Scrap aluminum and brass

Discussion in 'General foundry chat' started by KC M@, Jan 4, 2021.

  1. KC M@

    KC M@ Copper

    So my question is: I have a LOT of scrap aluminum...but most of it either is painted or has protective shield on it. Stripping it of paint is not an option large scale. Can I just chunk it up and burn it off in the crucible as I melt it for ingots for future use. And when I say a lot I mean 4-5 heaping truckloads. Maybe more. It ranges from sheet goods to extrusions to cast. All of it dirty. Pieces may include staples, screws, stainless pins and bolts, grease, oils, butyl tape, vinyl decals, and dirt. I’m thinking Tobho’s bulk scrapper would work quickest but not sure if it would work with smaller pieces. That being said if I can put it in the crucible as needed that would be ideal vs a day or several days doing a bulk melt. The last thing I want to do is ruin a new crucible for no other reason than not asking.

    As far as brass and bronze. How clean does it need to be? Or just burn it all and skim the crap off the top?
     
  2. HT1

    HT1 Gold Banner Member

    (rule of thumb) :if you have to run "poor scrap" you do not want it to be more then 10% of your heat,

    now in aluminum, sell the painted scrap , and Buy ingot, you are opening yourself up to too many issues that will just frustrate, extrusions cast poorly , the paint will cause gas issues

    Bronze (Tin bronze ) is far more forgiving , as long as you are degassing properly and dont add something that will mess up the metalurgy it will be fine,
    watch out for brass shell casings and oily scrap, as they will add Sulphur which will make the metal brittle.

    Yellow brass other then the above mentioned sulphur issue just dont care, melt anything add back the zinc loss, and cast it!!!


    For safety, once the heat is liquid you do not want to add dirty scrap, so you need some clean metal , if you are actually casting, and not just making ingots, your cutt off risers and runners will get you there

    V/r HT1
     
  3. Petee716

    Petee716 Gold Banner Member

    There are several ways of doing this, none of them terribly pleasant.
    Firstly the sheet material is going to be a loser especially if it has coatings on it. I would take it to the scrapyard as dirty scrap. The reason is this: the surface of aluminum oxidizes almost instantly, even when it's solid. That aluminum oxide is not recoverable by a back-yarder. When the aluminum is thick enough to form a droplet as it becomes liquid then at least the interior of the droplet is protected by an outer skin of oxide and remains usable. When that aluminum is 10 or 15 or even 30 thousandths thick and is exposed to air and combustion heat/gases it doesn't form a drop, it just keeps oxidizing until it turns to aluminum oxide ash. Toss a sheet of aluminum foil in a fire and you'll see what I mean. It burns up. And if it has a coating of whatever all you've described, all you'll be doing is incinerating garbage. Will you get anything from it, yeah probably, but not nearly enough to justify the work and the awful smoke. At least if it was clean you could fold and compress it to reduce the surface area and increase its density, but that's an awful lot of work, and as it is the coatings really kill the deal. The most effective way to melt thin aluminum is to completely submerge it in an already-molten pool, and that's a pretty tall order with sheet. I've tried melting sheet and ended up just scrapping the rest of what I had.
    Extrusions give you a much better opportunity. Because of their usual relatively long narrow shapes they can often be stuck into the crucible and protrude through the vent hole. The submerged end is protected from the atmosphere and as it melts the stick just lowers itself in Terminator-style. Once everything is hot it goes pretty quickly. Their thin profiles often don't lend to the stack melter for the reasons mentioned above, but thicker stuff works ok. Sometimes the best way to handle them is to cut them with a bandsaw to crucible lengths (bi-metal blade, 10-12 tpi, wood saw speed) and just feed them in as needed for your final castings.
    Castings can offer some challenges because of their shapes. They often don't fit into crucibles very well so they're often best reduced by wrench, saw, sledge, open fire or a stack melter like Jeff's. I've used all of these methods many times and they all work. If the material is clean enough it can go right into the crucible for the final casting without pre-ingotting. This is by far the best route in terms of labor, but you end up with piles of material instead of stacks of material.
    Ultimately the rule of thumb is to have your metal as clean as possible before you apply heat to it. That may involve scraper, wrench, wire wheel, whathaveyou. You will have to deal with the garbage and coatings one way or another. The strategy of separating the wheat from the chaff by just tossing it into a fire works sometimes, and sometimes it works very well. I once melted about 200lbs of aluminum push mower decks by simply sticking them in one after another in a stack melter in an afternoon. It was quite effective. Unfortunately in that particular session my last deck turned out to be magnesium. That disaster is a story for another day. Suffice it to say you need to avoid magnesium like the plague. At any rate the stack melter is very effective for rims and even whole lawnmower engines (plastic, oil plug, carburetor, and spark plug out).
    Lastly, before your metal is melted, keep it sorted. Different types of scrap aluminum are easy to identify in their present state. Once they're melted they're impossible to sort until you start trying to machine or cast them, and then it's too late.

    Pete
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    As others have suggested, you'd be miles ahead to scrap it all and use the proceeds to either trade or buy scrap castings from the same source. Call ahead and ask. Clean extrusions will bring good value but comingled painted sheet will not.

    Best,
    Kelly
     

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