Just wondering if anyone has encountered this issue. I have well tempered core-lite kiln shelves (26" rounds) I use at the base of my kilns. Just recently we started do fast low fire firings to set underglaze. The last two fires we lost the bottom shelf (bottom shelf only). I'm attaching photos.
We've been using the same pack pattern for more than 2 years including a 3 post lift to the next shelf without issue.
None of the other kilns have manifested the issue, but this is the only one we've been running fast fires to ^05.
I'm thinking the speed of the fire has something to do with it, but that's only a theory.
We have run fast fires to the same ^05 on the same program in our 18" kiln with 18" full rounds without incident. We've been doing this for more than 2 years.
The first time it happened (yesterday), the shelf was older, about 3 years old. I would say approximately 200+ firings on it. My first suspicion was that some sort of fatigue had occurred. So, I replaced it with a kiln that was less than 6 months old and had less than 50 firings on it. On the very first firing the exact same fracture occurred.
No shelves above the bottom shelf fractured or cracked. All had the same post layout, and all posts were directly above one another. The first time it happened there were only 2 full shelves above the bottom shelf plus one lightly loaded (3rd shelf). The second time it happened there was one single fully loaded shelf above bottom shelf.
The types of pots, loads, and weights per shelve were identical in the two firings.
After the first shelf fractured I added four (1) 1.5" x 1.0" posts around the center of the bottom shelf for additional support.
If there are any clarifying questions I can respond here, thoughts and suggestions are welcome...