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Don't know if this is the one of which you speak, but I found it to be very informative. It was authored by T Bone & Dave. "This is probably a great time to clear up some misconceptions on Cutting, Brazing, and Rosebuds that a lot of welders have. All the information can be applied to cutting, brazing, fusion or heating, except where noted: Backfire is 99% caused by to much fuel being supplied for too small of an orifice size, ie; using the wrong sized rosebud or cutting tip for the amount of output heat required. This is the first indication that the mixing chamber pressures are NOT set correct and the pressures are set too high for the given orifice size. All cutting/heating orifices have a designed pressure rating that's stated from the mfg as the orifice tip body is cooled by the gases flowing from the orifice while in use. Exceeding the designed orifice pressure rating will cause the ignited acetylene gas to leave the face of the tip body, thus at the same time the flame will add excessive oxygen (oxygen that is obtained from the surrounding air) to the acetylene gas that will cause the flame to momentarily extinguish, then as the mixed gas cools it reignites and causes a small explosion as it reignites thus you here the "bang" or popping noise. This condition is called backfire and can be very dangerous. When the backfire is not corrected by lowering the fuel pressure or volume, acetylene being the fuel in this case, then another EXTREMELY DANGEROUS condition will occur called flashback. Flashback is where the flame that contains oxygen and fuel, is sucked back inside the mixing chamber and will cause an EXPLOSION if not quickly corrected by shutting off the source of oxygen and then shutting of the fuel. Turn off the cylinders in that order as these three conditions are necessary to cause an explosion, those being oxygen, fuel and a source of ignition. I added volume to my descriptions as well as pressure because there are some fuels that can explode under the same conditions without any warning as described above. Weld Fusion: is where two metals are joined together by melting an equal amount of molten metal from each piece, either with or without the addition of a compatible filler metal. Never run Acetylene above 15-psi for any reason! A drip of liquid black goo from the tip, (ie; runny nose), is usually caused by condensation mixing with the by-products of combustion then dripping from the tip face. This condition is most likely caused by an air leak into the mixing chamber or tip connections. Fact: Acetone is a combustible fuel. You will usually smell acetone while using a touch because the acetylene tank is suppling too much volume of gas for a given tank size for the amount of fuel demand of the mixing chamber and tip OR the cylinder has been laid on it's side and has not been allowed to stabilize after returning the cylinder to the vertical position. Stabilize a vertical acetylene cylinder for 12hrs before using the fuel! Using too much preheat for the thickness of metal your cutting along with a dirty cutting tip will cause problems. It's most likely your cutting speed is also too slow but without correcting the first two problems, you will not be able to tell. What happens when you use too much preheat? The molten metal is very liquid in width and when you try to blow the heated molten puddle with oxygen, the puddle runs to the back of the direction your cutting and reforms a weak bond behind your cutting tip. This new molten puddle is highly enriched oxygen and carbon making it very hard and brittle thus when your try to reheat this area it takes longer to preheat as well resist being blown out by the oxygen from the hardness of the metal and will cause molten metal too blow out and back onto the cutter. With the correct preheat flame temperature the molten puddle will not form as wide thus you will achieve a narrow cut without any molten puddle run back. When using a dirty cutting tip, several problems will arise. First: With the preheat orifices dirty you will not achieve an even preheat to start the cut. It will take more preheat to start the cut with a dirty tip than with a clean tip. Second: Once preheat has been established if the center tip orifice is not cleaned then slag will collect on the backside of the base metal and the cut face will be ragged. The above problems will cause a slower forward cutting speed thus once again cause base metal over heating allowing the hardened slag to reform behind the cutting tip. The cleanest cut comes from a clean tip. After you clean all the orifice bores in the tip, fire up the torch and set flame for cutting, then depress the cutting lever and observe the flame. There should be a long very "uniform" inner flame cutting cone. If that inner cone is not "very" uniform then your cut will be ragged just like the flame cone is and the back of the metal will have slag. Reclean the center orifice until it's very uniform. A cut with a clean tip will have a very smooth cut surface with very little (if any) slag on the backside of the cut. If either one of these is not present reclean the tip. The center bore orifice can get deformed and the tip needs to be replaced or cut off. It's very important to hold the cleaning file straight in the bore hole and just remove enough material to clean the bore to make the tip last a long time. I've never used a new tip that was clean enough for cutting, brazing or heating right out of the box. Another consideration is as the tip size becomes smaller so does the orifice size and it becomes a bear to clean them itsy bitsy holes. If using an automatic cutting machine then changing tip size would be a production benefit. Always use a mfg. pressure chart, tip sizing chart and hose sizing chart for setting gas pressures for there brand of mixing chamber and tip combinations. Setting the proper neutral preheat flame, the orifice holes around the center cutting orifice, can be observed by the tip of the inner flame cone: A neutral flame has a blue colored flame outer shield with a light blue to white inner cone flame that is slightly rounded at the cone tip. An oxidizing flame (too much oxygen) has a sharp pointed very white inner cone. A reducing flame (not enough oxygen) would have a very round to a ragged third inner cone. Examples: I have found 5-psi acetylene and 30-psi oxygen, while cutting, to be a good all around setting for up to 50ft of �" hose. Your final pressure setting is regulated by the needle valve adjustments on the mixing body. For brazing or welding a size #0 tip works well with 5-psi acetylene and 20-psi oxygen. Again the needle valves on the mixing body sets the final pressure needed at the tip. I also use the above settings to preheat 2" round bar without any problems using the #0 size tip or the rosebud tip. The advantage of using a rosebud tip is that it expands the flame temperature over a wider area vs using a #0 size tip. I very seldom use my rosebud tip. Preheating with LP saves some expensive gas then finish heating with oxy/acet. Although there are many different tip sizes, I have a found a No3 makes for an all around good cutting tip as it will cut up to 1-1/2" or 18ga sheet metal depending on the preheat setting. I strongly urge you too research more information for your safety. T_Bone This is probably a great time to clear up some misconceptions on welding that a lot of welders have. 1. (Slag inclusion AWS defined): Inclusions are impurities or foreign substances which are forced into a molten puddle during the welding process.
