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Old June 15, 2011, 12:03 AM   #1
joneb
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I'm trying to grasp the alloy concept ?

So if lead melts at Y temperature and hardening alloys melt at X and Z temps, how do these different elements combine to make a homogenized molten melt for casting ?
Please excuse my ignorance but I do not understand how elements of various densities and melting temperatures can melt together and become a alloy

Thanks jib
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Old June 15, 2011, 12:29 AM   #2
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you have to think in terms of Atoms..think of pure lead as a box of marbles tightly packed..there are small spaces around each one..if the alloying agent has smaller Atoms..say Tin, Silver, or Antimony..these will fill up spaces around marbles. This new concoction is neather pure Lead, Tin, Silver, or Antimony anymore but a new metal with different melting point, and characteristics. I don't know if I've explaned it right but this is the jist of it.
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Old June 15, 2011, 08:13 AM   #3
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The three metals that make up the bullet alloy of casting are, Tin, Lead, and Antimony. If an amount of those pure metals are put into a melting pot and the temperature is raised, the Tin will melt first, then as the temperature continues to rise, the lead will melt and lastly the antimony will melt (but usually at a temperature (600+ degrees Celsius)too high for some/most home equipment to reach). When the metals have melted they combine as liquids into a homogeneous mixture.
The high melting temperate of the antimony is the reason that bullet casters do not try to alloy pure antimony into their casting alloys...they buy or obtain antimony already alloyed with lead/tin because the melting temperature of the combined metals is much lower than pure antimony.
As an alloy of Lead, Tin, and Antimony cool, the Antimony returns to the solid state first, resulting in the "mushy" appearance of the cooling bullet alloy.
Not a scientifically correct interpretation of what happens, but a pragmatic interpretation of what happens. But, for almost all bullet casters, the answer to your question would be: They just do.
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Old June 15, 2011, 09:30 AM   #4
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Understanding lead alloys is a subject of much debate on bullet casting forums for many years. There are some things you just can't get away with concerning some alloys. Such as putting too much antimony in a lead alloy WITHOUT the correct percentage of tin. Tin is required, in the correct percentage, to keep antimony in solution with the lead.

That last sentence is the key to understanding lead alloys. It's a solution more than anything else. Look at it like a water/salt solution. Once you put salt in water, you have a solution. Overly simplified, because you CAN separate the salt from the water by by distillation. You can only get just so much salt to dissolve in water, it becomes a saturated solution.

Same with lead and antimony. Not enough tin, the antimony shows up as separate crystals surrounded by pure lead. The bullet feels hard, but will lead horribly. Linotype is a eutectic alloy. It melts all at once at a very specific temp. Some solders, like 37/63 lead tin are also eutectic.

Now that you're thoroughly confused, want to continue? Then this is good reading over a lasc; http://www.lasc.us/
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Old June 15, 2011, 09:50 AM   #5
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An alloy involves its constituents in its solid structure. This means the combined properties are different than the properties of the constituents individually. Brass, for example, is made of copper and zinc, but has neither the color, nor the melting point, nor the same hardness nor the same lubricity of either copper or zinc.

Melting points can be depressed by alloying, owning to the stresses between the atoms helping the alloy to disassemble with less heat energy, even though those same stresses can make the solidified alloy stronger than its individual constituents. For example:

Pure lead melts at just over 621°F.
Pure tin melts at just over 449°F.
63% tin and 37% lead alloy melts at 369°F; lower than either constituent metal melts at.

If you melt lead and add some tin, then let it cool, you don't see the lead start to freeze until below 621°F. The more tin you add, the lower the temperature the lead starts to solidify at until you get to that 63% tin and 37% lead alloy with its 369°F melting point. Before getting to that much tin, the mix would start to solidify at a higher temperature (called the liqudus) and not finish solidifying until 369°F (called the solidus). There is a slush temperature range as lead solidifies until the remaining liquid has that optimal 63:37 concentration, at which point it finishes solidifying. 63:37 is called a eutectic alloy of tin and lead, characterized by its liquidus and solidus being the same temperature.

From the Wikipedia entry on Alloy:
"When a molten metal is mixed with another substance, there are two different mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each atom in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are replaced with atoms of the other constituent. With the interstitial mechanism, one atom is usually much smaller than the other, and so cannot successfully replace an atom in the crystals of the base metal. The smaller atoms become trapped in the spaces between the atoms in the crystal matrix, called the interstices."
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Old June 15, 2011, 02:09 PM   #6
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There is a slush temperature range as lead solidifies until the remaining liquid has that optimal 63:37 concentration, at which point it finishes solidifying. 63:37 is called a eutectic alloy of tin and lead, characterized by its liquidus and solidus being the same temperature.
In English this means that there is no mushy stage in an eutectic alloy. Linotype is such an alloy, which makes it such a pleasure to cast bullets with (albeit an expensive use of the Tin), it. By controlling the temperature of the casting pot very close to just enough heat to keep it liquid, the caster can fill a bullet mold and the metal in the mold freezes almost instantly and can be dropped without waiting. If this is done with a non-eutectic alloy (lead, tin, antimony in different ratio), the metal will have a mushy stage, take longer to freeze and if the caster strikes the sprue plate too soon, smears the small droplets of liquid alloy over to top of the mold and bottom of the sprue plate.
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Old June 15, 2011, 07:25 PM   #7
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By controlling the temperature of the casting pot very close to just enough heat to keep it liquid, the caster can fill a bullet mold and the metal in the mold freezes almost instantly and can be dropped without waiting.
I'd like to see those boolits if cast using just enough heat to liquify the linotype. In general you should be at least 100 degrees above liquidous to get complete fill-out of the boolit. The molds never get close to the temp of the metal in the pot. That would cause the boolits to freeze before conforming to every detail of the mold.
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Old June 15, 2011, 10:37 PM   #8
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Thank you.
I have about a 100 lbs of scrap lead mostly from remodels, the lead was used for roof flashing, plumbing roof vents and other plumbing stuff

