Abstract:
A consumable for a plasma arc torch, such as a nozzle, having a body and a head defining a shoulder portion having a frusto-conical portion and a flared portion. The flared portion increases the cross-sectional thickness to provide a greater heat-conduction path for removal of heat generated by a plasma arc, thereby extending consumable life. The frusto-conical portion provides a sharper, pointier nozzle head to simultaneously increase the operator&#39;s visibility of the workpiece. Methods of making and using the consumables are also included.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to gas-cooled plasma arc cutting torches, and more particularly to extending the working life of nozzles for gas-cooled torches with an increased shoulder thickness to decrease the thermal wear rate. 
     BACKGROUND 
     Welding and plasma arc torches are widely used in the welding, cutting and marking of materials. A plasma torch generally includes an electrode and a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, passages for arc control fluids (e.g., plasma gas), and a power supply. Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle. The torch produces a plasma arc, a constricted ionized jet of a gas with high temperature and high momentum. Gases used in the torch can be non-reactive (e.g., argon or nitrogen) or reactive (e.g., oxygen or air). In operation, a pilot arc is first generated between the electrode (cathode) and the nozzle (anode). Generation of the pilot arc can be by means of a high frequency, high voltage signal coupled to a DC power supply and the torch or any of a variety of contact starting methods. 
     During operation of the torch, certain consumable parts become worn and have to be replaced. A known problem in the art is increasing the lifespan of consumables. Specifically, these consumables include torch electrodes, nozzles, and shields. Previous patents assigned to Hypertherm, Inc. of Hanover, N.H. teach techniques for prolonging the lifespan of some of these consumables. For example, U.S. Pat. No. 5,317,126, the contents of which are incorporated herein by reference in their entirety, teaches that the life of a nozzle and an electrode can be extended by providing a plasma bypass channel to increase the mass flow rate of the plasma gas through the plasma chamber. U.S. Pat. No. 5,166,494, the contents of which are incorporated herein by reference, describes altering the flow of plasma gas in conjunction with the transfer of the current flow from the nozzle to the workpiece, and U.S. Pat. No. 5,170,033, the contents of which are incorporated herein by reference in their entirety, teaches that a chamber in the swirl ring can be created and sized to favorably affect the dynamic flow characteristics of the flowing gas when torch operating conditions are changed. 
     Another known problem in the art of gas-cooled plasma arc cutting torches is increasing the line of site from an operator to a workpiece, particularly along the torch head. A limitation to the sharpness of the torch head is the need to include various design parameters and electrical circuitry therein. 
     SUMMARY OF THE INVENTION 
     An aspect of the invention decreases the thermal wear rate of nozzles. One reason for the increased thermal wear rate relates to the minimum cross-sectional thickness of the shoulder region on the nozzle head. Previous designs do not provide a sufficient heat-conduction path for the heat generated by the plasma arc. It was also discovered that the thermal wear rate of the nozzle can increase as the length to width ratio (i.e., pointiness) of the nozzle head increases. Moreover, by simultaneously providing a sharper, pointier nozzle head, the operator&#39;s visibility of the workpiece can be increased. 
     The invention overcomes these and other problems by using a flared shoulder portion that provides an increased cross-sectional thickness of the shoulder, thereby providing a greater heat-conduction path for the heat generated by the plasma arc. In addition, the flared shoulder portion allows the nozzle head to have a substantially non-conical shoulder, thereby providing a torch operator with a better line of site to the workpiece. 
     A first aspect of the invention includes a nozzle for a gas-cooled plasma arc cutting torch. The nozzle includes a body comprising a hollow interior having a cylindrical portion that defines a central longitudinal axis and an inside diameter and a nozzle head. The nozzle head defines a plasma exit orifice disposed about the central longitudinal axis and a shoulder portion comprising a generally non-cylindrical portion and a second portion that, in combination, define an external contoured surface, the second portion disposed between the generally non-cylindrical portion and the body. 
     In an embodiment, the nozzle includes a contour line disposed on the external contoured surface identifies a region of a minimum shoulder thickness. The contour line can be disposed between the generally non-cylindrical portion and the second portion. In some embodiments, the second portion is disposed between the contour line and a second region on the body that identifies the intersection of the body and shoulder portion. The external contoured surface of the shoulder portion can define at least one of a nonlinear or irregular surface. 
     The generally non-cylindrical portion can be disposed nearer the longitudinal axis than is the inside diameter of the body. In some embodiments, substantially all of the generally non-cylindrical portion is between an end face of the nozzle head and a point on the nozzle body that corresponds to an insert depth (e.g., blowback position) of the electrode. In an embodiment, substantially all of the generally non-cylindrical portion is between an end face of the nozzle head and a bottom interior surface of the nozzle head. 
     The nozzle can be defined by a second angle measured between the longitudinal axis and a second tangent line to a second exterior surface of the second portion. The second angle can be greater than a first angle measured between the longitudinal axis and a first tangent line to a first exterior surface of the generally non-cylindrical portion. In some embodiments, the second portion is disposed between the generally non-cylindrical portion and a reference point located by extending the first tangent line to an exterior surface of the nozzle body. In an embodiment, the second tangent line passes through the second portion at a point of the nozzle head furthest from the longitudinal axis. In a preferred embodiment, the second angle is approximately 90 degrees. The second tangent line can substantially parallel the second exterior surface. The first tangent line can substantially parallel the first exterior surface. 
