Alloyed some brass today from scrap zinc and copper

Discussion in 'Sand Casting' started by Mark's castings, Aug 22, 2021.

  1. So today I managed to make some brass from scrap AC motor windings and some zinc ingots made from scrap anodes. This is the first time I've tried to do this so mistakes were made and I also wanted to try melting the zinc with the copper. My scrap enamelled copper ended up being 9.7 kilograms so with all the enamel and other bits of insulation I guessed 9.5 Kg of copper. I opted for "High Brass" which is 65% copper and 35% zinc and can be used for spring, screws, rivets etc., so that means I needed 5.12Kg of zinc. and one of the scrap ingots was 5.2Kg. I wanted to try dissolving the copper into molten zinc to avoid the fireworks so the zinc went into the new crucible and I packed as much copper wire as I could around it, maybe 1/3rd of the total as I could only get so much in, even by sorting the dense copper out and wadding up the loose wire into balls. Anyway I fired up the furnace and ran it low to preheat the furnace and new silicon carbide crucible: it's a Morgan AHM-25 which is supposed to be more flux resistant than a normal crucible and is a reddish brown colour.

    So the copper would get red hot, form globules of copper and I'd gently pack it down and add more copper, this is where I made my first mistake: I had a tight packed crust of semi solid copper on top along with maybe 1/4 of the zinc ingot, when I used a steel bar to break through the crust, into the liquid below the zinc got plunged in and reacted with the molten metal, blue flames, lots of white zinc smoke I avoided like the plague and suddenly I had nothing but 1/3rd of a crucible of molten metal (it melted any solids quickly like it was exothermic). The remaining copper got dumped in fast and began to melt when pushed below the surface. My second mistake was to skim to soon, I reckon I have 1-2 Kg of brass and unmelted copper skimmed out of the melt. I didn't use any flux which brass isn't supposed to need, but I think when using scrap metal it would be a big help. So after the pour into green sand with sea coal mixed in for iron, I let it cool for about an hour or so. My third mistake was pouring too hot and the surface finish was rough and nasty, never seen anything like it before with the brass forming spikes and needles in the sand. The three inch diameter bar casting had a 2" deep hole in the top from shrinkage and the 1.75" bars will likely have shrink defects too, I was warned about this when casting bar for machining use but there's wastage due to gripping the bar in the chuck jaws anyway, so you just add the scrap to the next melt.

    The castings needed to be hit with the belt grinder to take the nasty surface off and the 3" bar machined down to 2 & 7/8" to clean up fully and appears to be a sound casting at the end away from the top shrink defect. I got lucky and have a good casting although the smaller bars will likely have porosity and be rotten at the top due to the air cooling.

    Recycled zinc stash (free)
    zinc stash.jpg

    Copper motor windings (free)
    scrap copper.jpg


    Brass poured into the green sand, 1 x 3" and 2 x 1 & 7/8"
    Brass sand moulds.jpg

    11.1Kg yield from 14.7Kg starting materials (lots of metal lost in the dross skimming)
    brass yield.jpg

    Surface finish close up:
    sand cast brass close up 1.jpg


    3" bar finish after losing 1/8" off the diameter, so the casting was pretty sound.
    machined casting 2.jpg
    machined casting 1.jpg
     
    Last edited: Aug 23, 2021
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  2. oldironfarmer

    oldironfarmer Silver Banner Member

    Why does brass not need flux? I skim a lot less material off if I flux the brass.

    I think I would melt the copper into ingots to clean it up before proceeding with a brass melt. Additionally, getting a heel of brass before adding any additional alloys helps a lot.

    Did you consider pouring horizontally with a sprue and gate? That's how I make hex bar stock, primarily to avoid inclusions from pouring directly into the mold.

    Regardless, it looks like you got great results.
     
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  3. Zapins

    Zapins Gold Banner Member

    Super nice rod you got there. I have been thinking of doing something similar for machining stock. Seems I can't find local brass bar stock for various projects.
     
