TIL my vent rod placement was making my cores weaker

I was pouring a set of small gear housings last Thursday, same way I've done for maybe two years. The scrap rate was always a bit high, like one in five would have a small void. My lead, Carl, watched me set up a box and just said, 'Your vent is pointing at the wall, not the air.' I moved it to aim straight up out of the sand, and the next five pours were all solid. Has anyone else had a simple fix like that for core blow?

3 comments

3 Comments

angela_knight31mo ago

Wendy131 is right about the straight shot, but you also have to watch the vent's path through the sand itself. If it goes through a damp spot or a patch with too much binder, it can seal itself shut from the inside with baked gunk. I had that happen once, the vent looked clear but the middle was plugged.

wendy1311mo ago

Your vent is pointing at the wall" is the whole story right there. It's not just about having a vent, it's about giving the gas a clear, straight shot out. I've seen guys put a vent in but have it run parallel to the parting line for an inch before it turns up. That little pocket can trap enough gas to ruin a core. Always drill that sucker straight up and out, no turns until it's clear of the sand.

matthew3941mo ago

What about the vent diameter though? I've found that even a straight vent can choke if it's too small for the core box size. A big core needs a fat vent, like at least 3/8 inch, or the gas just backs up.