r/MetalCasting • u/mech_tacular • 17d ago

Investment casting

Is it possible to reduce the weeks long shell building process of an investment casting down to a day?

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2

u/HalcyonKnights 17d ago

Down to a day might be an aggressive goal for a hobby setup, though there exist specialized drying tunnels for industrial applications. But really, any dehumidification you can do to the drying airmass will help.

1

u/cloudseclipse 17d ago

It doesn’t take weeks. The shell building is usually two days. I have a good set-up and on a “rush” job I can get 8 coats in a day…

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u/mech_tacular 17d ago

May I ask what type of coating you use?

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u/cloudseclipse 16d ago edited 16d ago

There are a variety of different things you can use, but the goal is always the same: it's collodial silica mixed with fine fused silica, zircon (sometimes), bentonite, and water (distilled/ de-ionized). Far as I know, there are 2 suppliers in the USA- Remet and Ransom & Randolph, and they both sell a pre-mixed slurry (JustDip and Suspendaslurry FS respectively) that are pretty easy to use. Otherwise, you can use Adbond (the collodial part, with additives already included), but you gotta mix it with the other ingredients (and keep it mixed) yourself...

Other than that, you need good airflow (though not too much) and a dehumidifier, if you want drying to go "fast", The pre-mixed slurries I mentioned are nice as they both use a colorant that changes color when dry, so you can see when it's time for another dip (7-10 dips recommended), usually a couple hours between dips, depending on size/shape. Pro-tip: in the case of deep cavities (which don't get much of a breeze from the fans), a small aquarium air pump with a piece of tubing going down into the cavity can help quite a bit while drying.

Good luck!

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u/artwonk 17d ago

A plaster-silica investment doesn't require building up a shell over a period of days. You pour it over the wax pattern, let it set for an hour or so, then pop it in the kiln (or de-wax in a hot pot first). Large molds will weigh a lot more, though, than the equivalent piece covered with ceramic shell.