Fluxing with sawdust, how?

[RobsTV]

Is there any standards to go by with sawdust?
I see many posts that say toss in the sawdust, stir it well to mix it in, light it on fire, etc.

1. How much sawdust is used in for example a half filled Lee 20lb bottom pour? A tablespoon? 1/4 cup? 1 cup? What if you use too little or more importantly too much?

2. What does stir well mean? Stir deep and vigorously for 10 seconds? 30 seconds? 2 minutes? Stir slow and long?

3. Is that dross on top or sawdust? When mixing back in, should there still be a lot of dross on the surface? If you use too much sawdust, will it be on the top of the melt needing to be skimmed off, or will it always turn to black and disolve into the melt? Oatmeal, dross or sawdust?

4. Do you mix the sawdust into the melt before it turns black or after it turns black?

5. What temperature to flux at as it relates to sawdust? Should you flux as temperature rises just past molten, like around 500-550, or after it reaches your intended peak of around 700 (if keeping it cool enough to prevent zinc melt)?

6. When using clean ingots for final casting, any changes to the above answers?

These were just the first few questions that bugged me, hopefully someone will add in more.

[DukeInFlorida]

Wow, lots of questions. I'll be first to try and answer.

Some of this has been covered elsewhere, and I would urge you to do some of the stickied reading.

The concept of "fluxing", whether copper plumbing soldering, electrical soldering, or lead smelting is the same. It's a process by which impurities are removed with the use of an agent for that purpose.

With copper pipe (plumbing) soldering, the flux serves the purpose of removing and protecting the clean copper surface of oxidation, especially while the pipe is being heated, for the application of solder (lead). Without the flux, even a sanded copper surface would almost instantly oxidize, and the solder would not create a good joint. Electrical soldering is about the same function.


Soft pine dust, or any other resinous pine like wood dust/chips are better than hardwood dust/chips. It's the resin that does some of the work.
The dust/chips should be stirred into the lead, trying to get it as close to the bottom of the pot as you can safely get it, without splashing molten lead everywhere.
The stirring does several things. The resin attracts and causes the impurities to stick to it, allowing those impurities to clump together, where they can float to the surface for skimming off. The stirring also creates "pathways" for the impurities, which are lighter than lead (therefore would float), but are trapped inside the molten lead due to the lead's density.
The saw dust/chips will eventually char, and the resin will burn off. However, the charcoal hasn't lost it's usefulness. Much like a charcoal filter for anything else, the charcoal will continue to attract and filter the impurities, and keep opening pathways for the impurities to migrate up through the lead.
What you don't want to do is allow the sawdust/chips to turn to ash. Powdery ash then becomes the same type of impurity that you are trying to remove.
So, at some point, just after the resin has burned off, but before the charcoal has burned to ash, you want to remove the charcoal, and do another run through.
I do 2 or three runs with pine saw dust, and then do candle wax for another 2-3 runs of fluxing.
What I look for is the point at which deep stirring of a pot of lead, with no fluxing agent in it, will produce virtually NO residual impurities floating to the top. The impurities will look like very fine gray/black powder. That's the stuff that you don't want in your boolits.
I skim the impurities off the top of the lead with the edge of a spoon, so as to minimize the amount of lead I'd toss away with the skimmed impurities. A slow skimming speed will allow the impurities to stay in front of the spoon. Spoon = large cooking spoon with long handle.


What fluxing does for the smelting process is to assist with the removal of the impurities in the lead, so that the impurities can bet skimmed off.

So, with regard to sawdust...............

[Bored1]

Answered pretty much every one of the ?s I believe. Just read it 3 times to make sure I retain some of it. Thanks DUKEinMaine

[gbrown]

DukeinMaine answered it all, from my perspective. My question would be: Are you using clean ingots or raw material? My ingots are clean. I smelt various forms of lead and flux a bunch of times (5+). I use both wood, rice hulls & paraffin. I never use pariffin in my casting pots, Lee or ladle type. I don't like using any flux in my Lee. I keep it down around 700-750. Use one of NOE's thermometers. Never empty a pot. When thru, there is at least 1/3 of a pot with any junk on top. Every now and then, heat the pot up, empty and disassemble to thoroughly clean. Never had a problem. Lee's are known by various names-- Sir Drippy, Dripsalot, the Drip Master, etc. Mine do, but only in a minor way. Again, works fine for me. Also, I use one Lee for COWW (pistol) and one for a hard alloy (rifle). I don't change alloys in either.

[dRok]

I dont have a good supply of sawdust so I use confetti cut paper scraps that have gone through the shredder at my office. They are very small and work great for flux and also insulate the top of my lead when melting and seem to decrease the melt time when I throw a few handfuls on top of my pot when getting started (smelting wheelweights that is). Dont do that if your pot is empty or the paper will collect around the bottom as it melts and insulate the lead causing it to heat slower, but if it collects around the sides it doesnt hurt anything, it actually insulates I think. So I start with about 2 inches of lead in the bottom of my 2 gallon pot, dump in WW until it is full to the top, throw in a few handfuls of shredded paper and let it go, come back in 10-15 minutes and stir, skim the top and pour ingots.

[rbertalotto]

Why not just use a wood paint stirrer? I get these for free at the paint store. I simply stir the lead with them, they burn and deposit carbon into the melt and it floats to the top with the smuch. I used to dip them in molten wax. But I didn't see any improvement and a lot more smoke.

[captaint]

Plus one - what Roy said. I like to stir with a paint stick. I use the spoon as well, when doing a "full flux". In between, I stir with the stick and skim only the grey powdery stuff. Works for me. enjoy Mike

[Jim]

The range I'm salvaging uses 1" X 2" firring for target stands. That results in lots of shot up sticks that go in the dumpster. I drag 'em out and use 'em for fluxing the melt. Stiiring the melt with wood does a great job of driving the tin and antimony back into the melt and all the unwanted stuff to the top.

[Plinkster]

Kind of drifting here but I like sawdust for the fact that I can cut the sprue directly back into the top of my bottom pour. I leave a thin layer of burnt and stirred dust on the top and it eliminates splashes when the sprue plops in. This trick really extends my casting sessions when I get heavy handed on the sprues.