Saw dust Flux: Why not use this instead?

[milprileb]

Gentlemen,

The use of sawdust as a flux as detailed many times on this forum is very effective. Its a great flux. However, it gets smokey.

I was wondering why charcoal could not be crushed and used as a flux. No smoke and basically the same results. Its cheap enuff !

[btroj]

That smoke is important. It means that the top of the melt is held in an oxygen poor region. This is part of what allows the flux to reduce the oxides back into the melt.
Others will chime in with other advantages but flux is like a lube, it plays many, many roles. A substance may do very well in one role yet fail in others.

[2wheelDuke]

I'm pretty sure others have said that charcoal does just fine as a flux. I think the main difference is that the sawdust is a byproduct that's obtained for free.

[geargnasher]

Charcoal, even "activated" or porous charcoal, isn't very effective for reducing oxides. It's ok for "fluxing" or soaking up the elements we consider impurities to our alloy without removing the good stuff like tin, arsenic, copper, and antimony, but it doesn't do a very fast or good job of reducing oxide scum, here's why:

The reduction of oxides, and by reduction I mean initiating the the chemical process called reduction/oxidation reaction, is accomplished by actively oxidizing (in this case, combustion) one element and robbing outer valence electrons from another element which has already ben "oxidized". Basically to get metal oxides to "reduce" to their elemental state, something else has to be oxidized. In the case of grease/oil/wax/rosin/sawdust it's hydrocarbons, not inert carbon, that gets burned or oxidized, and that process of gaining electrons takes them away from the metalsl, which is what we want. This has to be an active process to be effective. That means an active smolder or flame. Light the smoke if you can because that helps create a low-oxygen enviroment at the melt's surface, and the poor combustion taking place makes lots of carbon monoxide, which is very reactive and wants to become carbon DIoxide, so it takes oxygen from the oxidized metals in the pot.

A layer of smoldering sawdust, particularly if it contains a lot of pine sap, is the most effective reducant and flux anyone has been able to come up with. It does three things:

1. Sawdust burns slowly and inefficiently, so it creates a carbon monoxide/dioxide shield at the melt's surface, which both excludes oxygen from the surrouding air and sucks oxygen from the metals, thus reducing them.

2. Any sap present will donate additional reactive hydrocarbons to the process, speeding up and fueling the redox reaction. A blob of boolit lube, paraffin, beeswax, etc. will also do this.

3. Sawdust is a highly effective FLUX as Glen Fryxell has discovered, which cleans the melt my absorbing certain impurities like a sponge. Impurities like aluminum, calcium, iron oxide dust etc. are removed if the pot is stirred well with the sawdust to maximize the melt's exposure to it.

So, you can see why plain carbon isn't all that great. It will serve to help keep the surface from re-oxidizing if added after the melt has already been reduced/fluxed/skimmed, but it is "dead" or inert, so it has limited reactivity to metal oxides.

Gear

[skeet1]

To reduce the amount of smoke get a butane lighter with an extension on it, the kind you use to lite a grill or your fireplace and when the sawdust starts to smoke just ignite it. The flame will creep over the entire layer of sawdust and burn it. This will reduce most of smoke, it will not eliminate all of it.

Ken

[geargnasher]

Let me pose a question: If your setup can't exhaust a little smoke from fluxing, then how will it eliminate the airborn heavy-metal dust/vapors from your breathing air?

Gear

[birdadly]

Can I be selfish and ask a question here for clarity... here's my process from my first batch in my LEE 4-20:

-get lead melted
-put teaspoon of sawdust on top (it starts to smoke)
-ignite the smoke

When exactly should I stir the sawdust into the lead?
And I think I read somewhere that, if using a bottom pour pot, to leave some (or all?) of the dross on top while bottom pouring?

gear-- if using a sawdust w/out sap, would you suggest adding a small chuck of wax as well? I'm using sawdust from a hand sander, that's not too fine is it? Thanks! -Brad

[oneokie]

Can I be selfish and ask a question here for clarity... here's my process from my first batch in my LEE 4-20:

-get lead melted
-put teaspoon of sawdust on top (it starts to smoke)
Personally, I would use more, like a handfull-
ignite the smoke
I never light the smoke from sawdust, however I do light off the smoke from wax
When exactly should I stir the sawdust into the lead?
As soon as you add the sawdust

And I think I read somewhere that, if using a bottom pour pot, to leave some (or all?) of the dross on top while bottom pouring?
Correct
gear-- if using a sawdust w/out sap, would you suggest adding a small chuck of wax as well? I'm using sawdust from a hand sander, that's not too fine is it? Thanks! -Brad

Hope my thoughts help you.

[geargnasher]

Oxide scum contains a large percentage of tin and antimony due to different rates of oxidation compared to lead, so if you want your alloy to be consistent, keep the "dross" or oxide layer reduced back into the melt. If you leave a layer of sawdust on top of your casting pot, it will seal the surface, reduce oxides, and keep working for you the whole casting session unless, of course, you are ladle-casting.

