Sources for tin

Dalerj wrote: Dicko, What does the copper and selenium do the alloy to make it unusable? Another thing, I hear that zinc will ruin alloy for casting. What does ruin mean? I have some ww that have zinc melted in with the lead & antomy ( I didn't know about the zinc ww when I melted the batch down and made bricks) I have not tried it yet. What do you predict will happen if I try to use the lead with zinc? Thanks Dalerj

There are traces of harmful impurities in most scrap lead.   "Harmful” does not mean dangerous, it means adverse effect on casting.   In that context “impurities” means any material that can cause such adverse effects.   There are various, but those most likely to be found in scrap lead are copper, aluminium and zinc.   More than 0.25% copper impedes castability ie the ability of the alloy to fully fill the mould.  It shows up in incomplete fill out of lube grooves and semi wadcutter shoulders that should be nice and square but are rounded.   No amount of addition of tin or antimony or increase of temperature cures it.   In sufficient concentration it can be seen as small lumps in the surface of the melt.   In theory it is not difficult to remove but I found the recommended method didn't work.

As little as 0.10% aluminium has the same effect and can precipitate crystals that can clog a bottom pour spout.   Zinc causes thickenning of dross and skin formation that also ruins castability.  

Copper, aluminium and zinc are the most common contaminants.  The most likely sources are copper from babbit metal, aluminium from type metal blocks and zinc from die casting moulds.   It is a bigger problem than it once was because many items these days are made from scrap which may itself contain these metals, like wheelweights.    

The effect of all three in preventing good quality castings is so similar that you can't tell which it is.   But it doesn't matter because the result is the same and you can't remove it nor can you use the alloy.   I'll return to that shortly, but first let's look at some others which are less common but may be encountered occasionally, some of which can be dangerous.   Calcium will combine with antimony to form an intermetallic compound which, having low solubility in lead and lower specific gravity, will float to the surface where it will be removed with the dross, thus depleting the antimony.

More importantly, the intermetallics in the dross can react with moisture or moist air to form stibine or arsine gas both of which can be dangerous in small quantities.   Strontium is somewhat similar.  Barium and Magnesium are in the same chemical family as Calcium and Strontium but neither is present to any extent in lead alloys.  Both would cause an increase in dross levels.   Magnesium will cause bullet disintegration over time by inter-granular corrosion.

The only source of calcium and strontium is maintenance free vehicle batteries which are best avoided as a source of lead bgecause they are too much trouble anyway.

I have never used solder containing selenium, but I would expect and effect similar to copper, aluminium or zinc.

The good news is that in two decades of commercial casting I have encountered only a few batches of scrap that caused problems.   In particular, copper is the biggest problem simply because you might encounter scrap that contains copper because some of the lead items have been made from scrap including some babbit metal.  If you avoid babbit metal you will be OK.   There are various babbit metals, not all of which contain copper.   But one formulation contains 8% copper.   The problem is you don't know which you have.

If you get a batch of alloy that won't cast properly don't persist.   Set it aside and mix it no more than 10% with good alloy.   Unless it has an unusually high % of contaminant, "watering” it down to 10% of its % will bring it below the level at which it will affect anything.

That's my recommendation for your zinc contaminated alloy.  There's nothing else you can do.   Prepare a small melt with 10% of the zinc contaminated alloy.   If you still get trouble reduce to 5%.   That should do the trick.

One other point that I'm sure will get me into more trouble is the superiority of ladle casting.   As well as its other benefits, I found that it would successfully cast alloy that would not cast bottom pour because of contamination.   I have investigated all these things in depth.   For example, on one occasion I spent two working months figuring out why I was getting particular problems with bottom pour that I was not getting with ladle casting.   So its your choice whether to believe me.   Some on this forum don't.