Sounds like the cooling rate is too high. Possible issues we've noticed over the years, especially when large/full arch frames are involved:
1) Insufficient drying times for larger structures (unlikely)
2) Heat rate too fast for larger structures / number of structures (likely)
3) Hold time insufficient for larger structures / number of structures (likely)
4) Cool rate too fast for larger structures / number of structures (very likely)
5) Stain and glaze cycle needs to be lengthened for both heat rate and cool rate (very likely)
6) Porcelain layering cycles also need to be adjusted for heat and cool rates, and longer hold time
7) Large structures also require a stabilizer to minimize warping.
Hey Everyone, so ive read through a bunch of threads on cracks in your zirconia after sintering. After reading honestly I think Im more in the dark than before. Ive read it can be my milling machine, sintering beads, oven calibration, drying time and manner, ETC....... We have been milling for over a year with only minor issues. 2 days ago i had a #8 on a 8-9 splint crack right where the spruee was then a singe full contour crack on a cusp now this morning I had a 8-11 framework crack where the connector met the coping. We have a Roland DWX-51D, Brand New Burs, No Recent Power Outtages or Errors. We have a WhipMix Infinity ZR oven 6 months old. I use a toaster oven to dry 300 degrees for 20 min. We use Whipmix Vericore Zirconia. Any s??? My beads are 7 months old and im using ZirkonZahn Colour Liquid Prettau Aquarell Please help..