forced air forge tuning questions

E

EricFroh

Joined
May 9, 2021
Messages
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Hi folks. New here and we are beginners. My wife and I recently bought a nice anvil and home made propane forge from a bladesmith who is retiring. The forge was built awhile ago and we're having a hard time tuning it to get the proper burn based on our internet research. Here is a pic of the forge and set up - I think it is pretty straight forward - hair dryer blower, with shut off valve. Propane entering with both shutoff valve and needle valve (1/4"). 1" pipe into forge.

see if this works for the pic ...
https://scontent-lga3-2.xx.fbcdn.ne...=1a0bb9232bf8f27cf3281e3a8ac151a1&oe=60BBB242

Here is our problem. We turn the hair dryer to low. open the needle valve all the way up - set the regulator to about 8 lbs, and fire it up. It burns very rich - large flames billowing out the door and it appears that all the "burning" is occurring outside the forge - so, for example, the paper I used to start the forge is mostly unburnt by the time I turn it off. We've adjusted the air intake up and down (up just means larger rich flames out of the forge) and ditto with the propane (adjusting it both at the regulator and at the needle valve)

See if this works for the video...
https://www.facebook.com/video.php?v=10219021576308127

Any thoughts as to what we are doing wrong? Thanks for your advice and hope I pasted this in the right spot.
Eric
 
You need a lot more air !

It looks like you are not getting any air flow and pushing gas through an open 1/4” pipe.

With the gas turned off and the air on can you feel the air blowing through the forge ?
What kind of tip is on the end of your gas line ?
 
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That hair dryer doesn't look like it provides anywhere near enough air. You might not be getting enough mixing of air/gas either. The propane "should" be injected into air stream right after the blower to allow the gas to mix with air better by making that elbow turn. The pipe between the elbow and forge body should be perhaps in the 3/4" to 1" diameter.

Here's a blower that should work good: https://www.amazon.com/dp/B071NQDNRK/

Did that forge with for the guy you got it from with that hair dryer?

Lucky man - your wife is interested.
 
You have a VERY rich (fuel-rich) mixture. Depending on how you view it, that means either not enough air or too much gas.

The first thing that jumps out at me is the "We turn the hair dryer to low. open the needle valve all the way up."

Without details of the hair dryer, it's not clear what "low" consists of. In many cases, there is only one fan speed and "low" just refers to the heating element. If there are different fan speeds, you want the fastest.

You don't want the needle valve fully open. You may not even need 8 PSI upstream of the needle valve. I'd try 2 PSI, which is a quarter of the pressure and should give around half the gas flow on the fully open valve (flow varies as the square root of pressure for simple jets). Once you have it lit, screw in the needle valve fairly gently to try to get the Dragons Breath down and the flame burning inside the forge.

It is much easier to tell what is going on if you do it in the dark.

As above, was the forge originally used with the hairdryer? If so, did it actually work? That looks like a big reduction in area between the hairdryer outlet (2") and the inlet to the forge (1", maybe even 3/4"?).
 
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Most blown burners run at a lower pressure. I use 1 to 3 pounds at the regulator. You can use up to 5 pounds on some burners. 8 sound really too high.
The needle valve is the way you control how much gas goes into the forge chamber. Start with it closed.

Here is how to tune the burner:
Set regulator at 5PSI with the needle valve closed
Turn on the blower
Close the air manifold valve about 3/4 closed
Stick a propane torch ( or some other flame) in the forge opening and slowly open the needle valve
Once the forge lights, open the needle valve until the flame gets rich
Open the air valve more until it gets lean
Repeat gas/air increases until the forge is running at the desired heat level
 
Too much propane. Stacy nailed the lighting procedure, as always. 100,000 BTU worth of propane only needs about 15 CFM of air, so that likely isn't the problem. Put the fan next to the gas injection so they begin mixing. A small orifice around 1/16" should let you control the propane volume at the regulator instead of the needle valve, and will create a jet for mixing the propane with the air in a shorter distance. With 1/16" orifice, you need about 8" of mixing tube. Always let the fan run until the forge cools off, or you will melt the fan. Or you can just remove the burner when done. Or you can stick the fan a long way from the chamber after an elbow and leave it connected. That's the reason why you normally see a long tube between the fan and the chamber.

Like they say, there's more than one way to skin a cat.

Here's mine, 100k BTU and a very small variable speed 12v centrifugal blower.
Graham-Forge-9-1200-x-960[1].jpg
 
thanks guys - all your directions were perfect. Worked like a charm ... until our 20 year old hair dryer crapped out, lol. I think we'll invest in the blower recommended above. So, again, thanks. And yes, I'm real lucky with my wife. She is awesome.
 
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