US1595382A - Method and apparatus for preventing flashbacks - Google Patents

Description

Aug. 10 1926. C. J. COBERLY METHOD AND APPARATUS FOR PREVENTING FLASHBACKS Filed Sept. e, 1922 ATTORNEYS.

Patented Aug. 10, 1926.

, UNITED STATES CLARENCE J. COBERLY, OF nos SIGNMENTS, TO PUROX COMPANY, OF DENVER, COLORADO, A CORPORATION OF COLORADO.

METHOD AND APPARATUS FOR PREVENTING FLASHBACKS.

Application filed September 6, 1922. Serial No. 586,536.

My invention relates to theart of welding and cutting metal by the use of high temperature flames produced by the combustion of various gases with oxygen. In practice, either acetylene or hydrogen is usually employed as the combustible gas, but various other gases, such as Blau gas, Pintsch gas, water gas, butane and so forth may be used with a considerable degree of success. Oxygen in different states of purity or nitrous oxide are usually employed as the combustion supporting gas. Torches for mixing and burning said gases are in very general use at the present time, being used for welding and cutting steel and other metal. It is usual practice in welding to supply about one-half the 0 required for complete combustion as pure 0,, the remainder being taken from the air surrounding the flame. In all such torches now in commercial use trouble is experienced by flash backs; that is, by a premature combustion inside the torch. Since the temperature of the flame is very high, and continued combustion inside the torch results in a rapid destruction to the torch and requires shutting .ifig to againestablish the proper flame at t e tip.

It is an object of my invention to prevent flash backs in such torches with any gas combination which it may be desiredto use.

Further objects and advantages will be evident hereinafter.

Referring to the drawing, which is for illustrative purposes only,

Fig. 1 is a cross section through one embodiment of my invention.

Figs. 2 and 3 are sections on a larger scale than Fig. 1 on planes represented by the lines 2-2 and 33 respectively of Pi 1.

ecause of the extremely explosive nature of mixtures of oxygen and acetylene,

' early experiments with oxy-acetylene welding apparatus had a great deal of difficulty in overcoming trouble due to flash-backs. These flash-backs not only in ured the torch, but at times even extended into the gas lines and caused more or less serious" explosions, causing much delay and difliculty in executing welds.

Early inventors of welding apparatus deoff, cooling and re-light Chatelier in France were among the first to suggest this form of flash-back prevention.

laude proposed to fill chambers in the gas line with porous substances which would permit the flow of gas therethrough, but which would absorb the heat of a flame so rapidly that the flame would be extinguished before passing through. Le Chatelier and others worked on the same principle but substituted small elongated .orifices for the porous disc. These small or'- fices were in the form of small holes or annular chambers formed by plugs and sleeves with very small differences in diameter. According to Le Chatelier, the operation of these methods of flash-back prevention depends upon the lowering of the flame velocity by the absor tion of heat to a point where the natural velbcity of the gases, due to the difference in pressure in the gasline and the exit of the torch, exceed the velocity of the flame. Under these conditions, of course, the flame would be forced to travel out and would ignite at the exit orilice of the burner.

Such methods principle and no doubt are of material benefit in overcoming this trouble. However, all of these forms of flash-back prevention ofler considerable resistance to the flow of gases through the torch and hence require greater pressures on the gas supply lines than would otherwise be necessary to deliver the required volume of gas. This is of special significance in the case of burners of very large ca acity, since the maximum pressure avai acetylene is that delivered by the generator, or at the most, the pressure at Wl'llCh acetylene in susceptible to spontaneous decomposition, generally accepted to be a pressure in the neighborhood of thirty pounds per square inch.

The high resistance to flow produced by this method led later inventors to discontinue the use of small orifices or porous plugs and to substitute therefor man other means of which a considerable num er are entirely inoperative. Several inventors specify the use of burners in PATENT OFFICE.

ANGELES, CALIFORNIA, ASSIGNOR, BY MESNE AS- which the able 7 in the case of gases are mixed at a point in close proximity to the point, of combustion so that the volume of mixed gas within the burner is extremely small and so that there are no unnecessary chambers or pocketsin which gas can accumulate. This method is effective at least for a certain range of burner capacity, but has the objection that when the gases are mixed at a point near the tip of the burner the time allowed for the thorough mixing of the gases is insuflicient and hence serious difiiculties in obtaining sound welds are encountered. In many cases the time allowed for the mixing of the gases is an extremely small fraction of a second and no special means is provided to cause the gases to mix.

Others have sought to overcome the trouble by interposing check valves in one or both of the gas lines or in the passage carryin the mixed gases and depending upon the orce of the explosion within the interior of the burner to close the valves and hold them closed for a suificient time for the flame to extinguish. The use of a check valve within the passage of a burner which carries mixed gas is entirely inoperative since the velocity of flame propagation in confined spaces is so extremely high that the action of a check valve is too sluggish to prevent the passage of a. flame. Some manufacturers have sought to'prevent flash-backs by using flames which issue from the tip at extremely high velocity. This also is of some value in the prevention of flash-backs but at the same time gives a flame which is termed too hard and causes a blowing action on the metal which is detrimental to the production of sound welds.

