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Hello. I had this lead bulb poured a couple months ago. It is supposed to have 3 to 5% antimony in it for strength. It has been sitting outside for 2 months waiting for boat completion. Last week we saw the lead coming apart. Have a look at these images. The producer says not to worry. I am worried. Does anyone know what this is?

Regards,
Dennis

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20200911_165018.jpg
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It looks like debris from the sand mold. Surface quality suggests temperature was not high enough.
 
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Too cold and poured too fast. To me it looks like the metal eroded the mold, and parts of the metal began to solidify before the still molten metal could join them. See 'cold flow' and 'turbulence'. The Technical Dictionary of Lead Casting Terms Also, check out 'pouring metal defects' and 'sand casting'. Casting defect - Wikipedia

All that said, I have never made a lead casting over 25 lb nor have I ever cast any metal in a sand mold.
 

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Discussion Starter #4
Lead melting point 320C. Antimony 630C. If the lead surface quality is affected by not being hot enough, then its likely that there would have been melting issues with the antimony.
 

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Lead melting point 320C. Antimony 630C. If the lead surface quality is affected by not being hot enough, then its likely that there would have been melting issues with the antimony.
Not really. If you check the lead-antimony phase diagram, you'll notice that there is a eutectic. In other words, adding antimony to lead will actually lower the melting point of the alloy, at least until you reach about 17 at% antimony.

That's a very large casting. Even if the casting temperature was too low, there is a good chance that the casting defects do not extend deep into the bulb given the huge thermal mass. Are the defects localized to just one area? Can you check how deep they are? The sand definitely points to defects in the mold and mold erosion.
 

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Discussion Starter #6
Not really. If you check the lead-antimony phase diagram, you'll notice that there is a eutectic. In other words, adding antimony to lead will actually lower the melting point of the alloy, at least until you reach about 17 at% antimony.

That's a very large casting. Even if the casting temperature was too low, there is a good chance that the casting defects do not extend deep into the bulb given the huge thermal mass. Are the defects localized to just one area? Can you check how deep they are? The sand definitely points to defects in the mold and mold erosion.
It looks like the sand is shallow and places are near front only.
There is supposed to be 3 percent antimony but in the testing using a handle machine, it's only showing 0.5 up to 0.7. should measuring the antimony show an actual 3 percent or would it be less due to percent by weight vs volume?
 

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It looks like the sand is shallow and places are near front only.
There is supposed to be 3 percent antimony but in the testing using a handle machine, it's only showing 0.5 up to 0.7. should measuring the antimony show an actual 3 percent or would it be less due to percent by weight vs volume?
What were the specs for the alloy? 3 weight percent or 3 atomic percent? Alloys aren't usually spec'ed by volume percent. Even if spec'ed in atomic percent, you're still short on antimony.

On the other hand, what are you using to measure the composition of the lead alloy? Many characterization techniques will not give you a very accurate composition and could easily be off by a couple percent.
 

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jvlassak, could the surface condition be a result of an attempt to cool the surface to quickly with a water spray or air hose?
 

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jvlassak, could the surface condition be a result of an attempt to cool the surface to quickly with a water spray or air hose?
Probably not, lead is very ductile and has a very low melting point, so the temperature difference would not be large enough. Some of the defects are probably due to flaws in the mold and or mold erosion. The fine cracks may well be because the casting temperature was too low, but I would be surprised if they penetrated deep into the casting. I would probably remove a thin layer of lead to see how deep the cracks penetrate and then fair.
 

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The real question is:

Would you feel comfortable risking your life with this lead bulb?

If it were me the answer would be NOT A FREAKING CHANCE!! And nothing anyone on a boating forum could say would change my mind. The only thing I would accept is an qualified inspection and testing report.

But that is just me I guess.
 

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Discussion Starter #11
What were the specs for the alloy? 3 weight percent or 3 atomic percent? Alloys aren't usually spec'ed by volume percent. Even if spec'ed in atomic percent, you're still short on antimony.

On the other hand, what are you using to measure the composition of the lead alloy? Many characterization techniques will not give you a very accurate composition and could easily be off by a couple percent.
The design is from Marc Lombard. When i spoke with him a while back, he said 3 to 5 percent but did not give specifics as you mentioned. Today the company that did the bulb measured again ( 3rd time with 3rd handheld device). Same consistency of .3 .5 7. variations around the bulb. The only difference was at the back on underside where it was 5%. SO This is interesting, obviously they did use antimony but as they have stated, it is not homogenous. They stated that even doing it again would result in the same distribution. I am no expert, but I would have thought there would be a way to properly mix.
 

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The real question is:

Would you feel comfortable risking your life with this lead bulb?

If it were me the answer would be NOT A FREAKING CHANCE!! And nothing anyone on a boating forum could say would change my mind. The only thing I would accept is an qualified inspection and testing report.

