Patent Publication Number: US-RE49153-E

Title: Consumable component parts for a plasma torch

Description:
BACKGROUND 
     Plasma arc torches are widely used in the cutting, welding, and heat treating of metallic materials. A plasma arc torch generally includes a cathode block with an electrode mounted therein, a nozzle with a central exit orifice mounted within a torch body, electrical connections, passages for cooling and arc control fluids, a swirl ring to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle, and a power supply. Sustaining a plasma arc causes the electrode, nozzle, swirl ring, and shield to wear requiring routine replacement; as such, the component parts are known as “consumables”. 
     Gas cooled plasma cutting torches exist which allow the consumable component parts to be changed without requiring tools. However, these gas cooled torches commonly use the same fluid (e.g. air) to support the cutting process and to cool the torch. Because only a single gas is used in such torches, there is less of a need to segregate the different gases between the various torch components (through the use of seals, o-rings, and the like). As a result of generally looser alignment of the components, gas cooled torches tend to be generally easy to disassemble. 
     Liquid cooled torches, by comparison, require tight seals for segregating the different fluids/gases between the torch components. While these seals effectively control the fluid/gas flow between the different torch components, they also tend to hold the torch components tightly together. As a result, liquid cooled plasma cutting torches commonly require a specially designed tool to install and remove each consumable component part. For example, a specially designed tool is needed to install and remove the electrode, while another specially designed tool is needed to install and remove the nozzle, etc. 
     SUMMARY 
     Various factors facilitate the need for these specially designed tools. One factor includes the size of the consumable component part. For example, many consumable component parts have outside diameters less than 1 inch (2.54 cm) in size, making it difficult to generate enough torque to install and remove the consumable component parts by hand. Another factor includes precision alignment of the consumable component parts which requires small clearances between the mating diameters of the parts and the torch body. For example, part designs with tight radial clearances frequently do not freely mate with the torch body. Yet another factor includes incorporating seals, such as O-ring seals, in the consumable component part designs for containing and separating the liquid coolant and the process gases. installing or removing consumable component parts with o-ring seals requires a force component to overcome the frictional drag force of the o-ring on the sealing surface. 
     These specially designed tools add cost to the system and complicate system usage. In addition, features must be added to the consumable component parts to interface with the tools adding to the overall cost of the parts. 
     Accordingly, a need exists to provide low-cost, readily-manufacturable, and easily-replaceable consumable components in a plasma arc torch, where the alignment and concentricity of the consumable components in the plasma arc torch can be closely controlled. 
     A component for a plasma arc torch includes a body portion, a tapered surface on the body portion, the tapered surface including a compressible member that provides a disengagement force relative to the body portion, and an axially disposed surface on the body portion for coupling to a mating surface on an adjacent structure of the torch. The component can be a nozzle and/or an electrode. The plasma arc torch can be liquid or gas cooled. 
     The compressible member can radially align the body portion with a central axis of the torch. The compressible member can provide a seal between the body portion and the torch. The compressible member can be an O-ring. 
     In one embodiment, the tapered surface on the body portion can have a clearance in the range of 0.00001 inches (0.000254 mm) to a value above zero with respect to a respective tapered surface of the torch. In another embodiment, the tapered surface may be touching at a point about the circumference of the body portion. The tapered surface can include a feature for receiving the compressible member, wherein the feature can be a recess defined by the body portion. 
     The axially disposed surface can be electrically coupled to the mating surface. The axially disposed surface can axially align the body portion in an axial position relative to the adjacent structure of the torch. 
     In another embodiment, a tool-free plasma torch includes a torch body, an electrode coupled to the torch body, a nozzle coupled to the torch body, the nozzle having a tapered surface including a compressible member that provides a disengagement force relative to an adjacent tapered surface of the torch body, and an axially disposed surface for coupling a mating surface on an adjacent structure of the torch body, and a retention cap coupled to the torch body to provide an engagement force for coupling the nozzle to the torch body. The electrode can further include a tapered surface including the compressible member for providing a disengagement force relative to an adjacent tapered surface of the torch body and an axially disposed surface for coupling a mating surface on an adjacent structure of the torch body. 
