温度・粘度
Block/Press Zone
Japanese: ブロック・プレス域
The 800–850°C temperature range. This high-temperature range is used for fusing thick glass sheets and for embossed forming. Block fusing (800–850°C) and press fusing (800°C) are performed in this range.
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The Block/Press Zone is a high-temperature range between 800 and 850°C used for the complete fusion of thick glass (block fusing) and for press fusing (§8.2). In terms of viscosity, this corresponds to a log η of 4–5 (Pa·s), a state in which the glass flows completely and can fuse into a single mass. At temperatures even higher than the full-fusing range (approximately 780°C), the glass becomes more fluid, allowing thick sheet glass—stacked nine layers or more—to melt and fuse together.
In block fusing (800–850°C), sheet glass secured within a ceramic fiber board frame is fused together into a solid block. In press fusing (800°C), release paper and a shelf as a weight are placed on top of glass arranged in parallel to fuse it into a single layer. While firing in this high-temperature range is fundamental to both processes, careful management of the dwell time in the devitrification range (600–750°C) and extended annealing times suitable for thick pieces are essential. Additionally, caution is required when using lead-based glass at temperatures above 800°C, as this increases the risk of sulfidation and blackening, as well as Pb⁰ precipitation.
Related Concepts
Understand the characteristics of the high-temperature fusing zone, including the full-fusing zone, flow-cast zone, block fusing, press fusing, and plate-count effect.
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.