Pure Lead Temperature

[GregLaROCHE]

I don’t have a thermometer for my Lee lead pot. With experience I have been able to make good boolits by paying attention to time sprue takes to harden and boolit quality. It seems most cast in the 700* range. I know when working with alloys, you need to be careful to not cook off added metals. For this question let’s keep it simple and talk only about pure lead.

What happens as lead is heated? What temperature does it normally melt at and as the temperature increases what happens. I assume impurities burn of or at least float to the top. At what temperature should fluxing be done? How hot can we cast with? I back off the heat when my boolits start getting frosty. What happens if you keep casting hotter and hotter? I’ve heard of people getting lead red hot. What temperature might that be. Does it have any effect on the characteristics of the lead?

I am just trying to get more in-site into the characteristics of lead and would appreciate any and all knowledge on the subject.

Thanks

[kevin c]

621*F for pure lead's melting point. If I remember right, it'll all melt at that temp (eutectic), whereas an alloy will start melting at some temperature but may still be partly solid (solidus temperature), and at some defined higher temp it will all be melted (liquidus temperature).

Pure or alloyed, hotter liquid metal expands and is lower density, so the boolit cast will be lighter and smaller once cooled. The higher temp affects the size and rate at which the component metals crystallize, which frosts the bullet more the hotter it's cast. IIRC, pure lead doesn't do this in the temperatures we cast at and at the ambient temps the boolits stay in after casting.

I guess it is oxidation that's happening to the tin and antimony so it's a form of burning, but unlike oxidation of carbon containing materials, you don't lose the oxidized metal to the air. That scum on top of the melt can be reduced back in. The hotter the melt, the faster the oxidation. I've read here debates on how much tin or antimony is actually lost this way. I dislike the way the scum cruds up my pot and casting tools so I reduce and skim all the time just to avoid that. I guess it's common to flux around casting temperature, whatever that might be for each individual. From a chemical reaction perspective, the reduction goes faster at higher the temperature, but of course, done that way, you'd have to let the melt cool back to proper casting temp, and in the meantime the newly reduced metal is busy reoxidizing faster because it's hotter.

I don't have equipment that will get my alloy much hotter than 800*, so I've never seen it glow red. 800 degrees is beyond the expected temp range for my molds: too hot and I get undersized boolits so frosty they look like misshapened BB's coated in silver glitter. Even if they came out OK, I'd be too impatient to wait the time it'd take to cool the molds between pours.

LASC's site has great articles on casting metals. There's a very good article in the Lyman Cast Bullet Handbook 3rd edition. LASC's articles by Glen Fryxell and others are more accessible.

But, really, what does it matter? It sounds like you're already casting good boolits, and you probably got to that point by just doing it. A little more trial and error is probably the most practical and the best form of learning if you want more.

[Rich/WIS]

Suspect the steel/iron pot got red, not lead. If casting pure lead temp, if it casts well, is not an issue as any oxidation of alloy metals just means a purer lead for projectiles. When running ball for my ML's want it as pure as possible. If an alloy like to keep the temp at 750 or less but your alloy, mold and cadence of casting will affect the temp needed. Adjust pot temp to get good fill and keep it as low as possible. Fluxing while casting will help reduce tin and antimony loss from oxidation. I use a Lee 20# pot and find that a setting midway between 5 and 6 works well, but not sure how repeatable that is between pots. My lead thermometer tells me that temp is about 725 +/-.

[Dusty Bannister]

Why are you getting frosted casting with pure lead. The frost is from antimony in the melt. I usually set the PID for 800 degrees when casting pure lead for good fill out and smooth castings. If you are using soft lead scrap for BP applications, yes, there will be antimony in the melt and yes, you will end up with some frost. Some will use about 1% tin to help reduce the amount of lead oxide that will form over time. It tends to reduce the oxide formation.

[GregLaROCHE]

That’s right that I don’t get frosting when casting pure lead round balls. I was thinking about casting an alloy when I mentioned frosting.

A friend who used to mix pure antimony into lead said he had to wait until the lead was red hot. I’m sure he wasn’t using an electric pot. Probably propane.

I’m interested in all comments and experiences. Please keep them coming.

[Bent Ramrod]

All I’ve noticed when casting pure lead very hot is that the resultant castings turn dark gray as they cool. Cast at lower temperatures, they stay silvery.

I only see frosting with antimony-containing alloys, like Lino-wheelweight range scrap. I’m not bothered by this, unless the mould and alloy get so hot that the melt shrinks away from the cavity surfaces. These are rounded, unfilled areas on the boolit, different from the wrinkles gotten when things aren’t hot enough, or the bubbles or gaps that are caused by oil or other contaminants in the mould. They look more like venting problems, except that when the mould cools down a little, it goes back to producing good castings again.

[Martin Luber]

You can get a free lead thermometer from a roadside junked bbq grille.

[lightman]

I cast for a long time by adjusting the pot temp until I got good bullets. Both with soft lead or lead alloys. I didn't know the temp, or even cared very much. Then I broke down and bought a thermometer and much later on, a PID. The sweet spot seems to be 725 to 735º for me.