3. Thermal Properties

Thermal properties are extremely important for the annealing, heat treatment, and coating of optical glasses. Our technical data sheets include the strain point, annealing point, softening point, transformation point, yield point, and thermal conductivity. The linear coefficient of thermal expansion is given for two temperature ranges.

3.1 Strain Point (StP)

The strain point corresponds to the lowest temperature in the annealing range at which viscous flow of glass will not occur. Viscosity of the glass is 10^14.5 dPa·s {poise} at this temperature. The strain point is measured in accordance with the Fibre Elongation Method prescribed in JIS-R3103 and ASTM-C336.

3.2 Annealing Point (AP)

The annealing point corresponds to the maximum temperature in the annealing range at which the internal strain of glass will be substantially eliminated. Viscosity of the glass is 10¹³ dPa·s {poise} at this temperature. The annealing point is measured in accordance with the Fibre Elongation Method prescribed in ASTM-C336.