Patent Publication Number: US-6910881-B2

Title: Flashback arrestor for use with head of oxy-fuel torch

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   The present application is a division of application Ser. No. 09/939,850, which was filed on Aug. 27, 2001, now U.S. Pat. No. 6,726,471, and is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to cutting torches and, more particularly, to cutting torches with flashback arrestors. 
   BACKGROUND OF THE INVENTION 
   Oxy-fuel cutting torches discharge fuel gas and oxygen from a nozzle for cutting purposes. A typical torch includes a control body for being connected to separate fuel gas and oxygen supplies, tubes for supplying the oxygen and fuel gas from the control body to a head, and a cutting tip mounted to the head. The cutting tip receives the fuel gas and oxygen from the head and discharges these gases from its nozzle. More specifically, the head includes an interior surface extending around and defining a head cavity, an oxygen port that is open to the head cavity for supplying oxygen to the head cavity, and a fuel gas port that is open to the head cavity for supplying fuel gas to the head cavity. The cutting tip includes multiple passageways for directing the gases from the head to the nozzle. 
   Conventional torches first generate a preheat flame with gases discharged from the nozzle, and the preheat flame is used to heat a metal workpiece. After the preheat flame has heated the workpiece sufficiently, a high velocity cutting oxygen stream is activated and delivered through the nozzle. The high velocity cutting oxygen stream physically removes molten material of the workpiece by oxidation, to cut the workpiece. Typically, a number of valves and related components are provided upstream of the nozzle, such as in the control body, to control the operations of the cutting torch. 
   Flashback is a reaction caused in cutting torches by the reverse flow and ignition of the explosive mixture of gases used in the operation of the torch. Flashback typically originates at the nozzle of the torch and is often caused by an obstruction at this point, operator error, improper gas pressure and/or defective equipment. Due to the rapid and explosive nature of flashback, it poses a major safety hazard to the operator of the gas torch and can damage the gas torch and associated equipment. Accordingly, and as disclosed in U.S. Pat. Nos. 5,407,348 and 5,470,227, it is common for flashback arrestors constructed of sintered material to be used at the entry point of the gases into the torch. Whereas this stops the flashback from traveling upstream from the torch into the gas hoses, regulators and cylinders that supply the gas to the torch, it disadvantageously does not eliminate the effects of flashback within the torch itself, which means that the torch can be damaged or the operator can be injured by flashback within the torch. 
   It is also known to install packing material into the head of a torch or in a tube that is immediately upstream from the head for arresting flashback, as respectively disclosed in U.S. Pat. Nos. 1,176,017 and 1,290,422. It is common for this packing material to become damaged, such as by becoming clogged with carbon deposits resulting from flashback. As a result, the packing material must be periodically replaced. Disadvantageously, the removal and replacement of packing material in cutting torches is labor intensive. Additionally, and of significant safety importance, if the packing material is not properly packed it may not perform its intended function, which can result in damage to the torch or injury to its operator. 
   It is also known for the few gas-carrying passageways that are machined into cutting tips and cutting tip adapters to be shaped so that they have abrupt directional changes which are intended to restrict flashback, as is disclosed in U.S. Pat. Nos. 1,439,861; 3,746,500; 4,431,167 and 5,688,469. However, because there are constraints on the size of some cutting tips, it is common for the number of directional changes that can be efficiently provided by machining passages to be very limited. This limitation can in at least some situations disadvantageously limit the effectiveness of these types of adapters and cutting tips with respect to restricting flashback. 
   Accordingly, there is a need in the art for a flashback arrestor proximate the head of a cutting torch for restricting flashback into head, and which can be readily used and replaced in a manner that is likely to ensure satisfactory functionality of the flashback arrestor. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, flashback protection is provided proximate the head of a cutting torch by a fitting, which is preferably in the form of an adapter or a cutting tip for mounting to the head. In accordance with this aspect, the fitting includes a body and porous structure that is carried by the body and is a distinct component from the body. The porous structure has a multiplicity of convolute passageways extending therethrough for restricting flashback, preferably by safely extinguishing any flashback proximate its source. Further in accordance with this aspect, the fitting can be readily used and replaced in a manner that is likely to ensure optimum functionality. Preferably for each fitting the porous structure is carried by the body in a manner that promotes the disposal of the used fitting rather than just the replacement of the porous structure of the fitting, which promotes safe operation of cutting torches by inhibiting end users from improperly installing the porous structure. Alternatively, the porous structure can be readily removable from the fitting and is replaceable. 
