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Old 01-26-2020, 07:47 PM
Art Freas Art Freas is online now
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Long annealing schedule.

when our furnace failed before our rebuild it was full. To get something out of it we saved the big chunks of glass when we broke it up. (it is an old style Greg Englesby 400lb). The biggest chunk I have is about 10 inches by 12 inches by 12, irregullarly shaped. This is crystalica glass. Looking for any and all thoughts on the schedule. My one big question is whether I shoul have any holds on the way up and if I should put extra holds for the way down. I am thinking that I should add at least one more hold on the way down.



Target Temp Deg/Hr Hrs Total Hrs Total Days
75 0 0.00 0.00 0.00
475 7 57.14 57.14 2.38
800 7 46.43 103.57 4.32
850 4 12.50 116.07 4.84
880 3 10.00 126.07 5.25
925 3 15.00 141.07 5.88
925 Hold 3.00 144.07 6.00
925 Hold 3.00 147.07 6.13
875 2 25.00 172.07 7.17
875 0 4.00 176.07 7.34
675 3 66.67 242.74 10.11
475 5 40.00 282.74 11.78
275 7 28.57 311.31 12.97
175 14 7.14 318.45 13.27
75 15 6.67 325.12 13.55


Note, not sure how to get this formatted. It seems to "correct" my formatting.
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Old 01-27-2020, 01:49 PM
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Pete VanderLaan Pete VanderLaan is offline
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I would suggest reading sections of "The Schedules" by Graham Stone which cover fibonacci and real world sequences that passed the strain tests applied to annealing sheet glasses laminated to large thicknesses.

I have reannealed Schott Optical glasses in big thicknesses and I would be the first to admit that I failed to achieve strain relaxation in any of those attempts. Schott used to make glasses referred to as Coarse annealed as well as fine annealed. I just about always wound up with the coarse since it came off the back lot at Schott.
The schedule as you have it laid out is indeed very difficult to read and I did go try to read the two posts you erased which I get to do. They didn't really help.
I would say that 75 days is a very expensive annealing program to run and I have to question why a chunk of Cristalica is worth that effort. I don't know if you've ever seen the comparative refractive indices between ordinary glasses and high quality glasses they have at Corning but it essentiall demonstrates why thick glass needs a nice index. Light bends as it passes through glass and the optical qualities of high lead/ barium/ potassium glasses don't bend the light much at all. Look in that setup they have at Corning and you can see the differences. You might be better off just buying a big chunk of F2 and you'd have nice stuff. With Cristalica? No.
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Old 01-28-2020, 09:13 AM
Art Freas Art Freas is online now
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Can you bring the post up in edit mode? In edit the original spacing is visible. The schedule is 13 days long. The site keeps collapsing the spaces and won't take HTML tables.
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Old 01-28-2020, 10:43 AM
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Pete VanderLaan Pete VanderLaan is offline
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I don't think 925F is sufficient enough in the first place. Try 970F . Your hold at annealing point upper is too short by a lot. When you do drop , drop to 700F, not 670 and hold there for a long time. Don't take this piece out of the oven until it reads room temperature for a day. I expect it to continue to show strain.

It doesn't answer my question anyways. Why?
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Old 01-29-2020, 07:15 AM
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An additional thought:
This chunk was not really annealed at all or, at best coarse annealed which has a boatload of strain and it makes me recall Frank Wooley's comments to me at the 2001 GAS Conference in Corning. Hopefully, Frank will be remembered as the senior melt engineer there, a title I really respect.

Frank said: " If a piece goes into an annealer too cold, it can take up to 30 times longer to anneal properly."

For me, that suggests that the time held at the top of the annealing range where I would like to see it should be massively longer. I suspect it was what went awry back when I was trying to fine anneal Schott Optical back in the 1980's. I never gave it a fighting chance.
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Old 01-29-2020, 08:08 PM
Art Freas Art Freas is online now
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Couple of questions.
1) On another thread you (Pete) mentioned that coming up you can go faster. Makes sense the soft part will be on the outside. Does my schedule waste time coming up too slow.
2) On the holding much longer at 975 how long do you think?
3) On the hold at 700, how long is really long.

On the why, simple fact is that folks will by a big a$$ chunk of glass for a fair amount, this will help pay for the rebuild. This chunk only has two small stones in it and it is about the volume of 1.75 bowling balls.
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Old 01-30-2020, 12:10 AM
Eric Trulson Eric Trulson is offline
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I just went through my copy of Graham Stone's schedules book. Nothing matching this exact situation, but there's a (slightly handwave-y) analogue in the schedules for a 6" thick open-mold casting (half the thickness of your piece, but since yours is going to be getting heated from all sides instead of just from one side the way an open-mold kiln casting would be, I don't feel awful about equating the two situations). That schedule is about as long as the one you posted, 350 hrs/15 days total. So you're probably in the right ballpark at least.

As far as specific changes to your schedule:
- I think you can speed up your initial bringup time a bit, but just pour that time right back into lengthening the soak at your upper annealing temp. Maybe cut 1-2 days off the ramp and add it to the soak.
- As Pete said, bump the soak temp right up to 970-975 (or whatever the high end of your annealing range was for Cristallica in this particular kiln)
- For the soak at 700, at least a half a day, maybe a full day

So a rough schedule might look like:
75F - 975F over 5 days
975F soak for 2 days
975F - 700F over 2 days
700F soak for 1 day
700F - 75F over 5 days

Disclaimer: I haven't done any casting or annealing work on this thickness scale before. All the above is decent rough figuring, but it doesn't beat experience. Also, for god's sake, if you're going to sell this thing to the public, check it out with a polariscope first. A piece of glass that size holding internal stress and then exploding would be no different than a bomb, don't put that in someone's home unless you can verify that the residual stress is gone.

Last edited by Eric Trulson; 01-30-2020 at 12:14 AM.
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Old 01-30-2020, 09:35 AM
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I'd increase the time between 975 and 925 substantially- double it.
I'd double the time to 700F.

I don't think it would blow up once coarse annealed. It could on the way up of course.

Keep in mind, what Frank said about "30 Times" and then consider that Stone's book was dealing with the times for glass that was actually already annealed before the new process started. You're starting with a time bomb and there's a difference.
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Old 01-30-2020, 02:09 PM
Larry Cazes Larry Cazes is online now
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Quote:
Originally Posted by Pete VanderLaan View Post

Keep in mind, what Frank said about "30 Times" and then consider that Stone's book was dealing with the times for glass that was actually already annealed before the new process started. You're starting with a time bomb and there's a difference.
I often get asked to repair broken pieces and I struggle with the fact that I dont know how the piece was originally annealed if at all. The way up to working temp is always exciting and I always err on the side of caution when re annealing.
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Old 01-30-2020, 03:32 PM
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Pete VanderLaan Pete VanderLaan is offline
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In reasonably annealed glass the strain should show a gray at max retardation in a good quality polariscope. If it shows greens, yellows, etc, it's really strained.
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