Abstract:
Electrically isolated gas cups for plasma transferred arc welding torches, plasma transferred arc welding torches including such gas cups, and related methods are disclosed. In one embodiment a gas cup includes a dielectric portion sized and configured to couple with a torch body and electrically isolate the gas cup from the torch body. In additional embodiments, a plasma transferred arc welding torch includes an anode, a cathode, a torch body coupled to the anode and the electrode, and a gas cup at least partially surrounding the anode and electrically isolated from the torch body. In further embodiments, a method of coupling a gas cup to a plasma transferred arc welding torch includes coupling a dielectric structure to a gas cup and coupling the dielectric structure to a torch body to electrically isolate the gas cup from the torch body.

Description:
TECHNICAL FIELD 
       [0001]    Embodiments of the invention relate to plasma transfer arc welding and, more particularly, to plasma transfer arc welding torches, electrically isolated gas cups, and related methods. 
       BACKGROUND 
       [0002]    Plasma transfer arc (PTA) welding is an advanced variation of the tungsten inert gas (TIG) welding process. PTA welding is well-suited for automated applications, when compared to TIG welding, as the arc generated by PTA welding tends to be more consistent and less sensitive to variations in the size of the gap between the electrode and the work piece. However, when the gas cup is contacted with the work piece an electrical circuit may be formed between the torch body and the gas cup that may be detrimental to the welding process, may damage the welding torch, and may cause defects in the work piece. In view of this, automated welding of certain work pieces, such as earth boring drill bits, may be difficult as the shape of the work piece may be complex and the gas cup of the PTA welding torch may unintentionally contact the work piece during welding operations, such as hardfacing operations, and may damage the PTA torch and the work piece. Additionally, molten metal spatter from the welding process may contact the gas cup of the welding torch and may stick to the surface of the gas cup and may disrupt the gas flow from the welding torch, which may be detrimental to the welding process and require cleaning and repair of the welding torch to correct. 
         [0003]    In view of the foregoing, it would be advantageous to provide improved PTA welding torches, gas cups for PTA welding torches, and related methods. 
       BRIEF SUMMARY 
       [0004]    In some embodiments, a gas cup for a plasma transferred arc welding torch includes a dielectric portion sized and configured to couple with a torch body and electrically isolate the gas cup from the torch body. 
         [0005]    In additional embodiments, a plasma transferred arc welding torch includes an anode comprising a central cavity, a cathode positioned at least partially within the central cavity of the anode, a torch body coupled to the anode and an electrode, and a gas cup at least partially surrounding the anode and electrically isolated from the torch body. 
         [0006]    In further embodiments, a method of coupling a gas cup to a plasma transferred arc welding torch includes coupling a dielectric structure to a gas cup and coupling the dielectric structure to a torch body to electrically isolate the gas cup from the torch body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows a cross-sectional view of a portion of a plasma transfer arc welding torch including an electrically isolated gas cup, according to an embodiment of the present invention. 
           [0008]      FIG. 2  shows a cross-sectional detail view of a portion of an electrically isolated gas cup including a dielectric coupler and a coolant channel, according to an embodiment of the present invention. 
           [0009]      FIG. 3  shows a cross-sectional detail view of a portion of an electrically isolated gas cup including a dielectric coupler having an integrated coolant channel, according to an embodiment of the present invention. 
           [0010]      FIG. 4  shows a cross-sectional detail view of a portion of an electrically isolated gas cup including a dielectric material coating thereon, according to an embodiment of the present invention. 
           [0011]      FIG. 5  shows a cross-sectional detail view of a portion of an electrically isolated gas cup having a body formed of a dielectric material, according to an embodiment of the present invention. 
           [0012]      FIG. 6  shows a cross-sectional detail view of a portion of a plurality of metal rings for forming coolant channels, such as included with the electrically isolated gas cup of  FIG. 1 . 
           [0013]      FIG. 7  shows a perspective top view of a metal ring of  FIG. 6 . 
           [0014]      FIG. 8  shows a cross-sectional view of a portion of a plasma transfer arc welding torch, such as shown in  FIG. 1 , during a welding operation. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Illustrations presented herein are not meant to be actual views of any particular plasma transfer arc welding torch, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation. The various drawings depict embodiments of the invention as will be understood by the use of ordinary skill in the art and are not necessarily drawn to scale. 
