Slag question for the wise ones

Ole_270

Active Member
I've been getting quite a bit of slag on the casting pot that Gulf wax nor bees wax will reduce back into the mix. I stir with a wooden stake before skiming, that doesn't help either. It's kind of a grainy looking thick meal. I've tested the slag with mureatic acid with no reaction, so I doubt it's zink or calcium. I'm getting great looking bullets out of the alloy so it can't be that junky. Alloy is range scrap with pewter and a few WW to bring it up to spec.
Today I was mixing more alloy in the big smelting pot and put the accumulated slag in with it. Threw a couple handfuls of wood shavings (pet bedding) in and started stirring. The slag reduced in seconds!? I run a 10" 200,000 Btu burner on the smelting pot without a thermometer so maybe more heat is contributing, but it appears the wood is the main answer.
I hate to run the wood shavings in the bottom pour casting pot, but it looks like I need to. I typically run close to 1-1.5 Sn, 2-2.7 Sb. Is the slag likely antimony because there isn't enough tin to combine with?
 
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freebullet

Guest
Waxes are a reducer but not a flux. Wood chips shavings ect is what you want. I use it all the time on my bottom pour pots.

Let's see what the wise ones say
 

Brad

Administrator
Staff member
You can use wood chips or sawdust in bottom pour. Be careful not to get them below the surface much. I like to get them beginning to char and dump ladles full of lead thru them. I then stir vigorously to get a swirling of lead. Ignite and keeps stirring.
The low order flame, Smokey is good, produces lots of carbon monoxide. That is the reducing agent.
Keep stirring and then skim. I sometimes repeat before skimming. The reducing takes time.
Again, the smoke and low order flame do the reducing, not the material itself.
Be sure to stir well from bottom to top. You want to create eddys that move debris to the surface. Lead is so dense that bits of debris don’t gravity separate well.
 
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freebullet

Guest
Let mine smolder, light the smoke off. Once it's black we have carbon. Stir in, pour through scrape pot sides & bottom. Nothing on top but the dirt & impurities. Little more saw dust keeps it from oxidizing sn & sb back out.
 

Ole_270

Active Member
I quit using sawdust in the old 10 lb lee pot when I started getting small black inclusions in the bullets. It was pretty hard to stir the full depth with tha angled valve rod. Now with the Mag 25 I may need to start using it again, just keep the level down far enough to stir up a storm.
 

Rick

Moderator
Staff member
Again, the smoke and low order flame do the reducing, not the material itself.
confused-small.pngHhmmm . . . Not according to . . . From Ingot to Target: chaper 4 Tis the wood turning to carbon and the carbon that both fluxes and reduces.

But as Brad also said lead is dense enough to hold light particles in suspension. You should never attempt to force it below the surface. Bring alloy up from the bottom and pour through the . . . . Carbon.
 

popper

Well-Known Member
Beeswax is a flux (physical barrier) and reducer. But you can't stir it in well so the reducer portion is not as effective. Both 'burn' to create the carbon and coat the top to restrict oxygen. Keep the melt temp to just above liquid where the wax is still liquid and mix. Hard to do and still will leave some very small particles in the melt. CuSO4 is a very good reducer but you really have to stir and scrape. It comes hydrated (H added) when that steams off the Cu & S combines with Sn, Zn (and most everything else) and Sb but the SbCu stays in the Pb. ZnS & SnS are fine powder.
 

Bret4207

Undesirable member in absentia, Northern NY
I'm no expert, thats for sure, but I'll give you my observations. I tried wax and lube at first, like all the books said. It was great for filling the room with smoke and the fire was impressive. I can't say it was a great flux for lead though. After some years of doing that I read about sawdust and then later about stirring with a stick. I found that method to be much, much better than using lube or wax or motor oil or Wesson Oil or any of the other gimmicks I tried. I also tried rosin, which I had on had from the gunshop. Don't use rosin unless you enjoy having a huge mess in your pot. Same for pine pitch, tried that too. Anyhoo, what works for me in the intial reduction melt from wheel weights, pipe, old solder or whatever you get is to fish as much junk out ahead as you can. Tire valve stems is what I'd get lots of. THey really stink. I find if you can wash the stuff off it helps too if it's junky like i got sometimes. Let it melt, I use a gasoline plumber furnace that sounds like a small jet engine running, and start stirring with a wooden stick. I tend to use strips of lumber I've saved from projects, but anything roughly broom handle size works. Actually an old broom handle itself would work! It's going to char as you do that. That's what you want. I scrape the sides and bottom of the cheapy dutch over I use and that gets more charred wood into the mix. If it's really nasty looking stuff I might throw in a few handsfulI of saw dust. Get it nice and liquid and good and hot. I think I let it get up to about 850 or so, but I don't recall for sure. Then I stir and stir and stir. All the crap comes floating to the surface and I skim with an old slotted serving spoon with a very elegant handle held to the stem with hose clamp. ;) Then I stir and scrape more. Skim whatever else shows up. I take a regular old cheapy gravy ladle, again with the elegant hose clamp handle thing, and I skim just the dusty stuff and try to get it clean. Then stir and scrape more until it looks like it's about as clean as that pot will get you. Then I make ingots.

