A Tale of Two Castings

[vtsteam]

Tom, these are the tools I use for scraping out slag before pouring. The longer one is used in the furnace, the shorter one is used once the crucible has been lifted out.

The long one is made from angle iron, with the end cut and bent. The short one is just a simple rake, with the bottom curve ground to match the curve of the crucible.

[ironman]

I think that one of the main causes of sticking is that the pasty ceramic crucible glaze and drips of slag move down the outside and find there way to the bottom and "braze" the crucible to what it's standing on. That happens at the perimeter of the crucible bottom, which, because it is necessarily exposed, can't maintain cardboard carbon as a release agent.

Well that's my theory anyway.   

You are sooo right because that is exactly what happens. I get that suggestion all the time on youtube by people who have never melted iron. Once the pedestal is stuck to the crucible there is no need to remove it. I use ceramic fiber instead of cardboard and if I do separate the pedestal from the crucible there is a very thin ring on the outside where the glaze makes the crucible stick to the pedestal.

[vtsteam]

Thank you Ironman! 

Slag and spilled iron seem really tough on the the furnace lining, when using blanket and hotface insulaton. My slagging tool is a bit clumsy, and slag sticks to it sometimes even after banging it out in a bowl while hot. I'd like to reduce or avoid drips inside the furnace.

Your slagging tool seems much thinner than mine, and better at non-stick, by comparison, yet it stands up to the temperatures. As a guess, is it a thin piece of stainless steel bent and welded to a steel rod, or some other material?

[vtsteam]

Latest stuck job. And proof that it's the outside of the crucible that sticks due to drips, not the underside where the cardboard is. This happened when there were 2 layers of cardboard under the crucible.

It was released when cool by tapping a small chisel around the outside welded joint. The underside was not stuck.

Also note that the firebrick itself did not stick to the floor of the furnace. No drips there.