Gas forge - external temp?

[russ57]

G'day all
Just fired up a long term project, a small gas forge based of course on a propane cylinder, this one was 5kg I think - a little smaller overall than a 9.

I have 1" of ceramic wool with itc100 coating.
The burner is a mikey style, 3/4" tube.

The problem is the outside gets a lot hotter than I expected. Barely touchable after 3 or 4 mins, which was enough time to heat a 3/8 rod to bright red.

Normal? Not enough insulation? More itc100?
All advice appreciated..

Russ

-Russell

[AndrewOC]

G'day Russell,
sounds like a great project.
I'd suggest at least another layer of Kaowool; see https://www.youtube.com/watch?v=1DyeESQpac0
for what you can achieve with (4 inches of?) the stuff- a tin can that can melt cast iron!
good luck,
AndrewOC

[Master Splinter]

The rule of thumb that I have seen is that the wall insulation should be about one-quarter of the total diameter thick - so that's 25% insulation, 50% furnace area, 25% insulation.

See this for the best introduction to the entire 'make things hot enough to melt' topic I've found to date (pdf file)

The Hobbyist's Guide to Casting Metal--2nd Edition (print).pdf (http://prometheus-foundry.com/The%20Hobbyist's%20Guide%20to%20Casting%20Metal--2nd%20Edition%20(print).pdf)

[russ57]

I posted a reply yesterday but it seems to have got lost in the ether.
I guess I'll have to add a second layer with another coat of itc100.
I was just surprised by how hot it did get so quickly.
Ps, thanks for the link to the casting book... Very informative.

-Russell

[BobL]

The shell of my mains powered gas forge (http://metalworkforums.com/f266/t168547-building-natural-gas-forge-wip) is 12" in diameter.
It has a 2" layer of insulation so it has a 8" diameter cavity.

This is what happens after an hour or so with one torch operating at full flow.
http://www.woodworkforums.com/attachment.php?attachmentid=355617&stc=1
I can put my hand on the outside of the back of the forge for about the first 15 minutes or so of operations.
I generally don't run it for longer than an hour.

[DSEL74]

The guys that I know of all use 2" of Isowool, The isowool by the way comes in 3 heat rating as well as 1" and 2" thicnesses.

Then rigidiser and a layer of castable ceramic. to seal the wool.

I just fitted the isowool to mine today but haven't tracked down any itc100 or castable yet.

[Ueee]

Just use satanite Dale. My "little pig" is 6" od with 1" of wool and the hard face, yes it gets hot to touch but it also keeps welding heat no problems without using much gas. No amount of insulation is going to be able to maintain a difference of 1200 degrees for long without so.e kind of active cooling.

[DSEL74]

Ewan is Satanite a castable refractory cement

[Ueee]

Yes and you can also use it to clay blades for quenching to create hamons.

[DSEL74]

Nice