     The tool-free plasma torch can further include a spring element disposed between the electrode and the nozzle for providing a coupling force between the electrode and the torch body. The tool-free plasma torch can further include a swirl ring that includes a compressible member for providing a disengagement force relative to a tapered surface of the torch body. The spring element can be integrated with a swirl ring. 
     The compressible members can align at least one of the electrode, the nozzle, and the swirl ring with a central axis of the torch. The electrode and the swirl ring can be fixedly coupled to the torch body. The electrode and the nozzle can be electrically coupled to a cathode and an anode of the torch body, respectively. The shield can be hand tightened to the torch body. 
     In another embodiment, a plasma torch component can include a body portion, a tapered surface on the body portion dimensioned to receive a compressible member that provides a disengagement force relative to the body portion, an axially disposed surface on the body portion for aligning the body in an axial position relative to an adjacent structure of the torch and a mating surface for electrically coupling the component on the adjacent structure of the torch. 
     In another embodiment, a plasma torch component can include a body portion having an axial length and a radial width, an axial stop for aligning the body portion in the direction of the axial length, and a tapered surface on the body portion dimensioned to engage a compressible member, wherein when the component is assembled the compressible member creates a force having an axial direction and a radial direction, wherein the radial direction of the force aligns the component radially and the axial direction of the force biases the component in an unassembled direction. 
     In another embodiment, a plasma torch component can include a first component, an axial stop for rigidly aligning the first component in an axial direction relative to a second component, and a radial stop for flexibly aligning the first component in a radial direction relative to the second component and for biasing the first component in the axial direction. The first component can be a plasma torch body. 
     A method for aligning a first component in a plasma torch assembly, the first component having an axial stop and a tapered surface for engaging a compressible member, the method can include slidably engaging the axial stop of the first component to a second component of the plasma torch assembly to position the second component in an axial direction and biasing the compressible member against the tapered surface of the first component to radially align the first component to the second component. 
     In another embodiment, an assembly of plasma torch components can include a first component having an axial disposed surfaces and a tapered surface, a second component having an axial disposed surfaces, wherein the first component and the second component are aligned axially by their respective axial disposed surfaces, and a compression member aligning the first component and the second component radially, the compression member engaging the tapered surface such that the first component and the second component are biased in a direction of disassembly. 
     Advantages of the apparatus include high precision consumable component parts that are easily changeable without tools leading to reduce the overall system cost and ease of system usage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
         FIG. 1  illustrates a plasma arc torch system; 
         FIG. 2  illustrates in simplified schematic form a plasma arc torch; 
         FIG. 3A  is a simplified schematic diagram of a tool-free plasma arc torch; 
         FIG. 3B  is an exploded view of the schematic diagram of  FIG. 3A ; 
       FIG. 3C is a simplified schematic diagram of another embodiment of a tool-free plasma arc torch; 
         FIG. 4  is a schematic diagram of a tool-free plasma arc torch; and 
         FIG. 5  is a schematic diagram of another embodiment of the tool-free plasma arc torch of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a plasma arc torch system  100  representative of any of a variety of models of torch systems, including hand cutting and mechanized cutting systems. A power supply  110  provides continuously variable current output within a range (e.g. from about 20 to 40 amperes). This range can be lower or higher depending on the torch system, the thickness of the work piece and the desired cutting speeds. The variable power supply  110  allows for wide variations in cutting speeds for a given thickness of metal. 