Cause: 1)improper base metal preparation. 2)improper cleaning of slag in a multipass weldment.
3)faulty electrode manipulation. As you can see, all three are caused by welder error. What a lot of welders tend to try when inclusions are incurred, is to push the electrode deeper into the weld puddle thus forcing the inclusion out into the slag puddle where it will be removed with the slag. That will rarely happen. What is more likely to occur is the slag will cold fuse to the hole wall, made from the electrode as the electrode is withdrawn to normal arc length, thus covering the inclusion with molten metal leaving the welder to believe he has removed the inclusion as the weld puddle will return to look near normal. On a multiple pass weldment, the electrode will deposit more slag on top of the existing slag inclusion but will have a near normal looking molten puddle this time. This inclusion will continue to grow with-in the weld until the cover pass is put on. During a bend test the slag inclusion will break out and will show the inclusion from the root pass to the cover pass. Under this circumstance this weldment would fail certification. A welder has a greater risk of a failed weld by not stopping to clean out the inclusion by grinding or other suitable means. Faulty electrode manipulation is mostly from the welder varying the arc length or too long of an arc length or the reverse too short of an arc length as described above. The best improvement a welder will see in his welds is when he learns to control the arc length. It doesn't matter what process is used, arc length is very important. Ever wonder why a machine weld looks so great? It's because of the precise control of the arc length and electrode speed! On x-rays I've see small slag inclusions though out the entire weld shown as small specks on the x-ray. These are usually electrode slag deposits not cleaned off during a multipass weldment but also can be scale and other impurities not cleaned off the base metal before welding. There is a myth that a welder does not have to remove all slag between passes on certain electrodes. This is not true and is what causes all the specks that I see in x-rays. If a welder hurries between electrode changes, he can sometimes restart a rod without chipping the slag without the worry of slag and porosity inclusions but this is no guarantee there will not be any slag or porosity inclusions. Another good practice is to start a bead in a different spot on each pass as this will help eliminate any inclusions following each pass. Depending on the size and spacing of the inclusion, some inclusions are acceptable as sound welds and will certify. Overhead weldments have a greater tendency to have both slag and porosity inclusions. As an AWS inspector I have seen a lot of this and started watching welders during certification tests and found that it is from the welder trying to hurry too much as his mind set is that the puddle is going to fall if he goes too slow. A overhead weld should be made just like a flat weld with a very slight increase in electrode speed. Vertical up welds are best made with good concentration on the molten puddle. This can best be observed welding in the flat position. The weld puddle will be very shinny and will have some swirling action within the molten puddle. The slag looks dull and lumpy and will roll to the back of the weld puddle as the puddle moves forward. As the weld puddle forward speed slows the slag will recombine with molten puddle causing the puddle to splatter and gather inclusions and encase the electrode tip causing the electrode to stick to the base metal. The weld puddle width should be about 2 times the electrode diameter. AWS code calls the maximum weave bead width of 8 times the electrode diameter in any position as any more width than this will cause slag inclusions because the slag cools too much before the electrode returns to deposit more weld. The best way that I've found to teach people to weld is to have them try what too many amps does, turn down the amps, move too fast, too slow, too long of an arc length, too short of an arc length, with stopping in between each change to see what the weld looks like. This way the welder learns what each wrong effect has. Then when they make a weld that looks wrong, they will know what caused it and how too correct it. An interesting note, a long arc length will have more uncontrollable heat than a short arc! Back to vertical up welding. Now that you've studied weld puddle control, pay close attention to the molten puddle shape and size. There's going to be slag running around the out side edges of the molten puddle but don't pay any attention to it as it will go where it goes and the slag distracts your concentration away from the molten puddle. Don't bother to look where your going as that will come with time as you have to look above the electrode to see where your going and at the same time concentrate on the molten puddle. A weld puddle of 1� times electrode diameter is much easier to concentrate on when first learning vertical up welding. Vertical down welding should be avoided if possible. AWS code does allow a maximum 2" of vertical down weld on most electrodes. There is a high risk of slag and porosity inclusions while vertical down welding. The slang "gap rod" will not certify under any circumstances. Too wide of a root opening will cause slag inclusions and porosity within root pass of the weld. The proper root opening is 2/3 of electrode diameter with a land thickness � of electrode diameter. (Land): the flat area between the back of the base metal extending just to where the bevel starts. (Porosity): Porosity is the formation tiny pinholes generated by atmospheric contamination or gas entrapment during solidification. (Root Opening): The gap between the base metals to be welded. (Root Weld): The first weld bead of a weldment. 