     In some embodiments, the region of minimum shoulder thickness corresponds to a heat transfer density proportionate to not more than about 2 amperes of torch operating current per square millimeter of nozzle cross-sectional conduction area at the region of minimum shoulder thickness. In a preferred embodiment, at least one of the generally non-cylindrical portion or the second portion is at least substantially conical. The external contoured 
     In some embodiments, the contour line is between the generally non-cylindrical portion and a point on the nozzle body that corresponds to an insert depth (e.g., blowback position) of the electrode. The contour line can be between the generally non-cylindrical portion and a bottom interior surface of the nozzle head. In an embodiment, the generally non-cylindrical portion and the second portion are at least substantially contiguous. 
     In another aspect of the invention, a nozzle for a gas-cooled plasma arc cutting torch is provided. The nozzle includes a body and a nozzle head. The body comprises a hollow interior having a cylindrical portion that defines a central longitudinal axis, an inside diameter, and an external body surface. The nozzle head defines a plasma exit orifice disposed about the central longitudinal axis and a shoulder portion defining an external contoured surface. A first section and a second section of the shoulder portion is disposed within a cross section of the shoulder portion that passes through the central longitudinal axis. The first section has a first external contour disposed between an end face of the nozzle head and an external surface of the nozzle body. The second section has a second external shoulder contour disposed between the external surface of the nozzle body and the first external contour, such that an angle φ 1  measured between the central longitudinal axis and a first tangent line to a first point on the first external contour is less than an angle φ 2  measured between the central longitudinal axis and a second tangent line to a second point on the second shoulder contour. 
     In an embodiment, a contour point correlates to a region of cross-sectional minimum shoulder thickness. The region of cross-sectional minimum shoulder thickness is identified at a location between the first external contour and the second external contour. In some embodiments, the contour point is disposed between the first external contour and a second region on the body that identifies the intersection of the body and shoulder portion. 
     The external contoured surface of the shoulder can define a nonlinear or irregular surface. In an embodiment, the second tangent line passes through the second section at a point of the nozzle head furthest from the longitudinal axis. In a preferred embodiment, φ 2  is approximately 90 degrees. In some embodiments, the first and second sections of the shoulder are at least substantially conical. 
     The first and second sections can be at least substantially contiguous. In an embodiment, the first tangent line substantially parallels the first external contour. The second tangent line can substantially parallel the second external contour. 
     An aspect of the invention includes a nozzle for a gas-cooled plasma arc cutting torch. The nozzle comprises a body and a nozzle head. The body comprises a hollow interior having a cylindrical portion that defines a central longitudinal axis and an inside diameter. The nozzle head defines a plasma exit orifice disposed about the central longitudinal axis and a shoulder portion between an end face of the nozzle head and the body. The shoulder portion comprises an at least substantially frusto-conical portion and a flared portion that, in combination, define an external contoured surface of the shoulder portion. At least a portion of the frusto-conical portion is disposed between an end face of the nozzle head and the flared portion, and the flared portion is disposed between the nozzle body and the frusto-conical portion. 
     In an embodiment, a contour line is disposed on the external contoured surface that identifies a region of a minimum shoulder thickness. The contour line can be disposed at the intersection of the frusto-conical portion and the flared portion. In some embodiments, the contour line is disposed between the end face of the nozzle head and a point on the nozzle body that corresponds to an insert depth (e.g., blowback position) of the electrode. The exterior surface of the flared portion can form a substantial portion of the external contoured surface. In some embodiments, the external contoured surface of the shoulder portion includes at least one of an irregular or non-linear cross-sectional shape. The contour line can be disposed nearer the longitudinal axis than is the inside diameter of the body. 
     A second angle measured between the central longitudinal axis and a second tangent line to an outermost exterior surface of the nozzle head can be greater than a first angle measured between the central longitudinal axis and a first tangent line to a point on the shoulder that corresponds to the contour line. In an embodiment, the second angle is approximately 90 degrees. The first tangent line can substantially parallel a first exterior surface of the shoulder. The second tangent line can substantially parallel the outermost exterior surface of the nozzle head. 
     In some embodiments, the region of minimum shoulder thickness corresponds to a heat transfer density proportionate to not more than about 2 amperes of torch operating current per square millimeter of nozzle cross-sectional conduction area at the region of minimum shoulder thickness. In an embodiment, the flared portion is at least substantially conical. 
     An aspect of the invention includes a torch tip comprising a nozzle and a shield. The nozzle comprises a nozzle body and a nozzle head. The nozzle body comprises a hollow interior having a cylindrical portion that defines a central longitudinal axis and an inside diameter. The nozzle head defines a plasma exit orifice disposed about the central longitudinal axis and a nozzle shoulder portion. The nozzle shoulder portion comprises a first generally non-cylindrical portion and a second nozzle portion that, in combination, define an external contoured surface, the second nozzle portion disposed between the first generally non-cylindrical shoulder portion and the nozzle body. 
     The shield comprises a shield body and a shield head. The shield body includes a fastener for securing the shield to the torch body in a spaced relationship relative to the nozzle, for routing a shield gas through a space between the shield body and the nozzle. The shield head defines a shield head, which defines a shield exit orifice disposed about the central longitudinal axis and a shield shoulder portion. The shield shoulder portion comprising a second generally non-cylindrical portion and a second shield portion that, in combination, define an internal contoured surface. The second shield portion is disposed between the second generally non-cylindrical portion and the body, the second generally non-cylindrical and second shield portions corresponding to the first generally non-cylindrical and second nozzle portions. 
     In some embodiments, a second angle measured between the longitudinal axis and a second tangent line to a second external surface of the second nozzle portion is greater than a first angle measured between the longitudinal axis and a first tangent line to a first external surface of the first generally non-cylindrical portion. In an embodiment, the second angle is approximately 90 degrees. In some embodiments, the first tangent line at least substantially parallels the first external surface. The second tangent line can be at least substantially parallels the second external surface. 
     The first generally non-cylindrical portion and the second nozzle portion can be substantially conical. In an embodiment, the generally non-cylindrical portion and the second nozzle portion are at least substantially contiguous. 
