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I Forge Iron

Difficulty getting the forge really hot.

Robert Simmons

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I am looking to get a gas forge to be hot enough to forge weld in the forge. The problem is that nothing I try has managed to accomplish the task as of yet. I will detail my attempts and then let people comment on what could be wrong or whether i am just barking up the wrong tree and should find another hobby until I can get a coal forge and move out of the city so I can use it.

I started working with an atmospheric burner and I had a hell of a time getting the burner to function properly. When I built my first burner it was quite complicated in nature and it worked like a dream out of the forge. When I put it in the forge it sends lazy yellow flames leaping out the end as well as any other direction the gas can get out. If I used only that burner in the forge, I would be lucky to get metal much past cherry red. I have tried using reil burners and just recently I thought about building one of frosty's burners to give that one a try. I am having essentially the same problems with every burner I try. The burners are hooking up to standard barbecue bottles for propane and a regulator that goes up to 60 PSI but I haven't tried to put it above 20.

When it comes to the forge itself, I first trid to do a cast forge with castolyte 3000 deg rated castable refractory. I cast what amounts to a mailbox in a 30 gallon drum. The floor 9" wide by 18" long. I had planned ot use firebricks in the forge to reduce the volume of the forge and thus its heating requirements. My burner when I put it in there had the same lazy flames issue. I was able to add air through using a hair dryer and then I got complete combustion with no fire leaping out of the sides. Using the blower i was able to get that forge to get the metal say a orangeish yellow but no hotter, certainly no pure yellow. This is despite putting bricks in to further reduce the forge's volume.

So recently i have been wondering if I am going about it the wrong way with all this complexity and if I should just use a pile of bricks as a forge with a hole drilled in a brick to allow entry of the burner. The idea could be called the brick pile table forge. Basically you use 8 insulating brick and make an 18"x18" table top with the bricks. Then on top of that you can pile bricks as you want to set the volume of the forge. If you wanted to create a forge that was bigger you wpuld need to drill some more burner holes of course. The advantage is that I could have the forge basically only the size of two bricks stacked on each other most of the time but I would have the advantage of being able to reconfigure the forge to suit the task and easily replace any bricks that become damaged. So I set up a tiny forge the size of 2 stacked bricks in internal volume and with only the 1" original black iron burner to heat and fired it up. I used a hard brick for the floor of the reconfigured floor to be more durable. The idea was sort of like frosty's variable volume forge with a bit less complexity.

Again the flames leaped out front and back for a good two feet. The forge got bright red to orange hot but not much hotter than that. This is despite varying the propane from 5 psi to 15psi.

I am beginning to despair of getting a propane forge good enough to reach welding temps but also of even reachign temps appropriate to do really good forging. Hitting metal when it isnt hot enough makes the whole thing much harder to get into. I still love to do smithing but I just cant figure this out. Is it the burners? The forge? The propane bottles? I have no idea at this point. I haven't been trying to invent anything new really, just filching other people's ideas and ad adapting them to my financial situation. Anyway. Any advice of a constructive nature would be appreciated.

I am at my wit's end here.

-- Robert

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I hear the angst in your post, it does seem like you have been through some frustration. After all you have put into your various projects you have posted here, it seems you might have been better off just finding a new or used manufactured forge with burners that would be ready to go right out of the box. If finances do not allow this, i can relate, however, the cost of suitable do it yourself materials can easily exceed the cost of purchasing a commercial outfit depending on how you go about it. It seems your main issue is getting your homemade burners to work properly. maybe you can post some good pictures and a description of how your burners are made (again) and you will probably get some feedback that will help. I got into gas forges like you by making my own and made 4 burners that worked (for forging, haven't welded with it)using info available on the internet; it is possible, but I am mostly using a commercial forge i bought from another smith as it gets to temperature quicker than the one I made and is easier to weld in. Homemade burners can and do work well but there is a narrow window that they have to be specc'ed at to make them functional.Yours don't sound as if they are made or tuned properly; pictures or a video would help us figure out why.
A closeup of your burner would be helpful; looking at the photo above it looks to me like your burner tube is too long. Also, the thermal mass of hard brick soaks up a lot of heat and takes a lot of BTU's to get up to temp.

