zinc in our molds

[smylee grouch]

There seems to be a lot of talk lately about zinc in our wheel weights and how they will ruin our molds and casting pots. I am un-sure as to what the zinc actually does to ruin those molds/pots. Does it ruin only cast iron molds or does it do the same to aluminum and brass molds also? In the interest of science I would like to know.

[mossyhorn]

Yes I to am interested in this as I saw this on a post recently. Can't Imagine how the melting of a few wheel weights can damage the pots and moulds enough to seriously change the complete chemistry of future castings. Would someone please explain!

[Leroyvdh]

As I understand it.. Zinc melts at a way hotter temperature than lead around 900F.. Aluminum molds and pots shouldn't take these temps..
Easy fix.. Sort your wheel weights.. They are marked.. Pair of side cutters will help you too, can't cut zinc weights, too hard..
When melting in the pot DO NOT GO OVER 750F... Lead will melt and steel and zinc will float to top.. Buy a thermometer

[P.W.Berkuta]

There seems to be a lot of talk lately about zinc in our wheel weights and how they will ruin our molds and casting pots. I am un-sure as to what the zinc actually does to ruin those molds/pots. Does it ruin only cast iron molds or does it do the same to aluminum and brass molds also? In the interest of science I would like to know.

I don't know about the molds but it will contaminate the pot full of lead . Some of the zinc will cling to the side of the pot and that will contaminate future lead that you add to the pot. You have to wire brush or otherwise clean the pot of the offending zinc before you start casting again.

[Daryl]

As I understand it.. Zinc melts at a way hotter temperature than lead around 900F.. Aluminum molds and pots shouldn't take these temps..
Easy fix.. Sort your wheel weights.. They are marked.. Pair of side cutters will help you too, can't cut zinc weights, too hard..
When melting in the pot DO NOT GO OVER 750F... Lead will melt and steel and zinc will float to top.. Buy a thermometer

Zinc, by itself, will melt at a higher temp than lead alloys. Trouble is, when it is in solution with lead, it melts at a lower temp, just as antimony does.

The liquid Zinc will enter the pores of steel in pot and moulds.(just guessing about the moulds) & thus contaminate future pots of metal. At some point,

this stops, of course, but how much lead is ruined?  Best not to put zinc in the pot in the first place. Someone did an article (G&A Annual) of casting & shooting zinc bullets, many

years ago & noted when he attempted to use lead in the pot after the experiment, he could not get non-wrinkled bullets, no matter what temperature he used. He surmised the zinc screwed

his pot for future lead casting.

[Leroyvdh]

Daryl - You have brought up some points..
For this reason I take any lead and do a rough melt to clean it.. Pour a couple bullets for hardness testing.. If I'm melting lead of unknown source problems can be identified before they are poured into ingots.. This scrap can be used for 8oz river fishing weights.. The fellows on CastBoolits forum Say that 3% zinc is ok for cast boolits makes it hard.. Never tried don't want to. 
Thanks Leroy