth through the pesticide stream and earthed supply tank could be created which would earth the inductor ring 48 and render it ineffective in charging the atomized particle stream. The barrier of air created by the channels 86 of the swirl plate 64 effectively prevents the waterborne pesticide from wetting the surface of the inductor plate 48 and therefore greatly enhances its charging efficiency. The charged particles emitted from the discharge orifice 32 of the air nozzle 28 are propelled toward a target plant by the air stream supplied from the air passageway 22. During normal operating conditions, it is possible that at least a portion of the charged particles will collect upon the inner surface 38 and the outer surface 42 of the annular wall 36 of the air nozzle 28. The charged particles will tend to migrate along the wall 36 and the outer wall 15 of the nozzle body 12 toward the earthed support bracket 16 due to the electrostatic attraction therebetween. Such migration of charged particles is resisted by the air nozzle 18 in two respects. Firstly, the inner surface 38 of the annular wall 36 is formed in a generally conical shape. It has been found that such shape tends to collect charged particles due to the lines of the electric field produced by the charged particles as they are emitted from the discharge orifice 32. The charged particles collected on the inner surface 38 of the annular wall 36 simply drip away instead of migrating to the outer surface 42 of the wall 36. Secondly, an electrical standoff is provided by the irregular-shaped outer surface 42 of the annular wall 36 and the nozzle nut 30 between the inductor ring 48 and the earthed bracket 16. The recesses and ridges formed by the grooves 40, and the radial flange 31 of the nozzle nut 30, tend to disrupt the flow of particles along the electric field produced by the charged particles emitted from the discharge orifice 32 which lengthens the electrical path between the discharge orifice 32 and the earthed bracket 16. In addition, the grooves 40 and radial flange 31 lengthen the physical and electrical path along which charged particles would have to move in order to migrate along the outer surface 42 of the air nozzle 28 toward the earthed bracket 16. The electrical and physical paths created by the grooves 40 and the radial flange 31 is effectively electrically lengthened without physically increasing the length of the air nozzle 28. This substantially eliminates the possibility of earthing the inductor ring 48 which would greatly reduce its efficiency in charging the waterborne pesticide stream. The spray nozzle structure comprises a multiple component assembly which is easily assembled and disassembled for maintenance and repair, or replacement of worn or defective parts. The nut 30 is threadedly secured to the nozzle body 12 and engages the air nozzle 28 compressibly to retain it against the nozzle body 15 through the compression of the interposed resilient sealing gasket 66. The inductor ring 48 and the swirl plate 64 are housed within the air nozzle 28 and these two components are thereby also compressibly retained against the sealing gasket 66 and the nozzle body 15 as shown in Figure 1. The swirl plate 64 supports the turbulence pin 89 and the orifice plate 78, and the strainer/check valve 76 is supported on the orifice plate 78 as previously described. The assembly can thus easily be assembled and can be easily disassembled for cleaning, replacement or repair of any of the components.