   In accordance with one aspect of one embodiment of the present invention, an end of the body of the fitting is inserted into the cavity of a head when mounting the fitting to the head, the end of the body is withdrawn from the cavity when unmounting the fitting from the head, the body defines at least one oxygen passageway that is in communication with the oxygen port of the head for receiving oxygen while the body is mounted to the head, the fitting defines at least one and preferably a plurality of fuel gas passageways that are in communication with the fuel port of the head for receiving fuel gas while the body is mounted to the head, and the porous structure is associated with the body so that the porous structure restricts flashback from entering the fuel port of the head while the body is mounted to the head. In addition, the porous structure is carried by the body so that it moves with the body when the body is moved from being completely separate from the head to being mounted to the head, and when the body is being moved from being mounted to the head to being completely separate from the head. As a result, the fitting can be easily initially installed and replaced with minimal risk of the porous structure being incorrectly installed and thereby failing to perform its intended function. Preferably the porous structure is positioned in the fuel passageways to restrict flashback through the fuel passageways. 
   In accordance with another aspect, a first part of the body is mounted to a second part of the body so that surfaces of these parts together define a chamber that contains the porous structure. This advantageously seeks to render the fitting tamper resistant and thereby enhance the disposable aspect of the fitting. That is, and in addition to the fitting being constructed so as to minimize the risk of the porous structure being incorrectly installed, in accordance with the present aspect a user will preferably be unaware of the possibility of disassembling the fitting to replace the porous structure should it become clogged, which will advantageously minimize the possibility of a user incorrectly installing a replacement porous structure within the fitting. Alternatively, the porous structure can be readily removable from the fitting and is replaceable. 
   In accordance with another aspect, the outer part of the body includes upstream fuel passageways, and the inner part of the body includes downstream fuel passageways. Further in accordance with this aspect, the inner part of the body includes a bore, the outer part of the body includes the oxygen passageway, and the oxygen passageway extends through the bore. Preferably the fuel gas passageways are positioned around and radially distant from the oxygen passageway. 
   In accordance with another aspect, the fitting is a cutting tip. In contrast and in accordance with another aspect of the present invention, the fitting is an adapter for having a cutting tip mounted thereto. In accordance with this aspect, there are multiple annular chambers that extend around and are isolated from the oxygen passageway, and that are open to the fuel gas passageways. 
   In accordance with one aspect of another embodiment of the present invention, the fitting is mounted to the head by engaging threads of the body to threads of head and rotating the body relative to the head through a plurality of revolutions in a first direction. Accordingly, the body can be unmounted from the head by causing relative rotation between the head and the body through a plurality of revolutions in a second direction which is opposite from the first direction. The porous structure is fitted to the body to restrict flashback from entering the fuel port of the head. As a result, the fitting can be easily initially installed and replaced with minimal risk of the porous structure being incorrectly installed and thereby failing to perform its intended function, since the porous structure is fitted to the body for installation and removal therewith. Alternatively, the fitting can be mounted to the head by means other than threads. 
   In accordance with another aspect, the fitting is an adapter and a cutting tip is mounted to the head via the adapter. Preferably the porous structure is annular and thereby defines a bore through which the cutting tip extends. 
   In accordance with another aspect, the fitting includes a port having an axis that extends radially with respect to the axis of the body. Preferably the body includes a channel that is adjacent and at least partially encircles the porous structure and is for passing fuel between the port and convolute passageways of the porous structure. 
   In accordance with another aspect, the porous structure is press-fit to the body, and in accordance with this same or another aspect, the porous structure is secured to the body by at least one fastening device, such as a pin-like shaft, that penetrates the porous structure and the body. This advantageously seeks to render the fitting tamper resistant and disposable. That is, the porous structure is preferably securely mounted to the body such that it will be difficult or at least inconvenient for a user to disassemble the fitting to replace the porous structure should it become clogged, which will advantageously minimize the possibility of a user incorrectly installing a replacement porous structure in the fitting. Alternatively, the porous structure can be readily removable from the fitting and is replaceable. 