Gear

[birdadly]

Oh you two and your answers are awesome, thanks so much for breaking it down one more time for a newb :) I hope it helps at least one more guy like me that just didn't quite know the exact ins and outs! -Brad

[noylj]

Heavy metal vapor? Where?
Heavy metal dust? Keep area clean and vent out. Don't breathe any of the dust from the dross.
I'm still old school, so I start stirring the pot as soon as the flux smokes/burns. I still flux vigorously and often.
I keep a layer of vermiculite over the melt--had a moth once come for a visit and the I got lots of tinsel around the work area.

[geargnasher]

Noylj, go get some lead indicator wipes and go over your casting area. How did it get on the walls? On your vent fan? Does it matter? It's airborne, doesn't matter what form it takes, you can breathe it without adequate ventilation. How a moth caused a pot explosion is beyond my ability to comprehend unless it was stuck to the bottom of an ingot you added.

Gear

[MikeS]

I don't have any sawdust, but I do have a package of pine shavings, the stuff used as bedding for hamsters, will that work as a flux as well as sawdust, or at least close to it?

[kbstenberg]

Hey Mike S You do know you have to use the shavings before the hamster does!!

[Charlie Two Tracks]

I tried the charcoal. I crushed a briquet up and put it on top of the mix. Stirred it in and it was pretty dusty. It turned into a very fine dust on top of the mix. It didn't hurt anything but I live near a lumber yard and get all the sawdust I need.

[smokemjoe]

I have used wood ashs after they have been shifted well, Any pieces of charcoal will burn again. Works good. Joe

[MikeS]

Hey Mike S You do know you have to use the shavings before the hamster does!!

Well, you could use them afterward, as long as you have no sense of smell :) Besides, the closest thing to a hamster around here are some Min Pin puppies, but I'm keeping them away from the hamster bedding!

[geargnasher]

I dunno, dog pee on used wheel weights seems to help the fluxing process.......:-P

Gear

[Boolseye]

Gear,
I'm glad you understand the chemistry; It's cool to understand why it works so well.
(I flunked chemistry the first time, had to take it again. If we'd done reloading and casting I bet I would have done better!)
-jp

[Boolseye]

-get lead melted
-put teaspoon of sawdust on top (it starts to smoke)
-ignite the smoke

When exactly should I stir the sawdust into the lead?
And I think I read somewhere that, if using a bottom pour pot, to leave some (or all?) of the dross on top while bottom pouring?

A couple tablespoons of sawdust, stir that in...lotsa smoke...keep that stirrer stick around for the whole session, you can use it to clear a place at the top of your melt, say to heat up a lee mold, then cover it back up with the charred sawdust. The stick does some fluxing, too. Yep, you rite, leave the dross on top for the majority of the session

-jp

[Lizard333]

Remember, an easy way to get sawdust is to go to Home Depot where they cut the wood for you and ask for some out of their vacuum bag. I get enough to last me for weeks at a time. Charcoal costs money, why bother??

[cajun shooter]

If using wood for flux, I prefer the shavings over the fine sawdust because of the time it takes fine sawdust to burn into carbon. I think a slower process gives the alloy more time to clean up and become one. I also leave a handful on top after the fluxing has taken place. This seals the alloy so that any oxidation does not occur. If you use the wood flakes sold by Pat Marlin they will fill the room with a very pleasant smell that even the wives like.

[milprileb]

Saw dust w/ shavings worked well for me. I took the hint to use it and it was a wise move. However, the smoke is such that I am glad I smelt and cast outside on the patio. I would not want that smoke drama in the house or inside a shed / garage. Out in open, its no issue and all goes well.

I just want to make mention to those who may try it: it makes smoke. Just understand that and its something to think about when you decide where you are going to use this stuff as flux.

Cedar shavings may smell good to some wives but not mine!

[mold maker]

The only negative to getting sawdust at big box stores is that it most likely includes the toxins from treated wood. That stuff shouldn't even be burned in a fireplace.
Most everybody can find a construction site that will allow you to collect their sawdust. You can see from the cutoffs what is in the sawdust. Most cabinet shops will have mostly particle board dust, and that too is bad stuff.
A saw mill, or lumber yard, will have the best, but should be well dried, before using as flux.

And Yes, a live moth can flutter on the surface, and introduce it's moisture beneath the melt to cause the tinsel fairy to visit. It won't happen every time, but ONCE IS ENOUGH.

Even a rain drop CAN do it, just not every time. It doesn't have to be immersed to the bottom, just under the surface. Have you ever felt a raindrop sting as it hit you??? It does fall with enough force to break the surface tension, and that's all it takes. Yes I know all about how a water drop on the surface just sings, and sputters, but that's just ON the surface.
When it happens you won't have time to tell it, that it's impossible, and run at the same time. Are you so sure, that you want to tell a nooby not to worry about it.

[gray wolf]

I got a bale of pine shavings all nice and compressed in a sack, about 40 pounds.
All clean and all the same, cost $4.80 It will last me for more years than I have left on the planet. People use it for there chicken coops as a covering on the floor.
Small handful in the pot and light it up, very little smoke while it burns.
Stir it into the mix and leave it on top for a O2 blocker.