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Building a home-made forge is trial by fire and can be very frustrating and time consuming until you get everything correct. Don’t give up.

If the burner works well when it is not in the forge but won’t work in the forge, the simple answer is back pressure in the forge is reducing the amount of air coming in from the burner. Those lazy yellow flames leaping out of the forge is an indication of not enough combustion air.

An atmospheric burner works because the velocity of the gas coming out of the orifice forces air in the burner tube in ahead of it and drawers in more air behind it. It works on very, very low pressure so anything that obstructs that air flow will starve the propane of oxygen. The flame is cool because of unburned gas looking for oxygen outside of the forge.

Try increasing the diameter of the burner tube.

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If still using the perforated air intake, you might consider enlarging a few holes and/or squaring off the forward ends. I discovered major turbulance choking off air intake because of too-narrow and rounded air intakes. When my flame was burning in the tube you could see the flame buffetting happening and it was pretty obvious that the jet was having to work pretty hard to get through the denser air.

Widenning the slots and squaring off the ends (and scooping them into the tube rather than being perpendicular) made a world of difference. I did the detail work with a dremel + orange grinding tip.

Also, I don't recall your tip placement, but when I slide mine forward (about 1/4" back from the forward end of the slots) performance improved greatly also. Pulling works better than pushing.

You may also want to buy some ceramic wool from Ellis. http://elliscustomknifeworks.hightemptools.com/inswool.html

and line the interior of the forge. If the problem is the time it takes to bring the castable up to heat, that would improve things dramatically. After that you could decide whether to leave it "as-is" or add a thin "hotface" of castable over it. The ceramic would act as a thermal break in that case, and you'll have a smaller diameter naturally.

Edited by kcrucible
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Robert, I feel your pain,
I have been following your posts on your efforts and I understand your frustration. I had similar issues with my first forge. It welded, but used a lot of gas to do it. Anyway, one thing I see is the shear mass you are trying to heat. I would take all but the floor bricks away and any extra bricks that you don't need. How long are you waiting to determine its not getting hot enough? Solid refractory forges take considerably longer to get to heat than ceramic wool liners. Solid holds heat better though. My first forge was a castable refractory 3" thick and took 20 - 30 minutes to get to heat.
Secondly, I can't see clearly what burner you have set up but if it isn't working well it could be a number of factors, as others have said. As frustrating as it may be, you may have to go back to square one. Find a design that is known to work (you mentioned Frosty's) and follow it to the letter. Don't deviate from the design except perhaps the orifice to suit your local altitude. Jets may need to be slightly larger at higher altitude. (Can't remeber how high you are; I used to live it Arvada and my school was in Broomfield). One final thought, I used the attached design (courtesy; Don Fogg) and only deviated in size of chamber, mine has 2" of wool and coated with refractory mortar instead of ITC, and size of burner tube. Instead of 2", I used 1.25", and used a "T" rather than an elbow. (No welding) It heats in about 5 minutes, forges at less than 5 psi and welds easily at 10 psi. Blown burners are so much easier to tune than naturally aspirated. Good luck.

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It is the burner still, that soft brick forge should get hot just fine. The soft brick has a high insulation capacity, the hard brick does not. Make sure there is an insulating brick under the hard brick floor. (the hard brick will eventually get to over 1000F on the back side and start to glow)

How long are you letting it run? As my little forge comes up in temperature the dragon breath goes down some. I also have a small exhaust at the back to allow long, narrow stock through. I also cannot even attempt for a welding heat till the forge has been on for a good half hour and fully up to heat, then I turn the gas up. I have had poor welding success because I think my forge runs slightly lean and scales up too quick.

I am also sure that living on a mountain top isn't helping you any.


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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.

...the flames leaped out front and back for a good two feet.

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.
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I have completed one of frosty's burners and it certainly is working great in the forge but it still isnt getting super hot. I can get it to a bright orange to beginning yellow fairly quickly but getting up to bright yellow or welding temps, I dont know what it would take. I upped the PSI to 15psi but then I started running out of propane.

