Abstract:
A shield device for a plasma arc torch includes an inner shield member defining an inner auxiliary gas chamber and an outer shield member surrounding the inner shield member. An outer auxiliary gas chamber is defined between the inner shield member and outer shield member. The shield device allows an auxiliary gas flow to be split into a first flow of auxiliary gas through the inner auxiliary gas chamber and a second flow of auxiliary gas through the outer auxiliary gas chamber. The inner shield member and the outer shield member are configured to be mounted to the plasma arc torch as an integral unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/850,012 filed on Sep. 4, 2007. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to plasma arc torches and more specifically to devices and methods for controlling shield gas flow in a plasma arc torch. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    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 during piloting. 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, often referred to as the plasma arc chamber, wherein the pilot arc heats and subsequently ionizes the gas. 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 with the aid of a switching circuit activated by the power supply. Accordingly, the workpiece serves as the anode, and the plasma arc torch is operated in a “transferred arc” mode. 
         [0005]    In high precision plasma arc torches, both a plasma gas and a secondary gas are provided, wherein the plasma gas is directed to the plasma arc chamber and the secondary gas is directed around the plasma arc to constrict the arc and to achieve as close to a normal cut along the face of a workpiece as possible. The secondary gas flow cannot be too high, otherwise the plasma arc may become destabilized, and the cut along the face of a workpiece deviates from the desired normal angle. With such a relatively low flow of secondary gas, cooling of components of the plasma arc torch becomes less effective, and piercing capacity is reduced due to splash back of molten metal. 
         [0006]    Improved methods of controlling the secondary gas are continuously desired in the field of plasma arc cutting in order to improve both cut quality and cutting performance of the plasma arc torch. 
       SUMMARY 
       [0007]    In one form of the present disclosure, a shield device for a plasma arc torch includes an inner shield member defining an inner auxiliary gas chamber and an outer shield member surrounding the inner shield member. An outer auxiliary gas chamber is defined between the inner shield member and outer shield member. The shield device allows an auxiliary gas flow to be split into a first flow of auxiliary gas through the inner auxiliary gas chamber and a second flow of auxiliary gas through the outer auxiliary gas chamber. The inner shield member and the outer shield member are configured to be mounted to the plasma arc torch as an integral unit. 
         [0008]    In another form of the present disclosure, a plasma arc torch includes a tip, a shield device, and a retainer. The shield device includes an inner shield member and an outer shield member. The inner shield member surrounds the tip to define an inner auxiliary gas chamber. The outer shield member surrounds the inner shield member to define an outer auxiliary gas chamber between the inner shield member and the outer shield member. The retainer cap secures the shield device to the plasma arc torch. The shield device allows an auxiliary gas flow to be split into a first flow of auxiliary gas and a second flow of auxiliary gas. The inner shield member and the outer shield member are configured to be mounted to the retainer cap as an integral unit. 
         [0009]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0010]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a cross-sectional view of a distal end portion of a plasma arc torch, including a shield device constructed in accordance with the principles of the present disclosure; 
           [0012]      FIG. 2  is an enlarged cross-sectional view of the distal end portion of the plasma arc torch and the shield device in accordance with the principles of the present disclosure; 
           [0013]      FIG. 3  is a perspective view of one form of the shield device in accordance with the principles of the present disclosure; 
           [0014]      FIG. 4  is an exploded perspective view of one form of the shield device constructed in accordance with the principles of the present disclosure; 
           [0015]      FIG. 5  is top view of the shield device in accordance with the principles of the present disclosure; 
           [0016]      FIG. 6  is a cross-sectional view of the shield device, taken along line A-A of  FIG. 5 , in accordance with the principles of the present disclosure; 
           [0017]      FIG. 7  is a cross-sectional view of another form of the shield device constructed in accordance with the principles of the present disclosure; 
           [0018]      FIG. 8  is a cross-sectional view of yet another form of the shield device constructed in accordance with the principles of the present disclosure; and 
           [0019]      FIG. 9  is a cross-sectional view of still another form of the shield device constructed in accordance with the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. It should also be understood that various cross-hatching patterns used in the drawings are not intended to limit the specific materials that may be employed with the present disclosure. The cross-hatching patterns are merely exemplary of preferable materials or are used to distinguish between adjacent or mating components illustrated within the drawings for purposes of clarity. 
         [0021]    Referring to  FIGS. 1 and 2 , a plasma arc torch is illustrated and generally indicated by reference numeral  20 . The plasma arc torch  20  generally includes a plurality of consumable components, including by way of example, an electrode  22  and a tip  24 , which are separated by a gas distributor  26  to form a plasma arc chamber  28 . The electrode  22  is adapted for electrical connection to a cathodic, or negative, side of a power supply (not shown), and the tip  24  is adapted for electrical connection to an anodic, or positive, side of a power supply during piloting. As power is supplied to the plasma arc torch  20 , a pilot arc is created in the plasma arc chamber  28 , which heats and subsequently ionizes a plasma gas that is directed into the plasma arc chamber  28  through the gas distributor  26 . The ionized gas is blown out of the plasma arc torch and appears as a plasma stream that extends distally off the tip  24 . A more detailed description of additional components and overall operation of the plasma arc torch  20  is provided by way of example in U.S. Pat. No. 7,019,254 titled “Plasma Arc Torch,” and its related applications, which are commonly assigned with the present disclosure and the contents of which are incorporated herein by reference in their entirety. 
