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Hot take: Everyone says to always preheat the sand for a full hour, but I lost a whole day on a simple core box because of it.
We had a rush job for a small bronze gear, maybe 20 pieces. The core box was a basic two-part aluminum job. I followed the old rule and preheated the sand mix in the muller for 60 minutes like always. The cores kept crumbling on the draw, every single time. I rechecked the binder ratio, the moisture, everything. After 8 hours of this, I was ready to scrap it. On a hunch, I mixed a fresh batch and only preheated for 20 minutes. The cores came out perfect, first try. I think that extra heat was baking out the binder before it even got to the box. Has anyone else run into a core mix that just can't take the long preheat?
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the_morgan6mo ago
That old hour-long rule is for the big production foundries running the same mix all day. Read a case study once about a small shop doing artistic castings. Their fancy resin binder system would start to go off if the sand got too hot for too long. They cut their muller time in half and their scrap rate dropped like a rock. Makes you wonder how many "standard" practices are just for one type of operation.
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victorb176mo ago
Yeah, the binder type changes everything.
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butler.abby6mo ago
Totally agree, and @the_morgan's point about small shops is spot on. We had the same issue with a cold-box system setting up way too fast in the summer heat. Cutting back our mulling time fixed a ton of surface finish problems. Makes you question all the old rules, right?
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