設計・制御
Anneal Soak (Stage F)
Japanese: アニールソーク（F段階）
Stage 6 of the firing program—the most critical stage. Hold at the slow-cooling point (482°C for COE 90) to relieve internal stress in the glass. The holding time is proportional to the square of the thickness.
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The Anneal Soak (Stage F) is the sixth stage of the eight-stage firing program and is considered the most critical stage (§8.1). By holding the glass at the slow-cooling point (482°C) of Bullseye COE90 for a set period of time, the internal stresses caused by temperature gradients within the glass during rapid cooling (Stage E) are relieved and eliminated through viscous flow. According to Narayanaswamy’s (1971) structural relaxation model, ensuring sufficient time during this hold stage is the only means of reducing permanent strain to nearly zero. In η-T-t trajectory terminology, this corresponds to the first half of the “anneal” phase.
The holding time for Stage F is calculated based on the Adams-Williamson rule (q ∝ 1/thickness²); according to the Bullseye Annealing Thick Slabs Chart, the allowable rate is 83°C/h for a 6mm slab, 27°C/h for 19 mm, and 4°C/h for 50 mm. The soak time is at least 1 hour (Bullseye COE90 standard, thin plates), but for thick plates (19 mm or more), several hours to several days may be required. If the F stage is insufficient, high retardation values will be detected in polarizer measurements, increasing the risk of long-term damage (§18.4). Rei Chikaoka (2021) adopts “cooling rate of 482°C for 1 hour” as a fixed value in the standard program.
Related Concepts
Rapid Cooling (Stage E) (firing-stage-e) · Annealing Cooling (Stage G) (firing-stage-g) · annealing zone (annealing-zone), polariscope test (polariscope-test), and retardation (retardation) to gain a comprehensive understanding of the overall design of the slow-cooling process.
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.