Bill Brown Posted February 4, 2016 Share Posted February 4, 2016 I am in the process of building my first propane gas forge. The question I have is it necessary to have extra vent to allow more oxygen into the forge? My forge is a square tube 8x8x12 horizontal forge. One end is welded close. The open end has a door on it with a 3x5 opening so that I can place my blades into the forge while it is running. The propane burner will be mounted on the right side 6" from the front of the forge, at a 45 degee angle. Link to comment Share on other sites More sharing options...
Caleb Harris Posted February 4, 2016 Share Posted February 4, 2016 I don't believe so. My forge is similar sizing, and the end is a sort of refractory circle thing with a hole in the center of it (one of these http://www.silversupplies.com/images/soldering/54116.jpgbut with a hole in the center), so really the only vent it has is an inch max diameter. I don't believe another vent is necessary, especially as the torch itself will draw a lot of the oxygen it needs to burn (venturi, blown, or just a standard plumber's torch or something). However, having the end open, or at least a closeable door, will enable you to do longer blades in the future, especially if you're going to want to do even heating for heat treating. Trying to make each knife just a little better than the last Link to comment Share on other sites More sharing options...
Wayne Coe Posted February 5, 2016 Share Posted February 5, 2016 Yes, you should have an opening in both the front and back to allow additional air to be drawn into the forge. The forge is depending on oxygen to burn the propane. If enough oxygen is not allowed to mix with the propane you will have unburned propane inside the forge looking for the needed oxygen. The only place to find this additional oxygen is out the front door. Of course a reducing (oxygen poor) flame is good if you are forge welding but during general forging this is just wasted propane. If you have the door in the back that can be closed down to allow for the control needed for an appropriate atmosphere in the forge. Check out the attachments on my web site at the Forge Supplies page for how I like to build a forge. Let me know if I can help you. Wayne Coe Artist Blacksmith 729 Peters Ford Road Sunbright, Tennessee 706-273-8017waynecoe@highland.netwww.WayneCoeArtistBlacksmith.com Link to comment Share on other sites More sharing options...
Doug Lester Posted February 5, 2016 Share Posted February 5, 2016 Number one I'm not a fan of square forges. Because it's harder to get good swirling of the burning gasses in them they have more of a problem with hot spots. What is the inside dimension of the forge? If it's 8X8X12" that's huge. My main forge, which is cast from a refractory, has a 4" diameter hole that is 7" deep. It has a rear port that can be blocked off but rarely is because it comes in too handy. With it I can austenize a blade that is over 12" and I can use it to avoid over heating the tip of the blade. Doug HELP...I'm a twenty year old trapped in the body of an old man!!! Link to comment Share on other sites More sharing options...
Jerrod Miller Posted February 5, 2016 Share Posted February 5, 2016 Also, when asking a question like this what type of burner you will be using is very important. Wayne's comments about fuel and gas mixing are accurate, but you really don't need an extra vent if you have a forced air (blown) burner and can control the air and gas volumes entering the forge. You may not need anything for the right sized venturi either. Link to comment Share on other sites More sharing options...
Bill Brown Posted February 6, 2016 Author Share Posted February 6, 2016 Jerrod, I am not using a forced air burner on this forge. This is the burner I purchased. http://www.ebay.com/itm/U-S-made-Gas-burner-blacksmith-forge-raku-kiln-propane-foundry-150-000-BTU-/231758543576?hash=item35f5e2bad8:g:Lu4AAOSwzOxUXlEH Doug the diamensions are correct. The forge is 8"x8"x12". It will have 1" of insulation on the sides and 2" at the ends. Link to comment Share on other sites More sharing options...
MSchneider Posted February 8, 2016 Share Posted February 8, 2016 Just one more question about the size...is the 8x8x12 dimension before or after the insulation? If it is before then you are going to end up with 6x6 right? The reason I ask is that 1" if insulation is awfully thin. At a minimum I'd go 2". If your finished interior size is currently really 8x8 then I'd add another layer of insulation. You will be glad in the long run that you did. It will easily pay for itself in fuel efficiency and help you to attain higher heat with your burner. On thing I have seen with venturi burners is that first you need enough opening so as to not create back pressure on the burner. The burning propane expands like 7:1 so you need an opening large enough to not limit that. The second thing is, in my experience, a venturi forge benefits from a rear opening even if back pressure is not a problem. It does not need to be as large as the front, but a small opening will help to even out the heat in the chamber. website: http://www.dancingotterforge.com/ Link to comment Share on other sites More sharing options...
