First Crack at sawdust fluxing - picture

[RogerDat]

I tried using sawdust to flux a melt about 20# of alloy that was about 9 bhn so known to not be plain lead. I started with some sawdust dusted over the lead before applying heat. Then stirred in with a wood stick things became liquid, and added a light covering once metal was entirely molten, stirred that in after it stopped smoking and appeared fairly burnt. Could not get smoke to ignite.

Melt temp was between 590 - 610 for the most part staying right at 600. A little cooler than I was shooting for but it was really cold in the garage this evening (in the teens) and the hot plate was turned as high as it would go.

The sludge that formed on top was dull, and despite pushing and stirring down with the flat stick the thin layer of sludge was persistent. When I decided to skim it off I felt from the weight I was clearly taking metal out of the pot.

Some questions:
1). Was that the "good stuff" coming to the top that I was skimming off?
2). Was air temp being cold causing the lead to coat and solidify on the sawdust on the surface?
3). Did I generally describe the right process for using sawdust.

Picture of the sludge.


BTW = The resulting ingots pencil tested to the same hardness as it did before melting. This makes me think that whatever I removed it did not impact the hardness.

[Stephen Cohen]

That melt looks a little too cold to me, I had some 30 pounds of range lead I was sweetening with about 4 pounds of Lino last weekend, I ran it at around 700 deg and used a good handful of Pine shavings and stirred with a pine stick. I must say I will never use wax again as I found the pine shavings to be so much better.

[dikman]

If the melting point of lead is 621.5*F, seems to me you're running way too cold?

[Moonman]

You're TOO COLD.

[Pb Burner]

I agree with the above replies. You need a hotter heat source and/or a warmer day. Other than that, you method with the saw dust sounds ok to me. I don't add the saw dust until the lead is at least mostly molten, but I don't think it would be detrimental to the alloy.

[Jailer]

Are you fluxing for casting or are you melting your metal for ingots? I wouldn't add sawdust to a casting pot, you're going end up with inclusions and other trash in your nice shiney booits. Save the sawdust fluxing for smelting.

For casting I stir the pot real good with a paint stir stick or wood shim using a slight lifting motion. This brings the crud to the top as the stick burns. When it's been stirred real good I add a small bead of wax about the size of a peanut to the mix and stir it in with a stainless steel spoon. The crud will accumulate in the wax and on the spoon and make it easy to remove leaving you with a nice clean pot to cast with.

[RogerDat]

Are you fluxing for casting or are you melting your metal for ingots? I wouldn't add sawdust to a casting pot, you're going end up with inclusions and other trash in your nice shiney booits. Save the sawdust fluxing for smelting.

For casting I stir the pot real good with a paint stir stick or wood shim using a slight lifting motion. This brings the crud to the top as the stick burns. When it's been stirred real good I add a small bead of wax about the size of a peanut to the mix and stir it in with a stainless steel spoon. The crud will accumulate in the wax and on the spoon and make it easy to remove leaving you with a nice clean pot to cast with.

Fluxing to make ingots, not casting. I read a post on using a small amount of wax after sawdust and since I already had the bees wax sitting there... forgot to mention that step. Lifting motion is about opposite of what I was trying to do. Held paint stick somewhat horizontal and was trying to stir the crud under thinking I needed to drive the "good stuff" back into the melt.

Thanks all for the feedback, I think it is unanimous pot too cold. I did not trash what I skimmed off due to concerns about what I was pulling out, so once it gets warmer or I get a more capable heat source I'll toss the skimmed material in the next batch.

[Wayne Smith]

Not only pot too cold, every time you stir or add something you add O2 to the mix. This allows the tin to oxidize and that is what is most of the skim. If your melt is hot enough adding wax allows this to return to the mix. I cast with a ladle and open pot so I see this all the time.

[Messy bear]

I too think too cold.
I really like sawdust as flux. Thanks for that tip castboolits!

[cbrick]

Are you fluxing for casting or are you melting your metal for ingots? I wouldn't add sawdust to a casting pot, you're going end up with inclusions and other trash in your nice shiney booits. Save the sawdust fluxing for smelting.

For casting I stir the pot real good with a paint stir stick or wood shim using a slight lifting motion. This brings the crud to the top as the stick burns. When it's been stirred real good I add a small bead of wax about the size of a peanut to the mix and stir it in with a stainless steel spoon. The crud will accumulate in the wax and on the spoon and make it easy to remove leaving you with a nice clean pot to cast with.

I use sawdust in my casting pot every single time I cast, not once has it given me inclusions or other trash in my nice shiny boolits. Never, not once.

What can get crud under the surface of the melt is using a wood stick to stir. You cannot get sawdust under the surface when properly fluxing with sawdust placed on the surface of the melt.

Wax is a reducer and will reduce tin, antimony that has oxidized on the surface of the melt but flux (remove impurities) it will not, cannot. It is not a flux.

Rick

[fastfire]

cbrick, when using sawdust on your casting pot, when the pot gets low do you remove the ash before adding MORE PB?

I use sawdust in my casting pot every single time I cast, not once has it given me inclusions or other trash in my nice shiny boolits. Never, not once.

What can get crud under the surface of the melt is using a wood stick to stir. You cannot get sawdust under the surface when properly fluxing with sawdust placed on the surface of the melt.

Wax is a reducer and will reduce tin, antimony that has oxidized on the surface of the melt but flux (remove impurities) it will not, cannot. It is not a flux.

Rick

[bangerjim]

You are TOOOOOOOOOOOOOOOOOO cold. Get it up to around 700F. Generally hotplates are not "strong" enough to do a good job melting lead. Most have safety controls to prevent overheating and will never get hot enough for what you are trying to do! I know....there are a few rare individuals out there that have 2,000 watt plates, but most are 500-800W and will NOT melt lead, at least at the quantity and quality we all want.

They are perfect for pre-heating a mold. Keep it for that and spend some money on a propane turkey fryer. Best there is. Some use old coleman stoves, but I just don't go there.

Use sawdust AND beeswax. The wax acts as an excellent reducer for the tin. I use ONLY wax in my casting pot, and both dust + wax to smelt. Some use candles, but paraffin just does not work as well, smokes too much, flames up too easily, and stinks too bad. Beeswax smells good and has a higher combustion point.

banger

[lwknight]

Definitely cold. The slush on top is slush phase lead. Your heat is at the bottom and the pot and not nearly enough of it..

[cbrick]

cbrick, when using sawdust on your casting pot, when the pot gets low do you remove the ash before adding MORE PB?

Yes when bottom pouring plus I add nothing to the pot while casting, not sprues, rejects, nothing. I use a 40 pound pot though and it's not to often I run low, that's a lot of casting. When ladle casting of course I remove it before starting.

Rick