Lead pouring question

[Nightprowler]

I'm fairly new to this hobby and seem to be having a slag problem. The lead melts easily but produces a lot (I mean lots) of slag floating on the top, which I spoon out. I also have to clear the nozzle between pour in the same mold and still yet the doesn't pour consistant. I flux the pot and burn off the residue. Any ideas of what might be going on?

 

[toadfrog]

Yes, take all the lead out of the pot. Clean the pot out . The lead is contaminated so it must be cleaned. More than likely was wheel weights at one time. If you have an old cast iron pot put itin that get the lead hot I mean hot as you can , stir it with a seasoned oak dowel rod . This may take a good amount of time to skim off the dross untill you don't get anything but the soot from the smoldering dowel. Then you can put it back in the pot to pour. If you don't know the origin of your lead this is the best way to go any time you start to use it.

 

[Nightprowler]

I read about the drop test for lead. About how the sound should be a thud when dropped on concrete. I compared the stuff I was using (which I was told was lead) to some lead I got recently. The stuff I had make a ping noise compared to the thud of the new lead I got. I cleaned the pot and the nozzle of all its contents. Loaded it with the new stuff and what a world of difference. This stuff pours like magic. No clogged nozzle and no slag on top. Thanks for the help.

 

[Hawnjigs]

I learned from Eric G. in CA that "agressively forming" slag is a symptom of zinc contamination. If so this surface slag will keep re-forming as floating silvery sludge no matter how many times the melt is fluxed and skimmed. Best to keep zinc contaminated lead out of a bottom pour pot - I've not tried "toadfrog"'s dowel cleaning method but can say that wax fluxing is unable to remove zinc from lead.

Every batch of wheel weights I've gotten in the last few years has a few zinc ones mixed in, and I'm now very careful to keep them from melting into the lead. Luckily, the melting point of zinc 787*F is higher than lead 622*F, so the zinc weights will float on top after the lead weights melt providing the melt temp is below the zinc MP. But, common zinc alloy Zamak has a much lower melting point than pure, so floating waste should be skimmed off the melt ASAP - for me immediately after the silvery lead no longer clings to the steel clips and dark powdery dross has formed. Here's a pic of zinc wheel weights and zinc contaminated sludge.

 

[Hawnjigs]

NP64, good hard lead will ping, so the drop test will not determine zinc contamination. While the zinc lead might not be a good choice for bottom pouring jig heads, it can be used for ladle pouring larger size simple sinkers.

BTW, zinc contaminated sludge will not reduce any further with heating and fluxing.

 

[meltleadalot2693]

If you accidentally contaminate your melt with zinc can't you add sulfur to the melt and it will remove the zinc?

 

[Fatman]

I've been pouring 35+ years and I've never heard that one, won't say it's not true as I don't know. I take plenty of time when sorting wheelweights, saves alot of hassles later. Hope Hawn or someone posts in on this I'd like to know about the sulfur thing.

 

[LedHed]

Ditto on the sulfer info - like to hear more. Very imformative post.

 

[meltleadalot2693]

They say if you add sulfur to zinc contaminated lead, the sulfur bonds with zinc in the melt to for a layer of zinc sulfide. The zinc sulfide can be skimmed off and you have lead that is supposed to be zinc-free. Never tried it but it might work. You also have to have pure sulfur or sulfur powder.

 

[Hawnjigs]

Very interesting, but I would be concerned about excess sulphur forming oxides which could react with moisture to form corrosive acids.

A "secret" flux from "The Antimony Man" I suspect was ammonium chloride made a mess of my cast iron tools, so I would be careful about outside the box melt additives.

 

[meltleadalot2693]

I forgot how much you put on the zinc contaminated metal but it shouldn't be enough to create any hazardous sulfur compounds. The sulfur should bond with the zinc before it causes a problem.

 

[Fatman]

I know some guys on a bullet casting forum and I'm going to pose this question to them. they work in the metal industry also so if anyone knows they will.

I'll post when I hear something.

 

[meltleadalot2693]

That seems really helpful. I would like to see what the response is.

 

[Fatman]

got a quick answer already!!! this thread has been going on over at the Cast Boolits site http://castboolits.gunloads.com/showthread.php?t=63082&page=4 One of the big things is the fumes when doing it, guess it's pretty bad. Up to each person but I'll stick with the sorting of the wheelweights first before melting them down.

Doesn't seem to be worth the risk.

 

[Hawnjigs]

I'm interested too, since I just aquired some pewter that appears to be oddly zinc contaminated.

"It is easily produced by igniting a mixture of zinc and sulfur. Zn2+ + S2− → ZnS"

Maybe, the melt heat will bond without requiring ignition?

 

[meltleadalot2693]

Yeah, I always hand sort my wheelweights. I really don't sort them because I only pick up lead tire weights and I can instantly identify the steel ones. Here where I live zinc is not used a lot on tireweights. Sulfur should work great for any zinc removing process.

 

[meltleadalot2693]

I'm interested too, since I just aquired some pewter that appears to be oddly zinc contaminated.

"It is easily produced by igniting a mixture of zinc and sulfur. Zn2+ + S2− → ZnS"

Maybe, the melt heat will bond without requiring ignition?

How do you think/know you have zinc contaminated pewter? I never heard of zinc in pewter. Send a pic of that contaminated pewter so we can see it. It might not be zinc but antimony added in the pewter.

 

[Fatman]

Hawn I really don't know. I've never had a contamination problem cause you guys told me what to look for when the Zinc weights came out and I've always sorted them out before melting. I'll wait to hear more from you guys but the original read of that thread that worries me is the toxic fumes from melting the sulfer in.

 

[meltleadalot2693]

If you are worried about fumes, wear a P100 respirator with hepa filters. If you don't want to mess with that, I understand.

 

[Hawnjigs]

Here's a pic of the cast ingots and the slag remaining. The ingots have a smooth tin-like shiny appearance without the frosty surface of antimony content. The weight suggests a lead content. In 12 years of scrap metals source casting I've never seen an ingot with this odd appearance.

View attachment 3