Everyone seems to think you have to flux your pot of lead.

WHY?

What does it really do?

Like welding, brazing, and soldering, the purpose of flux is to coat
the molten surface and protect it from rapidly reacting with
atmospheric oxygen. Some fluxes, such as acid or caustic flux,
will help clean the base metal so solder/braze will flow and adhere
(wet) better, while at the same time protect the molten metal.

So why flux a pot of lead at all?

The only thing I can think of is when you are trying to add pure
antimony. Antimony will form an oxide layer that will prevent it
from dissolving into the lead. I say dissolve rather than melt,
because the hottest most people ever get their lead is roughly half
the melting point temperature of antimony. The antimony
dissolves into the molten lead like sugar dissolves into water. If
there is a layer of oxides on the antimony, it won't dissolve.
The metallic antimony has to be in contact with metallic lead.

Flux is added to the pot primarily to prevent the antimony from
oxidizing in the first place. However it will also tend to reduce the
antimony oxide back into antimony metal, and lead oxide back to
lead metal. The clean metals in contact with each other will allow
the antimony to dissolve into the lead.

Why flux wheel weight lead when all you are doing is melting the
scrap weights down and casting ingots? Good question. There is
absolutely no reason to. Melt the weights, skim off the steel clips
and other debris, and cast into ingots. Easy as pie. The beneficial
alloying elements are in solution. Only the molten metal in contact
with the air will oxidize. Once the molten metal forms an oxide
skin, it is rather protected from further oxidization. Sure, you can
add flux to this to help reduce the oxides back into the metal, but
why? This oxide layer is a mixture of oxides from all of the metals
present. And when you have several pounds of molten lead, is it
really worth the time and energy and mess to flux when you only
have a few grams of metal oxides forming on the surface?

I've had an analysis done of a pot of molten lead alloy, as a fresh
melt and after an hour of sitting molten exposed to the air without
flux. No difference.

These people who say to add flux and "stir it into the pot"
obviously don't have a clue. You can't stir flux into the molten
metal. Period. The flux doesn't dissolve into the metal. The flux
stays on top and prevents oxides from forming. If you are
soldering or welding, that is critical to achieve a good bond
between two metals. But for casting, it is completely unnecessary.
The flux doesn't get into the mold. (hope not anyway)

Dirt doesn't get suspended in the melt. Lead is far too dense, and
any dirt that is free to move will float to the top. If you are
scraping it up from the bottom of the pot, the flux isn't going to
help bring it up. It is physically sticking to the bottom until you
scrape it off.

So unless someone knows something I don't, it is a waste
for anything other than adding alloying elements.

Dave

Only flux when mixing alloys to make bullet metal.

To get the crud out:

http://www.sixguns.com/crew/simplefluxing.htm

Can't add much more to that. I think that 'flux' is a term that means different things for different processes, hence some of the confusion....

__________________
MikeG

I'll have to agree with Mike G on that.

Good post....makes me think...and I've concluded that I only THINK I knew what fluxing does.

Thought (and I could well be wrong) that some of the Tin, Antimony, and Arsenic found in most "hard" alloys (from scrap lead) tended to from oxides on the surface..this surface layer is a mix of metal and of oxides. Fluxing (I thought) helped return these metals to the melt.


Lyman (Cast Bullet Handbook 3rd) has the following:

"With the realization that fluxing has nothing to do with keeping bullet alloys mixed, it is fair to ask - why do we flux?

For bullet casting, the principle function of the flux is to clean the metal of dross or dirt.....recent microscopic examinations of cast bullets by this author show that dross inclusion can cause localized recrystalization and softening...

(Evidently not only do the little incuslions "speckle" a bullet, the area around the "specal" is softer than the rest of the bullet.)

...dross exists as a mecahnical mixture of metal and metal oxides; the metal content ranges upm to 90% by weight. It is clear that fluxing seperates the dross from the metal, allowing the metal fraction to return to the melt and facilitate the removal of the oxides.

(here's a part you will like)

However, the mechanisim by which this seperationm occurs is not understood, none the less, fluxing provides a valuable function."
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Now if just melting down big ingots from some massive melt, and the ingots are to be later melted down for actaul casting of bullets, think you can forget the fluxing. Would still flux when getting ready to cast, but don't know that it's needed when making ingots from big piles of scrap lead.

