Measurement of Viscosity of Glass by Viscous Compression ASTM C1351M

Measurement of Viscosity of Glass by Viscous Compression ASTM C1351M

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 the standard.


    ASTM C1351 test method is essential for measuring the viscosity of glasses 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 C1351 test method, theBackground 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. When an operational deflection rate is reached then starts recording the extensometer, time, and temperature to reduce data. Corrected the viscosity using the calibration curve by multiplying the viscosity by the fractional correction factor corresponding to that viscosity.

    Specimen Size : 

    The Specimen circular cylinder’s dimensions should be 6 mm to 12 mm diameter, and thickness should be 3 to 6 mm.


    The equation for calculating the viscosity is:

    ‌ŋ=2πMgh5/30V (dh/dt)(2πh3+V)(1+aT)‌


    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, and α is the glass mean coefficient of thermal expansion.


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