Shrinkage and mystery metal question

[HangFireW8]

My last smelting session included 5 10-to-15 lb big, flat wide ingots of what looked like solder, and the first three (all that fit in the pot) melted at a real low temperature, so I figure it's 60/40 or 50/50 or something. Real shiny results. Melts somewhere around 300F. After spooning most of it out, I continued that batch by putting the last two in, leave the flame on low, go back to trying to cast boolits (that's another story) and check on it in a bit. Bottom feels real funny, like a smooth higher part and a rough part.

I spoon a bunch into mini-muffins and take a look. The smooth part is metal, glued to the bottom of the iron pot, in the shape of the bottom minus the shape of the bottom solder ingot. Think of a rectangle of iron pot bottom visible with the shiny metal filling out the circle. It definitely was not there after the first 3 ingots.

I spooned out what I could into the rest of ingot batch "SIA" (Solder Ingots batch "A", I don't usually make ingots out of solder, it usually comes in small enough chunks). I turned the fire up a bit and checked later. Its 400, later 450F, and still there on the bottom, still hard, smooth and shiny. I turn the fire up some more.

I come back later and find the melt is gold, oops, too high a temp, its like 800F and still climbing on the thermometer so I just put that aside, cut the flame and check the bottom. The reverse big ingot-molded metal on the bottom is gone. I spoon it into mini-muffins and mark in SIB (Solder Ingots batch "B").

A few days later I do a hardness check, low temp batch SIA is BHN17, high temp gold batch SIB is BHN18, very consistent. But that is not all. Take a look at the picture.

SIA has huge shrinkage. It is hard to see in the picture, but that sinkhole in the middle goes more than halfway through the ingot!

SIB on the other hand, has almost no shrinkage at all. On the right is almost pure lead, with a sizable shrinkage dent in the middle.

I compared to other ingots, it turns out Wheel Weights rarely have more than the slightest shinkage in the middle of the ingot. Now I know why they are so popular!

Pure (or Pure-ish) lead has a sizable shrinkage dent in the middle, as does Stick On Wheel Weights (marked SOWW).

So, I have questions:
1. Is the huge shrinkage cavity in SIA caused by Tin, low temps (just above 300F), or both?
2. Is the lack of shrinkage in SIB caused by high temps or the alloying of the mystery metal or both?
3. How does something in an upper ingot melt around a lower ingot with a lower melting temperature, and then harden and take high temps to get to melt again? I thought metal once alloyed stays alloyed. Is this Antimony, or is it Zinc?

[sagacious]

So, I have questions:
1. Is the huge shrinkage cavity in SIA caused by Tin, low temps (just above 300F), or both?
No, adding Sn decreases shrinkage. Low pouring temp also reduces the shrinkage. So, this is almost certainly not the explanation.

2. Is the lack of shrinkage in SIB caused by high temps or the alloying of the mystery metal or both?
It's certainly not caused by increased pouring temp. Pure lead has more thermal shrinkage that any of it's common alloys. Generally, alloying lead decreases shrinkage, high-temp pouring increases it.

3. How does something in an upper ingot melt around a lower ingot with a lower melting temperature, and then harden and take high temps to get to melt again? I thought metal once alloyed stays alloyed. Is this Antimony, or is it Zinc?
I'm not sure what the first part of your question is asking. No, metals alloyed together do not always stay in solution after cooling. One often sees this with high-tin lead alloys-- solders.

Briefly, what happens is that as the ingot cools, part of the mixture freezes at a higher temp (freezes sooner) than the rest of the melt. If that part is more dense than the rest (as it is in this case), it sinks to the bottom. The rest of the liquid continues to cool, and you end up with the eutectic or tin-rich mix at the top. It's common to see the top of a Sn/Pb solder ingot melt first.

Now for ther mystery. Are you sure the "shrinkage cavity" in the SIA ingot is not just a casting defect caused by lack of fluidity caused by the low pouring temp? That seems very much more likely, and that's what the pic looks like, but a closer photo would help.

[HangFireW8]

Thanks for your response.


Now for ther mystery. Are you sure the "shrinkage cavity" in the SIA ingot is not just a casting defect caused by lack of fluidity caused by the low pouring temp? That seems very much more likely, and that's what the pic looks like, but a closer photo would help.

When I poured the ingots, they were fully liquid and nice and flat across the top. That is because they were still liquid at 290F and I poured them at 320F (according to my RCBS thermometer, anyway). Watching them cool was amazing, they sucked the middle right down. Never saw anything like it. I have a few dozen like that, all the same.

