Abstract:
The present invention discloses an anti-electrostatic discharge spray gun apparatus and method for preventing crystallization of particles formed as a result of electrostatic discharge from forming on a spray gun nozzle and an associated pair of oppositely charged electrodes disposed on the gun. The apparatus has a housing; a nozzle attached to the housing for dispensing gas; means for dispensing a gas through the nozzle; means for electrostatically discharging a gas dispensed through the nozzle; and means for restricting the flow of a gas through the nozzle. The means for dispensing and restricting flow of a gas through the nozzle may be either a bypass piping having a flow control means or a stopper that operates to provide a constant but low volume flow of an inert gas such as nitrogen to the nozzle to prevent particle build up or crystallization from occurring.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to an anti-electrostatic discharge spray gun apparatus and method for preventing crystallization of particles formed as a result of electrostatic discharge from forming on a spray gun nozzle and on a pair of oppositely charged electrodes disposed on the gun.  
         BACKGROUND OF THE INVENTION  
         [0002]    An electrostatic air gun apparatus is well known in the art. Such an apparatus may be used in clean rooms for the manufacture of semiconductors. The apparatus normally includes a spray gun housing, a conduit for passing a fluid or gas therethrough, flow control means, a nozzle disposed between the electrodes, and a positively charged and a negatively electrode that cooperate to form an electric field and then discharge electrostatically charged particles that pass through the field. Typically, upon operation of the spray gun, a large volume of gas such as compressed air or an inert gas including but not limited to nitrogen and argon, flows through the conduit, and then through the nozzle disposed between the electrodes. Then the electrodes then discharge electrostatic ions present in the gas. However, over time, aerosol particles formed from the electrostatic discharge of the gas dispensed through the nozzle can cause a crystallized build-up of a material such as ammonium nitrate on the electrodes and the nozzle. This contamination of the electrodes and the nozzle can erode the electrodes and the nozzle, thus preventing the electrodes from performing their anti-electrostatic discharge function and preventing the nozzle from dispensing the gas.  
           [0003]    The present invention provides a new deionized air gun that avoids crystallization from forming on the electrodes and the nozzle.  
           [0004]    It is therefore an object of the present invention to provide an apparatus for preventing particle build up on the electrodes in an electrostatic air gun that does not have the drawbacks or shortcomings of the conventional electrostatic air guns.  
           [0005]    It is another object of the present invention to provide a method for preventing or reducing particle build up on the electrodes that utilizes a steady flow of compressed air or an inert gas such as nitrogen to prevent crystallization of the electrodes.  
           [0006]    It is a further object of the present invention to provide an apparatus that will not erode electrodes or a nozzle of an electrostatic spray gun.  
         SUMMARY OF THE INVENTION  
         [0007]    In accordance with the present invention, an apparatus and method for preventing electrostatic discharge from contaminating a nozzle and an electrostatic discharge-dissipating device are provided.  
           [0008]    In a preferred embodiment, an anti-electrostatic discharge spray gun apparatus for preventing electrostatic discharge from causing crystallization of the nozzle has:  
           [0009]    (a) a housing;  
           [0010]    (b) a nozzle attached to the housing having an orifice for dispensing gas;  
           [0011]    (c) means for dispensing a gas through the nozzle;  
           [0012]    (d) means for electrostatically discharging a gas dispensed through the nozzle; and  
           [0013]    (e) means for restricting the flow of a gas through the nozzle.  
           [0014]    The anti-electrostatic discharge spray gun is further directed to a hose in communication with a gas flow source and in further communication with the nozzle; a handle movably attached to the housing, wherein the handle is capable of moving between a first position and a second position wherein the handle is normally biased in the first position; and a trigger valve in communication with the hose wherein the hose, handle and trigger valve cooperate to define the means for dispensing a gas through the nozzle.  
           [0015]    Additionally, the present invention is further directed to a bypass piping that operates to provide a constant but low volume flow of gas through the nozzle. The bypass piping further defines the means for restricting the flow of a gas through the nozzle.  
