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Need help with propane forge


Rylan

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Hello everyone,

I have no idea if I am in the correct forum for this or not because this is my first time, but I picked what I thought was closest. I have recently built a 3 burner propane forge  8"X12"X24" long and I am having a bit of a problem. Long story short, I have diagnosed the problem and found out that the problem I am having is a build up of pressure inside where my burners are and no where for that pressure to go and in return I am not getting the Correct ionizing flame I need. Don't get me wrong, I am no expert by any means, the way I found this out is because if I blow through the forge with an air compressor, or even my mouth, I then start to get the correct flame I need. The only solution that I have came up with which might work or might not work, is to put a 90 degree flue on one end of the forge with an adjustment for the air to come in and go out. If anyone knows a solution for me other than completely rebuilding my burners, please let me know. Sorry for the not great pictures, I didn't know I would be posting this forum and am not available to take better pictures at the moment. Thank you all in advance.

 

Little more information, I am using half inch pipe until I get to top of burners, then it reduces to quarter inch. both top and bottom bell coupling is 1/2"x1.5" the nipples from top of burner to bottom of burner is 6 inches. Lastly, I am using a 30 psi regulator.

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It isn't unusual for three burner in a row to have a back pressure  problem. You would be better off with two burners. Perhaps, either shorten the forge, or remove the middle burner, and replace the two end burners with larger ones, if needed to keep the heat level up? Replacing the middle burner with a more powerful one might do the trick.

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DON'T USE IT LIKE THAT.

I'm no burner expert. Mikey is- one of the two most knowledgeable from my experience here.

But, you have open ceramic wool lining that forge. That is a health hazard. There's alot of information on the forumn here to help you sort it out- but I'd like to see you forging for a long time to come yet... not laying in a hospital bed unable to breathe in the next year or so.

It needs to be encapsulated in a refractory. The fibers from that will end up in your lungs.

There are many people here- worldwide who'll gladly give you tips and help getting it sorted out, they did help me.

My forge lining as a poor example-

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If an expert is someone who knows more than the average person on a given subject, than yes.

However, I prefer to let my "facts" standard or fall on their on their merits. It takes a whole lot of admitting mistakes to arrive on  solid ground; but precious  little self satisfaction to slide back into the mire. So, what facts are present here? It is a fact that back pressure is a common problem in forges with naturally aspirated burners.

Beyond this is speculation. It is logical that the middle burner will have more back pressure than either of the end burners. Logically two burners make an end run around this problem, by "simply not going there" (a favorite solution). Hopefully, increasing the flame size, or speed can overcome increased pressure in a middle burner; thus the suggestion of replacing it with a larger burner. this is only a possibility; by now means an assurance.

Looking at the photo, we see high orange incandescence, verging on yellow in a forge that is wide open on both ends. This photo says very good things about these burners, so no suggestion is warranted to change their design, or construction. So, rearranging the size and amounts appears to be the straightest path. I look forward to seeing his choice of answer.

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Mikey, I often tell people that I know a little bit about alot of things... but that I know everything about nothing.

To me- an expert is someone I judge by those very things, the experience to have made the mistakes, the wisdom to have learned from them, the knowledge to prevent them in the future- and the generosity to pass that onto those following in your foot steps.

You, and frosty both fall in that category as do many others here. 

Ryan I hope you get it sorted out, and enjoy the process you're delving into! I made the blunder of starting down the "bigger is better" path when i first built my forge. Several here gave me some great advice, and it set me up to start actually having some good results from my efforts. 

Like mikey- looking forward to your results.

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from my very limited experience with propane burned forges, I'd say the isolation needs to be thicker and covered (it really is a health hazard; the guys installing this wear respirators for a reason). Also; there is a relation between heath, flame, internal volume and gaspressure. I bet that forge would go a lot hotter if you doubled the isolation (and covered it with something to reflect even more heat); and covered the top half of the open hole on both sides. Or make doors.
It looks like too much heat is lost through the large openings on both sides.

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Hey everyone, thank you so much for responding. After looking into everything ya'll have told me I have a few more questions. I understand what you are saying Mikey about the forge possibly having too many burners, but that then leads me to the question why is it still not working when I only run one of the burners? Now, if it is because the burner is too small, would the solution to increase the burner be increasing the nipple size of the burner? And yes, I will absolutely deal with the ceramic fiber hazard, would the best thing for that be to coat it with refractory concrete?? 

