Hi all, in casting aluminium bronze 90/10, using a ceramic filter 10ppi, and using oil bonded sand. I’m getting what appears like a silver dross, and I’m at a loss at how to remove / reduce it. Metal is degassed and a flux is used, then skimmed off when poured. Any help would be greatly appreciated
Did you alloy the bronze yourself?, I've heard second hand of bronzes separating into the component metals under certain conditions but it's rare.
That stuff can be tricky - turn into foamy dross inside the mold - if the gating allows the metal to splash around. I only use it when I want that extra hardness in a part. Pics showing the gating might get you some suggestions for improvement. What are you using to degas and flux it? When I got low on "real" C954 aluminum bronze I made some 90/10 to supplement what I had to complete one project. I poured ingots to remelt before I tried to make castings with it, hoping that the second melt would ensure the ingredients were fully mixed. It seemed to work, but I was kinda winging it, so that might not be why. Good luck, Jeff
I’ve been gating directly above the casting (plaque), so the sprue is the gate (with a filter in). Reason I’ve been doing that, is the plaque is fairly large and it fills better when pouring into the middle rather than an edge. My fear was it was metal splash / turbulence, which I don’t see a solution to with pouring directly over the top
why are you making a plaque out of aluminum bronze??? yellow brass or Si Bronze depending on the color you want, Al Bronze is tricky and not appropriate for plaques (its major overkill)
Just a random guess here, but perhaps it is not enough or the wrong flux as Jeff suggested. The literal purpose of flux is to promote fluidity by blocking oxidation. The pic you showed indeed looks like a blob of AL sitting there, so perhaps the flux did the opposite and oxidized the AL or Si Bronze, preventing the two from mixing. Total guess though.
Every Cast AlBr alloy I could find requires a trace amount of Fe, do you have a trace of Fe? some of the alloys are actually quite high (up to 5% C95400) V/r HT1
When I started making Aluminum Bronzes I would occasionally have this issue from simply not stirring the metals enough. The liquid aluminum has a tendency to float to the top if not incorporated fully. Don't be afraid to add some iron and potentially nickel and manganese to get a C953, 954, or 955 alloy. They pour pour better than the 90/10 alloy and are stronger if you need it. 953 is the most 'golden' if that's what you're after.
