Abstract:
A grounding dissipation unit for a paint delivery apparatus for delivering paint is disclosed. The paint delivery apparatus includes a first paint line for carrying paint from a canister, a second paint line for carrying paint to an ionizing applicator for electrically charging paint, a first water line for carrying water to a grounding source, a second water line carrying water to the grounding dissipation unit, and a third water line for carrying water to a dump. The grounding dissipation unit includes a core comprising an electrically conductive material. A a paint bore in the core connects the paint lines, and a water bore in the core connects to the water lines to ground the system. The paint bore and water bore do no intersect within the core.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority from U.S. provisional patent application Ser. No. 62/221,792 filed on Sep. 22, 2015, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    An electrostatic paint spray system is a highly efficient technology for the application of paint to specific work pieces. Negatively charged atomized paint particles and a grounded work piece create an electrostatic field that draws the paint particle to the work piece, minimizing overspray. 
         [0003]    For this technology, an ionizing electrode, typically located at the paint gun atomizer tip, causes paint particles to pick up additional electrons and become negatively charged. As the coating is deposited on the work piece, the charge dissipates through the ground and returns to the power supply, completing the circuit. The electrostatic field influences the path of the paint particles. Because the charged particles are attracted to the grounded workpiece, overspray is significantly reduced. Paint particles that pass a workpiece can be attracted to and deposited on the back of the piece. 
         [0004]    The transfer efficiency is the percent of sprayed paint that is applied to the workpiece. Paint that is not applied to a work piece is captured in the paint spray booth&#39;s emission control system and ultimately disposed as waste. The typical transfer efficiency for an electrostatic paint spray systems is 75%. 
         [0005]    A potential drawback to electrostatic finishing, particularly for coating complicated surfaces, is the Faraday cage effect: a tendency for charged coating particles to deposit around entrances of cavities. The Faraday cage effect allows electric charges on a conductor to reside on the outer surface of the conductor. In the case of coating complicated surfaces, the electric charge resides on the entrances of cavities. High particle momentum can help overcome Faraday cage effects, since particles with greater momentum (larger particles or particles traveling at higher speeds) are influenced less by the electrostatic forces. However, high particle momentum also lowers efficiency. 
         [0006]    Electrostatic paint equipment is available in three basic types: air atomized, airless, and rotating discs and bells. High-speed discs atomize the coating more finely than air atomization and direct more paint to the target. This technology is particularly efficient for the application of difficult to disperse, high-solids paints. However, the Faraday cage effect is generally greater with rotary atomizers than with air or airless types. Rotary atomizers, therefore, may not provide adequate coverage for complicated surfaces. 
         [0007]    Electrostatic paint spray systems operate at high voltages (30 to 150 kV). Typical operation is to allow the system to go unused in order to dissipate energy prior to docking the applicator for paint refill, which extends the life of the valves in the paint gun. To more quickly dissipate energy in the system, it is necessary to provide a grounding dissipation unit in the system, preferably near the energized paint. All items in the work area must be grounded, including the operators, the paint booth, the application equipment (unless applying conductive coatings), and conveyors. Ungrounded items should be removed from the work area. 
       APPLICATION SUMMARY 
       [0008]    The features and advantages described in the specification are not all inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. 
         [0009]    According to one aspect, a grounding dissipation unit for a paint delivery apparatus for delivering paint is disclosed. The paint delivery apparatus includes a first paint line for carrying paint from a canister, a second paint line for carrying paint to an ionizing applicator for electrically charging paint, a first water line for carrying water to a grounding source, a second water line carrying water to the grounding dissipation unit, and a third water line for carrying water to a dump. The grounding dissipation unit includes a core comprising an electrically conductive material, a paint bore in the core having a paint inlet and a paint outlet. The first paint line is connected to the paint inlet for carrying paint to the grounding dissipation unit and the second paint line is connected to the paint outlet for carrying paint away from the grounding dissipation unit. A water bore in the core has a water inlet and a water outlet. The second water line is connected to the water inlet for carrying water to the grounding dissipation unit and the third water line is connected to the water outlet for carrying water away from the grounding dissipation unit to a dump. The paint bore and water bore do no intersect within the core. 
