maddog

I use a very small forge and run it at welding heat all the time. Over time, I've trashed a lot of refractory materials. Refractory temperature ratings are primarily based on their mechanical properties. When shrinkage, slump, distortion etc exceed acceptable limits, usually a few percent, then its above its max working temp. Often these small changes in shape, cause cracking when it cools. If you continue to heat it past that point things get progressively worse and finaly it will melt. 3100F is the theoretical combustion temperature for propane under ideal conditions. You are unlikely to get that in a forge but at welding heat, there will be regions above 2400. Temperature alone, is not the only issue. Some refractories become increasing vulnerable to oxidizing or reducing atmospheres as the temperature rises. Kaowool is very vulnerable to oxygen at high temps. If you dont coat it, or if the combustion gases find their way into the lining this will trash it quickly. But if its protected it seems to do fine even at welding heat. I have some Inswool rated 3000F. If the combustion gas gets to it, it dies just as fast as the regular stuff. One reason to use rigidizer is that makes the material less permeable and helps to prevent this. I bought a kiln shelf yesterday in the pottery supply store. These are used all the time as forge floors and are exposed to welding heat. I was surprised to learn it was only rated "cone 10" just below 2400F. Its essentially mullite which holds together well past 3000F. Then I realized that potters make stacks of these shelves in their kilns supporting them with small blocks, so slumping is an issue. In a forge the whole shelf is supported and it can be used at higher temps.

You got a great deal! But you are going to have to drop some money on cables. Fact is you probably would have had to even if the original cables were still attached. These units typically come with 12' #4 gauge leads, which are too short and too small a gauge. The lower the voltage, the larger the conductor has to be to push the same amount of power through a line. Which is why power transmission lines run at extremely high voltages. And, of course, the longer the run, the thicker the conductor has to be to supply the same current. Welding cables run low voltages and huge currents. They are heavy thick and expensive. It's much cheaper to put a long power cord on a welder than it is to buy long leads. But welders are heavy and clumsy, even small ones like yours. Even on a cart, do you want to be pulling it around the shop every time you need to weld? The best is probably a compromise. 25' Welding leads, #1 gauge will probably reach every where in your shop. On the day that you need to weld under a trailer out in the street or set up a swing set in the back yard, you can make up a 220v extension cord and drag the welder out to the job. And like someone says, the gauge will depend on the length of the run. I have 25' #1 cables on my Idealarc 300, with quick connects on the end so that I can snap in another 25' extension if I need. (the Idealarc weighs 800lbs so rolling out into the driveway is not an option). When I bought the cable, #1 is about $2/ft, I got red and black leads. I would like to make the first 25' out of 1/0 gauge. That will have to wait till I have made my fortune in blacksmithing. The stinger lead is 3ft of #4 which snaps into the quick connect on the end of the heavy red cable. This makes it easier to manipulate the rod and a few ft of small gauge doesnt have much effect at regular rod sizes. I have a variety of different ground clamps which I can snap onto the quick connect on the end of the black cable. I also have a quick connect lead attached to my welding table.

Great post Frosty. How do you set up a choke on your T burner?

I dont see that one has to be loyal to one design at the expense of the other. They both have their place. I use a forced air burner for my main forge (which is pretty small) and atmospherics for various heating jobs and temporary forges. Blown burners give much greater control over the air propane ratio. They can also run forges where there is quite a bit of back pressure. The blowers need not be expensive if you shop the surplus merchants or simply scrounge which is what I do. They are considerably more cumbersome, requiring electricity and several feet of 1" or greater plumbing for the air. Amospheric burners are very compact. The parts are cheap. You can move them around, set them up in different parts of the shop or run them in the back yard with little hassle. All they need is the propane hose. If you are a farrier and need a portable rig to take out into the field, the choice is a no brainer. I think they are a totaly neat design and I love making them and fooling with them. It's true there are a lot fewer parts in making an atmospheric burner, they are by no means simpler to make. The design and construction is critical requiring some precision and a good understanding of the operating principles. Blown burners are much more forgiving to build and operate. They also have a more limited operating range because air intake and fuel delivery are coupled. For this reason I would steer a newbie away from atmospheric burners as a first effort. I see so many posts from people getting started who have made an atmospheric burner and either dont know how to tune it or have made some critical mistake in the design. Blacksmiths tend to be the kind of people who look at something and are convinced they can design and build it better even if they never made one before. I admire that attitude but in this case it can lead to problems. That said, a lot of people have made an atmospheric burner for their first forge and had success with little frustration. This was my own experience. Other than that, they are both great. They both have their strengths and weaknesses and what you choose to use in your main forge is just a matter of preference.

