General Categories > Non Gun Stuff
Aluminum melting
unfy:
Piece of printer paper with some olive oil as kindling / tinder, 3 charcoal briquettes. Cover with lid. Block lid hole 75%.
3 hours later, do it again.
Metal pail is warm to the touch. Plaster is changing color slightly.
Starting to look like rain, so set lid aside on some concrete and dumped out what was left of the last 3 charcoal pieces. When I lifted lid to put it back on to furnace, there was a water mark disc on the ground. Soooo yeah, the heat is definitely helping to drive out more moisture. And is something I would suggest for other builders (although for plaster of paris, I dunno how required it might be).
This is just a bit of explanation, feel free to ignore it.
With normal refactory / furnace stuff, you slowly bake everything to drive out moisture very very slowly. As time goes on, you increase the heat to drive out even more moisture and other related stuffs. With the electric furnaces, the cook time is up to a week! By slowly driving out all the moisture, you avoid micro steam explosions that can cause cracks in the refactory (or far worse). And yes, at 1000-2000f - there is a lot more water in a rock / brick you might think heh.
shooter:
Im not sure about plaster . but you never heat cement. the water inside it will expand and explode, ive seen pictures of fireplaces that weren't allowed to cure, and they blew chunks into the next wall.
unfy:
--- Quote from: shooter on September 22, 2015, 05:27:43 PM --- Im not sure about plaster . but you never heat cement. the water inside it will expand and explode, ive seen pictures of fireplaces that weren't allowed to cure, and they blew chunks into the next wall.
--- End quote ---
Indeed! And most sources will give similar warnings. Also reminds me of boy scouts / don't use river rocks for camp fires.
Also, even when using a "proper refactory mix", everyone warns about long cure times and slow heating to avoid explosions :).
So far, heating plaster of paris very slowly seems to be driving out moisture.
http://www.backyardmetalcasting.com/refractories.html
The above discusses using portland cement with other things.
http://www.imarketingcenter.com/refractory.html
Has some other stuff, but also mentions slow firing.
http://makezine.com/2012/04/05/how-tohomemade-castable-refractories/
This shows 1 part premixed refactory cement to 4 parts perlite. I think that's the ratio anyway. This is similar to the mix mentioned in Gingerly's electric furnace (and maybe Dan Hartman's).
http://www.iforgeiron.com/topic/3392-homemade-refractory-recipe/
Has... well... a bunch of stuff. Dunno how much to trust the responses, and given the name of the site... if they're going for iron instead of aluminum... that is a large heat difference. They claim portland won't hold up. But... again, if going for iron melting temps, then maybe not.
Mali:
More good info I was not aware of, thank you.
With that knowledge I would say that leaving the PoP refractory outside would be bad since it will most likely get water back, correct?
unfy:
I have no clue how pop works.
I know that it likes water, then it rejects water. What happens after that, I dunno.
IE: you can mix PoP in a bucket. Eventually it'll set, possibly leaving water on top. If not, you can dump more water on top and it will *still* cure while the water remains clear. I think, though, that if you can mill it / grind it up, it's reusable ? Maybe ? I dunno.
PoP isn't really something I've messed with much (it's typically too fragile for anything I'd want).
There's probably a protocol for dealing with furnaces that are exposed to humidity. Something like "if it hasnt been fired in X time, do a slow firing for Y min before doing a full blast melt". But, I have NO clue. NONE.
It could also be that as long as you don't throw water on most types of cured refactory, they won't absorb water (ie: the won't suck it out of the air).
In other news - the slight sprinkles (cough) we're getting here in the Omaha area kinda makes continued slow firing difficult.
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