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hawnjigs

Wheel Weight Melt Sludge?

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Since learning proper fluxing courtesy of "sagacious", the only waste is a fine dark powder strained out of the fluxed skim. The chunkier remainder I save and re-heat & flux in a separate open pot to separate any remaining useable metal. But, heres a pic of some sludge skim from a portion of my last batch of wheel weights that refuses to reduce further with the additional heat & flux process. Also pictured are the zinc weights that I was careful to separate from the last WW melt, keeping the melt temp just high enuf to melt lead(622*F) but not zinc(787*F). Does anyone know whats up?

WWsludge.jpg

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Hard to say. It does look like classic zinc contamination, though. Sometimes, even when keeping an eye on the temp, a small zinc ww can slip through and melt, especially during fluxing.

If it's not zinc, fluxing the dross mass at increasing heat and in quarantine should reduce it to a pourable alloy. If it won't cooperate, it's probably got some zinc in it.

Hope this helps, let us know how it goes.

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Can zinc be substituted for antimony as a lead hardener? Zinc is way cheaper than antimony (currently $.70 versus $2.17 per lb.) & maybe some WW mfgs are economizing? Seems to be more & more zinc & steel weights lately in WW batches.

The sludge mass pictured was the remainder after reheating & fluxing skimmed dross to recover useable lead. Increasing heat some failed to melt sludge, not that I wanted to melt out any zinc since I have no use for it.

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I am not aware of any use for zinc in lead alloys. To my knowledge it's addition only has negative consequences, such as creating an aggressively-forming frothy dross scum and ruining the 'pourability' of the lead alloy.

However, you may find a use for zinc in a zinc/bismuth alloy. I haven't worked or experimented with zinc/bismuth alloys, but I believe that zinc and bismuth are completely miscible. Tin is miscible in that alloy. You may wish to ask your bismuth supplier for suggestions on a Bi/Zn alloy ratio. You've been saving all those zinc tire weights, right? :yes:

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"aggressively-forming frothy dross scum" being an accurate description I guess some zinc wheel weights crashed my melt party. Did some research, & zinc alloy Zamak actually melts at a much lower temp than pure zinc. 718*F considerably lowers the comfort gap between lead MP and its indeed possible that some smaller non-lead WW missed the sort and got lost in the clip pile floating on the melt. The pic shows how similar in appearance to lead some zinc WWs are making a pre-melt sort difficult.

I'm pretty satisfied with bismuth-tin alloys so the Zamaks & steelies go into the metal recycling bins. With the foundry price of zinc below even lead and the lead bans I suspect more & more Zamaks will be party crashing in the future.

Edited by hawnjigs
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UG, not counting the ones I missed which might have got melted in with the lead WW, there appear to be at least 3 different types of zinc/Zamak weights that I sorted out. One type is clearly marked "MC-Zn" on the metal, but the others are unmarked & only sortable because they float on top of the melted lead along with the steel clips - for awhile. The "sparkly" appearance is shiny bits of lead stuck to the ones that were pulled from the melt. As "sagacious" pointed out tho, its not hard to lose smaller zinc WWs in the floating clips and in the short time it takes to flux (if one fluxes clips & melt together) the melt temp could easily increase sufficient to melt the zinc especially if Zamak. So you don't have to look it up, Zamak is an alloy of zinc + aluminum & maybe copper which melts at a much lower temp than pure zinc.

edit: In other words many zinc WWs are very hard to distinguish from lead by appearance, unlike steel WWs with obvious rivet holes. You'll notice an absence of small zinc WW in my pic so I assume I missed sorting them out. Pre-melt, the only way I can sort the ones that are pretty much identical in appearance to lead is by testing the hardness (zinc is much harder than lead) by scratching the surface. With sensitive hands one might be able to distinguish the lighter weight of zinc approx 2/3 that of lead.

I prefer to have the clips cleaned of lead as much as possible by fluxing them in the melt, but with more zinc WWs showing up may have to skim off the clips before fluxing, or at least, more closely examine the contents of the floating clip pile.

Edited by hawnjigs
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Hawnjigs

Appreciate the info. Will be adding this to my lead file (3 ring note book) I keep w/ my molds and pouring gear for future reference.

Your post brings up a topic I've wondered about - namely - the sludge after fluxing.....what is in it when it's heavy?

On some of my lead, after flux, all I've got is the black, powdery ash. In other instances, I get metal when skimming off the ash. I initially thought it was lead - and some was - I recovered some w/ a remelt and reflux; but I've also got some metal sludge which will not melt. Looks much like your picture.

Also - any suggestions on the disposal of the ash and sluge? Toss in the trash - metal re-cycle bins at the county disposal center?

Thanks again

UG

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Because HI has a history of toxic chemicals showing up in municipal water supplies and massive marine fish kills from storm drain runoff, the state gov offers an annual "hazardous materials" collection for my skim waste. Prior to this program, with no better choice, my annual gallon or two of dross powder ended up in our trash landfill.

edit: I was wondering why the zinc(?) sludge won't remelt since the WWs apparently melted rather easily along with the lead first time around?

Edited by hawnjigs
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...

Your post brings up a topic I've wondered about - namely - the sludge after fluxing.....what is in it when it's heavy?

If it's heavy, it's still got a lot of lead in it. If the residue from fluxing (dross) leaves a solid metallic mass, then you need to flux the metal again. Often the lead will need to be fluxed more than once, especially with "scrap" lead-- simply repeat the fluxing process. Fluxing twice will usually separate all the dross into pure metal and black powder (metallic oxides and carbon compounds), and you'll recover all the lead that can be recovered.

