Tony Welch on Hot Faces

 Troye Welch

Satanite is good to fairly high temps, 3200 F IIRC, but it’s thin and brittle. What usually does it in is simple mechanical abrasion- lifting tongs scraping it or bumping into the RCF (wool) with the crucible- it will usually give, if you hit it hard enough and the satanite will crack and ultimately flame off. It’s easy to recoat, but a lot of people get complacent and run their furnace with bits of RCF exposed, which ends up being an inhalation hazard. Greenpatch 421 is more durable and goes on a little bit thicker, though still only a fraction of an inch- maybe 1/4 or so ( see http://zoellerforge.com/forgeparts.html ). The trade off you make for lower thermal mass is increased fragility. Neither better nor worse, just different with different pros and cons. I got some satanite from Zoeller forge years ago, but the last time I recoated my small propane RCF furnace, I used a product that BCS used to sell called a Matrikote. Very similar to satanite. Topped off with a coat of ITC-100 for good measure.
If you are careful with satanite and your furnace isn’t so small that you are tempted to stuff crucibles that are too large for it into it, it can last a while. When you get enough melts on it, you will inevitably get wear/tear on it. The specifics are unique to each furnace and its owner though.

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