timgunn1962
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- Location
- Lancashire UK
For Heat Treating, you don't need a particularly high temperature. For GFS (O1 steel), the Austenitizing temperature is usually around 800 degC. Depending on how permanent you want your setup to be, ceramic fibre blanket is probably the easiest stuff to use. For HT temperatures the Low Body Persistence stuff is fine, rated to 1200 degC. The LBP stuff is about all we can easily get because it seems likely to be less dangerous long-term than the "real" ceramic fibre. You can line a suitably-sized tube with a couple of wraps and use it as it is. It has very low thermal mass and insulates well. Look for "coffee-can forge" online. Some will be ceramic fibre blanket. Most will be Plaster-and-Perlite. Note how few of those are on their second, or later, run and apply some natural scepticism.
If you really want to try a DIY "refractory", I'd kick the plaster-of-Paris idea into touch and try a refractory cement with Perlite mix. It should be easy to find Perlite at garden shops and refractory cement at any decent DIY shed (or screwfix.ie list "Flomasta refractory cement 2kg"). I have access to the blanket, so have not used a perlite mix myself. I have used the cement as a quick-and-dirty rigidizer/coating for the blanket: not ideal, but it does actually work.
I take a good dollop of the cement, add just enough water for it to become properly liquid when mixed. I give it a good stir, wait 30 seconds for the sand to settle out, then decant off the liquid and leave the sand behind. The liquid contains the sticky stuff and should do a decent job of bonding the perlite. The reason for leaving the dense sand is that you want a good insulator with low thermal mass. Leaving the sand in will just add mass and take longer to heat up (at least, that's what I'd expect. I could be wrong).
When I have coated blanket in mini forges, I have been very careful about drying them properly before first fire. I usually put the forge in a low oven overnight (ideally: the reality is usually for however long I am confident the wife will be out). If you fire before it is properly dry, it fully-dries a paper-thin layer and flashes off steam underneath it, causing the dry layer to lift and become the surface of a bubble. This breaks and the process repeats. You get lots of loose flakes and not much solid lining.
If you really want to try a DIY "refractory", I'd kick the plaster-of-Paris idea into touch and try a refractory cement with Perlite mix. It should be easy to find Perlite at garden shops and refractory cement at any decent DIY shed (or screwfix.ie list "Flomasta refractory cement 2kg"). I have access to the blanket, so have not used a perlite mix myself. I have used the cement as a quick-and-dirty rigidizer/coating for the blanket: not ideal, but it does actually work.
I take a good dollop of the cement, add just enough water for it to become properly liquid when mixed. I give it a good stir, wait 30 seconds for the sand to settle out, then decant off the liquid and leave the sand behind. The liquid contains the sticky stuff and should do a decent job of bonding the perlite. The reason for leaving the dense sand is that you want a good insulator with low thermal mass. Leaving the sand in will just add mass and take longer to heat up (at least, that's what I'd expect. I could be wrong).
When I have coated blanket in mini forges, I have been very careful about drying them properly before first fire. I usually put the forge in a low oven overnight (ideally: the reality is usually for however long I am confident the wife will be out). If you fire before it is properly dry, it fully-dries a paper-thin layer and flashes off steam underneath it, causing the dry layer to lift and become the surface of a bubble. This breaks and the process repeats. You get lots of loose flakes and not much solid lining.