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Thread: Casting high temp lead?

  1. #1
    Boolit Master prickett's Avatar
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    Casting high temp lead?

    Is there any problem with casting lead at high temperatures?

    I cast yesterday at between 900 and 1000 degress to try to get better mould fillout. I've read an occasional post stating that at high temps the tin is affected. Any truth to that?

    Also, does the alloy separate into its constituent metals (e.g. does the tin and antimony separate)?

    When removing the dross, might I really be removing the tin?

    Thanks in advance

  2. #2
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    tin will oxide much faster at those temps.
    the good thing is that you should need less/almost none at those temps for good fill out.
    it's all an educated guess,,,, till the trigger is pulled.

    the more i find out about shootin boolits, the more it contradicts everything i ever learned about shooting jaxketed.

  3. #3
    Boolit Master leftiye's Avatar
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    Uh, pure lead , no (except it oxidizes like crazy). Alloys do all kinds of wierd stuff when cast real hot - including also oxidizing like crazy. If your mold gets hot enough that the alloy doesn't set up enough before you stop pouring, the whole boolit contracts rather than drawing lead from the sprue. Of course, there's frosting, which helps fillout if the mold/melt isn't hot enough to do the aforementioned, nor cause severe frosting. Best fillout in terms of boolit size happens with moderately hot molds, and moderate lead temps -again depending on the alloy.

    Concerning the alloying elements (tin, antimony) separating, they don't. But antimony oxidizes more readily than lead, and tin oxidizes more readily still. So oxidation loses you your hardening elements.

    Drossing is therefore more concentrated in tin and antimony than what is found in your melt. If you bottom pour, cover your lead with something (crushed charcoal) to keep the oxygen away.
    Last edited by leftiye; 02-16-2010 at 12:17 AM.
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  4. #4
    Boolit Master sagacious's Avatar
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    If you need to cast at 1000*F to get decent fill-out, there's certainly a problem. Casting at that temp introduces other serious problems and frustrations by itself. Very often, more heat is not the solution.

    Adding tin to a lead alloy reduces the required pouring temp. Adding tin and then casting waaaay hot totally defeats the purpose regardless of whether the tin will oxidize to any great extent.

    Properly fluxed alloy will not separate inot it's component metals. "Dross" is the powdery crud on the surface of the melt after it's been fluxed. If you are skimming the floating silvery scum off, you may indeed be reducing the lead's alloy content, and affecting the 'pourability.'

    Fluxing cures a host of ills. It helps increase 'fluidity' and 'pourability'-- usually to a very noticeable extent, and prevents alloy component depletion. Most any suitable lead alloy-- properly fluxed and maintained-- will usually cast without trouble and give good fill-out.

    Hope this helps, best of luck!

  5. #5
    Frosted Boolits

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    Properly fluxed alloy will not separate inot it's component metals.
    I always thought that lead alloys could never be broken down into their "component" metals while casting. Once an alloy is...well....alloyed, then it could not be broken back down. I was always told that such a seperation would require way more force than the heat generated by a casting pot. I could be wrong...
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  6. #6
    Boolit Master Slow Elk 45/70's Avatar
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    Ill coy, yup, you are barking up the wrong tree, without proper fluxing and a constant temp, you will seperate alloys IMHO
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  7. #7
    Boolit Master AriM's Avatar
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    Quote Originally Posted by prickett View Post
    Is there any problem with casting lead at high temperatures?

    I cast yesterday at between 900 and 1000 degress to try to get better mould fillout. I've read an occasional post stating that at high temps the tin is affected. Any truth to that?

    Also, does the alloy separate into its constituent metals (e.g. does the tin and antimony separate)?

    When removing the dross, might I really be removing the tin?

    Thanks in advance


    There is a safety risk with casting at very high temperature. Lead will start to produce proportionally large amount of lead vapor at high temperature. The boiling point is just of 3000 deg. F. I doubt you will be getting that hot. Just be cautious at high temperatures. Part of what makes boolit casting a "safe" use of lead, is the relatively low temperatures that we operate at.