Bill Brown Posted February 10, 2016 Author Share Posted February 10, 2016 A update to my forge project. There is now a 2" opening on the back side of the forge. It is treaded so I can cap it off if need be. The Support for the burner is also in place. It is also a 2". I checked with a distributor here in Tulsa about the insulation. They tell me the 1" insulation is good to 2300 degree. I can always add more. With the 1" insulation there will be a 6x6 work area in the forge. I plan on having a single insulated fire brick on the bottom of the forge to rest work piece on. I am contemplating buying a piece of 8" sch. 40 pipe and making a round forge to compare the two. Link to comment Share on other sites More sharing options...
Jerrod Miller Posted February 10, 2016 Share Posted February 10, 2016 They tell me the 1" insulation is good to 2300 degree. I can always add more. FYI, that just means it will survive up to that temperature, it doesn't say anything about the effectiveness of the insulation it will provide. I have about 1.5" in my forge and kind of wish I had more, but I didn't want to lose too much space in my pipe. If I ever need to build a whole new forge I'll probably go with a 10" diameter pipe and do at least 2" of insulation (giving a 6" internal diameter, minus the hard refractory coating I'd apply over that). Link to comment Share on other sites More sharing options...
Geoff Keyes Posted February 10, 2016 Share Posted February 10, 2016 BTW, the burner you posted is not a forced air type, it's a venturi. A forced air system uses a fan. It's not a big deal, but it's good to get the terminology right, especially when asking questions. It saves some time sorting out good info from bad. You may not have enough burner for the size of the interior. Normally the ROT is one burner per 350 ci (when talking about venturi systems). You may end up wanting a second burner for this forge. Just my .02 Geoff "The worst day smithing is better than the best day working for someone else." I said that. If a thing is worth doing, it is worth doing badly. - - -G. K. Chesterton So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy. Grant Sarver Link to comment Share on other sites More sharing options...
Jerrod Miller Posted February 10, 2016 Share Posted February 10, 2016 And when it comes to burners, the exchange rate on Geoff's $0.02 is insane, even considering the strong US dollar. Geoff knows his stuff. Link to comment Share on other sites More sharing options...
Geoff Keyes Posted February 10, 2016 Share Posted February 10, 2016 If you build enough of them, you've made most of the common mistakes. Geoff "The worst day smithing is better than the best day working for someone else." I said that. If a thing is worth doing, it is worth doing badly. - - -G. K. Chesterton So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy. Grant Sarver Link to comment Share on other sites More sharing options...
Bill Brown Posted February 11, 2016 Author Share Posted February 11, 2016 Geoff, I never said I had a forced air burner. I knew I did not have a blower pushing air into the forge. However, your statement is still valid. Thank you. With everyones input I am changing my plans about insulation. There will be 2" of insulation on all sides of the forge. Thanks everyone for your input. Will post pictures when forge is complete. Link to comment Share on other sites More sharing options...
Geoff Keyes Posted February 11, 2016 Share Posted February 11, 2016 My mistake, gotta start having my coffee before replying. Geoff "The worst day smithing is better than the best day working for someone else." I said that. If a thing is worth doing, it is worth doing badly. - - -G. K. Chesterton So, just for the record: the fact that it does work still should not be taken as definitive proof that you are not crazy. Grant Sarver Link to comment Share on other sites More sharing options...
Wayne Coe Posted February 12, 2016 Share Posted February 12, 2016 Geoff, by reducing down to the 1.5 from the 2" inlet you may be causing a restriction and letting propane back up in the tube. I would try removing the reducer, or better yet, build a Ribbon Burner. Let me know if I can help you. Wayne Coe Artist Blacksmith 729 Peters Ford Road Sunbright, Tennessee 706-273-8017waynecoe@highland.netwww.WayneCoeArtistBlacksmith.com Link to comment Share on other sites More sharing options...
Bill Brown Posted February 12, 2016 Author Share Posted February 12, 2016 Wayne, I am not sure what 1 1/2" reducer you are referring to. There is nothing on my forge that is 1 1/2". Everything I have is 2". Link to comment Share on other sites More sharing options...
Jerrod Miller Posted February 12, 2016 Share Posted February 12, 2016 That was a post to Geoff in response to a different thread on burners Geoff asked a question in. Link to comment Share on other sites More sharing options...
Wayne Coe Posted February 13, 2016 Share Posted February 13, 2016 Duh! Thanks Jerrod. That is what I get for not checking. You are 100% correct. Sorry Bill, if I confused you. Wayne Coe Artist Blacksmith 729 Peters Ford Road Sunbright, Tennessee 706-273-8017waynecoe@highland.netwww.WayneCoeArtistBlacksmith.com Link to comment Share on other sites More sharing options...
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