I'm curious and casually (for now) wondering if there's a way to accomplish a lost-PLA "burnout" without a kiln or any kind of fancy, expensive, precise heat control? For example, could a small sodium-silicate & sand block-mold be placed into a (cold) foundry-furnace with an incandescent light-bulb for a week? Or perhaps even cheaper, roasted over a BBQ grill for an hour? Or maybe just blasted in the foundry-furnace with the lowest possible (probably still way too hot) flame? Would there be anything cheaper/easier/better than a sodium-silicate + sand mold for this? (I'm mainly thinking of aluminum-casting, in case that makes any difference)
So PLA melts around 320f (150c) but doesn't ignite until about 662f (350c). There are several research papers on the web that not that after 10 mins at 842f 450c the PLAs sample was completely combusted. You're going to need one heck of a light bulb for that! PLA also is viscus so it doesn't flow well. (wax flows very well when heated). With that stated I'd still heat the whole thing up to 350-375f and leave it for at least an hour (depending on the size of the mold longer you have to get the center of the mold up to full temp. ) then ramp up to 850 over the next 2hrs and hold it at 850 for maybe 2hrs more. I'm guessing at a lot of things. I also don't know if SS would start to break down at these temps for this long. Normally you'd be using a block casting media and following the manufacturer's firing schedule. For smaller molds with a larger opening I'm sure you could figure something out (like the bbq Grill idea) but I'm not sure you'd get reliable results with more complex molds.
Thanks for all that helpful info. I have an oil-fired foundry furnace, but it doesn't "do" low-temps well. That's what made me think of the light-bulb. Sounds like maybe that could work for the melting-out phase. I hadn't thought about the SS breaking down. You're smart to suggest that, b/c my "Just toss it in the foundry furnace and blast-away" idea would require the mold surviving two heats. So maybe the "simple" solution here is to just build a small temp. controlled electric kiln from an old BBQ, refractory wool, and (I dunno) water-heater elements on low-power? Then the standard, well-known and documented Lost-PLA process can be followed.
I've given thought to making a temperature controllable propane furnace, my idea is to supply fuel to the burner though two valves in parallel with each other, one a needle valve and the other a solenoid valve. The solenoid would be activated by a PID temperature controller and the needle valve would be adjusted to allow just enough propane to bypass the solenoid valve to keep the burner lit when the solenoid is closed. I haven't had a chance to test this out so I have no idea how well (or poorly) it might work.
Ya, I'm positive it's possible to make lost-PLA MORE complicated (though, being an honest engineer, I am attracted to your motivations) My curiosity here is if it's possible to somehow make lost-PLA really simple and cheap. Like somehow: "toss the mold into a foundry furnace and blast it". But it sounds like a melt-out followed by a 842f 450c burn-out (that doesn't destroy the mold) might be the minimum viable method. Other than making the entire mold out of refractory cement Actually...it seems like that's effectively what this comes down to. Is it possible to make a mold that can somehow survive a fast, high-temp burn-out, followed by getting filled with hot aluminum and not crack (or be expensive). At this point I suspect the answer is "not really"
I can certainly appreciate wanting to keep things as simple as possible. FWIW, the "burn out kiln" for my one and only lost wax casting was an ordinary propane bbq. I ran it at low heat until the wax had melted out then, cranked up the heat to fully dehydrate the plaster. Worked like a charm.
Thanks, I'm glad to know the more complex process can be accomplished with simple/makeshift equipment. I did some poking around the web and found an article that said SS melts at 1,088 °C (1,990 °F; 1,361 K), it doesn't boil but instead decomposes directly. Though no temperature was listed for decomp. we don't really care. In my mind, once it melts and gets fluid "enough", a complex mold cavity could loose it's shape. Does that seem sensible? So if a furnace can be run such that the mold cavity walls stay below (roughly) 1100°C/2000°F, maybe a quick foundry furnace burnout could work? ISTM at this point, some experimentation is needed to: See if somehow an oil-fired furnace can be run on "low" heat (and measure that over time). Come up with some "block-mold mass vs time" ratio wherein the PLA burns out but the SS doesn't melt. If both of the above hold true across a range of pattern shapes and sizes. Sound reasonable or am I missing some parameters?
https://youtube.com/shorts/HbK4c3SSyQs?si=vmdVfLKXVu8Rh73v If your doing small castings then microwave might be your best bet for low cost setup.
Oh ya that guy I swear, if he could, he'd build a car in a microwave I saw a few videos of him doing aluminum vacuum-casting with a swimming cap and a shop-vac! I can't believe he did cast-iron in a microwave though, that's pretty amazing. In any case, given the number of discarded but working microwave's at the dump, this isn't a half-bad idea for really small parts. Thanks for sharing!
