Excess Tin In Alloy

[alamogunr]

It is common knowledge that a little tin added to WW can help castability. What is the downside to adding too much tin? I'm not talking about a lot too much. I know that adding tin so that it exceeds the percent of antimony is not good. I have a LOT of solder salvaged from work and graciously agreed to take a surplus off their hands rather than them have to pay a hazardous waste company to dispose of it. It is about evenly split between 40/60 and 50/50. If I just assume that it is all 40/60, would the excess cause a problem if it was 50/50?

And just so we don't get into a discussion about how much tin I'm talking about, the first number is the tin %.

John
"alamogunr"

[ANeat]

I sure wouldnt worry about the difference between 40/60 or 50/50 for bullets.

To me to much tin would just make bullets lighter and more expensive.

If you want consistency you might just smelt all the 50/50 and 40/60 together and make your own 45/55 ingots that would be the same.

[grumpy one]

John, up to the point where tin percentage equals antimony percentage, in most respects alloy is improved by increasing tin content. Toughness improves a lot, and it looks as if ductility improves as well. The downside is that response to heat treatment is decreased. If you weren't going to heat treat, more tin is just plain better. If you were going to heat treat, check that the hardness you want can still be achieved with a high tin content (just go look up the alloy closest to the one you want, in the Toughness of Lead-tin-antimony Alloys thread, and see what the maximum achievable hardness is.)

[runfiverun]

if you add more tin then antimony, you can have soft spots in your boolits.
however for most applications you can easily get away with less tin then antimony just fine.
if you are using ww's and need a bit more hardness figure 3% sn you will get the benefits
without the problems.
you can't get lyman #2 from ww's as there is not enough antimony in them.

1% sn is adequate for fill-out with ww alloy
and the boolit fit is really more important then hardness anyway.

[alamogunr]

Thanks, I sort of thought this was the case. It is not worth the trouble to me to smelt it together. There is just too much of it. Unless I decided to shoot solder boolets, I doubt if I will be able to use it up in the rest of my life. Basically it boils down to just add it by guess and by gosh for handgun boolets and sort of calculate tin needed for rifle applications.

[HeavyMetal]

How much do the bars of solder weigh? Once you have that you can figure out how much solder to add to a specific amount of wheel weights to get an aproximate alloy.

1pound bars of 50/50 would give you a 1/4 lb of tin per half bar. That's 1750 grains or 4 OZ of tin. Plus the lead of course.

In a 10Lb pot a 1% tin increase would be 700 Grains or 1.6 OZ. remember the lead as part of the figure and you should be able to come up with a fairly consistant alloy all the time with nothing more complicated than a scale and a calculator.

[JeffinNZ]

Yeap, as the Grump One says, the more tin, the less hardening in heat treating.

My clip on wheel weight will oven heat treat to 33BHN. Add about 2% babbitt (mostly tin - 85%) metal and 23BHN is as high as it goes.

[Lloyd Smale]

one problem ive seen with high percentage tin alloys is when your mold gets hot it will leave hot spots where the mold doesnt fill in properly..

[montana_charlie]

if you add more tin then antimony, you can have soft spots in your boolits.
I wouldn't mind having somebody explain that...if it wouldn't take too long to write up.
CM

[felix]

A cheap explaination: Tin likes lead, but tin likes antimony more, causing a divorce and remarriage, leaving lead high and dry. The result is that you have HARD spots, rather than soft spots. The hard spots will slice off of the soft spots, which is why too much tin and antimony will lead a barrel. ... felix

[runfiverun]

charlie
the way i understand it is , that as the antimonial/tin chain migrates during cooling.
it "tears" leaving the excess tin behind that doesnt bond properly with the lead.
causing minute soft spots around these areas.

that is how i understand it anyway.

[carpetman]

felix if tin likes antimony and leaves the lead doing without and you now have a hard spot---wouldn't it be the lead with the hard spot from doing without?

[felix]

Well, feeling it thataway, Ray, you gotta' be right! Maybe that is why they said I have lead in my pants, eh? ... felix

[carpetman]

felix---I rethought this and maybe the hard spot is in the antimony and thats why the tin left. And you have lead in your pants?

[grumpy one]

I'll add my perception of what happens, to contribute to the inevitable reader confusion.

