Abstract:
A novel cutting nozzle assembly for a postmixed oxygen-fuel gas torch is disclosed. The nozzle assembly includes a cylindrical shroud which surrounds and extends away from the gas discharge orifices in the gas discharge end of the cutting nozzle. The cylindrical shroud has the advantage of producing a tighter gas stream and of promoting a more thorough mixing of the preheat oxygen and the fuel gas to provide a hotter, more compact flame which produces a more parallel-sided cut through metal workpieces. The cutting tip therefore conserves metal as well as cutting gases. It also cuts faster than prior art postmixed cutting nozzles.

Description:
RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 08/995,827, filed on Dec. 22, 1997 now U.S. Pat. No. 5,944,915, which is a divisional of application Ser. No. 07/981,352, filed on Nov. 25, 1992 and issued to U.S. Pat. No. 5,700,421 on Dec. 23, 1997. 
    
    
     TECHNICAL FIELD 
     The present invention relates to oxy-fuel gas torches and, in particular, to a cutting nozzle for postmixed oxy-fuel gas torches. 
     BACKGROUND OF THE INVENTION 
     Oxy-fuel gas cutting torches are useful for cutting ferrous alloys. With the proper equipment, cuts can be effected through very thick billets. In operation, an oxy-fuel torch is used to direct an ignited stream of oxygen and fuel gas onto the surface of the metal to be cut. The metal is thus heated to its ignition temperature, at which point a stream of cutting oxygen directed at the surface oxidizes the heated metal to effect the cut. 
     The cutting torch may be one of a premixed or a postmixed type torch. In a premixed torch, preheat oxygen and fuel gas are mixed within the torch head before being discharged for ignition. In a postmixed cutting torch, the preheat oxygen and fuel gas are discharged from the torch in unmixed streams. Turbulence in the discharged streams mixes the oxygen and fuel gas before ignition occurs. A principal advantage of the postmixed cutting torch is that it is not subject to flashback, a potential hazard associated with the use of premixed torches. Flashback occurs when the oxygen and fuel gas mixture in a premixed torch ignites within the torch head. Postmixed torches are therefore preferred for heavy industrial applications where a torch is subjected to considerable heat. A further advantage of the postmixed torch is that postmixed nozzles produce a longer heat zone than premixed nozzles. This permits the postmixed torch to operate farther from the work, decreasing the heat stress on the torch and increasing the service life of the nozzle. 
     An example of a prior art postmixed oxy-fuel gas cutting torch and nozzle are taught in the U.S. Pat. No. 4,455,176 which issued to Fuhrhop on Jan. 19, 1984. That patent describes a combination cutting torch and nozzle assembly for postmixed oxy-fuel cutting using two separate annular streams of preheat oxygen gas surrounding the fuel gas stream with the inner annular preheat oxygen stream directed to impinge the fuel gas stream very close to the point of discharge from the nozzle assembly. The nozzle assembly is secured to the head of the cutting torch by a hollow retaining nut which forms an annular gap with the nozzle assembly for discharging the outer preheat oxygen gas stream. 
     All prior art postmixed nozzles for oxy-fuel gas torches operate in substantially the same way. A stream of cutting oxygen is discharged from an axial bore in the nozzle. A plurality of fuel gas discharge orifices arranged in a concentric ring around the axial bore discharge preheat fuel gas and a second plurality of gas discharge orifices arranged in an outer concentric ring discharge preheat oxygen which acts as an envelope that surrounds the fuel gas stream. As the gas streams flow toward the workpiece, a mixing of the fuel gas and the oxygen occurs and the mixture ignites to heat the workpiece. 
     Testing has shown that up to 50% of the preheat oxygen stream discharged from prior art postmixed torch nozzles is lost to the atmosphere before mixing with the fuel gas occurs. This contributes to inefficient combustion and slows the heating process. It also contributes to the cost of cutting since gases are not utilized to their potential. It has also been observed that prior art postmixed torch nozzles are incapable of effecting a parallel-sided cut through a thick workpiece. The cut is narrower along a top of the workpiece than along a bottom of the workpiece. The thicker the workpiece, the wider the cut at the bottom side. If many thick billets must be cut, a significant loss of metal occurs. 
