Patent Publication Number: US-6903301-B2

Title: Contact start plasma arc torch and method of initiating a pilot arc

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation in part of U.S. application Ser. No. 09/794,540, titled “Contact Start Plasma Torch,” filed Feb. 27, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to plasma arc torches and more particularly to devices and methods for initiating a pilot arc in a contact start plasma arc torch. 
     BACKGROUND OF THE INVENTION 
     Plasma arc torches, also known as electric arc torches, are commonly used for cutting, marking, gouging, and welding metal workpieces by directing a high energy plasma stream consisting of ionized gas particles toward the workpiece. In a typical plasma arc torch, the gas to be ionized is supplied to a distal end of the torch and flows past an electrode before exiting through an orifice in the tip, or nozzle, of the plasma arc torch. The electrode has a relatively negative potential and operates as a cathode. Conversely, the torch tip constitutes a relatively positive potential and operates as an anode. Further, the electrode is in a spaced relationship with the tip, thereby creating a gap, at the distal end of the torch. In operation, a pilot arc is created in the gap between the electrode and the tip, which heats and subsequently ionizes the gas. Further, the ionized gas is blown out of the torch and appears as a plasma stream that extends distally off the tip. As the distal end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece because the impedance of the workpiece to ground is lower than the impedance of the torch tip to ground. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode. 
     One of two methods is typically used for initiating the pilot arc between the electrode and the tip. In the first method, commonly referred to as a “high frequency” or “high voltage” start, a high potential is applied across the electrode and the tip sufficient to create an arc in the gap between the electrode and the tip. Accordingly, the first method is also referred to as a “non-contact” start, since the electrode and the tip do not make physical contact to generate the pilot arc. In the second method, commonly referred to as a “contact start,” the electrode and the tip are brought into contact and are gradually separated, thereby drawing an arc between the electrode and the tip. The contact start method thus allows an arc to be initiated at much lower potentials since the distance between the electrode and the tip is much smaller. 
     With contact start torches, however, the relative orientation and spacing of the electrode and the tip are critical to proper torch operation and cut quality, and providing a torch with a moving electrode and/or tip that retains the proper orientation and spacing during repeated operation is relatively difficult and expensive. Further, when a pilot arc is generated between the electrode and the tip proximate the bottom of the electrode, damage accumulates more rapidly on the tip near the orifice, which can negatively impact torch performance and cut quality. Additionally, with plasma arc torches in which the tip is movable, the tip is in different positions between the on and off modes, thereby causing difficulty in controlling the relative position of the tip with respect to the workpiece. Moreover, drag cutting, which requires the tip to be in contact with the workpiece, becomes difficult if not impossible since the tip would be moved back into contact with the electrode upon being placed into contact with the workpiece. 
     One known contact start plasma arc torch design employs a stationary electrode and tip, while a translatable swirl ring is in initial contact with the electrode and moves away to draw an arc between the electrode and the tip. However, such a starting method causes damage to accumulate more rapidly on the swirl ring, or the anodic element, thereby reducing the life of the swirl ring and resulting in reduced torch performance. Further, with a swirl ring as a translatable element, the gas dynamics inside the torch may be negatively impacted if the translatable swirl ring becomes misaligned and also as the translatable swirl ring becomes worn during operation. Moreover, repair or replacement of the translatable swirl ring is relatively difficult as several components within the distal end of the torch must be removed for access. 
     Accordingly, a need remains in the art for a contact start plasma arc torch and associated methods that reduce the amount of damage to the electrode and the tip while increasing torch performance. A further need exists for such a torch that provides for quick and efficient replacement of consumable components, (e.g., electrode, tip), disposed therein. 
     SUMMARY OF THE INVENTION 
     In one preferred form, the present invention provides a contact start plasma arc torch comprising an electrode, a tip, and an initiator that is in contact with the tip, the initiator being movable to separate from the tip and establish a pilot arc between the initiator and the tip. Preferably, the initiator is part of a start cartridge that comprises a cartridge body, a tip seat secured to a distal end of the cartridge body, and a biasing member (e.g., coil spring), disposed within the cartridge body, wherein the initiator is disposed between the biasing member and the tip seat such that the coil spring biases the initiator into contact with the tip. Generally, a working gas is directed through the start cartridge to overcome the spring bias and to move the initiator away from the tip to draw a pilot arc between the initiator and the tip. 
     The plasma arc torch further comprises a plurality of vent holes disposed within the cartridge body, within an insulating body, and within an anode, collectively referred to as head vent holes, which are in fluid communication such that the gas that is directed through the start cartridge to move the initiator is vented through the head vent holes. Further, another portion of the gas is directed through swirl holes and secondary gas holes in the tip to generate and stabilize a plasma stream that is blown from a central exit orifice in the tip. 