It has for some time been an accepted fact that torches which have the oxygen delivered to them at a pressure in excess of .the acet lene pressure are more susceptible to flashack than those in which the pressures were nearly equal. The principle here involved is that the restriction of flow, which tends to cause flash-back, retards most the flow of the gas which has the lower pressure. Therefore, byusing acetylene at a higherpressure than oxygen, a restriction of flow causes an excess of acetylene to be delivered to the flame which gives a flame of much lower rate of flame pro agation and hence there is much less ossil iility of the flame traveling back into the interior of the torch. Several torches are on the market which operate on' this principle. The rate of flame depends, however, u on the dimensions of the space in which t 1e gases are confined, and it is possible to set up a high velocity flame known as a detonating wav'e which has a velocity many times the normal flame velocity unrestricted. Some inventors who when burnin in air I liaye mterposed check valves or other devices in the interior of the torch to stop the ropagation of the flame have recognized t e fact that regardless of the velocity of exit of the flame gases or the ratio of oxygen to combustible gas in the flame, it is impossible at times to prevent the flame from entering the interior of the torch and that hence a means must be there located to prevent the continued combustion in the interior of the torch. The use of acetylene at excess pressure decreases the liability of the flame entering the interior of the torch, but does not prevent the continued propagation therein after the flame has once been established. It also has the practical drawback that the conditions which tend to cause flash-back cause an excess of acetylene to be delivered to the flame and hence does not give a flame which is.

suitable for welding. Also for cutting metals with oxygen, it is desirable to supply the oxygen at pressures materially higher than the acetylene pressure and hence a third hose is necessary with a separate pressure reducing means to supply lowpressure oxygen to the flame. It has further been found that exactly balanced pressures at the point of mixing is highly desirable from the standpoint of delivering a flame which will produce high quality welds. 'This necessitates a constructon' which will not give a variation in gas ratio due to partial restriction of the tip and hence requires the use of exactly balanced pressures at the point of mixing.

Also the use of unbalanced pressures is a hazard since an obstruction of the tip Will'cause a flow of the gas under the high pressure into the line at the lower pressure and hence will give an explosive mixture back of the normal point of mixing.

I have found that it is entirely impossible to prevent the flame from entering the interior of the torch with the gas mixing at od which is not intended to prevent the flame from entering the interior of the.

torch but which will cause the flame to become extinguished in a short interval of time in case it does. enter therein. This is accomplished without the use of mechanical devices or porous material and depends entirely upon the proper proportions of the orifices and volumes of gases in the torch and is a plicable to any gas combination which it is desirable to burn. The method employed for this purpose may be illustrated by means of the diagrammatic torch shown in Fig. 1. Gases are sup liedto thegas lines 5 and 6 at substantia equal pressures regardless of the nature 0 density of the gases used. The flow of oxygen is controlled by means of orifice 13 and flow of acetylene by means of orifice 14.

12 and leave the torch at orificell, where they are ignited and burned.

In case a condition is caused to exist wherein the flame is caused to burn back into the interior of the torch, the Velocity of combustion attains a very high value resulting in a high pressure bein established in that portion of the torch betwee-n the point of mixing and the tip from which the gases issue. This pressure is relieved by three means. First, by discharging the burned gases through the tip to the atmosphere. Second, by discharge of the burned gas back through the orifice 13 into the oxygen tube. Third, by discharge of the burned gas back through the orifice 14 into the acetylene tube. It is obvious that this reverse flow of gases in the supply line will cause a shutting off of the combustible and combustion supporting gases and hence it will extinguish the flame 1n the chamber following 12. e interior surface of the torch is quite highly heated by this explosion, in sufiicient oxygen is available for complete combustion, and carbon'is deposited on the interior walls of of a hydrocarbon oxygen should be chamber 12 after may be of sufficiently high temperature to again ignite in the presence of oxygen and the flow of acetylene mixed with the oxygen which follows sets up a combustion within the interior of the torch which can only be efitinguished by shutting off the gases manua I n he case of hydrogen as the combusthe passages in the case combustible gas. If the the first gas to enter the tible gas, the operation and result are the same except that carbon is not deposited in the passage 12- I have found, however, that if the oxygen is the first gas to'again enter the passage 12 after a flash-back that the flame is established within the torch and will continue to burn there until shut ofl. The reason that hydrogen operates the same as a hydrocarbon is probably due to the fact hat the explosion which takes place within the passages of the torch heats the interior surface to a very high temperature for an extremely small interval of time and that hydrogen is more eflicient than oxygen in cooling this surface because of the higher heat conductivity of the hydrogen. In the case of hydrogen, it is probable tha the shutting off of the flow of gases, as described above, would be 0 erative to prevent the combustion in the interior of the torch even though oxygen were the first to re-enter the torch if the interval between the entrance of the oxygen and the of the hydrogen were sulficient to permit sufiicientcoolmg of the surface. However, I have found it desirable to have t e ydrogen re-enter the torch first and the rule aid down in this specification is apthe flash-back this carbon plicable to hydrogen and oxygen as well as any combustible gas which it is desired to burn.

