That is severe porosity and tells you the same thing...rich flame. It takes very little heat to melt aluminium, treat it like a fair maiden, nice easy lean flame. Save the balls out roaring burner for the red metals and iron. It took me a couple years to figure that out.
I think I need to reduce my fuel tank pressure. I currently have it set to around 3 gph ... just because that's where the "iron guys" were at. I have so much turbulence in the furnace that once the aluminum gets molten it will actually swirl inside the crucible. This is something that I did not see before I pressurized the fuel.
One way to test for reducing flame conditions is to hold a piece of clean steel in the exhaust stream. If it soots, the flame is reducing. “Treat it like a fair maiden”. Ah, poetry! I like it. Denis
I should add the only reason I had my aluminium in this state was because I was chatting with someone and left it to the point where it was glowing orange hot in indoors light. All the other crucibles (8) poured before and after this one were perfectly fine, just melting faster and faster as the furnace warmed up. This is fresh, certified 601 alloy ingots with no recycled metal in the pot. I had muscle cramps in my forearm as this is the most I've ever poured in one session.
I got some new 100 mesh sand the other day, and poured this morning. Surface finish was MUCH improved, although I had a short pour (I think my gates were too thin). 100 mesh sand with, 6% bentonite (50:50 western/southern), 3% water. Made sure to brush with camel hair brushes and blew off. Rammed hard ... I think. New sand/pour on left ... old on right.
Yeah big difference Denis. Gates were about 1/8" (but it looks like they tapered a bit) x probably 1". It was on the low side of 1300 when I pulled it. Quick final skim and poured. I guess since its on the thinner side and a bit of surface area, I should have been a little hotter. The next one I will pull closer to 1400. ------------ Edit----------- I just looked back at one of my earlier posts and the first attempt was pulled at 1390ish.
Probably just cold metal but with finer sand the mold becomes more dense and does not permeate as well and can sometime trap gas just long enough for the metal front to cool off. If it is a recurring problem with the new grain size it may help to add some vents. Generally, we see streaking in the casting when it is a gas issue but not always. Still a much nicer finish than before!
I agree! but in green sand, vents are an "all the time" thing, cant hurt (if done properly) and may save castings V/r HT1
Thanks for that Billy & HT1. I will keep the permeability in mind. And just make the vents an "all time thing" ... If I make it routine to always do them, then I won't forget to do them when I really think I need them.