           [0016]    In an alternative embodiment, the present invention is directed to a stopper that defines the means for dispensing gas through the nozzle and the means for restricting the flow of a gas through the nozzle. The stopper is disposed between the handle and the trigger valve that is in communication with the hose and cooperates with the handle and the trigger valve to provide a steady but low volume flow of gas through the nozzle.  
           [0017]    Preferably, the means for electrostatically discharging a gas dispensed through the nozzle is a pair of charged electrodes, each having an opposite polarity that cooperate to form an electric field for discharging ions present in the gas dispensed through the nozzle.  
           [0018]    Additionally, a method of using the anti-electrostatic discharge apparatus is disclosed herein. The method provides for a steady flow of an inert gas to flow through the nozzle to prevent contamination, resulting from electrostatic discharge, of the electrodes and the nozzle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which:  
         [0020]    [0020]FIG. 1 is an elevational view of an electrostatic spray gun having a bypass piping in accordance with a preferred embodiment of the present invention.  
         [0021]    [0021]FIG. 2 is an elevational view of an electrostatic spray gun having a stopper in accordance with a preferred embodiment of the present invention.  
         [0022]    [0022]FIG. 3 is an enlarged view of a stopper and a portion of a trigger valve in accordance with a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring now generally to the drawings, FIG. 1- 3 , the present invention discloses an electrostatic discharge spray gun apparatus having a nozzle; means for dispensing and means for restricting flow of a gas through a nozzle; and means for electrostatically discharging ions in a gas to prevent contamination of the nozzle caused by a crystallization buildup byproduct of an electrostatic discharge process.  
         [0024]    As shown in a preferred embodiment in FIGS.  1 , the electrostatic discharge spray gun is further directed to an electrostatic discharge spray gun apparatus  10 ,  110  having a housing  12 ,  112 ; a nozzle  14 ,  114  attached to the housing; means for dispensing a gas through the nozzle; means for electrostatically discharging a gas dispensed through the nozzle; and means for restricting the flow of a gas through the nozzle.  
         [0025]    Preferably, a gas  36 ,  136  dispensed through the spray gun is dry compressed air or an inert gas such as nitrogen. The housing  12 ,  112  may be made from any durable material such as but not limited to metal or a high impact styrene material. The nozzle  14 ,  114  may be integrally formed with the housing or may be releasably and sealably attached to the housing  12 ,  112 . The nozzle  14 ,  114  has an orifice  16 ,  116  disposed therethrough for dispensing the gas  36 ,  136  from the means for dispensing a gas through the nozzle to the atmosphere.  
         [0026]    In a preferred embodiment as shown in FIG. 1, the means for dispensing gas through the nozzle  14  includes a hose  18 , a handle  20 , and a trigger valve  22 . Preferably, the hose  18  has a uniform diameter D having a first end  38  in communication with a gas flow source (not shown) and a second end  40  in communication with the nozzle  14 . The hose may be formed from any flexible material such as polyurethane Durometer or plastic.  
         [0027]    Preferably, the handle  20  is disposed on the housing and is moved in a reciprocating manner between a first and a second position. The handle may be made from a durable material such as a high impact styrene material that is injection molded.  
         [0028]    The handle  20  is movably attached to the housing  12  by a conventional fastening means well-known in the mechanical arts and moves between a first position and a second position. The handle  12  is normally biased by a biasing means in the first position, but in operation, is moved to the second position to dispense a large volume of gas through the hose  18 .  
         [0029]    The trigger valve  22  is disposed within the housing and is in communication with the hose  18 . The trigger valve  22  is preferably, a conventional valve well known in the pneumatic arts formed from a material such as nylon that is closed when the handle  20  is in the first position and is completely opened when the handle is in the second position. The handle  20  and the trigger valve  22  cooperate to dispense the gas  36  through the hose  18  by moving the handle  18  to the first position to close the trigger valve  22  and to the second position to open the trigger valve. Thus, when the trigger valve  22  is closed, the gas  36  is prevented from passing through the hose  18  and when the trigger valve  22  is open, a large volume of the gas  36  flows through the hose  18  from a gas source and then through the nozzle  14 .  
