PJames Posted December 26, 2011 Share Posted December 26, 2011 I have been reading as many sites as I can looking at plans for building my first gas forge. The one problem I have encountered is understanding some of the basic principles behind the designs. For instance: 1. Concerning a burner. from what I see, air comes into the tube then the gas. Where is the actual combustion taking place? In the forge itself or in the burner tube? To me it seems the actual fire has to be in the forge body (post flare) or the burner will get melted. 2. Along that line, what is the real difference between atmospheric and forced air burners? I noticed Y's (sometimes with chokes) built outside the burner tubes. I wondered if you could kick a regular atmospheric burner into overdrive by forcing air into the Y (and get a hotter fire with less fuel). I realize that if the burner is put into an idle mode, the forced air would have to be cut off and a way to open it back up to atmospheric pressures would have to be accomplished to avoid oxygen deprivation and extinguishing the flame.. 3.I looked at Larry Zoeller's simple forge and like the design. I was thinking of adapting that by covering the ceramic wool with a thick refractory cement coating. What are the reasons for NOT using 100% refractory cement..or a combination wool/cement coating? Is it weight, cost, slow time to cure or insulation properties? 4. I want to build a forge that I can get up to welding temps. It does not have to be large as right now anything that I can envision making will be relatively small in diameter. Just joined but have read through many of the posts and really like the forum.. Pat Quote Link to comment Share on other sites More sharing options...
kraythe Posted December 26, 2011 Share Posted December 26, 2011 I have been reading as many sites as I can looking at plans for building my first gas forge. The one problem I have encountered is understanding some of the basic principles behind the designs. Well you have come to the right place. If someone here doesn't know the answer or has an informed opinion, I don't know who will. For instance: 1. Concerning a burner. from what I see, air comes into the tube then the gas. Where is the actual combustion taking place? In the forge itself or in the burner tube? To me it seems the actual fire has to be in the forge body (post flare) or the burner will get melted. Well it depends on the burner type. If its a venturi burner (naturally aspirated without a blower) then the combustion will take place in the flare of the burner. The venturi effect is the result of high pressure gas shooting down the burn tube and then causing a low pressure situation which draws in air and mixes but the burn should take place on the flare. If it leaps off the flare and goes out, the port is too small or the position of the jet is wrong. If it takes place in the tube, the opening jet for propane is too large. The thing is propane doesn't burn instantly. It has a certain velocity and the back of that velocity is called the flame front. You are trying to balance the burner so the flame front speed matches the speed of the mix coming out of the burner stabilizing the flame in the flare. The reason for the flare is to slow down the gas so that its not pushed off the flare and goes out. If there is separation between the flame and the flare, the gas speed is too high. Blown burners have the same issue but you are controlling the amount of air going through with more precision and you can put things like baffles in to promote mixing of the fuel and air before they get to the burner. However, the burn will take place in the flare or the final nozzle block for a ribbon burner. 2. Along that line, what is the real difference between atmospheric and forced air burners? Venturis rely on the venturi principle which is sensitive to many things, the most important of them is back pressure. Running a burner outside a forge is not necessarily indicative of its performance in a forge in the case of venturi burners. The problem is that once in the forge, the outlet for the flame is shooting air into a small environment and then burning it but more air is going in than can get out of the forge easily so the pressure in the forge builds and that counteracts the venture effect because the high pressure in the forge backs up the burner. If you increase the size of the forge you may not get enough heat to smith, if you change the size of the burner you can have other problems. So venturi burners and forges must be precisely sized to each other. With blown burners you have a blower that can fine tune the air going in. Furthermore, your blower counteracts in forge pressure and overcomes the limitations of venturi burners. Also blown burners like ribbon burners are able to produce more heat because of the more surface area of the flame. You can't do a venturi ribbon burner. Furthermore with blowers, you can increase the efficiency of the mix by adding baffles to cause turbulence in the feed pipe. This results in a better burn. Baffles would just mess up a venturi burner. The downside to lbown burners is they require