Claims: 1. An electrostatic nozzle assembly for coating objects comprising: a nozzle body (12) having an air passageway (22) to receive a stream of air and a liquid passageway (24) to receive a stream of liquid; and an air nozzle (28) mounted on the nozzle body and formed with a discharge orifice (32); characterized by an inductor ring (48) formed with an aperture (50) and mounted between the nozzle body (12) and the air nozzle (28) so that the aperture (50) axially aligns with the discharge orifice (32); charging means (27) for applying an electrical potential to the inductor ring (48); means (78, 80, 75) communicating with the liquid passageway (24) for directing the stream of liquid into the aperture (50) of the inductor ring (48); and means (86) communicating with the air passageway (22) for imparting a swirling, rotational motion to the stream of air, the swirling stream of air being directed into contact with the liquid stream to form finely divided particles within the aperture (50) of the inductor ring (48), the particles becoming inductively charged by the inductor ring (48) and entrained within the swirling stream of air for discharge onto the objects to be coated. 2. An electrostatic nozzle assembly according to Claim 1, including a swirl plate (64) mounted between the nozzle body (12) and the inductor ring (48), the swirl plate being formed with a central bore (68) and a plurality of channels (86) communicating with the air passageway (22) for receiving the stream of air therefrom, each of the channels (86) extending generally radially outwardly from the central bore (68) along a respective axis substantially tangential thereto, the channels (86) imparting a swirling, rotational motion to the stream of air with respect to the axis of the central bore (68). 3. An electrostatic nozzle assembly according to Claim 2, in which the swirl plate (64) includes a top surface (70) and a bottom surface (72) facing the inductor plate (48) and an annular groove (88) extending inwardly from the top surface toward the bottom surface and communicating with the air passageway (22), the channels (86) extending from the bottom surface (72) to the annular groove (88). 4. An electrostatic nozzle assembly according to Claim 3, in which the central bore (68) of the swirl plate (64) tapers radially inwardly from the top surface (70) to a nozzle tip (74) which is of reduced diameter and has an outlet (75) extending outwardly from the bottom surface (72). 5. An electrostatic spray nozzle assembly according to Claim 4, in which the outlet (75) of the nozzle tip (74) extends into the aperture (50) of the inductor ring (48) forming a space therebetween in the path of the air stream produced by the swirl plate (64), the space forming a position of maximum constriction of the air stream thereby to obtain maximum velocity of the air stream thereat. 6. An electrostatic nozzle assembly according to Claim 5, in which the central bore (68) of the swirl plate (64) communicates with the liquid passageway (24) for receiving the stream of liquid, the liquid stream is discharged from the outlet (75) of the nozzle tip (74) into the aperture (50) of the inductor ring (48), the channels (86) of the swirl plate (64) decrease in cross section from the annular groove (88) to the nozzle tip (74) and thereby accelerate the air stream toward the nozzle tip (74) and the position of maximum constriction of the air stream is positioned immediately downstream of the outlet (75) of the nozzle tip (74) to achieve maximum velocity of the air stream thereat for optimizing the atomization of the liquid stream discharged from the outlet (75) of the nozzle tip (74) into the aperture (50) of the inductor ring (48). 7. An electrostatic nozzle assembly according to Claim 2, including: an orifice plate (78) mounted between the nozzle body (12) and the swirl plate (64), the orifice plate (78) being formed with a metering orifice (80) disposed in alignment with the central bore (68) of the swirl plate (64); and a pin (84) mounted on the swirl plate (64) substantially transverse to the axis of the metering orifice (80); the orifice plate (78) communicating with the liquid passageway (24) for transmitting the liquid stream through the metering orifice (80), and the liquid stream discharged from the metering orifice (80) being directed into engagement with the pin (84). 8. An electrostatic nozzle assembly according to anyone of the preceding Claims, including an earthed support (16) for the nozzle body (12) and means (36, 31) for forming an electrical standoff between the discharge orifice (32) and the earthed support (16). 9. An electrostatic nozzle assembly according to Claim 8, in which the means forming an electrical standoff comprise an annular wall (36) extending outwardly from the discharge orifice (32) and defining a cavity, the annular wall being formed with an inner surface (38) and an irregularly-­ shaped outer surface (42) spaced from the earthed support (16). 10. An electrostatic nozzle assembly according to Claim 9, in which the annular wall (36) is formed with a plurality of grooves (40) extending from the exterior of the annular wall inwardly forming the irregularly-shaped outer surface (42) with a plurality of ridges and recesses, the ridges and recesses of the irregularly-shaped outer surface forming an extended path of migration of the inductively charged particles from the discharge orifice (32) to the earthed support (16). 