     A torch body  120  configured for hand cutting is connected to the power supply  110  by a lead  122 . The power supply  110  is enclosed by a housing  112 . The lead  122  is connected to the power supply  110  by a strain relief system  124 . The lead  122  provides the torch body  120  with a plasma gas from a gas source (not shown) and electrical power from the power supply  110  to ignite and sustain a plasma arc. In one embodiment, air is used as the plasma gas, but other gases can be used to improve cut quality on metals such as stainless steel and aluminum. A clamp  130  connects to a workpiece  250  ( FIG. 2 ) through a workpiece lead  132  to provide a return path for the current generated by the power supply  110 . 
       FIG. 2  illustrates in simplified schematic form the plasma arc torch body of  FIG. 1 , representative of any of a variety of models of torches. The torch body  120  is generally cylindrical with an exit orifice  200  for allowing a plasma arc  240 , i.e. an ionized gas jet, to be created between the torch body  120  and a workpiece  250 . The torch is used to pierce and cut metal, such as mild steel or other electrically-conducting materials, in a transferred arc mode. The torch operates with a reactive gas, such as oxygen or air, or a non-reactive gas, such as nitrogen or argon, as the plasma gas to form the transferred plasma arc. 
     The torch body  120  supports an electrode  210  having an insert  212  in its lower end and a nozzle  220  spaced from the electrode  210 . The nozzle  220  has a central orifice that defines the exit orifice  200 . A swirl ring  230  is mounted to the torch body  120 . In one embodiment, the swirl ring  230  has a set of radially offset (or canted) gas distribution holes  232  that impart a tangential velocity component to the plasma gas flow causing it to swirl. This swirl creates a vortex that constricts the arc and stabilizes the position of the arc on the insert. 
     Referring to  FIGS. 3A-5 , the assembly and disassembly of some of the torch components can be accomplished without the need for tools. For example, torch components that have typically included threads for engagement to adjacent components can be replaced by components that slidably engage the other plasma torch components through the structures described in greater detail below. 
       FIGS. 3A and 3B  show a simplified schematic and exploded diagram of a slidable nozzle  370  of a tool-free plasma arc torch  300 . The slidable nozzle  370  is maintained in an assembled position through the use of a retention cap  392  that, when attached, holds the slidable nozzle to an anode block  308  of the torch body  300 . Conversely, when the retention cap  392  is removed, the slidable nozzle  370  can be removed without the need for any tools. 
     Moreover, a torch assembly, as shown in  FIG. 4 , can be created where a plurality of the torch components can be made to be slidably attached to the torch body, such that these components are coupled to the torch through the retention cap  392 . Again, once the retaining cap  392  is removed the slidably components can be unassembled without the need for tools. Because these components can be slidably assembled, there is no need for threads to be included in these components in order to assemble to them to the torch body. Thus, both assembly time and manufacturing cost can be reduced. 
     As shown in  FIGS. 3A and 3B , at least two torch components of a torch body are slidably coupled together such that in an assembled configuration, the two torch components (e.g., an anode  308  and a nozzle  370 ) are aligned in both a longitudinal direction and radial direction. The two torch components ( 308 ,  370 ) are also biased in an unassembled direction. The combination of alignment and biasing can be achieved by a number of embodiments and configuration, including the configuration described immediately below. 
     As shown, the first torch component ( 308 ) and a second, torch component ( 370 ) are aligned by a primary datum and a secondary datum with a compressible member ( 376 ) disposed between the two components ( 308 ,  370 ). The primary datum is an axial stop ( 318 ) in the first component ( 308 ), such that when assembled, the primary datum of the first component ( 308 ) abuts a corresponding feature or axial stop ( 378 ) in the second component ( 370 ). The axial stop may be a lip or edge in the first component ( 308 ) that engages a similar lip or edge in the second component ( 370 ) to establish the relative position of the two components along a longitudinal axis. The axial stop may be a hard or rigid axial stop such as created by a metal-to-metal contact. 