         [0010]    According to another aspect, a method of grounding a paint delivery apparatus for delivering paint is disclosed. The paint delivery apparatus includes a first paint line for carrying paint from a canister, a second paint line for carrying paint to an ionizing applicator for electrically charging paint, a first water line for carrying water to a grounding source, a second water line for carrying water to the grounding dissipation unit, and a third water line for carrying water to a dump. The method includes the steps of providing a grounding dissipation unit having a core comprising an electrically conductive material, a paint bore in the core having a paint inlet and a paint outlet, and wherein the first paint line is connected to the paint inlet for carrying paint to the grounding dissipation unit and the second paint line is connected to the paint outlet for carrying paint away from the grounding dissipation unit, a water bore in the core having a water inlet and a water outlet, the second water line is connected to the water inlet for carrying water to the grounding dissipation unit and the third water line is connected to the water outlet for carrying water away from the grounding dissipation unit to the dump. Water is run from a water source through the first water line to the grounding source, through the second water line to the core of the grounding dissipation unit, through the water bore, and through the third water line to the dump, wherein the water provide a grounding pathway from the grounding dissipation unit to the grounding source. The grounding dissipation unit and the paint delivery apparatus are grounded as water runs through the first, second, and third water lines and the grounding dissipation unit. 
         [0011]    According to yet another aspect, a grounding dissipation unit includes a first line carrying an electrostatic liquid to the grounding dissipation unit, a second line carrying the electrostatic liquid away from the grounding dissipation unit, a first water line for carrying water from grounding source, a second water line for carrying water to a dump, a core comprising an electrically conductive material, a bore in the core having a first inlet and a second outlet, wherein a first line is connected to the first inlet and the second line is connected to the second outlet, a water bore in the core having a water inlet and a water outlet, the first water line is connected to the water inlet and the second water line is connected to the water outlet, and wherein the bore and water bore do not intersect within the core. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is an embodiment of a paint delivery system for delivering electrically charged or electrostatic paint to a work piece; 
           [0013]      FIG. 2  is an embodiment of a grounding dissipation unit on the robot arm of a paint delivery system; 
           [0014]      FIG. 3  is an embodiment of the grounding dissipation unit; 
           [0015]      FIG. 4  is an cross-section of  FIG. 3  along A-A; 
           [0016]      FIG. 5  is an embodiment of a core of the grounding dissipation unit; 
           [0017]      FIG. 6  is an embodiment of the purge puck; 
           [0018]      FIG. 7  is an embodiment of the purge puck; 
           [0019]      FIGS. 8 a , 8 b , 8 c , and 8 d    are an embodiment of the top of the housing of the grounding dissipation unit; 
           [0020]      FIG. 9 a    is an embodiment of the base of the housing of the grounding dissipation unit; 
           [0021]      FIG. 9 b    is a cross-section of  FIG. 9 a    along line B-B; 
           [0022]      FIG. 10  is an embodiment of a manifold at the grounding point of the paint delivery system; and 
           [0023]      FIG. 11  is an embodiment of the manifold at the grounding point of the paint delivery system. 
       
    
    
       [0024]    The figures depict various embodiments of the embodiments for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the embodiments described herein. 
       DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a paint delivery system  10  for delivering an electrostatic liquid, such as electrically charged or electrostatic paint, to a work piece  12 , such as a vehicle body or vehicle component. The work piece  12  travels down a conveyor belt towards a paint booth  14 , where it is sprayed with electrostatically charged paint particles. The paint particles are charged typically by an ionizing electrode  20 , shown in  FIG. 2 , typically located at the paint gun applicator  22 , causes paint particles to pick up additional electrons and become negatively charged. As the coating is deposited on the work piece  12 , the charge dissipates through the ground and returns to the power supply, completing the circuit. After the workpiece  12  is coated, it continues on the conveyor belt to an oven, where the paint is cured. 
         [0026]    Everything in the area of the electrostatic paint delivery system  10  must be grounded to prevent static buildup and arcing, which can damage the hanging devices and/or the locations where the hanging devices rest on the conveyor. All hangers, conveyors, etc. must be cleaned often to ensure a good ground and prevent anyone in the area from getting a severe shock. Also, the paint delivery system  10  must be grounded prior to docking the applicator  22  before the paint delivery system&#39;s  10  paint canisters are refilled or changed out for a color change. 
