Dross removal

[jar-wv]

Newbie questions. I just finished up smelting about 1/2 5 gal bucket of WW in one batch. Done on a coleman propane stove and 8 qt stainless stock pot. I did some stirring and skimming before fluxing. After fluxing I stirred and scraped and skimmed some more. After about 6 or 8 good stirrings and scrapings I noticed that there was still lots of stuff coming to the top each time. I fluxed again and continued to stirr and scrape and skim. I never did get all the stuff out as I kept getting about the same amount on top each time I stirred and scraped the sides and bottom of pot. I finally tired of it and ladeled it out in my pop can ingots. Is my batch to large, (approx 70lbs) or is this normal. The first WW I melted was done in much smaller batches, about 20 lbs, and I didn't notice having so much trouble getting it cleaned up.

jar

[Turkeyfeather]

Jar,
Great question and everyone must encounter these things to advance in the metalurgical science of casting.

I melted pails and pails of wheelweights to cast ingots of which I save and use at convenient times in my bullet casting pot.  I have found it quite enjoyable to sit outside  in a lawn chair next to a campfire in which rests a cast iron pot full of wheelweights. I get a pot full of material and then do the same as you. I spoon off the clips and residual floating waste. Then I flux the pot and again spoon off the dross.  

Depending on the age and type of weight, there can be several scrapings from a twenty pound crucible. After fluxing you want to remove the blackened dirt and waste material without skimming the other usable parts of the alloy such as antimony which can seperate from the pure lead during the heating process.

The main part of this rough step is to get clean usable ingot stock which will enable you to melt in your casting pot. You can alway fine tune, such as a final fluxing and perhaps adding of alloys once you have properly cleaned the base material.  Have fun this is a great part of shooting. Along with being a great cost saver, shooting from scratch is very satisfying.

[jar-wv]

I wasn't aware that antimony would seperate during the smelting. There was some of the melt I ended up dipping out but not much. Mostly what I encountered was just the black dirty stuff. After examining the empty pot I noticed there was stiff a bit of it here and there on the bottom of the pot. Also my last ingot ended up with more dirt in it than I would like to see. I think I need to get a flat ended type of utensile to scrape with instead of my rounded skimming spoon.

I'm finding this to be a rather enjoyable addition to my shooting and reloading hobby. The wife just kind of gives me odd looks and tells me I'm easily entertained. :-)

[jar-wv]

double post

[JPH45]

I wasn't aware that antimony would seperate during the smelting. There was some of the melt I ended up dipping out but not much. Mostly what I encountered was just the black dirty stuff. After examining the empty pot I noticed there was stiff a bit of it here and there on the bottom of the pot. Also my last ingot ended up with more dirt in it than I would like to see. I think I need to get a flat ended type of utensile to scrape with instead of my rounded skimming spoon.

I'm finding this to be a rather enjoyable addition to my shooting and reloading hobby. The wife just kind of gives me odd looks and tells me I'm easily entertained. :-)

The antimony won't seperate out, neither will the tin. the oxidized metal that forms onthe top of the melt is the same stuff that is in the pot, except it has picked up oxygen molecules that keep it in suspension from the melt. For that metal to return to the melt, the oxygen must be replaced with carbon. So keep a 1/2" oak dowel in your pot, it will help reduce this dross. The other thing that will help reduce the dross is to flux with used motor oil. Yeah, definately smokey and flames real good too, but it provides a very rich carbon source for the melt. But note that aas soon as that carbon source is gone, the dross forms. So in your casting pot, cover the melt with kitty litter, or sawdust. The kitty litter will form a layer of protection fromthe oxygenrich atmosphere, the sawdust does the same as well as provides carbon.

But make no mistake, the idea that tin and anitmony seperate from lead in the melt is a wives tale, at least at the temperatures we run to cast. None I know of are running equipment that is capable of pushing the melt to and sustaining it above 1200dF and I'm not sure that temperature will seprate them. The alloys we make to cast bfraom are true solutions, that is what makes them an alloy. If they did not dissolve into solution, they could not make an alloy. Lead/tin/antimony alloys are every bit as stable as the tin/copper alloy we call brass, and every bit as stable as the alloys we call steel and stainless steel, were they not, they would be of no use to us, as if they wouldn't stay in solution in a molten state, they wouldn't stay in solution in a solid state. As soon as we cast and open the mold, our bullets would fall apart, of what good would that be?

[Nobade]

Two things could be happening. One is you're melting your metal at way too high a temprature. That will speed up the oxidation and keep making stuff float on the top of the melt. The other is you've got some zinc wheelweights mixed in there and let the melt get hot enough to melt them. In that case you'll keep getting a frothy looking dross on top, and the ingots you have made won't be worth beans for casting bullets. Try to use some of it, and if it casts OK you're in business. If not, I'd probably just sell the whole mess to the recycling yard and try again. Don't let your melt get any higher than 685 deg. and skim off anything that floats to the top.