Can we talk about inexplicable mold foam-ups?

I was preparing a sand mold for a cast iron part, and the mixture suddenly expanded and foamed over the edges... it was absurd, like baking soda and vinegar. We had to stop and clean up the mess, delaying production by hours. I'm genuinely curious if anyone has theories on what triggers such reactions in foundry sand.

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caseyr781h ago

Yeah, the baking soda and vinegar comparison is close but misses the real culprit. That's a simple acid-base reaction, but what you're seeing is almost certainly a gas generation issue from an organic contaminant. Could be leftover seacoal from a previous batch reacting with a new binder, or moisture getting into something it shouldn't. The foam-up happens when a gas forms faster than the sand's permeability can let it escape. It looks wild because it's trapped. We had it once from someone accidentally using a damp reclaim sand mix with a cold-setting resin. Total mess.