How long will a 20lb. propane bottle run a small forge. By small, I mean something that would be no larger than to heat 3/8" stock or smaller. I've only used coal/coke. Any input would be greatly appreciated.
Posted 07 December 2013 - 01:39 PM
How small a small forge? Just to heat the end of a 3/8" bar is a very different forge than a forge to heat 3/8" steel bent into a helix.
Anyway my small forge can run at non-welding heat for about 12 hours. It HUGELY depends on how good a burner you have. I have a burner from Stephen Gensheimer that radically reduced gas consumption in my teaching forge compared to my previous burner.
Posted 07 December 2013 - 06:35 PM
3/4" burner, coffee can forge - 8-10 hours at non-welding heat. Probably 5-6 hours at welding heat.
Posted 10 December 2013 - 05:38 PM
I've just weighed my cylinder before and after a day of playing with a new burner in my mini-forge.
The forge chamber is just over 2 1/2" diameter and about 12" long, so around coffee-can forge sized. I weighed the cylinder at 80lb before and 74 lb after, for 6 lb Propane used (possibly 7, as I was using a cheap luggage scale) over 9 hours of continuous running at 10 PSI (measured on a cheap gauge).
I can get temperatures from 830 degC/ 1526 degF to 1245 degC/2273 degF at 10 PSI just by adjusting the choke. The burner uses a 1/2" industrial Venturi Gas mixer made by Amal.
I was trying to get the full range of useful temperatures from Heat-Treat soak temperature at just under 800 degC/1472 degF to welding at around 1300 degC/2372 degF, or maybe a little higher, without having to adjust the regulator. I couldn't do it.
Welding temperature needs more pressure; 60 PSI will get over-range on my type K thermocouple, which tops out at 1370 degC/ 2498 degF, though I've not tried welding in this forge because it is lined with 2" of Ceramic Fiber and flux will kill it.
A 20 lb cylinder could be expected to last over 24 hours forging on a similar setup.
Gas consumption varies with the square root of the pressure, so 6 times the pressure would use almost 2 1/2 times as much gas, which means 20 lb should last 10 hours plus at welding temperature.
I've used a similar burner in a scaled-down version of a Don Fogg drum HT forge, made from an 18" length of 10" pipe and that will hold HT soak temperatures and go to forging temperatures by adjusting both the choke and the pressure, but it will not reach welding temperatures, even at 60 PSI.
Posted 10 December 2013 - 07:52 PM
Thanks for the input. I have considered a small gas forge, but have never used one. I wondered about the cost to operate one. A very small one would do all I am able to do anymore. I don't even forge anything larger than 3/8" stock. I still enjoy forging small knives, hooks, and other small items. I've only used coal and coke.
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