Abstract:
An electrostatic spray charging nozzle designed for optimum charge level over a wide range of liquid and air flow rates. The electrostatic spray charging nozzle includes a nozzle cap having an outlet, a nozzle body having a first bore, and a fluid tip assembly extending at least partially through the first bore. The fluid tip assembly further includes a liquid inlet adapted to be connected to a source of liquid, and a liquid outlet adapted to dispense the liquid through the outlet of the nozzle body. The electrostatic spray charging nozzle further includes an adjustment mechanism operable to move the fluid tip assembly within the first bore so as to adjust a longitudinal distance between the liquid outlet of the fluid tip assembly and the outlet of the nozzle cap.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and incorporates by reference the entire disclosure of U.S. Provisional Application No. 60/627,191 filed Nov. 12, 2004 and U.S. Provisional No. 60/627,480 filed Nov. 12, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     Embodiments of the present invention relate to electrostatic spray charging of conductive liquids, in particular to air-atomizing spray charging nozzles for conductive liquids that use the principles of induction or contact charging. 
     Electrostatic charging nozzles are well known and in widespread use in a number of commercial applications. Nearly every vehicle manufactured worldwide is painted electrostatically. Most of these industrial electrostatic spray systems charge spray by ionization and dispense powder or non-conductive liquids. There is a need for electrostatic spray devices that can reliably charge electrically conductive formulations, such as those that are water based. Several types of induction charging nozzles have been developed to produce electrostatically charged water sprays. U.S. Pat. No. 4,004,733 to Law shows an induction charging nozzle having a conductive ring surrounding a liquid jet inside a channel where high velocity air impacts the liquid stream, thereby creating a fine spray. Commercial versions of the nozzle described in the Law patent have been manufactured with deviations that include a liquid tip made from an insulating material, upstream grounding of the liquid, and lengthening the electrode to near the full length of the atomization channel. These modifications have made the nozzle of U.S. Pat. No. 4,004,733 reliable for use with water-based materials in most environments where the nozzle surfaces do not become excessively coated with conductive spray residue during a spraying operation. The conductive coatings on the surfaces of the nozzle can cause current leakage which reduces power supply voltage, damages surfaces, and reduces the internal charging field by elevating the voltage of the liquid stream. 
     Further patents to Cooper and Law, U.S. Pat. Nos. 5,704,554 and 5,765,761, utilize a fluid tip that is integral to the nozzle body, and utilize unique outside nozzle surface shapes to attempt to address some of the problems of stray electrical currents due to internal and external nozzle surface contamination. The fixed tip requires that the entire nozzle body be replaced in the event of mis-manufacturing, damage or wear, thereby increasing the cost and the effort of nozzle maintenance. The electrode portion of these nozzles is permanently pressed into the retaining cover. This does not allow replacement of the electrode alone—the entire cover assembly must be replaced. U.S. Pat. No. 4,343,433A to Sickles describes an induction charging nozzle with a fixed tip which utilizes air jets positioned around the main spray jet to prevent nozzle surfaces from becoming coated by spray. This method requires a significant amount of additional air energy, and the fixed tip and fixed electrode do not allow for adjusting for wear, machining tolerance, or replacing individual parts. 
     A series of electrostatic nozzle patents, U.S. Pat. Nos. 6,003,794, 6,138,922 and 6,227,466, to Hartman use an induction charging principle and liquid tip and air channel geometry that are similar to the above mentioned patents by Law, Cooper and Sickles. U.S. Pat. No. 6,003,794 describes nozzles having many components with stacked tolerances. These nozzles have a replaceable electrode but do not allow for adjustment. The nozzles mentioned in the above-identified patents charge well when made to precise, but expensive, machining tolerances, use matched components and are operated within a narrow range of liquid viscosities and liquid and air flow rates for a given internal spacing of components. 