-HF

[fryboy]

i like the gold color !!! it tells me there's some tin , i have some plumber's pipe, i tried to cut off and save the joints ( hi tin content) the remaining mass i melted poured into ye olde familiar 1# type ingots ,often when i smelt for alloying later i'll over fill all four of these in the mold ( makes a 5-6# chunk ) i had two batches that sank like ur SIA ,while not pure lead it did sink and left the sinkhole ,pure lead u also have to crank up the heat for unlike most of the alloys ,i've had whole pots melt before the mostly pure lead bars melt , i do know that some bismuth and other assorted alloys have low melting points and shrinkage but i'm just getting by on tin/lead/antimony ( as far as i know ..that one ingot is a mystery )

[sagacious]

290*F? If they were liquid at 290*F, what was the freezing temp? Have you double-checked your thermometer against boiling water?

If the SIA and SIB ingots are the same exact alloy, then I'm not aware of what mechanism would cause increased shrinkage as a result of lower pouring temp.

Sometimes an alloy will shrink more than another. I have seen this happen with lead alloys that contain a little copper. Shrinks down as you're watching it.

[lwknight]

If you actually have a correct thermometer then I would say that you might have bismuth in your mix. I have not ever gotten to play with bismuth so I don't know what the ingots look like. So this is just a wild guess. I don't know of any tin/lead mix that will melt at 300 degrees.
The picture of the cratered ingot looks just like pure lead to me.
The one marked some numbers and " Ingot" is what lead with a small amount of antimony in it looks like.

I'm voting for testing the thermometer cause this does not add up.

[sagacious]

I agree generally with LWKnight's assessment. Checking the thermometer seems like a good idea.

I have worked with bismuth, and bismuth/lead. The rub with bismuth is that when it freezes it expands, and when alloyed with lead in any significant percentage it makes all kinds of zany colors, and drosses like crazy. High heat would make it turn all kinds of colors pronto. Bi/Sn alloys are very popular as lead-free fishing lure/sinker alloys, but unless the tin content is very high, they are very brittle. I have some pure bismuth, but I didn't get anywhere with alloying it with lead, so I'm not going to try any more experiments along that line.

A few percent Bi is a possibility, but I'm fairly confident that there's more to this question than we yet know. Since the source of the alloy is unknown, or not described here, until more info is added, it may indeed remain a mystery.

[HangFireW8]

I agree generally with LWKnight's assessment. Checking the thermometer seems like a good idea.

Sorry about that... I looked up my notes... the alloy was non-eutectic (slushy) between 290 and 320. 330 and above that it was liquid. I kept temps low and after discovering the mystery bottom metal, actually lowered them more to find out where the slushy phase was.

When I got my thermometer last year, i checked it out with the purest lead I could find and it came out right around 620-ish, and called it good. I will try the boiling water test next.

-HF

[HangFireW8]

290*F? If they were liquid at 290*F, what was the freezing temp? Have you double-checked your thermometer against boiling water?


Sorry, slushy between 290 and 320, liquid above that.

Actually a little more complicated. Initially at 310 it was purely liquid. Then I let it cool off, got slushy immediately and below 290 really started to get solid here and there. Then brought it up to 320 for a while and couldn't get rid of all the slush. Had to get it to 330 to make it liquid again. Like some hysteresis or something.

-HF

[Greg5278]

Sound like you have some other low temp metal in the Mix. Tin or lead allloys are not going to be liquid below 425F. Perhaps you have some of the metal from Chnaber sating alloy or something mixed in. Doesn't Caddmium turn the melt yellow, and is bad for you health?
Check the Thermometer, and use the melt temp results against a chart of known of low temp alloys. Does the alloy shatter when struck, that might be a clue also?
Greg

[lwknight]

Well if it does have bismuth , you can mix in and dilute to desired hardness.
I believe that bismuth is a real good hardening agent. Its just entirely too expensive to be first choice. If you get it cheap then what the hay. Try it out.

[sagacious]

Bismuth is only about as effective as tin for hardening lead. Actually a little bit less effective.

I have seen where a small amount of copper in tin-based alloys will cause the same crystal/slushy effect, and the growth of the crystals during cooling causes a shrinkage cavity fast enough that you can watch it happen. If this solder was recovered from solder used on copper or brass, or a copper-containing alloy, it could have scavenged some copper.

[lwknight]

You just accidently answered a question that I have had for years.
When I have sweated copper joints and later tried to take them apart , a lot more heat was required to remelt the joint and it still is hard to separate.
Now I get the theory that copper is leeching into the tin and changing its melting point as well as where the copper is in contact with copper , the tin may actually be fusing the copper together by leechmosis.

I just made that word up and there is probably a proper term for it.

[DukeInFlorida]

I was on a site the other day.... they make and sell "tin soldier" molds, and they are crafted from some kind of material that requires LOW melt temp metals. The site seems to sell some metals that melt at about 300 degrees, and they indicate that the alloy contains bismuth.