   It is accordingly an aspect of the present invention to promote safe use of a cutting torch by suppressing flashback proximate its source through the use of a fitting that is substantially fool-proof, such as, for example, by being disposable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale and the majority of which are at least partially schematic, and wherein: 
       FIG. 1  is an exploded view of a cutting tip of the present invention and a head of a conventional cutting torch, wherein a nut encircling the cutting tip and the head are cross-sectioned along their axes, and a porous structure that is internal to the cutting tip is shown in broken lines, in accordance with one embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of the cutting tip taken along line  2 — 2  of  FIG. 4 ; 
       FIG. 3  is an isolated, cross-sectional view of an inner part of the cutting tip taken along line  2 — 2  of  FIG. 4 ; 
       FIG. 4  is a top plan view of the cutting tip, which is identical to a top plan view of the inner part; 
       FIG. 5  is a bottom plan view of the inner part; 
       FIG. 6  is an isolated, cross-sectional view of an outer part of the cutting tip taken along line  2 — 2  of  FIG. 4 ; 
       FIG. 7  is a top plan view of the outer part; 
       FIG. 8  is a bottom plan view of the outer part; 
       FIG. 9  is a side elevational view of the porous structure; 
       FIG. 10  is a plan view of the porous structure; 
       FIG. 11  is an enlarged, partial view illustrating pores of the porous structure; 
       FIG. 12  is an enlarged, cross-sectional view illustrating a representative convolute path formed by the pores of the porous structure; 
       FIG. 13  is a partial, cross-sectional view of a cutting tip that has been cross-sectioned in the same manner that is indicated by lines  2 — 2  of  FIG. 4 , in accordance with another embodiment of the present invention; 
       FIG. 14  is an elevational view of a combination of an adapter and cutting tip, in accordance with another embodiment of the present invention; 
       FIG. 15  is a partial view of the combination of  FIG. 14  cross-sectioned in the same manner that is indicated by lines  2 — 2  of  FIG. 4 ; and 
       FIG. 16  is an exploded view of an adapter and a head of a cutting torch, and a portion of a cutting tip, with each cross-sectioned along its axis, in accordance with another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
   Referring to  FIG. 1 , a fitting in the form of a cutting tip  20  is shown exploded away from a head  22  of a conventional oxy-fuel cutting torch, in accordance with a first embodiment of the present invention. Briefly described, the cutting tip  20  includes coaxial inner and outer parts  24 ,  26  that are mounted to one another and together provide a nozzle  28  that is located at a lower end of the cutting tip for discharging oxygen and fuel gas. In accordance with an alternative embodiment of the present invention, rather than including both the inner and outer parts  24  and  26 , these two parts are combined into a single piece. An internal porous structure  30  is within the cutting tip  20  for restricting flashback through the cutting tip. The porous structure  30  is hidden from view in FIG.  1  and is therefore illustrated by broken lines. The cutting tip  20  is removably mounted to the head  22  in a conventional manner by an externally threaded nut  32 , as will be discussed in greater detail below. 
   The head  22  includes an interior surface that extends around an axis to define a composite cavity  34  that is open at the lower end of the head. The interior surface of the head  22  includes annular upper and lower seating surfaces (i.e., upper and lower seats  36 ,  38 ) that are coaxial with the composite cavity  34  and define an oblique angle with respect to the axis of the composite cavity. The interior surface of the head  22  further defines interior threads  40  that are coaxial with the composite cavity  34 . The head further includes an oxygen port  42  that is open to the composite cavity  34  and is for receiving gaseous oxygen from an oxygen supply. Likewise, the head includes a fuel port  44  that is open to the composite cavity  34  and is for receiving fuel gas from a fuel supply. In accordance with the first embodiment of the present invention, the fuel gas includes a “premixed” mixture of oxygen and a gaseous fuel, such as acetylene, or the like. However, the present invention is also applicable to “post-mixed” cutting torches, as will be discussed in greater detail below. 
   The “oxygen supply” and “fuel supply” illustrated in  FIG. 1  are representative of conventional gas supplies and conventional cutting torch components that are upstream from the head  22 . In one specific example, the “oxygen supply” and “fuel supply” illustrated in  FIG. 1  are representative of a control body connected to separate fuel gas and oxygen supplies, and tubes for supplying the oxygen and fuel gas from the control body to the head, with the control body including valves and related components for controlling the operations of the torch. 
   The cutting tip  20  is mounted to the head  22  by inserting the upper end of the cutting tip into the composite cavity  34  and then engaging exterior threads  46  of the nut  32  to the interior threads  40  of the head. The nut  32  is rotated so that an annular upper edge of the nut engages a lower surface of a lower flange  48  of the cutting tip  20 , to force the cutting tip into the composite cavity  34 . Movement of the cutting tip  20  into the composite cavity  34  ceases when the cutting tip is coaxial with the composite cavity and fully engages the seats  36 ,  38  of the head  22 . More specifically, the cutting tip  20  includes annular upper and lower seating surfaces (i.e., upper and lower seats  50 ,  52 ) that extend coaxially around the axis of the cutting tip and at an oblique angle thereto, and the seats  50 ,  52  of the cutting tip respectively coaxially and securely engage the seats  36 ,  38  of the head  22  while the cutting tip is mounted to the head. 
   In accordance with the first embodiment of the present invention, an oxygen chamber is formed within the upper region of the composite cavity  34  while the upper seats  36 ,  50  are securely engaged to one another. The oxygen chamber is open to the oxygen port  42  and closed to the fuel port  44 , and an upper flange  54  of the cutting tip  20  is positioned within the oxygen chamber. At the same time, the lower seats  38 ,  52  are securely engaged to one another so that a fuel chamber is formed within the composite cavity  34  in the axial space between the upper seats  36 ,  50  and the lower seats  38 ,  52 . The fuel chamber is open to the fuel port  44  and closed to the oxygen port  42 , and an upper shoulder  56  of the cutting tip  20  is positioned within the fuel chamber. 