     Variations in geometry of components causes charging variations which are due to improper droplet size or contact of the spray liquid with the walls of the induction electrode channel. Very small deviations in the internal spacing and dimensions of the atomization channel and liquid tip length have been observed to greatly diminish charging unless the air and liquid flows are within a narrow tolerance. These deviations occur due to nozzle manufacturing, from damage to components, and normal wear of components during use. Nozzle manufacturing deviations require that nozzle components be matched for optimal initial performance. This presents a problem since individual nozzle components wear over use and the entire nozzle often needs to be replaced with matching components. Measurements of spray charging from commercial versions of some typical nozzles with cost effective machining tolerances, but without using matched components, show over 30% variation from the same manufacturing run. 
     All of the above mentioned nozzles use air-atomizing induction-charging principles. With these nozzles the spray is charged to the opposite polarity as the electrode. Neither the liquid emitted from the tip nor the atomized spray is meant to contact the electrode. The advantage of such a system is that it produces high spray charging with very low electrode voltage and power. The disadvantage is that spray is attracted back to the nozzle surfaces. The wetted surfaces become conductive and reach the same polarity of the electrode, further attracting liquid spray droplets. The moisture deposits on the nozzle surface form into peaked shapes in response to the spray cloud space charge. The sharp points formed on these water droplets emit air ions that discharge large portions of the spray charge in the cloud. This effect can be minimized by adjusting the spray jet to a narrow column, using the air energy to force the spray a distance away from the nozzle. Another solution when this becomes a problem is to utilize contact charging principles. With contact charging types of nozzles the liquid stream is raised to a high voltage. This renders nozzle surfaces the same polarity as the spray cloud space charge and droplets are electrically repelled from the nozzle. The disadvantage is that the liquid container holding the spray liquid is also raised to high voltage, and as a result small containers should be used or isolation systems must be employed. 
     Operation of electrostatic charging nozzles in situations where contact with the nozzle by humans is possible, such as in applications of spray booths used for sunless-tanning, presents additional safety considerations in their design. One consideration is in limiting the exposure by humans to the electrode itself during operation. Another consideration is the reduction of the amount of leakage current from any portion of the nozzle where human contact could be made. The previously mentioned nozzles by Law and Cooper use an electrode which is embedded between layers of plastic or ceramic. This is an effective method for reducing the chance of direct contact with the electrode. However, commercial versions of the nozzle of U.S. Pat. No. 5,704,554 use an electrical contactor that is exposed when the cover is removed. This pointed contactor can be touched with the fingers and a shock can be received. The current from this contactor is in the range of 1 mA, capable of producing a shock intense enough to make the person involuntarily draw back very quickly and risk injury. Nozzles such as those described by Cooper and Law, Sickles, Hartman, and U.S. Pat. No. 4,664,315 to Parmentar et al. are induction charging devices and have the unfortunate characteristic of attracting spray back to the nozzle itself. This causes wetting of the nozzle face. Wetting by conductive liquids, near the jet outlet, can cause a conductive bridge to form to the electrode and cause shock when these forward nozzle surfaces are touched, even though the nozzle parts are made from insulating materials. The nozzle of Hartman, which is mounted with the electrode through a hole in a PVC tube structure, is particularly susceptible to leakage currents forward from the electrode. After a period of use black electrical tracking lines are evident on the surface of the tube. In addition the thin electrode cover may be easily removed during use causing direct exposure to the electrode. 
     Accordingly, there is a need for an air-atomizing charging nozzle for conductive liquids that has adjustable components to allow tuning for optimized spray quality and charging levels for a wide range of liquid viscosities and flow rates. It is desirable that the nozzle be manufactured with cost effective machining tolerances and not require component matching. It is also desirable that these tuning adjustments can be made while the nozzle is operating. It is also desirable that these adjustments remain set in place during normal nozzle operation. In addition, it is desirable to be able to easily replace and interchange nozzle components without adversely affecting charging and spray quality. Furthermore it is desirable to have the option to use the same nozzle as a contact charging device when necessary. Safety design considerations dictate that the nozzle have reduced leakage currents on all nozzle surfaces, particularly those interior and exterior surfaces which are easily touched by untrained operators. 
