Patent Document

BACKGROUND OF THE INVENTION 
     The subject invention relates generally to an improved spray gun utilizing coating material with a wide range of conductivity in an electrostatic spray coating system. More specifically, the subject invention relates to a rotary spray gun capable of improving the transfer efficiency of the coating by generating ionic lines to shape the spray pattern of the coating material being atomized by the spray gun. 
     Apparatus used for electrostatically coating objects such as, for example, an automobile body, have been in use for some time. Primarily, a voltage potential is applied to a spray head of a rotary atomizer in order to produce an electric field between the spray head and a grounded object to be coated. The charge generated by the spray head is transferred to the atomized coating material by direct contact as it is radially disbursed from the spray head. 
     An additional charge ring has been added to the spray apparatus primarily, for water borne coating materials. The charge ring typically includes a plurality of electrodes concentrically aligned with the axis of the spray head. The electrodes are generally coated with an insulating material, with a small pin protruding therefrom. A high voltage cable specifically supplies the electrical potential to the electrodes necessary for generating an electrical field for charging the particles sprayed from the spray head. Often, the electrodes will be charged to generate the electric field, and the spray head will be grounded. In this type of arrangement, the entirety of the electrostatic charge transferred to the coating material is generated from the electrodes concentrically aligned with the spray head. 
     While this type of electrostatic arrangement has proven quite effective for water borne based coating materials, it is not proven to be as effective for solvent borne coating materials. Therefore, the entirety of the electrostatic charge transferred to atomized particles in a solvent borne coating system is derived from the rotary spray head that has an electrical potential less than ground. Frequently, the mass of an atomized coating particle is too large when radially disbursed from the spray head will derive a physical potential greater than the electrical potential produced from the spray head. When this occurs, the atomized particle will be thrown laterally from the spray head and thus, will not be directed toward the grounded object to be painted. The frequency from which this happens is known to reduce the transfer efficiency of the atomized coating material onto the object to be painted. 
     Accordingly, it would be desirable to introduce an ionization ring to a solvent borne painting apparatus that can generate an ionic field capable of overcoming the momentum of the atomized coating particles that are disbursed laterally from the spray head. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The present invention comprises an apparatus for electrostatically coating objects with an electrically conductive coating material capable of carrying an ionic charge. A rotary atomizer utilizes a spray head that rotates on an axis at a high speed. An external housing is affixed to a support member that is oriented either horizontally or vertically depending upon the application needs of the object to be coated. The external housing pivotally supports the spray head and includes a non-conductive surface. Conductive elements such as a limb or structural band are disposed upon the housing. The conductive elements derive electrical potential that is generally the same as the electrical potential of the spray head. The non-conductive surface of the housing is at neutral potential relative to the potential of the spray head and the conductive elements. 
     An ionizing device is positioned on the housing to contact the conductive elements. Thus, the ionizing device derives an electrical potential that is generally the same as the spray head and the conductive elements. A halo with a plurality of generally conical members spaced therearound directs ionizing lines to shape the atomized coating material being radially disbursed from the spray head. 
     The generally conical members generate ionic lines at substantially the same potential as the spray head and the conductive elements. The ionic lines are disbursed at an electric potential strong enough to overcome the momentum of many of the electrostatically charged, atomized particles being radially disbursed from the spray head thereby forcing these atomized particles toward the grounded object to be painted. Therefore, the ionic lines generated from the generally conical members improve the transfer efficiency of the coating material dispersed from the spray head onto the object to be painted. Further, it should be understood by those of skill in the art that a reduction in the amount of shaping air necessary to shape the atomized particles can be achieved through the utilization of the improved ionic field generated by the inventive ionization ring. Through the reduction of shaping air, a reduction in dirt trapped in the paint coating can also be achieved due to the reduction in air turbulence in the paint booth. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
     FIG. 1 shows three rotary atomizers affixed to a horizontal support member having the ionizing ring of the present invention affixed thereto; 
     FIG. 2 is an exploded view of ionizing ring and the rotary atomizer; 
     FIG. 3 is a bottom view of the ionizing ring of the present invention; 
     FIG. 4 is a side view of the ionizing ring of the present invention; 
     FIG. 5 is a side sectional view of the generally conical member; 
     FIG. 6 is an exploded view of the rotary atomizer and the ionizing ring showing the shrouds positioned over the generally conical members; 
     FIG. 7 shows an alternative embodiment of the conductive members; 
     FIG. 8 is a perspective view of the shroud; and 
     FIG. 9 is a sectional view of a shroud positioned over a generally conical member. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an apparatus for electrostatically coating objects with a coating material is generally shown at  10  affixed to a horizontally oriented support member  12 . FIG. 1 shows three of the apparatus  10  affixed to the support member  12 , however, one, two, three or more of the apparatus  10  may be affixed to the support member  12  as needed to sufficiently coat an object (not shown) with the coating material. As best seen in FIG. 2, the apparatus includes a rotary atomizer  14  having a housing  16  and a spray head  18 . 