Do belive that in skiming off the big chunks you're proably losing metal along with the dross if you don't flux...and that the metal being lost is problaby more Antimony that it is Tin or lead.
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Long as we're talking belief rather than fact, belive that Tin's main function in an alloy is to supply thinner oxide layer....think of it as reducing surface tension.


Also believe that lead alloy is a solution, not a mixture. Solutions don't seperate by gravity (or any other easy process)...sugar and water isn't going to "unmix".

But as temperature goes up, the ability of lead to hold MORE of these metals in solution also goes up. Can do that with sugar and water..heat the water, and it will hold more sugar..cool the water, and the sugar cryustals drop out.

What lead can hold in solution at 850F should be more than the amount it can hold at 730F. So to be safe, will crank the pot up to TOO HIGH a temperature at first, let it stabalize, then flux it. Then I will crank it down to casting tempeatue, let it stablize, and flux it again. Any metal floating on top at casting tempreature isn't going to be doing me any good, so I disguard it.

I think the article in your link says exactly the same thing I did.

Except I pointed out that the amount of metal oxides that
form are completely inconsequential.

Dave

Is the author suggesting that the dross inclusions are caused
by particles suspended in the molten pot of lead?

If so, how will flux change that when it floats?

If the author is referring to dross that got scooped up in
his ladle and poured into the mold, that is more a problem
with his casting process than a need for flux.

Dave

Author was Dennis Marshal (and the manual dates from 1980).

"Simply throwning a peas-sized lump of paraffin or beaswax on the surface, stirring for a moment and then skimming does little to lower the dross content of a melt and may even make matters worse, esp. at high temperatures. The reason for this is that the cleaning action of the flux only takes place on the surface of the melt, while the dross itself is distributed both on and below the surface. Sience the flux is not soluable in the melt, it cannot reach the dross which is below the surface so the dross must be brought to the flux by generaous stirring."

He goes on to describe three types of dross. (1) the layer that forms on the top of the pot. this is the one that is both mteal and metal oxides...flux helps return the metal to the mix and leave the oxides.

(2) Dross that clings to the sides of the pot. Here he mentions that melt pressure can pin residue agaisnt the sides of the pot, but can be carried along by the current of bottom pour pots to end up in the casting pour.

havign drained a few pots, can promise you that there is a nice crusty layer sticking to the sides...can easily belive that some of thise crud could shed and be carried either up to the top of the melt, or along with the currents and into the mold.

(3) Dross that is suspended in the melt.

"It is know that very small oxide particles, in the order of .00004",in diameter, can be trapped indefinately below the melt's surface becasue they lack the bouyancy to overcome thermal currents."

So...from inferance, it seems that NOTHING is going to get the particles that are really small out of a melt...vigorus stirring and scraping can help get the worst of the dross off the sides of the pot and up to the top where flux can act on it, and that fluxing does it's job on the surface. Stirring only helps bring more of the crud to the surface, it doesn't mix the flux into the melt.
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Haven't chaced down all his footnotss, but some that may be interresting would be as follows:

L.S. Darken and R.W. Gurry, "Physical Chemistry of Metals", McGraw-Hill, 1953

A.J. Hammer, "Dross and Fluxes", Precison Shooting, Nov. 1964

Wilhelm Hofman, "Lead and Lead Alloys" (English translation), Ed., by Dr. Gerwig Vibranms, Springer-Verlag, N.Y. 1970

Tin starts to oxidize out of the melt at around 700F. How much, and how fast, are things I can't answer. So I suppose part of the answer might depend on the temperature of the melt.

Might drop Glen a line, he seems to always be willing to help out with more detail, as desired. Has a PhD in chemistry, so you'll get all of the information you need, and then some

__________________
MikeG

[QUOTE=ribbonstone]Author was Dennis Marshal (and the manual dates from 1980).

"Simply throwning a peas-sized lump of paraffin or beaswax on the surface, stirring for a moment and then skimming does little to lower the dross content of a melt and may even make matters worse, esp. at high temperatures. The reason for this is that the cleaning action of the flux only takes place on the surface of the melt, while the dross itself is distributed both on and below the surface. Sience the flux is not soluable in the melt, it cannot reach the dross which is below the surface so the dross must be brought to the flux by generaous stirring."


