overheating lead when melting scrap

[12slugger]

just started using a johnson furnace today and i think i might have ruined a batch of dental lead, I melted the lead and tried to flux and it was like stiring very hot dirt, may have been over 1000 degrees, i shut it down and will try again today after some suggestions, I am afraid to smelt my wheelweights as i dont want to ruin them any help appreciated, thanks

[Wal']

If it was feeling like stirring hot dirt...................seems to me theres something else in there that shouldnt be.

[357shooter]

Getting the lead that hot won't ruin it. Speculating on the temp can get you chasing your tail, and it doesn't really matter in this case. Either there's something else in the pot, that should have floated to the top. Or it's more lead than you are used to and it's just heavy to stir. I'd get it melted, use the thermometer just so the temp is known, and see what's in there by pouring your ingots and draining the lead. Assuming you have tried to dip out some of the "dirt like" alloy to see how if there's anything there.

[12slugger]

Thanks for replying, the lead looked like hot ashes all the way through, or it looked like the dirt you skim off the top except the dirt was 6 inches thick and my dipper kept comming out with yellow dust on it I was wondering if when it hits a certain temperature that it changes to a powder

[captaint]

Sounds like you definately had something else in that lead. Try turning down your burner as soon as the mix melts thoroughly. Apply just enough heat to keep it liquid. Might help. enjoy Mike
I have about 20 lbs of dental foils to melt - hope mine doesn't go nuts like yours.

[mdi]

Most of the dental foils I get have a sticky side, mebbe to attach the foil to a guard/holder? May have something to do withit, but yellow "dirt" doesn't sound good. If you can adjust your furnace to where the lead just melts, watch it and stop when the melt just turns liquid. Mebbe different results. Otherwise it sounds like your lead is contaminated (or mebbe the dentist is using sumpin' besides lead?).

[prs]

Before I wised-up and got a thermometer, after skimming out any zinc or steel weights, I would set my lead rendering pot to a heat level the just allowed bees wax to flash ignite, then turn it down to where it just barely does not self ignite. That was probably around 800 degrees. I would hold it there at that heat level for almost an hour to be sure the whole batch was thoroughly heated and then flux the beejeebers out of it until no more dirt or ash would rise with vigorous stirring and folding. Your oatmeal-like batch may be zinc contaminated.

prs

[40Super]

I found some exray sheets and they were nothing but lead impregnated rubber'ish. I would've been lucky to get 5 lbs lead out of 50 lbs sheeting. Not much lead in certain types.

[12slugger]

looked at the cooled down batch this morning, there is about 30 lbs lead that cooled in the pot and there is 3/4 to 1 inch deep yellow dust on top of it. any ideas, and i know the temp was over 1000 when i turned off 2 of the 3 burners thanks

[12slugger]

I packed the pieces into the pot and then fired up the 3 burners, as it melted i kept adding the foil to the pot when it all melted i threw in a chunk of beeswax about the size of a heaping tablespoon, i than started stirring, there must have been about 30 to 40 lbs of lead, it was like looking into molten ash, or glowing dirt, so i gave up and shut down the pot, looked at it today and you can see about 3/4 inch or more of yellow dust on top of the cool lead

[cbrick]

What you experienced with the dental foils isn't anything I've experienced but it sounds very much like those foils aren't the percentage of lead that perhaps you thought, just has to be a bunch of something in them that isn't lead.

I suggest you get a thermometer and with a clean pot go ahead and melt your WW but do so at no more than 700 degrees. Anything that floats at that temp is likely zinc, skim it out before it melts. I'd bet you experience completely different results from your experience with the dental . . . stuff.

Rick

[40Super]

Skim off the yellow ash and throw away. It must be the dross of whatever junk is mixed in with the foil. Reflux after skimming to make sure everythings out, then pour into ingots.

[12slugger]

Thanks, I am going to try again tommorrow

[nonferrous]

Sounds a lot like the mess you get when you smelt stick on W-W's. All the glue and foam backing go to the top, make a thick glop and need a lot of skimming.

[shadygrady]

if you got zinc send it to me

[Bullwolf]

I have melted down a few small batches of lead dental X-ray films.

I "believe" that the X-ray film backings that I get are coated with some kind of plastic. I get a fair amount of ash in the pot from them, even before fluxing when I melt them down. The X-ray films are very thin and fluffy and really take up a lot of bulk.

