new wool on Hell’s forge

[ghost blood]

Aloha from hawaii, 

I'm about to redo my Hell’s forge 8” square tube forge.  im going for more efficient and hotter temps.  it came with 1”wool.  i’ve worked that lining pretty hard and recoated with refractory many times. its old and tired now so...  my question is if i put 2” of wool on the sides and 3”on top 2”on the bottom i get something like 3.5* 3 inches hole size, will that mess up my forge heat in any way?  i’ve seen mini forges with small chambers, but would a 3*3.5*18” chamber be a bad size? thanks very much, i tried to search for similar questions, sorry if this is a repeat

[Frosty]

Welcome aboard glad to have you. If you'll put your general location in the header you might be able to hook up with members living within visiting distance. Just telling the forum in one post isn't gong to stick in our memory once we open another one.

How many burners are you using? That's crazy long and narrow. That's less than 200 cu/in so a single 1/2" NA burner produces enough heat but it's not going to be anything like even. I'm not getting my calculator out but I figure you'd want four 3/8" burners spaced along it at least.

It may be a repeat, we see similar questions regularly, just not so extreme a ratio. I don't know how you're going to put work in without tearing the liner up. 

What do you need such a long narrow forge for? 

Frosty The Lucky.

[ghost blood]

thanks for your reply. 

i don’t have good any reason for a long narrow forge.   thank you for putting that into perspective. 

i wanted to have as much wool in there as possible so that i in theory could use little propane as possible.

i am now thinking of cutting an old 20 gallon propane tank to 16 inches long and putting 3” of wool inside.  if i put a flat floor on that with kasolite and wool then my chamber would be roughly half of a 6” circle x16”.  my calculations give me 464in cubed

would you say that 2 3/4 burners would work for that shape and size forge chamber?  

thanks so much, have a great day. 

[Frosty]

I don't have the measurements handy but a 20lb propane bottle makes in the range of 300-350 cu/in chamber. 3" of kaowool doesn't make much difference, after 2" the point of diminishing returns is on you. 

You're forgetting the kaowool and Kastolite on the end walls so subtract about 5" of length. 

A flat floor is nice, feather the edges of a strip of Kaowool so the sides meet the curve smoothly and plaster it in with the Kastolite and it'll be under 350 cu/in. A single well tuned 3/4" NA burner will bring it to welding temp. Or, if you want a more even temperature in the forge, two 1/2" burners will do it nicely. 

Rigidize the kaowool as you lay it. Don't forget to rigidize your ceramic blanket insulation. It's important, first because you don't want to be breathing loose fibers and secondly because it will provide a much better base for the Kastolite rigidized.

Frosty The Lucky.

[ghost blood]

thanks, i really appreciate your response. 

 

[Latticino]

Please recall that it is also possible to have too large a burner for the forge chamber size.  Each burner has a characteristic forge volume as well as flame length for a fully developed flame to burn properly.  If your chamber size is too small you will have a lot of difficulty keeping any flame burning inside the forge.  If the flame path is overly restricted, too short, you will have a flame that directly impinges on the forge wall to the extent that it does not burn as efficiently and you will see a dark circle on the wall opposite the burner in the center of the heated area.