Top view above Base view above I am just sharing (for better or worse) my notion of a useful plinth design. It is to be used in my very-low-mass iron-melting furnace. It is roughly 3 1/2” high by 7 1/2” wide and is cored out and has a shallow bowl top to hold play sand. I have found that with time my crucible spall at the base causing them to be a bit more tippy than when new. Using a play-sand -filled plinth outside the furnace has significantly improved stability there. (No actual spills yet.) So, I am hoping the sand plinth will be as favorable in the furnace. Since the new furnace will be as low in mass as possible, it makes sense not to plunk a heavy plinth in it. This one weighs in right at 4 pounds. I fired it to 1800 degrees last night. Hopefully it won’t collapse with first use. Comments welcome. Denis
I wonder if you are going to make glass?.... It's usually a thin layer of sand or card board. Let's see what happens.
Reasonable concern about glass-making. I use Olivine for molding. Probably better to use it as it has a higher melting point. Still might be a problem. Denis
One of the biggest problems I have seen another active iron casting person have is with plinth failure. I have not had any plinth failures, but then again I don't have iron pours that number into the hundreds either. I am also aware of people getting some serious 3rd degree burns on the hands through the gloves when trying to get a crucible full of iron out of the furnace after the plinth collapsed. You only have about 30 seconds when your gloves are in the vicinity of the open furnace/crucible to pull the crucible before your gloves overheat. I considered making a lightweight plinth, but have decided against that, and I use solid Mizzou with 5% stainless needles. I also keep the plinth coated with ITC 100, and that seems to help slow down the degradation. .
You can be sure, in the event of a plinth failure, I won’t try to pull out the crucible with gloved hands. I specifically made my new furnace so that the bottom can be removed from below and relining can be done relatively easily and cheaply. I can’t imagine grabbing a 2500 degree crucible with gloves. On the spur of the moment we can do odd things though. Denis
Nope, he did not grab the crucible, he was using the normal lifting tongs, but the intensity of heat from an open furnace and hot crucible will overheat gloves even when they are up at the top of the lifting tongs, after about 30 seconds. He had nice heavy gloves on too.
Aluminum oxide or zirconia blasting grit would have very high refractory. It would need to be unused so not contaminated with fluxes but you'd only need a few pounds. Best, Kelly
Kelly, You nudged me to look around at very high temperature abrasive media. Perhaps an optimal refractory abrasive for my purpose would be silicon carbide. It is readily available in 8 pound lots for 24 dollars. It has a 4900f melting point. Aluminum oxide is 3900 and also cheap. I had no luck (must have searched wrong) finding zirconia blast media in less than 50 pound units and that was from wholesalers who are not usually interested in small time sales. It’s melting point is around 4900 also. I think I will get some silicon carbide. Thanks for the nudge. Denis
Al2O3 is inexpensive. SiC is a bit more pricey (it's all circa $1/lb) but you can get it from the discount/import stores (Harbor Freight, Northen, Princess Aut, etc) in small quantities. It has the added benefit of being more thermally conductive. I also think it could be a good addition to dense refractory mixture for a cast plinth. Best, Kelly
