Had a core shift blowout on a big gear mold last Tuesday

We were pouring a 400 pound bronze gear blank at the shop in Erie, and I saw the sand core move just as the metal hit the sprue. The whole mold started to weep, and then a big jet of metal shot out the side. I yelled for everyone to get back and hit the emergency stop on the furnace. We had to let it cool for an hour before we could even break the flask open. The core had cracked and shifted about an inch and a half, ruining the whole casting. My boss thinks the core print was too small for the weight. Anyone ever have a core shift that bad and how did you fix the print design?

2 comments

2 Comments

king.river1mo ago

Ever think about how the core gets vented? @oliver242 is right that a weak mix can fail, but a small print can also trap gas. That pressure has to go somewhere. I've seen a core that looked solid crack and shift because the gas couldn't escape fast enough. It blew out a side wall just like you described. Maybe check if your print design lets the gas out easy, not just if it's big enough to hold the weight. Adding a few more vents off the core print might stop that pressure from building up.

oliver2421mo ago

Nah, sometimes the sand just gives out no matter the print size. Could've been a weak core mix or a bad ram-up.