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Unpopular opinion: is preheating molds always worth the extra time? | Foundry Workers - SMM Buzz

Unpopular opinion: is preheating molds always worth the extra time?

I keep seeing guys in our shop insist on preheating every sand mold to 300 degrees before pouring, but I've been skipping it on smaller runs lately and my castings are coming out fine. One time last month I poured a batch of 15 aluminum brackets without preheating and only had one reject from gas porosity. On the other hand, a buddy at a shop in Toledo swears preheating saved his whole job when he rushed a pour on a cold mold last winter. What's your take - do you preheat every time or pick your spots based on the part size?

3 comments

3 Comments

miam754mo ago

That's a solid take, Elizabeth. My buddy in Toledo really swears by it on cold days too but I wonder how much of that is just the weather factor. Like, have you ever noticed a bigger difference between preheating in winter versus summer in your own shop, or is it pretty consistent all year round for you? I'm curious if the ambient temp in the shop plays a bigger role than people give it credit for, especially on those small brackets where you're not worried about heavy sections.

elizabethhayes5mo ago

Oh for goodness sake, this preheating debate gets blown way out of proportion half the time. Look, I've been casting for over 20 years and I'll tell you, preheating every single mold is just not practical for small jobs. If you're running a big production line with expensive parts, sure, take the time. But for a few aluminum brackets on a Tuesday afternoon? I say skip it and save yourself an hour. The real problem is when guys in the shop act like the world will end if you don't follow their exact ritual. I've poured hundreds of small parts without preheating and maybe one or two had a minor gas issue. On the other hand, if it's a thick walled part or you're working with something tricky like bronze, then yeah, warm it up. But this idea that every mold needs to be 300 degrees is just old timers being stubborn.

diana205mo ago

Haha, tell me about it. I mean, I've definitely poured a few brackets cold and just prayed the gas bubbles wouldn't be too obvious. Maybe it's just me, but half the time I figure if the part's ugly, it'll just look more "vintage" or something.