11. An electrostatic nozzle assembly according to Claim 9 or Claim 10, including a nozzle nut (30) having a radial flange (31) for mounting the air nozzle (28) to the nozzle body (12), the nozzle nut (30) being disposed between the discharge orifice (32) and the earthed support (16) so that the radial flange (31) forms an extended path of migration of the inductively charged particles from the discharge orifice (32) to earthed support means (16). 12. An electrostatic nozzle assembly according to anyone of Claims 9 to 11, in which the inner surface of the annular wall (36) of the air nozzle (28) is formed in a generally conical shape which increases in cross section from the discharge orifice (32) outwardly. 13. An electrostatic nozzle assembly for coating objects comprising: a nozzle body (12) having an air passageway (22) to receive a stream of air, a liquid passageway (24) to receive a stream of liquid; and an electrical passageway (26) to receive an electrical conduit; characterized by a swirl plate (64) positioned adjacent the nozzle body (12) and having a central bore (68) and a plurality of channels (86) communicating with the air passageway (22) to receive the stream of air therefrom, each of the channels (86) extending radially outwardly from the central bore (68) along an axis substantially tangential thereto, the channels (86) imparting a swirling, rotational motion to the stream of air with respect to the axis of the central bore (68); a substantially disc-shaped inductor ring (48) formed with an aperture (50) and positioned adjacent the swirl plate (64); an air nozzle (28) formed with a discharge orifice (32) and positioned adjacent the inductor ring (48); charging means (27) for applying an electrical potential through the electrical conduit means in the electrical passageway (26) to the inductor ring; and releasable securing means (30) for releasably securing the swirl plate (64) adjacent the nozzle body (12), the inductor member (48) adjacent the swirl plate (64), and the air nozzle (28) adjacent the inductor member (48), with the central bore (68) of the swirl plate (64), the aperture (50) of the inductor ring (48), and the discharge orifice (32) of the air nozzle (28) in an aligned position. 14. An electrostatic nozzle assembly according to Claim 13, including a pin (52) secured to the inductor member (48) and projecting through an aperture formed in the swirl plate (64) and into the electrical passageway (26) of the nozzle body (12) to form an electrical connection between the electrical conduit means in the electrical passageway of the nozzle body and the inductor member. 15. An electrostatic nozzle assembly according to Claim 13 or Claim 14, wherein the exterior surface of the nozzle body is formed with external threads, the releasable securing means comprises an internally threaded nut (30) engaging the exterior surface of the air nozzle, the inductor ring (48) and the swirl plate (64) are supported in the air nozzle (28), and the internally threaded nut (30) is threadedly engageable with the external threads of the nozzle body releasably to secure the swirl plate (64), the inductor member (48), and the air nozzle (28), to the nozzle body (12). 16. An electrostatic nozzle assembly according to anyone of Claims 13 to 15, including an earthed support (16) for the nozzle body (12), wherein the air nozzle (28) is formed with an annular wall (36) disposed outwardly from the discharge orifice (32) and having an outer surface (42) with a plurality of grooves (40) in the outer surface (42); and wherein the nut (30) has a radial flange (31), the grooves (40) in the outer surface of the air nozzle and the radial flange of the nut providing electrical isolation between the inductor ring and the earthed support (16). 17. An electrostatic nozzle assembly according to Claim 13, wherein the central bore of the swirl plate (64) terminates in a nozzle tip (74) having an outlet (75), the outlet (75) being aligned with the aperture (50) of the inductor ring (48) and the discharge orifice of the air nozzle. 18. An electrostatic nozzle assembly according to Claim 17, wherein the nozzle tip (74) is aligned with the liquid passageway (24) in the nozzle body (12) and wherein an orifice plate (78) is positioned between the liquid passageway (24) and the nozzle tip (74), the orifice plate (78) having an orifice (80) which is aligned with the aperture (75) of the nozzle tip (74), and including a turbulence pin (84) mounted transversely with respect to the orifice (80) of the orifice plate (78) and located between the orifice plate and the nozzle tip. 19. An electrostatic nozzle assembly according to Claim 13, including a compressible fluid sealing member (66) positioned between the swirl plate (64) and the nozzle body (12), the releasable securing means (30) compressing the sealing member (66) to provide fluid seals at the outlets of the air passageway (22) and the liquid passageway (24), and to provide positive contact between the air nozzle (28) and the inductor ring (48), and the inductor ring (48) and the swirl plate (64).

Inventors: BURLS, GARY E., PARMENTAR, WILLIAM F.
Applicants: PARKER HANNIFIN CORPORATION
Application year: 1987
Main classification: B05B5
IPC codes: B05B5