Despite the extra amount of fine powdery ash, the backing films still melt into a usable lead alloy, just like wheel weights. I typically gather all the dust off the top with an old casting spoon or ladle, then put it in a empty soup can. When I'm all done, I will often go back and re-heat the powdery dross again to see if there was any missed lead in it. This extra step is often not worth the effort, but it makes me feel thrifty.

I smelt the lead X-ray backing films into ingots, much the same as I would wheel weights. I flux the melt with sawdust, and paraffin, and stir vigorously with a dry hardwood stick. Then skim off the dross until I get a clean looking alloy that is very similar to WW lead, and then pour it into ingot molds. I used to mark the top of the ingots with a permanent marker, but I have had it wear off and become hard to distinguish over time. I also kept using up marking pens. Now I simply scribe - X-ray Films - into the top of my ingots, with a metal punch. This way I don't find any mystery alloy lead ingots later on, and wonder what they were made of.

So far I have found no downside to using free dental X-ray film backings other than them having a bit more dross to skim off. I am sad that they are slowly disappearing, as more and more dentists move to digital X-rays. Fortunately I do some work on the side for my old fashioned dentist who still uses them, and is willing to save them for me.


This small batch sure looked like a lot more than 16lbs of lead, but free is free.
http://castboolits.gunloads.com/imagehosting/thum_187904f3b0b4b99eb0.jpg http://castboolits.gunloads.com/imagehosting/thum_187904f3b0b713d881.jpg

Melting down the X-ray films, then fluxing. Stir with a dry hardwood stick.
http://castboolits.gunloads.com/imagehosting/thum_187904f3b0caa9eb68.jpghttp://castboolits.gunloads.com/imagehosting/thum_187904f3b0cbeecffd.jpg

Mini-ingots for my small hand held electric pot, rusty muffin pan drops nicely.
http://castboolits.gunloads.com/imagehosting/thum_187904f3b0dd7648da.jpghttp://castboolits.gunloads.com/imagehosting/thum_187904f3b0de87c371.jpg

All done, next to bottom of the pot ingots. Not a lot this time, but it adds up.
http://castboolits.gunloads.com/imagehosting/thum_187904f3b0eaeb722d.jpghttp://castboolits.gunloads.com/imagehosting/thum_187904f3b0ec2500c9.jpg

- Bullwolf

[Beau Cassidy]

What bullwoof said. One of the first things I would do is flux with sawdust. I think you will get better results by doing that. Another good- actually really good- flux is the one from NEI. It brings stuff to the top other fluxes don't.

[minineo]

I just did this too. I had a bunch of wheel weights that I melted into my Lee Pro 4-20. I did the original melt a week ago and had about 1/2 of the pot full of cold mix. I put a lid on it to speed the melt and cranked it up to the max setting. I left it alone for about 15 minutes or so. When I came back, the whole mix was glowing a medium red like when you turn an electric range burner on High. I have a digital pyrometer with an Iconel thermocouple capable of safely measuring up to 2000F. I stuck the thermocouple in and it broke through a hard crust into the melt underneath. The temperature was 1437 degrees. After getting over my astonishment of the prowess of the little electric melter, I started trying to get it to remelt by stirring with a stick of pine. The wood ignited immediately as expected, but the hard crust just kept breaking up and floating. I scooped it out and dumped it into a steel cup and now it appears to be a brownish orange color like dirt with some clay in it. Two questions, 1) what is this crusty stuff? 2)did I screw up my boolit alloy? How can I test the lead remaining? (Ok 3 questions). I appreciate any insight especially from you chemistry types.

[Beagle333]

Now that is a good Lee 4-20! Mine won't get that hot.... but I do get the yellow-orange powder on top of my alloy, along with what looks like beach sand. I'm using isotope lead that I bought and so I don't know what he fluxed with.... but I'll get a teaspoon of what looks like sand and yellow dust off the top of the pot with every 3lb ingot I melt.

[40Super]

Yellow powder sound like sulfur ?????

My 4-20 pot will get awfully hot also, (it's the 220v model). With the dial on 4.5-5.0 it'll be 750-800F.