     In another form, a start cartridge is provided that comprises a cartridge assembly and an initiator disposed within the cartridge assembly that is used to draw a pilot arc between the initiator and a tip within a plasma arc torch. The cartridge assembly preferably comprises a cartridge body and a tip seat secured to a distal portion of the cartridge body, in addition to a biasing member that biases the initiator in contact with the tip in an idle mode of the plasma arc torch. Additionally, an initiator for initiating a pilot arc in a plasma arc torch is provided, wherein the initiator is movable against a resilient bias to establish a pilot arc between the initiator and a tip within the plasma arc torch. 
     In yet another form, the present invention provides a plasma arc torch head for use with a fixed electrode, a fixed tip, and a source of gas and electric power for initiating a plasma arc within a plasma arc torch. The torch head comprises head vent holes disposed at a proximal section thereof, wherein the head vent holes vent at least a portion of the gas from the torch head during operation of the plasma arc torch. 
     Additionally, the present invention provides a method of initiating a pilot arc in a plasma arc torch that comprises the steps of biasing an initiator into contact with a tip, providing a source of gas and electric power, and directing at least a portion of the gas to overcome the bias to separate the initiator from the tip, wherein a pilot arc is drawn between the initiator and the tip as the bias is overcome. A method of venting gas from a plasma arc torch is also provided, which comprises the steps of providing a source of gas and electric power, directing the gas and electric power to initiate a pilot arc, and venting at least a portion of the gas through head vent holes. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a manually operated plasma arc apparatus in accordance with the principles of the present invention; 
         FIG. 2  is a side view of a torch head disposed within a plasma arc torch and constructed in accordance with the principles of the present invention; 
         FIG. 3  is a perspective view of a torch head constructed in accordance with the principles of the present invention; 
         FIG. 4  is a perspective exploded view of a torch head and consumable components constructed in accordance with the principles of the present invention; 
         FIG. 5  is a cross-sectional view of a torch head and consumable components constructed in accordance with the principles of the present invention; 
         FIG. 6  is a bottom view of a distal end of a torch head constructed in accordance with the principles of the present invention; 
         FIG. 7A  is a cross-sectional view of a torch head in an idle mode and constructed in accordance with the principles of the present invention; 
         FIG. 7B  is a cross-sectional view of a torch head in a pilot mode and constructed in accordance with the principles of the present invention; 
         FIG. 7C  is a cross-sectional view of a torch head illustrating gas passages through a second embodiment of a start cartridge and constructed in accordance with the principles of the present invention; 
         FIG. 8  is a cross-sectional view of a torch head comprising a third embodiment of a start cartridge and constructed in accordance with the principles of the present invention; 
         FIG. 9  is an upper perspective view of a cartridge body comprising gas passages and constructed in accordance with the principles of the present invention; 
         FIG. 10  is a lower perspective view of the cartridge body comprising gas passages in accordance with the principles of the present invention; 
         FIG. 11  is a top view of the cartridge body comprising gas passages in accordance with the principles of the present invention; 
         FIG. 12  is a cross-sectional view of the cartridge body comprising gas passages in accordance with the principles of the present invention; 
         FIG. 13  is a cross-sectional view of a torch head comprising a second embodiment of an initiator and constructed in accordance with the principles of the present invention; 
         FIG. 14  is an upper perspective view of an initiator comprising vent holes and constructed in accordance with the principles of the present invention; 
         FIG. 15  is a lower perspective view of the initiator comprising vent holes in accordance with the principles of the present invention; 
         FIG. 16  is a top view of the initiator comprising vent holes in accordance with the principles of the present invention; 
         FIG. 17  is a cross-sectional view of the initiator comprising vent holes in accordance with the principles of the present invention; 
         FIG. 18  is a cross-sectional view of a torch head comprising a fourth embodiment of a start cartridge and constructed in accordance with the principles of the present invention; 
         FIG. 19  is an upper perspective view of a cartridge body comprising proximal radial holes and axial vent holes and constructed in accordance with the principles of the present invention; 
         FIG. 20  is a lower perspective view of the cartridge body comprising proximal radial holes and axial vent holes in accordance with the principles of the present invention; 
         FIG. 21  is a top view of the cartridge body comprising axial vent holes in accordance with the principles of the present invention; 
         FIG. 22  is a cross-sectional view of the cartridge body comprising proximal radial holes and axial vent holes in accordance with the principles of the present invention; 
         FIG. 23A  is a cross-sectional view of a torch head comprising an electrode defining spiral grooves along a central portion and constructed in accordance with the principles of the present invention; and 
         FIG. 23B  is a cross-sectional view of a torch head comprising an electrode defining axial grooves along the central portion and constructed in accordance with the principles of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring to the drawings, a contact start plasma arc torch according to the present invention is generally operable with a manually operated plasma arc apparatus as indicated by reference numeral  10  in FIG.  1 . Typically, the manually operated plasma arc apparatus  10  comprises the contact start plasma arc torch  12  connected to a power supply  14  through a torch lead  16 , which may be available in a variety of lengths according to a specific application. Further, the power supply  14  provides both gas and electric power, which flow through the torch lead  16 , for operation of the plasma arc torch  12 . 
