Zinc - what is the problem?

[theperfessor]

I've followed several threads concerning zinc contamination in casting alloys. I've also noticed that some old bullet molds used a zinc washer or gascheck.

My assumption is that zinc makes casting difficult but it isn't too hard to shoot through a gun barrel.

Is the problem bullet fillout? Zinc is widely used to make die-cast parts. I know that process creates a lot higher pressure head, so if a pressure casting method were used to cast bullets from zinc-contaminated alloy, would the bullets be OK despite their lighter weight?

Any comments?

[35remington]

Zinc tends to make poor bullets when intermixed with lead, head pressure or no. At least with the head pressure appropriate and acheivable in making bullets.

I'll quote you a learned source:

"The presence of zinc in an antimonial alloy causes an apparent thickening of the dross. When the alloy is cast, the skin of dross on the advancing stream of metal prevents fill out of mould details."

I've had more trouble with calcium in unknown sources of lead, but zinc won't help things by any means, and zinc is being found with wheelweights, which is the major lead supply for most of us. A little inattention when smelting your lead these days can be costly, but paying attention will keep you out of trouble.

[theperfessor]

35remington -

Would be interested to know how calcium got into your alloy and how you identified it as such, so I can watch out for it my alloys. What are the characteristics, etc.

Thanks.

[dakotashooter2]

Seems that I have heard the other concern is the hardness/brittleness of zinc. For plinking a "frangible "bullet may be OK but for hunting it would not be desireable.

I suspect for the home caster getting everthing right to cast with zink may be more trouble than it is worth. But I'm not ready to discount it all together. If lead restrictions get tighter at some point, it may be one of the few options we have.

:castmine:

[theperfessor]

One of the members of my Advisory Board is a manager in a die-casting facility. I'm planning on doing some research and then see if he will give me a tour of the plant.

I'm not really interested in making all-zinc bullets. I'd just like to know if there is a reasonable way to use lightly contaminated alloy instead of throwing it away or diluting with huge amounts of good alloy.

I suspect that the cost of the equipment normally used in die casting may be too high, but then again I have access to two machine shops and I have made some pretty unusual things so you never know.

[35remington]

perfessor, I suppose you could make duck decoy weights or sinkers or slingshot ammo out of it. Then when the contaminated supply is gone you might have to clean your lead melting pots thoroughly. A tiny bit of zinc is supposed to be highly contaminating.

Calcium is usually found in auto batteries, so I figure I've run into some strange sources of lead that got intermixed in my supply somehow. Calcium is nasty stuff; it may form toxic fumes.

Stay the hell away from auto batteries as a lead source.

[leftiye]

Pre fessor, I had 100 lbs of zinc contaminated lead. It was sold to me in block letters. After months of considering it, I've come to suspect that the printer added zinc on purpse to make it harder (or had zinc in his hands which he thought was tin). Consider that it was in the letter blocks when I got it, he had to have cast it afterwards. Some suggest that this mush (60% of melt) is due to too much antimony, others say that it is ink corruption. Can that still be said of wheelweights with the same mush on top? No ink involved, not enough antimony to bother anything in wheelweights.

[theperfessor]

35remington-

Not to presume too much, but do you mean cadmium instead of calcium? I have never used lead from old batteries and don't intend to, maybe that's why I have never noticed that form of contamination.

[35remington]

Not cadmium - calcium. Didn't misrepresent it.

[DLCTEX]

Calcium can be introduced by smelted pipe, for one. Calcium deposits left by water, which in our area is considerable, can become incorporated into the lead. Most of it can be skimmed off, and as with zinc, keeping temps down helps to keep it from blending. I find it easier to keep pure lead clean by lowering temps. I can really throw the heat to the smelting pot until melt is achieved, then turn it down to just keep a good melt until fluxing and skimming is finished. Lots of stirring with a hardwood stick floats the crap to the top. IMHO keeping temps lower produces less oxidation, so that should help save the tin.Dale

[theperfessor]

35remington

I checked some references and you're right - calcium is added to batteries to stiffen the plates. However, the only reference I could find about toxicity refers to arsine and stibine gas which is produced by the trace amounts of arsenic and antimony in the plates also.

Would be interested to know what makes the calcium toxic, or is does it just come along with the arsenic and arsenic is the real toxic devil? Do you have any references relating to calcium toxicity?

Thanks for any info you might share.

Dale - thanks for warning on water pipes and how to prevent incorporating into mixture.