Been thinking about it for years...

If portability is important, which it evidently is then kaowool is going to be the way to go. A thin poured refractory furnace will not be durable enough to take alot of jostling around. Think eggshell. A thicker furnace will be quite heavy- no getting around that. My heavy refractory furnace is on wheels but I never move it. It lives under a 55 gallon drum. My environment allows for that but not everyone's does.
I appreciate Bonz persistent enthusiasm.

Pete

 

Bonz, I tried this suggestion back on page 1. He's in Norway.

 

Pete: I agree, with a poured liner you can't go too thin. Luckily I'm using a solid tank, I didn't measure it when I cut it open but it's probably 3mm thick. And a backing of leca/fireclay should give additional support. I think I'll start with some small scale tests just to see how it behaves. They're claiming 60-65MPa cold crushing strength after firing at 110°C, that's actually decent compared to regular cement.
As for portability, it's so-so critical. It will probably be stored at the site under a a tarp, but I need to be able to move it a bit around on uneven surfaces.

 

I'm dragging my feet a bit when it comes to the furnace, I have enough on my plate right now. But I've started making a small flask (6x8x3" each) and plan on copying this for alignment:
http://forums.thehomefoundry.org/in...dier-flask-alignment-hardware.527/#post-10483
My first casting will probably be a couple of lead mallets, those are always handy to have around the shop. Anything special to watch out for when sand casting lead? I've cast plenty of lead bullets etc so I'm aware of the toxicity etc.

 

Lead is so low temp, you could cast your mallets in a hollowed out chunk of wood. Silicone works good too, but can get expensive.

 

@Jason: True, but I figured it would be a good place to start learning sand casting without burning up the flasks (or the garage). Later I might cast a metal mold for the job...
@Jeff: Thanks for the heads-up. I've already cut some angle iron into brackets, but if I run into problems I'll try wood.

 

Jeff: One possible cause could be the use of angle irons. The inside is not parallel to the outside, which could easily cause the pin to be off even if the hole is straight and true. Threading the angle iron and locking it with a single nut on the outside should solve that.

 

Here's todays results:


Getting everything straight is a matter of having the right tool for the job:


I suspect it's a bit overkill but I prefer that to half-assed work that fails at the worst time possible.

 

And here it is:

 

Progress is slow at the moment, too many projects that needs to be finished before I can put all my focus into this. In the mean time I try to work on the design.

One thing I'm not quite sure of yet is the burner size/capacity. I guess it boils down to how fast you need to melt stuff, but I'm sure you guys have some rough rule of thumb I should know about. I found this nice PDF covering the design of atmospheric burners, so all I really need is a ballpark figure (BTUs/pounds per hour) to get me started.

 

I had to do some small "forging" for some tools recently, and the coffee can furnace I made with fireplace mortar isn't really any good. Sloppy torch placement and high thermal mass. So I'm experimenting with vermiculite/sodium silicate for an improved version. Anybody here played with that stuff? It's made commercially for temperatures up to 1100°C. Seems to behave decently at a wide density range, the more you work it the denser it gets. Permeability seems low though, it dries very slowly in thicker layers. Perhaps it could work as insulation on the big furnace with a thinner cast refractory hard face, no? Especially if I can make it into prefab molded bricks.

 

I built a forge a few years back. I used Kaowool and spread on the Mizzou. I don't know if you do forge welding, but consider a replaceable firebrick floor section in your next build if you do.
If you want fast heat up, Use Kaowool with satanite smeared on it. I did this same design on a glory hole recently. It's fast, easy, cheap and works really well. To add strength to a small forge, again, I would recommend a proper replaceable fire brick floor. Mizzou is very strong stuff and you could form in into replaceable prefabbed bricks. I would shoot for around 1/2"-5/8" thick sections. One bag of Mizzou and you could form enough bricks for 3 little forges easily! Wrap the thing in kaowool for added insulation.

Never mind all of this. I forget you are in Norway. Stick with Satanite and Kaowool with a brick floor.

 

Nah, those products are too much work for me. I have a supplier for castable 1500C refractory, but that's about it. I could do a solid cast liner, but I won't be doing long runs. That makes low weight and thermal mass far more convenient. So far I've focused on the LECA-angle, but the vermiculite/waterglass-system show some potential.

As for the mini-forge it's for one-offs made from stuff like hex keys or 3mm silver steel (i have a few meters of the stuff). I have a small heat treatment furnace as well, but that's for more critical stuff.

 

Here it is:

A great improvement over the last one, but I can't imagine making a full size furnace from it.

Update:
It's definitively not refractory enough for sustained use, I see a lot of glazing after heating it to a bright yellow. But it seemed to slow down after a while, so it should work fine for it's use (simple "eyeball" hardening of makeshift tools).

The insulating properties makes up for any other drawbacks. It heats up in seconds and is cold to the touch at yellow heat.

The material is also extremely messy to work with. It can be kneaded into a spongy paste, but it has a "slimy" texture and sticks to everything within visual range.