Torch gas fusion welding VS propane forge welding.

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Here  is something that has been bugging me and I bet the answer is a simple one but I thought I would ask. I have been told that you cannot make a good gas fusion weld with oxy-propane since there will not be a cone of CO2 to protect the puddle and the O/P flame is too high in things like hydrogen. You can forge weld with an air propane burner as long as you have the right kind of flame, very clean steel and use flux. So the question is why can you forge weld but not torch weld? Is it because in forge welding you do not make a puddle and the work is pressed together during the welding process? Thanks all
Reply:You answered your own question. Flux, and the fact that in forge welding since the temperature of the steel is lower, the reactivity with the atmosphere is also much less. Acetylene is the only fuel for steel.....period.
Reply:Also note not all propane forges will get hot enough to forge weld. One advantage of propane forges over say a coal forge is that it's hard to burn the metal because the heat is lower. Most atmospheric gas forges are borderline at best on getting up to welding heat..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I have to agree with that last post. When I changed the brick out in my one brick forge I was able to get to forge welding temp with a high output hand torch connected to a 20 lb BBQ bottle. The reasona I was able to get there were:New soft fire brick = most of my heat staying in the forge and being reflected back at the work.20 lb tank = you can burn for a good long time before the bottle gets too cold that your flow slacks off. Thing is if you do weld in one of these and have flux spill in to the forge you will end up with a lot less IR reflection than you started with.
Reply:Hi, if you explore the possibilities of a plasma welder you will find that "gas" welding is not the impossible dream and you do not need the confines of a forge to get the metal up to temp.......in a plasma welder you have 8,000 deg C at your disposal.Ian.
Reply:8000 deg C, that would be something. Got to use a VERY light touch.
Reply:Just a note here (in case you haven't already thought of it).If you are using a "high consumption rate" of propane from a barby bottle, and have concerns of flow diminishing due to the bottle becoming chilled, place an electric fan to circulate air on the bottle while you work.If the ambient air temp is anything above 50 F, you will probably be able to keep the evaporation rate in the cylinder ahead of your consumption rate.
Reply:Originally Posted by puddytat.....in a plasma welder you have 8,000 deg C at your disposal.Ian.
Reply:Originally Posted by ESeemann8000 deg C, that would be something. Got to use a VERY light touch.
Reply:Walkerweld, by "barby bottle" would that be the 20lb gill bottle? If so I know what you mean, we do not have to worry that much about that in Alabama during summer but when it gets cool that could be an issue.
Reply:Yes, barby or barbie is "short" for barbecue or barbeque (as in your BBQ abbreviation.  And that would be the standard 20 Lb bottle used for such.Another way to assure a consistent volume of gas flow without worrying about chilling causing a reduced evaporation rate would be to stand the bottle in a galvanized (not plastic) laundry tub of water, not HOT water but just out of the tap.The volume of water coupled to the metal tub increases the effective surface area for heat to be absorbed and transferred to the fuel bottle.  Using that method without any fan or other device will keep your fuel gas supply ahead of the withdrawal rate.You will have weight the bottle to keep it from floating as the bottle empties.I doubt there are too many cases where you would have to resort to a fan or a tub method unless you are really using a lot of propane for a long time.
Reply:walkerweldThanks for the info. I have seen photos of the tub trick. I did not know if barby bottle might be some welding slang I was not cool enough to know.   I do not do much that would need the tub trick but I hope to get a bigger burner built soon. Why not use a plasitc tub?
Reply:No plastic tub 2nd lower heat conductivity I think, no?Although I would think that the mass/SG of the water would be enough heat sink, my physics lessons are too long ago to remember how exactly to calculate it through to a factual answer.Thomas
Reply:The diameter of the tub is much larger than the diameter of the propane cylinder, so the surface area of the tub will be greater than that of the propane bottle. Plus, the body of water has an upper surface to actively absorb heat from the ambient air while the propane bottle is nearly devoid of an active upper region. The area of the propane bottle that is above the level of liquid propane inside the bottle does not contribute much to the evaporation of propane because the propane is not in contact with those parts of the bottle.  Any heat absorbed by the portion of the bottle above liquid propane has to migrate by conduction down to the liquid propane level.The much larger overall surface area afforded by the tub will absorb a greater total volume of heat from the ambient air. With water as the heat transferring medium, the heat gained by the tub and water will set up good convection currents and keep the evaporation rate inside the propane cylinder higher than if the barbecue bottle was simply left standing in calm air.  It is the greater VOLUME of heat gain that makes the difference.The reason for recommending a metal tub instead of plastic is that plastic material of a tub acts as an insulator instead of a heat conductor.Last edited by walkerweld; 08-27-2013 at 01:03 AM.