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ASTM C338-24

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Standard Test Method for Softening Point of Glass

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1.1 This test method covers the determination of the softening point of a glass by determining the temperature at which a round fiber of the glass, nominally 0.65 mm in diameter and 235 mm long with specified tolerances, elongates under its own weight at a rate of 1 mm/min when the upper 100 mm of its length is heated in a specified furnace at the rate of 5 °C/min ± 1 °C/min.2

1.2 The values stated in SI units are to be regarded as standard. The values given in parenthesis are for information only.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.


2.1 This test method is useful to determine approximately the temperature below which the glass behaves as a rigid solid in glass-forming operations and for a control test to indicate changes in composition. It has been found useful for specification acceptance and for providing information in research and development work with glass.

2.2 The softening point corresponds to a viscosity ~106.5 – 107.0 Pa∙s. The exact viscosity at the softening point depends on the density of the glass. Sometimes, a viscosity of 106.6 Pa∙s for soda-lime silica glasses is used.3

SDO ASTM: ASTM International
Document Number C338
Publication Date Aug. 1, 2024
Language en - English
Page Count 3
Revision Level 24
Supercedes
Committee C14.04
Publish Date Document Id Type View
Aug. 1, 2024 C0338-24 Revision
Aug. 1, 2019 C0338-93R19 Reaffirmation
Oct. 1, 2013 C0338-93R13 Reaffirmation
April 1, 2008 C0338-93R08 Reaffirmation
Oct. 10, 1998 C0338-93R98 Reaffirmation
Nov. 15, 1993 C0338-93R03 Reaffirmation