Charcoal for Flux?

[Sawdust]

I discovered something interesting a couple of years ago that I've never seen mentioned anywhere. When any typical boolit casting alloy is heated much above 750 degrees, it's just about impossible to get the surface skimmed shiny. The tin oxidizes instantly into a thin film on top of the melt and continues to thicken as time progresses. This skin won't reduce back in until the temp is lowered. I wonder how many people are running their pots (knowingly or not) upwards of 800 degrees and wondering why all this "fluxing" isn't doing them any good!

Gear

Lyman Cast Bullet Handbook 3rd Edition has some good information on this on page 48 under the heading - High Temperature Casting.

They say at 750*F small amount of oxidation at this temperature.

They also talk about extremely high temps and the loss of tin.

"95Pb-5Sn at 1050*F. The majority of the tin drossed off in 30 minutes"

[geargnasher]

I was talking specifically about reducing the oxides back in as long as the melt was above 750: I haven't been able to do it with anything as long as the temp was above 750. Cool the alloy below that and the tin and whatnot easily reduces right back in with grease/wax/oil/ or sawdust.

Gear

[williamwaco]

. . .

I discovered something interesting a couple of years ago that I've never seen mentioned anywhere. When any typical boolit casting alloy is heated much above 750 degrees, it's just about impossible to get the surface skimmed shiny. The tin oxidizes instantly into a thin film on top of the melt and continues to thicken as time progresses. This skin won't reduce back in until the temp is lowered. I wonder how many people are running their pots (knowingly or not) upwards of 800 degrees and wondering why all this "fluxing" isn't doing them any good!

Gear

This is also interesting to me because I have also noticed that ( my ) oatmeal forms only when smelting clip-on wheel weights and only when I get distracted and let the pot "cook" for 20 to 30 minutes before fluxing.

Once they are smelted, well fluxed, well cleaned, and poured into ingots, they will not oatmeal again.

BUT

If I attempt to make ingots with this metal with the oatmeal present, the ingots willl have a frothy little volcano at the point the stream enters the ingot mold, and when these ingots are remelted, they will immediately oatmeal. I can tell at a glance by looking at an ingot if it will make oatmeal when it is melted.



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[Sawdust]

I was talking specifically about reducing the oxides back in as long as the melt was above 750: I haven't been able to do it with anything as long as the temp was above 750. Cool the alloy below that and the tin and whatnot easily reduces right back in with grease/wax/oil/ or sawdust.

Gear

Agree with this. It is stated several times in the Lyman Cast Bullet Handbook 3rd Edition. 750°F is the threshold above where, oxidation problems arise.

Tried high temp casting with 4 different pots. Waage 20#, Lyman Mag 20, Lyman 10#, Lee 10# and could never get them hot enough to use Boric Acid as an effective barrier. The oxides would clump up with the Boric Acid. Was able to make this work, once, using a propane turkey burner that is used for 100# alloying batches. But the problem then becomes toxic lead fumes. Tradeoffs.