From another thread. I know I'll eventually find these parts - like covered up in the back of the sock drawer. The replacements have been ordered. Naturally my 'squirrel' mind has wandered to what to do with the parts when I find them. Since these parts are for an electric kiln I've entertained the idea of building a unit capable of pulling a significant vacuum. A quick internet search didn't turn up anything in the DIY realm. Freon tanks will hold the vacuum, but are kind of small. I do have a tank from an old worn out 5hp air compressor??? Anyone here run across another similar project, or actually tried this? If so any input would be appreciated.
I've used an 11 gal Harbor Freight air tank to good effect.. It'll hold as hard of a vacuum as your vacuum pump can pull. I'm a little curious too . Fredo
Most important, at least at this stage, is to just scratch my curiosity itch. Second I do have some aluminum structural parts* in mind for the future where porosity and inclusions are not welcome. A lid on the crucible with Argon topping may prove to be adequate. I thought about trying to seal the lift off with something like a Viton tubular o-ring to reduce the loss of Argon out the bottom with an open top crucible. From there I thought if I can seal it tight enough I can forgo the expense of Argon. A vacuum in cheap. If it can be built it might also be a reasonable way to cleanup recycled aluminum? *A206 if I can find ingots in less than pallet quantities. A lot less cutting than 2024 billet
You won't think so if you actually try yo build a vacuum furnace. You're whizzin into the wind with Viton in a foundry furnace. If that's all you want to do, cast a crucible cap from castable refractory, using ceramic fiber cardboard as gasket and purge with N2. Much more practical and as effective. My whole furnace has those type of gaskets and the entire interior naturally goes low in O2. If you're willing to consider a vacuum oven for melt integrity why would you consider using scrap casting stock? Best, Kelly
Nice to get a real world example! Viton is within the range of temperature tolerance at the periphery. Vacuum is cheap (if you don't take into account the cost of the Kiln pressure vessel) unlike Argon. If I wasn't copying your style with a lift off I'd not worry about the permeability of the brick. Plugging the hole under the plinth would be about all that would be needed. Scrap? Depends on your definition of scrap. Reclaimed A206 from sprues and such with a known history should be perfectly good for projects that still need metal that don't need quite as much quality control but are still needing metal better than melted lawnmower engines? I did note in my search that most of the small scale vacuum melt units were induction. Without some gas in the chamber we loose one path of heat from the Kanthal to the crucible. I really have no idea if radiation would be enough. This could be the deal breaker..............
Besides the lift off furnace being able to accomodate a larger crucible for the furnace size and give good crucible access, I do think I get a significant benefit from the smaller crucible-to-wall clearance and since I have two heating elements in parallel. Having two elements for a given power level means I have more element surface area than with one coil to radiate from. Each element makes three trips around the 10" bore, with one nested inside the other like a double lead thread, (but they could be parallel rings connected in the same circuit). That means there is a 1/2" coil every 1.5" of height. With a set point of 1800F, when you look into the furnace the entire wall is red and the coils orange. The low wall clearance means a short path to radiate. Since I measure temp at the top center, it also means the temp between the furnace wall and crucible is likely 100-200F higher than measured. At only 8kw with its very low mass it melts 10lbs in 30 minutes and can still accomodate and A20.....works well for me. -Good luck with your build. Best, Kelly
Lots more study and thinking before 'the build' - and that is all dependent on if I ever find the box of missing parts. My other worry with regard to only radiated heat is the thermocouple. Potted into the wall is probably a reasonable solution but the crucible may absorb radiated heat faster than the walls. The crucible would also radiate back to the walls but there could be a good deal of lag between real crucible temp and the thermocouple. Tuning the PID could be fun.........if PID is even needed. The one I want to finish is also A20 sized but only 6kw so it is nice to get a real world validation of my calculated melt time. I'll be happy very with 45 minutes.
