Old timer at the shop told me to preheat my molds to 350 degrees before every pour

I always skipped preheating on small batches to save time. He said I was asking for gas porosity and cold shuts. After three straight pours where I had to scrap the castings, I finally listened. The difference in surface finish was night and day. No more trapped gas bubbles ruining my parts. Has anyone else found a specific preheat temp that works best for certain alloys?

4 comments

4 Comments

henry_anderson5418d ago

My buddy runs a small shop and he swears by 400 degrees for aluminum bronze. He does these intricate art castings, and he says anything less than that and you get this weird scale on the surface. I tried 350 on some 356 aluminum once and it worked fine for me, but my parts were pretty simple. I think it really depends on the mold thickness too, thicker molds need more time to soak through. I remember doing a bunch of test pours with a digital thermometer stuck in the mold to see when it actually hit temp compared to the oven setting, and there was always a gap.

gray31417d ago

400 degrees for intricate art castings makes sense to me... I've messed up enough simple pours to know thin sections hate anything less than even heat. My oven's off by about 30 degrees last time I checked with a thermometer gun, so I just crank it up and hope for the best... I'm the guy who forgets to preheat half the time and then wonders why my parts look like they got into a fight with a cheese grater.

rose_clark8117d ago

Preheating to 350 is what I do for brass and it works fine, but I tried going lower once and ended up with a part that looked like it had acne. @henry_anderson54 is probably right about that temp gap thing, I've checked mine with a temp gun and the oven lies worse than my bathroom scale. Just don't tell me I need to babysit with a digital thermometer too, I already have enough gadgets collecting dust in my garage.

taylor.brooke17d agoMost Upvoted

Has anyone tried just letting the mold sit in the oven for an extra 20-30 minutes after it hits temp? I found my thick brass molds need that soak time way more than the exact number on the dial, and it fixed my acne problem without needing a thermometer. Saved me from buying another gadget and my parts come out clean now.