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My response copied from another thread-

Generally, you want 2" of 8# wool for good insulation.

Coat that with rigidizer to stiffen the wool. Let that cure over nite. Google simwool rigidizer.

Spray your wool with a misting water bottle of plain water. Not soaking dripping wet- just a good misting to coat the wool- this is called "buttering" the forge,, and allows the refractory to bond to the wool better.

Then coat the rigidized wool with your choice of a good refractory. Satanite, kast o lite, mizzou... some choices. COVER ALL THE WOOL SURFACE.

Quick down and dirty explanation... there's more, but thats basics. Read the forumn threads a bit- there's tons of info here to do it safely.

Ryan- i used hellcote 3000 refractory cement. Its basically satanite. Anything that you're going to want to use would come in a powdered form. The stuff you get from the hardware store in a bucket- isn't gonna work in a forge... for long.

I got mine on amazon, its the brand hells forge sends with their forge kits to line them. Its rated to 3,000 degrees. It gets mixed with water, to a thick milkshake consistency and spread on the wool. You then let it cure over night til its dry to the touch.

Then, its fired up momentarily for about 30 seconds to drive out moisture. Let it cool down slowly, then fire it for a minute.... let it cool. Fire it for around 5 minutes or so... then you should be ready to run.

I've never used kast o lite 30 yet, but plan to soon. I do know that its a longer process and cures more like concrete in a slower time-frame with no heat cycles... 

if you go to your profile page/user control panel- you can add/edit your location and other info there...

That will allow anyone on the forumn to click on your name on any of your posts, and see where you are. Its useful to help give you advice on where to find things more local to you, or more technical stuff like what welder to buy for a us or other market. 

This is a world wide forumn with many smiths from all over... not everybody has the same possibilities for sourcing stuff!:unsure:

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On 1/4/2021 at 1:42 PM, Rylan said:

Little more information, I am using half inch pipe until I get to top of burners, then it reduces to quarter inch

Could this be a problem? Is 1/4" too small for a mixture tube to draw through enough air through? By the time it passes around mig tip nozzles- that'd be a fairly small opening yes? In effect choking the burners.

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Posted (edited)

I tried it with half inch pipe all the way and it wasn't working which led me to change to quarter inch in hopes to allow more air flow. So I still have no clue what the problem is

Edited by Mod30
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Been a while since i built a propane burner, but the 1/4" nipple is that what you are using as the jet? Or am i reading that wrong? 

I am no expert but i know what worked for me and 1/4" would be way to big. I used MIG tips that were, going on my old mans memory here, .060". 1/4" is .250" 

This is merely a guess on my part and i would like to see what the experts have to say. I would surmise that the 1/4" opening is not allowing enough velocity through the mixing tube. With out that velocity it is unable to "pull" the air through with it. 

One other question i have not seen asked, how much pressure are you using? You say a 30PSI regulator, are you running 30PSI or is it adjusted back. Again if memory serves you only need 8-12 PSI. If you have to increase the pressure that high that also increases the velocity which will explain why it is almost working like it is. 

Like i say i am no expert and i would really like to see what the experts do have to say about my theories.

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Posted (edited)

No, the jet for the burner is a pipe plug that I have drilled with a 1/6" bit. The quarter inch is the pipe size of the plug, and the other pipes that are inside of the top bell coupling. The pressure that I usually set it on when I fire it up is 10 psi. The reason I switched to a smaller pipe was in hopes of allowing a more venturi effect for more airflow.

Edited by Mod30
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Most likely your nozzle opening size and position are the culprit.  1/6" is far too large for an effective burner of the size pictured.  The larger orifice requires excessive gas flowrate to induce any air, which leads to the poor mixture proportion you originally indicated.  I recommend that you tap the existing pipe cap (if it is drilled exactly on center) and fit it with a 0.30 MIG tip then move the pipe up and down in the bell reducer to achieve a proper neutral or slightly reducing flame.

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I hope you meant 1/16". 

So i obviously misread that and went with it. Just got up at the time and having my "morning" coffee makes me a little wordy at times. I work 2nd shift so 1 PM is morning to me. Like i said no expert i have not used propane in a long long time. My propane forge has become a home for spiders.  

