Flux? Why?

[PTS]

Hello all; new to casting but not black powder, it’s time to make my own. I hear about flux being used in the casting process. I understand soldering and flux; why do I need flux in the casting process? Or do I need it in the mold? Or...? Tks in advance.

[littlejack]

PTS:
Welcome to the CastBoolits.
Fluxing keeps your lead, tin, and antimony mixed properly. It also allows the dirt, and other foreign debris from the mix to float to the top, so it can be skimmed off.
Reguards
Jack

[PTS]

Tks, Jack: so I put flux into the pot at the beginning of the melt or at a later point? At first I will be casting pure lead in REAL bullet moulds-will pure lead need flux? I’m assuming I can use the old flux I have in the basement? Any particular ratio? I don’t have a pot yet but will use a small pot on propane burner until I get an electric. Small scale casting.

[NSP64]

PTS, flux is used periodically during casting, you can use candle wax, bullet lube, sawdust(my fave). It will keep alloys mixed. Puse lead oxidizes, and the oxidation gets mixed in. It can cause voids and weight variences.
No you dont have to flux. Just like you dont have to clean your brass, or gun.
Your choice.

[geargnasher]

Alloys stay mixed all by themselves, that's why they're called alloys. What FLUX does is remove certain impurities that impede the flow (flux) of the metal and make casting perfect boolits somewhat difficult.

Wax is NOT a flux. It is a sacrificial reducant that reverts the oxide scum that forms on top of the molten metal back into its elemental state. Tin tends to oxidize faster than the other metals in the melt and therefore is depleted over time if you skim and discard the oxide scum rather than reduce it chemically with wax or similar.

Pine sawdust is both a flux and a reducant. It should be used when rendering scrap into ingots, and only cleaned and fluxed ingots should be added to the casting pot for best results. Wax can take care of maintaining oxides when casting, or you can use sawdust to do both jobs.

Gear

[hermans]

Gear, that is well explained....even I do understand fluxing and the need for it much better now! That is why I keep on reading these threads, you are never too old to learn!

[geargnasher]

Here are a couple of current threads that go more in-depth:

http://castboolits.gunloads.com/showthread.php?191467-Fluxing

http://castboolits.gunloads.com/showthread.php?184987-Fluxing-with-sawdust-tell-me-how

Gear

[Matt_G]

In addition to the links Gear posted you should read Glen Fryxell's book, From Ingot to Target.
Specifically, chapter 4 deals with fluxing.
From Ingot to Target (http://www.lasc.us/Fryxell_Book_Contents.htm)

[472x1B/A]

geargnasher, thank you very much for that information.

[littlejack]

I stand corrected Gear. You are correct. Very informative information.
I did go back and read Glen Fryxells write up. You stated it almost word for word. Anyway, thanks for information.
Jack

[mcnee229]

PTS, Flux for solder and brazing is used for a different purpose than flux for casting. In soldering, we are trying to kill the oxide layer on the wire/solder pad/pipe and allow a direct copper to solder bond. In casting you are looking to keep the lead and the alloy metals from reacting with atmospheric oxygen and coming out of solution. Read the book by Fryxell on casting, it'll explain a lot of things. The flux and reductants used in casting aren't the same as the fly we use for soldering.

Scott

[geargnasher]

I stand corrected Gear. You are correct. Very informative information.
I did go back and read Glen Fryxells write up. You stated it almost word for word. Anyway, thanks for information.
Jack

I think it's time that I went back and read it again, been a couple or three years since I read the fluxing articles (before the "book") and now can't recall just exactly what he said takes place between the carbohydrates and "contaminate" metals to pull the metals out of the alloy.

Gear

[uscra112]

In both cases the function of flux is to extract oxygen from metal oxides and carry it away. This is called "reducing". In soldering it's to "reduce" the oxide film on the metal to be soldered, in cleaning our melts it's to "reduce" the oxides in the dross, allowing pure metals (mostly the tin) to return to the melt. Many things can be used to "reduce" oxides. Generally speaking anything that will burn will do it. I once worked in a shop which heat treated and brazed stuff in a pure hydrogen atmosphere, not only allowing no oxide formation at all, but actually extracting any oxygen already on the metal surfaces. When allowed to cool before opening, the parts would come out looking like they'd just been beadblasted or pickled. I'm not enough of a chemist to be sure, but I suspect that hydrogen is always the prime actor in this reaction, so anything that can break down under heat and release hydrogen to the reaction zone will act as a flux.

Do not flux your moulds !

[JWFilips]

Do not flux your moulds !

What? I don't plan on smelting my moulds?:!:

[sergeant69]

how about mesquite as a fluxing agent? when I cut and run mesquite slabs through the planer I get lots of sawdust and use that for my flux.

[cbrick]

how about mesquite as a fluxing agent? when I cut and run mesquite slabs through the planer I get lots of sawdust and use that for my flux.

Should work just fine. As the wood chars it turns to carbon which is what you want, mesquite will do that and probably smell great too.

Rick

[theperfessor]

I have a couple of kitty litter buckets full of Brazilian Cherry shavings/chips that work fine as flux. Woodchips are all I use anymore. If I run out I'll go over to the Art lab woodshop and get more. I also stir and scrape with a BC stick.

Gear is pretty well right on about anything he puts out, worth paying attention to if you want to learn something.

Not disagreeing with uscra112, but wouldn't a hydrogen rich atmosphere be combustible/explosive? I know helium, nitrogen and carbon dioxide are often used in a heat treat furnace to exclude oxygen, but hydrogen? Wasn't that what caught fire on the Hindenburg (sp?). I'm really curious now, anybody care to explain?

[mcnee229]

Purge furnace with nitrogen, start filling with hydrogen from the middle, tap ends of furnace and route to burner to burn off excess hydrogen and provide visual confirmation that its still flowing. More nitrogen at the entrance and exit of furnace for good measure. Makes a heck of a noise when the operator "forgets" to purge or overrides the purge because they are in a hurry.

Scott

[cbrick]

Hydrogen? Really?

Hydrogen gas (dihydrogen or molecular hydrogen) is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume.

Hydrogen gas forms explosive mixtures with air if it is 4–74% concentrated and with chlorine if it is 5–95% concentrated. The mixtures spontaneously explode by spark, heat or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F). Pure hydrogen-oxygen flames emit ultraviolet light and are nearly invisible to the naked eye, as illustrated by the faint plume of the Space Shuttle Main Engine compared to the highly visible plume of a Space Shuttle Solid Rocket Booster. The detection of a burning hydrogen leak may require a flame detector; such leaks can be very dangerous. The destruction of the Hindenburg airship was an infamous example of hydrogen combustion; the cause is debated, but the visible flames were the result of a rich mixture of hydrogen to oxygen which produces a visible flame.

H2 reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially dangerous acids.

Rick

[mcnee229]

Hydrogen doesn't burn unless its got something to oxidize it. Keep oxygen out of the mix and its good to go. Unless of course you heat it up and put it under so much pressure that it fuses into helium, but now you've created a star...

Look up hydrogen annealing if you don't believe me.

Scott

[felix]

A star? More likely a hydrogen bomb. ... felix

[Matt_G]

A star? More likely a hydrogen bomb. ... felix

They are one and the same for all practical purposes...for a few nano seconds anyways.