Here's another "dross" question

[Whitespider]

On this board I’ve read a lot about “dross”. Being a newbie, I first thought “dross” was the gray ash like stuff that formed after fluxing. But, I’ve come to understand that “dross” is any and all stuff we skim from the top of the melt.

As I’m casting (I use a dipper) a “skin” forms on the top of the melt, I keep pushing it to the side of the pot. This “skin” builds up into a “glob”, I can push it down into the pot but it doesn’t melt back in. Every so often I stop and add sprues and rejects, flux and skim off this hard “glob” of built up “skin”.

On this board I’ve read a lot of opinions about what this stuff consists of. The consensus seems to be that it’s oxidized metal, some say mostly tin, others say antimony, and still others say lead/tin/antimony.

I’ve been saving this “dross”, had about two pounds of this lava looking stuff. Today I threw it in a small saucepan and put it on the old electric stove I use as a heat source. Set the burner on high and hit the top of the stuff with a propane torch. At first I didn’t think it was gonna’ melt, but it did melt. I fluxed it, and got a nice silvery pool of molten metal. This stuff acted just like my WW metal, after a couple moments the “skin” started to form, I could push it to the side, etc., etc...

So what’s my question?
If I can melt it down like I did today, why won’t this stuff melt back into the pot when I’m casting?

[monadnock#5]

If you had a special spoon type tool, and the patience of a saint, you could very carefully skim and remove just the powdery stuff. But, the melt is hot, the mold is hot, and you just don't want to take the time, so you end up with more lead than powder. Sound familiar?

Not to worry. Someone on this board had a great idea not very long ago. Save that dross, and the next time you smelt, dump it in with the rest of the stuff. I can't to try it myself.

Ken

[WHITETAIL]

Whitespider, Thats what I do. Throw the dross that you skim off when you make your boolets. Take that and put it in the bucket with your next batch of WW . So when you smelt again it will not be lost.

[Bass Ackward]

In this hobby we can get tied up with .... facts. While I enjoy learning, which is why I frequent here, sometimes reality is what we have to live with.

I received two metal water buckets that weigh 60# of dross from a laddler accumulated over the years. He was happy to get rid of it. I knew most of his casting was in the 60s and 70s and he used old WW (9%) and a lot of lino that he got for free at the time.

I decided to smelt the entire batch at once and decided I would live with what ever I got. Quite honestly, I was wanting and expecting a pistol mix of about 8-10 BHN.

I had 30# of WW left over from another smelting secession (still in the pot) to begin the melt and added that dross stuff. I then scientifically calculated how much pure lead needed to be added by simply filling the pot until it was full. End result was @ 50# of pure. After fluxing, I took back approximately 7# of stuff I didn't want.

The result? Air cooled that mix is now clean and casting well and thanks to my hardness tester, measures fairly close to 16 BHN. And the bullets do shine a bit. If you trust my experience, I'd say around a 2% shine. So I goofed. Thank God for hardness testers. Clearly, there was more in that dross than trash. :grin:

What's in this mix now and how it got there exactly? Who cares. Mixed 60/40 with more pure and a lb of Sn and it's right where I want it to be.

[montana_charlie]

Set the burner on high and hit the top of the stuff with a propane torch.

So what’s my question?
If I can melt it down like I did today, why won’t this stuff melt back into the pot when I’m casting?
If dross is actually oxidized metal (as I believe) it can't recombine with the pot of alloy because it is no longer tin (or lead, or antimony) it is tin oxide.

By using a source of carbon, we can encourage the oxide to lose the excess oxygen that it picked up, reducing it to it's original state. Then it can return to the melt.

When you played the torch over the top of that solidified dross while melting it, you might have burned away that excess oxygen, causing reduction.

As a matter of fact, it gives me an idea to try during my next casting session.
Perhaps a propane torch can replace my wooden stick...call it fluxing with fire.
CM

[454PB]

I did the same experiment as BA describes, on a smaller scale. I got the same result, about 80% by mass was usable alloy, the rest discarded as dross, "again". I did notice that the resulting alloy seemed to have less fluidity, and assumed that was due to tin lost. I keep a container for mixed scap boolits and alloy below my bench, and the recovered alloy from the dross was added to that for use in .45 ACP boolits.

[chevyiron420]

i did something a wile back that may or may not mean anything but, here it is. i decided to cast up a bunch of wadcutters without fluxing to see what happened. afterr melting the ingots i stirred with a old spoon and then let sit till the temp stabilized good. after that i just dipped out the junk from the top. i had about a rounded teaspoon full. then i bottom poured wadcutters till the pot was low and put the teaspoon full of junk back in and refilled the pot. you would think that when repeating this the junk would keep building up by an aditional teaspoon full each time, one the first pot full, two the second, ect. it didnt! after three pots of alloy i was tired and quit, but still got about one round spoon full of trash. i also didnt notice any diference in the rejection rate of the boolits. i dont have a hardness tester, so i dont know about that, but they seem good and the boolit dia. is the same. it may mean nothing, but seemed odd to me.-phil

[leftiye]

Chevy, Were you casting at a lower temperature? This would result in lower dross formation. Also, if not too hot the tin forms a skin that retards further oxidation of tin (may explain the slow formation, along with not further stirring). I like to use a layer of dross, or (way better) a layer of crushed charcoal and just leave it there on top of the melt.

Mt. Charlie has it right IMHO, The excess carbon in the flame reduced the oxides back into the melt. Also such oxides can be reduced by temperatures above 1100 and some(?) degrees. The flame is in the 1400 degree plus range and raises the temps of whatever it is played on quite high and fast. I.E., just using the flame is a way to reduce a pile of dross, or floating dross all by itself. Some fluxes are very good at reducing oxides (and at very low temps -say 450 degrees) rosin, and beeswax are what I use to reduce dross.

[shooter575]

I cast a lot of soft PB for minnes.I dip and cast hot 800-825.I get a lot of dross.I use sawdust to reclaim the lead from the oxide.Any carbon will work.But I would rather smell wood burning than motor oil and beeswax cost more than sawdust.
I rough guess that I get back 85-90% of my dross as good metal.