     As used herein, a plasma arc apparatus, whether operated manually or automated, should be construed by those skilled in the art to be an apparatus that generates or uses plasma for cutting, welding, spraying, gouging, or marking operations, among others. Accordingly, the specific reference to plasma arc cutting torches, plasma arc torches, or manually operated plasma arc torches herein should not be construed as limiting the scope of the present invention. Furthermore, the specific reference to providing gas to a plasma arc torch should not be construed as limiting the scope of the present invention, such that other fluids, e.g. liquids, may also be provided to the plasma arc torch in accordance with the teachings of the present invention. Additionally, the terms “biased” or “biasing” should not be construed as meaning an electrical bias or voltage as often used in the electrical field. 
     Referring now to  FIG. 2 , a torch head for use in the contact start plasma arc torch  12  of the present invention is illustrated and generally indicated by reference numeral  20 . As shown, the torch head  20  defines a proximal end  22  that is disposed within a handle  24  (one half of which is removed for clarity) of the plasma arc torch  12  and a distal end  26 , to which a plurality of consumable components are secured, as described in greater detail below. The proximal end  22  is also adapted for connection to a torch lead  28 , which provides both gas and electric power for operation of the contact start plasma arc torch  12 . The connection to the torch lead  28  may comprise a quick disconnect such as that disclosed in copending application titled “Modular Plasma Arc Torch,” filed on Feb. 26, 2002, and commonly assigned with the present application, the contents of which are incorporated herein by reference. Further, as described herein, proximal direction or proximally is the direction towards the proximal end  22 , and distal direction or distally is the direction towards the distal end  26 . 
     With reference to  FIGS. 3 through 5 , the torch head  20  further comprises a housing  28  in which fixed components of the torch head  20  are disposed. More specifically, the fixed components comprise a cathode  32  ( FIG. 5 ) that has relatively negative potential, an anode  34  that has relatively positive potential, and an insulating body  36  that insulates the cathode  32  from the anode  34 . The consumable components are generally secured to the distal end  26  of the torch head  20  and comprise an electrode  38 , a tip  40 , a start cartridge  42  that is used to draw a pilot arc as described below, and a shield cup  44  that secures the consumable components to the distal end  26  of the torch head  20  and further insulates the consumable components from the surrounding area during operation of the torch. The shield cup  44  also positions and orients the consumable components, e.g., the start cartridge  42  and the tip  40 , relative to one another for proper operation of the torch when the shield cup  44  is fully engaged with the torch head  20 . 
     As further shown, the start cartridge  42  comprises an initiator  50  and a coil spring  52  housed within a cartridge body  54  and a tip seat  56 . Accordingly, the start cartridge  42  is preferably a single replaceable consumable component. Further, the cartridge body  54  and the tip seat  56  together are referred to as a cartridge assembly  55 . In one form of the cartridge assembly  55 , the cartridge body  54  is conductive while the tip seat  56  is insulative. In another form of the cartridge assembly  55 , the cartridge body  54  is insulative, the tip seat  56  is insulative, and the cartridge assembly further comprises a conductive member  53 , which may be a washer as shown, disposed at a proximal end of the cartridge body  54 . The function and operation of the start cartridge  42 , its components, and the fixed and other consumable components of the torch head  20  are described in greater detail below. 
     As shown in  FIG. 5 , the torch head  20  is illustrated with the cathode  32  secured within the housing  28 , and the electrode  38  electrically connected to the cathode  32 . The generally cylindrical insulating body  36  surrounds the cathode  32  and insulates the cathode  32  from the anode  34 . As further shown, the cathode  32  abuts and electrically connects with a pin fitting  64  that is adapted for connection to the torch lead  28  (not shown). Accordingly, the cathode  32  is electrically connected to the negative side of the power supply  14  (not shown), and the anode  34  is in electrical communication with the positive side of the power supply. Further, the pin fitting  64  defines an internal bore  66  and the cathode  32  defines a central bore  70 , which are in fluid communication for the supply of a working gas from the power supply  14  to the torch head  20 . Although the cathode  32  and the pin fitting  64  are illustrated as being oriented at an angle relative to one another, the cathode  32  and the pin fitting  64  (or another adjacent component connected to the cathode  32 ) may alternately be colinear, or oriented 180 degrees relative to one another as commonly referred to in the art. 
