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.
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.
Referring now to
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.
Referring now to
Still referring to
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
The sealing surface 250a and/or the sealing surface 250b 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 250a and/or the sealing surface 250b 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 250a and/or sealing surface 250b 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.
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.
Number | Name | Date | Kind |
---|---|---|---|
1982509 | Frank | Nov 1934 | A |
2361144 | Loepsinger | Oct 1944 | A |
2728606 | Juvinall et al. | Dec 1955 | A |
2954146 | Hullman | Sep 1960 | A |
3332623 | Gallant | Jul 1967 | A |
3764068 | Lacchia et al. | Oct 1973 | A |
4004733 | Law | Nov 1977 | A |
4289276 | Bollina et al. | Sep 1981 | A |
4324361 | Moos et al. | Apr 1982 | A |
4343433 | Sickles | Aug 1982 | A |
4357900 | Buschor | Nov 1982 | A |
4545536 | Avidon | Oct 1985 | A |
4664315 | Parmentar et al. | May 1987 | A |
4688518 | Missier | Aug 1987 | A |
4731058 | Doan | Mar 1988 | A |
4750704 | Brundage | Jun 1988 | A |
4846525 | Manning | Jul 1989 | A |
4934602 | Mattson | Jun 1990 | A |
4941808 | Qureshi et al. | Jul 1990 | A |
5076500 | Daniels | Dec 1991 | A |
5085373 | Behr et al. | Feb 1992 | A |
5101679 | Smith et al. | Apr 1992 | A |
5163010 | Klein et al. | Nov 1992 | A |
5188290 | Gebauer et al. | Feb 1993 | A |
5268166 | Barnett et al. | Dec 1993 | A |
5277713 | Gelain et al. | Jan 1994 | A |
5314123 | Miller | May 1994 | A |
5322684 | Barnett et al. | Jun 1994 | A |
5387200 | Kronstadt | Feb 1995 | A |
5460192 | McClain | Oct 1995 | A |
5494674 | Barnett et al. | Feb 1996 | A |
5527564 | Napadow et al. | Jun 1996 | A |
5545140 | Conero et al. | Aug 1996 | A |
5577660 | Hansen | Nov 1996 | A |
5591412 | Jones et al. | Jan 1997 | A |
5603127 | Veal | Feb 1997 | A |
5664593 | McClain | Sep 1997 | A |
5685482 | Sickles | Nov 1997 | A |
5704554 | Cooper et al. | Jan 1998 | A |
5738727 | Cebola et al. | Apr 1998 | A |
5738728 | Tisone | Apr 1998 | A |
5765761 | Law et al. | Jun 1998 | A |
5765762 | Lee et al. | Jun 1998 | A |
5833751 | Tucker | Nov 1998 | A |
5863497 | Dirksing | Jan 1999 | A |
5868311 | Cretu-Petra | Feb 1999 | A |
5922333 | Laughlin | Jul 1999 | A |
5984985 | Malone | Nov 1999 | A |
6003794 | Hartman et al. | Dec 1999 | A |
6067673 | Paese et al. | May 2000 | A |
6138922 | Hartman et al. | Oct 2000 | A |
6199557 | Laughlin | Mar 2001 | B1 |
6206340 | Paese et al. | Mar 2001 | B1 |
6227466 | Hartman et al. | May 2001 | B1 |
6250601 | Kolar et al. | Jun 2001 | B1 |
6302122 | Parker et al. | Oct 2001 | B1 |
6302662 | Bensley et al. | Oct 2001 | B1 |
6326062 | Noakes et al. | Dec 2001 | B1 |
6387081 | Cooper | May 2002 | B1 |
6388609 | Paese et al. | May 2002 | B2 |
6390329 | Maddox | May 2002 | B1 |
6443164 | Parker et al. | Sep 2002 | B1 |
RE37888 | Cretu-Petra | Oct 2002 | E |
6481634 | Zosimadis | Nov 2002 | B1 |
6513787 | Jeromson et al. | Feb 2003 | B1 |
6554208 | Venuto, Sr. | Apr 2003 | B1 |
6568655 | Paese et al. | May 2003 | B2 |
6596983 | Brent | Jul 2003 | B2 |
6802830 | Waters et al. | Oct 2004 | B1 |
7004407 | Cooper | Feb 2006 | B2 |
7021494 | Mazooji et al. | Apr 2006 | B2 |
20030127542 | Cooper | Jul 2003 | A1 |
20040073186 | Cameron | Apr 2004 | A1 |
20050281957 | Cooper et al. | Dec 2005 | A1 |
Number | Date | Country |
---|---|---|
0031649 | Sep 1984 | EP |
0031649 | Sep 1984 | EP |
0224352 | Aug 1990 | EP |
456523 | Nov 1991 | EP |
0468736 | Mar 1997 | EP |
0468736 | Mar 1997 | EP |
0441501 | Aug 1997 | EP |
0441501 | Aug 1997 | EP |
1129784 | Sep 2001 | EP |
WO 0054892 | Sep 2000 | WO |
Number | Date | Country | |
---|---|---|---|
20060124780 A1 | Jun 2006 | US |
Number | Date | Country | |
---|---|---|---|
60627191 | Nov 2004 | US | |
60627480 | Nov 2004 | US |