I have misplaced my schedule book. ( Could be old age)
Looking at Grahams book it appears to start annealing at 1040 f and end at strain point 940f.
I'm using .250 float. I'm not comfortable with these numbers as I thought I remembered a strain around 800.
Will someone please check there number for me
Thanks
Joe
“If you tell me, I will forget.
If you show me, I will remember.
If you let me do it, I will understand."
Joe, no one number has the end all result. Stone stops at 1030 or 1040, I am too lazy to look, for a short soak and then does his long ramp to somewhere just above 900. I do a long soak at 1000 and take the same amount of time down to 900. Usually Stone and I spend the same amount of time. More of my time is spent in the lower range. I have inquired about this and was told by the senior glass techs at Bullseye (Dan and Ray) that my strategy is better.
6mm will probably anneal with a shut off. The formula I use for thicker profiles tells me to go faster, than the one I use for 6mm. Here is how I do it. My controller programs from setpoint to setpoint over a specified time.
> 1000 hold for .6 hr
1000 > 900 take .6 hr
900 > 700 take .4 hr
700 > 300 take .4 hr
Made me go back and do math again. Had to determine how long .6 hours is
I'm starting this one tonight and plan on 100 f to heat up to slump at 1200 f. Mine will slump starting around 1000 and might be even quicker
do to the glass weight and overhang of mold.
Catch up with you later,
Joe
“If you tell me, I will forget.
If you show me, I will remember.
If you let me do it, I will understand."
Joe Back in the 80's when I devised my schedules, I did a slump test to determine my anneal soak temperature. The test was this:
cut a strip of glass 1" wide and 12" long. Place it cantilevered between 2 fire bricks. At the far end, place another fire brick, beyond the glass, so you can gauge when the glass starts to move. Heat the kiln up to a temperature below where you think the glass will start to move, hold for 30 minutes. Raise the temperature 5ºF and hold 30 minutes. keep this up until the glass moves. Note when the glass moves. Anneal soak 100º F beneath this temperature. For me, float glass moved at 1100ºF, and Bullseye moved at 1020ºF.
One of the neat things about this test is that what your controller says the temperature is, doesn't really matter. What matters is working 100º below where it moves. I haven't done this test for a very long time, and I don't have anneal problems.
The strain point is the temperature, below which, annealing can not take place. Annealing tends to go faster at the lower end of the anneal range. Another story is that annealing can take place in about 15 seconds, when the entire mass of glass is within 5ºC, inside the annealing range. The time we spend is to get the glass to that place. Remember we control based on the air temperature, not the glass temperature. During the cooling cycle, the glass is hotter than the air, but as it sits in the kiln environment, it slowly takes on the temperature profile it is in. If the inside of your kiln has even temperature, the glass will become even. This is often not the case. Close to the walls, the temperature is different, and in the center, the temperature is different. The longer you hold a piece of glass in an uneven temperature environment, the more it's internal temperatures reflect it's environment. There comes a point when the temperature difference within the glass becomes greater than 5ºC. Once this happens, stresses can not be relieved without reheating.