     The housing  16  includes a non-conductive surface  20  and conductive elements  22 . The conductive elements  22  derive electrical potential from the support member  12  and transfer that potential to the spray head  18 . A paint line  24  feeds solvent borne coating material through the support member  12  to the spray head  18  in the direction of the target. An air line  26  feeds pressurized air through the support member  12  and through the housing  14  to shaping air apertures  28  disposed in the housing concentrically aligned with the axis of the spray head  18  to shape the coating material being disbursed from the spray head  18  in the direction of the target. 
     The spray head  18 , as known in the art, atomizes the coating material by spinning at a high rate of speed and radially disbursing the atomized coating from an annular spray edge  30 . The spray head  18  ionizes the atomized coating material at a potential that is lower than ground. Preferably, the potential is approximately −90 KV. However, the operating range is between −70 and −100 KV depending upon the coating operation being performed. The object to be painted is typically grounded and, therefore, the ionized particles are attracted to the object to be painted as is well known in the art. The support member  12 , the conductive elements  22 , and the spray head  18  each have an electrical potential that is generally at the same level. 
     Referring again to FIG. 1, an ionizing device  32  is affixed to the housing  16  of the apparatus  10 . The ionizing device  32  is positioned upon the housing  16  to contact the conductive elements  22 . The ionizing device  32  is formed from a conductive material such as, for example, steel or an equivalent, and therefore generally derives the same electrical potential as that of the conductive element  22 . 
     As best shown in FIGS. 2 through 4, the ionizing device  32  includes a halo  34  spaced from, and concentrically aligned with the axis of the spray head  18 . A pair of support arms  36  affix the halo to a band  38 . A plurality of generally conical members  40  are affixed to the halo  34 , the purpose of which will be explained further below. 
     The band includes a clamping element  42  used to tighten the band  38  around the housing  16  thereby affixing the ionizing device  32  to the apparatus  10 . In the preferred embodiment, the clamping element includes opposing tabs  44  spaced by a gap  46  in the band  38 . A fastener  48  (FIG. 2) is inserted through the tabs  44  to narrow the gap  46  in the band  38  and tighten the band  38  around the housing  16 . The band  38  is positioned to contact the conductive elements  22  on the housing  16 . The conductive elements  22  are shown in FIG. 2 as a conductive band  50  that circumscribes the housing  16 . Alternatively, as shown in FIGS. 6 and 7, the conductive elements  22  comprise a conductive rim  52  having a plurality of protuberances  54  disposed thereon. In this embodiment, the band  38  contacts the protuberances  56  deriving the ionizing electrical potential in that manner. 
     Referring to FIG. 5, each of the generally conical members  40  includes a threaded shaft  58 . The threaded shaft  58  is used to affix the generally conical member  40  to the halo  34 . Preferably, the generally conical member  40  will be permanently affixed to the halo  34  with adhesive, welding, or the like preventing the generally conical member  40  from being removed from the halo  34 . Therefore, it is not necessary that the generally conical member  40  include a threaded shaft as alternative methods of attachment may be used as will be appreciated by those of skill in the art. 
     Referring to FIGS. 8 and 9, a shroud  60  covers each of the generally conical members  40 . Each of the generally conical members  40  includes a tip  62  that protrudes through the shroud  60 . A shaping surface  64  is disposed upon each shroud  60  having the tip  62  of the generally conical member  40  centrally located therein. Each shroud  60  includes a pair of snapping arms  66  that secure the shroud  60  to the halo  34 . The shroud  60  is preferably formed from a fluorinated hydrocarbon, such as Teflon® available from DuPont Co. and is generally non-conductive. However, other equivalent non-conductive materials may also be used to form the shroud  60 . 
     The ionic lines that generate the ionic field around the atomized coating materials emanate from the tip  62  of the generally conical members. The shaping surface  64  on each shroud  60  helps shape the ionic lines into an ionic field capable of shaping the dispersion pattern of the coating material. Each tip  62  is preferably pointed. The pointed tips  62  have proven to improve the transfer efficiency from the spray head  18  to the object to be painted by generally 5%. However, some test data has shown the transfer efficiency has been approved by up to 11%. The pointed tips  62  have proven to be most effective for improving transfer efficiency. However, other shapes such as rounded tips and spherical tips have also proved effective. Generally, the shape of a tip  62  can be tuned to meet the transfer efficiency needs of the object being painted. 
     Preferably, for heads having diameters between 40 and 70 mm, each tip  62  is spaced behind the spray head  18  from ¾ to 1 ½ inches. More preferably, each tip  62  is spaced behind the spray head  18  a distance of 1 inch or slightly less. The shroud  60  is generally shaped as a bell and has a base diameter of approximately ⅝ inches at the halo  34 . At the tip  62 , the shroud  60  has a tip diameter of approximately 1 inch. The shroud  60  extends past the tip  62  a distance of approximately ¼ inch. The dimensions listed above are correlated to the diameter of the spray head and can be modified according the diameter of the spray head. 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.

Technology Category: 7