     BRIEF SUMMARY OF THE INVENTION 
     In the air-atomizing induction-charging nozzles described above, the most important dimension that affects charging level and droplet size is the depth that the liquid tip penetrates into the atomization/electrode channel. Variations in this depth can be caused by dimensional variations in tip and air channel geometry. Manufacturing variations or normal wear of either of these parts can cause droplet size and charging variations, as well as cause the spray to be misdirected in the slipstream of the atomization channel. In contact charging systems using an air atomizer, the droplet size and charging level are also affected by these same geometries. 
     An electrostatic spray charging nozzle according to at least one embodiment of the present invention comprises a liquid tip that can be accurately axially moved and set during operation of the nozzle to optimize charging and spray quality in both induction charging and contact charging configurations, as well as to increase the useable range of liquid flow rates and to reduce the effects of normal manufacturing variations. In addition, the key components of the nozzle in accordance with embodiments of the present invention can be easily removed and interchanged with those of other nozzles without affecting charging or spray quality. In one embodiment, the nozzle can be operated as a contact charging device by applying a voltage directly to the liquid. In an alternate embodiment, the nozzle can be operated as an induction charging device where a voltage is applied to the air cap/electrode and the spray liquid is earthed (grounded) near the nozzle. In accordance with at least one embodiment the air cap/electrode is easily removed from the retaining cap for replacement or substitution for a cap of a different geometry. 
     An embodiment of the present invention is directed to an electrostatic spray charging nozzle having a nozzle cap having an outlet, a nozzle body having a first bore, and a fluid tip assembly extending at least partially through the first bore, the fluid tip assembly having a liquid inlet adapted to be connected to a source of liquid, and a liquid outlet adapted to dispense the liquid through the outlet of the nozzle body. The electrostatic spray charging nozzle further includes an adjustment mechanism operable to move the fluid tip assembly within the first bore so as to adjust a longitudinal distance between the liquid outlet of the fluid tip assembly and the outlet of the nozzle cap. 
     Another embodiment of the present invention is directed to an electrostatic spray charging nozzle including a nozzle body having an air-channel bore; a nozzle cap having an outlet aligned with the air-channel bore, the nozzle cap adapted for removable coupling to a first side of the nozzle body; and a liquid inlet connector having a first end adapted to be coupled to a second side of the nozzle body, and a second end adapted to be connected to a source of liquid. The electrostatic spray charging nozzle further includes a fluid tip extending through the air-channel bore and having a fluid tip base adapted to be coupled to the first end of the liquid inlet connector, and a fluid tip outlet adapted to dispense the liquid through the outlet of the nozzle cap; and a conductive air cap having a bore aligned with the air-channel bore to receive the fluid tip outlet, the conductive air cap adapted to induce a charge to the liquid. The electrostatic spray charging nozzle still further includes an adjustment mechanism operable to move the fluid tip assembly within the air-channel bore so as adjust a longitudinal distance between the fluid tip outlet of the fluid tip and the outlet of the nozzle cap. 
     Another embodiment of the present invention is directed to an electrostatic spray charging nozzle having a nozzle cap having an outlet, a nozzle body having a first bore, and a fluid tip assembly extending at least partially through the first bore, and having a liquid inlet adapted to be connected to a source of liquid, and a liquid outlet adapted to dispense the liquid through the outlet of the nozzle body. The electrostatic spray charging nozzle further includes an adjustment mechanism operable to move the fluid tip assembly within the first bore so as to adjust an axial distance between the liquid outlet of the fluid tip assembly and the outlet of the nozzle cap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of one embodiment of the nozzle of the present invention shown disassembled to view the key components; 
         FIG. 2A  is a side view of the one embodiment of the nozzle of the present invention shown assembled; 
         FIG. 2B  is a section view of another embodiment of a nozzle of the present invention; 
         FIG. 2C  shows a section view of the liquid tip area of the nozzle of  FIG. 2B ; 