     The electrode  38  defines a proximal connecting end  72  for connecting the electrode  38  with a connecting end  74  of the cathode  32 . The connecting ends  72 ,  74  of the electrode  38  and the cathode  32  are configured for coaxial telescoping connection with one another as shown and described in coowned U.S. Pat. No. 6,163,008, which is incorporated herein by reference. To establish the connection between the cathode  32  and the electrode  38 , the cathode connecting end  74  and the electrode connecting end  72  are formed with opposing detents generally designated  76  and  78 , respectively. The detents  76  and  78  are interengageable with one another when the connecting end  74  of the electrode  38  is connected to the cathode  32  to inhibit axial movement of the electrode  38  away from the cathode  32 . However, it should be understood that the electrode  38  may be connected to the cathode  32  in other conventional manners, such as by a threaded connection, without departing from the scope of the present invention. 
     Additionally, an insulating body  80  is disposed in the proximal end of the cathode  32 , and an insulating cap  82  is mounted on the distal end of the cathode  32 , which results in a relatively small area within the cathode central bore  70  exposed for contacting the electrode  38 . Both the insulating body  80  and the insulating cap  82  are configured and positioned to inhibit electrical contact between an object other than the electrode  38  with the cathode  32  to reduce the risk of torch malfunction should such an object be inserted into the cathode central bore  70 . 
     The electrode  38  defines a central bore  84  that extends distally from the connecting end  72  and is in fluid communication with the central bore  70  of the cathode  32  such that the working gas in the cathode central bore  70  is directed down through the central bore  84  of the electrode  38 . The central bore  84  of the electrode  38  extends distally from the connecting end  72  into registry with gas distributing holes  86  that extend radially outward from the central bore  84  for exhausting working gas from the electrode  38 . The electrode  38  further comprises an annular collar  88  that extends radially outward as shown and defines a proximal shoulder  90  distal to the gas distributing holes  86 . The proximal shoulder  90  abuts a bushing  92  that is seated within an annular groove  94  formed in the insulating body  36 . The bushing  92  is made of a durable material, preferably a polyimide such as Vespel®, so that the torch head  20  can withstand repeated installation of an electrode  38  without causing damage to the insulating body  36 , which is more costly and difficult to replace. Further, a distal portion  96  of the electrode  38  defines a generally elongated, cylindrical shape with a fluted surface formed by longitudinally extending ridges  98 . The electrode  38  of the illustrated embodiment is constructed of copper or a copper alloy and preferably comprises an emissive insert  100 , such as hafnium, secured within a recess  102  at the distal end of the electrode  38 . 
     The generally hollow tip  40 , also commonly referred to as a nozzle, is mounted over the distal portion  96  of the electrode  38 . The tip  40  is in a radially and longitudinally spaced relationship with the electrode  38  to form a primary gas passage  104 , which is also referred to as an arc chamber or plasma chamber. A central exit orifice  106  of the tip  40  communicates with the primary gas passage  104  for exhausting ionized gas in the form of a plasma stream from the tip  40  and directing the plasma stream down against a workpiece. The tip  40  further comprises a hollow, generally cylindrical distal portion  108  and an annular flange  110  at a proximal end  112 . The annular flange  110  defines a generally flat, proximal face  114  that seats against and seals with the tip seat  56  of the start cartridge  42 , and a distal face  116  adapted to seat within and make electrical contact with a conductive insert  118  disposed within the shield cup  44 . The conductive insert  118  is further adapted for connection with the anode  34 , preferably using a threaded connection  119  such that electrical continuity between the positive side of the power supply is maintained. Accordingly, the tip  40  is in electrical contact with the positive, or anode, side of the power supply through the conductive insert  118 . 
     The tip  40  further defines a plurality of swirl holes  120  (further shown in  FIG. 4 ) offset from a center of the tip  40  and positioned around and through the annular flange  110 . Additionally, the tip  40  preferably defines a plurality of secondary gas holes  122  (also shown in  FIG. 4 ) extending radially through the annular flange  110  and into an annular recess  124  on the distal face  116 . Accordingly, the tip  40  regulates the plasma gas to form a plasma stream in addition to the secondary gas to stabilize the plasma stream, which is further shown and described in co-pending application titled “Tip Gas Distributor,” filed on Feb. 26, 2002, and commonly assigned with the present application, the contents of which are incorporated herein by reference. Further, the tip  40  is preferably made of a copper or copper alloy material. 
