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Thread: How can I remove small flimsy iron coating particles from aluminium melt?

  1. #1
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    How can I remove small flimsy iron coating particles from aluminium melt?

    Few days ago I bought my first BMW. Unfortunately just the crankcase It's a model N20 F32 engine and according to the official N20 Technical Engine Guide made out of AlSi9Cu3 aluminum. Being new to the melting-hobby my initial thought was that this engine would be a good clean scrap-alu source.

    photo_2017-05-19_01-36-50.jpgphoto_2017-05-19_01-36-53.jpg

    The first 'problem' I had to solve was how to get this 22kg piece in my crucible. After hitting it just once with the biggest hammer I could find, I quickly learned that I needed something bigger. The guys from our local scrapyard helped me out by dropping an old 8500kg safe on top of the engine. Entertainment-value = 100%!!

    photo_2017-05-19_01-36-55.jpg

    After 3 or 4 drops the job was done. The engine was reduced to nice chunks.

    photo_2017-05-19_01-36-58.jpg

    During the manufacturing process of the N20, the 4 cylinders walls of the engine are LDS (Lichtbogendrahtspritzen) coated. LDS is also known as a twin wire arc spray process. It is basically a plasma cutter/welder that has the molten iron blown with the droplets creating a coating. This procedure created a 0.2mm thin layer of iron inside the cylinders.

    Today I started making ingots. I filled the crucible 4/5. Then I poured a few ingots, leaving 1/5 of molten aluminum in the crucible to speed up the initial second melt.

    photo_2017-05-19_01-37-13.jpg

    When I finally poured the very last ingot, I discovered lots of very small, very thin particles accumulated on the bottom of the crucible. They ended up on top of the last ingot. I'm assuming that's the iron cylinder wall coating. (If anyone thinks differently, feel free to comment)

    photo_2017-05-19_01-37-01.jpgphoto_2017-05-19_01-37-06.jpg

    Is there an easy way to separate those flimsy iron particles from my melt? Or should I just give it some time during the melting so that the particles sink to the bottom? And how will those iron particles behave in the aluminum. Do they drop to the bottom or sink very slowly. Iron density more than doubles that of aluminum. 3kg/L vs 7kg/L.

    Any backyard/DIY ideas on how to solve this?

    Guess dropping a magnet in the crucible isn't a very realistic/safe option ;-)

  2. #2
    usually the iron just sinks to the bottom very quickly or floats on the surface of the melt and can be scraped off or scraped out afterwards. I usually just melt mine down, but I have a scooper that fits the profile of the bottom of the crucible but has holes drilled all throughout it, and I can scoop stuff like piston rings or odd nuts and bolts that ends up in the bottom of the crucible if I am worried about them coming out, which they never really do unless you completely pour it all out. A magnet in the crucible wouldnt work at all really, usually the molten metal's temperature is above the curie temperature of the magnet, and it'll just kill the magnet, if not causing it to melt or just burn up. All I can really say is just pour all but the very last little bit out, then pour it carefully into a seperate ingot tray making sure that most of the stuff doesnt go with it, then just scrape out the steel junk out of the bottom.

  3. #3
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    Thanks for the quick reply!

    Can iron (being heavier) float to the top??

    I agree, nuts, bolts and bigger parts you can scoop out easily. But the coating particles are to small to scoop. My concern was/is mostly, what happens to the particles when I degas just before the pour? I assume the degassing bubbles would 'stir up' the particles again and end up in the cast.

    Should I just wait like lets say 1 minute after degassing for the particles to sink again? If they would sink like sand in water even 10 seconds would do. Or should I first try to separate the particles as much as possible the way you described and degas the melt after most of the iron is removed?

    I currently do not degas/flux when pouring ingots. My intention is to degas and flux before a final casting. Can not find much info if that's good practice.

  4. #4
    My scooper is a piece of angle iron welded to a piece of steel threaded rod, but the angle iron part is shaped so the piece is rounded on the bottom so it conforms to the walls of the crucibles I use. It has a bunch of little holes in it, maybe 2mm big, but thats just enough to let the metal flow out of it, but grab any dross or junk in it. If I remember to do it, Ill take a pic of it for you but I find it's really handy for stuff like that. I tend to reuse old castings and such, and Ill end up with a little bit of old sprues and such that has sand on it that wants to collect in the bottom of the crucible. It doesnt take much time at all for the stuff to settle, and most of the time, I dont really degas when Im just making ingots. I flux only because the flux helps clean the impurities and oxides out of the metal and helps give a more pure metal, so better to do it to ingots, then you start with a cleaner source.

  5. #5
    Senior Member cjcaster's Avatar
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    If there are no particles in the other ingots, then I would just discard the last ingot.

    If you don't want to waste the last ingot, then remelt it, and carefully pour off all but the last bit, and then dump the small amount that contains the particles.

    They do make ceramic filters, but those particles look so small that they may pass through a filter.

    We need a video of the safe drop.
    I need one of those.

  6. #6
    I find it slightly surprising that the iron particles aren't being absorbed by the aluminum. After all, thin steel crucibles get very few pours before failure, and even my heavy-wall crucibles have to be looked after for thinning of the wall(s).
    I'd say do as Cjcaster suggests. Discard the last ingot, or half the last crucible contents, and call it loss as dross.

    Roger

  7. #7
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    Thanks for the replies. Guess I'll try pouring carefully and sacrifice the last ingot.

    Quote Originally Posted by cjcaster View Post
    We need a video of the safe drop.
    https://youtu.be/WzcLHeSr9IQ

  8. #8
    Senior Member cjcaster's Avatar
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    Awesome video.
    That would really be handy for scrap reduction.

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