     Another aspect of the invention includes a gas-cooled plasma arc cutting torch comprising a torch body, an electrode disposed within a swirl ring in the torch body, a nozzle, and a shield. The nozzle comprises a nozzle body and a nozzle head. The nozzle body comprises a hollow interior having a cylindrical portion that defines a central longitudinal axis and an inside diameter. The nozzle head defines a plasma exit orifice disposed about the central longitudinal axis and a nozzle shoulder portion. The nozzle shoulder portion comprises a first generally non-cylindrical portion and a second nozzle portion that, in combination, define an external contoured surface, the second nozzle portion disposed between the first generally non-cylindrical shoulder portion and the nozzle body. 
     The shield comprises a shield body and a shield head. The shield body includes a fastener for securing the shield to the torch body in a spaced relationship relative to the nozzle, for routing a shield gas through a space between the shield body and the nozzle. The shield head defines a shield exit orifice disposed about the central longitudinal axis and a shield shoulder portion. The shield shoulder portion comprises a second generally non-cylindrical portion and a second shield portion that, in combination, define an internal contoured surface. The second shield portion is disposed between the second generally non-cylindrical portion and the body, the second generally non-cylindrical and second shield portions corresponding to the first generally non-cylindrical and second nozzle portions. 
     A second angle measured between the longitudinal axis and a second tangent line to a second external surface of the second nozzle portion can be greater than a first angle measured between the longitudinal axis and a first tangent line to a first external surface of the first generally non-cylindrical portion. In some embodiments, the second angle is approximately 90 degrees. The first tangent line can at least substantially parallel the first external surface. In an embodiment, the second tangent line can at least substantially parallel the second external surface. 
     In some embodiments, the first generally non-cylindrical portion and the second nozzle portion are at least substantially conical. In an embodiment, the first generally non-cylindrical portion and the second nozzle portion are at least substantially contiguous. 
     An aspect of the invention includes a shield for a gas-cooled plasma arc cutting torch. The shield comprises a body and a head. The body includes a fastener for securing the shield to the body of the torch in a spaced relationship relative to a nozzle, the body having a cylindrical portion that defines a central longitudinal axis. The head defines an exit orifice disposed about the central longitudinal axis and a shoulder portion defining an internal contoured surface. The shoulder portion has a first section and a second section in a cross section disposed within a cross section of the shoulder portion that passes through the central longitudinal axis. The first section has a first internal contour disposed between an end face of the shield head and an internal surface of the shield body, the second section has a second internal contour disposed between the internal surface of the shield body and the first internal contour. An angle α 1  measured between the central longitudinal axis and a first tangent line to a first point on the first internal contour is less than an angle α 2  measured between the central longitudinal axis and a second tangent line to a second point on the second internal contour. 
     In some embodiments, the angle α 2  approximately equals 90 degrees. The first and second shield sections can be at least substantially conical. 
     Another aspect of the invention comprises a method for increasing the life of a nozzle. The method comprises the step of providing a nozzle having a body and a nozzle head, the nozzle head defining an at least substantially frusto-conical shoulder portion such that a first nozzle wear rate results. The method further includes defining a flared shoulder portion that, in combination with the at least substantially frusto-conical shoulder portion, defines a nozzle shoulder having an external contoured surface. At least a portion of the frusto-conical surface is disposed between an end face of a nozzle head and the flared portion, and the flared portion is disposed between the body and the frusto-conical portion, such that a second nozzle wear rate results, the second nozzle wear rate less than the first nozzle wear rate. 
     In some embodiments, the method includes the step of forming the flared shoulder portion such that a second angle measured between the central longitudinal axis and a second tangent line to an outermost exterior surface of the nozzle head is greater than a first angle measured between the central longitudinal axis and a first tangent line to a point on the shoulder that corresponds to the contour line. In an embodiment, the method includes defining the second angle to be approximately 90 degrees. 
     The method can include establishing a contour line on the external contoured surface that identifies a region of a minimum shoulder thickness between the generally non-cylindrical portion and the second portion. In an embodiment, the method includes positioning the contour line to be at the intersection of the frusto-conical portion and the flared portion. In some embodiments, the method includes disposing the contour line nearer the longitudinal axis than an inside diameter of the body. 
     The method can include the step of defining the external contoured surface with an irregular or non-linear cross-sectional shape. In some embodiments, the method includes defining the flared portion as substantially conical. In an embodiment, the method includes establishing the region of minimum shoulder thickness to with at least a minimum thickness to correspond to a heat transfer density proportionate to not more than about 2 amperes of torch operating current per square millimeter of nozzle cross-sectional conduction area at the region of minimum shoulder thickness. 
     An aspect of the invention includes a method of manufacturing a nozzle. The method comprises providing a nozzle having an at least substantially cylindrical body and a substantially cylindrical nozzle head disposed about a central longitudinal axis. The method further includes removing a section of the nozzle head to define a shoulder portion between an end face of the nozzle head and the body. The shoulder portion produced thereby comprises a generally non-cylindrical portion and a second portion that, in combination, define an external contoured surface between the generally non-cylindrical portion and the body. 
     In some embodiments, the method includes establishing a region of minimum thickness between the generally non-cylindrical portion and the second portion such that the shoulder region has a contour line that identifies the region of minimum shoulder thickness. The method can include defining the second angle to be approximately 90 degrees. In an embodiment, the generally non-cylindrical portion and the second portion are substantially conical. 