         [0027]      FIG. 2  shows an embodiment of a grounding dissipation unit  26  on the robot arm  24  of a paint delivery system  10 . The robot arm  24  includes a metal portion  24   a  and a non-conducting polymer portion  24   b . The grounding dissipation unit  26  is preferably mounted directly on the robot arm  24  in the polymer portion  24   b  of the paint delivery system  10 . The grounding dissipation unit  26  is able to, when engaged, ground the paint line  28   a ,  28   b  between the ionizing electrode  20  in the applicator  22  and the paint canister. 
         [0028]      FIGS. 3 and 4  show an embodiment of the grounding dissipation unit  26 . The grounding dissipation unit  26  includes a core  30  made of an electrically conductive material. The core  30  has two U-shaped bores  40 ,  50  formed inside. The first bore is a paint bore  40 . A first paint line  28   a  is connected to an inlet  44  of the paint bore  40 , and a second paint line  28   b  is connected to an outlet  46  of the paint bore  40 . The first paint line  28   a  is connected to the paint canister and receives paint from the canister. The second paint line  28   b  feeds paint to the ionizing electrode  20 . The first paint line  28   a , the inlet  44 , the paint bore  40 , the outlet  46 , and the second paint line  28   b  all form a continuous pathway for paint to flow from the canister to the ionizing electrode  20 . 
         [0029]    The core  30  also includes a water bore  50 . A first water line  52   a  is connected to an inlet  54  of the water bore  50 , and a second water line  52   b  is connected to an outlet  56  of the water bore  50 . The first water line  52   a  is connected to a water source  58  and transports water from the water source  58  to the grounding point  60 . A second water line  52   b  then transports from the grounding point  60  to the core  30 . A third water line  52   c  transports water away from the core  30  to be disposed in a dump  62 , as illustrated in  FIG. 2 . 
         [0030]    The grounding dissipation unit  26  operates by conducting electric charge from the paint line  28   a ,  28   b  through the electrically conductive core  30  to water flowing through the water lines  52   b  and the core  30 , to a grounding source  60  when the water is flowing. Operation of the grounding dissipation unit  26  allows the voltage in the paint lines  28   a ,  28   b  to be safely dissipated prior to the ionizing electrode  20  from being docked for cleaning or the paint canister being replaced or refilled. 
         [0031]    The core  30  of the grounding dissipation unit  26  is made of an electrically conductive material, preferably stainless steel. Each of the bores  40 ,  50  may be created in any suitable manner known to those of ordinary skill in the art. One method, as shown in  FIG. 5 , shows the inlets  44 ,  54  and outlets  46 ,  56  have been bored in by a tool (not shown, but on the type known to those skilled in the art), in the direction of the x-axis, and the remainder of the bore created by a tool boring into the core in the direction of the y-axis. After boring the U-shaped paint bore  40  and water bore  50 , the excess holes  63   a ,  63   b  along the y-axis may be filled by plug welds  64   a ,  64   b  in a manner known to those of ordinary skill in the art. 
         [0032]    As shown in  FIG. 4 , which is a central cross section of the  FIG. 3  along line A-A, the grounding dissipation unit  26  may include a purge puck  66  that surrounds the core  30  within a housing  70 .  FIGS. 6 and 7  show close up views of the purge puck  66 . The purge puck  66  is preferably made of a plastic with specific isolation thicknesses to provide isolation of the core  30  from any other parts to ensure proper operation, as well as to control airflow through the grounding dissipation unit  26 . In the embodiment shown, the purge puck  66  is made of the thermoplastic polyoxymethylene, also known as POM, acetal, polyacetal, and polyformaldehyde, and sold under the names Delrin, Celcon, Ramtal, Duracon, Kepital, and Hostaform. The purge puck  66  includes a vent slot  68  that allows purge air to move through the grounding dissipation unit  26 , which allows the purge air to push out any ozone that may build up in the electrically charged environment around the core  30 . 
