The annealing and strain points of a glass are widely used production control parameters. Changes in the annealing and strain point temperatures are indications of chemistry changes.
According to ASTM C-336 the annealing point temperature is the temperature at which a uniform fiber of glass (0.65 mm in diameter) elongates under an applied weight at a rate of 0.14 millimeters per minute while cooling in a special furnace at the rate of 4°C per minute. According to ASTM C-336 the strain point temperature is determined by extrapolation of the annealing point data and is the temperature at which the elongation rate is 0.0316 times the elongation rate observed at the annealing point.
This test is performed in an LVDT extensometer system that is manufactured by Orton. The Orton Model ANS Series has been designed to automatically monitor the elongation of the sample fiber and calculate the annealing and strain points according to the ASTM C-336 method.
(Note: If forming a fiber is not desired, is impractical, or impossible, annealing and strain point temperatures can still be determined by the Beam Bending Viscometer method, ASTM C-598.)
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