Tin and antimony combine in one-to-one proportions to form the compound SbSn. Because the atomic weights of tin and antimony are almost the same, this requires equal amounts of those two elements, by weight. Hence if you have exactly as much tin as antimony, you have a mixture consisting of a lead matrix with crystals of SbSn in it. If you have more Sb than Sn, you have crystals of Sb as well as crystals of SbSn, but you have neither crystals of Sn, nor Sn in solution in the lead matrix. If you have more Sn than Sb, you have a solid solution of Sn in Pb, with crystals of SbSn, but you have no crystals of Sb. Note that, as felix said, Sn would rather combine with Sb than form a solid solution in Pb. So, as you add tin up to the point where it equals the percentage of antimony, the only change that occurs is an increasing amount of crystals of SbSn and a decreasing amount of crystals of antimony in your alloy. SbSn has generally nicer properties than antimony alone, so this results in a tougher, more ductile alloy, with better castability.

Once you increase the amount of tin beyond the amount of antimony, you start to change the composition of the matrix, since that is where the excess tin has to go. Unfortunately I run out of theory at this point, since Weaver did not cover it. Apparently Iwase and Aoki did, but I haven't been able to get their paper.

[runfiverun]

tin has a much higher bhn then pb has.....if they ain't mixed, then you get hard and soft spots.
that is how i think of it anyway.
just cause that is the simplest way for me to think of it.

[deltaenterprizes]

Too much tin can cause wiskers to form by the alloy flowing into the air vent lines on the mold.According to my old Lyman manual, formula for #2 alloy is 9 lbs WW ,1 lb 50/50 solder.

[montana_charlie]

tin has a much higher bhn then pb has.....
What is the BHN of Tin?
CM

[runfiverun]

that was whaen ww's had antimony in them..
at one time ww's had about 7% sb in them nowdays it is more like 3%
10 years ago it was 4% that period is where 95% of the ww's i have are from.
and i know the older ones were much harder as i found about 25lbs of them from the 50's and
early 60's at my f.i.l.'s house from when he had his shop.

[Harry O]

I'll add my perception of what happens, to contribute to the inevitable reader confusion.


From my own experience, I have a rule that I can have equal tin and antimony up to twice as much tin as antimony. But, I never let the antimony get more than the tin. First, it is hard to cast with (it doesn't fill out well) and second, it leaves a brittle bullet (I have had some of the high-antimony/low-tin crack through when crimping).

My experience is that while tin is considered a "wetting agent", I consider antimony an "anti-wetting-agent". Are these the results of the changes you mentioned in your post.

[grumpy one]

From my own experience, I have a rule that I can have equal tin and antimony up to twice as much tin as antimony. But, I never let the antimony get more than the tin. First, it is hard to cast with (it doesn't fill out well) and second, it leaves a brittle bullet (I have had some of the high-antimony/low-tin crack through when crimping).

My experience is that while tin is considered a "wetting agent", I consider antimony an "anti-wetting-agent". Are these the results of the changes you mentioned in your post.

Harry, nearly all of us are using less tin than antimony. This results in less toughness and ductility than equal tin and antimony, but so long as the antimony is no higher than five to six percent, you still get decent bullets. As antimony continues to increase beyond six percent the bullets do indeed become unreasonably brittle. The optimum amount of antimony is somewhere near four percent.

If you have more tin than antimony, the surplus tin cannot combine with antimony and therefore ends up in solution in the lead matrix. At best, this is wasting the tin. At worst, Dennis Marshall in the RCBS Cast Bullet Manual says it will form soft spots. I do not understand the specific mechanism involved.

Up to the point where tin equals antimony percentage, adding tin does improve castability. Since that tin tends to combine with antimony if there is any antimony available, the metallurgy is likely to be different for alloys of lead-tin-antimony compared with lead-tin alone. Essentially antimony has some negative effects on ductility - I don't know specifically about castability. These negative effects are moderated by tin. However in the range where tin is less than or equal to antimony percentage, it is better to think about free antimony versus antimony combined with tin, the latter being a nicer ingredient than the former.

Sorry I can't offer a general explanation that covers both lead-tin and lead-tin-antimony situations, but I think they are just different. Your concept of tin as a wetting agent seems to work for lead-tin, but I don't think it works for lead-tin-antimony.