Today I decided to "use up" my last small crucible before going to the new A6 Salamander Super.
Instead of trying to pour the same pattern again, I decided to just make ingots. And to do that I would use my old broken up radiator material, rather than cleaner thicker iron.
And I decided to use flux, since i didn't care about the crucible. I would do two melts, one with oyster shell, in the form of the ground up powder they feed chickens. it is supposed to be calcium carbonate -- as is limestone or agricultural lime.
And for the second melt, I would go back to good old sodium carbonate (soda ash).
This would at least do something useful with the old crucible and convert the radiator scrap into clean metal, plus give me a comparison with the two fluxes.
Well actually, there was no cmparison. The oyster shell did little to liquify the slag -- it was still really bad -- black cottage cheese taking up half the melt, and sticking tightly to the crucible. In fact after the crucible cooled I could see a few places where it insulated itself in a chunk and hadn't even melted. I don't actually know what that stuff is made of -- could have concrete floor sweepings in it -- who knows. It's just grit for the hens.
But since it didn't all melt, and thinking I might not have enough furnace heat, I decided to increase the air pressure to the burner nozzle. This had been at 45 psi lately, and I upped it to 60 psi.
That really did seem to make a difference -- probably atomized the fuel better, because I noticed that I actually ended up using less throttle, even thought there was more heat and flame height. And the flame burned cleaner -- quite visibly better.
So, second trial with the sodium carbonate went MUCH better -- a faster melt by about 20% but the slag was totally different. I was a bit cautious with the soda ash flux because it's supposed to be much more destructive to crucibles -- I used about an ounce. I'd used 2 ounces of calcium carbonate earlier.
But what a difference -- the slag was easily scooped off in one piece to leave a pool of clean shiny metal in the pot. While I won't say it liquified the slag, it did compact it into a single "chewey" crust that I could scoop off with a spoon. It was also much lighter in weight (less contained iron).
All in all, just what I would have liked in a pour.
So, it looks like the radiator iron can be used, but it definitely needs a flux to slag well. And it probably should be poured into ingots before use to clean it up.
Next pour will be with the new crucible....