I'm sorry you are having so much disappointment. My first forge was dud too. It is very much to your credit that you have your own ideas and the determination to follow them through even after several failures. IMO this is a characteristic of good smiths. But sometimes it can lead to frustration. You are quite right in that if you are forging by hand, you need to get the stock to near welding heat to do the heavy initial forging. Orange is mostly used for bending and finishing. Hang in there. I think you are not far off. With an atmospheric burner, there should never be enough back pressure to force the hot gas out through the cracks or the back. The exhuast should be able to flow freely out of the mouth without having to find additional escape routes. I think your burner is way too big for the chamber size and is being strangled by the back pressure. As it happens, I currently have almost exactly the same set up as you do. I have a pile of soft bricks in the same configuration and the chamber is about the same size. With mine, the back is closed. I can't tell on yours. I also have a few pieces of broken brick in the chamber which are additional obstructions. I am running a 3/4" atmospheric burner. It heats up to lemon yellow in less than 10 minutes. I haven't tried to reach welding heat since this is only a temporary arrangement but I have little doubt it can get there. It is clear to me that my 3/4" is partially choked by the small chamber. I reduced the mig tip to 023 (030 would be right for this burner in open air at my altitude) and run it at 30 psi to compensate. At 4psi everything falls apart, the air draw fails and I get a large rich propane flame outside the forge. In open air this burner is happy to run with the gauge needle still at 0. At 20 psi it can no longer hold the flame and blows out. So if mine is choked, yours must be asphyxiated Intuitively, I would say that the air stream from the burner is hitting the opposing wall too soon and choking the air flow. I suggest: a. Introduce the burner at the back of the chamber so it points directly at the front entrance. This will give it room to develop a proper flow. And put a single fire brick across the front but two inches away from the mouth of the forge so that the dragons breath hits it and splays out sideways. b. Reduce the jet size like someone has already suggested to get more velocity for a given fuel delivery rate. Don't be afraid to crank up the pressure. Those two changes should be easy and quick to make and will give you an indication of whether this is the real problem. If the results are encouraging, I suggest you make a 3/4" Frosty T burner and try that. One might think that if a 3/4" burner is enough, a 1" burner oughta cook the hell out of it, but in fact these burners have a turn down limit. When the pressure difference between the intake and the nozzle falls below a critical point they just pump propane into the chamber. The variable size, pile o' bricks forge has never worked that well for me. The soft firebrick just falls apart when I move it around. You actualy dont need a large forge to do large work. I use a very small chamber, about 6"x6"x8", closed at the back and run it very hot. I put a wall in front of the opening, like I described above and lay the work across the mouth of the forge. I rarely put the work in the actual chamber.

I know this thread is over a year old but it's priceless. It's a classical example of a certain type who shows up on forums every now and then. If I were going to write a spoof on this kind of character, I couldn't have done better! I couldn't stop laughing while I read thru this thread In his own words: he's read everything that Google can find on gas forges: he admits he doesnt know much about gas forges; he went ahead and built a heavy welded steel shell anyway; only now does he wonder where the burner should be situated and he has given no thought to matching burner output to forge size; nor has he ever heard of simple atmospheric burners, even though these are all over the web; again, while he admits that he knows very little about gas forges he is adamant that refractory is entirely optional, in fact it's a luxury like music or TV; when half a dozen experienced smiths suggest changes (and they all say pretty much the same things) that might make the forge actually work, he accuses them of being trolling hypocrites and requests that they "move on" so that we can make some progress on his issue. :):)

