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


http://photos.yahoo.com/bc/xmissionbobo/

"nJb" wrote in message
...
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

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?

On Mon, 8 Dec 2003 17:28:28 -0500, "Javahut"
wrote:

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?


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


http://photos.yahoo.com/bc/xmissionbobo/

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

--
Connie Ryman
Cryman Studio
www.eclecticbeadery.com
"nJb" wrote in message
news
On Mon, 8 Dec 2003 17:28:28 -0500, "Javahut"
wrote:

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?


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


http://photos.yahoo.com/bc/xmissionbobo/

C Ryman wrote:

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

--

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

--
Jack


http://photos.yahoo.com/bc/xmissionbobo/