As I said earlier, one of my primary concerns in this adventure will be ensuring that the foundry is safe by design. While researching possible ways to form furnaces out of refractory cement, I’ve seen a great many designs on the internet that use galvanized sheet metal and pipes as furnace parts. For example, this furnace looks absolutely gorgeous and I’m sure it produces great results, but the amount of galvanized metal on that thing concerns me.
Galvanization is a rustproofing technique whereby a steel object is dipped in molten zinc, forming a thin layer of zinc-steel alloy on the surface. Though this certainly does resist corrosion, the zinc alloy will vaporize into gaseous zinc oxide at about 400°F. Effects of zinc oxide inhalation include, as Wikipedia helpfully points out, fever, chills, nausea, headache, fatigue, muscle aches, joint pains, shortness of breath, chest pain, burning sensations, shock, collapse, convulsions, yellow eyes, rash, vomiting, diarrhea and low blood pressure.
None of that sounds like a fabulous adventure.
Now, you might reasonably point out that the galvanized portions of the sorts of “steel bucket furnace” build are all on the external surface (the “cold face”) of the furnace, which typically will not get even close to 400°F. To which I would respond that the key word there is “typically”. If the furnace runs too hot for too long, or if something near the furnace catches on fire, or if molten metal is spilled onto the zincky (*) surface, or if you accidentally put a piece of magnesium into the furnace thinking it is aluminum and it starts burning uncontrollably, then odds are pretty good that some zinc will vaporize at exactly the moment when you have some larger disaster to manage. (And in that last case, you have the problem of inhaling magnesium oxide, which is just as bad; more on magnesium in a later episode.)
You might also reasonably point out that the furnace will already be vaporizing all kinds of nasty stuff; many impurities in the scrap will go up in smoke. We are going to need to ensure that the furnace is operated in a well-ventilated space. I would respond to that by saying let’s not make a bad situation worse if we can avoid it.
Therefore I’m planning on avoiding galvanized metals entirely. In fact, it is not clear to me why the exterior of the furnace needs to be faced in any metal at all. Why should the cold side not be plain refractory cement, as the hot side is?
(*) Good Scrabble word there.