slag

when I melt my wheel weights and skim the slag if I let it cool and remelt I get more slag. what am I skimming off? am I loosing alloy materials?

When you have molten alloy in contact with atmosphere a grey metal oxide layer will form on top. If you are skimming it off you losing alloy materials, especially then tin.
Instead add a source of carbon such as paraffin or bee's wax and it will reduce your oxide back to metal.

There is a lot of "fake news" when it comes to what alloys you are losing. I've done a LOT of XrF testing where I overheated the pot (~900F) and tried to skim just the top layer of alloy off and analyze that. Based on all the online discussions, I expected the layer to be Tin rich. It was no different than the base alloy.

Yes, the grey layer on top of a clean melt is probably Tin oxide. BUT it is too thin to make any difference in your alloy mix.


The initial gunk you are skimming off of wheel weights is who knows what. Unless you a skimming a pot off that is barely molten, you are not removing enough alloy to worry about it.

BNE

Here is some great info for you about Slag/Dross.
http://www.lasc.us/Fryxell_Book_Chapter_4_Fluxing.htm
"From Ingot to Target: A Cast Bullet Guide for Handgunners©" by Glen E. Fryxell and Robert L. Applegate.
Read the whole book when you get time.

Thanks BNE that makes a lot of sense. Keep Happy

Even after fluxing still some dross may appear on surface. Atleast i had some. Been skimming it off on tin can and at this moment i have 10ltr bucket half that dross. When it is full it is time to take it on to junk yard and get my paycheck from it. :p

Don't be in a hurry to scrap that dross, or slag as you are calling it.

I rendered several hundred pounds of assorted lead, mostly CWW, but had some SWW and plumbers lead too.

I saved all the dross, and rendered it separately into ingots. I put the dross ingots aside for a time, then sent a sample to BNE.
The dross sample came back as Sb 1.9%, Sn .4%, balance Pb.

IOW, the dross came back as CWW.

Now, all my dross collects in a coffee can, and gets tossed in with the next batch of CWW when rendered.

Like BNE says, its probably a mix of lead and tin oxides with whatever paint, dirt of grease that was on your scrap. I don't save this stuff when I'm smelting scrap but I do save it from my casting pot. This goes back into the next smelt, for whatever good it does.

I only smelt lead and it should be pure. I have corner on my basement where are "unknow alloys" need to give samples to my friend who has possibility to check what it holds in. So it is most likely some oxidation from lead. And i do use sawdust on smelting and flux all my smeltings

I've process thousands of pounds of antimonial lead, and saved all the dross. I've processed just a small fraction of it, but ended up with twenty odd pounds of a hard alloy.

I intend to process it all, combine the lots, and get an analysis.

Honestly, while some of my "dross" is what I skim off of the top of a pot of clean metal, most of it is metal containing sawdust ash. While I try to skim just the ash, and even though I don't often see liquid metal dripping out of left in the perforated skimmer, what gets dumped in the can often cools into a hard, heavy lump rather than fine light powder. So maybe I'm just scooping out alloy.