         FIG. 3  shows one embodiment of the nozzle according to the present invention in which the fluid tip is removable from the front of the nozzle; 
         FIG. 4  shows one embodiment of the nozzle according to the present invention in which the fluid tip is removable from the rear of the nozzle; 
         FIG. 5  shows a front view of the fluid tip of one embodiment of the present invention; 
         FIG. 6  shows an embodiment of the nozzle according to the present with the addition of a non-conductive element to the inside of the retaining cap; 
         FIG. 7  is a configuration for a tool to insert or remove the liquid tip in the nozzle according to the present invention; and 
         FIG. 8  is a mounting arrangement for use in an electrostatic spray charging system using a nozzle in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 1 , an embodiment of a nozzle of the present invention is illustrated in which a fluid tip  10  having a fluid tip base  20  with a threaded end is screwed into an inner threaded portion of a liquid inlet connector  30 . In accordance with some embodiments of the present invention, the fluid tip can be comprised of a dielectric material. A sealing boss  40  on the fluid tip  10  provides for liquid sealing between the fluid tip  10  and the liquid inlet connector  30 . The liquid inlet connector  30  is further provided with fluid tip length adjustment threads  50  along an outer circumference. The liquid inlet connector  30  is adapted to be connected to a source of spray liquid. The fluid tip length adjustment threads  50  are adapted to allow the liquid inlet connector  30  to be threaded into a back surface of a nozzle body  60 . With the fluid tip  10  mounted to the liquid inlet connector  30 , the selective threading of the liquid inlet connector  30  result in an adjustment in the axial/longitudinal positioning of the fluid tip  10  within a central air-channel bore  70  of the nozzle body  60 . 
     In various embodiment of the present invention, the fluid tip  10  is a dual fluid tip that allows for the passage of air as well as a spray fluid. In an embodiment of the present invention, the fluid tip  10  is provided with air path cuts  75  in the sides which longitudinally extend to allow air to flow through the central air-channel bore  70  between the fluid tip  10  and the walls of the central air-channel bore  70 . This allows for the passage of air while still allowing for concentric alignment of the fluid tip  10  with the central air channel. This design improves air flow uniformity in the atomization channel and helps prevent spray contact with the channel walls. The directed air within the nozzle further produces a narrow directed spray which provides concentrated air energy at the jet outlet of the nozzle and greatly reduces the return of charged spray to the nozzle and nozzle mounting components. The nozzle body  60  is further provided with an air inlet  80  for providing a flow of air or other gas from an external source through to the central air-channel bore  70 . An air cap  90  (or electrode) having a bore or channel is further positioned at a front end of the nozzle body  60  to form an atomization/electrode channel. An electrode wire  100  is provided to apply a charge to the air cap  90  when the nozzle is to be used for induction charging, and the air cap  90  is made from conductive materials. For a contact charging configuration, the spray liquid itself is raised to a high voltage and the air cap  90  may be made from insulating materials. In this configuration, the electrode wire  100  may be omitted. A nozzle cap  110  (or retaining cap) is further provided to retain the air cap  90  in the nozzle assembly. In accordance with some embodiments of the present invention, the nozzle cap  110  may be comprised of a hemispherical nozzle cap. In accordance with still other embodiments of the present invention, the nozzle cap may have alternate shapes. The nozzle cap  110  can be further provided with an aperture or recess adapted to removably receive the air cap  90 . In accordance with an embodiment of the present invention the air cap  90  is adapted to rotate freely about the fluid tip assembly, and is removable for repair and/or replacement if necessary. 
     Adjustment of the depth that the fluid tip  10  penetrates into the atomization channel is made by turning the liquid inlet connector  30  attached to the back of the nozzle body  60 . The thread pitch of the liquid inlet connector  30  determines the amount of axial/longitudinal movement that is provided with respect to the placement and positioning of the fluid tip  60  in the atomization/electrode channel for each turn of the liquid inlet connector  30 . The threads of the liquid inlet connector  30  act as an adjustment mechanism such that the longitudinal or axial distance between the liquid outlet of the fluid tip  10  and the outlet of the nozzle cap  10  can be adjusted within a predetermined range. 
