So, on occasion I miss my crucible when I'm adding more material. As a result I have a pool of molten metal in the bottom of my foundry. When it's cool enough to attempt to pry it out it has proven stubborn and refuses to come out. Is there a way to wick it out similar to solder? Any other suggestions for removing it?
Going forward, you should probably have a drain hole in your furnace anyways, so drill a hole in the bottom, get the furnace hot and let the metal drain through the hole.
Stubborn aluminum will pry up with little if any refractory damage, but bronze (and probably other copper alloys for that matter) are a different story. A drain is helpful if it's not plugged but incidental accumulations of bronze are generally well oxidized and flow about as well as well chewed bubble gum. Unfortunately you can't do much mechanically to it while the furnace is hot enough to melt it. Your options beyond trying to drain it out of a hole are to live with it or try to chisel it out which I've found to be very hard on the furnace as a whole. I leave a base that stays in the furnace so the crucible is never on the bottom. That base ends up firmly attached to the bottom and as long as its surface is clean I don't worry too much about the bottom. Prevention is the best action moving forward. I'm as careful as I can be but it still happens. Tossing small bits in while the furnace is running is the biggest culprit as well as having metal hanging over the exhaust hole which then melts and falls into the airstream inside the furnace. Lowering larger pieces in with tongs seems to be the best way to minimize it. I recently had a crucible failure which left several lbs of bronze on the bottom of the furnace. It turned out to be a colossal shit-mess and after tipping the furnace on its side to pour the bronze out, I ended up chiseling out the bottom with an air chisel and relining it. Ugh. Pete
I have Blu-ram "plastic" refractory in mine. A castable refractory like mizzou or castolite30 or even just a dense firebrick will do. My base serves as a plinth for my #18 crucible, and if I'm using a smaller crucible I stack on a 4" diameter refractory puck of whatever thickness I need to bring it up to within 2 " of the lid.
different designs of furnaces deal with this better, I put my drain hole out the rear of the furnace rather then the bottom , similiar to the design guys breaking up aluminum use . the floor of my furnace is taperd slightly towards this hole, and a tapered downward channel running under the Plith leads directly into the drain, the drain 1.5 inch diameter is about half below the furnace floor if I spill metal, with the furnace running I can use a piece of rebar to scrape this channel clean through the cleanout hole , I can also tilt up the front of the furnace an Inch or two and clean it out nicely this works much better then a bottom drain where the plith blocks the hole and cleaning the furnace requires scraping fron the top while the furnace is at full temp, or as mentioned above going at it with a chisel. depending on your furnace material you want to treat spilled metal differently, in a monolithic furnace spilt metal will creap into every crack and expansion/ contraction cycl;es from heating /cooling can litterally crumble the refractory , that is alot of heating cooling cycles though , as to sof firebick or hardened kaowool , I suspect once the metal gets through the hardened layer, it could lead to holes in the entire furnace , Someone with experience in those type of furnaces should chime in, im out of my expertese there V/r HT1
Yeah I have a helium tank furnace with firebrick for the floor and hardened kaowool walls, I'm using a propane torch for the heat source.
So is your flame hitting your crucible directly? Your crucible should sit on a pedestal (plinth) so the bottom of it is just above where the flame comes in. Pete
That probably contributed to or maybe caused this failure. It may very well have caused the aluminum crucible you mentioned in the other thread to crack. Of course proper preparation of the crucible by preheating/drying and proper handling of it goes a long way of course (not implying anything here).
