2% tin or 3%?

[machinisttx]

My thermometer and tin just came in. About to mix some alloy and can't make up my mind. My mold fills out fine with straight ww, but I know I was running hot since my boolits were frosted. The extra 1% won't add much hardness, how much will it help in filling out the mold at lower temperatures?

[docone31]

Why lower temps?
If it fills out without tin, why add the extra?
I run all my molds at full tilt. I heat them hot, and run hot alloy.

[Marlin Junky]

Good mold fill out depends on melt temp, mold temp (and mold properties) and pouring rate, with the latter related to sprue hole diameter and pouring method/technique. So what temp is your alloy? Are you using preheated ferrous molds? My point is, unless you're pouring into a big, complicated mold cavity, it's doubtful you need any tin. However, cheap Aluminum molds may require 1% tin because they can't be used over a long casting session at 800F without suffering some wear.

MJ

[BABore]

Use tin the same way you use asprin. Only when you have a headache.

[machinisttx]

Good mold fill out depends on melt temp, mold temp (and mold properties) and pouring rate, with the latter related to sprue hole diameter and pouring method/technique. So what temp is your alloy? Are you using preheated ferrous molds? My point is, unless you're pouring into a big, complicated mold cavity, it's doubtful you need any tin. However, cheap Aluminum molds may require 1% tin because they can't be used over a long casting session at 800F without suffering some wear.

MJ

I don't know what my alloy temp was when I cast before because I previously did not have a proper thermometer. My molds are NOE and aluminum, but will probably end up with some iron or steel molds in the future. This is part of the reason I want to lower the temps, and the addition of tin should do that, as well as add some hardness. If my calculations are correct, 2% should bring me to a little over 14 BHN without water dropping...which is entirely adequate for what I shoot.

[madsenshooter]

I'd go with the 2%, the more tin, the more antimony is locked up in a Sn/Sb alloy, and that interferes with heat treating, should you decide to do so at some later time. Concerning melt temps, I've found the iron molds take the lowest to get good fillout, next brass, and aluminum takes the highest. I was just working with a 2 cavity NOE mold and I had to run my little Lee pot up on 9 with the alloy I'm using. Drop back to 8 and an immediate difference was noted in fillout. In all fairness though, the big chunk of alloy I was using was mixed over 30 years ago by some then young men, and God only knows what's in it, maybe even some zinc. Casts at 19.3 air cooled. I wouldn't expect to have to run that high with WW.

[mold maker]

Adding tin to WW is an added expense. Frosting isn't a problem except for looks. Keeping an alumn. mold hot enough to get good fill is more of the problem than lack of tin.
When you get iron molds, they will hold heat better and should fill fine.

[machinisttx]

Adding tin to WW is an added expense. Frosting isn't a problem except for looks. Keeping an alumn. mold hot enough to get good fill is more of the problem than lack of tin.
When you get iron molds, they will hold heat better and should fill fine.

Frosting was simply an indicator of heat to me. I didn't have any trouble keeping the mold hot enough, but I was probably going a little faster than I should have been.

[cbrick]

Adding tin will "lower" the melting temp of the alloy and the higher the tin percentage the lower the liquidus temp, the reason solder melts at a lower temp than lead.

Proper for maintaining your alloy and not increasing the rate tin oxidizes out would be about 100 degrees over liquidus. If you run your pot as hot as you can and oxidize the tin out there isn't much reason to put it in in the first place. If you choose to use tin don't waste it by running the pot temp too high, vary the mould temp by casting faster or slower as needed.

There would be very little to nothing to be gained by using 3% over 2% tin, if you use the tin use 2% and it will go further.

Rick

[sagacious]

My thermometer and tin just came in. About to mix some alloy and can't make up my mind. My mold fills out fine with straight ww, but I know I was running hot since my boolits were frosted. The extra 1% won't add much hardness, how much will it help in filling out the mold at lower temperatures?

Why add any tin at all? Tin will only help with fillout, and that isn't a problem in your example. Frosting isn't a problem or a defect at all.

Water-quenching ww alloy is the best way to increase hardness. The addition of tin to the ww alloy will only serve to ultimately reduce the hardness level achieved by quenching.

3% is simply a waste of tin. In your specific case, 2% will likewise be a waste of tin. On occasion, I add 1/2 to 1% tin to ww alloy, and that small addition will usually cure fill-out in stubborn molds, and drops the required melt temp a bit.

There is no point in arbitrarily altering your alloy to some preset standard that has the benefit of "consensus" or publication.

For your mold, for your purposes, straight ww alloy is-- apparently-- perfect. Many of my molds also cast perfect bullets from straight ww alloy.