I have been melting these materials down to consolidate and remove impurities. While most of the 1 - 1.5 lbs ingots seems soft and fairly pure (with the exception of some unknown solder) I have one that is harder and has a ring to it when dropped on a hard surface, the color is more silver and the luster is more dull. This ingot had a threaded flange in the mix. The flange melted, but had a higher melting point ?

If a lead bullet alloy requires a certain percentage of ingredients, how do you deal with a lead alloy of unknown composition ?
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Old June 16, 2011, 08:41 AM   #9
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Roof flashing/plumber's lead is usually nearly 100% lead and is viewed by bullet casters as too soft to use alone as a bullet alloy. Lead roof flashings/lead pipes have not been used for some time now. Any solder joints would be likely to be tin-lead solder, but not enough tin to harden the large amount of lead in the flashings/pipes.
The threaded portion that had a higher melting point likely was lead/tin/antimony. In any event, if you melted it into the melt it is too late if it contained zinc anyway...the first bullets you try to cast with it will tell you if they contain zinc.
A note about lead roof flashings and other sources of "pure" lead, almost all sources of lead can be utilized for good bullets with the addition of some tin and can be heat treated (hardened) with the addition of anatomy and arsenic (in "chilled" lead shot).
If one has shooting friends who are more inclined to shoot muzzle loaders, often they are inclined to trade harder alloys for pure lead.
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Old June 16, 2011, 10:07 PM   #10
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Now that you're thoroughly confused, want to continue? Then this is good reading over a lasc;
Thanks snuffy
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Old June 17, 2011, 08:54 PM   #11
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jibjab , get yaself a bit of meuratic acid & place a drop of it on your shiney ingot if ya get a dancing reaction from the acid it`s zinc & no good for adding to your pure lead !!

Ifin ya can hook up with a muzzle loader that casts bullets I bet he`d make it worth ya while in $$ or trade !! Pure lead is hard to find these days !!!!

I bet there`s someone over at Castboolits.Gunloads.com that`ll trade ya 2#s Wheel weights for 1# pure, & very good info over there also !!!

If ya go look at the bottom of the page ,you`ll see "castpics" at the bottom of the page , very good info source !!!
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Old June 17, 2011, 10:26 PM   #12
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Old June 20, 2011, 09:04 PM   #13
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I had the very same thing and it turned out to be zink!!:barf:
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Old June 21, 2011, 02:06 AM   #14
joneb
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I had the very same thing and it turned out to be zink!!
I'm new at this, but if you have a lead zinc mix the two will separate at a certain temperature. The zinc will puddle at the top of the melt where it can be skimmed off. My limited experience tells me that zinc does not combine well with pure lead.
I do not know if zinc can be safely fluxed from lead ?
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Old June 21, 2011, 09:40 AM   #15
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One of the threads had a link to a solder making page. IIRC, it said up to 1.6% zinc will alloy with lead, then the rest refuses to stay in solution and floats to the top, as you say. The problem is, according to some, even .01% zinc will cause fill-out problems. I've not tested that claim personally. It's too much easier just not to get zinc into the mix in the first place.
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Old June 21, 2011, 10:28 AM   #16
joneb
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The problem is, according to some, even .01% zinc will cause fill-out problems.
I found some info on this over at Cast Boolits,

http://castboolits.gunloads.com/showthread.php?t=63082
http://castboolits.gunloads.com/showthread.php?t=62957

I have 1-2 LBS of lead that may have zinc contamination. I have set it aside, and will find out later if there is a problem with it.
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Old June 21, 2011, 11:21 AM   #17
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I've read those before. The first one is where I found the link to the solder page. I'd forgotten that.

Arcticbreeze got 4lb, 9 oz of sulfur/zinc slag from 40 lbs of contaminated lead. That's about 11.4% of the total weight. Well above the alloyable 1.6%. I'd be very surprised if his one-pass sulfur treatment got the zinc quantity down to a very small fraction of a percent, so I suspect the concerns over hundredths of a percent of contamination are exaggerated. It might even be true that the alloyed 1.6% is acceptable and only the excess zinc beyond that which hardens ahead of the alloy causes the problems. I've certainly seen fairly accurate zinc castings, (zinc wheel weights, for example) so it's not like the metal itself is not castable. It would be interesting to see an analytical assay of his final bullets.
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