By proportioning the orifices of the mixer to suit the characteristics of the gases being used, the relative reverse flow of gases can be governed so that when the pressure in the chamber 12 again becomes normal due to the release of the burned gases through the orifice of the tip, the acetylene will be the first to again enter the chamber 12. Therefore, any glowing carbon will be extinguished. The flow of oxygen follows that of the acetylene an instant later and the two issue from the tip in the normal manner. The flame will then be reestablished on the outside providing there is some material adjacent of sufture. This is nearly always the case in practical Work since the temperature of the volume in the oxygen line between 5 and 13 bv throttling the valve 15 in which the gas is at a that of the acetylene in order that the reverse flow volume in the oxygen tube will be greater than that in the acetylene tube. In case the pressures in the supply lines 5 and 6 are substantially equal and the volume of the tubes 7 and 8 are the same, then the degree of ease with which the gases are forced back into the tubes 0 and A respectively when an explosion occurs in passage 12 depends, among other things, upon the restriction in passages 13 and 14. By proper proportioning of these orifices for the gas combination in use. the reverse flow through passage 13 can be made greater 14 is greater than the ratio of the square root of the density of the gas in 13 to thesquare root of the density of the gas in 14. The has some efilect on the exact ratio required but the above ratio has been found to give good results regardless of the nature bustible gas. In case it is desirable to supply oxygen to valve 15 at a than that on the combustible gas at 6, the passage 7 should have considerable volume and if possible should be greater than the volume of 8. If the volume of 7 is app imately equal to the volume of 12, good results are obtained regardless of the pressure supplied to the gas lines. In order that flciently high temperature to ignite the mixpressure substantially equal to form of the passage 13 and 14 of the compressure greater the reverse flow in both lines is not excessive, which would sometimes cause decomposition of gas in 8, in the case of acetylene, the passage 9 should be equal to or less than orifice 11.

In using orifices of widely difierent sizes at 11, it is sometimes desirable to vary the total volume ofgas between 11 and 9, the desired volume being larger with the larger orifice at 11. This is accomplished by providing in each tip a supplemental chamber 16 to suit the orifice 11 which is arranged to be removed with the orifice when changing tips.

While I have used the word acetylene to designate the combustible gas, I wish it to be understood that hydrogen and various hydrocarbons are practically equivalent thereto and that the method of preventing flash-backs disclosed is equally operative in any case, and that I do not Wish to be limited to any particular gases, the terms oxygen and acetylene being used in the claims for the sake of clearness and not in any restrictive sense.

I claim as my invention:

1. In a torch for mixing oxygen and acetylene, the combination of: walls forming a mixing chamber; walls forming an oxygen inlet passage into said chamber; and walls forming an acetylene inlet passage into said chamber, said acetylene inlet passage having a cross sectional area related to that of said oxygen passage as the square root of the acetylene density is related to that of the x gen density computed upon a standard of substantially equal pressure.

2. In a torch for mixing oxy acetylene, the combination of: wa s forming a mixing chamber; walls formin an oxygen inlet passage into said cham r; walls forming an acetylene inlet passage into said chamber, said acetylene inlet passage havin a cross sectional area related to that of sai oxygen passage as the square root of the acetylene density is related to that of en and the oxygen density, computed upon a stand ard of substantially equal pressure; and an oxygen chamber having a volume substantially equal to that of said mixing chamber, said chambers being so proportioned to compensate for difference in pressure of the two gases.

3. In a torch for mixing oxygen and acetylene, the combination of: walls forming a mixing chamber; walls forming an oxygen inlet passage into said chamber; walls forming an acetylene inlet assage into said chamber, said acetylene in et passage havin a cross sectional area related to that of said oxygen passage as the square root of the acetylene density is related to that of the oxygen densit computed upon a standard of substantial y equal pressure; an oxygen chamber posterior of, and communicating with the oxygen passage; and an acetylene chamber posterior of and communicating with, said acetylene passage, the volume of said chambers being directly proportionate to the pressure of gas to be employed.

4. In a torch for mixing a combustionsupporting-gas havin a known density and ressure with a com ustible gas having a Enown density and pressure, the combination of: walls forming a mixing chamber; walls forming a combustion-supporting-gas inlet passage; and walls forming a combustible as inlet passa e into said chamber, said com ustible gas in ct assa e having a cross sectional area relate to t at of said combustion-supporting-gas passage as the square root of the combustible gas density is related to that of the combustion-support ing-gas density, this proportioning of passages being to insure entrance of the combustible gas into the mixin chamber prior to the entrance of the com ustion-supportinggas for preventing premature ignition in the mixing chamber. a

In testimony whereof, I have hereunto set my hand at Los Angeles, California, this 1st day of September. 1922. a

. CLARENCE J. COBERLY.

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