     The nozzle of various embodiment of the present invention allows for components of the nozzle to be removed and interchanged easily, for example for cleaning or replacement. The removable and interchangeable components of the nozzle include the fluid tip  10 , the nozzle cap  110 , the air cap  90 , and the nozzle body  60 . For example, it may be desirable to replace the air cap  90  with one having a larger bore in order to permit more air flow. It also may be desirable to replace the fluid tip  10  with one of different outside and inside diameters to provide different spray characteristics such as droplet size, spray pattern and spray volume. Nozzle cap  110  can be replaced to change its outside surface size and/or shape. 
       FIG. 2A  illustrates a side view of one embodiment of a nozzle in accordance with the present invention shown in an assembled form. In the nozzle of  FIG. 2A , the nozzle cap  110  is coupled to a front side of the nozzle body  60 , and the liquid inlet connector  30  is coupled to a back side of the nozzle body  60 . The nozzle of  FIG. 2A  may be further provided with a spacer ring  120  placed between the nozzle cap  110  and the nozzle body  60 . In alternate embodiment of the nozzle of  FIG. 2A , the spacer ring  120  may be removed for mounting of the nozzle to a panel. 
       FIG. 2B  shows a section view of another embodiment of a nozzle in accordance with the present invention. In this mounting configuration, he panel occupies the space previously occupied by the spacer ring  120 . Adjustment of the length of the fluid tip  10  is made by turning a fitting on the liquid inlet connector  30  connected to the back of the nozzle. The thread pitch of the fluid tip length adjustment threads  50  of the liquid inlet connector  30  controls the length of axial/longitudinal movement of the fluid tip  10  per turn. These fluid tip length adjustment threads  50  have been proven to seal the air very well even after many adjustment rotations have been made. The fluid tip  10  is shown inserted into the central air channel bore  70  of the nozzle body  60 . The fluid tip  10  is held concentric in the air channel by ridges formed on the sides of the fluid tip  10 . 
       FIG. 2C  shows a section view of the fluid tip  10  area of the nozzle of  FIG. 2B . One aspect in accordance with embodiments of the present invention is that tightening the nozzle cap  110  pushes a ledge on the inside of the air cap  90  against a front face of the nozzle body  60  to cause a seal. This design reduces stacked tolerances seen in previous designs, since only the air cap  90  inside dimension need be made with tight tolerances and the nozzle cap  110  and nozzle body  60  can be made with loose, non-critical tolerances. Any variation due to manufacturing of the nozzle parts can be taken out by adjusting the fluid tip  10  by turning the fitting of the liquid inlet connector  30  on the rear of the nozzle. By rotation of the fitting of the liquid inlet connector  30 , the fluid tip  10  is made to move in an axial direction  95 , thereby changing a length  105  of the fluid tip  10  that is exposed from the nozzle body  60 , as well as a depth  115  that the tip end penetrates into the channel of the air cap  90 . 
       FIG. 3  shows one embodiment of the nozzle according to the present invention in which the fluid tip  10  is removable from the front of the nozzle assembly. This is accomplished by first removing nozzle cap  110 , and then rotating fluid tip  10  to disengage the fluid tip  10  from the liquid inlet connector  30  while the liquid inlet connector  30  remains in place. Removal of the fluid tip  10  from the front is desirable in instances where the front of the nozzle is more accessible for maintenance. For instance, if the nozzle is panel mounted and closed in on the backside. The nozzle assembly of  FIG. 3  further illustrates the fluid tip base  20  of the fluid tip  10  as having threads  130  to facilitate removable of the fluid tip  10  from the liquid inlet connector  30 . The nozzle assembly of  FIG. 3  is further provided with an electrode wire  100  to provide a high voltage to the spray liquid during a spraying operation. 
       FIG. 4  shows one embodiment of the nozzle according to the present invention in which a fluid tip assembly  150  comprised of a fluid tip  10  and liquid inlet connector  30  is removable from the rear of the nozzle body  60 . This is accomplished by rotating the liquid inlet connector  30  to detach the liquid inlet connector  30  from nozzle body  60  while the fluid tip  10  remains attached to the liquid inlet connector  30 . In accordance with some embodiments of the present invention, the fluid tip can be comprised of a dielectric material. Removal of the fluid tip  10  from the rear of the nozzle body  60  may be desirable is some situations. For instance, if the nozzle were operating alongside other nozzles and only one nozzle needed service, the fluid tip  60  could be removed from the rear of the nozzle body  60  without interfering in the spray of the adjacent nozzles. 
