Propane tank/fueled furnace build

Discussion in 'Furnaces and their construction' started by Shawno, Dec 27, 2020.

  1. Shawno

    Shawno Copper

    Thanks again all!

    Once I got turning today, it got much better. Better shaped tool bit, WD40 for lube, higher speeds once I got the piece straightened out.....They actually feel much better than they look.

    Not beautiful, but I am ok for a first shot at it. :)
     

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  2. rocco

    rocco Silver

    Yes, we do indeed still have Aero bars. And for those unfortunates among you who don't know what Pete's referring too:

    Aerobar.jpg
     
    Shawno likes this.
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Already some good replies. The biggest issue with your present ingots is unknown composition. Opinions and ability will vary about the extent to which you can degass a melt, but you're never going to change the composition of melt to known and desirable composition without knowing where you're starting from.

    Petee raises a very good point about remelting wrought alloys for machining. The advise of using cast-to-cast is sound but the recommendation assumes you need and benefit from properties that facilitate good casting characteristics. The primary issue with using many of the wrought alloys with good machining characteristics is they have poor fluidity and high shrinkage, but if you are casting a machining billet in a can, those are not really much of concern.

    The only caveat is you can lose some of the elements that improve machinability, and temper. 6061 for example can be retempered but T6 is difficult in a home setting. It's like the difference machining T6 versus T0. If you think you have 300 series cast alloy, a T5ish schedule can help a lot and can be done in a household oven.

    Yes. The reason is to minimize hydrogen poristy, and since you are casting a slug/machining blank, you don't need the additional heat.

    Yes, it can be helpful (for aluminum), but your biggest gains would likely be using known alloy. There are aluminum alloys that have better as-cast machining properties. Zamak (high zinc alloys) actually have relatively high (compared to some common aluminum casting alloys) strength and good machinability, but it's more than 2x the density of aluminum if that matters.

    High temper, tooling geometry, coatings, and cutting fluid all help. TiN tool coatings are common for aluminum cutters and reduce adhering to the cutter.

    Iron contamination is a real problem with aluminum. It's a tramp metal and small amounts significantly reduce the mechanical properties of aluminum. Once it's in, you wont remove it in a home setting. Molten aluminum is a solvent and will dissolve steel with time and temp. Graphite crucible would be best.

    Best,
    Kelly
     
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  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I should have mentioned brasses and bronzes. Since you are a machinist, I'd have to think they'd be of interest as well. There are slightly different issues casting machining blanks for those depending upon the alloy, but many have obtained good results casting brass billets. Just need to pay attention to retaining zinc content and oxidation of melt.

    Best,
    Kelly
     
  5. Shawno

    Shawno Copper

    Woah Kelly....just getting going with aluminum. Talk to me in a year....;)
    And calling me a machinist is might kind of you! .....owning a lathe does not make one a machinist....but I like making chips!

    I am going to clean up the casts from yesterday and see if they are all about the same. Should be... and will get more serious about making the furnace fit my crucible...

    Big gains in the last 24 hours.....
    Thanks all
    Cheers,

    Thanks for replying to that Rocco. I noticed it but forgot to comment. Aerobars...a personal favourite....:)
     
  6. My take on remelting porous aluminum is that right at the melt front the aluminum is at the melting point, the solubility of hydrogen is at it's lowest. As it melts and falls to the heel in the crucible it will be low on hydrogen. The longer it is in the crucible the more it will pick up atmosphere hydrogen. Also if you submerge a gassy ingot you will collect hydrogen from the ingot in the existing melt.

    I put gassy ingots in for the first charge then add good ingots and I get very little porosity in new ingots. In castings the pouring method you use will affect the porosity of your casting.

    I made lots (several hundred) muffing ingots from aluminum soda cans. When sectioned they were very porous. When they are remelted then the new ingots are sectioned they are very clean. I never cast from raw scrap, always from ingots I've made from scrap and I get good results. I've never tried to degass. I accept a small amount of porosity in my castings. The pressure parts never leak.
     
    Billy Elmore likes this.

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