   Referring to the inner part  24  shown in  FIGS. 2-5 , an oxygen passageway  58  extends coaxially through the inner part. The oxygen passageway  58  has an inlet at the upper end of the inner part  24 , extends through a stem  60 , and includes an outlet at the lower end of the inner part. Multiple upstream fuel passageways  62  extend through the inner part  24  and are positioned around and radially distant from the axis of the inner part. Each upstream fuel passageway includes an inlet at the upper shoulder  56  and an outlet at an annular and coaxial lower shoulder  64  of the inner part  24 . Coaxial external threads  66  of the inner part  24  are for mounting the inner part to the outer part  26 . 
   Referring to the outer part  26  shown in FIGS.  2  and  6 - 8 , it includes an interior surface that extends coaxially around the elongate axis of the interior part to define a central bore  68  that is open at the upper and lower ends of the outer part. The interior surface of the outer part  26  includes coaxial interior threads  70  that engage the exterior threads  66  of the inner part  24  when the stem  60  of the inner part is inserted through the porous structure  30  and into the central bore  68 . Then, the inner and outer parts  24 ,  26  are coaxially rotated relative to one another so that via the threads  66 ,  70  the inner part is fully screwed into the central bore  68 , as illustrated in FIG.  2 . That is, the cutting tip  20  can be assembled by inserting the stem  60  through a coaxial bore  72  ( FIG. 10 ) defined through the porous structure  30 , thereafter inserting the stem through the central bore  68  of the outer part  26 , and then relatively rotating the inner and outer parts  24 ,  26  so that the threads  66 ,  70  mesh and the upper end of the outer part thereafter engages the underside of the lower flange  48  of the inner part. 
   The interior surface of the outer part  26  also includes a coaxial, cylindrical interior surface  74  and a coaxial, annular interior shoulder  76  which together with the exterior surface of the stem  60  and the lower shoulder  64  of the inner part  24  define a coaxial annular chamber that contains the porous structure  30 , and is preferably substantially fully occupied by the porous structure. While the cutting tip  20  is fully assembled as illustrated in  FIG. 2 , the annular chamber that contains the porous structure  30  is completely closed, except for being open to the outlets of the upstream fuel passageways  62  and inlets of downstream fuel passageways  78 . The downstream fuel passageways  78  extend through the outer part  26  and are positioned around and radially distant from the axis of the outer part. Each downstream fuel passageway  78  includes an inlet at the interior shoulder  76  and an outlet at the lower end of the outer part  26 . 
   Referring to  FIGS. 9-10 , the porous structure  30  is annular and includes cylindrical and coaxial and outer and inner surfaces  79 ,  81 . The outer and inner surfaces  79 ,  81  preferably respectively securely engage the interior surface  74  of the outer part  76  and the exterior surface of the stem  60  of the inner part  24  while the cutting tip  20  is assembled as illustrated in  FIG. 2 , in accordance with the first embodiment of the present invention. The inner surface  81  of the porous structure extends around and defines the bore  72  that receives the stem  60  and is opened at opposite ends of the porous structure  30 . The opposite ends of the porous structure  30  respectively securely engage the lower shoulder  64  of the inner part  24  and the interior shoulder  76  of the outer part  26 , in accordance with the first embodiment of the present invention. As a result of the porous structure  30  firmly engaging the interior surface  74 , stem  60 , lower shoulder  64 , and interior shoulder  76 , gas that flows from the upstream fuel passageways  62  to the downstream fuel passageways  78  is forced to flow through convolute passageways  80  ( FIG. 12 ) the porous structure. Likewise, any flashback attempting to travel from the downstream fuel passageways  78  to the upstream fuel passageways  62  is forced to travel through the multiplicity of convolute passageways  80  of the porous structure  30 , which preferably extinguishes the flashback. 
   Referring to the schematic and enlarged views of  FIGS. 11-12 , the porous structure  30  includes a multiplicity of pores  82  (only a representative few of which are identified by their reference numeral in FIG.  11 ), with each defining at least part of a convolute path  80  extending through the porous structure. In accordance with one example of the first embodiment of the present invention, the porous structure  30  is preferably sintered bronze or sintered stainless steel, or the like, with a pore size of about five microns, and preferably there are at least about, and most preferably more than, a hundred of the pores  82 /convolute passageways  80  in several square inches of the sintered material. The pore size is an approximate measure of a representative pore  82  in a direction perpendicular to the flow therethrough. In accordance with the first embodiment of the present invention, the preferred pore size and the number of pores may vary widely, depending upon many factors associated with the manufacture and operation of the cutting torch; therefore, pore sizes other than five microns and densities other than a hundred of the pores  82 /convolute passageways  80  in several square inches may be used in some applications. Further, and in accordance with an alternative embodiment of the present invention, the porous structure can be any type of material for both allowing the cutting torch to operate in a normal fashion and performing a flashback restricting function. In accordance with this alternative embodiment, the porous structure can be tightly packed steel wool, or the like, or one or more screens that are preferably arranged in layers, or the like. 
   Referring to  FIGS. 1-2 , the operation of the cutting torch of the first embodiment of the present invention will be described more specifically. Oxygen and fuel are supplied to the head  22  while the cutting tip  20  is fully mounted thereto, so that oxygen flows through the oxygen passageways  58 , and fuel flows through the upstream fuel passageways  62 , the porous structure  30 , and then the downstream fuel passageways  78 . That is, and more generally described, the porous structure  30  is positioned in the fuel passageways of the cutting tip  20 . The fuel is discharged from the nozzle  28  and ignited to form a preheat flame that is used to heat a metal workpiece. After the preheat flame has heated the workpiece sufficiently, a high velocity cutting oxygen stream is activated and delivered through the nozzle  28  via the oxygen passageway  58 . The high velocity cutting oxygen stream physically removes molten material of the workpiece by oxidation, to cut the workpiece. If during this operation flashback occurs as a result of reverse flow and ignition of the explosive mixture of gases, such as due to an obstruction at the nozzle, the convolute passageways  80  of the porous structure  30  advantageously restrict the flashback from reaching the upstream fuel passageways  62 . 
   When flashback reaches and is extinguished by the porous structure  30 , solid byproducts of the flashback, such as carbon, are deposited in the pores  82 /convolute passageways  80  of the porous structure. As a result, the porous structure  30  can eventually become clogged so that it is too restrictive to the desired flow of fuel gas therethrough. In this case and in accordance with the first embodiment of the present invention, the used cutting tip  20  is preferably discarded in its entirety and replaced with a new cutting tip. Completely discarding the used cutting tip  20  and replacing it with a new one prevents malfunctioning that could occur if a user incorrectly installs a new porous structure  30  or, even worse, removes and does not replace a clogged porous structure. In this regard, the cutting tip  20  can be generally characterized as a “one-piece” consumable item that is completely discarded if/when it becomes clogged. Alternatively, the porous structure  30  can be readily removable from the cutting tip  20  and is replaceable. 
   In accordance with another embodiment of the present invention, as an alternative to, or in addition to, the porous structure  30  being positioned in the coaxial annular chamber of the cutting tip  20 , as is illustrated in  FIGS. 1-2 , plug-like pieces of the porous structure can be coaxially positioned within each of the upstream fuel passageways  62  and/or each of the downstream fuel passageways  78 , or combinations of these passageways, and these passageways may be enlarged to optimally accommodate the plugs. Similarly, porous structure can be positioned at other locations in the fuel path(s) that are at least partially defined through the cutting tip  20 , or the like. 
   Referring to  FIGS. 1-2 , an exterior seam  84  is formed where the upper end of the outer part  26  abuts the lower surface of the lower flange  48  of the inner part  24 , in accordance with the first embodiment of the present invention. In accordance with another embodiment of the present invention that is partially illustrated in  FIG. 13 , at least the exterior seam  84  and preferably a substantial portion of the exterior surface of the cutting tip  20  is optionally covered with a coating  86  or otherwise machined in a manner that at least partially fills and/or obscures the exterior seam  84 . This advantageously prevents, or at least deters, disassembly of the cutting tip  20 , either mechanically by making it more difficult to unscrew the components, or visually by causing an operator to believe that the absence of visible seams indicates that the tip  20  is a unitary part that cannot be disassembled. That is and advantageously, the porous structure  30  is substantially inaccessible within the cutting tip  20 , so that it will be understood that the porous structure is not to be replaced. By deterring disassembly, the complete replacement of clogged cutting tips  20  is promoted, which will advantageously avoid malfunctioning that could occur if a user incorrectly installs a new porous structure  30  or, even worse, removes and does not replace a clogged porous structure. Accordingly, the cutting tip  20  is preferably a disposable component. Alternatively, the porous structure can be readily removed from the cutting tip and is replaceable. 