         [0016]    As shown in  FIG. 1 , a plasma transfer arc (PTA) welding torch  10  may include a torch body  12 , an electrode  14 , an anode  16  and a gas cup  18 . The torch body  12  may be coupled to each of the electrode  14 , the anode  16  and the gas cup  18 , and may include a plurality of fluid channels extending therethrough, including a plasma-gas channel  20 , a powder-gas channel  22 , a shielding-gas channel  24 , and a coolant channel  26 . 
         [0017]    The electrode  14  may be formed of an electrically conductive material with a relatively high melting point, such as tungsten, and may be generally shaped as an elongated cylinder with a conical point at one end. The end opposite the conical point may be electrically coupled to a power source and rigidly fixed to an upper portion (not shown) of the torch body  12 . 
         [0018]    The anode  16  may be formed of an electrically conductive material, such as a copper alloy, and may be electrically coupled to, and rigidly fixed to, a lower portion  28  of the torch body  12 . The anode  16  may include a central cavity  30  formed therein, the central cavity  30  defined by an inner wall  32  of the anode  16 . The central cavity  30  may extend to an open end of the anode  16  that may form a central nozzle  34 . The electrode  14  may be positioned within the central cavity  30  of the anode  16  and electrically isolated from the anode  16 . An outer surface  36  of the electrode  14  and the inner wall  32  of the anode  16  may define an annular plasma gas channel therebetween. The anode  16  may also include a powder-gas channel  38  formed therein that may be coupled to the powder-gas channel  22  of the torch body  12  and may extend to one or more openings  40  located proximate to the central nozzle  34 . 
         [0019]    In some embodiments, as shown in  FIGS. 1 ,  2  and  3 , the gas cup  18  may include a generally annular metallic body  42  coupled to a generally annular dielectric portion, such as a dielectric coupler  44 , at one end and having an opening at another end forming a shielding-gas nozzle  46 . The dielectric coupler  44  may be formed of a heat resistant dielectric material, such as one or more of a phenolic resin composite (i.e., BAKELITE®), thermoset plastic (i.e., Nylon and TEFLON®) and ceramic (i.e., BaSrTi) dielectric material, and may be sized and configured to couple to the lower portion  28  of the torch body  12  and may couple the gas cup  18  to the torch body  12 . In view of this, the dielectric coupler  44  may electrically isolate the gas cup  18  from the torch body  12  and the anode  16 . 
         [0020]    As shown in  FIGS. 1 and 2 , the dielectric coupler  44  may be coupled to the metallic body  42  of the gas cup  18  and to the torch body  12  with helical threads. For example, the dielectric coupler  44  may include an inner threaded portion  48 , which may mate with threads  50  formed on the outer surface  51  of the torch body  12 , and an outer threaded portion  52 , which may mate with threads  54  formed on the inner surface  56  of the metallic body  42  of the gas cup  18 . However, in additional embodiments the dielectric coupler  44  may be coupled to the metallic body  42  of the gas cup  18  by other coupling means. For example, the dielectric coupler  44  may be coupled to the metallic body  42  by a friction or interference fit, as shown in  FIG. 3 . In additional embodiments, the dielectric coupler  44  may be integrally molded to the metallic body  42  or may be adhered to the metallic body  42  by an adhesive. Likewise, the dielectric coupler  44  may be coupled to the torch body  12  by a coupling means other than, or in addition to, a threaded connection. 
         [0021]    An inner surface  56  of the metallic body  42  of the gas cup  18  and an outer surface  58  of the anode  16  may define a generally annular shielding-gas channel  60  therebetween, and the generally annular shielding-gas channel  60  may be in fluid communication with the shielding-gas channel  24  of the torch body  12  and may extend to the shielding-gas nozzle  46 . Additionally, the gas cup  18  may also include at least one coolant channel  62 , which may be coupled to a cooling system (not shown) of the PTA welding torch  10  and may be electrically isolated from the torch body  12  and the anode  16 . 
         [0022]    In additional embodiments, as shown in  FIG. 4 , the gas cup  18  may comprise a metallic body  42  that may include a dielectric material coating  63  disposed thereon. The dielectric material coating  63  may extend over at least a portion of the metallic body  42 , and may be positioned between the metallic body  42  of the gas cup  18  and the torch body  12 . In view of this, the dielectric material coating  63  may electrically isolate the gas cup  18  from the torch body  12 . 