When I actually go to make a melt for bullets I also use a wooden stick. I used to use a cast iron/steel Lyman type pot but a decade or so ago I ran across a large stainless very heavy duty measuring cup in a now defunct hardware. I think it's 6 or 8 cups. Anyways, when I started using that my dross production dropped to darn near nothing. Maybe it's just me, but I think cast iron/steel pots corrode or rust under the surface and stainless doesn't. So I stir and scrape and so on and skim the very small amount of dross I get, which I think is mostly dust and fly poop and maybe some rat pee. I get practically no crap in my castings. Pock marks and incomplete fillout because I'm impatient, yes, but not much garbage. The stick works for me. I don't think the saw dust is all that necessary if you give the stick time to char good. Consider it a consumable.
 
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JWFilips

Well-Known Member
I remove all my impurities in the smelt .....Way before it goes into my casting pot! That has solved all my problems in a bottom pour!
All i get in the bottom pour then is oxidation which I reduce with a pea size piece of beeswax!
Here are two of the best articles I ever read They have change my casting life for the better!
Jim
 

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Brad

Administrator
Staff member
View attachment 13386Hhmmm . . . Not according to . . . From Ingot to Target: chaper 4 Tis the wood turning to carbon and the carbon that both fluxes and reduces.

But as Brad also said lead is dense enough to hold light particles in suspension. You should never attempt to force it below the surface. Bring alloy up from the bottom and pour through the . . . . Carbon.
I believe the carbon works as the flux as carbon has a strong ability to adsorb materials that we don’t want in the melt.

I realize that Wikipedia isn’t the most reliable source at times but here is a segment about a reducing atmosphere.

reducing atmosphere is also used to produce specific effects on ceramic wares being fired. A reductionatmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of oxygen. This diminished level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes. This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form. A reduction atmosphere can also affect the color of the clay body. If iron is present in the clay body, as it is in most stoneware, then it will be affected by the reduction atmosphere as well.
 
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Rick

Moderator
Staff member
confused-small.pngYour wiki example is talking about keeping oxygen off clay pots during firing. Yes the smoke you refer to will help keep air off the top of the melt while the smoke is still there. Still the wood charring into carbon that does the work. With any luck the smoke is gone quickly.
 

Ian

Notorious member
Yes, the carbon from wood adsorbs non-reduced oxides of metals such as Ca and others which do not reduce simply from a CO atmosphere and heat from the reducing environment of combustion.

The lead, tin, and antimony oxides reduce easily with burning anything (wood ,grease wax oil whatever) so the carbon forming as a byproduct of combustion doesn't do anything for those metals.

Carbon gets out what we don't want and anything that burns reduces to elemental from oxidized state the metals we want to keep.

Grease/wax/oil can't get under the surface easily and don't produce enough carbon mass to do much if any adsorbing of oxide impurities and should only be considered a sacrificial reducant of bullet metals. Wood does make carbon mass and can physically get at lumpy oxides of (good and bad stuff) just under the surface and reduce the good and adsorb the bad. I think thisbisbwhy wax wouldn't get rid of the oatmeal and wood did. I've found that trying to add pure antimony is near impossible without sawdust to keep the stuff constantly reduced as it sublimates into the mix.
 

popper

Well-Known Member
Technically flux (weld/solder/whatever) is a clean by 'collecting' junk and reduction. Carbon is a very active element with 4 molecular attaching points. Normal carbon 'reduction' is stripping electrons from metal oxides (o-) so they surrender O to the carbon. Oxides are generally lighter so they can float to the top. Beeswax is high in hydrocarbons and fatty acids. I add wax to my pot when cooling and stir into the alloy (lots of fines collect), then leave a good coating on top of the cold pot. Problem with the wood is it will always make ash that stays in the melt. Before casting I add some wax and it burns to eliminate (smoke) the junk left is very little (kinda like PC when it's burned).
 
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fiver

Well-Known Member
carbon allows the alloys constituents to bind together better.
if we used steam to clean the alloy we could get the carbon back out much easier.

if your really interested in how it works google carborization.
 

Ole_270

Active Member
Thanks guys, I'll go ahead and start with the wood again in the casting pot. This bigger pot without the valve rod angled through the center of it should make it easier to stir enough to bring the stuff to the top. I do need to get some sawdust instead of the bigger shavings for the casting pot. I've always used the shavings in the smelting pot (half propane tank) and stir it vigorously with my "special" tool, an old hoe blade welded on about 5 feet of 3/4 inch pipe. When a double handful of the shavings light up it's nice to stand back a ways. Wife picked it up at an auction with some garden tools and I stole it. Need to rig up a long handled dipper instead of the 1 qt sauce pan I've been using to pour the lead through the charred wood.
 

Bret4207

Undesirable member in absentia, Northern NY
I believe the carbon works as the flux as carbon has a strong ability to adsorb materials that we don’t want in the melt.

I realize that Wikipedia isn’t the most reliable source at times but here is a segment about a reducing atmosphere.

reducing atmosphere is also used to produce specific effects on ceramic wares being fired. A reductionatmosphere is produced in a fuel fired kiln by reducing the draft and depriving the kiln of oxygen. This diminished level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes. This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form. A reduction atmosphere can also affect the color of the clay body. If iron is present in the clay body, as it is in most stoneware, then it will be affected by the reduction atmosphere as well.
That's also basically how charcoal is made. Heat with little O2 and you drive off the impurities and are left with the good stuff.