     The shield cup  44  surrounds the distal end  26  of the torch head  20  and generally secures and positions the consumable components therein, in addition to insulating an area surrounding the torch head  20  from the conductive components during operation and while the power supply  14  (not shown) supplies electric power to the torch head  20 . When secured to the torch head  20  through the threaded connection  119 , a primary gas chamber  126  is formed between the conductive insert  118  of the shield cup  44  and the insulating body  36 , the start cartridge  42 , and the tip  40 , through which the primary working gas flows during operation of the torch as described in greater detail below. Additionally, the shield cup  44  is preferably made of a non-conductive, heat insulating material, such as phenolic or ceramic. 
     The insulating body  36  further defines a plurality of radial gas distributing holes  128  that are in fluid communication with the electrode gas distributing holes  86  and also with the primary gas chamber  126 . Referring also to  FIG. 6 , the insulating body  36  further defines a plurality of axial vent holes  130  extending through a distal face  132 , which are in fluid communication with a set of radial vent holes  134  defined in a proximal section  136  of the insulating body  36 . The radial vent holes  134  are in further fluid communication with a set of radial vent holes  138  defined in a distal section  140  of the anode member  34 , which are in fluid communication with an opening  142  near the proximal end of the shield cup  44 , formed between the shield cup  44  and the torch head housing  28 , which is exposed to atmosphere as shown. Accordingly, gas is vented through the series of vent holes in the insulating body  36 , the anode  34 , and the shield cup  44  during operation of the torch is described in greater detail below. Further, the insulating body  36  is preferably made of a non-conductive, heat insulating material, such as phenolic or ceramic, and the anode member  34  is made of a conductive material such as brass or a brass alloy. 
     Referring to  FIGS. 7A and 7B , the start cartridge  42  in accordance with the principles of the present invention is operable between an idle mode ( FIG. 7A ) and a pilot mode ( FIG. 7B ) of the torch. In the idle mode, the initiator  50  is in electrical contact with the electrode  38  and is resiliently biased into contact with the tip  40 . The initiator  50  preferably defines a beveled distal contact surface  152  that is in contact with a conical interior surface  154  of the tip  40 . Further, the initiator  50  is resiliently biased into contact with the tip  40  with any suitable biasing member or means, such as a spring, or an elastic or elastomeric member, among others. In the preferred embodiment as shown, the biasing member is the coil spring  52 , which is sufficiently stiff that gas pressure from the gas supply overcomes the spring force to separate the initiator  50  from the tip  40 . Further, the initiator  50  and the coil spring  52 , along with the cartridge body  54  and the tip seat  56 , are preferably part of a replaceable start cartridge  42 . Accordingly, the tip seat  56  defines an annular shoulder  57  that engages an annular flange  59  of the cartridge body  54 , wherein the connection between the annular shoulder  57  and the annular flange  59  may be press fit or adhesively bonded, among other methods commonly known in the art. 
     As further shown, the cartridge body  54  comprises a recessed end wall  155  that abuts a distal shoulder  156  of the electrode  38 , and a generally cylindrical sidewall  158 . When fully assembled, a chamber  160  is defined within the start cartridge  42 , in which the coil spring  52  and a portion of the initiator  50  are disposed. The cartridge body  54  further defines axial vent holes  162  that extend through the recessed end wall  155  and that are in fluid communication with the chamber  160  and with the axial vent holes  130  in the distal face  132  of the insulating body  36  as previously described. Additionally, a series of radial gas holes  164  are disposed around the sidewall  158 , which direct a portion of the working gas into the start cartridge  42  to overcome the bias of coil spring  52  to move the initiator  50  away from the tip  40  and against the bias of the coil spring  52  as described in greater detail below. 
     The initiator  50  defines a generally cylindrical portion  166 , an annular flange  168 , and a tubular portion  170  that defines the beveled contact surface  152 . As shown, the proximal section of the tubular portion  170  is in electrical contact with the electrode  38 , and the distal section of the tubular portion  170  projects distally through a central aperture  172  of the tip seat  56 . Further, the coil spring  52  is disposed within the cylindrical portion  166  and is seated against a proximal face  174  of the initiator. The proximal face  174  further defines axial vent holes  175 , which are in fluid communication with the chamber  60  and also with the cartridge body axial vent holes  162 , such that the gas in the chamber is vented from the torch head  20  as further described below. Preferably, the initiator  50  is made of a conductive material such as copper or a copper alloy, the coil spring  52  is a steel material, the cartridge body  54  is a conductive material such as brass, and the tip seat  56  is a nonconductive material such as a polyimide. Alternately, as previously set forth, the cartridge body  54  may be insulative, or nonconductive, while the tip seat  56  is insulative. 