     A further disadvantage of prior art cutting nozzles for postmixed oxy-fuel gas torches is their direct exposure to splashback of molten metal from the cut. Splashback metal tends to stick to the discharge end of the nozzle, frequently blocking discharge orifices. When this occurs, the torch must be shut down to permit the nozzle to be cleaned or replaced. This interrupts workflow and increases operating expenses. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a cutting nozzle assembly which overcomes the disadvantages of the prior art. 
     It is a further object of the invention to provide a cutting nozzle assembly which promotes more efficient combustion of oxy-fuel gas mixtures. 
     It is yet a further object of the invention to provide a cutting nozzle assembly which minimizes nozzle damage due to the splashback of molten metal onto the discharge end of the nozzle. 
     It is yet a further object of the invention to provide a cutting nozzle assembly which provides a cleaner cut that minimizes the loss of metal during a cutting operation. 
     In accordance with the invention, there is provided a cutting nozzle for a postmixed oxy-fuel gas torch, the nozzle comprising a plurality of bores for respectively conducting fuel gas, preheat oxygen and cutting oxygen through the nozzle, each of the plurality of bores terminating in a respective discharge orifice; and a shroud disposed about and extending axially from the discharge orifices, the shroud having an axial extent sufficient to protect at least the discharge orifices from splash-back, promote mixing of gases discharged through the bores, and channel the discharged gases to produce a gas stream that maintains its shape over a greater distance than a similar nozzle not having a shroud. 
     The present invention therefore provides a cutting nozzle assembly for a postmixed oxy-fuel gas torch having a shroud which may be integrated with the discharge end, and which extends away from the discharge end of the nozzle to protect the discharge end of the nozzle from molten metal splashback and to concentrate, direct, and promote the mixing of the oxygen/fuel gas streams. This results in a narrower, cleaner, more parallel-sided cut which conserves metal at the cut and increases the speed and efficiency of cutting. The service life of the nozzle is further increased because the discharge end of the nozzle is shielded from splashback. Molten metal splashback having a trajectory which enters the throat of the shroud is generally cooled by the gas stream to a point that it does not fuse with the nozzle before it contacts the nozzle discharge end. Nozzles in accordance with the invention have been operated for weeks under industrial work conditions without requiring maintenance or replacement. 
     In accordance with a first embodiment of the invention, the shroud is an integral part of a retainer nut used to couple the nozzle to the torch and the retainer nut further includes a flange which is pierced with bores that discharge the preheat oxygen. This embodiment is particularly cost efficient to produce because it minimizes the quantity of metal required in the nozzle as well as the machining time required to form the nozzle assembly. 
     In accordance with a second embodiment of the invention, the shroud is an integral part of the retainer nut used to couple the nozzle to the torch, but the nozzle includes all of the gas discharge bores. 
     In accordance with third and fourth embodiments of the invention, the nozzle assembly is made of a single unit and the shroud is an integral part of the nozzle. These embodiments are evermore cost efficient to produce than the first or second embodiments because the unitary structure of the nozzle avoids the hollow structure of the retainer nut which is used to couple the nozzle to the torch. This minimizes the quantity of metal required to be removed and wasted during manufacturing, as well as the machining time required to form the nozzle unit. It is also advantageous to use a cutting nozzle having a unitary structure because it saves time for assembly and no assembly clearance exists between the nozzle and the retainer nut which may affect the accuracy of axial alignment of the gas passages of the nozzle and, therefore, the performance of the nozzle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will be more fully described by way of example only and with reference to the following drawings, wherein: 
     FIG. 1 is a longitudinal cross-sectional view of a preferred embodiment of a postmixed torch nozzle assembly in accordance with the invention; 
     FIG. 2 is a top plan view of the postmixed torch nozzle assembly shown in FIG. 1; 
     FIG. 3 is a longitudinal cross-sectional view of a second embodiment of a postmixed torch nozzle assembly in accordance with the invention; 
