ASTM C1351M Measurement of Viscosity of Glass by Viscous Compression

ASTM C1351 measures the viscosity of glass from 104 Pa·s to 108 Pa·s by determining the rate of viscous compression of a little, solid cylinder. The values in SI units are to be considered as standard.... Read More

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    ASTM C1351 test method is essential for measuring the viscosity of glass between the range within which rotational viscometry and the field in which beam bending viscometry are helpful. It can be used to calculate the temperature/viscosity curve near the softening point. ASTM C1351 is useful for offering information about the behavior of glass.

    Test Procedure:

    In the ASTM C1351M test method, the background deflection curve is generated against temperature by measuring the upper loading plate in contact with the lower support plate. Then, the thickness change of the specimen is calculated by algebraic subtraction of this background curve from the measured angle. The extensometer, time, and temperature data are recorded when an operational deflection rate is reached. The viscosity is corrected by using the calibration curve. This is done by multiplying the viscosity by the fractional correction factor corresponding to that viscosity.

    Video 01: Viscosity measurement using a lab viscometer

    Specimen Size : 

    For ASTM C1351M, the specimen’s (circular cylinder) diameter should be between 6 mm to 12 mm, and thickness should be between 3 mm to 6 mm.


    The equation for calculating the viscosity in ASTM C1351M testing is:


    Ŋ is viscosity, Pa·s 

    M is the applied load 

    dh/dt are the compression rates 

    g is the acceleration of gravity 

    h is the specimen thickness at time t 

    V is the specimen volume 

    α is the glass mean coefficient of thermal expansion


    ASTM C1351 measures the viscosity of glass from 104 Pa·s to 108 Pa·s by determining the rate of viscous compression of a little, solid cylinder.


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