Fluxing with freshly made sawdust

[Kenk]

I was cutting up some sizable tree limbs this morning, and decided to save some of the sawdust for fluxing. Is it realistic that the high moisture content in the freshly made sawdust could cause the tinsel fairy to come alive?

[Rvrrat14]

I?d be more concerned about the MOISTURE popping?.

[James8719]

I was cutting up some sizable tree limbs this morning, and decided to save some of the sawdust for fluxing. Is it realistic that the high moisture content in the freshly made sawdust could cause the tinsel fairy to come alive?

It is very realistic! Moisture from any source is bad news! The tinsel fairy will likely bite you hard!

[Kenk]

That was my concern, I have a bunch of beeswax for the time being, or at least until the moisture content lessens
Thanks

[sqlbullet]

I no longer put anything in my casting pot but lead ingots and the occasional chunk of crayon/wax if the top gets gunky.  If you are going to use sawdust, I would not use it to clean the lead, but to create a barrier layer over freshly cleaned lead.  Using it this way will avoid the tinsel fairy as she only visits if something wet gets below the surface.  As long as the moist is on top, it will just cook off.

Putting sawdust on top is supposed to prevent a lead oxide layer from forming since there is not any oxygen on top.  As the sawdust chars, it creates a layer of CO(x) gas that is heavier than air which creates a barrier to normal atmosphere.  Also, the carbohydrates in the wood, as they decompose, are supposed to help pull the oxygen molecules off any lead oxide that had formed, returning elemental lead back to the melt.

In my experience, while wood may provide these benefits, it has some very significant drawbacks IMHO.

First, excessive dross.  All the sawdust that goes in has to eventually come back out.  And there will be a huge amount of it, especially compared to the relatively small amount of lead oxide I get with just bare lead melt on top.

Two, constant smoke/off-gassing.  It smokes lots.  And even after the obvious smoke stops, there is still lots of off-gassing based on my nose.  Lots more than I can detect with just lead.  Which leads to....

Three, lead oxides caught in the smoke.  I don't know how much there is, but I do know the worst thing for your lead levels is to inhale lead oxides.

I do think there are some benefits to sawdust when cleaning scrap lead to make ingots. This is where I will use a fair bit sometimes, especially if I have lead that has been painted.  After getting the lead melted, a cup or two of sawdust goes into my dutch oven and it gets a lid put on for several minutes.  Care and protective gear must be taken when removing the lid as the in-rush of oxygen often causes the trapped gases to ignite.  Tip the lid up on the side opposite you, have welding gloves and a long sleeve shirt of a dense cotton, not poly, wear a face shield, etc (or just close your eyes to squints, look away and be prepared to have hairless arms, hands and maybe eyebrows for a few weeks). 

Once the lid is off give that lead a good stir as it burns down.  By this time any moisture that was in the wood is long gone, so no risk of the fairy.  Stir/scrape to burning pot until the flames die off, then use a slotted spoon from a restaurant supply house to get the remaining ash and charcoal out.  This results in some of the cleanest lead I ever get.

[Kenk]

Thank you, I?ve been using small amounts of sawdust for the same reason I use wax, to bring the impurities and skid to the top of the pot. Once again I?m reminded how little I know about casting, but that?s ok, I?m moving in the right direction

[The_Shadow]

When I am reducing wheel weight, plumbing lead, or just dirty alloy, I use old motor oil (outside in the open) to flux with.  It will flash to flame, and I stir the melt vigorously which brings the trash to the top for skimming.  It can also add some carbon to the alloy.
Sawdust when casting works well on top of the clean alloy as sqlbullet has mentioned.
I have also used the used oil as a recleaning before casting but don't use as much as it will flash to flames.

[Kenk]

Thanks Wade

[Rvrrat14]

I went to a local business that builds wood storage barns and they let me rob their sawdust collector bags.  I then pour the into large plastic coffee containers and place lids on them.   The clean, dry sawdust does great when needed.

[sqlbullet]

I use motor oil as well.  Couple of advantages:

1.  It does do a good job of cleaning.

2.  It adds a lot of heat.  Often I will get the pot about a quarter full, get the oil burning, and then add more un-melted lead.  Greatly reduces the amount of propane I use.

3.  Disposes of waste oil.