Yes this idea is used in furnace combustors though I dont think Ive ever heard of one being cast around a sausage balloon!. The air/fuel mix is forced through some kind of labyrinth to expose it to as much surface area as possible. Sometimes there is a parallel channel for the incoming unburnt mix which is preheated by heat exchange through the walls. I think the "muffle furnace" is a special version in which the combustion gases are kept separate from the work. Closely related ideas are "porous matrix" combustors, where the gas is forced through a porous block of refractory and perforated refractory burners where the combustion mix is split up into a multitude of small channels, like ribbon burners. Then there are various recirculating burners which draw some of the hot combustion gas back into the unburnt mix for pre heating. P-Tube burners are a version of this idea that I find particularly interesting. I've made a "combustion manifold" burner pretty much along the lines of kcrucible's idea. When I fired it up, it oscillated at about 50bps. It sounded like a small briggs and stratton running without a muffler. The vibration shook the refractory structure apart before it got up to heat. I realized I had no way of analysing this design for resonant frequencies and I was out of my depth. Next I tried forcing the air through a pile of refractory chips. Much like the ceramic chip forge idea. This worked great, it burnt white hot and very clean. But at that temp, the chips welded together and then began to slump into a fused lump of something that looked like refractory vomit. I tried different refractories like mizzou plus, greencast plus. Sooner or later the same thing happened. The last thing I tried was making perforated blocks, much like a ribbon burner though I hadn't heard of those at the time. The blocks held together well enough and burned great but the back pressure required to force the air through the block found its way through small cracks in the refractory housing that held the block and the plenum chamber. Once this happens, the crack continues to grow and flames start appearing at various points around the back of the burner. The ribbon burner design which is now being used by some smiths in their forges looks like it could solve all these problems. A particularly nice version is the Pine Ridge Burner. In this design, the housing is made of steel and kept cool by a deep barrier of refractory and by air flow through the narrow steel tubes. I really have no idea what the hell I am doing, but I love messing with this stuff. PS: Grant thats a very interesting link. I am reading it carefully. Thanks

Yes that's the key, the combustion has to be complete before the steel is exposed to the hot gas. The main advantage of a blower in this respect is that you can push the air/fuel mix through some kind of baffle and not worry about the back pressure. Im not sure what a "combustion manifold" is, but it sounds like the same idea. Is there a drawing of this kind of setup? I have experimented with various kinds of combustion baffles, forcing the mix through a pile of refractory chips, a block of porous refractory or a labyrinth and they are all effective at improving the combustion but have other practical problems of their own. My next mad scientist project is going to be a ribbon burner based on the Pine Ridge design. There is a very interesting thread in this forum where prburner explains his design. It looks like a very promising idea. Forges are a particularly demanding application for burners. Industrial furnace, kilns etc have large chambers for mixing, they ramp up to temperature slowly and there is less concern about the composition of the atmosphere. Some furnaces even control their temperature by forcing excess air into the chamber for cooling. Forges by comparison are small, required to reach very high temps (higher than most other applications), need to be able to change temperature very rapidly and all this while maintaining a benign atmosphere. Robert, I've heard of other people doing the same. I think Frosty once mentioned it. But for myself, I dont want to have to feed pure oxygen into my forge. Certainly not when I can use a forced air system and get good results. I use atmospheric burners as auxilaries for heating jobs around the shop that cant go into the forge or for the Raku kiln that my lady wants to set up in the back yard. I made this last burner so that I can align the hinge on a 5" leg vise.

Of course I adjust my burner for atitude. I am using a 023 tip in a 3/4" burner. It isn't practical to swap out tips in the middle of forging to run the burner in different temperature ranges. A blown burner doesnt have this problem. Yes there is less oxygen available and I still have unburnt fuel and free oxygen in my forge. Tube velocity may be higher in my case because of the smaller jet but once the mix enters the forge and expands, the speed is not much different. Altitude only accounts for some of this. The difference in air pressure is about 20% which is considerably less than the variations between different burner designs. A design that cant tolerate a perturbation of this magnitude is "brittle". It is pretty much an established fact in the combustion industry that you cant expect to get complete combustion of any gas in a flame front. There isnt time and propane is more difficult than most other fuel gases.

