What is this scummy stuff?

slug

slug

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Sudbury, Ont.
I've been making some Minie balls from sheet lead and I've been getting this scum on top of the melt and it ends up in the nose of the Minie ball.
I've been fluxing like mad and it seems to generate even more scum.

I thought that my pieces of lead sheet were contaminated and I washed them as well.

Someone on the cast boolit board mentioned that he had to cast with the heat turned up high so I was casting at 10 on the Lee furnace.
I cleaned out the pot and tried again at level 8 and uncontaminated metal and the balls came out very nice.
I added a small brick with a small amount of scum and fluxed well and things went well.
I added another ingot with a little more crud on it and things started going down the toilet.
The pot was crudded up big time and fluxing and skimming brought up more scum than I had added to the clean metal.

So now I have another 6 or 7 more pounds of crappy metal.

Does anyone have any ideas for the cause and especially a cure?
I have about 25 pounds of this junk and I don't want to have to toss it.

TIA

QUKUs2n.jpg
 
My immediate thought is that it's oxides and you are still running too hot. Any chance you have a thermometera and what are you using for flux? Does look a bit like contamination but I've never had issues with roof sheeting.

I've been using a PID controller for quite a while now but feel like I seldom ran the Lee pot much above 7.

Worst case, instead of throwing it out adding small amounts seems to work and you can eventually use it.
 
Those blues and golds are from over heating the lead - I do not know if it changes the lead, but I have got many pounds of that from getting impatient and melting lead sheeting with a propane torch, instead of waiting for it to melt in the pot.

Found a very good, cheap flux - ordinary sawdust from my miter saw - spruce, fir - does not seem to matter - throw a hand full into the melt, then made a "stir stick" from small piece of fire-wood - stir in the sawdust well - I think when it turns to carbon it is doing its work (?) - thoroughly scrap sides and bottom of the pot - unbelievable amount of crap comes up to the top to be skimmed off, but no getting away from the blues and golds...

I do not yet use a PID controller, but I did buy a Lyman lead casting thermometer that lives in the pot so that I can keep an eye on the "real" temperature in there - I never did trust or rely on the numbers on the dial of those melting pots, except when starting it up from cold...
 
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I have done this before in my outside smelter where the temps get near 2000f. melt at a lower temp and repour and what slag is there you should be able to skim off.
 
Colours say its pure lead...over heated and oxidized.

Yes pine shavings are the best for flux. Meaning it will CLEAN the lead.

Candels are reductants. Meaning it will help with oxides, but wont clean it.
 
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Great.
Thanks, guys.

I've been using chips from my jointer,
, mainly walnut and cherry, as well as candle wax and NEI flux.
I guess I have to flux more often and more vigorously.

I just bought a new Lyman furnace with the built in PID.
I'll only use really clean alloy in that one.
 
OP - I re-read your initial post. You might have noticed that clean liquid lead is very much "silver" coloured - colour does not change a lot if you let it go hard. I have never seen "used" lead that is not black or very dark grey - no matter how many times it has been "washed". I think that dark stuff is the pure lead combined with some oxygen (PbO2 ?) in the air - that is the stuff that you are trying to "flux out" of your melt - if you get more "crap" when you add flux, you are not done - add more flux!! I use about a handful of sawdust in a 10 pound cast iron pot - and I repeat at least twice. I had read somewhere about using a "pea sized" piece of wax as "flux", and maybe that works with very cleaned ingots - but I do not think that is anywhere near enough to clean "used" lead. Lots of flux - well stirred in - multiple scraping of sides and bottom of the melting pot - can produce very "clean" ingots... Of course, all the flux that you put in there, has to be skimmed off again with the "crap" that is stuck to it... So, even if you make really clean silver or nickel coloured ingots - in a few years they go darker - have to re-flux to get that out when you go to use the stuff to make bullets...
 
If the "scum" is only on the surface, you could use mechanical means to remove it - e.g. a coarse grinder or a stiff coarse wire wheel.
 
Andy said:
If the "scum" is only on the surface, you could use mechanical means to remove it - e.g. a coarse grinder or a stiff coarse wire wheel.
Click to expand...

Common..imagine the lead dust particles this method will get airborne. It’s definitely not the way to do this.
Best way it to melt it and flux - remove the scum.
 
