Homemade Furnace Liner(also can be used in a fire pot)

[saintjohnbarleycorn]

thanks for keeping up with all my questions. I do appreciate it. kevin

[JWBIRONWORKS]

Richard,
Good to hear from you,

John

[Ken Kelley]

What's the purpose of the borax powder? Doesn't it tend to melt under high heat?

[Ice Czar]

Originally Posted by Ken Kelley

What's the purpose of the borax powder? Doesn't it tend to melt under high heat?

good question,

lets look into the crystal ball....

patent 4233078 (pdf)

Sodium borate, preferably a hydrated sodium borate and most preferably borax (the decahydrate), is added to a graphitic refractory composition suitable for forming a refractory monolith, for example a plastic or a ramming mix, in order to reduce the loss of plasticity of the mix during storage, to inhibit fungi formation in the mix during storage, and to improve the intermediate temperature strength of the composition

Dehydration Behaviour of Borax Pentahydrate to Anhydrous Borax by Multi-Stage Heating in a Fluidized Bed Calcinator (PDF)

Anhydrous Borax (BA) is an industrial product produced from borax decahydrate and borax pentahydrate. It is used as a flux material in metallury, and in the production of high quality glasses, ceramic materials and enamels.

it goes on to say that the amorphous form we know as a metallugical flux, is actually just one of several states, there are also 3 different crystalline forms with melting points of 1015K (1367F), 993K (1327F) 936K (1225F)

anhydrous of course means without water, so its likely we arent employing BA specifically

The low melting point of BA causes very dangerous corrosion problems which can only be prevented by forming a layer of solid calcined borax on the refractory material of the furnace.

best guess its added for multiple reasons but one of the most likely is to form calcinated borax on the refractory
still researching

[philip in china]

Re the use of sawdust am I getting this right? The idea is that the sawdust actually burns and thereby leaves small empty pockets or pockets containing charcoal which due to it's lack of mass increases the thermal insulation properties of the monolith. Please let me know if I am wrong! I am looking for a good insulator for round my cupola.

[Ice Czar]

thats my understanding, reduces the mass of the refractory

Ceramics, Clay and Insulating Brick
A Low Cost Kiln Brick for Production of an Appropriate Purifier