         [0022]    As used herein, a plasma arc torch, 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 automated 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, as used herein, the words “proximal direction” or “proximally” is the direction as depicted by arrow X, and the words “distal direction” or “distally” is the direction as depicted by arrow Y. 
         [0023]    The consumable components also include a shield device  30  that is positioned distally from the tip  24  and which is isolated from the power supply. The shield device  30  generally functions to shield the tip  24  and other components of the plasma arc torch  20  from molten splatter during operation, in addition to directing a flow of shield gas that is used to stabilize and control the plasma stream. Additionally, the gas directed by the shield device  30  provides additional cooling for consumable components of the plasma arc torch  20 , which is described in greater detail below. Preferably, the shield device  30  is formed of a copper, copper alloy, stainless steel, or ceramic material, although other materials that are capable of performing the intended function of the shield device  30  as described herein may also be employed while remaining within the scope of the present disclosure. 
         [0024]    More specifically, and referring to  FIGS. 2-6 , the shield device  30  comprises an inner shield member  32  that surrounds the tip  24  to define an inner auxiliary gas chamber  34  between the inner shield member  32  and the tip  24 . The inner auxiliary gas chamber  34  directs a first flow of auxiliary gas around the plasma stream  36  as the plasma stream  36  exits the tip  24  in order to constrict and shape the plasma stream, thus improving cut quality and cut speed. 
         [0025]    As further shown, the shield device  30  comprises an outer shield member  42 , which is secured to the inner shield member  32  in one form of the present disclosure. In another form, both the inner shield member  32  and the outer shield member  42  form a single piece such that the shield device  30  is a unitary body. An outer auxiliary gas chamber  44  is formed between the outer shield member  42  and the inner shield member  32 , which directs a second flow of auxiliary gas through a distal end portion  46  of the outer shield member  42 . This second flow of auxiliary gas functions to protect the plasma arc torch  20  during piercing and cutting and also cools components of the plasma arc torch  20  such that thicker workpieces may be processed with a highly shaped plasma stream  36 . Moreover, the second flow of auxiliary gas functions to add momentum to the removal of metal and acts as a buffer between the plasma stream  36  and the outside environment. Therefore, the shield device  30  comprises an inner auxiliary gas chamber  34  and an outer auxiliary gas chamber  44 , which provide multiple injection mechanisms of the auxiliary gas around the plasma stream  36  in order to achieve improved cut quality and speed, in addition to improved life of consumable components. Therefore, the shield device  30  in accordance with the teachings of the present disclosure provides a hybrid injection mechanism for the auxiliary gas. 
         [0026]    As used herein, the term “auxiliary gas” should be construed to mean any gas other than the plasma gas, such as a secondary gas, tertiary gas, shield gas, or other gas as contemplated in the art. Additionally, the first and second flow of auxiliary gas in one form are provided from a single gas source (not shown), and in another form, these auxiliary gases are provided from a plurality of gas sources (not shown). The plurality of gas sources may be the same gas type, such as air, or different gas types, such as, by way of example, air, oxygen, nitrogen, and H35, among others, which may be further mixed as required. 
         [0027]    Referring back to  FIGS. 1 and 2 , the shield device  30  is adapted for being secured to the plasma arc torch  20  by a retaining cap  50 , which is in one form threaded onto (not shown) the plasma arc torch  20 , but may also be attached by way of a quick disconnect or other mechanical device. The retaining cap  50  comprises an annular shoulder  52  ( FIG. 1 ) as shown, and an extension  54  around a proximal end portion  56  of the outer shield member  42  engages the annular shoulder  52  of the retaining cap  50  to position the shield device  30  within the plasma arc torch  20 . Referring also to  FIG. 6 , the outer shield member  42  further comprises a recessed shoulder  58  disposed around its proximal end portion  56 , and the inner shield member  32  comprises an annular flange  60  disposed around its proximal end portion  62 . The annular flange  60  of the inner shield member  32  abuts the recessed shoulder  58  of the outer shield member  42  as shown to position the inner shield member  32  relative to the outer shield member  42 . 
         [0028]    As further shown in  FIGS. 4 and 6 , the outer shield member  42  comprises a proximal inner wall portion  64 , and the inner shield member  32  comprises a proximal outer wall portion  66 . The proximal outer wall portion  66  of the inner shield member  32  engages the proximal inner wall portion  64  of the outer shield member  42  to secure the inner shield member  32  to the outer shield member  42 , in a press-fit manner in one form of the present disclosure. It should be understood, however, that in this form of the shield device  30  having separate pieces, the pieces may be joined by any of a variety of methods, including by way of example, threads, welding, and adhesive bonding, among others. Such joining techniques shall be construed as being within the scope of the present disclosure. 
