New Graphite Clay Crucibles

[Pipescs]

I know if I dig thru old threads I would find this answer but am in kind of a hurry

I have purchased two new Crucibles.

Understand I need to preheat them in the oven to dry them out before use.

Question is:

Is there any reason I cannot do this in the "Wife's Oven"?

Such as smell or residual problems that could put me in a position that I might have to buy a new oven?

[Fender]

Years ago, I used the wife's oven to bake some cores containing molasses and linseed oil (recipe from British foundry book.). That didn't end well. But you should be OK with crucibles.

[steamin10]

pipsecs:
Uh, no. It is my experience that crucibles are to be preheated EVERY time they are to be used. This drives off any atmospheric moisture that can be high enough to spall the vessel, when the pourous material is in equlibrium with its surroundings. Warming it up past the boiling point of water is sufficient, to lower the moisture content.

New crucibles must be seasoned. That means they should be raised to a dull glow in the least, not only to dry them , but to chemically set the mix fully by high firing. Without a charge in them they will have little stress from inside to outside temp diference, and you will wind up with a stronger unit than if unfired. They can be immediatly used after seasoning. (still hot)

That is two diferent issues, like breaking in running shoes, way before the marathon.

Another No-No is to wedge cold scrap into a crucible. It is asking for trouble as the heat growth of the material may stress the walls of the vessel, while it is too cool to be pliable enough to avoid the stress. I try to warm some of the scrap on the furnace lid, or rim, to reduce the room temperature diference.

The devil is in the details.

As far as cores, sugar based cores are fine in the family oven, like baking cookies til dry. Using linseed oil cores will generate quite a smell that most will find unpleasant in the house, like painting varnish. There are many such core recipies, settle on a simple one and stay with it. Your work is small and does not reflect complex industry, or its economics. Rely on whats at hand and go by the KISS rule.