     In some embodiments, the method includes a step of establishing the contour line nearer the longitudinal axis than an inside diameter of the body. In an embodiment, the method includes, during the removing step, defining the generally non-cylindrical portion and second portion such that a second angle measured between the longitudinal axis and a second tangent line to a second exterior surface of the second portion is greater than a first angle measured between the longitudinal axis and a first tangent line to a first exterior surface of the generally non-cylindrical portion. The method can include disposing the second portion between the generally non-cylindrical portion and a reference point located by extending the first tangent line to an exterior surface of the nozzle body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages of the present invention, as well as the invention itself, will be more fully understood from the following description of various embodiments, when read together with the accompanying drawings. 
         FIG. 1  is a cross-sectional view of a known gas-cooled nozzle. 
         FIGS. 2A-B  are simplified cross-sectional views of a gas-cooled nozzle according to an aspect of the invention. 
         FIGS. 3A-B  are simplified cross-sectional views of a gas-cooled nozzle according to an aspect of the invention. 
         FIGS. 3C-D  are simplified perspective views of a gas-cooled nozzle according to an aspect of the invention. 
         FIGS. 4A-B  are simplified cross-sectional views of gas-cooled nozzles according to an aspect of the invention. 
         FIG. 4C  is a simplified perspective view of a gas-cooled nozzle according to an aspect of the invention 
         FIGS. 4D-E  are simplified cross-sectional views of gas-cooled nozzles according to an aspect of the invention. 
         FIGS. 5A-I  are exemplary embodiments of simplified cross sections of a nozzle. 
         FIG. 6  is a cross-sectional view of a gas-cooled torch tip according to an aspect of the invention. 
         FIG. 6A  is a perspective view of a gas-cooled torch tip according to an aspect of the invention. 
         FIG. 7  is a cross-sectional view of a gas-cooled torch according to an aspect of the invention. 
         FIG. 8  is a cross-sectional view of a simplified shield according to an aspect of the invention. 
         FIGS. 9A-B  are illustrations of a method of increasing the life of a nozzle according to an aspect of the invention. 
         FIG. 10  illustrates a method of manufacturing a nozzle according to an aspect of the invention. 
         FIG. 11A-E  are illustrations of various embodiments of the method of manufacturing a nozzle. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a simplified view of a known gas-cooled torch tip  50 . The nozzle  100  includes a substantially cylindrical body  105  having a hollow interior  110  to receive an electrode  115 . A swirl ring  120  can be disposed between the electrode  115  and an interior edge  107  of the body  105 . A nozzle head  125  is integrally connected to the body  105 . The nozzle head  125  includes a shoulder  140  and an exit orifice  130  disposed about a central longitudinal axis  135 . 
     A shield  170  can be disposed in a spatial relationship with the nozzle  100 . The shield  170  defines a channel  173  for flowing a shield gas  175  to cool the nozzle  100  and to minimize material spatter on the nozzle tip  180 . 
     It was discovered that for a given torch operating current, as the diameter  160  of the nozzle head  125  is decreased, the nozzle  100  lifespan decreases. It was also discovered that as the length  163  to diameter  160  ratio (i.e., the pointiness) of the nozzle head  125  increases, the nozzle  100  lifespan decreases. The nozzle  100  lifespan decrease seems to occur due to thermal wear, as the minimum cross-sectional thickness  165  of the nozzle head  140  does not provide a sufficient heat conducting path to remove the heat generated by the plasma arc near the tip  180  of the nozzle head  125 . 
       FIG. 2A  is a simplified cross-sectional view of a gas-cooled nozzle  100  according to an aspect of the invention. In some embodiments, the shoulder  140  includes a generally non-cylindrical portion  145  and a second portion  150 . The second portion  150  is disposed between the generally non-cylindrical portion  145  and the body  105 . The second portion  150  increases the minimum cross-sectional thickness  165  of the shoulder  140 , thereby increasing the minimum cross-sectional area of the heat conducting path, enhancing heat removal capacity and increasing the working life of the nozzle  100 . The generally non-cylindrical portion  145  and the second portion  150  can, in combination, define an external contoured surface  155 . In some embodiments, e.g., as discussed below, the external surface  155  is nonlinear or irregular. 
     The generally non-cylindrical portion  145  and the second portion  150  can be at least substantially contiguous. In some embodiments, such as the embodiment depicted in  FIG. 2A , the generally non-cylindrical portion  145  and the second portion  150  are at least substantially conical.  FIG. 2A  depicts that the generally non-cylindrical portion  145  can be disposed nearer the longitudinal axis  135  than the inside diameter  117  of the body  105 . A contour line  200  disposed on the external contoured surface  155  can identify a region of minimal cross-sectional thickness  165 . In an embodiment, the contour line  200  is disposed between the generally non-cylindrical portion  145  and the second portion  150 . In some embodiments, the second portion  150  is disposed between the contour line  200  and a second region  230  on the body  105  that identifies the intersection of the body  105  and shoulder  140 . In some embodiments, the minimal cross-sectional thickness  165  corresponds to a heat transfer density proportionate to not more than about 45 amperes of torch operating current per 24 square millimeters of nozzle  100  cross-sectional conduction area, i.e., a heat conduction transfer rate that corresponds to less than about 2 amps of torch operating current per square millimeter of minimum nozzle heat conduction area at the region of minimum shoulder thickness. Still referring to  FIG. 2A , substantially all of the generally non-cylindrical portion  145  can be disposed between the end face  215  of the nozzle head  125  and a bottom interior surface  225  of the body  105 . 
     In some embodiments, substantially all of the generally non-cylindrical portion  145  is disposed between an end face  215  of the nozzle head  125  and a point  210  on the nozzle body  105  that corresponds to an insert depth of the electrode  115  when the electrode  115  is in a blowback position. U.S. Pat. Nos. 4,791,268 and 4,902,871, the contents of which are incorporated herein by reference in their entirety, teach that a plasma can be ignited by contact starting. An electrode can be in a first position, close to the nozzle head, to start the plasma, and then slide backwards to a blowback position due to gas pressure buildup at the nozzle head. 
