Another flux question

[Fly]

I know sawdust,wax, ect, works.But do any of you use charcoal ash?The
reason I ask, is I do alot of BBQ & have so much.If I can use it, how good
does it work?
Fly

[buck1]

I dont think the ash will help you , but the charcoal might.

[geargnasher]

I don't know why, but it seems that unburned wood reduces the oxides better than charcoal (I've only experiemented with dry, leftover charcoal from the fireplace). It's the carbon that is necessary to react with the oxides so charcoal should work faster, but smoldering sawdust just works better IME. Maybe the smoke itself floats over the oxides and the smaller particals react better.

Ashes probably won't do any good, all the goody is gone from them except for soap making.

A dry hardwood stick works well for reducing. Stir until it starts to smoke, scrape, skim and rake the oxides into a pile on one side of the pot, mash and smear them against the pot side with the stick and they will dissolve. Skim the remaining fluffy ash with a spoon.

Gear

[sagacious]

I suspect it's the hydrocarbons in unburned sawdust that are facilitating the reduction. Ordinary carbon can bond/adsorb molecules, but does not have the hydrogen to supply to the reaction.

Consider that hydrocarbons supply reactive hydrogen, and that adding hydrogen to PbO might give you this:
PbO+H2 ---> Pb+H2O
Lead oxide plus hydrogen produces pure lead and water vapor.
The excess hydrogen also likely produces acids that help form a reducing atmosphere.

Using a fluxing agent such as wax is using pure hydrocarbons. The result is positive fluxing, and a black powdery residue-- probably some left-over unreactive carbon. Sawdust has hydrocarbons plus resin/rosin, and rosin is a powerful fluxing agent as it both wets and reduces lead oxide, which helps in dross separation. This is why when you put a good flux, such as sawdust or wax, on the surface of oxidized lead, the oxide will rapidly clump together and expose a mirror-bright melt surface-- sometimes even without stirring.

A few years ago I mixed up some paraffin and rosin for fluxing. The rosin makes the wax rock hard. It is about the most aggressive fluxing agent I have ever seen. For normal scrap lead, most fluxes work fine, but when fluxing lead particulates/dust or heavily oxidized lead, the wax/rosin flux is far superior, because the huge surface area of the lead dust benefits from a flux with superior wetting ability.

[mtgrs737]

Last weekend I bought a really huge, ugly old candle for 50 cents at a garage sale to use in fluxing. That thing must weigh in at least 5 pounds. Gulfwax at Wally world is $2.50 a pound and too expensive for fluxing IMO.

[gray wolf]

So my question would be-- is there a right and wrong time to use rosin for a flux ?
If it does such a good job would it be detrimental to use it as a standard flux ?
Or is it for a special purpose ?

Thank you SAGACIOUS for the in dept explanation.

[John Boy]

For a really good flux, go to the supermarket and buy a box of 20 Mule Team Borax.
http://www.20muleteamlaundry.com/

[lwknight]

Rosin is nasty and hard to keep it out of everything. Its hard to burn off completely.

[sagacious]

So my question would be-- is there a right and wrong time to use rosin for a flux ?
If it does such a good job would it be detrimental to use it as a standard flux ?
Or is it for a special purpose ?

Thank you SAGACIOUS for the in dept explanation.
No "wrong" time to use rosin. Folks buy and enthusiastically use rosin-core solder, because it's convenient and easy to use--- and after all these years it's still one of the most poweful fluxes for lead alloys. Hollow core solder can only hold a tiny bit of flux in the core, and rosin is used because it's very powerful even in tiny quantities.

That's a clue right there. It's a very strong fluxing agent. I save it for those times when scrap lead is resistant to fluxing, such as really corroded lead pipe and the lead dust from range scrap. Otherwise I use paraffin for "normal" fluxing of fairly clean lead. But there is never a time when one would damage the melt by using rosin.

Here's an easy way to use rosin as flux for scrap lead. If you have pine trees handy, collect some dried pitch/rosin. Melt 1/2lb of paraffin and add a walnut-sized chunk of rosin. The rosin usually has volatile compounds in it, so it may fizz slightly while melting. Stir it for a few minutes until it's all melted and dissolved. Then pour the wax onto a pan covered with aluminum foil and let it cool completely. Then break it into small chunks to use for fluxing.

It only takes a very small amount to flux effectively. It's very economical because of it's strength, I mixed up a pound a long while back, and I still have a good amount left. This flux is pure hydrocarbon combined with pure rosin, so it's not hard to see how effective it is. The wax itself provides a strong reducing flux, and reduces the surface tension of the lead-- in the same way a surfactant (soap) reduces the surface tension of water molecules and allows for better cleaning. The rosin is a strong de-oxidizer and breaks-up, wets, and causes rapid clumping of oxides. These combined properties make this flux really go to work on dross.

The wax/rosin flux is not sticky, is easy to handle and use, doesn't get everywhere like powdered rosin, works fast and will flux the dirtiest lead easily. Be sure to light the fluxing smoke so it doesn't flame-up unexpectedly. If you have some really dirty lead, or lead with a lot of oxides, give it a go.

Hope this helps, good luck.

[sagacious]

Laundry borax is not the most user-friendly flux at typical hobbyist lead-pouring temps. It is still partially-hydrated to make it dissolve easier, and when heated the dehydration process generates a mini-snowstorm of tiny white puffy borax flakes. The result is that some of the borax leaves the pot as tiny puff-flakes, which settles over any surrounding equipment.

Borax also has reduced wetting ability, but on the positive side it does clump and hold dross in such a way that it cannot recombine with the melt, and does provide an oxide barrier. On the minus side, borax is hygroscopic, and melt tools with residual borax may pose a steam explosion risk. Be careful if you use borax as flux.

I briefly assisted with a project in Dakar, Senegal to help reduce the lead exposure of workers at small-scale battery "breaking" (recycling) centers. Battery lead is reclaimed at much higher temps than the home lead pourer deals with, and in that application borax is more fluid and reactive and works well as a lead flux. It also makes dealing with the toxic dross easier, as the borax dross is virtified and glassy-- and thus disposal does not pose a dust-borne lead hazard. This properties are great at the industrial level, but not optimal for the hobbyist lead pourer. Good luck.