ASTM C177 is a test that describes the steady-state heat flux measurement using a guarded-hot-plate apparatus under spec ified test conditions. The test provides thermal transmission properties based on test measurements. In contrast, ASTM C518 is the measurement of steady-state thermal transmission properties by a heat flow metre apparatus.... Read More

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    The standard method ASTM C177 describes the measurement of steady-state heat flux of flat, and homogeneous specimens, that have “low” conductivity, at specified test conditions. Test measurement is conducted with a guarded-hot-plate apparatus. Data from the measurement can be used to specify the thermal transmission properties of the specimen. However, the test method does not specify the operation of the apparatus. Precision and accuracy of test results depends on the technician’s knowledge of thermal measurements and testing practices of heat transfer theory relating to thermal insulation materials and systems. Alternatively, ASTM C518 is a comparative test method which utilises a heat flow metre apparatus. This method is advantageous for the design of electronic products. Results of ASTM C177 are more recommended compared to ASTM C518 if non-identical results occur.

    Test Procedure:

    ASTM C177 procedures involve specimens with known mass and dimension installed to the guarded-hot-plate apparatus and with adjustment of test conditions. The start time and date of the test should be recorded. Thermal steady state must be achieved for the test. Prior to test termination the pressure of the chamber should be recorded. After testing, the characteristics and conditions of the system and specimens should not change and should be confirmed. For ASTM C518, the specimens are placed in between heating and cooling plates and a heat flow metre is used.

    Video 01: ASTM C177 Thermal Conductivity

    Test Specimen:

    Dimensions of the flat and homogeneous specimens for ASTM C177 are supposed to cover the whole guard area; details are described in section 7.1. Specimens of ASTM C518 should have a parallel surface with a size of 150-300 mm2.


    In ASTM C177 testing, the heat flow, metered section, heat flux and density are calculated. In ASTM C518, thermal transmittance and thermal conductivity is calculated. 


    The standard method ASTM C177 and ASTM C518 describes the steady-state heat flux measurement of flat materials with low conductivity using a guarded-hot-plate apparatus under certain test conditions and measurement by a heat flow metre apparatus, respectively. 


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