Lead oxidation

[dearslayer]

Why might my lead be turning this color? The temp on my PID is set at 390 Celsius and it's dropping good bullets. My mix is usually 50% COWW and 50% SOWW with just a smidge of pewter added if the boolit edges are not sharp.

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[Idz]

When I smelt range scrap a blue color indicates the melt is too hot. As lead oxide forms on the surface it makes a sheen like oil on water. I suspect your lead level is dropping below the heater band causing hot spots. I run my pot about 670F (354C) and don't get the colors.

[Hannibal]

As mentioned above, it's oxidation. You can try leaving some flux/dross on top to minimize it. It's not going to be down in your alloy so I'd not worry about it if it were me. Do remove the flux/dross if you refill the pot during casting or it will get carried down into the molten alloy.

[baogongmeo]

A tiny bit of beeswax or candlewax will reduce that back into your alloy... just don't do that inside and what's with all that splatter in the second photo?

[dearslayer]

A tiny bit of beeswax or candlewax will reduce that back into your alloy... just don't do that inside and what's with all that splatter in the second photo?

The splatter is due to the sprue being broken off and dropped back into the pot.

[dondiego]

The splatter is due to the sprue being broken off and dropped back into the pot.

Which in turn is causing a lot of the oxidation.

[dearslayer]

Which in turn is causing a lot of the oxidation.

I did not know that. So what is the theory behind it? I've been doing it for quite some time but only recently noticed the oxidation. It's never been this bad before and I haven't changed anything as far as temperature is concerned.

[Hannibal]

The splatter is due to the sprue being broken off and dropped back into the pot.

So I suggest you wait until the melt in the pot starts getting low before dropping in the sprues. If you drop them in while casting for one it will cause fluctuations in your pot temp and for another it will introduce contaminates in the melt as it falls through the oxidation/swarf on the top of the melt. Along with causing the splatter. You might even find you can drop your melt temp enough to reduce oxidation if you aren't constantly adding sprues to your pot.

Ultimately, the best way to achieve consistent cast bullets is to control as many variables as possible. That's why folks do things like using a large pot, add a PID controller and use alloy from a source that checks their lead before shipment. Even switching to a different batch of tin/pewter will change things.

That doesn't mean you can't cast a shootable bullet without worrying about such things.

[dearslayer]

So I suggest you wait until the melt in the pot starts getting low before dropping in the sprues. If you drop them in while casting for one it will cause fluctuations in your pot temp and for another it will introduce contaminates in the melt as it falls through the oxidation/swarf on the top of the melt. Along with causing the splatter. You might even find you can drop your melt temp enough to reduce oxidation if you aren't constantly adding sprues to your pot.

Ultimately, the best way to achieve consistent cast bullets is to control as many variables as possible. That's why folks do things like using a large pot, add a PID controller and use alloy from a source that checks their lead before shipment. Even switching to a different batch of tin/pewter will change things.

That doesn't mean you can't cast a shootable bullet without worrying about such things.

Good to know. Thanks for the advice. I'll try it the next casting session.

[JonB_in_Glencoe]

Over heated !

read post #7
https://castboolits.gunloads.com/sho...and-blue-Oh-My!

[dearslayer]

Over heated !

read post #7
https://castboolits.gunloads.com/sho...and-blue-Oh-My!

Excellent info. Thanks so much. Will make some changes and see what happens. It's a little weird because as stated before I haven't changed my temperature since I've been casting and it's always been at 390.

[JonB_in_Glencoe]

Maybe double check your melt with a analog thermometer...sometimes a TC can start to go bad.

[dearslayer]

Maybe double check your melt with a analog thermometer...sometimes a TC can start to go bad.

Speaking of TC, the one I have is only about 4" and doesn't go to the bottom of the pot. Can anyone recommend a longer one? When I built my PID the 4" one was the one suggested and at the time I figured it must be ok but a longer one would be better so it can still control the temp further down into the pot so I wouldn't have to add more lead so soon so that the TC registers.

