設計・制御
Rapid Heat (Stage C)
Japanese: 急速加熱（C段階）
Stage 3 of the firing program. Rapid heating to quickly pass through the risk zone for glass devitrification (600–750°C). The temperature is rapidly raised to the maximum temperature to protect the glass from devitrification.
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Rapid Heating (Stage C, Rapid Heat) is the third stage of the eight-stage firing program; it is a rapid temperature-rise phase designed to quickly pass through the decarburization risk zone (600–750°C) (§8.1). This step directly implements the strategy for minimizing the transit time through “Zone III (No Contamination)” in Reo Chikaoka’s (2012, 2021) four-zone control framework, thereby minimizing the dwell time in the temperature range (660–750°C) where the precipitation rate of crystalline phases such as devitrite is high. In η-T-t trajectory terminology, this corresponds to the “late heat-up phase.”
The rate of rapid heating depends on the furnace’s performance, but with the standard settings for Bullseye COE90, the temperature rises toward the maximum at a rate of 500°C/h or higher (in some cases, AFAP). Although there may be instances where the temperature is held for less than 30 minutes in the bubble squeeze zone (660–680°C) (e.g., §12.1 pot melt), the standard fusing process typically passes through this zone without stopping. For the rapid heating in Stage C to function effectively, it is a prerequisite that temperature equalization within the furnace be completed during Stage B. If Stage C is entered before Stage B is sufficiently complete, there is a risk of localized thermal shock in the glass due to temperature differences within the furnace.
Related Concepts
Temperature Equalization (Stage B) (firing-stage-b) · Peak Temperature Hold (Stage D) (firing-stage-d) ・Rapid cooling (Stage E) (firing-stage-e), the bubble squeeze zone (bubble-squeeze-zone), and surface crystallization (surface-crystallization)—understand the temperature design required to prevent loss of transparency.
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.