    Out of curiosity, what kind of lead pot do you have that is reaching 1000 deg. F? Also how are you measuring that temperature? I think you are either misreading or using the wrong kind of temperature probe.

    Tin and antimony are contained in the dross due to metal oxidation. The dross will also contain other heavy elements. If you are using a bottom pour pot, don't be too concerned about what comes up to the top. Let your melt reach FULL temperature, then flux. If you use a bottom pour pot, you can simply fill the top of the pot with a thin, but complete, layer of sawdust. This will keep oxidation to a minimum. Just be sure to never let your pot go below half full. Also when you add more alloy, be sure to flux again and stir from the bottom of the pot up. Also be sure to scrape the sides as you stir. The impurities will come to the surface and bind to the sawdust and/or fluxing agent.

    In my opinion (I could be wrong) fluxing is less about cleaning and more about rebinding the alloy compounds. This is how flux works in welding, as well as low temp brasing/soldering. The flux creates flow and binds the tin within the solder, this promotes better flow and joint fill-out.

    Both tin and antimony have considerably higher melting points than pure lead. The tin and antimony remain in micro-crystaline structures, within the molten lead. This is normal, and is not possible to overcome.

    My guess is that you would get poor fill-out at very high temperature (especially in a bottom pour pot) because your alloy components would float to the top of the mix. Fluxing will not help you much here. By the time you flux and get your mould ready for a pour, you will have considerable oxidation and the alloy components will separate again. This is where that layer of sawdust on the top can help you. Think of it as an insulating blanket.

    Hope this helps. I am no expert on casting, but my family has been in the metalworking business (grandfather was a welder, and uncle is a precision machinist) for a few generations. I have been around various metalworking process' my whole life. So I do understand the nature of alloying and metal plasticity/dynamics.

    Bring that temp down. If you are getting poor fillout, my guess is that your mould cavities have some kind of oil/grease in them. Clean that mould well. If that fails, add some tin. Just be sure that you don't get the alloy harder than is appropriate for you specific chamber pressure. I learned this the hard way recently. Harder alloy is not necessarily better, in all circumstances. Alloy BHN should be mated to chamber pressure. To hard of an alloy will not properly obturate, and your barrel will be subjected to flame cutting and premature throat erosion.

    Good luck.



    Simple formula for determining proper BHN is this

    chamber pressure divided by 1440 = BHN

    for example

    45 auto
    200 gn. SWC
    5 grains Bullseye
    1.26 OAL
    approx. 13000 psi
    13000 psi / 1440 = 9.02 BHN (that's right about where air cooled WW would be)


  8. #8
    Frosted Boolits

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    Very interesting. I always thought the lead alloys we commonly used for casting were solutions and "once dissolved in it couldn't come out." IIRC, this is what the Lyman Cast Bullet Manual states. I will have to re-read that section when I get home. I guess you do learn something new everyday!
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  9. #9
    Boolit Buddy
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    Two posts ago is right, high temps means LOTS more lead vapors. Check my previous posts to find one I did on lead concentration. I personally don't want to go over 800 or 900, lead concentration is expotential. Below 800 or 900 I feel safe casting indoors.

    If you are casting outdoors, then don't worry about temperatures as far as lead vapor concentration goes.

  10. #10
    Boolit Master



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    Is there any problem with casting lead at high temperatures?
    do you mean lead as in pure or is it an alloy? seems everyone is talking about it as it was
    a mix of sorts. I know you said tin also. Just trying to understand.
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  11. #11
    Boolit Master
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    HI,
    DO NOT WANT TO STEP ON ANY TOES.
    But Pb melts at less than 800*F.
    You do Not get Pb vapors at those temp. You get rubber burning, wood burning, & paint burning & other Vapors.
    You do not get Pb vapors till it boils at about 1,760*F/C, can't remember which. This is way higher than the temp. we work at.
    you are in more danger from inhaling Pb dust or burning yourself.
    Last edited by BOOM BOOM; 02-16-2010 at 08:01 PM.

