Zinc in small percentage in bullet alloy

[Rick]

If I add much monotype I get the oatmeal dross. Takes more heat and a heap of fluxing to get it mixed in. Once mixed in it seems to remain stable and in solution. More antimony seems to cause the oatmeal like dross. It can be mixed in but it takes some work and patience.

Never had zinc. I rarely use wheel weights so that isn't a possible source.

That's my take on it, silvery oatmeal on the melt is more than likely antimony. With the antimony a bit high the only way I have ever been able to get the oatmeal is when heating the alloy slowly, at a temp that melts the lead/tin antimony with a much higher melting point can form on the surface. Sawdust and pot temp around 700 to 725 and it will reduce right back into the alloy.

 

[JonB]

But it doesn't look like 1% zinc had any significant drawbacks, either?

Yeah, I think you are right.
also we'll have to see what happens with the unmolested samples once they get older. If Zinc has any long term hardening characteristics like Cu ?

 

[williamwaco]

I haven't experienced zinc contamination as "oatmeal", that's usually calcium contamination or simply an abundance of antimony oxide. When zinc is present in concentrations beyond the saturation point for the temperature, the zinc floats in a molten puddle on top like oil on water.

Williamwaco, when you say "flux", I seem to remember that you use beeswax. Beeswax is an excellent sacrificial reducant, but flux it does not and will do absolutely nothing for your zinc contamination or "oatmealed" antimony. Sawdust mixed and mashed around with the oatmeal stuff using a stick will do wonders for a variety of stuff. If you get the liquid, shiny zinc on top after a good fluxing, it can be skimmed with a spoon and gradually "frozen" out of the melt by lowering the temperature and fluxing/skimming frequently. You'll never get it all, but you'll get the excess out to the point that the alloy can be used if you cast at a slightly higher than normal temperature.

Your memory is correct. I flux with sawdust when smelting wheel weights and with candle wax when casting. So the fluxing I was referring to in this case was sawdust. I tried fluxing with sawdust and skimming "until it quit forming" but it never did and I wound up with an empty pot and a sprue bucket full of oatmeal. You are right. the fluxing with sawdust would reduce the amount of the "stuff" by about 50 percent for about 10 minutes then it would come right back. I doubt if it was antimony for two reasons. I was smelting clip on wheel weights. and they were not particularly hard. Around BNH 12.

I have witnessed this twice in my career and I think this is significant. Both times, I was smelting COWW and walked away for a minute that turned into 30 and the pot temperature exceeded 800 when I returned to find a thick bloom of "stuff" that looked like silver oatmeal.

 

[Ian]

WW have a lot of calcium in them from recycled battery plates getting into the scrap stream that WW manufacturers buy (look where WW have been made for while and it explains a lot), but if you used sawdust to the end of the pot I bet your original assessment of zinc is right. Another thing that I'm pretty sure zinc WW alloy has in it is aluminum (some form of Zamac alloy), and that combined with zinc probably exacerbates the oatmeal issue.

I sort by hand and still miss one or two zincers per bucket, but I use a wood-fired melter and it's about all it wants just to get lead alloy up to fluxable temperature. I'd be hard pressed to get it hot enough for zinc to melt in.

 

[williamwaco]

WW have a lot of calcium in them from recycled battery plates getting into the scrap stream that WW manufacturers buy (look where WW have been made for while and it explains a lot), but if you used sawdust to the end of the pot I bet your original assessment of zinc is right. Another thing that I'm pretty sure zinc WW alloy has in it is aluminum (some form of Zamac alloy), and that combined with zinc probably exacerbates the oatmeal issue.

I sort by hand and still miss one or two zincers per bucket, but I use a wood-fired melter and it's about all it wants just to get lead alloy up to fluxable temperature. I'd be hard pressed to get it hot enough for zinc to melt in.

And threin lies the rub. Every time it has happened to me I walked away and let it get way too hot.

PS I forgot to mention that the sulphur treatment cleaned it up nicely but the fumes were so toxic I did not continue after the first test.

 

[Ian]

I did the sulphur thing too, once, just to see if it worked. I think that one episode probably caused acid rain events for the next year, but dang that alloy cast well. Again, temperature was a problem, have to keep the alloy in a condition like brown sugar and mixed up with the granulated sulphur. When it poofs it's a real fun time.

Jon's experiment was interesting to me because it goes against popular wisdom that zinc is a show-stopper and to be avoided at all costs. We hear that all the time and it's valid...BUT...how valid is it really? Everyone avoids it or shoots up zinced alloy in handguns because they assume it's no good, but is there some advantage to hardening/toughening that has been missed?

 

[williamwaco]

I did the sulphur thing too, once, just to see if it worked. I think that one episode probably caused acid rain events for the next year, but dang that alloy cast well. Again, temperature was a problem, have to keep the alloy in a condition like brown sugar and mixed up with the granulated sulphur. When it poofs it's a real fun time.

Jon's experiment was interesting to me because it goes against popular wisdom that zinc is a show-stopper and to be avoided at all costs. We hear that all the time and it's valid...BUT...how valid is it really? Everyone avoids it or shoots up zinced alloy in handguns because they assume it's no good, but is there some advantage to hardening/toughening that has been missed?

The most fun I can have ( legally ) is doing something that "Everyone Knows" you can't do.
I hope to never see another pot of oatmeal but If I do, I will promptly turn it into 148 grain wad cutters.