   An acceptable coating  86  is an anodized coating. A suitable anodized coating can be applied to the cutting tip  20  by a conventional anodic coating process, or the like. Anodic coating includes electrolytically treating the cutting tip  20  so that a film of oxides is formed on its outer surfaces to form the coating  86 . Other coating techniques are also within the scope of the present invention, with the resulting coatings preferably being sufficient for deterring disassembly of the cutting tip. Alternatively, the coating  20 , or the like, can be formed to obscure the exterior seam  84  by brazing the inner and outer pieces  24 ,  26  of the cutting tip  20  in the region of the external seam, so that disassembly of the cutting tip is substantially deterred. 
     FIGS. 14-15  illustrate a cutting tip  90  coaxially mounted to a fitting that is in the form of an adapter  20 ′, in accordance with another embodiment of the present invention. In accordance with this embodiment, the adapter  20 ′ is like the cutting tip  20  of the first embodiment of the present invention, with or without the coating  86  (FIG.  13 ), except for variations noted and variations that will be apparent to those of ordinary skill in the art. In accordance with this embodiment, the adapter  20 ′ includes exterior threads  92  that mesh with interior threads  94  of the cutting tip  90 , so that the cutting tip can be screwed onto the adapter to achieve the configuration illustrated in  FIGS. 14-15 . The cutting tip  90  includes a hexagonal outer structure  96  for receiving a wrench and facilitating the screwing of the cutting tip  90  onto and off of the adapter  20 ′. 
   Referring to  FIG. 15 , a terminal oxygen passageway  98  extends coaxially through the cutting tip  90 , and terminal fuel passageways  100  of the cutting tip are positioned around and radially distant from the axis of the cutting tip. The passageways  98 ,  100  of the cutting tip  90  will now be described for the configuration in which the cutting tip is fully mounted to the adapter  20 ′, as illustrated in  FIGS. 14-15 . The inlet of the terminal oxygen passageway  98  is open solely to the outlet of the oxygen passageway  58  of the adapter  20 ′, and the outlet of the oxygen passageway  58  is open solely to the inlet of the terminal oxygen passageway  98 . The outlet of the terminal oxygen passageway  98  is open at the lower end (i.e., nozzle) of the cutting tip  90 . 
   The adapter  20 ′ and cutting tip  90  include coaxial annular channels that face and are open to one another to form an annular chamber  102  that encircles and is coaxial with the oxygen passageways  58 ,  98 . The annular chamber  102  is completely closed, except for being open to the outlets of the downstream fuel passageways  78  and inlets of the terminal fuel passageways  100 . The outlets of the terminal fuel passageways  100  are at the lower end of the cutting tip  90 . 
   The upper end of the adapter  20 ′ is mounted to the head  22  ( FIG. 1 ) and functions just like the cutting tip  20  of the first embodiment of the present invention, except that the oxygen and fuel are discharged out of the nozzle of the cutting tip  90 . Additionally, if the cutting tip  90  becomes damaged, it can be advantageously replaced with a new one while the adapter  20 ′ remains mounted to the head  22 . In this regard, the combination of the adapter  20 ′ and the cutting tip  90  can be generally characterized as a “two-piece” item, with the tip  90  being the consumable item. Conversely, if it is necessary to change the adapter  20 ′ because of debris from previous flashbacks, the cutting tip  90  currently being used can be removed from the old adapter and placed on the new adapter, to avoid discarding a usable cutting tip. 
   Referring to  FIG. 16 , a fitting in the form of an adapter  110  is shown exploded away from a head  22 ′ of an oxy-fuel cutting torch, in accordance with another embodiment of the present invention. The cutting torch of this embodiment of the present invention is identical to the cutting torch of the first embodiment of the present invention, except for variations noted and variations that will be apparent to those of ordinary skill in the art. For example, the head  22 ′ illustrated in  FIG. 16  is identical to the head  22  of the first embodiment illustrated in  FIG. 1 , except that the composite cavity  34 ′ in the head  22 ′ is shaped differently below the upper seat  36 . More specifically, the interior surface of the head  22 ′ includes annular middle and lower seating surfaces (i.e., middle and lower seats  112 ,  114 ) that extend around, are coaxial with, and perpendicular with respect to the axis of the composite cavity  34 ′. 
   The adapter  110  includes a body  116  and a porous structure  30 ′ that are coaxially positioned with respect to one another, and in some examples of the present invention they are mounted to one another via one or more means, as will be discussed in greater detail below. Except for having different overall dimensions, the porous structure  30 ′ of the present embodiment is identical to the porous structure  30  of the first embodiment of the present invention. The body  116  includes an interior surface that extends coaxially around the axis of the body to define a bore  118  that is open at the upper and lower ends of the body. The interior surface of the body  116  includes a cylindrical interior surface  120 , an annular interior shoulder  122 , an annular seating surface (i.e., interior seat  124 ), and interior threads  126 , all of which coaxially extend around the axis of the body. Additionally, the interior seat  124  defines an oblique angle with respect to the axis of the body  116 . 
