Rick,
So just to be clear: Zinc melts at 785 F unless it's floating on molten lead, then it melts at 604 F?
So just to be clear: you think the only way two substances can combine is if they melt? One can't dissolve in another for example, as salt (melting temperature about 1475F) will in ice water?
I have observed zinc wheelweight floating on top of molten lead that was just over 700 F and it remained intact (but I didn't leave it there for a long time to see if it would dissolve, and neither did I add any "enrichment alloy" like used with antimony to help it along). I regularly run the pot at 650 F.
Throwing out the name of an expert is common when people try to bolster their arguments, but be careful what words you put in someone else's mouth. Why not send Bill Ferguson an e-mail to confirm that's what he says (the exact statement in the first sentence).
Sure thing Andy. I emailed Bill and said you wanted an explanation from him because you thought I was just throwing his name out there. Here's his answer for you:
For references IF you are able to find an english translation of Wilhelm Hoffmann's book on "LEAD and LEAD ALLOYS in English and/or the ASM VOL 8 Metals Handbook on metallography and phase diagrams it is quite clear.
Not trying to use big words, the term EUTECTIC is the key to WHY some metals when they get close together in the liquid state or when one is liquid and the other (or others) is/are still solid, things just 'happen'.....
Easiest example is tin, lead,antimony......
I know you already know this, however....tin melts at 466F
Lead melts at 620 or so F
And if you drop a chunk of lead in the tin and do not raise temperature much, the lead dissipates into the lead-tin eutectic (366+/-F 'melt temp) eutectic composition of 62/38 wt % rather quickly...throw in a small chunk (or even LETS infamous 'fines&dust' ) antimony, melting normal at 1147F, and as the frenchys say, voila', by a SLIGHT temp increase to 465+F one has liquid LINOTYPE as the antimony disappears...WOW
If you, not me, had a small chunk of arsenic, (assumed melt temp 809C like centigrade, (hot)) you would have that wonderous heat treatable lead alloy called WW (I get my arsenic from magnum grade fine shot, the SAFE way....). Similar monkeying around allows ZINC to do lots of things, almost all troublesome, at temperatures below its melting temp.
That's my part. Now if you want to pull your weight and go on any of the forums you mentioned and declare "A solid metal like zinc or antimony cannot be absorbed by a molten metal at a temperature below their melting point", be my guest. Particularly as you apparently think this is not possible, that I am reading too much, don't understand the chemistry, and am drawing incorrect conclusions.
I've done it enough times in the past that I know it's quite possible - although there's certainly easier ways to get antimony into lead than in its pure form. And I've ended up with zinc contamination in a batch of alloy once - a batch that never approached the melting temperature of zinc.
I'm all for keeping things as simple as possible. I'm also all for eliminating possible causes of trouble, including contamination - and that contamination can occur when you're running a pot at around 700 F. And at even lower temperatures if you screw it up good enough.
Now I'm not quite sure how you can declare you aren't getting any zinc into your alloy at 700F - unless of course you pay for an assay on all the WW's you melt down to confirm this. Most of us don't do that. I do know that because most are floating on the top and appear to have their original shape doesn't mean that zinc over the surface of the WW's isn't entering the alloy. I have had some of my earlier batches of WW assayed a time or two back when I had the mine assay department's services available to me in their spare time free of charge - and I did have zinc in my resulting alloy when I melted my wheelweight salvage down and allowed the temps to get above 650F. I didn't follow that up with any kind of organized inquiry into how that affected the accuracy in my cast bullet rifle; it was sufficient to know that if the temperature got much above the melting point for very long, zinc was getting into the alloy.
Whether that contamination ultimately makes a difference in the castability of your resulting alloy is probably a combination of how many zinc WWs were mixed in with the lead, how hot you got your molten alloy (particularly at the bottom of the pot while waiting for all the WWs at the top to also melt), how long they remained in there, how much time you spent stirring and fluxing - and how fussy you are about the results you get from your casting session. Somebody casting "shooters" isn't going to be anywhere near as critical as somebody involved in CBA benchrest matches. I do wonder how many people who just can't quite seem to get a mould to fill out properly for them are in fact trying to cast with contaminated WW alloy.
However, anyone who assumes that zinc cannot possibly contaminate molten wheelweight alloy as long as the temperature remains below the melting point of zinc is quite simply wrong.
I will repeat a line from my original post to start summing up here:
I think you're hitting the critical point. If you bring the temperatures just up to the point where the wheelweights are melting, anything solid is crap to be removed.
I generally agree with your methodology in how you turn salvaged wheelweights into bullet alloy. I don't agree with how readily you dismiss the potential for zinc contamination while claiming a person has to be extremely careless for that to happen.
I prefer to go one better. I make a concerted effort to pick all the non-lead WWs out of the salvage before it ever goes in the pot. I melt to the point of a barely molten alloy, and yes, I do use an accurate thermometer to ensure I'm not getting up into temperatures where I don't want to go. A thermometer, for example, will tell me in a big pot that while the temperature of the molten alloy at the top of the melt might be just a little below 600F, the molten alloy right next to the sides of the pot where the flame is being applied may be well over 700F. Hmmmmm... not exactly what I want to see.
If I can't afford an "expensive" $35 laboratory grade thermometer to keep track of my pot and as an indicator of how consistent my alloy is by its' melting temperature, then I probably shouldn't be spending money on shooting in the first place.
The beauty of it is, at the end of the day, each of us is his own quality control/quality assurance expert; that's true no matter what anyone else says here or anywhere else. What you believe, or I believe or anyone else believes doesn't affect that. However, I do think it is worthwhile for people to see the different sides of any issue and then make their own choices or conduct their own experiments.
Who knows... a few people here might just go melt a bit of tin and then drop some lead in with its much higher melting temperature to see if the lead happily floats around - or instead becomes a lead/tin alloy with the tin. Just to see if in fact a solid metal with a higher melting point will alloy with a molten metal at a significantly lower temperature.