         [0023]    In yet further embodiments, as shown in  FIG. 5 , the gas cup  18  may not include a metallic body  42  and may consist essentially of a dielectric material. For example, the gas cup  18  may be composed entirely of a dielectric material, such as a ceramic dielectric material  64 . 
         [0024]    As shown in  FIGS. 1 ,  6 ,  7  and  8 , coolant channels  62  may be located at interfaces between a plurality of generally annular metallic structures, such as metal rings  66 , which may be coupled to the metallic body  42  of the gas cup  18 . Each ring  66  may include a groove  68  formed therein, and may have a surface  70  that is shaped and configured to mate with a surface  70  of another ring  66 . Each ring  66  may be welded to another ring  66 , such as by providing a soldering material at an interface between the mating surfaces  70  of the rings  66  and soldering the rings  66  together. Additionally, the rings  66  may be joined to the metallic body  42  of the gas cup  18 , such as by soldering. The grooves  68  may then define coolant channels  62  having at least one coolant inlet  72  and at least one coolant outlet  74  ( FIG. 7 ). 
         [0025]    In another embodiment, as shown in  FIG. 2 , the coolant channel  62  may be formed in a single, generally annular structure, such as a metallic ring  76 . Additionally, the ring  76  may be configured to be removed and replaced with relative ease. The ring  76  may include a groove  78  formed in an inner surface  80  that mates with a portion of an outer surface  82  of the metallic body  42  of the gas cup  18  to define the coolant channel  62 . In view of this, the coolant may be directed into contact with the metallic body  42  of the gas cup  18 . The ring  76  may also include grooves  84  formed in the inner surface  80 , positioned on either side of the coolant channel  62 , sized and configured to receive a seal, such as a gasket  86  (i.e., an -O-ring), which may assist in containing a fluid coolant within the coolant channel  62 . Mating features, such as interlocking threads  88 , may be formed in the ring  76  and the outer surface  82  of the metallic body of the gas cup  18  to couple the ring  76  to the metallic body  42 . Additional embodiments may not include threads  88 , and the ring  76  may be retained on the metallic body  42  by friction between the gaskets  86 , and the outer surface  82  of the metallic body  42 . 
         [0026]    In some embodiments, as shown in  FIG. 3 , the coolant channel  62  may be formed in the dielectric coupler  44  located between the metallic body  42  of the gas cup  18  and the torch body  12 . A groove  90  may be formed in a surface  92  of the dielectric coupler  44  that mates with the inner surface  56  ( FIG. 1 ) of the metallic body  42  of the gas cup  18  to define the coolant channel  62 . Additional grooves  94  may formed in the surface  92  of the dielectric coupler  44 , positioned on either side of the coolant channel  62 , sized and configured to receive a seal, such as a gasket  96  (i.e., an -O-ring), which may assist in containing a fluid coolant within the coolant channel  62 . In such embodiments, an inlet and an outlet may be located within the dielectric coupler  44  to direct coolant into and out of the coolant channel  62 , or an inlet and outlet may be formed through the metallic body  42 . However, in some embodiments, such as shown in  FIGS. 4 and 5 , the gas cup  18  may not include a coolant channel  62 . 
         [0027]    Additionally, existing PTA welders may be retroactively modified according to the present invention. A conventional PTA welding torch includes a metal gas cup that is in electrical communication with a torch body and an anode of the PTA torch (not shown). The metal gas cup may be removed from the torch body, and an electrically isolated gas cup  18  according to the present invention, such as those described with reference to each of  FIGS. 1-5 , may be installed onto the PTA welding torch. For example, a dielectric coupler  44  may be coupled to the metal gas cup, and the dielectric coupler  44  may be coupled to the torch body to electrically isolate the gas cup from the torch body. Additionally, a coolant channel  62  may be added to the gas cup and a cooling system may be coupled to the coolant channel  62  of the gas cup. In another example, the electrically conductive metal body of the gas cup may be coated with a dielectric material coating  63  and then the gas cup may be installed on the torch body. In view of this, the dielectric material coating  63  may electrically isolate the metallic body of the gas cup from the torch body. 