     The secondary datum may be established by a tapered surface ( 314 ) in the first component ( 308 ) that aligns the first component ( 308 ) and the second component ( 370 ) in the radial direction through the compressible member ( 376 ). In one embodiment, the compressible member ( 376 ) sits on the tapered surface ( 314 ) of the first component ( 308 ) and, when assembled, is compressed between the first component ( 308 ) and the second component ( 370 ). During compression of the compression member ( 376 ), a compression vector is created having both an axial component (A) and a radial component (B). 
     The radial component (B) serves to align the first component ( 308 ) and the second component ( 370 ) radially. The axial component (A) serves to bias the first component ( 308 ) and the second component ( 370 ) in an unassembled direction such that the two components ( 308 ,  370 ) freely disengage when the torch body ( 300 ) is being disassembled. The compression of the compressible member may also serve as a fluid seal between the first component ( 308 ) and second component ( 370 ). Because the secondary datum is positioned at the location of the contact of the compressible member, the secondary datum may be flexible. It should also be noted that the secondary datum may still allow for contact at a single point, between the first component ( 308 ) and the second component ( 370 ) and still perform the aligning and biasing functions. Through the use of two datums, the first component ( 308 ) and the second component ( 370 ) are aligned in a manner that allows for ready disengagement and assembly. 
     In FIG. 3C, a slidable nozzle 370a is maintained in an assembled position through the use of the retention cap 392 that holds the nozzle to an anode block 308a of the torch body 300. The anode block 308a includes a tapered alignment surface 314a. The nozzle includes a feature (e.g. a recess) 374a dimensioned to receive a compressible member 376. In this embodiment, the compressible member 376 sits within the recess 374a formed on the tapered surface 372a. When assembled, the compressible member 376 is compressed between the tapered surface 314a of the anode block 308a and the tapered surface 372a of the nozzle 370. 
       FIG. 4  shows an embodiment of a lower body portion, or “working end”  400  of a liquid or gas cooled-type plasma arc torch as shown in  FIGS. 1 and 2 . The working end  400  has a centrally disposed longitudinal axis  302  and includes a cathode block  304 , a torch insulator  306 , and an anode block  308 , each block having respective tapered alignment surfaces  310 ,  312 ,  314 . The cathode block  304  and the anode block  308  include respective axial stops  316 ,  318 . In some embodiments, the tapered alignment surface  308 ,  314  of the cathode block  304  and the anode block  308  can include respective lead-ins  322 ,  326  for protecting consumable components from damage during installation. Further, the lead-ins  322 ,  326  are beneficial for component ejection by increasing axial force and reducing drag force on the components. The working end  400  further includes radially centered consumable components (an electrode  330 , a swirl ring  350 , a nozzle  370 , and a shield  390 ). In some embodiments, each tapered alignment surface  308 ,  312 ,  314  can further include a compressible member (not shown) for providing a seal, a radial alignment force, and an axial disengagement force between the torch and the consumable components. In some embodiments, the torch is liquid or gas cooled. 
     The electrode  330  includes a tapered surface  332  for aligning with the first tapered alignment surface  310  of the working end  400  of the plasma arc torch. The tapered surface  322  includes a feature (e.g. a recess)  334  or is dimensioned to receive a compressible member  336 . The compressible member  336 , such as an O-ring, provides the following functions: 1) a seal between the electrode  330  and the plasma chamber to contain and separate process gases and torch coolant; 2) a radial stop creating a radial alignment force for flexibly aligning the electrode  330  in the radial direction; and 3) an axial disengagement force between the working end  400  and the electrode  330  for biasing the electrode  330  in an unassembled direction. In some embodiments, the tapered surface  332  has an axial extent of less than about 0.5 inches (1.27 cm) and, in some embodiments, less than about 0.25 inches (0.635 cm). The electrode  330  further includes an axial stop  338  for aligning the electrode  330  with the axial stop  316  of the cathode block  304 . In some embodiments, the axial stops  316 ,  338  are rigidly coupled. Further, axial-to-axial stop  316 ,  338  allows for conduction of electrical current and thermal energy needed to operate the torch. It should be understood that electrically coupling of the electrode  330  to the cathode block  304  can be accomplished in other manner known in the art. 