     FIG. 4 is a top plan view of the postmixed torch nozzle assembly shown in FIG. 3; 
     FIG. 5 is a partial cross-sectional view of the postmixed torch nozzle assembly shown in FIG. 1 coupled to a postmixed cutting torch; 
     FIG. 6 is a schematic view of a cut through a 4¾ inch steel billet effected with a prior art cutting nozzle and a cut through the same billet effected with a cutting nozzle in accordance with the invention; 
     FIG. 7 is a longitudinal cross-sectional view of a third embodiment of postmixed torch nozzle assembly in accordance with the invention; 
     FIG. 8 is a top plan view of the postmixed torch nozzle assembly shown in FIG. 7; 
     FIG. 9 is a longitudinal cross-sectional view of a fourth embodiment of a postmixed torch nozzle assembly in accordance with the invention; and 
     FIG. 10 is a top plan view of the postmixed torch nozzle assembly shown in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a longitudinal cross-sectional view of a cutting nozzle in accordance with a preferred embodiment of the invention. The cutting nozzle assembly, generally referred to by reference  10 , includes a nozzle  12  and a hollow retainer nut  14 . The nozzle  12  includes an axial bore  16  for discharging cutting oxygen from a cutting torch (see FIG.  5 ), a plurality of fuel gas bores  18  arranged in an inner concentric ring around the axial bore  16 , and a plurality of preheat oxygen bores  20  arranged in an outer concentric ring around the axial bore  16 . Each of the bores  16 ,  18  and  20  terminates in a discharge orifice  22 ,  24  and  26  respectively in a discharge end  28  of the cutting nozzle assembly  10 . 
     The retainer nut  14  surrounds the nozzle  12  and is used to couple it with a cutting torch (see FIG.  5 ). In accordance with the preferred embodiment of the invention, an annular flange  15  in an inner periphery of the retainer nut  14  forms a portion of the discharge end  28  of the cutting nozzle assembly  10 . The retainer nut  14  includes a spiral thread  30 , a hexagonal rib  32  to provide a gripping surface for a wrench, and a shroud  34  which surrounds and extends away from the discharge end  28  of the cutting nozzle assembly  10 . The shroud  34  is preferably a circular cylinder although other cylindrical shapes may also be used. 
     As described above, the retainer nut  14  preferably forms a part of the discharge end  28  of the cutting nozzle assembly  10 . The hollow retainer nut  14  surrounds the nozzle  12 . The preheat oxygen bores  20  in the nozzle  12  communicate with a cavity  36  in the retainer nut  14 . The annular flange  15  of the retainer nut  14  is provided with preheat oxygen bores  38  which communicate with the preheat oxygen discharge orifices  26 . Thus, preheat oxygen entering preheat oxygen bores  20  passes through the cavity  36  in the retainer nut  14  and exits through the preheat oxygen bores  38  via the preheat oxygen discharge orifices  26 . This configuration of the cutting nozzle assembly  10  provides the most economically produced assembly because it minimizes drilling and material requirements. 
     FIG. 2 shows a top plan view of the cutting nozzle assembly  10  shown in FIG.  1 . As is apparent, the hexagonal rib  32  of the retainer nut  14  provides a gripping surface for a wrench to facilitate coupling the cutting nozzle assembly to a torch. The shroud  34  surrounds the discharge end  28  of the cutting nozzle. The discharge end  28  includes discharge orifices  22  for cutting oxygen,  24  for fuel gas and  26  for preheat oxygen. The discharge orifice  22  for cutting oxygen is preferably flared. This creates a swirl effect within the interior of the shroud  34  to promote the mixing of fuel gas and oxygen. The shroud  34  also shields the discharge end  28  from molten metal splashed back from the cut. This enhances the service life of the nozzle because it substantially eliminates nozzle damage resulting from splashback metal contacting the nozzle and fusing with it. 
     FIG. 3 is a longitudinal cross-section through a second embodiment of the invention. The cutting nozzle assembly is substantially identical in structure to the assembly shown in FIGS. 1 and 2. In this embodiment, the nozzle  12  includes all of the discharge bores. The retaining nut  14  supports the shroud  34 . The cutting oxygen discharge orifice  22 , the fuel gas discharge orifices  24  and the preheat oxygen discharge orifices  26  are all located in the discharge end  28  of the nozzle  12 . In all other respects, the cutting nozzle assembly  10 , as shown in FIG. 2, is identical to the cutting nozzle assembly  10  shown in FIG.  1 . This embodiment of the invention requires slightly more material to manufacture as well as more machining time but produces identical cutting results. 