       FIG. 5  shows a front view of a fluid tip  10  of one embodiment of a nozzle body of the present invention. The fluid tip  10  is removable and inserted into the central air channel bore  70 . Cuts along the length of the side of the fluid tip  10  allow air to flow evenly around a liquid outlet  160  of the fluid tip  10  and mate the tip concentric with the inner wall of the central air channel bore  70 . The ridges formed on the length of the fluid tip  10  hold the fluid tip  10  concentric with the central air channel bore  70  of the nozzle body  60  and provide for air channels  170  through which air or another gas can flow. This arrangement improves the concentricity of the removable liquid tip  10  with the nozzle body  60  and the air cap  90 . An electrode contactor  180  is provided in the case of induction charging nozzles where a conductive air cap  90  is used in order to couple a high voltage from electrode wire  100  to the air cap  90 . The electrode contactor  180  includes a contact pad adapted to contact a surface of the air cap  90 . In one embodiment of the present invention, the contact pad may be comprised of a spring-loaded contact pad. The electrode contactor  180  is recessed in a ring cavity  190  or channel of the nozzle body  60  to prevent touching with fingers while operating. The ring cavity  190  allows for the seating of air cap  90  as can also be seen in  FIGS. 2B and 2C . Although the embodiment of  FIG. 5  is illustrated as having a ring cavity  190 , it should be understood that in other embodiments a nozzle body can be used that does not have a ring cavity. 
       FIG. 6  illustrates and embodiment of the present invention which includes the addition of a non-conductive element  200  to the inside of the nozzle cap  10  positioned between the ends of the retaining cap  110  and a top surface of the air cap  90 . The function of the non-conductive element  200  is to increase human safety by reducing shock hazard at the nozzle tip area by providing an electrical isolation between the air cap  90  and the nozzle cap  110 . The non-conductive element  200  further acts to reduce leakage currents from surfaces surrounding of the jet outlet  210  of the nozzle cap  110  that may be touched by human hands in certain applications. In accordance with various embodiments, the non-conductive element  200  is a non-conductive or substantially non-conductive disc. It is preferred that the non-conductive element  200  be a material with low electrical conductivity and low surface wettability, such as Teflon or UHMW Nylon. The addition of the non-conductive element  200  can be made without affecting any critical geometry or performance of the nozzle. The jet outlet hole  210  of the non-conductive element  200  is preferably made larger than the hole of the air cap  90  so as not to introduce any discontinuities along the wall of the air channel. Although the embodiment of  FIG. 6  is illustrated as having a non-conductive element  200 , it should be understood that in other embodiments the non-conductive element  200  may be omitted. 
       FIG. 7  illustrates a configuration of a tool  220  used to insert or remove the fluid tip  10  in the nozzle according to the present invention. The tool  220  has an inside bore  230  of a similar shape as the outside of the sides of the fluid tip  10 . The tool  220  is positioned over the fluid tip  10  such that a portion of the fluid tip  10  extends through the inside bore  230  of the tool  220 . The tool  220  is then turned by hand to tighten or loosen the fluid tip  10  from the liquid inlet connector  30  as needed. An advantage provided by an embodiment of the tool  220  is that it contacts only the sides of the fluid tip  10  in order to prevent any damage to the liquid outlet end of the fluid tip  10 . 
