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After having read a lot about fluxing and skimming, I've started to wonder about one thing:
What exactly happens to the alloy when you flux it? I find it darn fascinating that by adding saw dust, lube, candles, oil or WHATEVER the impurities come together and float to the top! But why does this happen, what can be said scientifically about it?
Now please indulge me, I'm a curious fella [smilie=6:
I can't give you the "scientific" version but I've read an explanation written by a metallurgist/chemist on another site. My "layman's" interpretation is this.
In common boolet alloys, you have metals that alloy and others that only mix or blend. Try to grasp the difference, it's got to do with the bonding of electrons or not.
You'll not that all of the successful additives have one thing in common. They reduce to a form of Carbon. Carbon is the catalyst, I think that's the word, which facilitates the actual bonding in an alloy. The others just blend in the stirring.
The alloys, for all PRACTICAL purposes is permanent. Sometimes, if a fellow knows what he's doing, has enough time, a modest laboratory and a good reason, he can encourage a separation of some of the mixes,( Not alloys) but it's tough. IE. not practical.
I always tell newbies that separating zinc from a lead mix is akin to removing too much water from your Jack Black.
Hope this helps.
Whoops; Forgot where I was, IIRC the original author of the tech. explanation came from Felix.
While it may seem more like Alchemy than Science, from what I understand it is that fluxing keeps the alloy from separating. Keeps the tin in the mix. There are others that say that at the temperatures we cast at, the alloy won't separate anyway.
Real or not, I do it. Twice. It gets all the junk out of my wheel weight alloy. I melt them and separate the clips/debris and make ingots. When I add the ingots to my pot I reflux. It's amazing how much crud you still take out after the second fluxing.
When I was working in Foundries and Steel Mills, flux was added to the slag to fluidize it. The slags were otherwise very thick, and therefore less reactive, as well as they did not flow out of the furnace well.
When people talk about flux around here, many seem to be talking about something that separates the trash and slag from the Lead alloy.
Others seem to be talking about something that keeps Tin from separating from the Lead. I don't see any scientific basis for this belief, because the Lead-Tin phase diagram says that the two will not separate. Tin will oxidize out more vigorously than Lead, and one will likely see Tin Oxide on the surface of a pot, but no flux I am aware of will both reduce the Tin Oxide and get it back into solution.
Lead pots were used around the Met Lab for lots of purposes, and my Professors typically had something on top of the Lead to slow down oxidation of the Lead, frequently just granular charcoal or graphite.
CDD
Interesting question. In layman's terms as I understand it the flux acts kind of like a soap in water. It lets the garbage separate itself from the lead/tin alloy. It's also supposed to help the lead/tin adhere to each other as they "like" to stick together, kind of like soap breaks the surface tension of water on oily plates..
That's a really poor explanation of how I understand it works
I've found Glen Fryxell's articles to be informative, here is his take on fluxing:
http://www.lasc.us/FryxellFluxing.htm
Thanks, that surely answered my question!
So the way I understand it the main ideea, besides gathering the crud, is to get the tin to re-mix with the alloy after it has oxidized?
The carbon based flux burns the oxygen out of the oxidized metal, there by reducing it back to the base metal.
A layer of anything (charcoal, kitty litter) on the surface of the casting pot reduces the surface area exposed to the atmosphere, thus slowing down the oxidization of the alloy.
The flux doesn't help the tin remix because it didn't separate.
In addition, many believe the flux "brings up" the dirt from beneath the surface.
This really doesn't happen. The flux floats, and it can't work on what it can't reach.
Stir vigorously first, scraping the side of the pot to release dirt and crud trapped by tension and adhesion. The crud then floats to the top, where the flux can act on it.
Thanks for that, I got a lot out of itQuote:
Originally Posted by dromia
Doesn't Pb, Sb and Sn form a solution? I think Glen should have his dross chemically analysed. BTW, there's enough Sn in clip-on WW metal to cast very nice bullets if you're willing to run your pot a bit over 750F. In fact, I cut my WW metal with half soft lead and my bullets come out very nice while casting at 800+F. The only reason I'll add 5% - 10% range scrap to my alloy is to increase the Sb slightly so BHN 30 can be reached after HT'ing at 500-520F. Lately, I actually have little use for Sn because all it does for me is lower the melt temp of my bullets.
Back on topic though: don't we need fire for a good flux? I've always used something that burns on the melt's surface. I tried floating carbon on top of the metal but since I only ladle cast, that didn't work out too well.
MJ
Well, Marvelux doesn't burn.