  12. #12
    Boolit Master sagacious's Avatar
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    Quote Originally Posted by IllinoisCoyoteHunter:aka BB View Post
    I always thought that lead alloys could never be broken down into their "component" metals while casting. Once an alloy is...well....alloyed, then it could not be broken back down. I was always told that such a seperation would require way more force than the heat generated by a casting pot. I could be wrong...
    BB,
    You are not entirely wrong-- but I think you're referring to 'gravity separation', which you correctly state does not happen. I was referring to the practice of fluxing as a critical and essential aid to preventing alloy component depletion. The Lyman handbook addresses this subject:

    Quote Originally Posted by Lyman Cast Bullet Handbook, p57
    As the metal melts, a gray scum will rise to the surface, contrasting sharply with the silver brightness of the molten lead. DO NOT REMOVE THIS SCUM. This contains tin, the most valuable component of the bullet metal. Fluxing will recombine the tin-lead-antimony mixture. This operation is extremely important, and should be done carefully.
    If one just skims and doesn't flux the melt when melting raw ww's, he may very well reduce the tin and antimony content of the alloy. Proper fluxing is required to maintain the alloy and prevent depletion of alloy components. An alloy can be a delicate thing, for example: overheated pewter can easily suffer from alloy component impoverishment, and common 70/30 brass kept molten for much time at all will likely suffer from zinc depletion. Lead alloy maintentance is critical to keeping it the component percentages the same as original specs, and fluxing is an integral part of that.

    I hope this explains my point a little better. Good luck!

  13. #13
    Boolit Master sagacious's Avatar
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    Quote Originally Posted by BOOM BOOM View Post
    HI,
    DO NOT WANT TO STEP ON ANY TOES.
    ...
    You do not get Pb vapors till it boils at about 1,760*F/C, can't remember which. This is way higher than the temp. we work at.
    ...
    I definitely do not mean to step on any toes either, but if I recall correctly, lead starts to outgas at closer to 1100*F, well before the boiling point. Working with lead at around 1000*F would pose some risk, and is inadvisable.

    Keep on keepin on!
    Last edited by sagacious; 02-16-2010 at 09:37 PM.

  14. #14
    Boolit Buddy
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    Quote Originally Posted by BOOM BOOM View Post
    HI,
    DO NOT WANT TO STEP ON ANY TOES.
    But Pb melts at less than 800*F.
    You do Not get Pb vapors at those temp. You get rubber burning, wood burning, & paint burning & other Vapors.
    You do not get Pb vapors till it boils at about 1,760*F/C, can't remember which. This is way higher than the temp. we work at.
    you are in more danger from inhaling Pb dust or burning yourself.
    Sorry, but you are completely wrong. My B.S. in chemical engineering calls BS on your chemistry skills. While I don't remember a ton of schooling, vapor pressure isn't one of the hard concepts, especially when I FINALLY found a vapor pressure curve that included lead. Everything has a vapor pressure. Water, alcohol, gasoline, even lead.

    If your statement were true, then we shouldn't have water vapor in the air until water boils at 212 degrees F. My white front yard though says that isn't the case.

    Also, nothing would ever burn since it is the vapors that burn. If nothing gave off vapors until it boiled very few fires would start.
    Last edited by Spudgunr; 02-16-2010 at 09:30 PM.

  15. #15
    Boolit Buddy
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    Here are the values, based on a pressure temperature curve I found online for lead (a scan of an academic book).

    I found an OSHA letter stating the max lead concentration for an indoor range is 50 micrograms per cubic meter (this should be the PEL, permissible exposure limit, based on breathing this for an 8 hour shift).

    At lead's melting point (621F) the vapor pressure is 4X10^-7 Pa (400 parts per trillion)
    @815F its 1X10^-4 Pa (1 part per billion)
    @1300F it is 1Pa (10 ppm)

    So, at 815F that is 12 micrograms per cubic meter, at the molten leads SURFACE, 1/4 of OSHA's PEL (and you KNOW they are conservative!)
    800 would be a good casting temperature. At 1300 it would be significantly higher, 10,000 times higher actually.