     Referring now to  FIG. 8 , a mounting arrangement for use in an electrostatic spray charging system using a nozzle in accordance with an embodiment of the present invention is illustrated. In the mounting arrangement of  FIG. 8 , components of a nozzle are mounted to an electrically insulating panel  240 . The components are illustrated in  FIG. 8  as suited for an air atomizing induction charging system. However, it should be understood that the system could be easily configured for contact charging by applying voltage directly to the liquid rather than an induction electrode. The main components of an induction charging system as shown include a nozzle body  60 , a fluid tip  10 , a nozzle cap  110 , and an air cap  90  as previously described. The mounting arrangement of  FIG. 8  further includes a sealing surface  250   a ,  250   b  on the nozzle body  60  and/or the nozzle cap  110 , and an electrically insulating panel  240 . In accordance with various embodiments of the present invention, the electrically insulating panel  240  is substantially electrically non-conductive. In accordance with various embodiments of the invention, the electrically insulating panel  240  may be made of a plastic material. In a preferred embodiment of the invention, the electrically insulating panel  240  is made of an insulating material such that electrical resistance of the insulating panel to earth ground is greater than 2 Megaohms. The nozzle body  60  is preferably made from insulating material. The nozzle body  60  further includes an air inlet  80  adapted to receive a supply of air or other gas from a source. The insulating panel  240  is further provided with a plurality of mounting holes  260 . In one embodiment, the nozzle body  60  is fixedly mounted to the insulating panel  240  using mounting hardware that is coupled to the nozzle body  60  and passes through the mounting holes  260 . In still another embodiment, the nozzle cap  110  is mounted to the insulating panel  240  using mounting hardware that is coupled to the nozzle cap  110  and passes through the mounting holes  260 . In accordance with an embodiment, the mounting hardware can include bolts, screws, rods, attachment clips, etc. In still other embodiments, the nozzle body  60  and/or the nozzle cap  110  can be affixed to the insulating panel  240  using an adhesive. 
     Still referring to  FIG. 8 , the electrostatic spray charging system further includes a liquid inlet connector  30  adapted to be connected to a source of spray liquid and supply the spray liquid to the fluid tip  10 . The electrostatic spray charging system still further includes an electrode wire  100  adapted to supply an electrostatic charge to the air cap  90 . The nozzle cap  110  is provided with an spray outlet  270  allowing for a spray of electrostatically charged liquid to be sprayed from the spray nozzle assembly. 
     At the beginning of a spraying operation, deposition of a small amount of spray on the surface of the insulating panel  240  causes the insulating panel  240  to be charged by accumulation to the same polarity as the spray cloud. As a result, during the remaining portion of the spraying operation the spray cloud is repelled from the insulating panel  240 , resulting in a reduction in the amount of spray returning to the spray nozzle and surrounding surfaces, as well as blocking nozzle surfaces from becoming coated with conductive residues. Although  FIG. 8  illustrates a mounting arrangement in which a nozzle in accordance with an embodiment of the present invention is mounted to an insulating panel, it should be understood that other mounting arrangements can be used. 
     The sealing surface  250   a  and/or the sealing surface  250   b  functions to prevent, or at least to inhibit, current flow between the air cap  90  of the electrostatic spray nozzle assembly and a pathway to an electrical potential difference, such as a ground. The sealing surface  250   a  and/or the sealing surface  250   b  serves to prevent or inhibit the formation of charge leakage paths, the presence of which will inhibit optimal charging of the spray by the air cap  90 . The prevention or inhibition of current flow between the air cap  90  and components of the electrostatic spray nozzle assembly that are positioned on the opposite side of the insulating panel  240  from the air cap  90  provided by sealing surface  250   a  and/or sealing surface  250   b  also serves to isolate a person that may come in contact with these components from electrical shock. In various embodiments of the present invention, the spray is charged to a negative charge potential with respect to ground, whereas in other embodiments the spray may be charged to a positive charge value with respect to ground. 
     Although various embodiments of the nozzle assemblies of the present invention have been illustrated as including fluid tip length adjustment threads on a liquid inlet connector, it should be understood that other adjustment mechanisms may be used to adjust a longitudinal distance between the liquid outlet of the fluid tip assembly and the outlet of the nozzle cap. For example, in some embodiments the adjustment mechanism can include a frictional coupling between a first end of the liquid outlet connector and a side of the nozzle body. In still other embodiments, the adjustment mechanism can include a mechanism which provides a step-wise adjustment of the longitudinal distance between the liquid outlet of the fluid tip and the outlet of the nozzle cap. In still other embodiments, the adjustment mechanism can include a threaded coupling between the fluid tip  10  and the liquid inlet connector  30 . 
     Although a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the claims.