       FIG. 2B  illustrates a simplified view of some embodiments where the second portion  150  is disposed between the generally non-cylindrical portion  145  and an end face  215  of the nozzle head  125 . In these embodiments, the generally non-cylindrical portion  145  is disposed between the end face  215  of the nozzle head  125  and the second portion  150 . The body has an interior surface  205  that can be substantially cylindrical in some embodiments, such as the embodiment depicted in  FIG. 2A , or tapered, such as the embodiment depicted in  FIG. 2B . In some embodiments, the interior surface  205  can have rounded and/or angled corners. The nozzle head  125  can be configured with a generally non-cylindrical portion  145  having a high length  163  to width  160  ratio (i.e., pointy), to provide a torch operator (not shown) with a better line of site to the workpiece (not shown). 
       FIG. 3A  illustrates a simplified cross-sectional view of a nozzle  100  according to an aspect of the invention. The shoulder  140  includes a substantially frusto-conical portion  245  and a flared portion  250 . The frusto-conical portion  245  is disposed between an end face  215  of the nozzle head  125  and the flared portion  250 . The flared portion  250  is disposed between the nozzle body  105  and the frusto-conical portion  245 . The substantially frusto-conical portion  245  and the flared portion  250  define an external contoured surface  155 . In an embodiment, the flared portion  250  is at least substantially conical. 
     In some embodiments, a contour line  200  disposed on the external contoured surface  155  correlates and corresponds to a region of minimal cross-sectional thickness  165 . In an embodiment, the region of minimal cross-sectional thickness  165  corresponds to a heat transfer density proportionate to about 45 amperes of operating current per 24 square millimeters of nozzle  100  cross-sectional conduction area, i.e., a heat conduction transfer rate that corresponds to less than about 2 amps of torch operating current per square millimeter of minimum nozzle heat conduction area at the region of minimum shoulder thickness. In some embodiments, the contour line  200  is disposed at the intersection of the frusto-conical portion  245  and the flared portion  250 . In some embodiments, the contour line  200  is disposed between an end face  215  of the nozzle head  125  and a point  210  on the nozzle body  105  that corresponds to the insert depth of the electrode  115  at the blowback position. In some embodiments, the external contoured surface  155  includes at least one of an irregular or non-linear cross-sectional shape. 
       FIG. 3B  illustrates a simplified view of some embodiments where the exterior surface  255  of the flared portion  250  forms a substantial portion of the external contoured surface  115 . The flared portion  250  can form a curve. In some embodiments, the interior surface  205  of the body  105  has rounded corners.  FIG. 3B  illustrates an embodiment where the contour line  200  correlates but does not directly correspond to the region of minimal cross-sectional thickness  165 . As illustrated in this figure, although the contour line  200  does correlate to the region of minimum cross-sectional thickness  165 , it does not directly correspond, as the contour line  200  is nearer the end face  215  than is the region of minimum cross-sectional thickness  165 . 
       FIG. 3C  illustrates a simplified perspective view of a gas-cooled nozzle according to an aspect of the invention.  FIG. 3C  depicts that the contour line  200  can be disposed at the intersection of the frusto-conical portion  245  and the flared portion  250 . 
       FIG. 3D  illustrates a simplified perspective view of a gas-cooled nozzle according to an aspect of the invention.  FIG. 3D  depicts that the contour line  200  can be disposed on the flared portion  250  (i.e., the curved surface), and not at the intersection of the frusto-conical portion  245  and the flared portion  250 . 
       FIG. 4A  is a simplified cross-sectional view of a gas-cooled nozzle  100  according to an aspect of the invention. The shoulder  140  can include a first section  345  and a second section  350  disposed within a cross-section through the central longitudinal axis  135 . The first section  345  has a first external contour  355  and the second section  350  has a second external contour  360 . A first angle φ 1  measured between the central longitudinal axis  135  and a first tangent line  365  to a point  375  on the first external contour  355  is less than a second angle φ 2  is measured between the central longitudinal axis  135  and a second tangent line  370  to a point  380  on the second external contour  360 . The first tangent line  365  can at least substantially parallel the first external contour  355 . In some embodiments, the second tangent line  370  at least substantially parallels the second external contour  360 . The second tangent line  370  can pass through the second section  350  at a point  435  of the nozzle head  125  furthest from the longitudinal axis  135 . 
     U.S. Patent Publication No. 2007/0007256, the contents of which are incorporated herein by reference in their entirety, teaches that a first angle φ 1  can be between 20-60 degrees, and preferably, between 30-50 degrees. In some embodiments, the second angle φ 2  can be between 44-90 degrees.  FIGS. 4B-C  illustrates an embodiment of the invention where φ 2  is approximately ninety degrees. 
     Referring back to  FIG. 4A , in some embodiments, a contour point  385  correlates to a region of cross-sectional minimum shoulder thickness  165 . In an embodiment, the contour point  385  is identified at a location between the first external contour  355  and the second external contour  360 . In some embodiments, the contour point  385  is disposed between the first external contour  355  and a second region  390  of the body  105  that identifies the intersection of the body  105  and shoulder portion  140 . 
     In some embodiments, the external contoured surface  155  of the shoulder portion  140  defines a nonlinear or irregular surface. In some embodiments the first section  345  and the second section  350  are at least substantially conical. In some embodiments, the first section  345  and the second section  350  are at least substantially contiguous. 