I was not successful at getting the blue and gold out of the ingots, even after several cycles of flux with sawdust - I just presumed it was what I had done by using a torch to melt the sheet and got the lead "too hot", by doing so. Maybe I was not doing it correctly. Would be nice to hear how to get rid of those colours to salvage any "good lead" that is still in there. My impression was that the problem is throughout the lead - whatever surface came to the top displayed those colours - I could be mistaken, but I don't think it is a contaminant in the lead that can be "fluxed out"; I think it is the over heated lead that I was seeing...
 
slug said:
I've been making some Minie balls from sheet lead and I've been getting this scum on top of the melt and it ends up in the nose of the Minie ball.
I've been fluxing like mad and it seems to generate even more scum.

I thought that my pieces of lead sheet were contaminated and I washed them as well.

Someone on the cast boolit board mentioned that he had to cast with the heat turned up high so I was casting at 10 on the Lee furnace.
I cleaned out the pot and tried again at level 8 and uncontaminated metal and the balls came out very nice.
I added a small brick with a small amount of scum and fluxed well and things went well.
I added another ingot with a little more crud on it and things started going down the toilet.
The pot was crudded up big time and fluxing and skimming brought up more scum than I had added to the clean metal.

So now I have another 6 or 7 more pounds of crappy metal.

Does anyone have any ideas for the cause and especially a cure?
I have about 25 pounds of this junk and I don't want to have to toss it.

TIA

QUKUs2n.jpg
Click to expand...


Looks like the lead has been waaay overheated
 
Oxides are a surface phenomenon. If they are indeed lead oxides from overheating they will be very shallow along the bottom and sides, but somewhat thicker at the top as all oxides that formed during the melt will have floated to the top when the ingots were poured.

Take a rasp or coarse file to a spot on the bottom of the ingots and let us know how far you go in before you get to clean, silvery metal.
 
I remelted it all this morning.
I used the 7 setting and then 6 & 1/2, lots of fluxing and scraping.
They're nice and clean now.
Thanks for your help, guys.
 
In your case "fluxing like mad" isn't going to be detrimental to your pure lead/roof sheeting but if you ever decide to try a harder slug alloy such as WW, you have to be very careful with the fluxing-skimming operation. it is very easy to over-skim and remove the metal elements that add the hardness feature to your lead alloy. Actually good fluxing is supposed to alleviate some of the dangers of this, but poor fluxing habits can make it worse. Skimming crud from a harder alloy without fluxing first will immediately remove tin/antimony from a mix.
 
fingers284 said:
In your case "fluxing like mad" isn't going to be detrimental to your pure lead/roof sheeting but if you ever decide to try a harder slug alloy such as WW, you have to be very careful with the fluxing-skimming operation. it is very easy to over-skim and remove the metal elements that add the hardness feature to your lead alloy. Actually good fluxing is supposed to alleviate some of the dangers of this, but poor fluxing habits can make it worse. Skimming crud from a harder alloy without fluxing first will immediately remove tin/antimony from a mix.
Click to expand...

Actually, quite a few years back, a contributor to Precision Shooting or perhaps The Fouling Shot, who was a metallurgist wrote that once a true solution is attained, the tin and antimony won't separate. Apparently the idea of losing your tin and antimony this way is the tale of an old wife.
 
The best read I can recommend on this is a downloadable publication called "From ingot to Target, A cast bullet guide for Handgunners" by Glen E Fryxell and Robert Applegate with a forward by John Taffin.

One of the authors is a chemist and the other a mold manufacturer.

The characteristics of saturation and reintroducing the elements of an alloy we might want are very well covered in the flux chapter.
 
I don’t have a lot of experience with making ingots. Prob have 1000lb laying around in bread loaf sizes. I made my pot poor off the bottom. Took a bit to make a valve that would withstand the heat. Lots of tire weights and roof lead. Flux with sawdust. Usualy fur or pine. Never had discolouration like that.
 
buckhunter78 said:
I don’t have a lot of experience with making ingots. Prob have 1000lb laying around in bread loaf sizes. I made my pot poor off the bottom. Took a bit to make a valve that would withstand the heat. Lots of tire weights and roof lead. Flux with sawdust. Usualy fur or pine. Never had discolouration like that.
Click to expand...

I once visited the Royal Canadian Mint and put a finger of a giant gold ingot. It was bigger than a bread loaf. The armed guard told me not to try that again.
 
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