mahonrimorian Posted February 1, 2021 Share Posted February 1, 2021 Hi guys, I'm new here and I've been building a forge for most of last year. Or rather, I spent a few months building it, found some flaws, and then put it on the back burner for a while (get it?). Now I'm trying to fix the errors I made and I'd love some advice. The forge itself is made out of a repurposed propane tank (one of the small ones) with twin burners that I welded to the top. Those burners are made of bell reducers on either side, 4.5"x3/4" stainless pipe nipples, and 3"x1/8" pipe nipples with tweco tips as the nozzles for propane. I also had a butterfly valve between the two burners so I could have an easy shutoff if I needed it, or to otherwise modulate the flow of propane. I think it's a fairly common design, but the issue I found was that when I turned on the burners they would pulse rather than burning smoothly and evenly. I understand that's an inefficient and expensive way to heat a forge so I'm trying to rectify it now. I bought 1.5" to 3/8" bell reducers to replace the 1" to 3/8" reducers I had, and a set of 6"x3/8" pipe nipples to replace the 4.5" ones. My question is this: is there a way to know how long my burner necks should be/what size bells I need in order to make sure it runs smoothly? Or is it more trial and error? Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted February 1, 2021 Share Posted February 1, 2021 "One of the small ones" you mean the cannisters used for cheap propane torches or a 2 gallon camping one? Or is small to you anything under 200 gallons? I assume you are talking about the standard size BBQ tanks common in the US; I'm not up on tank sizes in Australia, or German, or Chile, or...with people all over the world participating here it's generally best to be specific on details. (I'm guessing USA because of the units...but I've posted in metric several times before here.) Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 1, 2021 Share Posted February 1, 2021 26 minutes ago, mahonrimoriancumer said: My question is this: is there a way to know how long my burner necks should be/what size bells I need in order to make sure it runs smoothly? Or is it more trial and error? Looking at your stated measurements I am assuming that your forge is made from a five gallon cylinder and that the first pair of burners are 3/4" size. In that size forge they should have been 1/2" size. Furthermore, you appear two be putting together a pair of 3/8" in burners this time. Your first pair probably suffered from back pressure. The second pair will be insufficient to head that forge to welding temperatures. I like 3/8" burners, and don't like to discourage their use. But I like people being dissapointed in them even more. Build two 1/2 burners and be happy with your result. Head? That should read "heat." So, two answer the question you asked about the burner size you should be building: Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted February 1, 2021 Share Posted February 1, 2021 A 1/2" linear burner will need at least a 1-1/2" to 1/2" reducer fitting; bigger is fine, but smaller will be weaker. The actual inside diameter of a 1/2" nominal schedule #40 water pipe, whether mild steel or stainless steel is about 5/8"; when used as a high speed burner's mixing tube multiply that diameter nine times and you get 1-7/8" so go ahead and cut the pipe 2" long. Yes, I know that seems short; just do it anyway. The smallest MIG contact tip is for ,023" welding wire; the actual inside diameter of its orifice is supposed to be 0.031" but these days a lot of those tips are more likely to be 0.033". The optimal size for the gas orifice on a 1/2" high speed burner is 0.028" You can find this in hypodermic needles, dispenser needles, and the smallest refrigeration tubing, which is 0.070" O.D. and 0.028" I.D. You can also find 0.028" I.D. in some heavy wall S.S. tubing (my personal favorite) through Amazon.com and others. Next question is how long, because in these small diameters friction comes in to play. I would suggest 1" long tubes will put you in the ballpark, and #400 grit sandpaper can be used to tune performance. What about flame retention nozzles? Slide-over nozzles made of 1" S.S. pipe with 3/4" spacer rings work best. The amount of overhang past the mixing tube will end up equal or just a touch longer than the inside diameter of the flame retention nozzle, whith is the outside diameter of the spacer ring. Further questions? Quote Link to comment Share on other sites More sharing options...
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