       FIG. 4D  illustrates an embodiment of the invention where the shoulder  140  is defined in terms of a generally non-cylindrical portion  145  and a second portion  150 . Preferably, a second angle φ 2  measured between the longitudinal axis  135  and a second tangent line  370  to a second exterior surface  400  of the second portion  150  is greater than a first angle φ 1  measured between the longitudinal axis  135  and a first tangent line  365  to a first exterior surface  395  of the generally non-cylindrical portion  145 . In some embodiments, the second portion  150  is disposed between the generally non-cylindrical portion  145  and a reference point  425  located by extending the first tangent line  365  to an exterior surface  107  of the body  105 . In an embodiment, the second tangent line  370  passes through the second portion  150  at a point  435  furthest of the nozzle head  125  furthest from the longitudinal axis  135 . The first tangent line  365  can substantially parallel the first exterior surface  395  of the generally non-cylindrical portion  145 , as depicted in  FIG. 4D . In addition, the second tangent line  370  can substantially parallel the second exterior surface  400  of the second portion  150 , as depicted in  FIG. 4D . 
       FIG. 4E  illustrates an embodiment of the invention where the shoulder  140  is defined in terms of a generally frusto-conical portion  245  and a flared portion  250 . The flared portion  250  can define substantially all of the external contoured surface  155 . In some embodiments, a second angle φ 2  measured between the longitudinal axis  135  and a second tangent line  370  to an outermost exterior surface  435  of the nozzle head  125  is greater than a first angle φ 1  measured between the longitudinal axis  135  and a first tangent line  365  to a point  450  on the shoulder  140  that corresponds to the contour line  200 . Referring to  FIG. 4E , the first tangent line  365  can substantially parallel the exterior surface  255  of the generally frusto-conical portion  245 , and the second tangent line  370  can substantially parallel the exterior surface  260  of the flared portion  250 . 
       FIGS. 5A-5I  are exemplary embodiments of simplified cross sections of nozzle  100 . The exemplary embodiments can be combined in many combinations, and are not limited to the examples illustrated in these figures. For example,  FIG. 5A  illustrates that the first external contour  355  can be linear  355 a or non-linear  355   b,  and that the second external contour  360  can be linear  360   a  or non-linear  360   b.  In some embodiments, the first external contour  355  and the second external contour  360  can be contiguous, such as, for example, the first external contour  355   b  and second external contour  360   b.  In addition,  FIG. 5A  illustrates that the first external contour  355  and the second external contour  360  can be asymmetric. 
       FIG. 5B  illustrates that the first external contour  355  and the second external contour  360  can, together, define a curve. Referring to  FIG. 5B , a first tangent line  365  can be drawn to a first point  375  on a first shoulder section  345 , such that the first tangent line  365  substantially parallels the first shoulder section  345 . A second tangent line  370  can be drawn to a second point  380  on a second shoulder section  350 , such that the second tangent line  370  substantially parallels the second shoulder section  350 . A first angle φ 1  can be measured between the first tangent line  365  and the central longitudinal axis  135 , and a second angle φ 2  can be measured between the second tangent line  370  and the central longitudinal axis  135 . In some embodiments, the first angle φ 1  is less than the second angle φ 2 . 
       FIG. 5C  illustrates that the first external contour  355  and the second external contour  360  can be non-linear with a regular pattern. Referring to  FIG. 5C , a first tangent line  365  can be drawn to a first point  375  on a first shoulder section  345 , such that the first tangent line  365  substantially parallels the first shoulder section  345 . A second tangent line  370  can be drawn to a second point  380  on a second shoulder section  350 , such that the second tangent line  370  substantially parallels the second shoulder section  350 . A first angle φ 1  can be measured between the first tangent line  365  and the central longitudinal axis  135 , and a second angle φ 2  can be measured between the second tangent line  370  and the central longitudinal axis  135 . In some embodiments, the first angle φ 1  is less than the second angle φ 2 . 
       FIG. 5D  illustrates that the first external contour  355  and the second external contour  360  can be non-linear with an irregular pattern. Referring to  FIG. 5D , a first tangent line  365  can be drawn to a first point  375  on a first shoulder section  345 , such that the first tangent line  365  substantially parallels the first shoulder section  345 . A second tangent line  370  can be drawn to a second point  380  on a second shoulder section  350 , such that the second tangent line  370  substantially parallels the second shoulder section  350 . A first angle φ 1  can be measured between the first tangent line  365  and the central longitudinal axis  135 , and a second angle φ 2  can be measured between the second tangent line  370  and the central longitudinal axis  135 . In some embodiments, the first angle φ 1  is less than the second angle φ 2 . 
       FIG. 5E  illustrates that the first external contour  355  can be linear and the second external contour  360  can be irregular.  FIG. 5F  illustrates an embodiment in which the first external contour  355  can be irregular and the second external contour  360  can be linear.  FIG. 5G  illustrates that the body  105  can have a tapered portion  106 .  FIG. 5H  illustrates that the first external contour  355  and the second external contour  360  can comprise multiple angles.  FIG. 5I  illustrates that the contour line  200  that identifies the region of minimum cross-sectional thickness  165  can be disposed within the flared portion  250 , the second portion  150 , or the second shoulder section  350 , closer to the nozzle body  105  than the generally non-cylindrical portion  145 , frusto-conical portion  245 , or the first shoulder section  345 . 
       FIG. 6  is a cross-sectional view of a gas-cooled torch tip according to an aspect of the invention. The torch tip  50  includes a nozzle  100  and a shield  170 . The nozzle  100  includes a nozzle body  105  comprising a hollow interior  110 . The nozzle body  105  includes a substantially cylindrical portion  113  that defines a central longitudinal axis  135 . The nozzle  100  also includes a nozzle head  125  defining a nozzle shoulder portion  140  and an exit orifice  130 . The nozzle shoulder portion  140  comprises a first generally non-cylindrical portion  145  and a second nozzle portion  150  that, in combination, define an external contoured surface  155 . The second nozzle portion  150  is disposed between the first generally non-cylindrical portion  145  and the nozzle body  105 . 
