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Thermal Properties

Miele
Foto: Miele
Its low thermal expansion, its high thermal shock resistance and its ability to withstand temperatures up to 450 °C for long periods make BOROFLOAT® 33 a good choice for applications which call for good temperature stability (e.g. internal panels in pyrolytic self-cleaning ovens and cover plates for high-power floodlights).
Coefficient of Linear Thermal Expansion
α (20 - 300 °C) 3.25 x 10-6 K-1
(to ISO 7991)


Specific Thermal Capacity

cp (20 - 100 °C) 0.83 KJ x (kg x K)-1


Specific Thermal Conductivity
λ (90 °C) 1.2 W x (m x K)-1


Maximum Operating Temperature
For short-term usage δ max (< 10 h) 500 °C
For long-term usage δmax (≥ 10 h) 450 °C


The maximum temperatures in use indicated apply only if the following RTG and RTS values are observed at the same time.

Resistance to Thermal Gradients (ability to withstand a specific temperature difference between the hot center and the cold edges of a panel)
Test method: Test panels measuring approx. 20 x 20 cm2 are heated up in the center area to a specified temperature while the panel edge is maintained at a constant temperature. The RTG value is quoted as the temperature difference between the hot center of the panel and the cold edge area. Only 5 % of the test pieces are permitted to fail as a result of breakage due to thermal stress. To simulate extreme wear and tear in use the panels are abraded with SIC 40 grade sandpaper before the test.
RTG 1 - 100 hours 90 K
> 100 hours 80 K


Resistance to Thermal Shock (ability to withstand a sudden temperature decrease)
Test method: Test panels measuring approx. 20 x 20 cm2 are heated up in an oven and then cooled down with 50 ml of cold water (room temperature) in the center area. The RTS value is quoted as the temperature difference between the hot glass and the cold water. Only 5 % of the test pieces are permitted to fail as a result of breakage. To simulate the surface condition in practical use, the panels are treated with SIC 220 grade sandpaper before the test.
RTS for glass thickness     ≤ 3.8 mm 175 K
5.0 - 5.5 mm 160 K
6.5 - 15.0 mm 150 K
    > 15.0 mm 125 K


Thermal Properties of BOROFLOAT® 33: diagrams:



thermal_expa.pdf Thermal Expansion
cryogenic_temperature.pdf Expansion Behavior in Lowest Temperature Range
specific_heat.pdf Specific Thermal Capacity
thermal_conduct.pdf Specific Thermal Conductivity
Viscosity of Borosilicate Glasses

Working Point 104    dPas 1270 °C
Softening Point 107.6  dPas 820 °C
Annealing Point 1013  dPas 560 °C
Strain Point) 1014.5dPas 518 °C
Transformation Temperature (Tg) 525 °C


viscosity.pdf Viscosity of BOROFLOAT® 33 diagram:
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