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Old 06-24-2017, 02:48 PM
Art Freas Art Freas is offline
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Strain, Anneal, and Melting points

Can anyone point me to a good write up on what the difference between the annealing point and strain point and how that affects the temp you set your annealer to? In the change from Sys 96 to New Sys 96 the annealing point and the strain and annealing points have gone up about 8 degrees. Our annealers have never been set to the Sys 96 annealing point and I know none of the fusers anneal at the annealing point. Would it make sense to do the annealing test with the cane assuming my starting point as 8 degrees higher then current?

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Old 06-24-2017, 04:06 PM
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Pete VanderLaan Pete VanderLaan is offline
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There is no annealing point. There's an annealing range. Beyond the top of the range is softening glass. At the bottom of the range no further relaxation of strain can occur. Thickness of the ware will play hell on you but the higher in the range, the faster you can relax the strain in the work. Below Strain point, at the bottom of the range no further annealing can happen. At that point, you are now trying to get it to room temperature without thermal shocking it.

Determining the sane point at which to anneal, take two bricks and put them in the lehr and stick a cane of your glass (about 5mm) in between them so it's cantilevered out from the bricks. Make that about six inches long. Start at about 900F and watch the cane for 25 minutes. If there's no sag, turn it up 25F. Watch again for 25 minutes. If no results, 25F more, wash rinse repeat. At one of these junctures, usually around 975-1000F, it's going to sag- hard. At that point, subtract 50F and you have a happy place to anneal. Going down to the strain point which is individually determined for every glass has a functional resting point at about 700F ( but not in some glass types). I stop there, usually for at least 90 minutes to make sure the work is stable. If it's really thick I stay a lot longer.

Reading Dan Schwoerer's paper on viscosity as opposed to Linear expansion is a good read. I think you can access it from Bullseye. It is always in my tech handouts when I teach. It makes life more complicated but worth scratching your head over.
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Old 06-24-2017, 08:25 PM
Art Freas Art Freas is offline
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What confuses me is that when you look at the spectrum info on the glass both new and old it has the strain point, annealing point, and the melting point. Thanks for the pointers in checking temp and the paper.
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Old 06-25-2017, 07:45 AM
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Pete VanderLaan Pete VanderLaan is offline
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The entire fascination with glass per se is that it does not have a determined "melting point" like aluminum or silver might. It softens, that's it. Once you have passed the top of the annealing range, you're in the softening range.
If you are trying to measure physically linear expansion, it becomes a major problem once you have passed out of the range

Why am I not surprised that that would be printed on the bag.

Dan's paper makes a very cogent argument about the need to keep viscosities in line as well as expansions when one is trying to make two glasses fit each other. Glassblowers tend to place high value on expansion while people casting or doing heavy fusing tend to look at viscosity much more.
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Old 06-25-2017, 11:24 AM
Art Freas Art Freas is offline
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"Once you have passed the top of the annealing range, you're in the softening range." Can I take from this that the annealing point is the temp at which things haven't fully melted (what ever metaphysical manner we determine melted for an amorphous non crystalline solid) but start to move?
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Old 06-25-2017, 02:14 PM
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Again, do the slump test with the cane stuck between two brick. If you carefully observe this, you will see the cane very slowly sagging when it's about 60 degrees lower than it hard sag point. It's a SOFTENING RANGE as well. The exact point of a glass becoming ductile varies from glass to glass within a specific type ( Like soda lime). As you get hotter in the range, the rod goes down more quickly. Put it in a furnace at 2000F and it collapses in seconds.

You can ideally anneal at 50F below the softening point as observed. Some very thin ware will be more sensitive to deformation than thick stuff will be and then you get to the question of whether the piece goes in the lehr too hot in the first place. That takes us back to Frank Wooley retired senior melt engineer at Corning ( and he knew his stuff). Frank asserted that if a piece went in the lehr too cold it can take 30 times longer to anneal than a piece put in at the right temperature. If you put it away too hot, and you are at the top of the annealing range, you are more at risk to see a mild slump or marring of the surface. It's a fine line to walk. To really know, you need to measure the strain with polarizing filters that just never lie to you. I used to hear the phrase "Like a beacon in the Dark" and that's how a paperweight gets put up.

When I was in Shanghai, the workers made a lot of stuff that was never going to stand up in the lehr and they had an interesting solution to the problem. They would take a very large gather of glass and make it into a pancake on a table top. they would mush it out and indent it repeatedly with anything they had lying around until it was like choppy water in the wind. Then, the piece got stuck down to that like a big punty and they would put it away, standing up on the Patty. The next day, you could knock the work off of the patty very easily in the same way that you can clean up a punty. I thought it was pretty smart.
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Old 06-27-2017, 02:00 PM
Jordan Kube Jordan Kube is offline
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Here's a good read Art:

http://www.bullseyeglass.com/methods...eye-glass.html
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Old 06-28-2017, 07:36 AM
Steven O'Day Steven O'Day is offline
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Another benefit of the slump test is to calibrate your thermocouple. The readout is relative. Our kiln room is outside, I run a test in the winter and the summer and end up with about a 20 to 30 degree difference.
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Old 06-28-2017, 09:58 AM
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Indeed. It's hard to estimate how many times incompatibility is confused with poor annealing in studio glass.
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Old 06-28-2017, 06:36 PM
Art Freas Art Freas is offline
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Setting up to do the test next week.
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Old 06-28-2017, 06:38 PM
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Quote:
Originally Posted by Jordan Kube View Post
Very interesting. Thanks for the pointer.
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