I wonder if one of the problems I am having is the propane bottles themselves not letting me pull propane out of them fast enough.

Oh there was one issue. With the frosty burner the flare which was a piece of 1" ID pipe slipped on the 3/4, turned bright red and I imagine if I got the forge to welding temps, it would definitely melt.

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Your nozzle/flare/what ever should not extend past you refractory. In fact it doesn't usually hurt for it to be recessed 1/2" or more from the inside of the refractory. Again, how long are you giving it to heat fully? It may seemto heat quicly to a orange but take a while to come up fully. Once to get your propane refilled (many will recommend a larger tank or manifold mutiple 20#ers. You regulator is NOT a BBQ regulator is it? They don't have the volume required. One design I have seen is to use and gauged needle valve in favor of a regulator. You can get more volume that way. I think your on the right path. Don't give up. :)

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Zoeller sells a manifold kit for propane tanks, or you can make one up using off the shelf parts. If you pilfer a few grill regulators for the fittings and buy new hose you can have a manifold for reasonable money. I run 1 20# tank for 1 burner and almost can run it out in warm weather without a water bath. In cool weather I need a water bath or 2 tanks, and in winter it 2 tanks AND a water bath for each.

Shopping for bigger tanks, but they are expensive.

My nozzle extends past my shell about 1/2 inch where it is packed with wool to prevent flow outside. I have 2 inches of insulation in my forge, so the nozzle is 1 1/2 inch from the inside of the forge. The insulation is cut in a flare shape, as in a cone is removed.

Glad you are getting positive results. Sounds like you are almost there!


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Well frosty's burner seems to be working much better than all others i have tried. I have welded up the start of a table to hold my brick pile so I can get it off my fabricating table. My fabricating table could hold a car if you could get it up there but it is overkill for the brick pile. I thought about getting some lockable casters, putting some expanded metal over the cross supports (because since they are there we might as well have a shelf, and putting in some other things. It could be the beginning of something great. However, the heat of the forge is still task number 1.

I had thought of putting the burner through the roof in a downward manner as frosty did but I still have to solve the problem of the flare that would melt in there if I give it a chance. I thought of devising a flame holder since the flame for that originates outside the burner tube but I dont know if that would help. Even the flare coming from the side was absolutely red hot. I am wondering if a flare with a piece of female threaded pipe embedded in a cast flare of castolyte refractory would work.

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Your nozzle/flare/what ever should not extend past you refractory. In fact it doesn't usually hurt for it to be recessed 1/2" or more from the inside of the refractory. Again, how long are you giving it to heat fully? It may seemto heat quicly to a orange but take a while to come up fully. Once to get your propane refilled (many will recommend a larger tank or manifold mutiple 20#ers. You regulator is NOT a BBQ regulator is it? They don't have the volume required. One design I have seen is to use and gauged needle valve in favor of a regulator. You can get more volume that way. I think your on the right path. Don't give up. :)

Thanks for the encouragement.

No, the regulator is not a barbequeue one. I ran it for about 15 min before i started to run out of propane. During that time i dont think my propane PSI was reliable. I have three old 20# bottles so maybe I will try to manifold all three together. I have to check for safety first of course. One modification i made to the Frosty burner is that I used the much more gas tight flare fittings instead of compression fittings. As for the flare, it was about a half an inch from the edge of the brick, but not inside the forge. I will try and back it off even more.

What I need to do is figure out a way to hold the burners on the new table but that shouldnt be too hard. What i was thinkign was casting a 3" thick roof with castolyte 3000 degree refractory and then cover that with itc 100. I am also wondering if the dust from my soft bricks is hazardous and I might coat them as well.
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You mght try cutting your flare in the brick. Lotsa process burners work like that. They use different burner blocks for diffrent flame patterns.

I was able to achive welding heat using an 1-1/4 atmospheric burner. The fuel usage was out of site.
I switched to a blown ribbon burner, which is much more economical.

here's an easy blown forge that works.


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