Some don't like it because it builds up on pot surfaces and holds moisture from the air, which is asking for the tinsel fairy if crusted on cold stirring implements, but I'm pretty darn sure it doesn't burn.
I burn the other stuff because it's an easy way to get rid of the flux after it's served its purpose.
BTW, still haven't organized the stainless .350 Ruger M77 Mark II cast groups fully yet. Also haven't determined if it's 1-12 or 1-14. I did the rifling twist thing using a cleaning rod and got 1-13 - go figure! I'll have to try that again.
35R,
It's a 12" twist. You wanna start a new thread discussing Ruger .35's?
MJ
Marlin Junky -- To answer your question, "Doesn't Pb, Sb and Sn form a solution?", the answer is yes and no. The solubility of Sn in lead is pretty high, and at the concentrations that we're talking about for bullet alloys, yes it does form a true solid solution in a lead matrix. Tin is very well-behaved.
Then there is antimony. The solubility of antimony in lead is actually fairly low, and VERY temperature dependant (this is why lead-antimony alloys age harden, the antimony slowly comes out of "solution" and forms dendrites that harden the alloy). Moderate amounts of antimony are soluble in lead at the melt temps, but very little (less than 1%) at room temp.
Yes, you're right, one can cast good bullets with straight WW alloy if one cranks up the pot temp somewhat. Bullets may turn out somewhat frosty using this strategy, but in and of itself that's not a problem. What you have to look out for is this approach can lead to more bullet shrinkage shrinkage (Dan Lynch at Mountain Molds has studied this in detail), and IF you're dealing with a mould that's at the lower end of tolerances, then you've just made bullets that are too small to shoot well.
No fire is needed for flux. Some folks light the smoke coming off of certain fluxes (like beeswax) to keep the emissions more manageable. That flame doesn't do anything to improve the bullet metal, that is just to keep the hot wax vapors under control.
I would think that the flame would temporarily remove O2 from the melt's surface thus promoting better reduction.Quote:
Originally Posted by Glen
MJ
I was going to stay out of this thread since the point has been made pretty well. But the salt quote got my attention. It's a good example for anyone who might not grasp how the metals bond.Quote:
Originally Posted by Marlin Junky
Salt is such a stable compound that even after it's dissolved or digested it is still salt. Lead and tin will combine almost as well but can seperate if they're held at too high a temperature or for too long. In the meantime, if they find oxygen they will bond with it. The reason fluxing works is because the flux is more attractive, stealing the oxygen and other contaminates, freeing the metals to bond with each other.
Administrators, please make Glens' response or this entire thread a "sticky". Way too much great info to loose. Gianni
I think it's hard for bullet casters to explain 'fluxing' in a scientifc way because we use a single term for two different jobs.
When you melt down a bucketful of lead-rich junk you 'flux the smelt'.
Then, when you are managing the crud on your casting alloy you 'flux the melt'.
The first is (probably) close to true fluxing. You will reduce (de-oxidize) the oxides of beneficial metals because they do that easily, and you will leave the calcuim (and others Fryxell mentions) to be skimmed off and discarded.
(It really makes no sense to save this stuff.)
But what we are trying to accomplish, when managing crud on the casting metal, is to hang onto valuable metal that has oxidized out of the alloy. The process is called 'reduction', but we still call it 'fluxing'.
Since it IS a different process, it has a different name...and is also DONE differently.
In 'fluxing the smelt' you WANT a layer of crappola to form so you can skim it off.
In 'reduction', you don't want to get rid of ANYTHING because all the bad stuff went away during the 'smelting' phase. Everything in there now is 'valuable stuff'.
If your 'reduction program' leaves you with skimmed metal saved in a coffee can, it is not an effective method.
Proper use of a wooden stick will 'manage your crud' and leave you with only dust to be removed.
CM
When smelting linotype shavings and dust there's a lot of crud that comes along with the whole mess. Will the stuff that burns off act as a flux? When cleaning up this linotype "trash" is there a wrong way to do it, like getting the pot too hot?
Quote:
Originally Posted by montana_charlie
Nicely done Charlie, that makes sense. Guess I'll "stick" with my stick for fluxing. I've always stirred the heck outta the melt when it comes up to temp. I still get crud every time I start a pot full. Since going to a stainless pot I get a lot less crud, but now I'm wondering how much good metal I've tossed out.
This thread is such a good starting point, I thought I'd link to an even better one, sort of "Why flux?" "How flux?" "What flux?" http://castboolits.gunloads.com/show...xing-technique