Fluxing with saw dust

[ssn vet]

A couple questions for the crew....

When I flux with saw dust, should I light the smoke cloud? I've done it twice and it definitely ignites. But I don't know what's burning and whether it helps or hurts.

After stirring in the saw dust (I've been using a painters stir stick), should I scrape off the burnt carbon? Or just leave it?

I seem to develop a darker gray film on the surface soon after fluxing with saw dust. Is this probably tin re-oxidizing? Should I drop in a small chunk of wax to form a surface film in hopes of keeping the tin in solution?

Thanks for any tips....

Part of my problem is that I don't really know what a tin film looks like. Anybody haves a link to good photos or a you-tube video?

[runfiverun]

the burnt ashes are what you want to stir throughout your alloy it's carbon.
carbon is used to carbourize the alloy which makes it's make-up bond together better.
you want a fire to initiate an oxygen free surface to allow the oxidized alloy to reduce and return back..

[ssn vet]

Any thoughts on the film?

[luigi's mongey]

i flux with left over bullet lube then cover the surface with about 5-10 mm saw dust which smokes for a while and prevents oxidisation on the surface.

[geargnasher]

i flux with left over bullet lube then cover the surface with about 5-10 mm saw dust which smokes for a while and prevents oxidisation on the surface.

Boolit lube does nothing to "flux". It reverts oxides to the elemental state, but doesn't remove impurities, which is what FLUXING does. The sawdust fluxes as well as reduces oxides.

Gear

[geargnasher]

SSN, the oxide film is a like a "skin" coat on the surface. It wads up like crepe paper if you slowly push a spoon across the surface like stirring a cup of hot tea, leaving a temporarily shiny surface in the wake. The skin piles up as a light silvery/grey clumpy residue if you "round it up" with a spoon. No need to do this, it will just form again in a few seconds. A coating of sawdust on the surface like Luigi's Mongey wrote above will pretty much keep the air off the surface of the melt if you leave it alone and let it smolder down to powder. Kitty Litter will do the same thing, as will the borate fluxes, but borates have their own set of major drawbacks so I don't personally recommend them for most casting purposes.

Light the sawdust smoke or not, no matter really. Combustion helps reduce oxides, especially yellow, low-oxygen flame, but you're getting more than enough of a reduction/oxidation reaction from the sawdust smoldering, so lighting isn't really necessary unless you prefer to cut down on the amount of sooty smoke produced.

Gear

[gundownunder]

When you set fire to the smoke cloud all you're doing is burning off the wood gas produced by heating the wood.
The only benefit to doing this would be environmental, as there is a high methane content in this gas and they say methane is part of the global warming problem.

I use free sawdust that I pick up by the bucketful from the local Bunnings store cutoff bench. This stuff contains sawdust from MDF, chipboard, pine, jarrah and several other woods and it seems to work perfectly well at keeping the top of the alloy silver.
As I use a dipper to cast I put enough dust on the pot to cover about half the surface when it's pushed to one side, then dip from the clean side. This method usually works and I only occasionally need to return a bullet to the mix due to inclusions.

Adding lube, grease, oil, etc to your alloy will not help, it's bad for you, bad for the environment, highly flammable, and too much of it will cause a thick, sticky scum to form on top of your alloy that will stick to the pot and the utensils, and be a real pita to clean up.

[blackthorn]

Sawdust from MDF, chipboard, plywood and/or treated lumber etc. contains chemicals that produce unhealthy fumes as they burn off. If you use sawdust from manufactured/treated wood products, flux outside, stand with the wind from your back and do not breath the fumes.

[John Boy]

SSN ... the best sawdust is from wood that has a high percentage of rosin such as pine. Rosin has been used as an excellent flux for decades to remove the oxygen from the melt and produce more impurities to rise to the top as dross.

[ssn vet]

I'm using saw dust from my table saw and it is mostly pine so I guess I'm in pretty good shape.

Thanks for all the replies

[MikeS]

When I use a bottom pour pot along with fluxing with wood chips, I also leave a layer of wood chips about 1/2" thick on top of the melt to form a barrier keeping air away from the surface to slow oxidization. When using a ladle it's kind of hard to keep a barrier on the melt, so I just flux it more often than I would otherwise. Since switching from wax to wood for flux my alloy along with the pot and all tools used in it are much cleaner.

[High Lord Gomer]

Brand new guy here...

I don't have sawdust but I do have a fair bit of ashes from the fireplace. Could I use that?

If so, do I need to stir it in as much as possible or just let it cover the surface?

[on1wheel01]

I use mdf shavings from my table saw from building sub boxes. As soon as o add it to the molt it ignites. I then add tea light candles to furture flux it. I then scrape the heck out of the bottom and sides. Seems to work pretty well.

[Crashbox]

This is really good information as I'm gearing up to cast (probably) this spring. I have a source of sawdust from my neighbor across the street who assembles shipping pallets part-time and he said I could get a five-gallon bucket of sawdust gratis. I wonder how long such a container would last for fluxing...? FWIW, I have an RCBS Pro-Melt bottom-pour furnace to work with...

[John Allen]

I bet you if you went to home depot the guys would give you a bucket full.


Brand new guy here...

I don't have sawdust but I do have a fair bit of ashes from the fireplace. Could I use that?

If so, do I need to stir it in as much as possible or just let it cover the surface?

[cajun shooter]

We have a member by the name of Pat Marlin who sells a wood flake not real fine sawdust such as that from a table saw. His flakes are from different types of evergreens. This goes along with what my friend John Boy posted.
I have been using his flakes for many years and they are the best. Not only do they flux but I leave a coating on top of my alloy and it gives off a nice scent while I'm pouring. It also stops any oxidation from taking place. Later David

[Jack Stanley]

When I'm working down in the dungeon I will sometimes light the sawdust because my exhaust fan has trouble with large volumes of smoke . If my metal is rather clean already I don't light it so while inside it's just a matter of how much smoke is produced .

When melting scrap outside it really doesn't matter to me , I'll add a couple inches to the top of five hundred pounds of lead and stir untill it's clean .

Jack