Lead foam?...

[glockguard]

Been casting for sometime and have used a variety of lead products but very recently during a casting session I noticed a buildup of a sort of foamy material on top of the melting pot. Have no idea what caused it or what it is. I removed it and observed shiny metal underneath, this stuff was much lighter then lead sort of grainy and about ½ inch thick. I think most of the metal I was using during this session had come from wheel weights linotype and some new lead wool, all products I used before.
If anyone on the list has any ideas I would appreciate sharing them,
Tnx. Tom g

[leftiye]

Sounds like you got some zinc. Also sounds like you might have been lucky, and didn't stir it in before skimming it off? Zinc is a PITA.

[runfiverun]

smelting hot?
always turn the smelting pot down after melting,fluxing etc.
one bat pot of smelt is way better then 4-5 of casting melts.

[docone31]

Some lead alloys have aluminum additives. I have run into that when melting pewter.
It makes a "crud" that is really foamy looking. To a certain measure, aluminum will alloy with lead. So will silver, gold, tin, antimony and a bunch of other metals. Most alloy with heat. Zinc will stay in solution at the proper temperature. As the temperature lowers, zinc, being lighter will begin to rise ultimately congealing at the top near the oxide layer in the melt. Same with aluminum.
Some alloys stay alloyed at "normal" temperatures. Tin is an example.
I have run into that "foam" with zinc in the melt. It is a total pain in the butt.
I gradually lowered the melt temperature in the pot untill I could remove the zinc float. It also looked somewhat foamy, to an extent.

[DLCTEX]

I agree with the zinc diagnosis. If fluxed and stirred it will gradually seperate and float to the top, but will be present to a small degree for some time. It is not a big problem in small amounts to the bottom caster, but may be more of a problem for the ladle caster. You may have to run hotter than normal to keep it flowing, but it will make good looking boolits that will be mallable. It remains to be seen if it affects the balance of the boolits due to lumps of the lighter metal in off center spots. So far I can't tell the difference in pistol boolits, but have not bench rested for accuracy, but offhand shooting does not indicate a problem, as yet. The boolits from cleaned contaminated metal weighed the same as WW boolits. DALE

[glockguard]

Thanks for all the thoughts on the zinc, that more then likely is what i am incountering.
Good shooting to all... gg

[LAcaster]

Zinc whel weights Zeeh

[Brownie]

I had some weird looking foam in my melting pot too. I was using that new Lyman lube that needs to used it a heated lubrisizer to flux the metal and I think that is where the foam can from.

[runfiverun]

if it was a grey like fluff that is oxides and junk.
you want that out.

[cbrick]

I disagree with the zinc theory. If it looks like silvery oatmeal and appears as the melt heats up and begins to turn liquid it is antimony. Been there . . . Done that. Next time you see this try sprinkling some saw dust on top of the oatmeal and watch it disapear, an amazing thing to see.

My SWAG is simply that with the melting temp of antimony so much higher than lead and/or tin as the lead begins to turn liquid the antimony hasn't yet, at least not completely and it looks like oatmeal floating on top. You want to flux this back in, not remove it. No point in depleating your alloy, not only will your air cooled as cast bullets be softer but if you water quench or oven heat treat you will greatly increase the hardening time curve to acheive the final BHN.

What my SWAG doesn't address is why I only get this condition on occasion and not always or never, could have something to do with how fast the alloy heats up but that's a WAG, not a SWAG.

Rick

[leftiye]

"C", Yeah, but it doesn't always flux back in. At least not until about 800 degrees is reached. It reappears the next time that you melt it again too. I skimmed 60 lbs. of this off 100 lbs. of my alloy, and the remaining alloy was still BHN28!

[ForneyRider]

I extremely new too.

Also getting this sludge from wheel weights recovered from truck tire shop.

Dad been using it for sometime for sinkers.

We decided to try bullet casting.

Doing research on my waved bullets, I came across the Zinc theory. Antimony has higher melting point than zinc, which has higher melting point than Tin and Lead.

When I did a good amount of skimming and fluxing(wax and pecan shell dust) and cranking the temperature, my bullets are less wavy. I have some loaded and waiting for a good day to test.