[minineo]

I did a test today with my Lee Pro 4-20. I'm new to all this and fascinated. The pyrometer's new too, I highly recommend it so far. it can be had at auberins.com here's the info:High temperature thermometer, Pyrometer (THS-192) Sensor Type Option 10" (250mm) Inconel Probe = $52.98 + shipping. Anyway, it's nice because it reads to .1 degreeF from -199 up to +1000F and then reads in 1.0 degreeF from 1k to 2k degrees. (You can get a ceramic thermocouple that will read to I think 2,300F) so, at setting "5" on the Lee pro, the reading was 1,075F. The lowest setting gave me 745F! I even dunked an ingot in it to make sure I wasn't just experiencing residual heat and it still hovered at 750ish after waiting for 15 minutes! I could probably melt aluminum in this puppy! If I had the time and money to waste, I'd give it a try, but I might ruin the machine and it's the only one I have. Still no exact ID of the grey&brown crust powdery stuff. Does anybody know if it could be lead oxide? Does lead oxidize faster when it gets hotter? Does it get crusty like that?

[gunoholic]

The yellow powder is "litharge," lead monoxide, which on further heating turns to a brown powder called "massicot." Further oxidation gives a red form, called (of course) "red lead."
i read that in a post by "bent ramrod" in a post here- http://castboolits.gunloads.com/showthread.php?103336-Yellow-powder-in-lead
this maybe what it is, i get a little of this yellow powder in my shotmaker from having the gas turned up too high.

[Tate]

The yellow powder is "litharge," lead monoxide, which on further heating turns to a brown powder called "massicot." Further oxidation gives a red form, called (of course) "red lead."
i read that in a post by "bent ramrod" in a post here- http://castboolits.gunloads.com/showthread.php?103336-Yellow-powder-in-lead
this maybe what it is, i get a little of this yellow powder in my shotmaker from having the gas turned up too high.


My area of interest is in aluminium but I reciently needed some fishing weights so I used my simple aluminium forge which runs on coal and gets way too hot (I didn't know better). After little success keeping the fire going in the rain, I cranked up the air supply to max and the coals glowed (I could melt steel at these temps) I walked away from the furnace to pick up a skimmer and heard a noise similar to that of boiling water, confused as the rain had stopped earlier I turned around to see a white plume of smoke suddenly glow bright green. My jaw dropped, after seeing a few green fireballs shoot out I figured the coast was clear. I immediately killed the air and the fire died in shock I looked into my crucible (half expecting to find an alien mother ship ) where the green had darkened and white ash had coated the sides. I took this as a sign that the remaining metal was ready to be cast. As I normally do when making fishing weights i use aluminium cans with an eye and extension in steel sitting in the can. As I poured I noticed it wouldn't collect and poured the rest on the ground after further inspection it melted holes through all of the sides of the can and deposited much of the lead alloy. I probably should mention that the most of the 'lead' I had had tin in it and was post consumer solder that got a second life I also used some leftovers from my old lead and tin electronics parts. I am even more scared of lead than before. Not sure about using lead anymore except for making circut boards, I rarely have uses for it. After washing cleaning it I kept the fireball looks cool. Defiantly oxidizing but for me more like combustion.

[mto7464]

Why are you scared, sound like you just got it way too hot. Do it properly and you have nothing to fear.

[40Super]

I'd rather deal with 650F molten lead than 1375F(?F) molten aluminum. The lead will burn 1/2" less deep into flesh:shock:

[bdecker9]

i just had this happen today. the have no idea what i the crust that formed is, but my boolits weighed in 5 grains less after this happened. i was afraid i had cooked out tin and such. but the weight of the boolits says different. this happened when i switched to a 2 banger mold and slowed production way down. the crust on top was glowing red like when you get steel very hot. i dumped this on my pizza box that i use for landing zone for clips and fluxing trash. this yellow crusty stuff ignited the box. i thought that tin and such burned off at a lower temp than lead, am i wrong?

[Echo]

Hmmm - I'm no expert (!), but I suggest trying to remelt the crust, with a healthy dose of sawdust. If what I read here is right, the oxygen will migrate from the lead oxides to the carbon in the sawdust, forming CO2, and you will recover your Pb. Maybe...

[Pakprotector]

With a Lee 20 pounder and only 5 lb in it of 20:1 I turned it to the same setting I had used on a full pot. It got waaay hot I discovered later, and a lot of that yellow stuff came to the top. Only 1 5 lb ingot. I keep it full and temp stays quite consistent.
cheers,
Douglas

[docone31]

Vegetable oil helps also. Add some and it will bring a lot back from being crud.
It helps.