Abstract:
A manual gas cutting torch to be used for fusion-cutting iron materials such as steel frames or iron plates includes a flame port at its cutting tip, a plurality of ports connected with gas and oxygen cylinders at its rear edge, and a handle section for holding the torch with one hand at its middle. A freely detachable back-fire preventive device is incorporated into a gas channel or oxygen channel or to both channels which shift(s) to the cutting tip side from this handle section. The back-fire preventive device serves to stop any flash-back from the cutting tip just before the handle section for preventing the flame from passing through the handle section and escaping back to the cylinder.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates particularly to a back-fire preventive unit for a gas cutting torch for fusion-cutting of metal frames and plates by ejecting out of a cutting tip a mixed gas obtained by mixing a fuel gas and oxygen for igniting it, and thus by utilizing the flames which have been built up on the cutting tip. 
     In a manual gas cutting torch, a flame port is formed at its tip, a handle section for holding the torch with one hand is formed at the middle, and the connection ports with gas and oxygen cylinders are built up at the rear section, or in many cases, at the rear end of said handle, to whose connection port and handle section the adjusting valves for regulating the flowrate of gas and oxygen are fitted. 
     The manual gas cutting torch in this way serves to help an operator to hold it with his one hand for performing the fusion-cutting work while moving it freely. However, flash-backs sometimes happen in this type of gas cutting torch. A back-fire phenomenon occurs when the jet speed &#34;Uf&#34; of mixed gases and oxygen becomes smaller than the combustion speed &#34;Sb&#34; of the mixed gases while the relation between them usually remains at Uf=Sb. A back-fire is usually found when regulating the gas and oxygen volumes or when extinguishing the fire. The biggest reason for the back-fire to happen in such a case is that the equilibrium between the jet speed &#34;Uf&#34; and the combustion speed &#34;Sb&#34; of mixed gas is disturbed by the adjustment of gas and oxygen, and the value of &#34;Uf&#34; frequently becomes smaller. 
     Should a back-fire happen in a gas cutting torch, this back-fire runs back up to the gas or oxygen cylinder which might explode. 
     Therefore, in the past to avoid the possibility of explosion a fire preventive unit is attached to the outlet port of the cylinder or to the hose connecting the cylinder with the gas cutting torch. However, this type of conventional means is not satisfactory for the operator&#39;s safety although it can prevent the cylinder from exploding. 
     In many cases the operator holds the gas cutting torch in his one hand during work with the other effective hand, and while, adjusting the gas or oxygen, he holds the gas cutting torch with the hand opposite to his effective hand. For this reason, once a back-fire should happen, this gas cutting torch instantaneously becomes high in temperature and his one hand is burned. Also, due to this instantaneous high temperature he sometimes drops the gas cutting torch from his hand, and this is especially dangerous when dropping the gas cutting torch from a high place. Further, there may be an explosion to the handle section which incorporates a valve for adjusting the gas or oxygen. In case of this explosion, a serious injury may be invited to the operator&#39;s body in addition to the burn to his hand or a part of his body. 
     SUMMARY OF THE INVENTION 
     The invention provides a back-fire preventive unit in a gas cutting torch, for protecting an operator using the gas cutting torch from suffering from a burn. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects obtained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a side elevational view of a gas cutting torch constructed in accordance with the invention; 
     FIG. 2 is a top plane view of the gas cutting torch of FIG. 1; 
     FIG. 3 is a sectional view taken along the line A--A of FIG. 1; 
     FIG. 4 is a sectional view taken along the line b--b of FIG. 1, 
     FIG. 5 is a sectional view taken along the line C--C of FIG. 1; 
     FIG. 6 is a front elevation viewed from the direction of the line D--D of FIG. 1; 
     FIG. 7 is the sectional view taken along the line E--E of FIG. 2; 
     FIG. 8 is a side elevational view partly in section of the backfire preventive device; 
     FIG. 9 is cross sectional view of another embodiment of gas cutting torch indicating the state incorporating the back-fire preventive device inside the oxygen passage; and 
     FIG. 10 is the sectional view taken along the line F--F of FIG. 9. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A back-fire preventive unit in a gas cutting torch 1 according to this invention is built into the manifold block A area of FIG. 2 in front of the handle section of a gas cutting torch. The gas cutting torch 1 is equipped with a cutting tip 2 at its tip, and is provided with the gas supply port or connection port 3 and an oxygen supply port or connection port 4 respectively at its rear edge for supplying gas and oxygen to the aforesaid cutting tip 2, but also is structured in such a manner that the gas and oxygen which have entered from the gas supply port 3 and the oxygen supply port 4 may be fed through bores formed in the manifold block to a mixture chamber 5 (FIG. 9) formed in the manifold block adjacent a lower face and opening to the rear face in front of the handle 1a via the gas passage 3a and the oxygen passage 4a which connect at a rear face of the manifold block to bores found therein. The passages leading to the cutting tip 2 from the mixture chamber 5 are interconnected to each other by use of the mixed gas channel 6 provided by a pipe extending from the front face of the manifold through the cutting tip. A further branching of the oxygen entering from the oxygen supply port 4 is effected to a side of branched jet gas passage or bore 16a inside the handle section 1a. A jet gas passage 7 supplies the oxygen directly into the cutting tip 2 from the front face of the manifold, where the gas entered from the gas supply port 3 is branched by the branched gas passage 3b in the downstream side of supply port 3. Gas is supplied also via a pilot gas channel 9 provided by a pipe extending from the front face of the manifold through the cutting tip (FIGS. 3 and 4), to a pilot fire port 8 attached to the vicinity of cutting tip 2. 
     A needle valve 10, which extends behind the rear face of the block under the handle, is capable of optionally setting the mixed gas flowrate passing through the interior of the mixed gas channel 6 by means of the knob 11. 
