温度・粘度
Pot Melt Zone
Japanese: ポットメルト域
The temperature range of 810–820°C. The temperature range at which glass flows out through the hole at the bottom of the crucible (pot). According to Hagen–Poiseuille’s law, the flow rate is proportional to the fourth power of the hole diameter.
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The pot melt zone is the temperature range of 810–820°C (820°C for the Bullseye system, 810°C for the Oceanside system), and refers to the temperature range at which glass flows out through a hole drilled in the bottom of the crucible (pot) during the pot-melt technique (§12.1). In terms of viscosity, this corresponds to log η 4–5 (Pa·s) and is set as the peak temperature for the soak phase. In this temperature range, the glass flows down through the hole under the force of gravity, forming a freely shaped sheet of mixed-color glass on the shelf.
Flow behavior in the pot-melt region is described by Hagen-Poiseuille’s law (§12.2), where the volumetric flow rate Q is given by Q ∝ r⁴/η(T) (where r is the pot pore diameter and η is the viscosity). The dependence on the fourth power of the pore diameter is dominant; doubling the pore diameter increases the flow rate 16-fold. An empirical formula for the peak retention time is Q = max(20, weight of contents [g]/100 × 6) minutes (§12.4). The standard firing program is designed to include a hold in the bubble squeeze zone (660–680°C), and the design of the temperature profile leading up to this range is critical for achieving both bubble removal and prevention of devitrification.
Related Concepts
Understand the design of temperature profiles for the pot-melt method in conjunction with the flow-cast zone, bubble-squeeze zone, pot-melt, and η-T-t framework.
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.