I hope this doesn't amount to hijacking a thread. This is a topic that interests me. I sure would like to understand this whole issue better. I live at 7000' and my experience with induction burners is that at high temps they just dont perform as well as blown systems. If I run my forge with an induction burner at or near welding heat I always get a lot of scaling. These burners seem to run hottest when they are set lean which is not ideal for the steel. But I also see conditions where I clearly have a rich burn and the iron is still scaling rapidly in the forge. This means that there is both free oxygen and unburnt propane in the forge. Frankly, I am skeptical of the technique of judging the burn by its color and shape. Propane is hard to mix and hard to crack. Which means that even if you have perfect mixing, it takes time for the fuel to combust completely. This is not likely to happen in the short time it spends in the flame front. Various strategies are used to overcome this, preheating the propane, precombustion, recombination and flameless combustion etc. None of these can be implemented in an induction burner. Inducing turbulence at the end of the burner by means of a threaded flare (great looking flame btw), bends in the burner tube or refractory rubble to improve performance shows that the induction tube itself does not do the job completely. But any turbulence causes some back pressure and thus reduces the maximum power output of the burner. In the canonical burner designs, the nozzle is smooth. It is designed to reduce turbulence and preserve laminar flow which is considered necessary to get full performance from the burner and also to achieve flame stability without a flame holder, another source of back pressure. I have found that when I finally get enough mixing and ignition surface to get an environment that's kind to the metal, the burner output has been significantly reduced. And the back pressure also affects the turndown ratio. I have to run higher pressure just to keep the gas flowing to cool the tube. These limitations are probably more severe in my shop because of the altitude. But I am convinced that induction burners, while very useful, are not an optimal design. From an engineering design point of view its a serious weakness that you cant change the pressure of the airflow without increasing the amount of fuel you put in the system. Systems like this tend to have a rather small sweet spot and if that isnt where you need it... too bad. This is partly why carburettors have been replaced by fuel injection systems. Grant once suggested an interesting idea of waving a piece of copper wire around in the forge chamber and watching the oxide colors to judge the balance of the burn. Unfortunately, when I try this at welding temps, I cant read the colors before the wire glows red and is about to melt.

It's my opinion (just that and no more since I have no scientific data to support it) that mixing propane properly is a problem with induction burners and they never do that good a job. When I use a blown burner, I notice improved performance if I put a mixer in line before the burner. Frosty and others have mentioned that their forges seem to do better when they introduce the gas into the squirrel cage in the blower. Another issue is that propane is hard to crack and even when well mixed it takes time to burn completely. I'd love to hear comments on this topic.

Generaly, solid refractories are not good insulators by design. They need the heat to spread as evenly as possible to avoid mechanical stresses due to expansion. That said, what you have in your forge should be good enough. I agree with Grant. You arent putting enough heat in to the chamber and there is too much air. You ought to see orange flames at the mouth of the forge and when its heating up it should sound loud. And you dont need an orifice. The blower is moving air for you. Try cranking up the heat, and if you dont have an air gate, for the moment you can partially choke the blower input with a piece of cardboard. When people fire up their first forge ever, they are often timid about putting the pedal to the metal. Thats a fairly big forge. It's going to need some serious burn in there.

The valve on propane and acetylene tanks are lefthand threads. They wont take n non fuel regulator. People do use acetylene hoses and regulators for propane and seem to get away with it. But you arent supposed to for the reasons kcrucible mentioned. For the price of a proper propane regulator, $30 why take these chances? If your hose gets burned or cut while at full tank pressure thats a catastrophe. If the regulator seems to work but is slowly leaking propane, the gas can pool on the floor and flash suddenly. You wont like that either.

Refractory rubble: It's my guess that the the broken surfaces cause turbulence and promote mixing, the hot sharp edges provide ignition points and the large surface area increases radiative transfer. I said "cover the floor" but a small pile of refractory chips placed in the right part of the forge can be enough. I should add that the pieces of refractory will tend to stick together and to the forge. If you drop flux on them they will weld together. If you are fussy about that, break them loose while they are still hot.

H, That sounds like AP Green's Pyramid Super Airset which they stopped producing somet time ago. That was fantastic stuff much like you described. Could you dig out the name? I'd love to get some. Thx Steve, Thats a beautiful forge!

My experiments with burners mounted under the forge feeding up through the floor is that crud falls in the hole and welds itself in place. If flux is involved its even worse. I have tried the ceramic chips idea but with every refractory I have tried, the chips stick together and to the side of the cavity they sit in. I think refractory material is designed to become soft and a bit gummy at high temps so it can relieve the mechanical stress from thermal expansion. Welding heat. I find that covering the floor of a forge with refractory rubble can significantly increase the temperature in a gas forge.

kcrucible, Ive looked at some of your stuff online and see you have been seriously interested in burner design for some time. For my primary forge, I prefer to use a blown system. It's a lot less fussy and gives you more options. But the atmospheric burners are very useful and way cool. They are also very useful as a general purpose heating torch in the shop. My gf wants a Raku Kiln so I thought I would start making a couple. Those will probably be sidearm design with off the shelf parts. I wasnt aware that Porter was involved in the Trex design. Looking at the Trex, I see the air slots have round ends, which Porter is quite adamantly opposed to in his book, claiming that this induces turbulence. I am going to have to buy a Trex soon. After the time I spent making a Porter design, the price seems very reasonable Yeah thats my problem right now. In open air, the Porter burner needs a jet between 030 and 035. (I am at 7000'). The back pressure from a forge might make the 030 a good match, otherwise I will try to enlarge an 030 with a tip cleaning file. Thank you for the drawing of the Trex. It will be very useful

