Dear colleagues, the protective hot plate method is the core method for testing the thermal conductivity of insulation materials. The core logic is to "construct one-dimensional heat flux+accurately control steady state+quantify parameters", which conforms to the GB/T 10294-2008 standard. The specific operation is divided into six steps:
The first step is sample pretreatment and preparation. Place the sample in an environment of 23 ± 2 ℃ and 50 ± 5% RH for ≥ 72 hours according to the standard to balance the moisture content. Processing size matching measurement hot plate, commonly used 100mm × 100mm or 300mm × 300mm, thickness 10-50mm, surface roughness ≤ 0.8 μ m. Measure the thickness three times with a 0.01mm precision caliper and take the average value to ensure that the sample is flat and not tilted.
The second step is instrument calibration and parameter setting. Calibration before testing: The temperature difference between the measuring hot plate and the protective hot plate is ≤ 0.1 ℃, the accuracy of the temperature sensor is ± 0.05 ℃, and the full-scale error of the power sensor is ≤ ± 1%. Set the temperature of the hot plate (50 ℃, 70 ℃, or 85 ℃), with the cold plate being 20-50 ℃ lower than the hot plate. Enter basic data such as sample thickness and effective heat transfer area.
Step three, sample installation and cavity sealing. Place the sample in the center between the measuring hot plate and the cold plate, and apply a thin layer of thermal paste with a thermal conductivity coefficient of ≥ 1.5W/(m · K) (thickness ≤ 0.1mm) when the fit is not tight. Low thermal conductivity materials (λ ≤ 0.03W/(m · K)) need to be evacuated to 10 ⁻³~10 ⁻⁴ Pa to eliminate air convection interference, and then the chamber should be sealed.
Step four, start temperature control and heat flow stabilization. Turn on the heating and cooling system, measure the constant temperature of the hot plate, synchronize the temperature control of the protective hot plate to compensate for lateral heat dissipation, and force the heat to pass vertically through the sample - this is the core advantage of this method, avoiding errors in heat dissipation and patiently waiting for thermal steady state.
Step five, thermal steady state determination and parameter acquisition. According to the standard judgment: Within 30 consecutive minutes, the fluctuation of heating power is ≤± 1%, the fluctuation of temperature difference on both sides of the sample is ≤± 0.1 ℃, and the temperature difference between the two hot plates is ≤ 0.1 ℃. Automatically collect three sets of data after steady state: heating power (Q), temperature difference (Δ T), sample thickness (d), and heat transfer area (A).
Step six, data calculation and report output. According to Fourier's law of heat conduction, calculate automatically according to λ=Q × d/(A × Δ T), and take the average of 3 sets as the final result (with 4 significant digits retained). The report should include pre-processing records, vacuum degree data, steady-state curves, and standard numbers to ensure data compliance and traceability.