*** Rules Of Thumb for Forge Design ***
(For the 3/4" diameter Reil or EZ burners only)
*Do not use these rules for the Mongo series of burners*
If you want to design your own gas forge there are a few simple "rules of thumb" to keep in mind. These are not exact, and may not even result in a successful forge, but they are a starting place for designing your own propane forge system. There are a great many variables involved with any forge system, insulation "R" value, exhaust opening area, smoothness of burner penetrations, elevation, quality of forge and burner construction, jet diameter, tuning, etc., to name but a few. Any one of them can cause problems. To design forges using other burner types, use the BTU Calculator, along with the information in paragraph #1 below.**
1. You will need at least 450 BTUs per cubic inch of forge chamber volume if your forge is going to be able to forge-weld. Some would argue for a figure as high as 540 BTUs per cubic inch.
2. The "Reil Burner" will deliver about 135,000 BTUs at medium to higher gas pressures, and can be cranked up to almost 200,000 BTUs by raising the pressure to 20 psi or more. In the lower pressure range of from 1-6 psi, where I do most of my work, it will produce about 60,000 BTUs, or even a little less. Use the middle figure in any design calculations.
3. Shoot for a burner to volume ratio of 1:300 or less. Some smiths who are very knowledgeable would say a more conservative ratio of 1:250 would be safer and insure that your forge will be able to weld. To calculate how many 3/4" burners you will need just divide the total chamber volume of your forge, in cubic inches, by 250 or 300, and then round up. If you come out to a burner requirement of 2-1/3 burners, then you will need 3 burners for your planned forge volume. Always plan conservatively or you may end up with a forge that is too cold to forge-weld.**
It should be apparent that a 4' long by 2' diameter pipe forge will require far too many 3/4" burners to be practical. Keep your forge chamber as small as possible. If you can't build what you need with these burners you may need to look at the "Monster-Burner" as a possible alternative to heat your forge. I will not provide rules of thumb for them, so please don't ask. You can easily enough get a "propane jet diameter/BTU output table" and figure this information out yourself. These tables are available locally through your propane dealer or on the Net.
** The above information is assuming that you will build a well insulated forge, having at least 2" of Kaowool lining coated with ITC-100, not Satinite, on the interior surface of the chamber. A 3" lining of Kaowool would be even better, and would probably pay for itself in fuel savings over the long run. If you elect to use a rammable or pourable refractory, or bricks, you will have to address the lower insulation values associated with these materials. One option is a composite design, a pourable refractory shell for durability, inside a Kaowool shell for insulation value. These are more difficult to build but are long lasting and can work very well.