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Welcome aboard Rylan, glad to have you. If you put your general location in the header you'll have a chance of hooking up with members living within visiting distance. Believe it or not a few folk have turned out to live within 20 minutes of me. Lots of information is location specific, even propane varies by location, especially country.

I see a couple potential issues that jump out at me: #1, Size, your forge is huge, I roughly figure more than 2,000cu/in volume IF the dimensions you list are accurate. Telling us the shell size is wasting time, I stopped doing arithmetic for folk long ago. The only dimension that counts is the cubic inch volume and shape of the flame chamber. If the chamber really IS in excess of 2,000cu/in it needs three each, well tuned 1" naturally aspirated burners preferably ejector type. 

Don't sweat this, it's mostly a matter of getting your jargon straight. There is a language of words, terms and usages that allow folks to discuss a subject without having to spend more time explaining what they mean than exchanging information. I'm not trying to give you grief but we need to start talking the same jargon. Yes?

#2 As Mike says the center burner is fighting much greater back pressure than the outer ones. I don't have much to add for now.

#3 Your burners are aligned straight at the far wall, floor in this case. Being such a deep narrow chamber the flame MUST disperse in only 3 directions, two of which deflect it back at the burners. This REALLY causes back pressure. You can alleviate this, at least partially, by aligning them towards one side so the flame forms a swirl in the chamber rather being blown straight back. At this point nothing changes the chamber being so large and long.

You have already diagnosed the back pressure issue I'm just tossing in what I see are causes. 

#4 (This maybe should be issue one but the others are major so . . )The burners are WAY too small and their ratios are far enough off ideal as to be detrimental. The bell reducers you are using for intakes are good. The mixing tube length is way long, a mixing tube should be 8x it's ID. 8x 1/2' = 4", not 6". The excess length reduces induction through skin friction in the tube. This forces you to use a smaller propane jet at a higher pressure to compensate. This means the burner is delivering less fuel air mix into the forge per second. Less HEAT. Yes?

The fix is as easy as replacing the 6" nipples with 4" nipples and retuning the flames.

The real issue with using 1/2" burners is heat output, get them perfect and they have the capacity of heating about 150 cu/in to welding temp. Doing a little head math I figure you'd need what 15 ea. 1/2" burners to bring 2,000cu/in to welding temps. Or 7 ea. 3/4" burners, OR 3ea. 1" burners. 

 

I highly recommend you build a reasonable sized forge. Especially for your first one. Don't think you're unusual, most folk myself included build too large forges, heck I have one on my shop floor that's on a scale with yours. It's only saving grace is being variable size and geometry in nature. It has 4 ea. 3/4" T burners of my design. The T burner is a jet ejector type A induction device.  Anyway, a sad fact of the blacksmith craft is we can't effectively forge more than about 6 linear inches per heat. Heating steel without refining the crystal (grain) structure by forging it encourages crystal (grain) growth and embrittlement. This is especially true of high carbon steels and high alloy steels can be more touchy about poor heat management.

Don't sweat it, most of us who've been at this a while have too large forges collecting dust in out of the way corners in the shop. Join the club you're in good company. 

The manifold supplying propane doesn't need to be anywhere near as large as yours. I supply 4ea. 3/4" burners through 1/4" copper tubing after a short 3/8" iron pipe manifold, valves and fittings. My burners have never starved for fuel even with all 4 running at max. Having so much pipe in your intake bells is blocking air flow and reducing output. 

You've made a nice build your shop skills look  pretty good. You just need a better handle on how forges and burners work to tune your design.

Some questions to ask yourself are: What do I want to make? What's the smallest size forge that will do what I need? What shape does the forge need to be? Do I want even temps through out the forge OR do I want a hot zone two cooler zones? 

Remember efficient and effective are two related but very different things. For example one of the guys in our club does almost all his work in forges under 120 cu/in, his large forge is 240 cu/in. The smaller is powered by a single 1/2" T burner and the larger by two 1/2" T burners and both are SCREAMING HOT. As in melt your project if you don't pay attention HOT. There are no doors or thermal baffles closing off the ends either. They're so hot because they are well below the capacity of the burners heating them. A single well tuned 1/2" T burner will bring approx. 175 cu/in to welding temp and a pair 2x the volume. 