     FIG. 5 indicates a pilot gas control valve 12a, which is mounted in a chamber formed in the block adjacent a rear face thereof and connected to the branched gas passage 3b. 
     An ignition lever button 13 protrudes above the upper face of handle section 1a and is structured so that when it is pushed in, the pilot gas control valve 12a is opened by the spindle 14 and can be automatically returned by a return spring 12b. 
     A piezoelectric type ignition unit 15 discharges electricity between electrodes 8a of the pilot fire port 8 is mounted in a chamber formed in the manifold block opening to the upper face of the block and when the pilot gas control valve 12a is opened by use of the said ignition lever 13. 
     A jet gas valve 16 is mounted in a chamber formed in the manifold block opening to the upper face of the block and controlled by a knob 17 fitted to the handle section 1a, which is mounted to the branched jet gas passage or bore which interconnects oxygen passages 4a and 7, 16 in order to regulate the flowrate of jet gas passing through the inside of the jet gas passage 7. 
     A back-fire preventive unit 18 is releasably mounted in a chamber 18a formed in the manifold open to a lateral face thereof and includes a back-fire preventive device 18c of cylindrical wire net shape (FIG. 4) by utilizing the fixture 18b inside the chamber 18a formed in a bore connecting gas passage 3a with gas mixture chamber 5 on the downstream side of handle section 1a. The back-fire preventive device 18c of wire net shape can be replaced by a back-fire preventive device 18d made of sintered metal as illustrated in the embodiment of FIG. 8. The back-fire preventive device can also be of the combination of heat resistant materials, for example, such metals high in melting point as stainless steel or tungsten or other ceramics or the materials. The back-fire preventive device exemplified in the embodiments have the advantage in practical application that they may be capable of freely setting the area (size) of said device meeting the gas (or oxygen) volume. In FIG. 8 and FIG. 9 an O-ring is shown for sealing the backfire device in position. 
     A practical use example of the gas cutting torch is described below: 
     First, connect the gas supply port 3 and the oxygen supply port 4 respectively to the gas and the oxygen cylinders using hoses. Open the valves on the side of respective cylinders, further open the knob 3c for supplying the gas and the oxygen which then enter into the mixture section 5 via the gas passage 3a and the oxygen passage 4a and are mixed therein. This mixed gas adjusted by the needle valve 10. 
     Next, push in the ignition lever 13, open the pilot gas control valve 12a for supplying the gas to the pilot fire port 8, and at the same time control the piezoelectric ignition unit 15 for allowing a spark discharge between the electrodes 8a and for igniting the pilot fire port 8. 
     The mixed gas which has been mixed in the mixture section 5 is fed to the cutting tip 2 via the mixed gas channel 6 and is jetted out. A fire is shifted to this jetted mixed gas from the flame of pilot fire port 8 which has been previously ignited. After this fire shift, the operators hand is released from the ignition lever 13, then the lever 13 is automatically returned by the return spring, and the flame of the pilot fire port 8 goes out. In the next step, the needle vale 10 for mixed gas is controlled for regulating the fire intensity and for performing the preheating in advance to the cutting work by use of the flame which has been produced on the cutting tip 2. 
     When the preheating work is over, the jet gas valve 16 is opened by means of a knob 17 for supplying the jet gas to the cutting tip 2 through the jet gas passage 7 so as to form an intensive flame for cutting service, on the cutting tip 2. The cutting work is not ready to be conducted. 
     When the work is through, close all the valves respectively. For reference, as a procedure for setting a fire to the cutting tip 2, it is permissible to have the mixed gas jetted out first from the cutting tip 2 and to have a pilot flame formed for setting a fire to the cutting tip 2 at a later stage. 
     The back-fire preventive unit 18 serves to prevent the flashback from entering into the gas passage 3a inside the handle section 1a. via the mixed gas channel 6 from the side of cutting tip 2. This is to say, in the section of the back-fire preventive device 18c of wire net shape or the back-fire preventive device 18d made of sintered metal, the gas flowrate becomes quicker than the combustion speed and thus the back-fire is checked. Further, being cooled down by the back-fire preventive device 18c of wire net shape or the back-fire preventive device 18d made of sintered metal, the combustion speed goes down, thereby the back-fire is prevented. 
     If carbon has become stuck to the back-fire preventive device 18a of wire net shape or to the back-fire preventive device 18d made of sintered metal with subsequent increased resistance in gas flowrate, slacken the retainer 18b for taking out the back-fire preventive device 18c of wire net shape or the back-fire preventive device 18d made of sintered metal and replace it with a new one, or flush it clean. 
     FIG. 9 and FIG. 10 illustrates an embodiment example where the back-fire preventive units 18 have been mounted both to the gas passage 3a side and the oxygen passage 4a side, and serves to prevent the back-fire from running back to the handle section 1a side through the oxygen passage 4a side. What&#39;s more, this embodiment example in FIG. 9 and FIG. 10 represents the gas cutting torch having no pilot fire port for ignition. Next, the back-fire preventive unit 18 can be attached to the gas passage 3a side or the oxygen passage 4a side as shown in the embodiment example, or the units may be mounted orthogonally in bores connecting to the sides if so necessary. 
     According to this invention, the back-fire does not pass through the interior of the handle section since the back-fire preventive unit or units has or have been incorporated into the gas passage or the oxygen passage or both the gas passage and oxygen passage on the downstream side of the interior of the handle section as mentioned earlier. As a result the handle section can not get overheated and burn an operator nor cause explosion. Therefore, at a time of the flashback which usually happens with a gas cutting torch, the operator is protected. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principals of the invention, it will be understood that the invention may be embodied otherwise without departing from such principals.