         [0028]    In operation, the central nozzle  34  of the anode  16  of the PTA welding torch  10  may be positioned proximate a work piece  98 , as shown in  FIG. 8 . An inert gas, such as commercially pure argon  100 , may be directed through the central cavity  30  of the anode  16  toward the central nozzle  34 . Then a pilot arc may be ignited between the electrode  14  and the anode  16  and an electric current may pass through the argon  100  to form a plasma  102 , which may exit through the central nozzle  34  of the anode  16 . Additionally, a shielding-gas  104 , such as argon or a gas mixture (i.e., argon and hydrogen), may be directed through the shielding-gas channel  22  of the torch body  12  and into the generally annular shielding-gas channel  60  defined between the inner surface  56  of the gas cup  18  and the outer surface  58  of the anode  16 . The shielding-gas  104  may exit the shielding-gas nozzle  46  of the gas cup  18  and may substantially surround the plasma  102  that is exiting the central nozzle  34  of the anode  16 . The plasma  102  exiting the central nozzle  34  of the anode  16  may then come into contact with the work piece  98  and the plasma  102  may carry an electric current from the electrode  14  to the work piece  98  and a molten weld pool  106  may be formed in the work piece  98 . Additionally, a powder-gas  108 , comprising a powdered material suspended in a gas, may be directed through the powder-gas channel  22  of the torch body  12  into the powder-gas channel  38  of the anode  16  and may exit the powder-gas channel  38  proximate the central nozzle  34  of the anode  16 . The powdered material suspended in the powder-gas  108  may be directed into the work piece  98  and may contact the molten weld pool  106  and become fused with the work piece  98  as the weld pool  106  cools and hardens. For example, such a welding process may be utilized by an automated machine, such as a robotic arm, to apply a hardfacing material, such as a powdered metal or a powdered composite material, to an earth-boring tool, such as an earth-boring drill bit. In view of this, unintentional contact between the gas cup  18  and the work piece  98  would not create an electric circuit between the torch body  12  and the work piece  98  through the gas cup  18  that may damage the PTA welding torch  10 , disrupt the welding process and cause defects in the work piece  98 . 
         [0029]    Such welding processes may generate a relatively large amount of heat. In view of this, a coolant system may be utilized to cool components of the PTA welding torch  10 . During operation a coolant  110  may be directed through the coolant channel  26  in the torch body  12  to draw heat from the torch body  12  and cool the torch body  12 . Additionally, as the anode  16  may be in direct contact with the torch body  12 , or may be in close proximity to the torch body  12 , heat may be drawn from the anode  16  by the torch body  12 . In some embodiments, the gas cup  18  may be cooled by a fluid coolant directed through one or more coolant channels  62 , as described with reference to  FIGS. 1-7 . Cooling the gas cup  18  with a coolant channel  62  that is integrated with the gas cup  18  may enable improved cooling of the gas cup  18 , which may reduce the amount of molten metal spatter from the welding process that may stick to the gas cup  18  and disrupt gas flow. 
         [0030]    In some embodiments, a dielectric coolant  112 , such as shown in  FIG. 8 , may be directed through the coolant channel  62  of the gas cup  18 , which may prevent an electric current from the PTA welding torch  10  from being carried through the coolant  112 . For example, at least one of deionized water and distilled water may be directed from the cooling system into an opening of the coolant channel  62 , through the coolant channel  62 , and then directed out of an exit of the coolant channel  62  and returned to the cooling system. In view of this, the cooling system of the PTA welding torch  10  may include a single loop system that cycles the same coolant  110 ,  112  through both the coolant channel  26  of the torch body  12  and the coolant channel  62  of the gas cup  18 . In additional embodiments, the cooling system may comprise two or more separate coolant loops and the coolant  110 , cycled through the coolant channel  26  of the torch body  12 , and the coolant  112  cycled through the coolant channel  62  of the gas cup  18 , may be separate. In view of this, the gas cup  18  may be effectively cooled, which may prevent damage to the gas cup  18  and may prevent the adherence of molten metal splatter to the gas cup  18 , while the gas cup  18  is electrically isolated from the torch body  12 , which may prevent an electrical circuit between the work piece  98  and the torch body  12  through the gas cup  18 . 
         [0031]    Although this invention has been described with reference to particular embodiments, the invention is not limited to these described embodiments. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent devices and methods.