It's not some secret, it's simple arithmetic. 

Frosty The Lucky. 

 

 

 

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Hi Frosty,

Thank you so much for your reply. I now understand how much of a mistake it was for me to make such a big forge. Since I have already been through so much trouble of getting that forge going, I would like to keep the same shell. Now talking about the burners, aligning the burners to one side of the forge instead of on top in my mind would not allow enough heat to get on whatever I am forging because the main heat would be on the side of the burner and not the floor? Second,  since we have stablished the problem of getting the correct flame is the back pressure, would welding some sort of 90 degree flue with an opening and closing act as an exhaust to help with some of that back pressure? Please let me know if their is something else I am missing and I look forward to hearing back from you.

 

Thanks,

Rylan

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This type furnace is called a "reverberatory furnace", the flame heats the furnace walls and radiated IR heats the steel. Google hits some good explanations. 

No, a flue won't help, the bulk of the back pressure is caused by the flames blowing into a pocket, the center burner getting the worst of it. The open ends of the forge are more pressure relief than a flue can provide unless you make it silly tall. 

You haven't made any worse mistakes than most of us have at one time or another.

One last piece of advice for now. Don't paint yourself into the corner of thinking you need to use a thing because you have it. I can think of other good uses for that piece of rectangular tubing than as a forge shell. 

All a forge shell has to do is contain the liner and support a few lbs. of work and burner(s) in a stable manner.  Before I knew about the breathing hazard represented by Kaowool I had a largish cylindrical forge with a chicken wire shell and it worked a treat. It was also a test bed until I learned what volume and shape worked well with the early T burner. My first T was a 1" and easily melted 1/2" square stock in about a minute. 

Ancient history. My point being the shell doesn't need to be thick, my recent forges have been 14ga. because I have it, I'd much prefer them being 16ga. maybe even 18ga. My last cylindrical build was stainless steel stove pipe and it's still on the job in the  fellow's shop I built it for. 

My first cylindrical? Why yes it's a piece of 10 1/2" x 3/8" pipe and just the shell weighs about 30lbs. It only has 1" Kaowool outer liner with 3/4" of Pyramid Super, a 4,000f phosphate bonded plastic refractory. No longer available <sigh>. That forge is 700 cu/in powered by the first effective T burner in 1". I haven't lit it off in a long time, it's NOT an economy forge and it's a beast to move. 

Sorry for the ramble, I just got up and the coffee is starting to come up to acceptable levels. Don't let me or anybody overload you on information, this post is a good example of a lot of stuff you don't really need to worry about to make an effective forge.

Frosty The Lucky.

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I have been doing some more research, Could the problem possibly be fixed by just changing my orifice to a smaller Mig tip? Maybe like a .035 " tip? It is currently a 1/16" hole.

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Laying your forge on it's side has no effect on propane flow, pressurized gas doesn't care about gravity.

YES, lose the 1/16" orifice, it's WAY too large! I thought Mike was pretty clear about that but I'll reinforce the advice. 

I started using mig contact tips in burners to make them easy to change while I was tinkering early on. It was immediately apparent they worked much better than a drilled hole of the same diameter. Mike calls it an "accelerator effect" I thought of the long tube as refining the gas into a laminar flow making for a more uniform expansion cone in the mixing tube. I'm pretty sure we're just using different terms for the same thing, Mike's reasoning is sound. 

Anyway, a mig tip is WAY better than a hole and oh goodness yes 0.035" is within tunable range, where 1/16" or 0.0625" is outside tunable range. At least in my experience it's too much propane to tune to even close to a neutral flame. 

Frankly it's rare to see someone put larger than a 0.023 mig tip in a 3/4" linear type burner but a 0.030" will work even if it's touchier to tune.

Have you looked at making a T burner? They're much easier to build and get right than linear burners and more efficient. There are pretty complete step by step directions posted here, and the designer can be coaxed into giving you a hand.

Frosty The Lucky.

 

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23 hours ago, Frosty said:

YES, lose the 1/16" orifice, it's WAY too large!

 

Hey Frosty, I had one more question. So I decided obviously I am going to change to a MiG tip, I do not know how I am going to attach that to my burner though. Is the MiG tip able to thread into a pipe coupling or do I need to drill and tap a hole? Which is the best way to attach it? 

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