I built a new 'roaring furnace'. My old one made from Mizzou concrete takes up too much heat which prevents heating it up much.
So I ordered a 60 liter barrel (56cm/22" height and 36cm/14" diameter) and made a furnace of it.
I use only Kaowool instead of 'traditional' refractory. The floor is lined with YTONG cell concrete of 5cm /2" thick and a plinth of 10cm/4" diameter and 7.5cm/3" high in the center of the same material. This is all covered with a single 1" layer of Kaowool and a graphite pad on top of it to prevent sticking the crucible to the plinth.
The inner walls are a single layer of Rockwool and the outer layer and two 1" layers of Kaowool. Finally, the inner diameter is 23-25cm (9-10") which fits even a 1 liter crucible (I have one of it, rest are 0.5 liter ones). The inner height is 30cm/12", with plinth under it, the top of the crucible is a few cm below the top of the furnace.
The lid has two layers of Kaowool which are kept inside by bending the cut off top and the center hole inward. When cutting off the top of the barrel (about 13cm/5") which is the lid, I cut perpendicular vertical cuts of about 5cm/2" to allow them bending inward which holds the kaowool inside. Moreover, I'll bend it in the furnace body only 45-60 degrees and in the lid 135-120 degrees, so it appears a bit conical which helps preventing sideways venting.
The top hole I'll use a similar approach: cut 4-5 10cm/4" long cuts in the center which have a star-like appearance initially with the angle grinder and then bend them inward for holding the kaowool in the center and leaving the exhaust hole in the center.
I'll leave the original hole at the rim of the lid barely covered with kaowool to allow an extra peephole for e.g. pyrometer access.
Furthermore I'll use two handles made of rebar with M10 bolts welded to it and mounted on the lid with corresponding nuts + washers.
The burner hole is about 10cm/4" above the (gross) bottom which is about 3cm above the inside bottom. I cut this out the same way as the exhaust hole and bending it inward, but then elliptically because of the tangential anticlockwise burner entry.
I use a propane burner with forced air which I already have (see photo).
First fire failure
Unfortunately, the lining melted like plastic at the first fire, it was not 1500°C rated as expected. So I used the old Mizzou furnace built in 1992, which is 1650ºC resistant, but not well insulating. I put it inside the insulation wrapped within the Kaowool which then will not be heated above 1200°C. The first (second) fire succeeded and melted some brass.
Photos of building of the furnace June 2018
The plain barrel just received
This is how the burner will enter the barrel
The grooves cut for folding down later
Grooves for the exhaust hole
The grooves cut for folding down later
The barrel cut open
Handles ready for installation
Drilling holes for handles
The lid prepared
The lid lined
... and edges folded around it
Lining of the furnace with Kaowool
Furnace and lid, unfinished yet
After first fire, the Kaowool appeared to have a too low temperature rating....
The Kaowool removed from the barrel
Empty barrel again with old furnace inside it
Step 1 for new setup of old furnace insulated by the Kaowool
Step 2, bottom lining
Step 3, old Mizzot furnace inside it
Step 4, kaowool above it
Step 5, kaowool above it, finshed
... and burner in it
Crucible in it
... and lid closed gain, ready for use
Prepared for copper melt
Castings (blanks for sheet rolling) remainder
Jan 2020: Refurbishment by lining the inside with Chamotte mortar
It is a good idea to line the inside with Satanite, but I could not find a supplier. But as an alternative I got Fermit via Amazon for $11 for 3kg which works excellent. I made a kind of porridge by adding some more water and applied it on the inner Kaowool lining by 'painting' it with a paintbrush. I let it dry and was ready to use. I did an earlier test in a 10 liter barrel furnace lined with Kaowool in which I melted cast iron and the inside temperature was 1500°C. The walls did not get sticky and were left undamaged, except for a few tiny cracks.
I did a short test on 2020 Jan 15 by roaring it a few minutes, when it was cold, a few blue flames appeared on the wall and even on the outside, but suddenly it disappeared with a little non-dangerous boom sound and burned better.
The 'Fermit' chamotte mortar for lining the Kaowool
Preparing the mortar
'Painting' the mortar on the inner wall of Kaowool
The furnace finished (left) and lid (right), crucible and plinth
Furnace inside with plinth in place
Furnace inside with plinth and crucible in place
Just lit on, some gas escaped through the wall (small blue flames), due to still cold furnace ?
After closing the lid, a small thud occurred and it burned better and no gas ecape anymore
With open lid, now better burn
Powered, developed under Linux and Mac and hosted under Linux.
This site is best viewed with Firefox, Safari, Chrome and Opera. Using landscape mode on a smartphone gives a better view.