a blower. I tried hair dryers and other appliances before and they just burn out. A good blower will set you back about 150 bucks or more. Its a good investment but an investment nonetheless. Also blown burners require a good nozzle config to make them work well. Building a venturi is easy. There are some recipes around that won't take thou more than an hour. A ribbon burner will take you several days over the course of two weeks. I noticed Y's (sometimes with chokes) built outside the burner tubes. I wondered if you could kick a regular atmospheric burner into overdrive by forcing air into the Y (and get a hotter fire with less fuel). I realize that if the burner is put into an idle mode, the forced air would have to be cut off and a way to open it back up to atmospheric pressures would have to be accomplished to avoid oxygen deprivation and extinguishing the flame.. Not really. Venturi burners don't work on the same principle. Better fuel economy comes from better mixing and better heat transfer. If you want to mix better, cause the system to pressurize and swirl around. If you want better heat per gallon of propane you have to spread out the flame to get more burner surface area. The reason for chokes on venturi burners is to alter the atmosphere in the forge to change the way it heats metal. However that is way beyond the scope of this post. If you try to add a blower to a venturi, you are more lilely to push the flame front off the flare than anything else. 3.I looked at Larry Zoeller's simple forge and like the design. I was thinking of adapting that by covering the ceramic wool with a thick refractory cement coating. What are the reasons for NOT using 100% refractory cement..or a combination wool/cement coating? Is it weight, cost, slow time to cure or insulation properties? Refractory cement creates thermal mass. There is more mass to heat with the burner and so the forge takes longer to come up to temp. A three inch layer of castolyte on the whole forge will take near forever to come up to temperature. If you are a pro doing it all day, its probably not an issue. If you are a hobbyist you probably don't have the time or money for propane to bring it up to forging temp in half an hour to an hour. Also refractory cement is denser than blanket and thus doesn't insulate as well, requiring bigger burners and more fuel consumption. At the same time the blanket is hazardous to your health in the case of most blankets (though hitemp refractory store on ebay sells one that isn't and I love it) so you have to cover the blanket with something or start saving for the Silicosis bills and lung cancer. Also the blanket isn't rated as high a heat as the castable. Kastolyte 30 will hold up to 3k temps but super wool only 2300 which is just barely welding temp. Best combo is to use a /2 to 1 inch castable hot face surrounded by blanket. Then cover the internal hot face with a coating like itc-100 to improve heat retention. 4. I want to build a forge that I can get up to welding temps. It does not have to be large as right now anything that I can envision making will be relatively small in diameter. Start small and work up. Use a hot face construction and a blown burner. You will spend more at first but will thank me later. If you have the means, build a ribbon burner. Just joined but have read through many of the posts and really like the forum.. Pat Welcome, hope I helped. Quote Link to comment Share on other sites More sharing options...
PJames Posted December 27, 2011 Author Share Posted December 27, 2011 now i will have to look up what a ribbon burner is... another thing in the learning list... :) Quote Link to comment Share on other sites More sharing options...
ThomasPowers Posted December 27, 2011 Share Posted December 27, 2011 "I noticed Y's (sometimes with chokes) built outside the burner tubes. I wondered if you could kick a regular atmospheric burner into overdrive by forcing air into the Y (and get a hotter fire with less fuel)." Let me rephrase this: "When I'm running a burner with the proper air/fuel mix to get 100% fuel burn; will adding a lot of cold atmosphere make things hotter?" No, the advantage of a blown system is that you can generally *increase* the *fuel* and *air* keeping the mix *correct* but with more of it to increase the total BTU's going into the forge making it hotter. Venturi burners are often more touchy in keeping a proper mix over wide ranges of fuel input. "What are the reasons for NOT using 100% refractory cement..or a combination wool/cement coating? Is it weight, cost, slow time to cure or insulation properties?" Yes all of the above; with insulation properties being the heavy hitter. With an all wool forge the time to get to welding temps is minimal. With a solid cast forge it may be over an hour before you get it to welding temp and will take a similar amount of time to cool off at the end of the session. Unfortunately flux for forge welding eats wool like boiling water through cotton candy su you have to figure out a dual lining if you plan to weld in your forge. Quote Link to comment Share on other sites More sharing options...