     A shield  170  includes a shield body  605  and a shield head  625 . The shield body  605  includes a fastener (not shown) for securing the shield  170  to the torch body  105  in a spaced relationship relative to the nozzle  100 , for routing a shield gas through a space  615  between the shield body  605  and the nozzle  100 . The shield head  625  defines a shield exit orifice  630  and a shield shoulder portion  640 . The shield shoulder portion comprises a second generally non-cylindrical portion  645  and a second shield portion  650  that, in combination, define an internal contoured surface  655 . The second shield portion  650  can be disposed between the second generally non-cylindrical portion  645  and the shield body  605 , such that the second shield portion  650  and the second generally non-cylindrical portion  645  correspond to the first shield portion  150  and the first generally non-cylindrical portion  145  respectively. 
       FIG. 6A  is a perspective view of a gas-cooled torch tip according to an aspect of the invention. The torch tip  50  includes a nozzle  100  and a shield  170 . An electrode  115  is also shown in  FIG. 6A  for clarity. The nozzle  100  comprises a first generally non-cylindrical portion  145  and a second nozzle portion  150  defining an external contoured surface  155 . The external contoured surface  155  can define a contour line  200 . 
     Still referring to  FIG. 6A , the shield  170  can include a second generally non-cylindrical portion  645  and a second shield portion  650 . The second shield portion  650  and the second generally non-cylindrical portion  645  can correspond to the first shield portion  150  and the first generally non-cylindrical portion  145  respectively. 
       FIG. 7  is a cross-sectional view of a gas-cooled torch according to an aspect of the invention. The torch  700  can include an electrode  115  disposed and a swirl ring  120  disposed within a torch body  705 , and the torch tip  50 . In a preferred embodiment, the nozzle  100  includes a shoulder  140  having a generally non-cylindrical portion  145  and a second portion  150 . The generally non-cylindrical portion  145  and the second portion  150  can, in combination, define an external contoured surface  155 . A first angle φ 1  measured between the central longitudinal axis  135  and a first tangent line  365  to a point  375  on the external contoured surface  155  of the generally non-cylindrical portion  145  is less than a second angle φ 2  is measured between the central longitudinal axis  135  and a second tangent line  370  to a point  380  on the external contoured surface  155  of the second portion  150 . The first tangent line  365  can at least substantially parallel the first external contour  355 . In some embodiments, the second tangent line  370  at least substantially parallels the second external contour  360 . The second tangent line  370  can pass through the second portion  150  at a point  435  of the nozzle head  125  furthest from the longitudinal axis  135 . In some embodiments, the first angle φ 1  can be between 30-50 degrees and the second angle φ 2  can be approximately 90 degrees. The generally non-cylindrical portion  145  and the second portion  150  can be at least substantially conical. In some embodiments, the generally non-cylindrical portion  145  and the second portion  150  are at least substantially contiguous. 
       FIG. 8  is a cross-sectional view of a simplified shield according to an aspect of the invention. The shield  170  includes a shield body  605  and a shield head  625 . The shield body  605  includes a fastener (not shown) for securing the shield  170  to a torch body (e.g., the torch body  105  of  FIG. 3A ) in a spaced relationship relative to a nozzle (e.g., the nozzle  100  of  FIG. 3A ), for routing a shield gas through a space  615  between the shield body  605  and the nozzle. The shield head  625  defines an exit orifice  630  disposed about a central longitudinal axis  135  and a shoulder portion  640  defining an internal contoured surface  655 . The shoulder portion  640  has a first section  647  and a second section  653  disposed within a cross section of the shoulder portion  640  that passes through the central longitudinal axis  135 . The first section  647  has a first internal contour  695  disposed between an end face  715  of the shield head  625  and an internal surface  607  of the shield body  605 . The second section  653  has a second internal contour  697  between the internal surface  607  and the first internal contour  695 . 
     The first section  647  and the second section  653  are configured such that a first angle α 1  measured between the central longitudinal axis  135  and a first tangent line  665  to a first point  675  on the first internal contour  695  is less than an angle α 2  between the central longitudinal axis  135  and a second tangent line  670  to a second point  680  on the second internal contour  697 . In some embodiments, α 2  approximately equals 90 degrees. In some embodiments, the first section  647  and the second section  653  are at least substantially conical. 
       FIGS. 9A-B  are illustrations of a method of increasing the life of a nozzle. In an aspect of the invention, as illustrated in  FIG. 9A , the method includes providing a nozzle  100  having a body  105  and a nozzle head  125 . The nozzle head  125  defines a shoulder  140  having an at least substantially frusto-conical shoulder portion  245  such that a first wear rate results. As illustrated in  FIG. 9B , the method further comprises defining a flared portion  250  that, in combination with the at least substantially frusto-conical portion  245 , defines a shoulder  140  having an external contoured surface  155 . At least a portion of the frusto-conical portion  245  is disposed between an end face  215  of the nozzle head  125  and the flared portion  250  and flared portion  250  is disposed between the frusto-conical portion  245  and the body  105 , such that a second nozzle wear rate results, the first nozzle wear rate less than the second nozzle wear rate. 
     The method includes a step of providing a nozzle (e.g.,  100 ) having a body (e.g.,  105 ) and a nozzle head (e.g.,  125 ), the nozzle head defining an at least substantially frusto-conical shoulder portion (e.g.,  245 ) such that a first nozzle wear rate results. The method also includes a step of defining a flared shoulder portion (e.g.,  250 ) that, in combination with the at least substantially frusto-conical shoulder portion, defines a nozzle shoulder (e.g.,  140 ) having an external contoured surface (e.g.,  155 ), at least a portion of the frusto-conical surface disposed between an end face (e.g.,  215 ) of a nozzle head (e.g.,  125 ) and the flared portion, the flared portion disposed between the body and the frusto-conical portion, such that a second nozzle wear rate results, the second nozzle wear rate less than the first nozzle wear rate. 
