ASTM C336 Fiber Elongation to check Annealing and Strain Point of Glass

ASTM C336 is used to measure the viscosity of the glass and provides valuable data about the strain points, annealing points, and setting thresholds for seals. It was proposed that the viscosities at the strain point and annealing point should be 1014.50 and 1013.00 poise respectively at 4°C temperature. Viscosity is expressed in poise.

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    By calculating the viscous elongation rate of the fiber of the given glass, using ASTM C336, the annealing and strain points of the glass can be determined. ASTM C336 provides information to develop an appropriate annealing schedule, stress release estimation, and estimation of setting points for seals.

    Test Procedure:

    ASTM C336 test takes place in a specialized furnace made up of a copper core with a glass fiber attachment. After the formation of glass at a high temperature, it is cooled carefully, typically at 4°C. The size and diameter of the given sample are measured. The following factors are evaluated while assessing the strain and annealing points; choice of glass, optical lever adjustment, temperature correction, fiber support, cooling rate, sample length, expansion, and viscosity.

    Specimen Size : 

    For ASTM C336 testing, the specimen size can be up to 6 cm in length.


    The viscosities are calculated by using the following formula



    η is the viscosity (poise), 
    L denotes effective fiber length (cm), 
    mg represents suspended force (dynes), 
    d denotes fiber diameter (cm) and e is the elongation rate (cm/sec).


    ASTM C336 is used to measure the viscosity of the glass and provides valuable data about the strain points, annealing points, and setting thresholds for seals. 1014.50


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