  4. HT1

    HT1 Silver Banner Member

    like Andy said, you are so much better off if you start with at least half of your melt being the target alloy or near to it , when I make up brass, I normally shoot for 70-30 with no effort to be more then close,
    I weight the copper and put it in the bottom of the crucible, cover it with as much Brass as it takes to fill the crucible , as it melts down, I add the remaining Brass if any, zinc does not go in til the melt is almost ready to go, then it is preheated and plunged to the bottom,
    I dont flux brass, but I normally work with clean scrap, anything that forms dross, is normally an obvious contaminant, in your case the enamel

    V/r HT1

    P.S. casting round stock (billet) upright is a good practice, it really helps with directional solidification, but pouring directly down the billet is bad, you can easily bottom gate, of even horn gate to get a gentle bottom feed
     
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  5. I've been told that melting fresh brass ingot just needs a skim to be ready to pour just like aluminium. This scrap could have benefited a lot from fluxing, what do you normally use?. I'd like to avoid borax if possible.

    I can see why you'd cast copper ingot first, it took a bit of sorting and prep for the copper to get it into manageable lumps. By melting contaminated scrap with a lot of surface area like enamelled wire, and zinc together I ended up with a lot of oxides and dross, so I had about an inch of white/yellow oxide powder with significant amounts of brass and oxidized copper wire mixed into it. I'd been watching a video where an induction furnace is used to make a heel of molten zinc with copper wire melting into it as the heat increased and wanted to try something similar with an oil fired furnace. My understanding about casting bronze bar is that casting vertically will ensure a sound casting at the bottom with unsound, porous "rotten" material at the top in the last few inches due to the top solidifying first. So you can just grip the top of the bar casting in the lathe chuck and recycle into the next casting.

    Extruded brass bar is super expensive here, maybe $200 worth for that 3" bar on Ebay Australia. The bar surface cleaned up beautifully with only 1/16" removed, it remains to be seen if the casting is sound and non porous throughout although with that 3" thickness and the 2" deep contraction hole down the middle, the rest might actually be ok. The smaller bars have to be machined yet some casting defects are visible. I think with the air exposed brass cools faster so the top solidifies first when it would be better for the bottom to do so: I might try using some steel chill plates embedded at the bottom, that worked for stopping sand wash when casting grey iron but made the end too hard form the chilling.



    That's some good advice about brass, I did want to try a zinc heel with an oil furnace, it appeared to work with mixed results, maybe something to use later if I don't have some brass to start it with. I was worried about sand washing in so I had fairly hard rammed sand, I might try placing some round mild steel discs at the bottom for the brass to hit and also chill the brass from the bottom if these smaller bars turn out to be too porous and rotten inside. I'll have to make some suitable cope and drag boxes to allow bottom gating for bar, I think it's better to cast bar than make ingots if you can later use it for machining stock.
     
    Last edited: Aug 23, 2021
  6. Zapins

    Zapins Gold Banner Member

    I doubt it will be rotten at the bottom only the top where the shrinkage hole was. When you get to the bottom of the hole it should be perfect after that.
     
  7. Whatever I see when using it, I'll report back. If anything the smaller bars have much less shrinkage, could be cooling metal in the crucible, could be porosity.
     
    Last edited: Aug 25, 2021
  8. oldironfarmer

    oldironfarmer Silver Banner Member

    I use a brass flux from Budget Casting Supply. If you save your dross you can flux it back to brass. I was melting scrap brass and getting a fair amount of dross. Upon remelting bad castings I would get even more dross. The flux is valuable for me. I can see not needing it if you're melting ingots.
     
  9. I'll have to go through mine, the dross actively hindered the scrap from melting into the main pool of metal. Time to go get some flux and coagulant


    brass dross.jpg
     
    Last edited: Aug 24, 2021
  10. I just went through the dross and sieved it for brass and got 1.6Kg of unmelted copper and brass droplets, so the thick layer of zinc oxide on top of the melt was hindering the formation of a uniform melt. The bars are machined for a total of 9.2Kg and I left the shrinkage on one end as you always have one end in the lathe chuck jaws that can't really be used anyway. Swarf from the machining came to 1.8Kg so with the dross, that comes to 3.4Kg of brass for the next melt.

