The Home Machinist!

Hi All,

I baked my first cores in the oven, but made the mistake of not using a dead flat pan/surface. I was thinking about using a pizza/baking stone to make sure everything sets right. Are there any better alternatives?

Regards,

John

I have never baked a core, I use the CO2 (Carbon Dioxide)- Sodium Silicate method for making cores.

It's a "Cold Box" method and requires no heat. There is no toxicity/fumes associated with this method.

I usually will mull 400 milliliters of Sodium Silicate with 25 pounds of sand. I use AFS 105, but any sand should work.

Can be stored for many weeks in a sealed container, but eventually it will harden by itself if not hardened by CO2.

Look up the method on the Internet, lots of info available.

and if gassing the SS bound core just is not your thing, you can buy a catalyst to cure it here.
http://shop.clay-planet.com/metal-casting.aspx

I have a 2 part resin system I'm using already. Baking is optional but I dis it to harden them up even more. I screwed up in using an old baking pan which wasn't dead flat. I was hoping there were oven safe surfaces/slabs that are good to use to maintain a true surface while baking

The cores that get baked in the foundry I work in are baked on what appears to be clay slabs. They are heavy and brittle. I wonder if ceramic tiles would work.

My wife is a ceramic artist; a kiln shelf is a flat slab of refractory ceramic that stays stable and stiff through high temperatures and is made to cycle many times.
They seem to be very flat; I don't know if you mean machinist flat, I haven't ever checked them.

They're inexpensive and available from refractory supply shops.

I have not heard of anybody baking cores for years! Are you making traditional oil sand cores? If so you need to bake them on a flat surface if the core is flat. If it has an irregular shape you will have to make what is called a "bedding frame". The bedding frame gets rammed with green sand, compacted hard. A suitable talc parting is liberally sprinkled on the bedding sand. The oil sand core is then placed on top of the bedding frame sand with parting agent. The bedding frame supports the oil core while it is curing and holds its shape until properly baked. If I were you it might be best to use a more modern core sand that does not require baking. Call a foundry supply and seek their advice on what types of core sand best suit your needs. Good luck with your castings. Optigman

The recipe I have for core sand is 90% sand and 10% white flour, dampened with water that contains 10-20% molasses. Baked till dry and used immediately so it won't soak up moisture from the environment. I would think ceramic floor tile would work fine for baking plate. Long as it really is kiln fired ceramic and not some imitation. No different than baking bread, smells like good bread too. Might be hard on the teeth.