   In accordance with some examples of this embodiment, the porous structure  30 ′ is preferably substantially permanently installed to the body  116 , such as by at least one of several mounting techniques. In contrast, and in accordance with other examples of this embodiment, the porous structure  30 ′ is associated with the body  116  such that the porous structure can be readily removed from the body and replaced. In accordance with the illustrated example of this embodiment, two mounting techniques are used, namely a press-fit and an attachment device are used to install the porous structure to the body  116 , although the press-fit alone is preferred in another example. Regarding the press-fit, the interior surface  120  of the body  116  and the outer surface of the porous structure  30 ′ are sized so that when the porous structure is forced into the upper end of the bore  118 , the frictional interaction between the outer surface of the porous structure and the interior surface  120  holds the porous structure in the configuration illustrated in FIG.  16 . In this configuration, the lower end the porous structure  30 ′ securely engages the interior shoulder  122  of the body. 
   One or more fasteners in the form of retaining pins  128 , or the like, may extend through a portion of the body  116  and into the porous structure  30 ′, as illustrated for one pin  128  in FIG.  16 . In accordance with an alternative embodiment of the present invention, retaining pins  128  for mounting the porous structure  30 ′ to the body  116  are not included in the adapter  110 . Alternatively, the one or more retaining pins  128  can be replaced with other fastening devices, such as retaining rings or any other fastening means. 
   One or more ports  130 , each having an axis that extends radially with respect to the axis of the body  116 , extend through the body and have an inlet at a cylindrical outer surface  132  of the body  116  and an outlet at the interior surface  120  of the body. The cylindrical surface  120  further defines an annular groove  134  that is coaxial with the body  116  and encircles, or at least partially encircles, the axis of the body. The outlet of each port  130  and convolute passageways  80  ( FIG. 12 ) of the porous structure  30 ′ are open to the groove  134 . In some alternative embodiments of the present invention the groove  134  is omitted or alternatively formed in the outer surface of the porous structure  30 ′, and likewise all but one of the ports  130  can be omitted in some circumstances. 
   The upper end of the body  116  is inserted into the composite cavity  34 ′ of the head  22 ′, and then the body is rotated so that its exterior threads  136 , which are coaxial with the body, mesh with the internal threads  40 ′ of the head. The bottom surface of the body  116  includes two receptacles  138  for receiving the tips of a forked tool that can be used to rotate the adapter  110 , so that it is screwed into the head  22 ′. Means other than the receptacles  138  can be used to facilitate the screwing and unscrewing. Additionally and accordance with alternative embodiments of the present invention, the threads  136  and  40 ′ can be replaced with other means for facilitating the attachment, and preferably also the unattachment, between the body  116  and the head  22 ′. For example, different types of threads can be used; various “snap-fits” or press-fits can be used; a lateral retaining screw or pin, or the like, can extend radially through the head  22 ′ and engage the body  116 ; and any other connecting means can be used. 
   The upper surfaces of the body  116  and porous structure  30 ′ sealingly engage the middle seat  112  of the head  22 ′ while the adapter  110  is fully mounted to the head. Likewise, an annular exterior seat  140  of the body, which is coaxial with and encircles the axis of the body, sealingly engages the lower seat  114  of the head while the adapter  110  is fully mounted to the head. The outer surface  132  of the body  116  defines a smaller diameter than a cylindrical inner surface  142  of the head  22 ′. The inner surface  142  encircles the outer surface  132  while the adapter  110  is fully mounted to the head  22 ′, so that these surfaces do not contact one another and a plenum-like, annular outer chamber, channel or space is defined between these surfaces while the adapter is fully mounted to the head. It is advantageous for the outer chamber between the surfaces  132 ,  142  to be formed so that it can function as a fuel passageway, so that the port  130  of the adapter  110  need not align with the fuel port  44  in the head  22 ′. Alternatively, the port  130  substantially coaxially aligns with the fuel port  44 . 
   A conventional cutting tip or a cutting tip  20  as described above, or the like, is mounted to the adapter  110  while the adapter is fully mounted to the head  22 ′. For example, the cutting tip  20  is mounted to the adapter  110  by inserting the upper end of the cutting tip into the bore  118  of the adapter and then engaging the threads  46  of the nut  32  ( FIG. 1 ) to the interior threads  126  of the adapter. The nut  32  is rotated so that an annular upper edge of the nut engages the lower surface of the lower flange  48  of the cutting tip  20  to force the cutting tip into the both the bore  118  of the adapter and the composite cavity  34 ′ of the head  22 ′. Movement of the cutting tip  20  into the bore  118  and composite cavity  34 ′ ceases when the cutting tip, adapter  110  and head  22 ′ are coaxial and the cutting tip fully engages the respective seats of the body and head. More specifically, the upper and lower seats  50 ,  52  of the cutting tip  20  respectively coaxially and securely engage the upper seat  36  of the head  22 ′ and the interior seat  124  of the adapter. 