But that is just me I guess.
AGREE TOTALLY. Its a matter of life and death. Thats why I am checking it all out. Ultimately I will just follow the rules. I am preparing the results, images etc and will send to the designer of the boat, keel and bulb. If he states the 0.3, 0.5, 0.7 percents are not satisfactory, then i can not use this bulb. I have scraped away the areas with sand/dirt and its ok. Will need some patch work but its the presence and distribution of antimony that is of most concern. If the correct amounts are not around the bolt holes then this is where the problem will arise being too soft.
 

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Discussion Starter #13
jvlassak, could the surface condition be a result of an attempt to cool the surface to quickly with a water spray or air hose?
Possibly. I was not present when it was poured. The company is Başaran Döküm | salma döküm işleri,bronz döküm, kurşun döküm, pik döküm, kızıl döküm, alüminyum döküm, tutya döküm, dökümcü, döküm firmaları, dökme salma işleri, döküm tava, döküm kalıp, döküm teknikleri, ucuz döküm işleri, dökümhane, hassas döküm, salma imalatı, gemi ve yatlarla ilgili her türlü döküm işleri, kum döküm which I thought given their experience would produce something of high quality and in a professional nature.
 

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What were the specs for the alloy? 3 weight percent or 3 atomic percent? Alloys aren't usually spec'ed by volume percent. Even if spec'ed in atomic percent, you're still short on antimony.

On the other hand, what are you using to measure the composition of the lead alloy? Many characterization techniques will not give you a very accurate composition and could easily be off by a couple percent.
This is the device that was used. There were 2 others like it as well. Same readings on all 3.
20200915_113439.jpg
 

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The design is from Marc Lombard. When i spoke with him a while back, he said 3 to 5 percent but did not give specifics as you mentioned. Today the company that did the bulb measured again ( 3rd time with 3rd handheld device). Same consistency of .3 .5 7. variations around the bulb. The only difference was at the back on underside where it was 5%. SO This is interesting, obviously they did use antimony but as they have stated, it is not homogenous. They stated that even doing it again would result in the same distribution. I am no expert, but I would have thought there would be a way to properly mix.
Interesting - it is possible that the alloy was not mixed properly when first prepared. More likely, different parts of the bulb solidified at different rates, resulting in segregation of the antimony. When the alloy first solidifies, the solid is lead-rich, i.e., the antimony concentration in the solid phase will be lower, and higher in the liquid phase. So, if the casting solidified from top to bottom, then you would indeed expect a significant difference in composition between top and bottom of the casting.
 

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The yellow device looks like a handheld x-ray fluorescence spectrophotometer (XFR metal alloy analyzer). It should be good to about 0.1%.

Bill
 

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AGREE TOTALLY. Its a matter of life and death. Thats why I am checking it all out. Ultimately I will just follow the rules. I am preparing the results, images etc and will send to the designer of the boat, keel and bulb. If he states the 0.3, 0.5, 0.7 percents are not satisfactory, then i can not use this bulb. I have scraped away the areas with sand/dirt and its ok. Will need some patch work but its the presence and distribution of antimony that is of most concern. If the correct amounts are not around the bolt holes then this is where the problem will arise being too soft.
I just looked up a paper on the mechanical behavior of Pb-Sb alloys. A reduction of the antimony content from 3 to 1.5% results in a decrease of the tensile strength by about 25% - that's significant.
 

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I just looked up a paper on the mechanical behavior of Pb-Sb alloys. A reduction of the antimony content from 3 to 1.5% results in a decrease of the tensile strength by about 25% - that's significant.
Wow thats a big difference. Do you have a link to the document?
The vendor has stated they can not get it to be homogenous but what I would like to know is, why do I see a consistent 0.3 to 0.7 on all spots of testing. Would it be correct in thinking, done the right way I should see something like 2.5% to 3.5% ?
 

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I have no metallurgy experience to weigh in on the alloy issues. It’s common to have antimony, but have no idea how to check for it, nor what to reasonably expect.

I have, on the other hand, blasted keels down to bare metal to rebuild epoxy and antifoulant. It is not uncommon to see significant surface distortions, from the mold. I can’t tell, if the OP’s pic is a symptom of something worse, but needing to fair out keel imperfections is pretty common. My last even had a molded logo/number that needed to be filled.
 
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Wow thats a big difference. Do you have a link to the document?
The vendor has stated they can not get it to be homogenous but what I would like to know is, why do I see a consistent 0.3 to 0.7 on all spots of testing. Would it be correct in thinking, done the right way I should see something like 2.5% to 3.5% ?
I sent you the paper by PM. It's not the best paper, but it should give you a good idea of how the antimony affects the strength of your alloy.

I'm not surprised that there is such a large difference in antimony content. It's a very large casting, and if it solidified from top to bottom, then segregation would lead to large composition differences. This, in turn, would lead to large différences in strength. The main areas of concern would of course be the attachment points. It shouldn't be too hard to calculate the required strength if the designer knows the anticipated loads on the keel.

Good luck!
Joost
 
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