         [0033]    As shown in  FIGS. 3, 4, and 8   a ,  8   b ,  8   c , and  8   d , the core  30  and purge puck  66  sit on and within a housing  70 . Preferably, the housing includes a top  72  and a base  74 . The top  72  of the housing  70  is designed to securely receive the core  30  and the purge puck  66 . The top  72  of the housing has open ends  76   a ,  76   b  along the longitudinal direction and is solid material, preferably plastic, in the lateral directions for protecting the core  30 . On each longitudinal end of the top  72  of the housing  70 , the housing  70  receive first and second caps  78   a ,  78   b  that have open centers  80   a ,  80   b  that allow the first and second paint lines  28   a ,  28   b  and first and second water lines  52   a ,  52   b  to exit the housing  70 . 
         [0034]    The housing also includes a base  74 , also preferably made of plastic, and is preferably a separate part from the top  72  of the housing  70 . An embodiment of the base  74  is shown in  FIGS. 2, 3, 4, 9   a , and  9   b . As shown in  FIG. 9 b   , which is a cross section B-B of  FIG. 9 a   , the base  74  generally has a U-shaped cross section having a bottom portion  76  and two upwardly extending side portions  78 ,  80 . The bottom portion  76  of the base  74  is attached to the polymer portion  24   b  of the robot arm  24 . The top  72  of the housing  70  is removably attached to three upwardly extending portions  92 ,  93 ,  94  extending from the side portions  78 ,  80 . These upwardly extending portions  92 ,  93 ,  94  include with holes  96 ,  97 .  98  for receiving pins  100  and one additional upwardly extending expanded projections  102 . The upwardly extending expanded projection  102  has a threaded hole  106  for receiving a bolt  108 . The top  72  is secured to the base  74  by creating an interlocking fit between the upwardly extending projections  92 ,  93 ,  94  and upwardly extending expanded projection  102  on the base  74 , and downwardly extending projections  110 ,  112 ,  114 ,  116  on the top  72  which also have holes  118 ,  120 ,  122 ,  124 . The top  72  is then slid so the holes  118 ,  120 ,  124  in the downwardly extending projections  110 ,  112 ,  116  on the top receive the pins  100  extending from the upwardly extending portions  92 ,  93 ,  94  of the base  74  creating an interference fit. Finally, a bolt  108  is threaded through hole in the downwardly extending projection  118  of the top  72  an into the threaded hole  106  in the upwardly extending expanded projection  102  on the base  74  to securely fit the top  72  to the base  74 . By removing the bolt  108 , the top  72  can then be slid to disengage the top  72  from the pins  100 , thereby allowing the top  72  of the housing  70  and core  30  to be replaced. Replacement may be necessitated by a desire to change paint lines  28   a ,  28   b  or to replace the core  30  for performance. 
         [0035]    In the embodiment shown, the housing top  72  and housing base  74  are made of the thermoplastic polyoxymethylene, also known as POM, acetal, polyacetal, and polyformaldehyde, and sold under the names Delrin, Celcon, Ramtal, Duracon, Kepital, and Hostaform. However, the housing top  72  and housing base  74  may be made of any other suitable non-conducting material known to one skilled in the art. 
         [0036]    As shown in  FIG. 10 , the first water line  52   a  runs to a manifold  130  mounted to a tubing clamp assembly  132  on the metallic portion  24   a  of the robot arm  24 . The manifold  130  is grounded at this location and provides the grounding point  60  for the electrostatic paint delivery system  10 . The manifold  130 , as shown in  FIG. 11 , has a bore  134  therethrough in a longitudinal direction, into which the second water line is attached. Water runs though the bore and into a second water line  52   b , which takes the water to the core  30  of the grounding dissipation unit  26 . A third water line  52   c  takes the water to the dump  62 . In the embodiment shown, additional bores  136 ,  138  are located in a lateral direction for connecting the manifold  130  to the tubing clamp assembly  132 . Any suitable attachment method for the manifold  130  and method of grounding to one of skill in the art may be used. 
         [0037]    Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment. The appearances of the phrase “in one embodiment” or “an embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
         [0038]    In addition, the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter. Accordingly, the disclosure of the embodiments is intended to be illustrative, but not limiting, of the scope of the embodiments, which is set forth in the claims. 
         [0039]    While particular embodiments and applications have been illustrated and described herein, it is to be understood that the embodiments are not limited to the precise construction and components disclosed herein and that various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatuses of the embodiments without departing from the spirit and scope of the embodiments as defined in the appended claims.