   An oxygen chamber is formed within the upper region of the composite cavity  34 ′ while the upper seats  50 ,  36  are securely engaged to one another. The oxygen chamber is open to the oxygen port  42  and closed to the fuel port  44 , and the upper flange  54  of the cutting tip  20  is positioned within the oxygen chamber. At the same time, the lower seat  52  of the cutting tip  20  and the interior seat  124  of the adapter  110 , and the exterior seat  140  of the adapter and the lower seat  114  of the head  22 ′, are securely engaged to one another so that a fuel chamber is formed within the composite cavity &#39; 34 . The fuel chamber is open to the fuel port  44  and closed to the oxygen port  42 . 
   While the adapter  110  is installed to the head  22 ′ and the cutting tip  20  is installed to the adapter as described above, the upper stem  144  of the cutting tip extends through the bore  72 ′ of the porous structure  30 ′. The inner surface  81 ′ of the porous structure  30 ′ defines a larger diameter than the outer surface of the upper stem  144  so that a plenum-like, annular inner chamber is defined between the upper stem and the inner surface of the porous structure, and the inlets of the upstream fuel passageways  62  of the cutting tip  20  are contiguous with and open to this chamber. More specifically, and in accordance with the embodiment illustrated in  FIG. 16 , the inner surface  81 ′ of the porous structure  30 ′ is in opposing face-to-face relation with the outer surface of the upper stem  144  of the cutting tip  20  while the adapter  110  is installed to the head  22 ′ and the cutting tip  20  is installed to the adapter. In accordance with a similar alternative embodiment of the present invention that is not illustrated in the drawings, the porous structure  30 ′ is positioned in a recess, or the like, defined in the adapter  110 , so that the upper stem  144  of the cutting tip extends through the bore  72 ′ of the porous structure  30 ′, but the inner surface  81 ′ of the porous structure  30 ′ is not in opposing face-to-face relation with the outer surface of the upper stem  144  while the adapter  110  is installed to the head  22 ′ and the cutting tip  20  is installed to the adapter. 
   Oxygen and fuel are supplied to the head  22 ′ while the adapter  110  and cutting tip  20  are fully mounted thereto as described above. As a result, oxygen flows through the oxygen passageway  58  of the cutting tip. The fuel flows from the annular outer chamber defined between the outer surface  132  of the adapter  110  and the inner surface  142  of the head  22 ′ to the annular inner chamber defined between the inner surface  81 ′ of the porous structure  30 ′ and the outer surface of the upper stem  144 . The flow between these chambers is via the port  130 , groove  134  and convolute passageways  80  of the adapter  110 . Then the fuel flows from the inner annular chamber, which is defined between the inner surface  81 ′ of the porous structure  30 ′ and the outer surface of the upper stem  144 , into the upstream fuel passageways  62  of the cutting tip  20 . Thereafter, the oxygen and fuel are discharged from the nozzle  28  of the cutting tip  20  as described above. If during operation flashback occurs as a result of reverse flow and ignition of the explosive mixture of gases, such as due to an obstruction at the nozzle  28 , the porous structure  30 ′ advantageously restricts the flashback from reaching the one or more radial ports  130  of the adapter  110 . 
   When flashback reaches and is extinguished by the porous structure  30 ′, solid byproducts of the flashback, such as carbon, are deposited in the porous structure. As a result, the porous structure  30 ′ can eventually become clogged so that it is too restrictive to the desired flow of fuel gas therethrough. In this case, the used adapter  110  is preferably discarded in its entirety and replaced with a new adapter. Completely discarding the used adapter  110  and replacing it with a new one will advantageously prevent malfunctioning that could occur if a user incorrectly installed a new porous structure  30 ′ or, even worse, removes and does not replace a clogged porous structure. Removing the porous structure  30 ′ from an adapter  110  and installing a new porous structure to the same adapter is advantageously discouraged by the secure mounting of the porous structure to the body  116  of the adapter. Alternatively, the porous structure  30 ′ can be connected to or otherwise associated with the adapter  110  such that the porous structure can be readily removed from the adapter and replaced. 
   Those of ordinary skill in the art understand that oxy-fuel torches include both “post-mixed” and “premixed” cutting torches, and that the present invention has been described in the context of premixed cutting torches. That is, in accordance with illustrated embodiments of the present invention, the fuel supplied via the fuel ports  44  is a mixture of oxygen and a fuel gas, such as acetylene, or the like. Although the present invention has been described above in the context of “premixed” torches, the present invention is also applicable to “post-mixed” cutting torches. 
   Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.