     The initiator  50  according to the present invention is free from fixed connection to the electrode  38  and the cathode  32  (i.e., the cathode side) and the anode  34 , the conductive insert  118 , and the tip  40  (i.e., the anode side). The term “free from fixed connection” as used herein means that relative movement is possible between the initiator  50  and the cathode side and the anode side in at least one direction, such as axially and/or radially. For example, in the illustrated embodiment, the initiator  50  is free to move axially along a central longitudinal axis X of the torch head  20  within the chamber  160  of the start cartridge  42 . More particularly, the initiator  50  is axially movable relative to the electrode  38  and the tip  40  between a first, distal position ( FIG. 7A ) corresponding to the idle mode of the torch, and a second, proximal position ( FIG. 7B ) corresponding to the pilot mode of the torch. However, it should be understood that the initiator  50  may be free to move radially relative to the cathode side and the anode side. It is also understood that the initiator  50  may instead be stationary within the torch and either the cathode side, the anode side, or both may be free to move, axially and/or radially, relative to the initiator  50 . 
     As further shown, a plurality of o-rings and associated o-ring grooves are disposed within the torch head  20  to seal the gas flow during operation of the torch. More specifically, an o-ring  180  is disposed between the insulating body  36  and the start cartridge  42  at the distal end  150  of the insulating body  36 . Additionally, an o-ring  182  is disposed between the anode  34  and the conductive insert  118  of the shield cup  44  near the distal section  140  of the anode  34 . Accordingly, the o-rings  180  and  182  seal the gas flow within the torch head  20  during operation. 
     Referring to  FIGS. 7A and 7B , which correspond with the idle mode of the torch and the pilot mode of the torch, respectively, the operation of the start cartridge  42 , and more specifically the initiator  50 , to initiate a pilot arc and to operate the torch according to a method of the present invention is shown and described in greater detail. As illustrated, the torch head  20  is connected to a supply of gas and electric power, preferably through the pin fitting  64  as previously described. The application of electric power causes current to between the electrode  38 , the initiator  50 , and to the tip  40 , which are all in direct electrical connection. When the gas supply is activated, a working gas flows through the internal bore  66  of the pin fitting  64  and through the central bores  70  and  84  of the cathode  32  and the electrode  38 , respectively. The gas then flows through gas distributing holes  86  of the electrode  38  and through gas distributing holes  128  of the insulating body  36 , which causes the gas flow distally into the primary gas chamber  126 . The gas then partially flows through the radial gas holes  164  of the start cartridge  42 , which causes the initiator  50  to move proximally away from the tip  40 , as shown in  FIG. 7B  in the pilot mode of the torch. Accordingly, the gas pressure is sufficiently high to overcome the bias of the coil spring  52 . As the initiator  50  moves proximally away from the tip  40 , a pilot arc is drawn between the initiator  50  and the tip  40 , and more specifically between the conical interior surface  154  and the beveled distal contact surface  152  which are configured relatively parallel to one another as shown. 
     Further to the gas flowing partially through the radial gas holes  164  to move the initiator  50 , the gas continues to flow distally and into swirl holes  120  as the plasma gas and also into the secondary gas holes  122  as the secondary gas. As the plasma gas, the gas swirls in the gap between the initiator  50  and the tip  40  and is ionized by the pilot arc formed between the initiator  50  and the tip  40 . As shown, the swirl holes  120  are preferably positioned proximally from the area where the conical interior surface  154  of the initiator  50  contacts the beveled distal contact surface  152  of the tip  40 , in order to provide a more stable plasma stream. However, the swirl holes  120  may be positioned distally from the area where the initiator  50  contacts the tip  40  and remain within the scope of the present invention. As a result of the gas swirling and pilot arc creation, the ionized gas is blown out the central exit orifice  106  of the tip  40  in the form of a plasma stream. Additionally, the gas that flows through the secondary gas holes  122  flows into the annular recess  124  and then distally along the generally cylindrical distal portion  108  of the tip  40 . As a result, the secondary gas forms a cylindrical gas envelope to stabilize the plasma stream that is blown from the central exit orifice  106 . The tip  40  with the swirl holes  120  and the secondary gas holes  122  is further described in the copending application titled “Tip Gas Distributor,” filed Feb. 26, 2002, and commonly assigned with the present application, the contents of which are incorporated herein by reference. 
