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Casting Schedules?

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Barbara Cashman
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Casting Schedules?

Postby Barbara Cashman » Mon Mar 25, 2013 11:48 am

Is there a website (besides BE) that has annealing schedules for large, thick castings? Especially interested in float glass.
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Bert Weiss
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Re: Casting Schedules?

Postby Bert Weiss » Mon Mar 25, 2013 12:23 pm

Barbara Cashman wrote:Is there a website (besides BE) that has annealing schedules for large, thick castings? Especially interested in float glass.
Get the book, Firing Schedules for Glass by Stone
Bert

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la suisse
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Re: Casting Schedules?

Postby la suisse » Sat Mar 30, 2013 9:11 am

Dear Bert

In the book, are there firing schedules only for float glass or are there schedules to adapt also to BE or other glass?
I would buy me the book, but never used float till now.

Thank you

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Re: Casting Schedules?

Postby Brock » Sat Mar 30, 2013 9:22 am

Yes, there are schedules for many glasses in the book.

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Re: Casting Schedules?

Postby Bert Weiss » Sat Mar 30, 2013 10:02 am

la suisse wrote:Dear Bert

In the book, are there firing schedules only for float glass or are there schedules to adapt also to BE or other glass?
I would buy me the book, but never used float till now.

Thank you
Many of the main schedules are written for float, and there is a chart for adapting to other glasses. Bullseye Tested Compatible and System 96 use the same anneal schedules. Stone is good at explaining the why's of what he suggests.

Do understand that there is not only one way to accomplish an anneal for glass, especially considering that we control based on air temperature and not glass temperature. I have float schedules that I devised based on info I got from a glass engineer at PPG. My schedules use about the same amount of time as Stone's, which makes sense to me. However, I soak longer at a lower temperature than Stone does. He has a short soak at a higher temperature, followed by a slow ramp down. I once asked Dan and Ray, both founders of Bullseye, about the difference in strategies. To my surprise they liked my approach better. Several years later, they revised the Bullseye anneal schedules for thick glass castings. So, applying the paradigm used by Stone, I add 80ºF to Bullseye's schedules to get one for float. Sometimes these schedules go a bit faster than mine, and they seem to work OK, if I am in a rush. Bullseye did extensive testing and research to devise their schedules. They got a recording pyrometer with 6 thermocouple inputs. 3 were in the air and one beneath the glass, one in the core of the glass, and one on the glass surface. What they were looking for was the time it took at a particular air temperature for the 3 thermocouples in the glass to equalize. Annealing takes place when the entire mass of glass is within 5ºC, inside the annealing range. Once this happens, it is only a matter of seconds for the stresses to be relieved. (BTW, you can make thermocouples by welding very thin specific wires at their tips. Fortunately these wires have a higher COE than glass, so the glass remains intact during these tests.)

So, for me, I often look at Stone, Bullseye, and my own charts to decide where to go with annealing. Be very aware that these charts are all assuming uniform thickness for the glass. When you have thick and thin spots, within the glass, it takes longer to get the different sections to equalize within the range. Also be aware that if your kiln has uneven temperatures inside it, the longer you hold the glass in that environment, the more those gradients are transferred to the glass. If the difference in the glass is greater than 5ºC, it CAN NOT anneal. There is a sweet spot between too long and too short, where it can work just fine.
Bert



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