     During installation, as the electrode  330  is installed in the working end  400  of the plasma arc torch, the tapered surface  332  is guided by the first tapered alignment surface  310  until the compressible member  336  comes to rest against first tapered alignment surface  310 . The lead-in  322  on the first tapered alignment surface  310  prevents the compressible member or O-ring  336  from being damaged. As shown, in one embodiment a nominal clearance of 0.002 inches is provided between the taper surface  332  and the first tapered alignment surface  310  to prevent binding during installation. 
     In some embodiments, a swirl ring  350  can be disposed between the electrode  330  and the nozzle  370 . The swirl ring  350  controls the fluid flow patterns on the plasma chamber front between the electrode  330  and the nozzle  370 . The swirl ring  350  includes at least one feature (e.g. a recess)  354  or is dimensioned to receive a respective compressible member  356  for aligning with the second tapered alignment surface  312  of the working end  400  of the plasma arc torch. The compressible member  356 , such as an O-ring, provides the following functions: 1) a seal between the swirl ring  350  and the plasma chamber to contain and separate process gases and torch coolant; 2) a radial stop creating a radial alignment force for flexibly aligning the swirl ring  350  in the radial direction; and 3) an axial disengagement force between the working end  400  and the swirl ring  350  for biasing the swirl ring  350  in an unassembled direction. In some embodiments, a spring element  358  is disposed between the electrode  330  and the swirl ring  350  to provide an engagement force of the electrode  330  and the cathode block  304  during installation. It should be understood that the spring element  358  can be disposed between the swirl ring  350  and the nozzle  370 , integrated with the swirl ring  350 , or provided in any configuration that provides engagement force of the electrode  330  to the cathode block  304 . 
     During installation, as the swirl ring  350  is installed in the working end  400  of the plasma arc torch, the compressible member  356  comes to rest against second tapered alignment surface  312 . It should be understood a non-integrated spring element  358  can be installed before or after the installation of the swirl ring  350  or in replacement of the swirl ring  350 . 
     The nozzle  370  includes a tapered surface  372  for aligning with the third tapered alignment surface  314  of the working end  400  of the plasma arc torch. The tapered surface  372  includes a feature (e.g. a recess)  374  or is dimensioned to receive a compressible member  376 . The compressible member  376 , such as an O-ring, provides the following functions: 1) a seal between the nozzle  370  and the plasma chamber to contain and separate process gases and torch coolant; 2) a radial stop creating a radial alignment force for flexibly aligning the nozzle  370  in the radial direction; and 3) an axial disengagement force between the working end  400  and the nozzle  370  for biasing the nozzle  370  in an unassembled direction. In some embodiments, the tapered surface  372  has an axial extent of less than about 0.5 inches (1.27 cm). The nozzle  370  further includes an axial stop  378  for aligning the nozzle  370  with the axial stop  318  of the anode block  308 . In some embodiments, the axial stops  318 ,  378  are rigidly coupled. Further, axial-to-axial stop  318 ,  378  allows for conduction of electrical current and thermal energy needed to operate the torch. It should be understood that electrically coupling of the nozzle  370  to the anode block  308  can be accomplished in other manner known in the art. 
     During installation, as the nozzle  370  is installed in the working end  400  of the plasma arc torch, the tapered surface  372  is guided by the third tapered alignment surface  314  until the compressible member  376  comes to rest against third tapered alignment surface  314 . The lead-in  326  on the third tapered alignment surface  314  prevents the compressible member or O-ring  376  from being damaged. As shown, in one embodiment a nominal clearance of 0.002 inches is provided between the taper surface  372  and the third tapered alignment surface  314  to prevent binding during installation. 
