Piece Broke While Slumping

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Ross
Posts: 52
Joined: Sun Mar 09, 2003 6:01 pm
Location: Charleston, SC

Piece Broke While Slumping

Post by Ross »

Does anyone have any ideas as to why this piece broke during the slump. It's Spectrum, 16" in dia, about 3/8" thick in middle and 1/4 on rim.
Schedule:
300-1150-10
300-1225-15
normal spectrum anneal
And no, I didn't peek. I opened the kiln at 68 degrees. I've done this schedule with Spectrum combing numerous times with no problem.

http://community.webshots.com/scripts/e ... ity=blGJoZ

Any ideas?
Image Ross
BillBrach
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Joined: Fri Apr 11, 2003 1:06 pm
Location: Gainesville, FL

Post by BillBrach »

Going from 300 to 1150 degrees in 10 minutes ??

If this is so, this is why it broke.

I'm guessing that this is WAY too fast for that thickness and diameter.

EDIT: Duh !! 300 DPH !!
Last edited by BillBrach on Wed Mar 10, 2004 2:33 pm, edited 2 times in total.
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charlie
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Post by charlie »

BillBrach wrote:300 to 1150 degrees in 10 minutes ??

If this is so, this is why it broke.

WAY, WAY too fast for that thickness.
300 dph to 1150, hold 10 minutes.

the answer depends upon whether the broken edges are sharp or rounded. if sharp, bad annealing. if rounded, 300 dph is too fast.
Lisa Allen
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Post by Lisa Allen »

Any time you have differing thicknesses in a piece, you have to be much more conservative. Also with a consistant 3/8th" thickness, I would have gone up much more slowly, probably 150dph to 1150. But as Charlie said, the nature of the crack will tell you more. If they are rounded then it broke on the way up from thermal shock (too fast heating to slump temp). If the cracks are sharp, then it broke from poor annealing. You don't mention your annealing schedule, so it is hard to comment on whether that is potentially the problem.

Lisa
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Ross
Posts: 52
Joined: Sun Mar 09, 2003 6:01 pm
Location: Charleston, SC

Post by Ross »

The edges are very sharp! I can't remember the annealing schedule because it's pulgged in and I use it over and over unless it's an extremely deep piece. When I get home, I'll check it out and post it on thi sthread.

I suppose it was the annealing. That's what I sort of assumed!
Image Ross
Cynthia

Post by Cynthia »

Ross wrote:The edges are very sharp! I can't remember the annealing schedule because it's pulgged in and I use it over and over unless it's an extremely deep piece. When I get home, I'll check it out and post it on thi sthread.

I suppose it was the annealing. That's what I sort of assumed!
I can't pull up your picture, it says I am not the owner of the album...so without seeing the piece...I have one more question. are the breaks together...the seams of the breaks, or is there some gapping and variation of width between the breaks. If it broke before it bent, it would probably show some gaps. If it broke after it bent, it will be all together without the gaps left from bending.

Even in a bend cycle, the edges would soften a touch from the heat, but not much. If they are very crispy sharp and seams are together, you are probably right to think that the break was from being improperly annealed. AT 1225, there won't be much softening though, so look closely at those edges.

Your ramp rate up was too fast for something 3/8" thick (as has been pointed out), and particularly if you have a variation of thicknesses throughout the piece. Being on a mold also puts the glass closer to the heating elements...so slowing it down would be helpful.

I would anneal a piece that thick for 30 minutes to allow the temp to equalize throughout the piece at the anneal point, then ramp down at 50 dph to just below your lower strain point....Others might offer a more conservative anneal...
Tim Swann
Posts: 83
Joined: Mon Mar 10, 2003 9:47 pm
Location: San Diego, CA

Post by Tim Swann »

I suspect that the piece broke on the ramp up and not in the annealing phase. A break in the ramp up into a slump will leave the edges looking sharp and well defined until you look very close. If it broke before the peak temperature the edge will look like it had been barely fire polished. With a piece having that much thickness variation I slow down to about 50DPH on the ramp up and down. Better safe than sorry.

Tim
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