     FIG. 4 shows a top plan view of the nozzle shown in FIG.  3 . The nozzle is identical to the embodiment shown in FIG. 2 except that there is no seam between the fuel gas discharge orifices  24  and the preheat oxygen orifices  26 . 
     Cutting nozzle assemblies  10  are preferably constructed from brass alloy, although other materials such as copper, stainless steel and the like may also be used. The shroud  34  is preferably at least 0.65″ (16.5 mm) long. Longer lengths may be used but much shorter lengths are not recommended. The thickness of the sidewall of the shroud  34  is preferably about 0.22″ (5.58 mm) for good resistance to heat fatigue although a thinner sidewall may be used successfully. At least the outer surface of the sidewall of the shroud  34  is preferably plated with chrome or nickel to inhibit the adhesion of metal molten splashback. 
     FIG. 5 shows the cutting nozzle assembly  10  illustrated in FIG. 1 connected to a typical postmixed oxy-fuel gas torch. The oxy-fuel gas torch includes a torch head  40  to which the cutting nozzle fuel assembly is coupled using the retainer nut  14 . The torch head  40  is supported by a tubular handle  42 . The tubular handle is hollow. Extending through the tubular handle are supply tubes for cutting oxygen, fuel gas and preheat oxygen. Supply tube  44  supplies cutting oxygen from an oxygen source. Supply tube  46  supplies fuel gas from a fuel gas source, and supply tube  48  supplies preheat oxygen from the oxygen source. The fuel gas supply tube  46  and the cutting oxygen supply tube  48  terminate in circumferential distribution grooves  50  and  52 , respectively. The operation of postmixed oxy-fuel gas torches is well understood by those skilled in the art. 
     FIG. 6 shows a schematic diagram of two steel billets cut using a postmixed oxy-fuel gas torch. Each billet is approximately 4¾″ (12 cm) thick. A first billet  54  was cut using a typical prior art postmixed cutting nozzle. A second billet  56  was cut using a cutting nozzle in accordance with the invention. As is apparent, the kerf of the cut through the second billet  56  is narrower and more parallel-sided than the kerf of the cut through the first billet  54 . The kerf of the cut through the first billet  54  is approximately 0.305″ (7.75 mm) wide where the cut commences at the top surface  58  of the first billet. The kerf is approximately 0.478″ (12.14 mm) wide at the bottom surface  60  of the first billet  54 . In contrast, the width of the kerf at the top surface  62  of the second billet  58  is approximately 0.21″ (5.33 mm) wide and the kerf at the bottom surface  64  of the second billet  56  is also approximately 0.21″ (5.33 mm) wide. It is, therefore, apparent that the cutting nozzle in accordance with the invention cuts a much thinner kerf and produces cut ends which are much more square than kerfs achieved with the prior art postmixed nozzles tested. Experimentation has established that a postmixed cutting nozzle in accordance with the invention produces approximately 40% less slag than a prior art nozzle of the same type. In a production environment, this represents a considerable saving in energy and cut materials. The cleaner kerf produced by a cutting nozzle assembly  10  in accordance with the invention is due to the tighter, more cylindrical gas discharge stream promoted by the shroud  34  (see FIGS.  1  through  5 ). The shroud  34  promotes a more thorough mixing of the preheat oxygen and the fuel gas and produces a gas stream that maintains its shape over a much longer distance than a gas stream discharged by prior art postmixed nozzles. 
