Granulated Tin?

[fireball]

I got a hold of some tin bars a good while ago and recently went to use them in an alloy mix of 9 lb. wheel weights, 1/2 lb. tin, and 1/2 lb. pure lead. It is a mix I have used before that is supposed to approximate a Lyman #2 alloy. I noticed right away that the tin bars had partially oxidized?? leaving silver colored sand in the bag. I scrapped off the grains still on the bar and put the un-oxidized? tin into the mix. End result, the first ingots I poured into a Lyman mold looked OK, the last 2 ingot pours had a frosted appearance typical of too high of a casting temperature. I dialed back the furnace temperature to 600 degrees and got the same result on a second batch. This time on the second ingot pour, a bar broke in half as it dropped free of the mold. I noticed the same granular sand texture in the broken bar. Not sure what is going on here and was hoping someone in the forum could clue me in

[Rcmaveric]

How hot was that bar that broke?

I have seen my lead look like an icy while it melts. I have had ingots break like that when i dumped them before the sufficiently cooled.

Has to do with how different alloys and their phase shift and how long each phase last.

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[jsizemore]

That high temp will do that. Even at 600degF your still very high and they will have a "granular sand texture" and be frosty.

[quail4jake]

The breaking of the hot ingot sounds like the alloy may have a wide phase / temperature range and you hit it during solidus. Did you reduce the alloy with a lipid, beeswax etc? 600 is hot for a trinary alloy in that range, may just be high temp and inadequate reduction. You may be able to take the granular material from the tin, melt it (low temp) and reduce it, add flux and render useable tin from that. No chance those bars contain zinc?

[fireball]

Thanks for the input guys. To answer some of the questions brought up, I flux with a commercial compound from a company called LETS in Missouri. It is a white powder meant for bullet casting. No idea what it's made of and the container does not say. Been using it for years with good results. I weeded through my wheel weights pretty good and do not believe any zinc ones made it into the mix. I did dump the Lyman mold soon after the surface solidified. Am I correct in guessing the silver sand coming off the commercial tin bars is oxidized tin? Is that normal and is it still usable? I take from the response from quail4jake I can do just that. Jake could you explain what the "reduce" part of this procedure is about? Thanks.

[Jeffrey]

Don't know where in the world you are, but tin exists in two forms: "white" and "grey". White tin is the form with which we are most familiar. Grey tin occurs when white tin is cooled to -58* F, -50* C. Grey tin is a powder. Could your tin have gotten this cold? Scroll down to "Properties of the element".
https://www.britannica.com/science/tin

[Jeffrey]

The "reduce" part of the procedure is this. When a substance combines with oxygen, this is referred to as oxidation. When a substance (metal) is already oxidized and we want to get back in its metallic unoxidized state, in our case we have a pot of molten tin / lead / antimony some of which is oxidized. A carbon source (wax or sawdust) is placed on the molten metal and ignited. The burning carbon doesn't care from where it gets its oxygen. Some of it is going to come from the surrounding air. Some of it is going to come from the metal oxides. This reaction is referred to as an "oxidation reduction reaction". The carbon is "oxidizing", the metallic oxides are being "reduced" back to their metallic forms.

[Skipper]

tin disease

https://en.m.wikipedia.org/wiki/Tin_pest

[mozee]

I’ve got some lead alloy (94% lead 6% antimony) and I want to add some Tin (2%) to it. What is the consensus to get this done the consistently? The tin is in ingot form if it makes any difference.

Melt the alloy first to casting temperature and then inserting the tin?


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[fireball]

Jeffery, thanks for the response and link. I am getting a bit of a chemistry refresher class here.While I live in Alaska, we have not seen temperatures in this range especially where I live not far from Anchorage (ocean influence keeps us warmer than in the interior like Fairbanks). In recent years, we see a few days of 20* below a few times a year, and in the last few, not even that.
I will try melting my tin and add some old bullet lube to see if I can salvage what tin I have.

Skipper, I read the link and I think this is what is going on. My tin was fine for years and then it started deteriorating, a process that I believe is accelerating. Thanks!

[quail4jake]

sorry to be slow on the response...Jeffry has it right and I like the Wikipedia article about "Tin Pest" ! I use a small lump of beeswax to reduce alloy once it looks like there is any amount of oxide on the surface, which I think may help with your Tin woes. I use sawdust for flux and as it chars it covers the surface to prevent the air / alloy interface (I use a bottom pour pot).

[alamogunr]

Thanks for the input guys. To answer some of the questions brought up, I flux with a commercial compound from a company called LETS in Missouri. It is a white powder meant for bullet casting. No idea what it's made of and the container does not say. Been using it for years with good results. I weeded through my wheel weights pretty good and do not believe any zinc ones made it into the mix. I did dump the Lyman mold soon after the surface solidified. Am I correct in guessing the silver sand coming off the commercial tin bars is oxidized tin? Is that normal and is it still usable? I take from the response from quail4jake I can do just that. Jake could you explain what the "reduce" part of this procedure is about? Thanks.

I haven't seen LETS mentioned in years. Just when did you acquire that flux? I think LETS stood for Leading Edge Tool Supply. Many years ago it supplied flux, antimony(pulverized), ingot molds, etc for castors. Bill Ferguson bought out that part of their business at least 20-25 years ago. He has been gone several years. I have a jug of the flux that I got off Ebay at least 10 years ago. Haven't used any of it since sawdust does at least as well.

Sorry for the hijack. I have no idea about the tin.

[fireball]

I really can't tell you how long ago I got the LETS flux. Best guess mid to late 90's. I got several cans of it and I am on my last one now. Still works well. I have never tried saw dust. Sounds like it is a good alternative.
Jake, I will try some beeswax bullet lube and see if it helps salvage my tin. Thanks.