Some day you will encounter a batch of lead, or a stubborn mold, and it will require the addition of some of that tin. To my mind, the wisest choice would be to reserve your tin for a time and a purpose when it is actually necessary-- instead of seeking to replicate an alloy that won't better your end results. Remember, it's results we're after here.

Hope this helps, good luck!

[machinisttx]

Adding tin will "lower" the melting temp of the alloy and the higher the tin percentage the lower the liquidus temp, the reason solder melts at a lower temp than lead.

Proper for maintaining your alloy and not increasing the rate tin oxidizes out would be about 100 degrees over liquidus. If you run your pot as hot as you can and oxidize the tin out there isn't much reason to put it in in the first place. If you choose to use tin don't waste it by running the pot temp too high, vary the mould temp by casting faster or slower as needed.

There would be very little to nothing to be gained by using 3% over 2% tin, if you use the tin use 2% and it will go further.

Rick

This is what I was looking for. I do not want to run any hotter than absolutely necessary with aluminum molds. The pot was cranked up as high as it would go since I initially had problems with the bullets not filling out properly. It appears that 2% will better suit my purpose.

[geargnasher]

This is what I was looking for. I do not want to run any hotter than absolutely necessary with aluminum molds. The pot was cranked up as high as it would go since I initially had problems with the bullets not filling out properly. It appears that 2% will better suit my purpose.

Keep in mind that MOULD temp has a lot more to do with good fillout than POT temp. Preheat your mould somehow and cast FAST with aluminum and cool the sprueplate on a wet sponge sitting in a pan of water to keep it from overheating.

If you use 2% tin you will likely never need to be hotter than 650-700* depending on the amount of antimony present.

If you heat treat, ww+ 2% tin is about perfect. Not a eutectic alloy, but cheap and heat treats well. If you want a eutectic alloy (always the best for castability but not necessarily the best for your shooting application) try Lyman #2 or Linotype, both are eutectic and Linotype has a 4% Sb/Sn intermetallic bond (100% of the contained tin) and Lyman #2 behaves as a "true" binary consisting of 90% lead and 10% Sb/Sn. WW +2% Sn is a tertiary alloy with somewhere around 4% Sb/Sn, 1-2% Sb, and the balance Pb with trace arsenic, copper, zinc, calcium, etc.

We don't use tin to harden tertiary alloys, in fact it tends to soften them some because, as has been mentioned, it ties up about an equal percent of antimony. It is used to impart toughness and (in effect) lower surface tension, casting temp, and provide a protective dross layer while casting. This last is probably most important as poor fillout in the moulds is partially attributed to the surface of the molten pool of metal in the mould cavity oxidizing and hardening before the alloy has a chance to find the nooks and crannies of the cavity. Tin dross on the surface is much softer and flows better than lead or antimony surface dross.

Gear

[machinisttx]

Keep in mind that MOULD temp has a lot more to do with good fillout than POT temp. Preheat your mould somehow and cast FAST with aluminum and cool the sprueplate on a wet sponge sitting in a pan of water to keep it from overheating.

If you use 2% tin you will likely never need to be hotter than 650-700* depending on the amount of antimony present.

If you heat treat, ww+ 2% tin is about perfect. Not a eutectic alloy, but cheap and heat treats well. If you want a eutectic alloy (always the best for castability but not necessarily the best for your shooting application) try Lyman #2 or Linotype, both are eutectic and Linotype has a 4% Sb/Sn intermetallic bond (100% of the contained tin) and Lyman #2 behaves as a "true" binary consisting of 90% lead and 10% Sb/Sn. WW +2% Sn is a tertiary alloy with somewhere around 4% Sb/Sn, 1-2% Sb, and the balance Pb with trace arsenic, copper, zinc, calcium, etc.

We don't use tin to harden tertiary alloys, in fact it tends to soften them some because, as has been mentioned, it ties up about an equal percent of antimony. It is used to impart toughness and (in effect) lower surface tension, casting temp, and provide a protective dross layer while casting. This last is probably most important as poor fillout in the moulds is partially attributed to the surface of the molten pool of metal in the mould cavity oxidizing and hardening before the alloy has a chance to find the nooks and crannies of the cavity. Tin dross on the surface is much softer and flows better than lead or antimony surface dross.

Gear

My fillout problems weren't solved until pot temperature was turned up. I don't think the alloy was carrying quite enough heat to the mold to keep the temperature at a suitable level.

I am not well versed in lead or lead alloys, but I have done quite a bit of work with tools steels, including heat treatment...so I do understand the difference between hardness and toughness. From the formula I found on the rotometals site, adding 2% tin will increase the hardness.