Thank you metalab I can now put photos on my posts. Three of the photos are close ups and the fourth one is a photo of the whole defect. It is easy to see what happened because I poured too slowly the cope surface sagged so much it cracked nearly all the way and this would of happened before the mold filled up. As the metal reached the cope surface it filled the crack.
I do not have any way to know the exact mechanism of surface rupture. But, another possibility is based on the observation of just how much surface tension molten iron exhibits. Maybe the iron was forming like a mushroom head (no stem) with generously rounded top edges as the iron entered the chamber. It also cooled enough to form a weak shell. That round-shouldered mass rose slowly until it hit the top of the cavity. Now hydrostatic pressure forces the round shoulder to conform to the square upper inside edge of the mold cavity thus stretching the skin. It tears as it stretches. Iron continues (more easily now) to fill the cavity and oozes up through the cracked skin. I am disappointed you were not running your high-speed CT camera imaging the filling mold! ;-). The x-ray sequencing would have shown clearly what was going on. Nonetheless, congrats on getting some stills up. They too were helpful and your explanation interesting and may well be true. Denis
Veins...usually sand related..I haven't dealt with those since we got all the hand molding jobs out. We used to use foofoo dust to help.LOL I have no idea what was in the foofoo dust but it was some kind of mix with meal in it. I was told it help the sand stay intact during thermal expansions and reductions in sand volume. I think pouring faster may be all you need to do to eliminate it. They usually happen in places where the metal sits idle while other parts are filling up and then moves again which reheats the area.