I like to try out my own designs and ignore accepted wisdom too. It can be fun, though the results are often disappointing. I do it anyway. I learn alot from my failures. I don't mean to criticize, disparage, put down or talk down to anyone in any way when I say that, in this case, the current designs in atmospheric burners among the smithing community represent a wealth of valuable knowledge. Burner technology is crucial to smiths and they have thought about them a lot. Bear in mind that the smithing community is a cross section of society. Among those involved have been numerous engineers and at least one professional combustion engineer. As far as I know there are basically four atmospheric designs currently in use. I rank them in order of performance with the best first. Hybrid Trex Michael Porter's jet ejector. Zoeller Side Burner Ron Reils Aussie burner. I haven't tried the Trex. You have to buy it. I dont know if it outperforms Porter's design. From reports, it sounds like it. But I've made a lot of atmospheric burners, some my very own design which performed poorly, and I have made the other three. Rons burner was the first serious attempt to come up with a high performance atmospheric burner and yes, it has the draw backs that Richard mentioned. The side arm is a big improvement, easy to build with mostly off the shelf parts. I have just finished up a 3/4" Porter type burner and its a beast! But it takes at least a day to make, more if you haven't made one previously. I've done a fair amount of research reading technical papers on burner technology and AFAIK, no one has analyzed or modeled small atmospheric burners of the type we use. Its too much work. It's only done for big industrial applications where serious money is involved. However, there is now a body of well tested empirical knowledge and as Thomas says, real data trumps everything else. Burner design remains something of a black art but over time a number of dependable design rules have emerged. I thought I would list these in a later post. It might be useful to us to have the information in one place where it can be easily found. I would be very grateful if people would add their knowledge or correct what I have written.

If you think of the surface of the plate as a drum skin, the flatter and more homogenous it is, the more likely it is to resonate at or around a single frequency. In other words to concentrate all the energy into a single tone. Any dimples or hard spots in a drum skin would break up a wave that tries to vibrate across the whole surface requiring a mix of frequencies and harmonics and so giving more of a thud than a ping. I guess that was a long winded way of saying - yeah I agree :)

buzz boxes dont work well on 120 and stick arcs are harder to maintain at low currents. For learning one should start with 1/8" or even larger. Stick is very useful and a basic 220v machine will weld a wide range of thicknesses but stick is not suited for stuff below 3/32 and even then its tricky. Yeah there are some guys who can do nice stick welds on sheet but they are very good welders. In your case I would consider one of the 120v mig outfits. They are nice and easy to use but limited in their upper range. You should probably practice a straight fillet weld before doing it with pipe. What rod are you using? 6010/6011 gives very good penetration with little slag. You might try a small gap in the weld using thin wire as a spacer.

It takes a while to learn stick. They say you have to burn about 50# of rod. But you will get a higher rated buzzbox for your money. Its also a lot easier if you have DC

my understanding of the yield strength is that its tensile strengh. the test would be to weld two rods together and grind the weld flush and smooth. Then to pull them apart. If the weld gives at, lets say, 50,000lbs of tension on the rod then the yield strength would be 50,000 lb divided by the x section area of the weld. If the weld had a x section of 0.5 sq ins then the yield strength would be 100,000 psi

Yeah it does look upside down. But as Philip says, they would flip the anvil around and use every surface. It may well be that that is the hardy hole. The face was small and the maker may have wanted to avoid compromising the face and the steel plate if there is one. No doubt it was used as a handling hole during forging. Hardy holes werent standard in those days. Is the bick included? If I were in Europe, I would buy it in a heartbeat

Bending angle iron means upseting one leg and the stock is going to fight you every inch. If I understand the design specs its up to you how you attach the expanded metal so why not consider a different approach? Roll the rim out of 1"x1/8" which is easy and then add something to hold the expanded metal. You could roll a 3/8" sq bar, you could weld or rivet on tabs intermittently and the tabs could be some pretty forged shape, you could make a simple attractive grill perhaps involving concentric circles or you could just weld the expanded metal to the inside of the rim. After all it only has to support birds. Its not a helicopter landing pad.

Thanks for all the advice. I appreciate it very much. I will check out both options. I think I am going to need some kind of cheater lens as the dim light makes it harder to get a good focus. But I could use a clipon over my prescription glasses.