Q: Annealing around trapped air
Posted: Fri Dec 14, 2007 1:51 am
Hello, first post and I'm pulling out a big pounderous question...
I'm working with half inch plate and am trapping pockets of air purposely.
The air entrapment is several cubic inches easy. In a couple of instances I can ascertain that the air is completely trapped before annealling. I'm computer ramping the anneal and other than having a inch thick kiln shelf under the piece am pretty sure I hit all the necessary ramp points coming down.
Here's the problem...I'm having stress problems, the glass doesn't show that it is under stress but a couple of months after sitting around a couple have split into two, not along the seams but straight across the whole piece like a stress fracture (but then those split peices didn't show having any other stress???
Could the air entrapment be the problem. Perhaps triggered by a change of atmospheric conditions. I'm familiar with pumping down glass, but not able to be certain that soda-lime glass would take the pressure of a negative atmosphere. I was thinking that the pressure of the air trapped under the contracting glass wouldn't be all that great, but would it throw off the annealing? Thanks...Any feedback would be helpful.
I'm working with half inch plate and am trapping pockets of air purposely.
The air entrapment is several cubic inches easy. In a couple of instances I can ascertain that the air is completely trapped before annealling. I'm computer ramping the anneal and other than having a inch thick kiln shelf under the piece am pretty sure I hit all the necessary ramp points coming down.
Here's the problem...I'm having stress problems, the glass doesn't show that it is under stress but a couple of months after sitting around a couple have split into two, not along the seams but straight across the whole piece like a stress fracture (but then those split peices didn't show having any other stress???
Could the air entrapment be the problem. Perhaps triggered by a change of atmospheric conditions. I'm familiar with pumping down glass, but not able to be certain that soda-lime glass would take the pressure of a negative atmosphere. I was thinking that the pressure of the air trapped under the contracting glass wouldn't be all that great, but would it throw off the annealing? Thanks...Any feedback would be helpful.