         [0029]    Referring now to  FIGS. 2-6 , the inner shield member  32  comprises gas passageways  70  formed through the annular flange  60 , which are radially spaced in one form of the present disclosure. The gas passageways  70  direct the second flow of auxiliary gas to the outer auxiliary gas chamber  44 . The first flow of auxiliary gas is directed through gas passageways  72  formed through an auxiliary gas distributor  74 , which in one form are oriented such that the first flow of auxiliary gas is swirled as it enters the inner auxiliary gas chamber  34 . Accordingly, the inner auxiliary gas chamber  34  directs the first flow of auxiliary gas around the plasma stream  36  in a swirling manner in one form of the present disclosure. 
         [0030]    As further shown, the outer shield member  42  comprises an exit orifice  80  formed through its distal end portion  46 . A recess  84  is also formed in a distal end face  86  of the outer shield member  42  in one form of the present disclosure, wherein edge extensions  88  function to further protect the inner shield member  32  during piercing and cutting. As an alternative to the orifice  80 , the outer shield member  42  may comprise individual gas passageways (not shown) rather than the orifice  80  as illustrated and described herein, wherein the gas passageways direct the second flow of auxiliary gas around the plasma stream. 
         [0031]    The inner shield member  32  comprises a distal extension  90 , which defines an outer distal wall portion  92  as shown. In one form as shown in  FIG. 6 , the exit orifice  80  of the outer shield member  42  is aligned with the outer distal wall portion  92  of the inner shield member  32 . In this form, both the exit orifice  80  of the outer shield member  42  and the outer distal wall portion  92  of the inner shield member  32  are axial, and thus the second flow of auxiliary gas directed through the outer auxiliary gas chamber  44  flows in a coaxial manner in one form of the present disclosure. 
         [0032]    In another form as shown in  FIG. 7 , the second flow of auxiliary gas directed through the outer auxiliary gas chamber  44  defines an axial component and a radial component. More specifically, in this form, the second flow of auxiliary gas directed through the outer auxiliary gas chamber  44  is angled inwardly, and the outer distal wall portion  92  of the inner shield member  32  is aligned with the exit orifice  80  of the outer shield member  42 . 
         [0033]    In another form as shown in  FIG. 8 , the second flow of auxiliary gas directed through the outer auxiliary gas chamber  44  is angled outwardly. It should be understood with these various forms of the second flow of auxiliary gas, the exit orifice  80  of the outer shield member  42  need not be aligned with the outer distal wall portion  92  of the inner shield member  32 . 
         [0034]    Referring to  FIG. 9 , yet another form of the outer auxiliary gas chamber  44  is shown, in which the second flow of auxiliary gas is directed in a radial manner around the plasma stream  36 . It should be understood that such variations for the flow of auxiliary gas through the outer auxiliary gas chamber  44  and the inner auxiliary gas chamber  34 , both individually and in combination with each other, may be employed according to specific operational requirements while remaining within the scope of the present disclosure. Additionally, with each of the forms of directing the second flow of auxiliary gas, namely, coaxial, angled, and radial, the flow may also be directed in a swirling manner with each of these forms. For example, the second flow of auxiliary gas may be coaxial with a swirling component, angled with a swirling component, or radial with a swirling component. Therefore, other components to the second flow of auxiliary gas, and also the first flow of auxiliary gas, other than those set forth herein shall be construed as being within the scope of the present disclosure. 
         [0035]    Therefore, in general, the inner auxiliary gas chamber  34  surrounds at least a portion of the tip  24  and directs a portion of the auxiliary gas flow around the plasma stream  36  in one of a swirling manner and a radial manner. The outer auxiliary gas chamber  44  directs another portion of the auxiliary gas flow around the flow through the inner auxiliary gas chamber  34  in one of a coaxial manner, an angled manner, and a radial manner, each of which may also have a swirling component. Accordingly, the outer auxiliary gas chamber  44  may define a coaxial configuration, an angled configuration, or a radial configuration around a distal end portion of the shield device  30 . 
         [0036]    The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the invention. For example, the inner shield member  32  in one form is recessed from the outer shield member  42  proximate the distal end portion  46  of the outer shield member  42  (e.g.,  FIGS. 6 and 9 ). In another form, the inner shield member  32  is flush with the outer shield member  42  proximate the distal end portion  46  of the outer shield member  42  (e.g., FIGS.  7  and  8 ). However, although not illustrated herein, the inner shield member  32  may extend beyond the distal end portion  46  of the outer shield member  42  while remaining within the scope of the present disclosure. Therefore, the inner shield member  32  may be recessed, flush, or protruding relative to the distal end portion  46  of the outer shield member  42  and be within the scope of the present disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the invention.