     As further shown, the gas that flows into the start cartridge  42  to move the initiator  50  proximally away from the tip  40  is vented through the axial vent holes  175  of the initiator, through axial vent holes  162  in the annular end wall  155  of the cartridge body  54 , and proximally through the axial vent holes  130  (shown dashed) in the insulating body  36 . The gas then flows through the radial vent holes  134  in the insulating body  36 , through the radial vent holes  138  in the anode  34 , and out through the opening  142  at the proximal end of the shield cup  44 . Accordingly, the torch head  20  according to the present invention incorporates head vent holes (i.e., radial vent holes  134 ,  138 ) to vent gas from the torch head  20 , which facilitates a more rapid restart of the torch after the gas and electric power are turned off. When the gas and electric power are turned off and the gas is vented as previously described, the force of the coil spring  52  causes the initiator  50  to move distally towards the tip  40  such that the conical interior surface  154  and the beveled distal contact surface  152  come into contact, wherein the plasma arc torch is in the idle mode. 
     Alternately, as shown in  FIG. 7C , gas passages  165  may be formed between the cartridge body  54  and the tip seat  56  rather than radial gas holes  164  through the cartridge body  54  as previously described. Accordingly, the gas within primary gas chamber  126  partially flows through the gas passages  165 , which causes the initiator  50  to move proximally away from the tip  40  and draw a pilot arc as previously described. Additionally, as used herein, whether in a singular or plural form, the term “hole” may also be construed as being an aperture or opening of a different shape through the various components as described rather than the circular or cylindrical shapes as illustrated throughout the present application. 
     As described herein, the initiator  50  is shown and described as engaging the tip  40  in the idle mode of the torch to provide an electrically conductive path between the anode side of the power supply and the cathode side of the power supply. However, it should be understood that the initiator  50  need not engage the anode side or the cathode side in the idle mode of the torch, as long as the initiator  50  is positioned sufficiently close to at least one of the cathode side, e.g., electrode, and the anode side, e.g., tip, to provide an electrically conductive path between the positive and negative sides of the power supply. Accordingly, an arc may be formed between the initiator  50  and the anode side or the cathode side in the idle mode of the torch, but such an arc is not considered to be a pilot arc as that term is commonly understood and as used herein because the arc is not adapted for initiating operation of the torch by exhausting working gas from the torch in the form of a plasma stream. 
     Rather, any spacing between the initiator  50  and the anode side or the cathode side in the idle mode of the torch would be relatively small compared to the spacing therebetween in the pilot mode of the torch such that gas flow between the initiator  50  and the anode side or cathode side is substantially restricted and is therefore incapable of blowing any arc formed therebetween in the idle mode of the torch down toward the exit orifice of the tip to exhaust working gas from the torch in the form of a plasma stream. Therefore, reference herein to a pilot arc formed in the torch upon movement of the initiator  50  toward its proximal position corresponding to the pilot mode of the torch means an arc formed between the initiator  50  and at least one of the cathode side and the anode side when the initiator  50  is sufficiently spaced from the cathode side and/or the anode side that the arc formed therebetween can be blown through the exit orifice of the tip for initiating operation of the torch, such that working gas is exhausted from the torch in the form of a plasma stream. 
     Furthermore, the electrode  38  and the tip  40  are shown and described as being secured in the torch head  20  in a fixed relationship with each other as the initiator  50  moves between its proximal and distal positions. However, the electrode  38 , the tip  40 , or both may move relative to one another and remain within the scope of the present invention, and the initiator  50  may or may not be secured against movement within the torch head  20 , as long as the initiator  50  is free from fixed connection with the electrode  38  and the tip  40  in at least one direction so that the initiator  50  can assume different positions relative to the electrode  38  and the tip  40  in the idle and pilot modes of the torch. 
     Moreover, while the initiator  50  is moved between its distal and proximal positions pneumatically, such as by a force generated by pressurized gas (e.g., the primary working gas flowing through the start cartridge  42 ), it should be understood that the initiator  50  may alternately be mechanically driven between its distal and proximal positions without departing from the scope of the present invention. Further, an initial supply of gas may be used to bias the initiator  50  into electrical contact with the tip  40  when required, such as when the start cartridge  42  does not comprise a coil spring  52  and the initiator  50  is resiliently biased into contact with the tip  40  using, for example, gravity. The supply of gas may be initiated using a gas control device as shown and described in copending applications titled “Torch Handle Gas Control” and “Plasma Arc Torch Trigger System,” filed Feb. 26, 2002, which are commonly assigned with the present application and the contents of which are incorporated herein by reference. Additionally, as used herein, the term “resiliently biased” should not be limited to the use of a coil spring  52  as shown and described. Rather, the term “resiliently biased” may comprise, by way of example, a canted coil spring, gravity, gas pressure, or other methods commonly known in the art. 
