設計・制御
anneal hold time
Japanese: 徐冷キープ時間
The time spent holding at the slow-cooling point. The larger or thicker the piece, the longer this time should be.
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The anneal hold time is the duration of the process during which the glass is held at a temperature near its annealing point for a set period. This time is necessary to relieve residual stress caused by temperature differences within the glass; the thicker the piece and the greater the number of glass sheets, the longer the hold time required. Insufficient hold time can lead to sudden cracking at a later date (delayed cracking).
For COE90 glass, the annealing point is around 482°C. As a general guideline, it is recommended to hold the temperature for 30 to 60 minutes for 6mm pieces and for at least 2 hours for pieces 12mm or thicker. However, since this depends on the furnace’s temperature uniformity and the shape of the piece, it is important to start with conservative (longer) settings when trying these conditions for the first time and gradually optimize them.
Related Concepts
Below the strain point, there is no permanent change in stress, and stress is most effectively relieved near the annealing point. Transmitted light inspection using a polarizing filter is an effective method for detecting residual stress.
This entry is written in Japanese by Rei Chikaoka and translated for readers outside Japan. If something reads oddly, the original is the source of truth.