kraythe Posted December 27, 2011 Share Posted December 27, 2011 Unfortunately flux for forge welding eats wool like boiling water through cotton candy su you have to figure out a dual lining if you plan to weld in your forge. I am working on a dual insulation forge with a blown ribbon burner. I will post it when I get it done. There are some neat tricks I have put together that make it easy. Also with the flux, I have found that a drip pan is the only way to fly. I weld a lot of cable and that uses borax like mad. So I have found that it is best to take a 1" x 1/4" flat bar and weld it to the sides of a 1/4" plate that fits in the forge and then put in a drip spout that clears my forge lining. I put a catch pan underneath and it works like a charm. Its a ton easier replacing the pan than the forge. Quote Link to comment Share on other sites More sharing options...
PJames Posted December 27, 2011 Author Share Posted December 27, 2011 "With a solid cast forge it may be over an hour before you get it to welding temp and will take a similar amount of time to cool off at the end of the session." So I guess the same holds true for a forge built of firebricks? I found a local supplier of firebricks for a reasonable price. (Another, a fireplace company, was over 3X as expensive) I know cutting/drilling firebrick is problematic in itself but I was also trying to figure a way around ceramic exposure. Which leads me to another question.... I was planning on simply covering the ceramic wool with a decent layer of refractory cement. I was curious how the hole in the wool could be coated without either messing up the air/gas flow or making the hole a tad too large and having a sloppy fit for the burner flare. One description somewhere described cutting an X in the wool and push the flare thru.. then the wool would kind of seal around it. I guess he snipped away around the flare to make sure it did not impede gas flow or blow particles around... Thomas, I had realized that you have to maintain a proper gas to air ratio for complete burning. I just did not know if i could simply put a blower on a venturi style burner, and then have a turbo charged burner for times I wanted welding heat. Quote Link to comment Share on other sites More sharing options...
MattBower Posted December 27, 2011 Share Posted December 27, 2011 "With a solid cast forge it may be over an hour before you get it to welding temp and will take a similar amount of time to cool off at the end of the session." So I guess the same holds true for a forge built of firebricks? I found a local supplier of firebricks for a reasonable price. (Another, a fireplace company, was over 3X as expensive) Correct; hard firebricks are dense, and thus relatively poor insulators, just like castable refractory. Also be aware that not all firebricks are created equal. Find out what the temperature rating is. The common firebricks that are sold for fireplaces are rated something like 2000 deg. F. I get them from a brick yard for a little over a buck a piece. But for forge use you'd probably want something rated more like 2300 or 2500 deg. F. If you put a blower on venturi burner, you have a blown burner. In which case, why not build a blown burner? What you propose might work if you closed off the air intake for the venturi when you turned on the blower. I have an intuition it might not work so well if the venturi air intake were still open, As for forming the hole in your ceramic blanket, one way to do it is to make a flare-shaped wooden plug that fits into the end of your burner tube, coat it with a release agent (like Vaseline), then stick that in the hole and mold castable around it. Once the castable hardens, pop out the plug and you have a castable refractory flare, which also locks in the ceramic fibers around the opening. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted December 27, 2011 Share Posted December 27, 2011 Use a wet saw to cut ceramic, no problems then! Everything I have seen cuts up to 1 inch firebrick with no problems with a diamond blade. (I am looking into a saw to tile some bathrooms and a kitchen) Some saws are a lot easier to use than others, and some will cut much thicker (3 inch brick anybody?) You can also take your bricks to a rental place and spot the guy $ cash for a few cuts, usually a lot less than a 4 hour rental. If you push a plug from the inside to the outside you can get your flare shape in your refractory and "seal" it to the burner. The plug can be from any material that is convenient including cardboard tubes, foam insulation, small paper cups...The strength required for the plug is actually quite low because the refractory will become self-supporting before it is done curing. Otherwise the wool will press against the burner and hold itself in shape after the shape is formed and the burner inserted. Phil Quote Link to comment Share on other sites More sharing options...
