Pure Lead - Dross

[MaverickNH]

I’m casting pure lead (99.5% from RotoMetals) in a Lee 20-4 pot for Lee REAL 250gn 50cal ML bullets. I find quite a lot of very light dross floating on top after running the pot up to 750-775F when fluxing. What that accumulating? I don’t scoop it off until I’m done - should I scoop during bottom pours? Thanks for the advice!


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[redhawk0]

It's likely just some oxide forming during the melt. Its the 0.5% impurity in the lead. You can leave it floating. since you bottom pour...you won't get it in your castings.

redhawk

[Hardcast416taylor]

If you are melting commercial pure soft lead then the `scum` is either from your pot or the 0.5% impurity that is industry standard or it is the flux you are using. Bottom pouring is fine for not having a `scum` problem, go ahead and skim it off as it occurs.Robert

[Silvercreek Farmer]

I flux with pine shavings then leave the resulting carbon in my pot while I cast. It insulates the lead, slows oxidation, and seems to reduce splashing when I drop my sprues back in.

[longbow]

Lead oxidizes easily so yes, while there is some impurity in your lead that is most likely "alloyed" elements. The majority of the dross is lead oxide. You can skim it off or leave it since you bottom pour.

The more stirring and splashing you make will make more lead dross due to exposure to oxygen.

I spend a lot of my working life in a lead refinery surrounded by five or six 235 ton pots and a couple of small pots full of molten lead. The refinery produce 99.999% pure lead through the Betts electrolytic refining process. Most lead refineries use only pyro refining and they cannot get the lead as pure. Whatever remains is a contaminant but the "alloy" should be relatively dross free. The dross forms as the lead oxidizes when molten.

Longbow

[country gent]

There may be some impurities that are coming out along with oxidation. Flux as needed. Sometimes a light layer of wood chips shavings lightly sprinkled on top evenly and left there keeps the air from oxidizing the surface. If you go this route don't empty the pot while its there as it may pull this into the "valve" causing it to leak. At 775* the .5% may be small amounts of tin antimony and other things releasing from the lead.

[Hick]

You could try running a little cooler. I do that and it slows down the dross formation dramatically. Lead melts at 621 F-- so you have a little room to reduce without the bottom spout freezing.

[lightman]

I'll 2nd running lower temps. It seems that the higher the temps the more dross that I get.

[MaverickNH]

On the flip side, many recommend 800F+ for successful cast of pure lead bullets. Maybe I should just bump my mold pre-heat temp up from 400F?


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[WHITETAIL]

I am using a 20lb Lyman bottom pour.
And my way of molding boolets is.
Put the ingots in the pot and when it is
melted and the top has a little scum on top
I skim it and put it in a metal coffee can.
then when I selt later, I just put that in the
new melt. It is not rocket science, KISS!