Ramping up

As a follow up to another thread.

Last night I was refiring 3 bowl blanks. 11" Diameter ~.280 thick. I ramped to 1000F at 450F/hr. one of the blanks cracked. I think I'll stick with the 300/hr rate. Jack

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Reply to
nJb
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Now I am curious .

11" diameter, was this bending, so the glass was over a mold? Cold air in the mold under the glass? Most of what I am bending is 1/2 that thick, with no precious "heat history", other than manufacture.

Guess safe is better than sorry, did you do this in a big kiln, or a smaller one, wondering just for the amount of time the element would have been on high during the firing, and where the objects were in relationship to the thermocouple?

Reply to
Javahut

They were on a flat kiln shelf being refired after some tough up. Two were predominantly green and one was black. The black one broke.

I'm using an SSR on my controller so the power goes off and on very fast unlike using relays.

Maybe it's the altitude.

Jack

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Reply to
nJb

I think black absorbs the heat faster than the other colors.

Reply to
C Ryman

That's probably the answer right there. I'll just use a slower ramp on the thicker pieces.

Reply to
nJb

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