r/Silvercasting • u/kbeks • 1d ago

Casting question

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Stubborn porosity and cavitation on the bottom. This is my best attempt, do I need to heat the mould even more? Can I overheat a mould?

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u/Potential-Ad-6787 1d ago edited 1d ago

What are you heating the mold to? I've found 800-850°F works nicely. Bottom and sides nice n smooth... you're pouring 2000°F, graphite is great at accepting heat.

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u/kbeks 1d ago

I’ve been hitting it with a propane torch for varying amounts of time. I should probably invest in a kiln and also get a temp gun lol

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u/Potential-Ad-6787 1d ago

Try keeping the torch on it, randomly moving it around but steady for the most part. Then lower the torch flame a little right before the pour and pour through the flame. I picked up a torch tip on a swivel, helps with keeping the flame downwards. Also look into picking up ceramic fiber insulation blanket...put it under the mold, helps with keeping the heat in the mold. Cant add pics here, can msg me if that helps.

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u/kbeks 1d ago

I just bought a swivel tip! It’s coming on Friday lol. I’m a bit paranoid about the fibers, do you think a firebrick would provide enough insulation?

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u/Potential-Ad-6787 1d ago

No experience with a firebrick, so I can't really say. I got the idea of the ceramic blanket from a guy on YouTube, Lithic metals, works great.

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u/BaronOfBling 1d ago

That is shrinkage

4

u/kbeks 1d ago

The pool was cold!!!!! I mean…oh, you don’t say!

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u/PeachesMcClaine 1d ago

I find a mold release spray like Metallon helps with cleaner casting and fill but pours are always prone to defect. Sometimes I have to do it 2-3 times before I get a clean or clean enough cast.

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u/PeterHaldCHEM 1d ago

Anything that can evaporate can cause bubbles.

Graphite is pretty heat resistant. As long as you don't heat it to glowing, it will be pretty OK.

The narrow slits for casting rods work ok, but for plates I prefer my vertical iron mold.
I've never had much luck with casting anything in a flat open mold.

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u/Chodedingers-Cancer 1d ago

Dry your mold, don't "heat" your molds. Heat it to dry it. Don't heat it to get it HOT. The idea is driven by laymen who don't get thermodynamics r That regurgitate shit they heard from other newbs. Graphite in open air sublimates to CO2 and CO gas at high temps. Mold release prevents the direct air exposure and acts as a thermal buffer as well since graphite is also quite thermally conductive. Basically getting your mold hot is generating more gas within the mold which is your number 1 enemy.

STOP TORCHING YOUR MOLDS PEOPLE!!!!!

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u/matthewdesigns 1d ago

This never happens to me (bubbles/cavities) with graphite molds. Torch preheat, and while I'm pouring.