PJames Posted December 27, 2011 Author Share Posted December 27, 2011 Ok. I am getting the picture. Part of my problem was not knowing if I insulate, cover with cement etc with an open hole or with the burner in place. I sort of had the idea that only the burner support tube was fixed and that was on the outside of the forge body. That the burner itself would slide down a hole in the insulation. (Kind of like a 1 inch pipe inserted into a 1 and 1/8" tunnel.) I could not figure how that would seal. I've never seen one of these forges. Hell, for that matter, I have never tapped threads into a fitting. or done alot of the other things ya'll take for granted. I was reading about the Frosty burner and it was more than 1/2 way through that I realized the MIG fitting was what you might see on a MIG welder. I was thinking it was some kind of acronym that I would find later on for a plumbing part.. And it's NOT that I am a complete dummy when it comes to the dynamics of running fluids and gases under pressure. I run a heart/lung machine during cardiac surgery for a living. But then I have a different set of problems moving blood than something that will mix and then burn at ultra hot temps.. Quote Link to comment Share on other sites More sharing options...
PJames Posted December 30, 2011 Author Share Posted December 30, 2011 I got the stuff to build my burner like Phil described. And most of the stuff to build the forge itself except for the firebricks which I will put in on the floor as a disposable. (Well the door too, unless I come up with some other design.) My kaowool and refractory cement mix only set me back about $78). The burner assembly, lines and associated tools cost me a fair amount. The easiest part of the assembly so far has been mounting the burner support tube. Even with few decent tools, (I used a hand drill, wire cutters and a 1/2 round file) I got the body together. Weather permitting I plan to cut and install the kaowool and refractory cement this weekend. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted December 31, 2011 Share Posted December 31, 2011 I ended up taking a strip of kaowool and tucking it in to seal up the burner because I had a gap between the burner and body. Phil Quote Link to comment Share on other sites More sharing options...
PJames Posted January 1, 2012 Author Share Posted January 1, 2012 Not sure why my earlier post did not go through... BUT since I started this thread I'll use it as sort of a blog for the next entry or so.... Today I installed kaowool in my new forge. then covered it with a (hopefully thick enough) layer of refractory cement. (If I knew how to post pics here I would..but they would look the same as everybody else's) except i am trying to mold a door for the front of my forge.. I measured and have molded a refractory/ kaowool combination to make a door/front for my forge. I figure I can cut a usable area out of the front piece. And if it does not hold up like I hope it will, I can always stack bricks.... Quote Link to comment Share on other sites More sharing options...
oscer Posted January 3, 2012 Share Posted January 3, 2012 Hi fellas, I noticed kraythe posted about a wool insulating material that is not a health issue. I did a search on e bay and came up empty can you elaborate on this krathe? Thanks, oscer Quote Link to comment Share on other sites More sharing options...
pkrankow Posted January 3, 2012 Share Posted January 3, 2012 http://www.ebay.com/itm/SAFE-Non-Ceramic-Fiber-Blanket-1-6-dens-SW607-HT-/130451549975?_trksid=p3284.m263&_trkparms=algo%3DSIC%26its%3DI%26itu%3DUCI%252BIA%252BUA%252BFICS%252BUFI%26otn%3D21%26pmod%3D140429516714%26ps%3D54 It is just as nasty after it has been fired as regular wool, so you do need to coat it. Phil Quote Link to comment Share on other sites More sharing options...
kraythe Posted January 3, 2012 Share Posted January 3, 2012 Yeah but its not as bad as the other stuff for creating the forge. And gives you a bit more peace of mind until its coated. Quote Link to comment Share on other sites More sharing options...
oscer Posted January 3, 2012 Share Posted January 3, 2012 Thanks Phil Quote Link to comment Share on other sites More sharing options...
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