6010 and 6011 have very different penetration characteristics with 6010 having the best penetration of any stick electrode. All carbon base metals will weld very similar whether old or new depending on how they are prepared. A lot of welders forget steel on equipment will work harden from vibration thus changing to a tighter grain structure or take on stress. You have to relieve this stress before welding or the weld will soon crack or brake away from the base metal. The easiest way to remove the stress is to heat the base metal to approx 1100F (dull red) and let it cool before welding. This will allow the grain structure to return to near normal before welding. As I've stated before, Lincoln 6010 is the finest 6010 I've ever used. Welding galvanized is an art all to it's own. Technique has every thing to do with making a sound weld. As I stated previously 6010 ran DCEN (straight polarity) is a great electrode for welding galvanized. I have ran hundreds of certification tests over the past 35yrs with 6010 and yet to have a test fail because of the electrode. However, I have seen a lot welds fail due to welder error." T_Bone "Backfires can occur for a few different reasons. For gas welding the torch should be equalized. Usually when using a rosebud it is not as critical because you are not melting the steel or holding the flame as close. I have never had a problem with acetone coming out but have seen the odd rosebud with a black liquidy stuff around the end. It may or may not have been from acetone. I have seen a lot of people put a big rosebud on and not adjust their pressure at all from a cutting or welding tip. I have also seen people use a rosebud where they didn't need it, so they didn't turn the gas on enough and it causes multiple backfires like a machine gun. Pressure settings on regulators shouldn't be relied upon as a precise indication of actual pressure. The best thing to do for safety as well as proper set up is to equalize the torch. If you want to set the maximum gas flow for any tip, either welding or a rosebud, and equalize the pressures, there is a proper method of doing it. With a cutting tip, pressures aren't equalized because oxygen needs to be higher. To equalize a tip: First back both regulators completely off. Then open the acetylene valve on the torch all the way and turn the regulator adjusting screw in just until you hear gas come out the tip and light it. Slowly turn up the acetylene pressure until the flame just starts to jump from the end of the tip and then back off the regulator just so the flame stays on the tip. It does not matter what the regulator gauge says. Many times it won't even register with a small tip. You can now turn the acetylene down on the torch a little if you prefer. It's easier to add oxygen with it turned down a bit. Open the oxygen valve on the torch all the way. With the acetylene burning, slowly turn in the oxygen regulator till you start to get an inner blue flame. Now open the acetylene valve on the torch all the way. Keep adding oxygen with the regulator until you get a neutral flame as mentioned. You should have an equalized torch or one that is close to it. To be sure, turn the acetylene regulator in just slightly and see if the flame changes. If it doesn't you're good to go. If it does, turn the oxygen regulator in to get a neutral flame again. 99% of the time this will be good but sometimes you can do this last procedure a couple times. When the acetylene flame jumps from the end of the tip it is an indication that this is the most gas flow the tip can handle. Once the tip is equalized the torch valves can be turned down a little to fine tune the heat you want. Tips and/or rosebuds should be cleaned before equalizing and each different tip has to be equalized on its own. If you need more or less heat, then you have to use a different size tip because you need to operate at close to the maximum gas flow for the size of tip. This is the best way to hopefully eliminate backfires. This method of equalizing tips works for every make of torch and you don't need a chart. With a rosebud it isn't quite as critical as a welding tip. If you had a chart, for gas pressures for your rosebud, that would probably work without any problems. You do however have to have a large enough acetylene cylinder so you don't draw too much out of the tank which would cause acetone to come out. All gasses have a maximum withdrawal rate. Acetylene is 1/7th. the cylinder capacity per hour. In the interests of safety and proper set up, I hope this will clear up any mis-conceptions. Backfires can occur for different reasons, sometimes only because your weld is going perfect, so proper set up and use helps to reduce problems and is very important. I should add that if you're using a big rosebud or long hoses, use the proper size hoses. There are charts for this. I'm sure several chapters could be written on setting up oxy/fuel equipment, but most people wouldn't bother to read it all. That's why accidents happen.
I always try to give the most accurate info, especially when people I've never met are relying on it. In the case of torch set up I learned this from welders with decades of experience. Might explain why I've never had any accidents with torches. They did have an acetylene cylinder, on display, that had exploded at the tech. school. It didn't happen there though. Pretty scary looking. Hope this helps." Dave
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