30 years ago when I was poorer than I am now,I did a lot of casting for my handguns.Since I scrounged all my lead,i figured I could load .357's and .44's for 2 cents a cartridge,assuming I had the cases - even using gas checks.
The "experts" (Phil Sharpe,Lyman,etc.) at that time stressed that the flux should be "plunged deep into the pot and stirred vigorously".
I used pure beeswax - bought from a beekeeper in large quantities - and put a chunk about the size of a small marble into my old-style Lyman dipper.This dipper will retain the beeswax and let you "plunge" it to the bottom.Then,if you rotate the dipper handle,the beeswax will be released from the dipper.
Then you had to skim the dross from the surface.
Since I used a cast iron pot and dipper,keeping the surface of the mix clean appeared to contribute to better bullets with sharp,square lands.

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In all of the laboratory methods I've seen for effectively
scrubbing a liquid for one reason or another, a fine
dispursement of bubbles was necessary, as well as enough
time to get the job done. More like how an aquarium
bubble-stone works, compared to undiffused air.

If a person considers how much gas a piece of wax
produces as it vaporizes, and the surface area of the
bubbles it generates, and the amount of lead that never
comes into contact with the surface of one of these
bubbles, I personally question the effectiveness.

IF, on the other hand, there was a way to finely dispurse
the bubbles, it would certainly have a better chance of
working efficently. The problem is that I don't think it is
possible to generate a large stream of fine bubbles in lead.


I certainly won't argue with that. If a person's method
of casting allows for surface contaminants to get into
the mold, it is very important for the surface of the melt
to be clean. But, you still have to skim the flux before
casting. SO, do you flux, skim, then cast. And then flux,
skim and cast? You can't cast too many times until the
melt has formed an undesireable oxide skin.

Dave

I may have read this somewhere, so it probably isn't news
to anyone here. But back when I was in grade school my
dad was casting SCUBA weights for a local dive shop.

When making ingots from wheel weights, he showed me how
the metal oxide dross on top of the freshly poured ingot
could be made to "disappear" if he waved his rosebud
acetylene torch flame across it. This left showroom quality
ingots.

When I'm making wheelweight ingots, I do the same thing
but with a much less expensive propane torch.

You can achieve the same effect in the pot of molten lead,
but it is much harder to keep the fire going, and the little
propane flame can't quite keep up with the rate at which
the oxides form a skin.

Dave

Made a little tin lid for the casting pot...cast out doors. Serves 4 uses:
1. Keeps susicide bugs from aming that final plunge (and the eruption that follows once the bug hits the melt).
2. Keeps heat IN...can turn down the thermostat and maintain casting temp.
3. Keeps splatter down when adding new lead.
4. Makes a nice flat pre-heating area.


I too flux like I've been tought...stirr deeply, scrape the sides, and skim off the flating bits. Not the floating dross...that gets mixed with the flux and only after that is it skimmed off.

Can put a layer of kitty litter on top or sprinkle boric acid crystals on top...that last sems to form of seal and no oxidation occurs until you have to distrub it by adding more lead.

As in thelast post...I only thought I knew what fluxing does...now I'm not too sure. If nothing else, it seems to speed the process of getting the "crud" to rise to the top.

Right.... same effect as the shielding gas on a MIG or TIG welder, displaces the oxygen. Good tip!

__________________
MikeG

Makes sense...in on bullet-applications, if you want to make a complicatged detailed pour (or injection) into a mold, it's flushed with in inert gas before injection...can't "oxidize" without oxygen.

My Father worked in the Printing industry (newspapers ) for 30 years as a stero-typer working with linotype .They used the type from a furnace of 10,000 gals .At the begining of the shift the "pot" was fluxed with a crucival of Potatoes.Which was stired through to clean the mixture of any impurities.I use a half a spud to this day when first smelting into ingots for latter casting.To clean out any foriegn bodies that may be trapped in the mixture.I do not have any faith with the ball of wax/lube theories .As has been mentioned just sit on top of the mix

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I can not remember how many years it has been since I fluxed an alloy. 10+ maybe.

I wanted to see what effect fluxing would have on bullet weights and visual rejection rates so years ago I cast several batches of bullets using a couple very nice single cavity blocks. In each of these studies I saved the bullets in their as cast order and then weighted and visually inspected them. Weights always dropped after a casting interruption and visual rejects increased. Breaking the casting rhythm to flux clearly changed the temperature of the mould and that, I think, is what caused these problems.

If I still had hundreds of pounds of raw wheelweights I would undoubtedly flux them when making ingots but that is the only time I would flux.