[geargnasher]

The only negative to getting sawdust at big box stores is that it most likely includes the toxins from treated wood. That stuff shouldn't even be burned in a fireplace.
Most everybody can find a construction site that will allow you to collect their sawdust. You can see from the cutoffs what is in the sawdust. Most cabinet shops will have mostly particle board dust, and that too is bad stuff.
A saw mill, or lumber yard, will have the best, but should be well dried, before using as flux.

And Yes, a live moth can flutter on the surface, and introduce it's moisture beneath the melt to cause the tinsel fairy to visit. It won't happen every time, but ONCE IS ENOUGH.

Even a rain drop CAN do it, just not every time. It doesn't have to be immersed to the bottom, just under the surface. Have you ever felt a raindrop sting as it hit you??? It does fall with enough force to break the surface tension, and that's all it takes. Yes I know all about how a water drop on the surface just sings, and sputters, but that's just ON the surface.
When it happens you won't have time to tell it, that it's impossible, and run at the same time. Are you so sure, that you want to tell a nooby not to worry about it.


OK. I didn't say it was impossible, I said IT WAS BEYOND MY ABILITY TO COMPREHEND HOW IT COULD HAPPEN. I quench molten ingots in the moulds with a pistol-grip garden sprayer. Makes HUGE clouds of steam and hot water spatter. Haven't blown an ingot up yet. If you're smelting in a driving sleetstorm, you have bigger "ones" than me. If your moths are big enough to create a steam explosion big enough to be concerned about, then they are a helluva lot bigger than the ones we have around here, sounds like you need to take precautions, but anything "just" under the surface IME isn't anything to freak out about. Take the safety measures you deem necessary.

Gear

[MikeS]

The last time I was smelting it started to rain. at first it was just a drizzle, so I kept filling ingot moulds. then just as I got the last one filled the sky opened up! The turkey fryer is out in the open, not under cover, so I quickly turn off the propane, and retreat about 20' away, right by the door, and under an overhang, so I'm out of the rain. Let me tell you, the pot was steaming up a storm, and the ingot moulds were making all sorts of hissing noises! 20 minutes later, after the sun had come back out, and everything was dried off (you couldn't even tell it had rained) the only place there was any rain left was IN the pot on the turkey fryer, there was at least an inch of rain, maybe more in the pot, and the lead underneath it had a pock marked surface from rain drops hitting it, but there was no tinsel fairy visit, just lots of hissing! I poured off the water, and put away the fryer, and will finish smelting another time.

[Boolseye]

OK. I didn't say it was impossible, I said IT WAS BEYOND MY ABILITY TO COMPREHEND HOW IT COULD HAPPEN.
lmao.

[Bloodman14]

Question; if sawdust/shavings absorb all the impurities from an alloy, could we not use battery plates for the lead if one were to flux enough?

[oneokie]

Question; if sawdust/shavings absorb all the impurities from an alloy, could we not use battery plates for the lead if one were to flux enough?

NO! There are too many nasties in battery plates. And the chemicals used to render the plates are just as bad.

[milprileb]

Battery Plates? Glad some one asked that. Never thought of using that stuff although have been offered old batteries and chose not to mess with them. Now I am glad to know this was a real good move on my part to avoid them .

[truckmsl]

Tried some of Pat Marlin's flakes that came with the Checkmaker, and was impressed by how slow they burned and how little smoke was generated. I hate the idea of spending money on flux, but they are the best flux I've used in terms of the stated qualities.

[milprileb]

I guess one could test a lot of stuff for flux that smokes less than saw dust. I will admit that large size corn cob media sold for pet cages (worthless for cleaning brass .. sad to say) is a decent flux and does not smoke like saw dust.

Saw dust is pretty much a common item one can find for free so its got that going for it although it does smoke !~

[H.Callahan]

I've always wondered if thoroughly dried grass clippings from the yard would be as effective (and cheaper, since one would not have to use gas to go pick it up) as sawdust. Both are fibery plants...

[Boolseye]

Shoot, sawdust only smokes for a couple minutes...casting area should be well ventilated anyway.

[geargnasher]

I've always wondered if thoroughly dried grass clippings from the yard would be as effective (and cheaper, since one would not have to use gas to go pick it up) as sawdust. Both are fibery plants...

It would work, I'm sure, but it would smell like, well, burning grass. Which kinda smells like some other kinds of grass burning, do you have nosey neighbors? :kidding:

Gear

[milprileb]

Shoot, sawdust only smokes for a couple minutes...casting area should be well ventilated anyway.

Yes Indeed that is so and let not my comments about smoke detract about saw dust doing a bang up job as a flux. Of course, next time, I will put up a wind sock so I can stand up wind !!!

It sure does work fine and I have no regrets using it from now on. Not sure I am going to chase what kind of saw dust it is and etc etc. Just stand up wind and go for it.

[truckmsl]

It would work, I'm sure, but it would smell like, well, burning grass. Which kinda smells like some other kinds of grass burning, do you have nosey neighbors? :kidding:

Gear

Yikes! Occasionally I have worried about neighbors mistaking the funky smell of outdoor smelting for a meth lab, now I gotta worry about being accused of being a pot head? This boolit casting is going to get me in trouble!