What problems does Zinc cause in casting

[ripper90]

I would like to know what problems zinc causes in casting bullets. I know from reading post on this site that zinc in your lead is a big NO-NO but what should you look for to tell if it is the problem or something else.
Thanks Ripper90

[Bent Ramrod]

Zinc contamination will turn your molten alloy into a slush that resembles silver oatmeal. It will cast about as well as oatmeal, too. Partially melted lead alloy which has not yet come up to temperature has this same appearance, but no practical increase in temperature will fluidize zinc contaminated lead.

[geargnasher]

Depending on zinc concentration, it will only cause some fillout problems because the alloy acts "thick" and has a high surface tension. If the zinc concentration is high, like 3% or more, it will be visible as a separate layer of metal floating around on your lead in the pot that won't mix in. A certain, small percentage of zinc is miscible in lead alloy depending on temperature. At normal casting temps, only a percent or less will blend in, and it will cause fillout problems similar to those experienced then the mould is too cold.

Gear

[MikeS]

Zinc is a bad thing to have in your lead! Having said that, small amounts don't make much of a difference. I had some of my home made Lyman #2 alloy analysed, and it has .244% zinc in it, and it doesn't make a difference to how the lead casts. I do most of my casting at 650F degrees, and have no problems with fillout, or not getting flat bases, both of which can happen when the zinc concentration in the alloy goes up.

So I guess the moral of the story is: Avoid getting zinc in you alloy, but if you do get a little bit in it, the lead might still be usable.

[Shiloh]

How did it get into your melt or did it??
When smelting, zinc WW float to the top and are easily removed.

Shiloh

[MikeS]

I'm not sure how it got there. I mix up the alloy using a 26lb brick of pure lead, 2 10lb pieces of Linotype and 2lb of tin. I suspect the zinc was in the Lino, as the other were pure.


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[BOOM BOOM]

HI,
If the Zn % is low enough you can dilute it out. I did this once, & it is a bit of a chore.
The out method to get rid of the Zn is to melt then spoon out the oatmeal layer which is at the top, you lose some Pb but you can save a lot. Afterwards you my have to cast at a higher temp, say 850*.:Fire::Fire: