Help with forge propane usage? Design?

C

cartierusm

Joined
Feb 23, 2017
Messages
69
So this is my friend's forge. He's not forum friendly; so I'm posting for him.

He runs through a BBQ size propane tank in about an hour.

Originally he was not using a regulator and had to turn up the propane all the way up to get welding heat. Now with a regulator he can't seem to get welding temps.

If you look at the pics you can see his setup. He doesn't know what blower it is, but it puts out a good amount of air.

The forge is 2" of kaowool, then 1/4" fire clay, and some unknown refractory cement (I think it's like satanite). Before adding the refractory cement and no regulator he couldn't get welding temps. The interior size is 21" x 6" x 7". He's using 2" pipe for the burners with a .068 orifice size.

Also when starting the forge if he has the air up too much or if the propane is up too much then it back burns into his burners.

The dragon's breath comes out about 5'.

What he's concerned about is the dragon's breath coming out so much, hard to get welding heat and running through too much propane.

Any help would be appreciated.

https://www.dropbox.com/s/1ssn3aexjao8szi/IMG_5704.JPG?dl=0
https://www.dropbox.com/s/iodle7aoudtd2ip/IMG_5913.JPG?dl=0
https://www.dropbox.com/s/31npup1zftwxewx/IMG_5914.JPG?dl=0
https://www.dropbox.com/s/5r62du605kznv5t/IMG_5915.JPG?dl=0
https://www.dropbox.com/s/wamqc5xc6vghi8k/IMG_5916.JPG?dl=0
https://www.dropbox.com/s/iwmekyos70r1noe/IMG_5928.JPG?dl=0
https://www.dropbox.com/s/h21hjz0iejp1i4g/IMG_5929.JPG?dl=0
https://www.dropbox.com/s/apxcunv77kg53vo/IMG_5930.JPG?dl=0
https://www.dropbox.com/s/y7uwymx4sf85nke/IMG_5744.MOV?dl=0
 
I'm of no help but I am amazed that he is going through a bottle an hour.
I can't see how it isn't freezing on him that quickly.
Interested in seeing others takes.
 
dragon's breath = bad setup, wasted propane
.068" orifice requires 40 PSI to produce 370k BTU for welding. That's just over an hour per tank. Does the regulator go to 40 PSI?
My guess is that you need some baffles inside the tubes to mix the propane and air better.
 
3fifty7 3fifty7 , you are correct, he had to switch to a different system because he'd get an inch of ice on the bottle.

@atlas, you're too are correct, LOL. I figured the same; that his setup wasn't mixing correctly. And you're right, when he did get to welding temps in the beginning he wasn't using a regulator just going from the tank to the burner with a needle valve, so full pressure.

He added a regulator, per my suggestion, as I thought not having one was a bad idea and might be leading to wasting more fuel. But as I said in the original post, now he can't get welding heat; or so he thinks.
 
If using a blower, you don't use a orifice. An orifice is to create a gas jet to draw air by the Venturi Principle. With a blower, you have all the air you need.
Just use the needle valve to control the gas flow. Most folks have the gas line connected to a 1/4" needle valve at the manifold. The regulator should run at a few pounds pressure with a 1/4" valve.

The air flow is normally controlled by a manifold gate valve, or by a choke plate on the air intake to the blower. As said, the gas is controlled by the needle valve.
Make sure the blower is supplying sufficient air. For welding in a large chamber, you need 150cfm at least.

There is a whole section in the stickys showing the build of a blown gas forge.
 
If your is blowing that much flame out of the forge and not reaching welding temp then your blower is not delervering the needed air. I discover just recently that CFMis not the only factor to consider in a blower. You need pressure to move the air. If you dont have pressure then once the air experance any resistance you CFM tanks. I allways thought my blower was good enough but little did I know what a real blower could do. If it was my forge the first thing I would look at was the blower. Using a good blower is absolutely amazing. Knowing what I know now I would not hesitate to buy a good $100-$200 blower from blacksmith depot. My forge is 1" of wool that's coated and at the lowest gas setting I'm able to run at a very nice temp. Bump the air and gas alittle and I'm easily forge welding temp.

So find out what blower is being used. Take a picture of it and post it here. If you can't post it ten send it to me and I will post it for you.
 
Within the burner tube, the speed of the mixture travelling toward the forge needs to be faster than the speed of the flame-front moving in the opposite direction. If it is not, the flame will burn back along the burner tube. The speed at which the mixture moves toward the forge only just a tad faster than the speed of the flamefront through the mixture is what sets the minimum operational mixture flow through the burner.

Your given dimensions of 21" x 6" x 7" would give a volume of 882 cu in for a "square" forge. The photos show a somewhat rounded construction and a 7" diameter x 21" long forge would give 808 cu in. For the 6" x 7" x 21 with rounded corners, It seems reasonable to assume a forge volume of "about" 800 cu in or a little less.

There are various rules-of-thumb for burner sizing, but 350 cu in of forge heated to welding temperature by a 3/4" burner seems quite common, 600 cu in on a 1" burner can also be found. These numbers suggest that you'd be marginal on 2 x 3/4" burners and that 2 x 1" burners would be more than necessary, but almost certainly workable. The burner output varies with the burner area, so 2 x 2" burners will have 4 times the area of 2 x 1" burners and 4 times the heat output.

In the case of a small forge with massively oversized burners, the lowest mixture speed that prevents burnback is likely to result in a heat input way in excess of that needed to heat the forge.

Sleeving down the inside of the 2" burner openings to 1" would probably go a long way towards solving the problem.
 
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