I hoped to melt some old marine hardware and re-cast it as some small marine-adjacent parts. I melted some aluminum then switched over to a clean crucible for these parts. Metal melted while I was ramming the flask. Came out and there was a large amount of a chunky/flaky dross. I suspected the springs would not melt but anticipated that the grommets would. I did not have a good spoon for dross and ended up pouring after fumbling around for a minute. I got some poured in the sprue and then it froze up on the size of the crucible, never seeing the mold cavities. So, did I melt brass or mixed bronze and brass thinking it was bronze? Anything worth saving? It was about 10oz (300g) before it 'flaked out'. There were also a couple of small un-melted pieces of the parent metal in the mix even though it seemed fluid in the crucible. Thanks!
If you remelt at least you'll start with clean metal. I know you use small crucibles, do you melt a full crucible of metal each time? The more metal in the pot, the longer it will stay hot.
I was using my smallest crucible but it was still less than 1/4 full. The pour before that I was all full in another crucible for aluminum. I'll have to make some better skimmers, think there is a recent Olfoundryman that covers that. (Edit, last minute of this video: )
That's a good demonstration of thermal mass and why it's good to have extra molten metal mass to slow the rate of cooling. Was the metal glowing orange-yellow with blue-ish (tin) and pale green (zinc) flames coming off?.
I would say yes to all of the colors but not so much blue and green and a little more yellow and white with the flames when I poked at it. There is a yellow ring at the 'load line' of the crucible when all was said and done.
Bronze and brass in a smaller crucible has to be literally boiling and poured fast into the mould to get a good casting, cold metal is a major problem.
I suppose it all looked 'hot' to me coming from the lead and aluminum side of things, but not hot enough. Any clues from the pictures as to what metal(s) I was messing around with? Do both bronze and brass burn out some of their alloyed metals (tin, zinc) from the copper during the melt?
It does burn a tiny bit but not enough to really matter even when re-melting the stuff, I guess as the exposed surface area to air is trivial compared to the volume of the molten metal. The foundry where I help out has remelted a lot of red brass runners and on the occasions where it's been analysed in a lab, the alloy was still within specification. This was certificate traceable ingot as the starting material and remelting runners from that, so not constantly melting bronze over and over again. A camera photo doesn't really portray colours too well due to the IR sensitivity of CCD sensors so everything seems to swamp out white. Orange to yellow for a smaller crucible with give you time to extract it and slam the metal down the mould as fast as you can (skimming done while still in the hot, shut down furnace to preserve heat). For red brass/leaded gunmetal you will know if it's on the too hotter side as you will see the yellow glow and the pale flames as well as hear the bubbling of the metal. The first photo shows a whole lot of dirty scrap bronze and brass hot enough to smoke (not healthy) inside a slag coated furnace lining that glows readily. The second photo shows a freshly lined furnace (doesn't glow much, no slag) just barely hot enough to melt brass in a cheap crappy crucible (my home efforts). So you probably want something like the third photo which is a lot of marine scrap bronze with a thick layer of crud needing skimming glowing nice and yellow hot to the camera and bright orange-yellow to the human eye.
I like the lever action on the lid of you furnace! I want to say I saw some yellow heat in the crucible before I took it out. Could it had also just been that the slag was hotter than the main bit of metal?
If anything the slag looks cooler than the metal as you'll see when you skim the dross and slag off the surface and see bright yellow molten metal underneath. The lid works but it's kind of a pain to get aligned when making it. The lid is rigid and strong enough to take the weight of preheating ingots which is it's main advantage.