So, as others have pointed out, I would also guess that some of what you had in there was this low melt temp stuff for toy soldiers.

[sagacious]

You just accidently answered a question that I have had for years.
When I have sweated copper joints and later tried to take them apart , a lot more heat was required to remelt the joint and it still is hard to separate.
Now I get the theory that copper is leeching into the tin and changing its melting point as well as where the copper is in contact with copper , the tin may actually be fusing the copper together by leechmosis.

I just made that word up and there is probably a proper term for it.
Yes, you're exactly right. The tin can dissolve/scavenge some copper and the melting temp of any trapped solder in the joint can go way up. The tighter the joint, and the higher the applied heat, the greater the potential for leechmosis.

I like the term 'leechmosis' much better than 'dissolution'..... although leechmosis sounds like something you get from too much wading in the swamp! :mrgreen:

[sagacious]

I was on a site the other day.... they make and sell "tin soldier" molds, and they are crafted from some kind of material that requires LOW melt temp metals. The site seems to sell some metals that melt at about 300 degrees, and they indicate that the alloy contains bismuth.

Low melt-temp metals can be cast using RTV silicone molds. The flexible mold allows for easy demolding when there are large undercuts in the casting. The RTV silicone will take the heat of small-volume castings like toy soldiers. You can even pour lead (add some tin to lower the temp and increase fluidity) with this material, but the higher heat will eventually wear out the mold.

[1time]

Howdy shooters, fisher here casting lead free jig heads commercially.
The mystery alloy sounds like this:
http://www.rotometals.com/product-p/lowmeltingpoint281338.htm

In my experience casting Bismuth-Tin alloys with Bi>Sn the 58-42 281*F eutectic component will liquify in a pot first with the I presume high bismuth remainder solid on the bottom if high Bi or suspended sludge if low. The greater the Bi component of the alloy the higher the final complete liquidus melt temp will be.

I agree with "Sagacious" that bismuth serves no functional purpose in a lead casting alloy except for extreme low melting temp. Yes, its HJ from TU.

OK, probably won't be back, just came across this thread Googling tin alloy properties.

[sagacious]

Sounded like HJ! Hope all is well in the sunny Pacific.

1Time knows his stuff when it comes to low-melt alloys, so he may just have nailed the ID on this "mystery metal".

[Molly]

Hi fellows,

I've got another mystery metal I'd like to identify. It's a solder-like material in the form of a large brick, weighing maybe 10-15 lb. It's ROUGHLY 2 inches deep by 4 inches wide by 7 1/2 inches long. It is crudely stamped on the bottom with the legend "Motor Marine". The stamping was obviously done one letter at a time, as evidenced by the irregular spacing and allignment.

It came with another heavier ingot (partly melted on both ends) that measures 4 inches wide, 3 inches deep and very roughly five inches long. This one has no stamping or other identification except for a handwritten "SOLDER" in black ink on one end.

Both give the impression of commercial ingots, for what that might be worth. Does anyone know what "Motor Marine" signifies?

[lwknight]

You need specific gravity and melt point tests to make an educated guess as to its content.
Of course the physical properties can be deceiving but you are likely to make a good ID on it that way.

[Molly]

You need specific gravity and melt point tests to make an educated guess as to its content.
Of course the physical properties can be deceiving but you are likely to make a good ID on it that way.

Well, I can do a specific gravity easily enough, but my thermometers only go up to about 250F, and my lead pots lack sufficient precision to be useful. I wouldn't trust them to be closer than the nearest hundred degrees.

Let me run SpGr and get back to you. I was really hoping that someone could say something like "Motor Marine" is the name of a common marine bearing babbit. No such luck though, eh?

[1time]

Me again, thought I could further elaborate on "HangFireW8"s mystery metal.

1. Altho the melt temp properties of SIA parallel Rotometals "281-330" Bi60-Sn40 lead free alloy, other metals contamination is suspect because:
2. Maybe at least one of the last 2 ingots had a lead component which could lower the melting point below the BiSn eutectic 281*F and explain the eroded cavity in the unmelted SIB remainder.
3. Then again, assuming the same BiSn alloy composition in all 5 blocks perhaps the physical contact of a fresh ingot melting eroded the cavity?

Was a melt temp test performed on SIB? If metals components of all 5 ingots were lead free BiSn the final liquidus temp should be close to the 520*F melting point of Bismuth - higher would certainly indicate other metals contamination.

[sagacious]

...
Altho the melt temp properties of SIA parallel Rotometals "281-330" Bi60-Sn40 lead free alloy, other metals contamination is suspect
I agree-- seems very likely.