    870 degrees - 5X10^-4 Pa - 60 micrograms per cubic meter (just above OSHA PEL)
    925 - 1X10^-3 Pa - 125 micrograms per cubic meter (2.5 times OSHA's limit for an 8 hour shift).
    1000 - .01 PA (.1 ppm) = 1200 micrograms per cubic meter.
    1100 (Added in on the edit just because this value was mentioned above) - .13 PA - 15,600 micrograms per cubic meter, three hundred times the OSHA guidelines.

    The academic book I found the vapor pressure temperature curve at:

    http://books.google.com/books?id=S20...ead%22&f=false

    While I have no qualms casting indoors, I base than on NOT going above 800 degrees. Telling people 1000 degrees is no big deal is not just wrong, but it is irresponsible as it is TWENTY FOUR times osha's permissible exposure limit.

    To be fair, the vapor pressure concentration is at the surface of the molten lead. The vapor will slowly permeate the room, but would take a long time for the entire room to reach the above levels.
    Last edited by Spudgunr; 02-16-2010 at 10:10 PM.

  16. #16
    Boolit Master BPCR Bill's Avatar
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    Temps should never get to 1000 degrees for a good cast. That being said, some molds cast better a [I]bit[I] hotter than other molds. I have a custom Hoch nose pour that casts best between 850 and 900 degrees. It's a big 550 grain 45 caliber boolit. Any of my Lyman molds get above 750, and there is frosting (not a big deal) or finning. I would check the venting on that mold. If air isn't being pushed out on the pour, then you'll have bad fill.

    Regards,
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  17. #17
    Frosted Boolits

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    Thanks for the clarification Sagacious.
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  18. #18
    Boolit Master leftiye's Avatar
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    You're in more danger if you get lead on your hands (from handling) and fail to wash than vapors (from lead) will ever get you into. Vapors from your fluxing agent are probly vastly more dangerous (especially if you use Marvelux - waxes and wood shavings, and such aren't good, but aren't strongly toxic) and we don't even worry about them. As was said the vapor pressure is measured at the surface of the lead, and this concentration only involves a couple of cubic inches. It reduces exponentially for every inch you get further away from the lead. And as was said, unless you cast for many hours straight the concentration will not reach high enough levels to be of concern.
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  19. #19
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    BB,
    You are not entirely wrong-- but I think you're referring to 'gravity separation', which you correctly state does not happen. I was referring to the practice of fluxing as a critical and essential aid to preventing alloy component depletion. The Lyman handbook addresses this subject:
    Gravity separation can and will happen when there is significant antimony without tin as a binder. You could never dip off pure antimony but definitely could dip off a very concentrated mixture. Even at 6% antimony tries to float some off till you get the tin up to about 2%. I'm not talking about dross from oxidation but the oatmeal looking stuff that you can make a hole in with a spoon and watch it fill with liquid lead.
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  20. #20
    Boolit Master AriM's Avatar
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    Quote Originally Posted by leftiye View Post
    You're in more danger if you get lead on your hands (from handling) and fail to wash than vapors (from lead) will ever get you into. Vapors from your fluxing agent are probly vastly more dangerous (especially if you use Marvelux - waxes and wood shavings, and such aren't good, but aren't strongly toxic) and we don't even worry about them. As was said the vapor pressure is measured at the surface of the lead, and this concentration only involves a couple of cubic inches. It reduces exponentially for every inch you get further away from the lead. And as was said, unless you cast for many hours straight the concentration will not reach high enough levels to be of concern.


    not so. the reason that lead vapor is more dangerous, is because it enters the bloodstream through the lungs. the digestive tract is a very poor way to enter the blood stream. lead vapor is a very real hazard. not trying to argue, just trying to clarify.

    the chances of getting overexposure at low temperatures are very low. over 1000 deg., however, in an enclosed space, without adequate ventilation. well i would rather not take my chances. the scariest part, is that you wouldn't even see signs of poisoning for 6 months to a year.

    i agree that the dangers are blown WAY out of proportion, by a lot of policy makers, that have no understanding of the facts. there is, however, a reason to play it safe.

    what is the chance of a 1911 hammer falling on it's own, without the safety engaged? damn near nil. yet we still put the safety on. best to keep that practice with ALL firearms related topics, right?


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