Technology · Thermal Conductivity (λ)
Thermal conductivity is the rate at which heat passes through the board. For calcium silicate it is governed mainly by density and mean temperature: the high-density grades trade a little conductivity for strength, while lower-density grades conduct less. Every value below is stated at 800°C (1472°F) mean temperature, in both metric and US units.
Definition
Thermal conductivity (symbol λ, also written k) measures how readily a material transmits heat. A lower λ means the board resists heat flow more, so less energy is lost through a furnace wall or back-up lining. Calcium silicate λ rises with mean temperature, so a figure only has meaning together with the temperature it was measured at — here, 800°C.
| Quantity | Metric | US |
|---|---|---|
| Thermal conductivity (λ) | W/m·K | BTU·in/hr·ft²·°F |
| Unit conversion | 1 W/m·K | ≈ 6.93 BTU·in/hr·ft²·°F |
| Reference mean temp | 800°C | 1472°F |
Values are for dry boards at 800°C mean temperature. Conductivity increases with temperature and with absorbed moisture.
Data
High-density structural grades at 800°C (1472°F) mean temperature, in dual units. λ rises with density — the 800 grade is lowest, the 1020 grade highest.
| Grade | Density | λ @ 800°C (W/m·K) | λ @ 800°C (BTU·in/hr·ft²·°F) | Positioning |
|---|---|---|---|---|
| 800N-17 Carbon-Fibre | 800 kg/m³51.2 lb/ft³ | ≤ 0.14 | ≤ 0.97 | Lowest λ |
| 850N-14 Structural | 850 kg/m³53.1 lb/ft³ | ≤ 0.16 | ≤ 1.11 | Structural balanced |
| 980Thermal Shock | 980 kg/m³61.2 lb/ft³ | ≤ 0.22 | ≤ 1.53 | Thermal-shock resistance |
| 1020Molten Aluminum | 1020 kg/m³63.7 lb/ft³ | ≤ 0.23 | ≤ 1.59 | Molten aluminum contact |
| 1200Heavy-Duty Strength | 1200 kg/m³74.9 lb/ft³ | On request | On request | Maximum strength |
All λ values at 800°C (1472°F) mean temperature, dry boards; confirmed on request. Lower-density insulation grades — 250 · 300 · 650 kg/m³ — conduct less heat than the structural grades; datasheet λ available on request.
Factors
λ rises with density: 800 reads ≤ 0.14 W/m·K, 1020 reads ≤ 0.23 W/m·K at the same 800°C.
Conductivity increases with mean temperature. Every value here is stated at 800°C (1472°F).
Absorbed moisture raises λ until the board is dried out. Figures are for dry boards.
Reinforcement and binder shift the result — the 800 grade uses N-17 carbon-fibre reinforcement.
Comparison
Same 800°C mean temperature — λ spreads with density.
Applications
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