Nate Struening Posted July 7, 2018 Share Posted July 7, 2018 We are building a small forge in our shop. We have 40psi natural gas fed by a 1" line tapped off of a 12" main, volume shouldn't be an issue, and want a Venturi setup so it is portable. Our question is what orifice size do we need and what pressure should we regulate down to. We have 35 and 45 welding tips handy. Anyone have any tips? We were thinking about 2 or 3 2inch ID burners with diffuser plates, so ribbon burners. The forge is 15.5" wide, 18.5" deep, and 12" tall without refractory or bricks. We'll have 4 bricks laid flat in the bottom, then bricks on each side and refractory in the top giving us ~972 cubic inches (18"x9"x6"). Any help would be appreciated! Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted July 7, 2018 Share Posted July 7, 2018 Natural gas always ends up rated at about 2/3 the heating potential of propane. So, larger faster flames are needed whatever burner design you choose. Expect that lower temperature input to give you some other limitations in getting the forge to work as a radiant oven. this doesn't mean you can't build a good forge with it; what it does mean is that you don't have any slack in your chain to make mistakes like using hard clay bricks, etc. What you read about jet orifice sizes in your gas jet are increased, even in naturally aspirated burners; increase the orifice to at least the next larger size to what you see recommended in a propane burner; you may have to go up two sizes. Even though you have the gas pressure to employ a naturally aspirated burner, you will probably find a fan-blown burner more practical, simply because there is sufficient information on them, and no information on naturally aspirated methane burners. Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted July 8, 2018 Share Posted July 8, 2018 Portable? You have access to natural gas at that pressure at more locations? Here in the USA regular home NG service is way under that;measured in inches of water column. (14.7 PSI is about 32 FEET of water column!) Quote Link to comment Share on other sites More sharing options...
Nate Struening Posted July 8, 2018 Author Share Posted July 8, 2018 Lol, portable so we can put it up when not in the shop not so we can move around. But yes we have that pressure in MANY locations where we're building. I am in the US and this is in my workplace so you can understand why I don't want to say too much, there's just a lot of time to kill on night shift... Ok I'll do some more research and see what we come up with, we have plenty of raw materials to work with and it's already hot as balls so we're going to get this forge going to see what we can do! Quote Link to comment Share on other sites More sharing options...
timgunn1962 Posted July 8, 2018 Share Posted July 8, 2018 With 40 PSI available, you should be looking at burner outputs that do not differ wildly from Propane: I'd regard 3 x 2" burners as massive overkill and my gut feel is that either a single 1 1/2" or 2 x 1" burners would be sufficient for the forge size you are considering. The jet sizing for NG will be larger than for Propane, but the actual sizing will depend a lot on the detail design of the burner(s) you use. Useful jet sizing information is likely to be elusive. I use Amal long-Venturi atmospheric injectors for my burners and their datasheet is one of the few sources of information I have found that provides relative jet sizing information for Propane and NG. On Propane at least, they will run at pressures to 60 PSI in forges, despite having been designed for low-pressure use. http://amalcarb.co.uk/downloadfiles/amal/amal_gas_injectors.pdf Their jets are sized by petrol (gasoline) flow, rather than by diameter, and the flow can be expected to vary with area. NG jetting seems to be about 3-5 times the flow (area) of the Propane jetting, so a reasonable starting point would probably be to use a jet twice the diameter of the Propane jet used/recommended for whichever burner design you decide to use, then tune from there. Quote Link to comment Share on other sites More sharing options...
Mikey98118 Posted July 8, 2018 Share Posted July 8, 2018 There are more advantages in methane flames than just a cheap and ready fuel source, where high pressure natural gas is available. This fuel molecule is simpler than any other, except hydrogen, making clean burning flames much simpler to accomplish; it is also one of the best candidates for oxygen enrichment, because it takes much smaller amounts of added oxygen to increase flame temperature. Quote Link to comment Share on other sites More sharing options...
WayneCoeArtistBlacksmith Posted July 8, 2018 Share Posted July 8, 2018 Check out the attachments on the Forge Supplies page of my web-site. You can find the url and other contact info on my Profile. The Ribbon Burner instructions were written by John Emmerling and he runs his Ribbon Burner off of NG. His instructions give some instruction about using NG. Let me know if I can help you. Wayne Quote Link to comment Share on other sites More sharing options...
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