    Adding the scrap weight to the bar weight comes to 12.6Kg with 14.7Kg of copper scrap and zinc to start with.... so 2.1Kg went up the furnace exhaust as burnt insulation or white zinc oxide dross. Just jamming the ingredients into the crucible and firing it up is a pretty lossy method: about 15% loss. At one point when the unmelted chunk of zinc got pushed into the melt there was a column of white zinc oxide smoke with a blue-white cone of light shining out through the smoke that was rather spectacular in daylight, kind of Chernobyl-like in appearance :eek:.

    brass bar yield.jpg brass scrap.jpg
     
    Last edited: Aug 28, 2021
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  11. rocco

    rocco Silver

    You know the rule, unless there are pictures, it never happened!:p
     
  12. Just added them and saw your post :p. As far as the spectacular furnace shot goes, taking a photo was the farthest thing from my mind.
     
  13. Petee716

    Petee716 Gold Banner Member

    I'm wondering if burning that insulation off the copper and getting rid of as much of the solid residue as possible before melting it would make some difference in the overall process. I think we often take it for granted that contaminants like that just separate off into the dross or go out the top as smoke. Maybe they do, but it seems just as likely that they might be contaminating the alloy to some degree.
    Thoughts?

    Pete
     
  14. I could see the enamel (probably polyurethane) burn off without much residue or ash at all and as the copper got hotter, you could see the copper constantly tarnishing and then going bright shiny copper as the hydrocarbon rich atmosphere fluxed it clean again. If you heat a copper wire with a blowtorch you can see the same phenomenon when the flame plays over the copper: the area in the flame is bright pink and the wire in the air going black immediately. Where pre melting the copper into ingot would help is you can easily fit it all into the crucible in one go. I had to put some gloves on and wad all the three inch copper needles into tennis ball size lumps and bend the longer bundles of very stiff wire into crucible friendly lumps. Would have taken maybe half an hour and after all that prep I could only fit 1/3rd of the copper in to begin with.
     
    Last edited: Aug 27, 2021
  15. Chazza

    Chazza Silver

    Well done anyway Mark, despite the hiccups, you have ended with some very nice billets,

    Cheers Charlie
     
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  16. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Those look pretty darn nice to me Mark and saved you some coin along the way.

    Best,
    Kelly
     
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  17. Based on Ebay Australia prices, the 3" bar would be close to AUD $200 and the two 1.75" would be around $300 AUD for extruded brass bar. For the price, I'm willing to accept a few minor casting defects.
     
    Last edited: Aug 27, 2021
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  18. So I was lucky machining my first item from the brass bar: a knob for a fuel needle valve for the furnace with much finer flow adjustment for the fuel nozzles. The knob was machined from the bottom 2.5 inches of the last brass bar to be cast and during the parting off operation a contraction void was exposed. The knob is perfectly fine and machined without any issues identically to extruded brass bar right up until the parting off operation where the knob broke off with 3/8" of the bar diameter still to go. There is a core of highly porous brass with long fine crystals like barbed wire or ice crystals, very beautiful in appearance. So future bars will need shrink feeders at the top and maybe a steel chill plate under 1/2" of green sand at the bottom to start the solidification at the bottom while the feeder is still liquid. For this knob I still need to bore out the middle for the brass needle part of the valve so the bad area has to go anyway. The rest of the bar will have a usable section so long as you don't need the core.



    brass core contraction.jpg

    brass core contraction 2.jpg


    brass knob.jpg


    brass knob thread 2.jpg

    brass knob thread.jpg
     
    Last edited: Aug 29, 2021
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  19. Zapins

    Zapins Gold Banner Member

    Yup that was my experience too. Just need to replace the metal with a shrink bob
     
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  20. Melterskelter

    Melterskelter Gold Banner Member

    How exactly would you do that? I am thinking that maybe rather than casting a straight-sided cylinder, maybe cast one that is, say, six inches high and 4 inches diameter for maybe 1.5 inches at the base where it is fed and 3 inches diuameter for the rest of its height. That way the hottest and most massive area, the base, will freeze last and top freezes first. A blind hot riser makes sure the bottom gets fed. Maybe, just using a 1.5" diameter by 1.5" high blind riser on the straight sided cylinder would work. Is that the general idea? What seems to have gone on here is the casting was so massive that what filled first or last was not so important as the overall mass and it just froze all over on the outside and more or less uniformly to the center leaving no metal to compensate for shrinkage and thus vacuum defect formation.

    Denis
     
    Last edited: Aug 29, 2021

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