Tried a new sand mix ratio for a core and the whole thing crumbled during the pour

We were casting a set of brackets for a local machine shop, nothing too crazy. I mixed the core sand at 85 parts base sand to 15 parts binder, thinking a little extra binder would give us a stronger core. Poured the iron at about 2,700 degrees Fahrenheit... and the core just disintegrated halfway through. Turns out, I messed up the moisture content big time by not accounting for the humidity in the bay that morning. The binder couldn't set right. Anyone have a good rule of thumb for adjusting the water add based on the weather?

3 comments

3 Comments

joel_jones29d ago

Man, humidity is a silent killer. We lost a whole batch of manifolds last summer because the overnight dew point messed with our green strength. Now we just keep a cheap hygrometer on the bench and add like 5% less water if the reading is above 70%.

joel_clark3729d ago

Wait, you lost a whole batch, @joel_jones? That's brutal!

violah4329d ago

Heard a guy on a podcast say he mixes in a little bit of silica sand when the air feels thick, says it soaks up the extra moisture before it can ruin the mix. I mean idk if that actually works for big parts like manifolds, but it made sense when he explained it. Seems like a lot of this stuff is just old tricks people figure out after getting burned. Your hygrometer idea is probably way simpler though, and cheap is good.