General Categories > Non Gun Stuff
Aluminum melting
unfy:
--- Quote from: SS_N_NE on April 09, 2016, 12:14:46 PM ---Always get a kick outta these posts since I have done a lot of similar tinkering. Have a paint bucket furnace sitting in the garage somewhere.
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Then pipe up with any obvious 'duh' things I'm missing :D
--- Quote ---For a crucible, I have used steel pipe/tube with 3/16 wall and 1/4 plate welded to bottom and made tongs to fit. Hot things are just soft and need good tong to reduce stress....even on the red hot steel.
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shooter's offered to have us dig through his scrap iron pile to see what we can come with. I can prolly hit a local welding shop.... etc.
I should try to find a scrapper that would let me walk the yard looking for ferrous material to snag. If such a place exists...
--- Quote ---The steel will contaminate aluminum...but in a lot of cases it is not a real problem and didn't seem to hurt any cast projects I made. There were usually few inclusions since a lot of stuff was cleaned off with the dross or just didn't follow the pour or floated out of the part. Round pipe works since it doesn't have corners for the dross to stick into....your concerns on using square...didn't work on my attempts :( It is just easier to use round pipe since cleaning off the dross is easier and pour direction is anywhere instead of a corner.
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I've heard about the contamination - haven't actually gotten to the point of casting anything in sand yet, though. Been just making muffin ingots.
Have seen some crucibles on ebay that aren't terribly expensive - but the tongs for them are like really expensive. I imagine they're not too difficult to build out of flat stock, though.
--- Quote ---Didn't catch why you are using pop cans. The resulting aluminum is just scrap. Aluminum from previously cast items like transmission cases, cylinder heads, etc. will have better casting properties simply because it is a already figured out casting alloy. Aluminum is often referred to as "alloy" simply because it is rarely just "aluminum". I know this is a kind of elementary statement, but if the intention is to make sand castings at some time, a casting alloy will greatly ensure success. I worked in an industry where there were a lot of scrap to play with and found salvaging cast items just eliminated a lot of wasted effort.
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Doing work with cans just to get experience with all of it. They're more or less a free source of material to work with. As mentioned - I've not done any real casting with it, so look forward to fighting with it in the future. I appreciate the heads up that the closer to 'pure' AL that pop cans are will cause possible issues later.
--- Quote ---Great part is that I started my attempts at aluminum casting via a booklet, the internet has since opened way more information than I ever had access to.
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Indeed!
And hopefully this thread is helpful to others as well.
So far what I've learned: it's not too difficult to melt metal. The crucible is of all importance, though.
I'm curious if the burner I'm using needs some choke mechanism added to it. Won't know until later.
Furnace continues to cure - hit it with another light spray of water when I got home from work. Flipped the lid and rotated furnace body on it's side so as to expose the sides that have been on garbage bags the entire time. In the morning I'll stand it back up, maybe even put the lid on it with cardboard separating it. I will prolly get one more spray in the morning and then leave it alone from there on out.
I have some concerns about the build. Dunno if I got the refactory wet enough. It was more or less on the slightly too wet side of casting sand.
SS_N_NE:
The steel pipe crucible will work OK for small and less significant parts.
A carbide crucible will not contaminate the aluminum alloy but are fragile. The tongs have to be a very good fit so the red hot crucible full of molten metal doesn't get crushed or otherwise damaged by handling and dump the hot load. Tong are easy enough to make, just have to fit well, and lock in a hold that doesn't squeeze the crucible. Eventually if you start green sand casting, you may be fluxing, which is a real corrosive process to a steel crucible and is more likely to put ferrous contamination into the aluminum.
Although pop cans are available....it takes a lot to make a small amount of metal....and that metal will not be very usable for casting...just doesn't have the right composition/alloy.
Something like a junk transmission case will yield a lot of casting material. Usually can be found laying around or bought cheap from someone on Craigslist wanting to be rid of the junk. The case can be put on a pile of wood and the wood burned to heat the case. A hammer can be used on the hot aluminum to break off chunks fairly easily (at the right temperature) that can be put in your crucible. Not melting the case, just softening it up a bit. It will be sort of crumbly when hot enough.
