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Jason Fry

huffing at high temp?

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I've got a 3/4" burner built on Mike's design, but it has been a couple of years since I put it together.  It'll get to welding heat in a roughly 300 cubic inch chamber, and runs ok from about 5 on up to 12ish PSI.  Haven't pushed it higher than that.  It tends to want to huff a bit, like it's back burning or something, even at 10 PSI and welding heat.  The choke tunes the flame just fine as far as oxidizing/neutral/reducing.  Any ideas on the huffing?

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It's probably intaking exhaust from the forge or perhaps it's inserted to deeply in the liner. You might have to mitigate the situation, I use a deflector on the openings on my shop forge and designed the ribbon burner intakes to be low and well behind any forge openings.

Avoiding exhaust is a solid reason for horizontally oriented or even updraft forge burners.

Frosty The Lucky.

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You could try turning it up. Huffing is often a result of the flame speed through the mixture being faster than the mixture speed along the burner tube. Flame speed tends to increase as the temperature increases. Increase pressure and the mixture speed should increase, maybe enough to stop the huffing. It might not work but it’s easy to try.

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Could be, Frosty.  I can sure check those variables.  Currently the burner is in about a 2.5" opening in the bottom of the forge, but the opening is unfilled.  Could be exhaust, alright.  Also could need to be further back.  Currently the nozzle is flush with the inside of the forge.  Also could be, Tim.  That's one of the first things I've tried in the past.  Turn it down till it huffs, then turn it up a little, and there's the minimum it'll run.  This seemed to be different, though, as I was running at fairly high pressure and had been running over a half hour before it started. Even so, may try cranking it up a bit more.

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how new is your refractory? Any moisture in the refractory or insulation will leak steam until it is eliminated; that would be consistent with what you are describing; just a thought...

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Could be, Mike.  This is the cast forge from the other thread.  It had run about an hour and a half total before the huffing started.  I did two short 20 min or so heats that pushed off a lot of steam, but that was with the other burner. 

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I have made lots of casting furnaces with two-inch thick refractory linings and never managed to drive all the chemically locked water from them until I turned the refractory yellow all the way through to the steel shell. Furthermore, the outer layer of refractory will regain moisture from Seattle town's air until that is accomplished :rolleyes:

Just a little friendly advice from the REAL rust belt :D

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With the burner nozzle flush with the inside of the forge I'm thinking it's getting hot enough to pre-ignite the air fuel mix in the nozzle heating the tube to the point the rate of propagation (flame front velocity) is higher than the velocity of the fuel air mix.

Pull your burner back till it's only 1/4" inside the liner. If that solves the problem you'll need to apply a hard refractory flame face to the burner port and perhaps reshape it as a tapered nozzle.

Once my hard liners are cured and fired I couldn't care less about a little moisture in the Kaowool, it'll dry right out. 

Frosty The Lucky.

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I bet we have 15% humidity on a wet day here :)  I think you're on to something there, Frosty.  It was worse when the forge was really hot.  I'll try the nozzle further back and see how it goes. 

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Yes, please let us know how it works. I'll keep my fingers crossed.

Frosty The Lucky.

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Haven't fired it in a couple of weeks.  Building that power hammer is taking up all my time.

Yes 20 lb, but no frost.  No moisture in the air to speak of.

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Alright, forged about four hours today. Welded some Damascus also, very clean welds. Huffed intermittently all day running at 10 psi. Pulling the nozzle past the edge of the forge wall, further from the chamber, has no impact. 

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Huffing is normally a sign that your gas pressure is too low, or that there is an obstruction somewhere in the gas passages; usually in the gas jet.

also, the larger the gas orifice is the higher minimum gas pressure will be; below minimum pressure, ANY burner will huff. what are the orifice diameter and the inside diameter of the mixing tube?

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Could the position of the mig nozzle relative to the air intake impact this problem?  I have slack to move the nozzle forward or back in the tube. 

Took it apart and verified no clogs or junk in the nozzle. 

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If you change the position of the mig tip it will most likely affect the fuel to air ratio and therefore the forge atmosphere.

Intermittent huffing at moderate to high pressure suggests to me a breeze affecting the inlet air flow, recycling exhaust gases, or a pulsing/temporary decrease in gas pressure.  Do you have another regulator you can try?

Just to sort out the problem you could also try a needle valve with no regulator to see if that's where the problem originates.  I do not recommend eliminating the regulator permanently though.

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Those are all good points, Buzzkill. He should also try using a smaller MIG contact tip, on a temporary basis, to change mixture flow speed, to see what happens.

A flame photo would be helpfull in figuring out just what is going on.

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I'll try and capture a flame pic.  Also have a couple of different sizes of mig tips around, may try a smaller and see how it goes.  I am 100% sure part of it is wind, as I've observed that on multiple occasions.  Still, seems to do it even when it's not windy.  

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