     The method can include at least some optional steps. In some embodiments, the method includes a step of forming the flared shoulder portion such that a second angle (e.g., φ 2 ) measured between the central longitudinal axis (e.g.,  135 ) and a second tangent line (e.g.,  370 ) to an outermost exterior surface (e.g.,  445 ) of the nozzle head is greater than a first angle (e.g., φ 1 ) measured between the central longitudinal axis and a first tangent line (e.g.,  365 ) to a point on the shoulder that corresponds to the contour line (e.g.,  200 ). In addition, the method can include a step of defining the second angle to be approximately 90 degrees. 
     In some embodiments, the method can include a step of establishing a contour line on the external contoured surface that identifies a region of a minimum shoulder thickness (e.g.,  165 ) between the generally non-cylindrical portion and the second portion. The method can include a step of positioning the contour line to be at the intersection of the frusto-conical portion and the flared portion. In some embodiments, the method can further include a step of disposing the contour line nearer the longitudinal axis than an inside diameter of the body (e.g.,  117 ). 
     The method can include a step of defining the external contoured surface with an irregular or non-linear cross-sectional shape. In some embodiments the method includes a step of defining the flared portion as substantially conical. The method can include a step of establishing the region of minimum shoulder thickness with at least a minimum thickness to correspond to a heat transfer density proportionate to about 45 amperes of torch operating current per 24 square millimeters of nozzle cross-sectional conduction area, i.e., a heat conduction transfer rate that corresponds to less than about 2 amps of torch operating current per square millimeter of minimum nozzle heat conduction area at the region of minimum shoulder thickness. 
       FIG. 10  illustrates a method of manufacturing a nozzle according to an aspect of the invention. In a first embodiment, as illustrated in  FIG. 10A , the method includes providing an at least substantially cylindrical nozzle  100  having an at least substantially cylindrical nozzle head  1025  disposed about a central longitudinal axis  135 . The method further includes removing a section  1050  of the nozzle head  1025  to define a shoulder portion  140  between an end face  215  of the nozzle head  1025  and the body  105 , the shoulder portion  140  produced thereby comprising a generally non-cylindrical portion  145  and a second portion  150  that, in combination, define an external contoured surface  155  between the generally non-cylindrical portion  145  and the body  105 . 
       FIG. 11A-D  are illustrations of various exemplary embodiments of section  1050 . As depicted in  FIG. 11A , section  1050   a,  corresponding to section  1150  in  FIG. 10 , can include a first sidewall  1145   a  that is substantially linear, and a second sidewall  1045   b  that is substantially linear. As illustrated in  FIG. 11B , section  1050   b  can include a first sidewall  1145   a  that is substantially linear, and a second sidewall  1045   b  that is substantially nonlinear. Referring to  FIG. 11C , section  1050   c  can have a larger cross-sectional area than  1050   a,  and can have a substantially nonlinear first sidewall  1045   b  and second sidewall  1050   b.  As depicted in  FIG. 11D , section  1050   d  can have an irregular first sidewall  1045   a  and a linear second sidewall  1050   b.  Referring to  FIG. 11E , section  1050   e  can have a linear first sidewall  1045   a  and an irregular second sidewall  1050   b.  Some embodiments include various combinations of linear, regular, and/or irregular sidewalls (e.g.,  1045   a  and  1050   b ). 
     Referring to  FIG. 10 , the method comprises a step of providing a nozzle (e.g.,  100 ) having an at least substantially cylindrical body (e.g.,  105 ) and an at least substantially cylindrical nozzle head (e.g.,  1025 ) disposed about a central longitudinal axis (e.g.,  135 ). The method also comprises a step  1320  of removing a section (e.g.,  1050 ) of the nozzle head to define a shoulder portion (e.g.,  140 ) between an end face (e.g.,  215 ) of the nozzle head and the body, the shoulder portion produced thereby comprising a generally non-cylindrical portion (e.g.,  145 ) and a second portion (e.g.,  150 ) that, in combination, define an external contoured surface (e.g.,  155 ) between the generally non-cylindrical portion and the body. 
     Still referring to  FIG. 10 , the method can include at least some optional steps. In some embodiments, the method includes a step of establishing a region of minimum thickness (e.g.,  165 ) between the generally non-cylindrical portion and the second portion such that the shoulder region has a contour line (e.g.,  200 ) that identifies the region of minimum shoulder thickness. The method can include a step of establishing the contour line nearer the longitudinal axis than an inside diameter (e.g.,  117 ) of the body. 
     Still referring to  FIG. 10 , the method can include a step of during the removing step, defining the generally non-cylindrical portion and second portion such that a second angle (e.g., φ 2 ) measured between the longitudinal axis and a second tangent line (e.g.,  370 ) to a second exterior surface (e.g.,  400 ) of the second portion is greater than a first angle (e.g., φ 1 ) measured between the longitudinal axis and a first tangent line (e.g.,  365 ) to a first exterior surface (e.g.,  395 ) of the generally non-cylindrical portion. In some embodiments, the method includes a step of disposing the second portion between the generally non-cylindrical portion and a reference point (e.g.,  425 ) located by extending the first tangent line to an exterior surface (e.g.,  107 ) of the nozzle body. In addition, the method can include a step of defining the second angle to be approximately 90 degrees. In some embodiments, the method includes a step wherein the generally non-cylindrical portion and the second portion are substantially conical. 
     While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.