     In addition to application within a contact start torch as shown and described herein, the start cartridge  42  according to the present invention may also be employed within a non-contact start, or high frequency/high voltage, torch. The operation of the start cartridge  42  in both a contact start and a non-contact start torch is disclosed in copending application titled “Dual Mode Torch,” filed Feb. 26, 2002, and commonly assigned with the present application, the contents of which are incorporated herein by reference. 
     Referring now to  FIG. 8 , another form of the present invention is illustrated, wherein an alternate start cartridge  200  is employed within the plasma arc torch  12  (not shown). The start cartridge  200  is similar in construction and operation as the previous start cartridge  42 , however, the start cartridge  200  comprises a cartridge body  202  that further comprises an internal annular flange  204  that surrounds a central portion  206  of the electrode  38 . The internal annular flange  204  extends distally from the recessed end wall  155  along the central portion  206 , wherein a relatively small gap  208  is defined between the internal annular flange  204  and the central portion  206  of the electrode  38 . Additionally, the cartridge body  202  defines at least one gas passage  210  formed on a proximal face  212  of the recessed end wall  155 . Accordingly, the gas used to overcome the bias of the coil spring  52  within the start cartridge  200  is vented through the gap  208 , the gas passage  210 , and through the axial vent holes  130  (shown dashed) in the insulating body  36  as previously described. In operation, therefore, the internal annular flange  204  provides venting and additional cooling for the electrode  38 . 
     With reference to  FIGS. 9 through 12 , the cartridge body  202  is further illustrated with the internal annular flange  204  and a plurality of gas passages  210  formed on the proximal face  212  of the recessed end wall  155 . As shown, the gas passages  210  preferably define a partial cylindrical configuration that are in fluid communication with a central bore  214  extending through the cartridge body  202 . Additionally, a total of three (3) gas passages  210  are employed in one form of the present invention, however, one or more gas passages  210  may be used according to specific operational requirements. 
     Referring to  FIG. 13 , yet another form of the present invention is illustrated, wherein an alternate start cartridge  220  is employed within the plasma arc torch  12  (not shown). The start cartridge  220  is similar in construction and operation as the start cartridge  200  previously described, however, the start cartridge  220  further comprises an initiator  222  that defines a recessed proximal face  224  and an annular wall  226  formed between the proximal face  174  and the recessed proximal face  224 . As further sown, at least one vent hole  228  is formed through the annular wall  226  such that the gas that is used to overcome the bias of the coil spring  52  within the start cartridge  220  is vented through the vent hole  228 , and then through the gap  208 , the gas passage  210 , and through the axial vent holes  130  (shown dashed) in the insulating body  36  as previously described. Accordingly, the vent hole  228  provides venting and additional cooling to the central portion  206  of the electrode  38 . 
     As shown in  FIGS. 14 through 17 , the initiator  222  is further illustrated with the recessed proximal face  224  and a plurality of vent holes  228  formed through the annular wall  226 . As shown, the vent holes  228  are preferably positioned off-center from the initiator  222 , and a total of six (6) vent holes  228  are employed in one form of the present invention, although one or more vent holes  228  may be used according to specific operational requirements. Further, the vent holes  228  are in fluid communication with an interior portion of the initiator  222  such that the gas may be vented as previously described. 
     Referring to  FIG. 18 , another form of a start cartridge  230  is illustrated, wherein the start cartridge  230  comprises a cartridge body  232  that defines a distal face  234  formed at a distal portion of the internal annular flange  204 . As shown, a distal collar  236  formed on the electrode  38  is in electrical contact with the distal face  234  such that the initiator  222  remains in electrical contact with the negative, or cathode, side of the power supply. Additionally, the start cartridge  232  defines a plurality of proximal radial holes  238  that are used to direct the primary working gas that flows through the central bore  84  and gas distributing holes  86  of the electrode  38  into the primary gas chamber  126  to generate and stabilize a plasma stream as previously described. 
     Referring to  FIGS. 19 through 22 , the cartridge body  232  is further illustrated with the distal face  234 , the proximal radial holes  238 , and a plurality of vent holes  240  that are formed through the proximal face  212  and are employed to vent the gas from the start cartridge  230  when the initiator  222  is moved against the resilient bias as previously described. As shown, the proximal radial holes  238  are formed normal through the cylindrical sidewall  158 , wherein a total of eight (8) proximal radial holes  238  are employed, although one or more proximal radial holes  238  may be used according to specific operational requirements. 
     Referring now to  FIGS. 23A and 23B , the central portion  206  of the electrode  38  may be configured to provide additional cooling of the electrode  38 , wherein the central portion  206  may define spiral grooves  230  or axial grooves  232  as shown. Accordingly, the grooves  230  and  232  direct and control the gas being vented through the start cartridge  220  along the central portion  206  of the electrode  38  to provide additional cooling as necessary. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the substance of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.