[cbrick]

Wow leftiye, 60% of your alloy skimmed off? I can see where that would be a problem. Hard to believe that's WW alloy. Also hard to believe much of any alloy would be 60% zinc. Monotype is 28 BHN air cooled but its 19% antimony, not zinc.

On another subject, its always fluxed back in for me (WW alloy) but it has only happened a few times. In fact, most of it disappears just sprinkling saw dust on top of it.

Let us know what you figure this problem out to be.

Rick

[BOOM BOOM]

HI,
I HAVE HAD THE SAME PROBLEM FROM TIME TO TIME.
I WILL TRY FLUXING 2-3 TIMES, IF IT DOESN'T GO BACK INTO MIX I SPOON IT OUT & CHUCK IT.
Zn IN THE MIX CAN BE DILUTED OUT TO THE POINT THAT IT DOESN'T AFFECT YOUR BULLETS BUT IT TAKES A WHOLE LOT OF DILUTING. BEEN THERE & DONE THAT.

[leftiye]

CB, As boom Boom said zinc takes a lot of diluting. I don't figure what I skimmed off was all zinc, but I skimmed off over 55 lbs of mush. Other than this, I've never had this "mush", even with stereotype. BTW, zinc in lead solution does harden the alloy.

[44man]

I use a lot of pure antimony as I add it to WW's to get harder boolits. It will melt in and alloy at 600* and leave nothing floating on the surface and none will come back to the surface once alloyed with a small amount of tin added.
I suppose if the tin is lacking, some might leave the alloy. I can see it if monotype is used with the tin depleted.
Once lead, tin and antimony is alloyed it is almost impossible to separate out or have one metal float on top with our pots.
If you start the pot at 600* and leave it sit, zinc will float. It does not alloy well and melts at a higher temp. It does not look like foam. It looks like a semi molten boolit that breaks in half when dropped. Lots of crystal looking stuff. It is also pretty heavy when skimmed. Don't flux it in, just remove it and you won't lose any antimony or tin.
You can tell if you have zinc with one cast boolit. It will not fill out and looks like a galvanized rain gutter.
You can avoid zinc when smelting by starting the lead melting, then adjust the temp to 600* and don't get any hotter. Anything we don't want can be skimmed off with the clips before fluxing. The tin and antimony will stay in alloy. (As long as there is some tin.)
The foam might be aluminum. If smelting was done with real high heat, any crap will melt in. I watched guys with WW's that would not melt in and they kept dunking them under, got tired of that and turned the heat WAY up because they didn't want to lose those few weights.
It always helps to add a small amount of tin to the clean smelt before making the ingots. Then when you put it in the casting pot, the good stuff stays alloyed.
The best thing to use is a thermometer. I had a pot that the thermostat would not cycle right and the surface would cool and look like contamination. You don't want to remove it because it is good alloy that got cold.
Anyway, I have never seen antimony floating on my alloys. When alloyed properly, the melting temp goes way down. It is no longer at the antimony melting temperature.

[garandsrus]

I bought some Foundrytype (it was in single characters so it was sold as Monotype) and smelted it into ingots. It had an inch or so of stuff that looked like oatmeal/whipped cream/lead foam on the top of the melt. I added heat and flux and it went back into the solution.

I had the alloy analyzed after it was smelted. Here's the composition:

Tin 15.8%
Antimony 24.5%
Lead 52.5%
Bismuth 2.7%
Copper 3.0%
Total 98.5%

I don't know what the other 1.5% is. You will notice that there is no Zinc.

You might be throwing away "good stuff".... If you still have the "foam" and want to send me a couple lbs, I can get it analyzed to see what it is. My recycler has a "gun" that identifies the percentage of each component in the metal in just a few seconds.

John

[44man]

Good idea. Some are throwing away good stuff. I have no experience with the real heavy antimony alloys but can see where it can form on top. The question is what do you have before you get excited?
The biggest problem will be with contaminated WW's. Linotype and monotype should have known metals in it. I would not be scrapping anything from those.
Melting all kinds of scrap lead together can give all kinds of weird stuff that we can't identify.