     A hand-threaded retaining cap  392  may be employed to couple the consumables components to the torch body. The retaining cap  392  causes a force to be placed on the nozzle  370 , the swirl ring  350 , and the electrode  330  (through the spring element  358 ) that causes the longitudinal axis of these components to align with the torch axis  302 . The force further seats these components with their respective counterparts of the working end  400  of the torch (e.g. the cathode block  304 , the torch insulator  306 , and the anode block  308 ). 
     The shield  390  is typically the outermost component of the working end  400  of the torch. In some embodiments, the shield  390  may be threadedly attached to the torch working end  400  or attached in a press-on configuration. In other embodiments, shield  390  may be connected to the torch body by retain cap  392 . In such embodiments, the shield  390  may likewise include a tapered surface  372  for aligning with adjacent components. The tapered surface  372  may also include a feature (e.g. a recess)  374  to receive a compressible member  356 . In some embodiments, the shield  390  may serve to function as the retaining cap thereby providing the necessary force to seat the consumable components. 
     During torch operation, the electrode  330 , the swirl ring  350 , the nozzle  370 , and the shield  390  are subjected to harsh conditions, including high temperatures and other physical stresses. Consequently, these components degrade over time and eventually must be replaced, typically in the field. Prior techniques required the use of specialized tools to remove these components. In the above embodiment, the retaining cap  392  need only be removed by hand thereby allowing the axial component of the compression force on compressible members to assist in ejecting these components from the torch. 
       FIG. 4  demonstrates an embodiment incorporating both tool-free and conventional torch components. That is, some components may be conventional type threaded consumables and some components may be slidable as described above. This allows for a reduction cost for the components that are more likely to be replaced than others. That is, the consumable components closest to the plasma arc are more likely to wear and need replacement before the components further from the plasma arc. For example, the electrode  330  and the nozzle  370  are more likely to wear before the shield  390 , and the shield  390  is more likely to wear before the swirl ring  350 , etc. 
     In the embodiment of FIG. 5, the electrode  330  is threadedly attached to the cathode block  304  eliminating the need for the spring element  358  ( FIG. 3 ) FIG. 4. The swirl ring  350 , the nozzle  370 , and the shield  390  are each coupled to the “working end”  400  of the plasma arc torch as mentioned above. 
     The electrode  330  of  FIG. 5  includes a threaded surface  339  and a deformable surface, such as a lip. The threaded surface  339  engages a cooperating thread  319  of the cathode block  304 . By threadedly attaching the electrode  330  to the cathode block  304 , the electrode  304  is axially aligned with the torch axis  302  and properly spaced from the nozzle  350  during torch operation. The engagement of the threaded surface  339  with the cooperating thread  319  also serves as an electrical connection to conduct the requisite current between the cathode block  304  and the electrode  330 . 
     In some embodiments, the swirl ring  350  may also include a threaded surface that engages a cooperating threaded surface on the torch insulator  306 . In general, however, the swirl ring  350  is simply captured in the working end  400  of the torch by the retention cap. In either configuration, it is desirable to center the swirl ring  350  about the electrode  330  so as to provide a concentric uniform annular plasma chamber to provide uniform gas flow therein and facilitate torch operation. 
       FIGS. 3 and 4  show each tapered surface as a linear taper surface, however it should be understood that each tapered surface can be any number of shapes, including contoured surfaces and arcs. In general, the shape of the “tapered” surface can be understood to be any shape such that when two torch components are assembled, the tangent to the surface at the point of contact with compressible member is angled in the unassembled direction relative to the torch axis. 
     From the foregoing, it will be appreciated that the working end provides a simple and effective way to ensure the proper alignment of consumable components in the working end of a plasma arc torch. The problems of securing the critical alignments while operating under harsh field conditions, compounded by the need to replace components as they deteriorate from use, are largely eliminated. This avoids the unacceptable production errors affecting workpieces caused by improperly aligned apparatus and facilitates quick and easy replacement of the consumable components. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.