[Dusty Bannister]

Speaking of TC, the one I have is only about 4" and doesn't go to the bottom of the pot. Can anyone recommend a longer one? When I built my PID the 4" one was the one suggested and at the time I figured it must be ok but a longer one would be better so it can still control the temp further down into the pot so I wouldn't have to add more lead so soon so that the TC registers.

I am not sure a longer probe will take care of the issue. The probe should not be too close to the bottom and sides of the pot. It might also be helpful to keep the build up off the probe as that might act as an insulation. I remove crud from the probe after every session. Since the heating coil is about the middle of the way down the pot, you are making the heating coil work a lot harder when you let the melt get lower than that point.

I do add the sprues back into the pot as I cast, but only by picking them up from the catch pan and lowering them into the melt. And not all at once. Watch the PID read out and you can see how much you can add back in and keep on rolling at an adequately hot temp.

My normal casting temp in an unheated shed at ambient 40F or warmer is 720F. That is a little cooler than what you are running. Clean the junk off the pot since you are perhaps losing heat from the pot with those cooling "scabs" of lead. Clean the junk off the probe as well. I do not know if that will affect anything, but it will look better and might work better as well.

With a different oxide formation, it might just be something in a different batch of alloy that is now showing up and will disappear when you change lots of casting alloy.

[Rickf1985]

Looking at that splatter it looks like it is not melted on the sides of the pot? if that is the case the pot is cold. I have seen pure lead turn those colors all the time. But with all my pots the lead will not just splatter on the side and stick there, it melts right away and runs back into the pot. Even the stuff on the top edge melts. I think you might need a new sensor.

[dearslayer]

I do just happen to have a new spare TC same as the one that's currently there. I'll clean things up and replace it and see if anything changes and go from there.

[JonB_in_Glencoe]

In my mind, I think I want the TC probe tip near the pour spout as possible (like 1/4" to 1/2" away). So that's how I designed the clip-on bracket to hold my 4" TC. I don't recall ever disagreeing with Dusty Bannister, so maybe I better clarify, this is my personal opinion and not something I read in a book or an expert told me. Also, the clip-on design allows easy removal for cleaning and repositioning.
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This also explains why set my PID at lower temps, than what some other members post that they set their PID. If my TC is reading a pour spout temp of 675º (that's my temp setting for COWW alloy), the middle of the melt is likely closer to 700 or even a bit higher.
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I'm just posting those thoughts, as you think about any redesign you are considering when you install your new TC.

[dearslayer]

I posted another thread in casting equipment forum to ask how most people are attaching their thermal couplers. I'd like to see some photos of brackets etc and also to see if they are easily removable after a casting session. I always left 3/4 of a pot of lead to cool with the thermal coupler still in the mix. I had read somewhere that this was the best practice but perhaps it isn't. Your thoughts?

[Rickf1985]

I got tired of trying to flux and stir around the probe so I finally just said the hell with it and I just drop it in there (place it actually to prevent breakage) so it is near the spout on my bottom pours and in the center in my dipper pots. This way when I flux I just take it out and lay it on the hot plate so it does not have a heart attack and when I am done stirring I place it back in. I have had no issues what so ever. Once in a while when I am starting up I will run the learn program just to make sure it is still setup. I have found it is good to do that even when the probe is permanently mounted.
Leaving it unmounted also makes it easy when I am switching pots.

[Mike W1]

Not the exact one I'm using now but similar. Puts my TC tip about 1/2" from bottom and side of pot. Hole is drilled oversized so the thing can be moved around with the fluxing spoon. Maybe I'm just used to that but I have not had any problems and I leave it in all the time. Only the 10 lb. pot and I've measured the temperature of the melt a number of times with depths, etc. Hot lead is just what's in there when it's in melt stage. Conducts heat very well and I could not find any real difference throughout using 3 TC's at a time. I'll also stick the pix of the holder I used to do those little chores.