         [0030]    In a preferred embodiment as shown in FIG. 1, the means for dispensing a gas through the nozzle further has a bypass piping  24  in communication with the hose  18  and in further communication with the nozzle  14  for dispensing gas through the nozzle  14  when the trigger valve  22  is in a closed position. The bypass piping  24  has a uniform diameter less than the diameter D of the hose and allows a restricted flow of gas to flow through the bypass piping  24  and then through the nozzle  14 . The bypass piping  24  further has means for restricting the flow of a gas through the nozzle. The means for restricting the flow of gas through the nozzle preferably has a flow control niddle valve  26  that is capable of being adjusted to allow either a maximum amount of restricted gas to flow through the bypass piping  24  or to prevent gas from flowing through the bypass piping  24 . However, the flow control means is not limited to the niddle valve  26  but may be other conventional means for controlling flow of gas well known in the mechanical and pneumatic arts. The smaller diameter of the piping also cooperates to prevent a large volume of gas to flow through the bypass piping  24  when the niddle valve  26  is open.  
         [0031]    Additionally, the bypass piping  24  further has a first end  42  disposed between the hose first end  38  and the trigger valve  22  in communication with the hose  18  and a second end  44  disposed between the trigger valve  22  and the hose second end  40  in further communication with the hose  18 . The flow control niddle valve  26  is disposed between the first end  42  and the second end  44  of the bypass piping  24 . The niddle valve  26  provides a restricted flow of gas through the bypass piping  24  when the niddle valve  26  is in an open position and stops a flow of gas through the bypass piping  24  when the niddle valve  26  is in a closed position. In operation, the niddle valve  26  is biased in an open position to allow a steady flow of gas  36  to flow through the bypass piping  24  and then through the nozzle  14 .  
         [0032]    The first end  42  of the bypass piping  24  is preferably, connected to the hose  18  by a first tee-shaped connector  28 , and the second end  44  of the bypass piping  24  is preferably, connected to the hose  18  by a second tee-shaped connector  30 . However, in an alternative embodiment, the first end  42  of the bypass piping  24  may be connected directly to the nozzle  14  and the second end  44  may be connected directly to a gas source (not shown).  
         [0033]    The electrostatic discharge spray gun  10  further has a positively charged electrode  32  preferably having a first pointed tip; and a negatively charged electrode  34  preferably having a pointed tip. Each electrode  32 ,  34 , respectively, is connected to a charging source (not shown). The charged electrodes  32 ,  34  define the means for electrostatically discharging gas dispensed through the nozzle  14 . The electrodes  32 ,  34  preferably surround the nozzle  14 , thus the nozzle  14  is disposed between the two electrodes  32 ,  34 . In operation, an electric field is formed between the charged electrodes that operate to deionized ions dispensed through the orifice  16  in the nozzle  14  and then through the electric field.  
         [0034]    According to the preferred embodiment shown in FIG. 1, in operation, the handle  20  is biased normally in the first position and accordingly, the trigger valve  22  is biased in a closed position to prevent gas from flowing through the hose  18  when the handle  20  is in the first position. As the handle  20  moves from the first position to the second position, the gas  36  flows from the fluid source through the hose  18 . When the handle  20  is moved to the second position, the handle  20  completely engages and opens the trigger valve  22 , thus, allowing an unrestricted flow of high volume of gas to flow through the hose  18 . After the gas  36  is dispensed through the hose  18 , the handle  20  returns to the first position and thus, causes the trigger valve  22  to close.  
         [0035]    The gas  36  dispensed through the hose  18  may become ionized while passing through the hose  18  but before being dispensed through the orifice  16  in the nozzle  14 . The gas  36  is deionized after being dispensed through the nozzle  14  and passed through the electric field.  
         [0036]    The bypass piping  24  flow control niddle valve  26  is normally biased in an open position to allow a restricted flow of low volume of gas to flow through the bypass piping  24  at a constant rate. The operation of the flow control niddle valve  26  is preferably, independent of the trigger valve  22  such that gas flows through the bypass piping  24  when the flow control niddle valve  26  is open regardless of whether the trigger valve  22  is opened or closed. The constant flow of inert gas  36  flowing through the bypass valve  24  prevents crystallization build-up resulting from electrostatic discharge on the electrodes  32 ,  34 .  
