Just noodling on something... I put a fair amount of effort into cleaning my sprues and scraps before remelting. This material starts life as commercial Everdur bought from Belmont. Each pour generates roughly eight pounds of cast parts and seven pounds of sprues. I investment cast using Rancast, and getting that stuff off perfectly is something of a chore. So it occurred to me, why bother? My thinking was I didn't want the stuff contaminating any remelts, but wouldn't it just float to the top and get skimmed off? Any of you bronze guys have an opinion on this? How much work do you put into cleaning metal before remelting?
I dont remove the stuff that i cant knock of with a hammer (ceramic shell) which isnt nuch as my sprues pouring cup etc are quite smooth. It does float to the top and is skimmed off. I havent noticed any effect on the bronze. But i just use for art bronze, nothing that is for engineering or needs milling
I've remelted old heavily corroded bronze from marine hardware and apart from the stink of antifouling paint and the odd barnacle it all skims and cleans up fine. Same for aluminium castings like car wheels with paint and dirt although I do skim it multiple times and let sit a bit to aid the rise of contaminants without the furnace combustion flames stirring it up. I've yet to try some unexpanded perlite as a coagulant to aid skimming on either iron, brass or bronze. The recycled bronze machines fine afterwards. Sand cast aluminium does benefit from sand blasting cleaning to remove sand from recycled runners as I've heard the sand can increase the silicon content as well as embed sand in the castings due to the similar density of sand and aluminium. Bronze is so dense any crud floats easily on the surface.
That's encouraging. Appreciate it. Here's a followup question: If the goal is clean metal, does it make sense to remelt (with associated skimming, etc) and cast into ingots first, or would you remelt and cast straight into a finished part?
Remelt to ingot is always going to give you "Cleaner" metal. But you're going to lose more to oxidation in the process. If care is taken in the melt and you're not going to be making life saving mission critical parts Clean enough might be good enough. Outside the theoretical thought process of this. Clean enough is up to the caster. If I spent the better part of a month on a 1 off mold with no chance at a second try... I might use brand new ingots. If it's something that I can knock a mold together in under an hour I'd give it a skim or two and pour. I'm pretty flippant on my pours because I don't do those 1 month one offs (not talented enough with the clay and wax)... I do a bunch of 3d printed patterns because I'm good on the putter. I guess this is a long way of saying.... know your risks and gamble accordingly.
i just pour straight into the mould saving the expense of additional propane to remelt ingots. Those ingots are the same metal as the sprues etc they came from
