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Warning: That cheap crucible from online cracked on me after 3 pours

I've been using this $30 graphite crucible I got off Amazon for about 2 months now, mostly for aluminum and small brass jobs in my backyard foundry. Last week on my third pour of the day, I heard a loud pop and saw a crack running right down the side, lost about 4 pounds of molten metal onto my floor. Lucky I was wearing my PPE and nobody got hurt, but it made a real mess. My buddy at the shop said those cheap ones are often made with lower grade graphite and can't handle the thermal shock of repeated heating and cooling. He swears by the SiC clay graphite crucibles from a proper supplier, even if they cost 3 times as much. Has anyone else had a cheap crucible fail on them, or am I just unlucky with this batch?

2 comments

2 Comments

benwilliams1mo ago

and that thermal shock is EXACTLY the problem, I've seen it happen more times than I can count. Those cheap graphite jobs are basically pressed together with low quality binders that give out fast. Once you hit that third or fourth heat cycle the material just can't take the expansion and contraction anymore and it pops like a firecracker. Your buddy is right about SiC clay graphite being way more forgiving, I switched to one of those about a year ago and it's still going strong with no cracks. Plus that mess you had to clean up with molten metal everywhere is a nightmare, I've been there and it takes forever to chip that stuff off concrete. For the price of three cheap ones you could buy one good crucible that lasts five times longer anyway.

ben4021mo ago

Yeah, but here's something I don't see anyone talking about - maybe it wasn't just the graphite quality, could be how you preheated it. I've seen guys throw a cold crucible straight into a hot furnace and that alone can crack even the good ones if you don't ease it in.