ASTM C338

Standard Test Method for Softening Point of Glass

The softening point of a glass is defined as the temperature at which a round fiber, nominally 0.65 mm in diameter and 235 mm long, elongates under its own weight at a rate of 1 mm/min when the upper 100 mm of its length is heated at a rate of 5°C/min. A representative sample of 50 gm or more of flame workable glass in pieces a minimum of 5 mm in diameter is required. Fritted or ground samples must be remelted to obtain a piece large enough from which fibers can be drawn.

$250 per glass to 1000°C
$300 per glass for fiber preparation

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Significance and Use

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.


Scope

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 ± 1°C/min.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

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 and health practices and determine the applicability of regulatory limitations prior to use.

 

Copyright Notice

Extracted, with permission, from ASTM C338 Standard Test Method for Softening Point of Glass, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the standard may be purchased from ASTM International, phone 610-832-9555, e-mail: service@astm.org, website: www.astm.org.

 

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