Metallurgical apparatus – Means for cutting solid metal with heat – e.g. – blowpipes – Having torch spacing means
Reexamination Certificate
1999-07-07
2001-08-21
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for cutting solid metal with heat, e.g., blowpipes
Having torch spacing means
C266S048000, C266S077000
Reexamination Certificate
active
06277323
ABSTRACT:
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.
REFERENCES:
patent: 3590212 (1971-06-01), Corrigall et al.
patent: 3923448 (1975-12-01), Guth
patent: 4443003 (1984-04-01), Bleys
patent: 4455176 (1984-06-01),
Kastler Scott
Oxy-Arc International Inc.
Pearne & Gordon LLP
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