On some of my lead, after flux, all I've got is the black, powdery ash. In other instances, I get metal when skimming off the ash. I initially thought it was lead - and some was - I recovered some w/ a remelt and reflux; but I've also got some metal sludge which will not melt. Looks much like your picture.

Could be zinc contamination, or it could be an antimony sludge buildup. If it's the latter, then an additional fluxing at higher heat (be generous with the flux) should reduce the dross to a liquid metal and a bluish-gray or black powder. If it's zinc contamination, additional heat usually won't do anything useful (you probably won't recover zinc or anything else).

Also - any suggestions on the disposal of the ash and sluge? Toss in the trash - metal re-cycle bins at the county disposal center?

Thanks again

UG

You can call your municipal waste-management authority and ask what to do with residue and ash from foundry work. They should have some suggestions/answers for you.

Hope this helps, good luck!

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...

I was wondering why the zinc(?) sludge won't remelt since the WWs apparently melted rather easily along with the lead first time around?

When many metals are mixed together in the molten state, they combine chemically. That chemical reaction can produce a pourable, liquid, easy-to-use alloy. It can also produce an alloy with reduced pourability, and often it produces an alloy with much-reduced resistance to oxidation. The admixture of zinc and lead seems to exibit both of those deleterious characteristics, and when molten it forms dross aggressively. Soon the entire melt reacts chemically into a mass of slag or dross. At that point, the lead and zinc need to be separated by other means, and fluxing is of little help.

It's very much like baking a cake. Once zinc and lead are melted together, it's difficult to unbake them. It would be a whole different world if we could mix any metal with another metal and expect to only combine the beneficial qualities of both.

Hope this helps, good luck!

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Well, that explains why a tiny zinc wheel weight or two I might have missed can result in the formation of such a largely disproportionate amount of terminal slag. Also explains why a previous batch of soft appearing ballast lead tended to continually form surface slag and exhibit poor pouring characteristics.

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Update: new bucket of wheel weights: modified large open pot refining procedure:

1. Hand sort to separate clip-on lead WWs from stick-ons, riveted steelies, trash.

2. Melt clip-ons only till dark powdery dross just begins to separate and float, then immediately skim out clips into large stainless mixing bowl.

3. Agitate clips in bowl with ladle while hot to knock off as much clinging metal residue as possible. Remove clips and strain residue to separate powder waste from useable metal pieces which can be reprocessed later.

4. Skim any remaining floating dross from melt, flux, & pour ingots.

This batch had 3 zinc/zamak WW in the clip pile. Skimming the clips before fluxing seems to have avoided the possibility of heating the zinc sufficient to contaminate the melt. From experience I can say that a zinc contaminated melt will continually form a frothy waste slag and the alloy's pourability will be negatively affected. Its possible to process the slag by adding tin to separate hard metal from powder waste, but the amount of recovered metal will be small in proportion to the amount of tin needed, and the salvaged metal will contain zinc as well as lead. Only practical if you've got cheap tin like garage sale pewter or solder scrap handy.

Thanks to "sagacious" for the necessary information.

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Hi guys,

I'm no lead expert or anything like that, but when I noticed the thread on lead sludge, I figured I'd poke my nose in. My girlfriend is a radchemist who works with lead on a regular basis, and she tells me about her research on occasion, so this is what I know. Pure "old" lead is an expensive commodity in the research world, because as lead ages, the heavy metals in it decay (like polonium) into lead 210, and a whole bunch of other also radiactive things. Eventually, that also decays and you have clean lead (it takes a really long time). So how do you clean it yourself? Exactly like you guys do in your garage or wherever, by skimming the crap that floats on the surface when the pure lead is melted. This isn't a very effective method since the pb 210 and some other metals also melt, but it helps. So moral of the story, that pile of sludge and ash you guys are gettign could be mildly radioactive, and you may want to keep it far away from where you work consistently. Just a heads up.

dhockey11

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Hi guys,

I'm no lead expert or anything like that, but when I noticed the thread on lead sludge, I figured I'd poke my nose in. My girlfriend is a radchemist who works with lead on a regular basis, and she tells me about her research on occasion, so this is what I know. Pure "old" lead is an expensive commodity in the research world, because as lead ages, the heavy metals in it decay (like polonium) into lead 210, and a whole bunch of other also radiactive things. Eventually, that also decays and you have clean lead (it takes a really long time). So how do you clean it yourself? Exactly like you guys do in your garage or wherever, by skimming the crap that floats on the surface when the pure lead is melted. This isn't a very effective method since the pb 210 and some other metals also melt, but it helps. So moral of the story, that pile of sludge and ash you guys are gettign could be mildly radioactive, and you may want to keep it far away from where you work consistently. Just a heads up.

dhockey11

Dhockey11,

The fluxing or "cleaning" of lead that we're referring to here is the separation of lead from other non-alloying compounds and metals, such a carbon compounds or metallic oxides.

What you're probably referring to is isotopic separation. Isotopic separation of lead species does not confront the foundry-worker or lead user. No lead specie presents a radioactive hazard to the lead-user, even 210Pb, since 210Pb decays by alpha-emission and thus poses no hazard.

Fluxing produces "clean" lead because it removes extraneous material, but not by separating the lead isotopes. Lead fluxing residue doesn't contain any radioactive materials. "Pure" labratory-grade lead is expensive because it is very nearly pure lead. 99.9% pure lead is not pure enough for lab use, and super-pure lead is costly because it's expensive to purify and certify. That's not the level of purity we're dealing with here. By clean, we mean, "has hardly any dirt in it.";)

Hope this clarifies it a bit. :)

Good fishing,

sagacious

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