The refractory in an oven is a lot like casting sand, you only want it wet enough to hold the materials together while being formed. After a bit of drying time, you make short runs of heat in the oven to drive out any remaining moisture. Once completely dry, the oven is brought up in a few cycles to operating heat which will ultimately vitrify the refractory sort of melting it together into a porous glass-like state. Each time you heat up the oven, you will need to go slow at first to drive out humidity it collects. If heated without driving out the moisture (from build or air) the heat will steam the water trapped inside the refractory and pressure will blow out chunks of the refractory or turn it crumbly. The effect is usually referred to as spalling. Sometimes spalling can be fixed somewhat by troweling some refractory back into defects...but spalling is best avoided.
I have plans for an electric furnace...but never went that way. I now generally machine things from billet aluminum.
unfy:
Crucibles:
This weekend will be the first couple heatings of the furnace. I may attempt a melt, I dunno. I plan on attempting to weld up a crucible but we'll see... time may be against me, etc.
I did order a graphite / salamander crucible off ebay. It's a #4 A shape, which is big enough to drop cans into. Will be making my own tongs for it. Part of the "gonna do it eventually anyway, might as well just get one now" ...
I've gathered up a fair amount of ingotized pop cans. Just looking at how it poured into muffin tins and how the failed crucible stuff looks - yeah, I can see it not doing so well for casting or serious work. Granted, I did not flux nor degas it when pouring into muffin tins etc. Not quite sure if can be alloyed with something 'at home'. It's been useful as a learning experience, at least.
By your description of how wet the refactory should have been during the ramming process, I think I hit it on the head. Grab it and squeeze - it holds it shape and breaks cleanly. And while ramming it up, the 'spray' / 'excess' did act kinda dry, but still would clump if squeezed. Sooooooo I'm far less nervous about things now.
I am aware of the slow starting heat, and pre-heating any metal molds ya might use (ie: muffin tin) to drive off moisture. I should find that video of a couple high school or college kids that try to pour some molten aluminum into a metal mold that had a drop of water in the corner (thus, subsequent explosion). Quite dramatic and a solid reminder of safety heh.
I've seen some folks heat up parts in a barbecue grill before breaking them, too. Also seen others take a skill saw and just chop it up. I'm not quite there yet, sooooo dunno what I'd do heh.
Electric furnace: I did buy Dan's electric furnace plans... and I am 50% done building it. In fact, I was working on it the night of the burglary a couple years ago. Just haven't been able to drag myself back to it to finish it off.
Keep the advice coming <3
SS_N_NE:
--- Quote from: unfy on April 15, 2016, 11:17:12 PM ---I should find that video of a couple high school or college kids that try to pour some molten aluminum into a metal mold that had a drop of water in the corner (thus, subsequent explosion). Quite dramatic and a solid reminder of safety heh.
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I went to an aluminum extrusion plant in SD that had a good part of it's roof missing. They dropped a load of scrap into a furnace and missed a pop bottle that had been tossed in the load (tried to skip pre-heating a load of clean scrap). Don't even want to know what that experience would have been during the event.
unfy:
Did the initial cure / test firing of the furnace today. Was real slow and gentle with it, had it running on as low as I could get it for an hour or two before cranking it up.
I'm happy with the burner.
I'm happy with the furnace.
It was kinda of interesting to watch the furnace 'cry' from a couple of the bolt holes as it drove the water out.
After it stopped forming any condensation on a metal plate semi-covering the top vent hole, started to slowly crank the gas up.
After turning it off, covering the vent hole with a thin sheet of metal so it can cool as slowly as possible.
I'll get some pictures posted later.
Although no melt was attempted, I will say that so far I am thoroughly impressed with propane / propane furnace. Is the charcoal furnace worth a go for some early learning ? Yes. Is moving to propane worth it ? So far a resounding yes.
So far, I'm not entirely convinced that the 3-3.5" hole in the lid was the correct size. Burner didn't seem to suffer from any back pressure when the hole was 2/3-3/4 covered. I suppose I could just slap a firebrick on top of the hole in the mean time. And it's larger size should make adding more metal to the crucible easier... we'll see.
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