     FIG. 7 shows a longitudinal view of a cutting nozzle in accordance with a third embodiment of the invention. The cutting nozzle, generally referred to by reference numeral  110 , is substantially identical in structure to the combined nozzle/nut assembly shown in FIGS. 1 through 4. In this third embodiment, the nozzle  110  includes a nozzle portion  112  and a shroud  134 . The nozzle portion  112  includes an axial bore  116  for discharging cutting oxygen from a cutting torch, a plurality of fuel gas bores  118  arranged in an inner concentric ring around the axial bore  116 , and a plurality of preheat oxygen bores  120  arranged in an outer concentric ring around the axial bore  116 . Each of the bores  116 ,  118  and  120  terminates in a respective discharge orifice  122 ,  124  and  126 , in a discharge end  128  of the cutting nozzle portion  112 . The discharge orifice  122  of the axial bore  116  has a flared portion. All of these features are closely similar to the embodiment shown in FIG.  3 . However, the shroud  134 , a spiral thread  130  for engaging a complementary thread in the postmixed oxy-fuel gas torch and a hexagonal rib  132  adapted to provide a gripping surface for a wrench are formed as an integral part of the nozzle  110 , instead of a separate part of the nozzle assembly  10  as shown in FIG.  1 . The entire nozzle  110  can thus be conveniently manufactured from a single piece of bar stock, such as, for example, commercially available 1.25″ hexagonal copper bar stock. In this case, the shroud  134  can conveniently be provided as an axial bore in one end of the nozzle blank. The exterior surface of the shroud can be turned (e.g. on a lathe) to provide a circular cylindrical surface as shown in the illustrated embodiments, or alternatively, left in its original hexagonal shape. 
     This embodiment of the invention avoids producing a hollow retainer nut  14 , as shown in FIGS. 1 and 3, which requires material removal therefrom to form a cavity to receive the nozzle  12 . The unitary nozzle  110 , therefore, requires much less machining time and decreases material waste. 
     FIG. 8 shows a top plan view of the nozzle shown in FIG.  7 . The view is identical to the view shown in FIG. 4 even though FIG. 8 illustrates the top view of the unitary nozzle  110  but FIG. 4 illustrates a nozzle assembly  10  made of two pieces. 
     FIG. 9 is a longitudinal cross-section through a fourth embodiment of the invention. The cutting nozzle  110  is closely similar in structure to the cutting nozzle shown in FIG.  7  and is a unitary structure. In this embodiment, the nozzle portion  112  includes a flat intake end  136  and all bores  116 ,  118  and  120  extend from the flat intake end  136 , terminating in orifices  122 ,  124  and  126  on the discharge end  128 . The axial bores  116  has an entrance portion which has an enlarged diameter for connecting with a respective gas passage in a torch head, not shown. The bores  118  and  120  have an entrance portion defined by respective circumferential grooves which form distribution channels for the pre-heat oxygen and the fuel gas when the nozzle is installed in a torch (not shown). The flared portion of the orifice  122  at the discharge end is longer and the flared angle is smaller than those of the similar structure shown in FIG.  7 . The shroud  134 , in this embodiment, can be thinner than the shroud in the other embodiments, for example, by about 0.139″ (3.53 mm). In all other respects, the cutting nozzle  110 , as shown in FIG. 9, is identical to the cutting nozzle  110 , shown in FIG.  7 . This embodiment of the invention is used for coupling a type of postmixed oxy-fuel gas torch having a flat seat on which the flat intake end of the nozzle is seated. 
     FIG. 10 shows a top plan view of the nozzle shown in FIG.  9 . The view is identical to the view shown in FIG. 8, except that the sidewall of the shroud  134  is thinner. 
     INDUSTRIAL APPLICABILITY 
     The cutting nozzle for a postmixed oxy-fuel gas torch in accordance with the invention is useful in cutting steel and other ferrous alloys, particularly in industrial production environments such as steel mills where large slabs must be cut into billets for handling or processing. Because the cutting nozzle provides a cleaner and narrower cut than prior art nozzles of the same type, the nozzle conserves materials and energy. The cutting nozzle assembly also has a prolonged service life because it is less susceptible to damage due to the splashback of molten metal. Operating overheads are therefore reduced. The cutting nozzle assembly  10  in accordance with the invention may be used in any application where metals must be rapidly and efficiently cut by oxidation. 
     It is therefore apparent that a new and useful cutting nozzle for postmixed oxy-fuel gas torches has been invented. 
     The embodiments described above are intended to be exemplary only. Those skilled in the art will understand that certain prior art postmixed nozzle constructions may be modified to accord with the invention by welding or soldering a shroud to either the retainer nut or the discharge end of the prior art nozzle or by redesigning a retainer nut to include an integral shroud. Changes and modifications to the specifically described embodiments may be made without departing from the scope of the invention which is intended to be limited solely by the scope of the appended claims.