Of Slag and Sludge-What is it? (1 Viewer)

[Whistlinghen]

When I was little (a very long time ago) my dad used to cast little German soldiers from an ancient mold (which I still have) and I later inherited my aunts' set of Rappaport molds*. Lately, I've been casting in RTV. But now my question: What exactly is in that sludge that one scrapes off the top of the molten lead? Some of it obviously is lead and tin oxide, but sometimes you'll get a skin of bronze coloured stuff. The stuff won't melt at stovetop temperatures and has to be discarded (I'm saving a bucket to take to the toxic dump), but lately I've started to wonder if I'm tossing out some of the antimony or bismuth that is supposed to be in the mix. Any thoughts? Thanks, Emily
*What follows is simply a reminiscence, and not intended as a springboard for the discussion of the rightness or wrongness of safety regulations!
Those were happy, carefree days, when we made toys of sharp, toxic metals for children to play with. I can still see my dad, Pall Mall in his mouth, probably half toasted on Prince Alexis vodka, heating the lead and mold with a home butane torch, in a basement filled with volatile substances. Those were the days when children not only didn't use seatbelts (who had them, let alone car seats), we rode around curled up in the deck underneath the rear car window with our mothers loaded on tranquilizers. We hid from big brothers with BB guns and wrist rockets, blissfully played with real iron horseshoes and lawn darts, played in the streets until well after dusk, and climbed trees that would frighten a lumberjack. We made the "Darwin Awards" and "*******" look like pikers. Any parent that showed what we would consider basic common-sense concern about their child's safety was sneered at by other parents as treating their children like "hot-house plants". Nowadays, I take any safety precautions I can, whatever I'm doing-I figure I'm already on my ninth life.

 

[bromhead]

I did casting as a kid also,,what a horror it would be regarding safety,,lead and other laws now,,what fun it was.

I had a home business a few years back using the "new" molds etc,,had my own metal blend using alloys,,tin -not much lead,,the stuff is impurities rising to the top with the temps,,any foreighn stuff in the pot or the metal,even dirt and dust getting in,,the simple skim with the stick was a part of it. Cant beat the fun of your own soldiers

 

[theBaron]

Very good question about the composition of the dross. It would probably take some chemical analysis to determine for sure. But as a percentage of the volume of metal in the pot, it's probably a negligable amount.

I do the same thing, I skim off the dross at intervals. Mine also includes traces of sulfur, and other compounds on the surfaces of some of the lead scrap I pick up for melting.

I usually run a melting pass to remove those impurities and make casting pigs, so during a casting pass, I don't have as much skimming to do between pours.

Can we see some of your castings?

Prost!
Brad

 

[1879fanatic]

The dross or sludge on the top of melted solder is simply all the impurities from the solder surfaces, alloy surfaces and whats been in the solder pot. We use the solder pots for tinning wire for electronic work... A little stainless steel spatula or knife will wisk it off the top. Just slap the dross on a piece of board an toss it away. It's no more dangerous than the molten solder/metal itself. The kids working in the shop always wonder what would happen if you stick your finger in the pot. Please advise
Mike

 

[kilted vampire]

The dross or sludge on the top of melted solder is simply all the impurities from the solder surfaces, alloy surfaces and whats been in the solder pot. We use the solder pots for tinning wire for electronic work... A little stainless steel spatula or knife will wisk it off the top. Just slap the dross on a piece of board an toss it away. It's no more dangerous than the molten solder/metal itself. The kids working in the shop always wonder what would happen if you stick your finger in the pot. Please advise
Mike

(said in South Park school counselors voice) That would be baaaad. You should not put your finger in the poooot That would huuurt. You should not hurt yourself. That would be baaaad. (

 

[1879fanatic]

KV,
I saw a guy do it once, merely wetted his hand first anplunged it in. The water prevented his hand from burning! True story!
Mike

 

[theBaron]

"I don't think so, Tim!"

 

[trooper]

Personally I always use an alloy with a built in dross inhibiter. However, before I switched to this I used to save the dross in a bucket. When I had a reasonable amount I would empty the pot of metal and fill it with the dross. I then turned the heat up to about 400 degrees and shaved an ordinary wax candle into it. This must be done outside, or at least in a very well ventilated area as it gives off some smoke and fumes. after a while the surface is covered with a black powder which should be carefully scooped off and disposed off at a toxic dump. The amount of metal that is left can be reused and you will be surprised at how much you can reclaim. The reclaimed metal may have a surface colour of gold or purple but don't worry, this is only a sign of the heat that was used to reclaim it and it will vanish the next time you heat up the pot.

 

[kilted vampire]

KV,
I saw a guy do it once, merely wetted his hand first anplunged it in. The water prevented his hand from burning! True story!
Mike

I have heard similar stories but I will let you try it first. That way you can have all the glory!

 

[Wraith]

I have heard similar stories but I will let you try it first. That way you can have all the glory!

Well, if a plain old coffee mug can withstand molten lead, then I can't see what your worried about.

 

[1879fanatic]

KV,
It's not SILVER...Go ahead, I dare ya!

 

[trooper]

My mate, Lefty, did that once.