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-   -   Annealing issue (http://talk.craftweb.com/showthread.php?t=12523)

Mike Kaplan 01-22-2020 09:07 AM

Annealing issue
 
I had a bunch of products in my inhaler and it was cooled down to room temperature when someone in my shop turned it back on by accident and it went up to about 800 before they shut it down.
When it cooled down the next day one of the paperweights has split in half and everything else in there looks fine.
Next time would it be safe to bring it all the way up to annealing temperature and leave it there for the typical amount of time and then bring it down so that it anneals properly again or would that still introduce stress just because it went up so fast(one hour usually from room temp to 950f)
What is the safest way?

Shawn Everette 01-22-2020 10:28 AM

Yes, I would want to take all the way back up and reanneal. Unless you peeked, it's hard to say when that paperweight broke, on the way up or down, but I'm guessing up. If you only went up to 800* on a fast ramp, then you've introduced stress into everything else, just maybe not enough to break right now.

If I'm taking medium stuff back up I'm usually on a 200* ramp to anneal, then run the program per usual once I'm done. If it's real thick then a 150* ramp. Glass is fairly forgiving on the way up, just maybe not 950* an hour forgiving.

Richard Huntrods 01-22-2020 04:23 PM

I dunno. I think once it's shot up to 800, whatever has cracked has cracked. And now it's at 800, take it back up to 'soak' temp (maybe not so fast) and then give it extra soak (double or maybe triple time) then run the ramp-down annealing shedule as usual.

Once you're hot, you're hot. Once you are at the soak temp, a long soak should relieve the strain induced by the fast temp increase. Once strain is removed, regular annealing should be all that's necessary.

Your paperweight broke because it's probably the thickest piece in the bunch.

Pete often observes that thick things like paperweights are often never properly annealed in a 'normal' annealing schedule.

(I figger if they bounce when cold from 4ft off a concrete floor they are good enough for my purposes). :-D

Pete VanderLaan 01-22-2020 04:51 PM

Inhaler?Nice visual.

Mike Kaplan 01-22-2020 05:50 PM

Lol. Thanks for that Pete. I need to laugh at this point

Art Freas 01-22-2020 07:59 PM

If 800 is above the strain point the stress introduced would be permanent until you reanneal. If 800 is significantly below the strain point the stress would be thermal only and thus would go away when it cooled down. My personal choice would be to reanneal with a really slow ramp up. YMMV though.
Art

Greg Vriethoff 01-23-2020 06:34 AM

If I'm not mistaken, you have to increase the anneal soak to remove strain that has been introduced past the strain point (I think Richard already addressed this).

There are far too many variables here, but my hunch is that the breakage that occurred was due to thermal shock. You don't say how long it was at 800 before shutting it down. If the box was still ramping-up, the glass (especially the thick paperweights) probably didn't get much above the actual strain point.

I know if Ed were here he'd set me straight on this.

Pete VanderLaan 01-23-2020 01:06 PM

No, Ed would get mad at me for quoting Frank Wooley on annealing.

I tend to think that work can be brought up fairly quickly from Room temp to the upper annealing range. The reason I caution going very slowly is when the issue is of a shutdown in a crucible full of glass. At that point you are dealing with two very different animals.

In the glass, the critical issue is simply heating uniformly- harder to do with weights, particularly if they have other inherent strains built into them, like colorful inclusions. If I was bringing a weight back up that had already been in a crash, I would be inclined to take five hours getting to 700F and then scoot up to the upper annealing range ( remember it's a range) and holding there for two hours before beginning a downward ramp. The easiest way to check whether this is sufficient would be a witness weight, always made in clear. It will tell you the story.

The lower you attempt to anneal in the range, the longer it will take to anneal.


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