Gas forge questions

[MickSCollins]

I'm thinking about building me a gas forge, but I want to get a good idea of what I'm looking at in terms of fuel consumption and efficiency.

What are the dimensions of your forge?
How many burners do you use?
What PSI do you forge at, and if you weld, what do you take it up to?
What size and how long does a bottle of propane typically last you?
How long does it take your forge to get up to temp?
Is it naturally aspirated or blown?

If there's anything else that could be considered pertinent, I'd be much obliged if you shared it.

[Mike Turner]

I have to gas forges one I use for shoeing horses and the other for knife making. My shoeing forge is a NC Whisper Mamma, I am not very fond of this forge at all but it was expensive so I use it. It is a venturi burner forge and just heating shoes I have to run it at 11psi. My knife making forge is a blown forge it is 18" long and has a 7" ID in 15 minutes it is up to temp. I used a 3000º castable refractory for this forge. I can forge weld 1 1/2" X 3" X 6" billets about 30 minutes after lighting maybe quicker but I like to soak my billets before I weld. I forge weld at 2 1/2psi and I use a 134cfm blower, I use a 100# bottle and it lasts me about a month with serious forging, this forge I can turn it way down for general forging. The castable yes takes a bit longer to heat but rebounds on the second heat very quick.

[Valentin]

MIKE: it lasts me about a month with serious forging...1 month(How big is the tank ?) mine only abount 15....20 Hours

[djhammerd]

Before you worry too much about efficiency, you need to decide what you are going to be heating in your forge.

The size, shape, and number of burners of the gas forge you build should be determined by what you intend to forge. If you are going to be making small stuff, a single burner (1/2" aspirated), 6" OD tube (maybe 8" long), lined with thermal blanket (and coated) will probably do the job.

If you are going to do heavy larger work, the forge would need to be bigger, with more, and larger burners. With aspirated forges, the number of burners is determined by the internal measurement (cubic inches) of the forge. If I recall, it's one 3/4" burner for each 320 cubic inches.

You obtain efficiency by using the right size forge for the job, and having the ability to adjust the pressure of the propane and the amount of air that goes in with it.

How much propane pressure you need varies with the size of the pipe, orfice, and whether you use aspirated or blown.

[looper567]

Originally Posted by Mike Turner

I have to gas forges one I use for shoeing horses and the other for knife making. My shoeing forge is a NC Whisper Mamma, I am not very fond of this forge at all but it was expensive so I use it. It is a venturi burner forge and just heating shoes I have to run it at 11psi. My knife making forge is a blown forge it is 18" long and has a 7" ID in 15 minutes it is up to temp. I used a 3000º castable refractory for this forge. I can forge weld 1 1/2" X 3" X 6" billets about 30 minutes after lighting maybe quicker but I like to soak my billets before I weld. I forge weld at 2 1/2psi and I use a 134cfm blower, I use a 100# bottle and it lasts me about a month with serious forging, this forge I can turn it way down for general forging. The castable yes takes a bit longer to heat but rebounds on the second heat very quick.

What size orifice is in the Blown Forge?
If it's .0625 (1/16") it will flow as much fuel at 2.5 PSI as an Atmospheric burner running a .040 orifice at 17 PSI. The fuel pressure can't be looked at as an indicator of efficiency without knowing the orifice size. Blown burners generally run larger orifices so naturally the pressures will be lower. My Atmospheric burners tend to run a tad on the lean side, so if anything, they can be choked down a bit. Blown burners are great if you have a good valve to control airflow, then the flame can be dialed in precisely, like with an Oxy/Fuel torch. Atmospheric burners will work very well also, especially in a properly designed forge. I have a 2 burner that will do cable Damascus all day at 5 psi. I avoid castables at all costs, very inefficient material. I prefer a dense ceramic for the floor (to withstand the mechanical wear) and ceramic board for the walls and ceilings. The ceramic board is 6 to 8 Times more thermally efficient than the castables. Another tip is try using a layer of ceramic blanket under the Dense floor to minimize heat loss through the shell floor. The dense and castable refractories act like heat sinks, they suck up all the heat until they are at temperature, and then they begin to radiate it back off, problem is, they radiate a ton of it off into the shell. They were never designed to insulate really, and today they are generally used as a "Hard Face" to protect the insulating ceramics (Ceramic Fiberboard and Blanket) from Chemical Attack in the harsh environments of the Steel Mill furnaces. IFB (Insulating Firebrick) is another good choice, it has excellent thermal characteristics, it's inexpensive, and is easily replaced in a properly designed forge.

[mtforge]

What are the dimensions of your forge?
It varies. The top is 10" x 15" with the front opening 1 1/2" I mounted it on a scissors jack and can raise it up to accommodate larger pieces. I raise it up and put fire brick around the side and back then lower it onto the bricks.
How many burners do you use?
One, I built in a spot for a second but never needed it
What PSI do you forge at, and if you weld, what do you take it up to?
Depends what I working on. 2# to 30# I'm full time and when I'm making 1/2" tent stakes I put in 7 to 10 and turn the heat up.
What size and how long does a bottle of propane typically last you?
I use a 330 gal. tank. It lasts a year
How long does it take your forge to get up to temp?
When I'm working smaller stock it may take 3 min.
Is it naturally aspirated or blown?
Naturally aspirated I make the burners myself. But after reading about the blown burners gas useage I might try a blown one to see how it does

[MickSCollins]

MT: The scissor jack idea is ingenious, I may just have to borrow it.

I work a large range of stock and some very strange shapes, so the ability to change the volume of the forge to match is ideal.

I didn't figure that the type of insulation would make that big of a difference, but it does make sense.

As to not worrying about efficiency, if you don't have time to do it right the first time, you've got time to do it again. It's a lot easier and cheaper to change the shape of something before you've made it than after you got it all put together and working. If you can make something in such a way that it'll save you a lot of money and hassle trying to fix it if you didn't, shouldn't you?

[ThomasPowers]

I have a 10" OD blown pipe forge about 16" long. 1 layer of 1" kaowool with a hard brick floor. It runs about 6-8 hours on a BBQ tank at a good high heat with the front "door" wide open for teaching a class.

I have a 9" OD 2 aspirated burners pile forge about 14" long that will run 8 hours on the same sized tank.

I have welded in the blown one when turned up; but have not tried it in the aspirated. I still use coal for my billet welding.