         [0037]    In a preferred embodiment as shown in FIGS.  2 - 3 , the means for dispensing gas through a nozzle includes a hose  118 , a handle  120 , and a trigger valve  122 .  
         [0038]    Preferably, the hose  118  has a uniform diameter D having a first end  138  in communication with a gas flow source (not shown) and a second end  140  in communication with the nozzle  114 . Preferably, the handle  120  is moved in a reciprocating manner between a first and a second position.  
         [0039]    The handle  120  is movably attached to the housing  112  by conventional fastening means well-known in the mechanical arts and moves between a first position and a second position. The handle  120  is normally biased by a biasing means in the first position, but in operation, is moved to the second position to dispense a large volume of gas through the hose  118 .  
         [0040]    The trigger valve  122  is disposed within the housing and is in communication with the hose  118 . The trigger valve  122  is preferably, a conventional valve well known in the pneumatic arts that is closed when the handle  120  is in the first position and is completely opened when the handle  120  is in the second position. The handle  120  and the trigger valve  122  cooperate to dispense a gas  136  through the hose  120  by moving the handle  120  to the first position to close the trigger valve  122  and to the second position to open the trigger valve  122 . Thus, when the trigger valve  122  is closed, the gas  136  is prevented from passing through the hose  118  and when the trigger valve  122  is open, a large volume of gas flows through the hose  118  from a gas source and then through the nozzle  114 .  
         [0041]    The means for dispensing a gas through the nozzle further has a stopper  124  disposed between the handle  120  and the trigger valve  122 . The stopper  124  is preferably, a resilient member made from a material such as rubber. The stopper  124  further defines the means for dispensing a gas through the nozzle and defines the means for restricting the flow of gas through the nozzle. The stopper  124  cooperates with the handle  120  and the trigger valve  122  to provide a restricted flow of gas through the hose  118  by engaging and thus, partially opening the trigger valve  122  when the handle  120  is in the first position, and to provide an unrestricted flow of gas through the hose  118  by engaging and completely opening the trigger valve  122  when the handle  118  is in the second position. The trigger valve  122  is normally biased in a partially open position when the handle  120  is in the first position to allow a restricted flow of gas to flow through the hose  118  and then through the nozzle  114 .  
         [0042]    The electrostatic discharge spray gun  110  further has a positively charged electrode  132  preferably having a first pointed tip; and a negatively charged electrode  134  preferably having a second pointed tip. Each electrode  132 ,  134 , respectively, is connected to a charging source (not shown). The charged electrodes  132 ,  134  define the means for electrostatically discharging gas dispensed through the nozzle  114 . The electrodes  132 ,  134  preferably surround the nozzle  114 , thus, the nozzle  114  is disposed between the two electrodes  132 ,  134 . In operation, an electric field is formed between the charged electrodes  132 ,  134 , that operates to deionize ions dispensed through the orifice  116  in the nozzle  114  and then through the electric field.  
         [0043]    In operation, the handle  120  is biased normally in the first position and accordingly, the trigger valve  122  is biased in a partially open position to allow a low volume and constant but restricted flow of gas  126  to flow through the hose  118  when the handle  120  is in the first position. As the handle  120  moves from the first position to the second position, gas flows from the fluid source through the hose  118 . When the handle  120  is moved to the second position, the handle  120  completely engages and opens the trigger valve  122 , thus, allowing an unrestricted flow of high volume of gas to flow through the hose  118 . After gas is dispensed through the hose  118 , the handle  120  returns to the first position and thus, causes the trigger valve  122  to be partially open.  
         [0044]    Inert gas  136  dispensed through the hose  118  may become ionized while passing through the hose  118  but before being dispensed through the orifice  116  in the nozzle  114 . The gas  136  is deionized after being dispensed through the nozzle  114  and passed through the electric field.  
         [0045]    The constant flow of inert gas flowing through the hose prevents an electrostatic discharge crystallization build-up on the tips of the electrodes and on the nozzle.