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ASTM C338-93(2019)

(Test Method)

Standard Test Method for Softening Point of Glass

Standard Test Method for Softening Point of Glass

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, 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.

General Information

Status
Published
Publication Date
31-Jul-2019
ICS
81.040.10 - Raw materials and raw glass
Technical Committee
C14 - Glass and Glass Products
Drafting Committee
C14.04 - Physical and Mechanical Properties
Current Stage
Ref Project

Relations

Replaces
ASTM C338-93(2013) - Standard Test Method for Softening Point of Glass
Effective Date
01-Aug-2019
Referred By
ASTM E438-92(2018) - Standard Specification for Glasses in Laboratory Apparatus
Effective Date
01-Aug-2019
Referred By
ASTM C1350M-96(2019) - Standard Test Method for Measurement of Viscosity of Glass Between Softening Point and Annealing Range (Approximately 10<sup>8</sup> Pa&#xb7;s to Approximately 10<sup>13</sup> Pa&#xb7;s) by Beam Bending (Metric)
Effective Date
01-Aug-2019
Referred By
ASTM C1351M-96(2022) - Standard Test Method for Measurement of Viscosity of Glass Between 10<sup>4</sup> Pa·s and 10<sup>8</sup> Pa·s by Viscous Compression of a Solid Right Cylinder [Metric]
Effective Date
01-Aug-2019
Referred By
ASTM F79-69(2019) - Standard Specification for Type 101 Sealing Glass
Effective Date
01-Aug-2019
Referred By
ASTM F105-72(2019) - Standard Specification for Type 58 Borosilicate Sealing Glass
Effective Date
01-Aug-2019
Referred By
ASTM C336-71(2020) - Standard Test Method for Annealing Point and Strain Point of Glass by Fiber Elongation
Effective Date
01-Aug-2019
Referred By
ASTM C162-05(2015) - Standard Terminology of<brk type="line"/> Glass and Glass Products
Effective Date
01-Aug-2019

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ASTM C338-93(2019) - Standard Test Method for Softening Point of Glass
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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.
Designation: C338 − 93 (Reapproved 2019)
Standard Test Method for
Softening Point of Glass
This standard is issued under the fixed designation C338; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope heating rate of the furnace, equipment for measuring the
temperature of the furnace, and equipment for measuring the
1.1 This test method covers the determination of the soft-
elongation rate of a fiber of glass suspended in the furnace.
ening point of a glass by determining the temperature at which
3.1.1 Furnace—The furnace shall conform in all essential
a round fiber of the glass, nominally 0.65 mm in diameter and
respects to the requirements shown in Fig. 1.
235mmlongwithspecifiedtolerances,elongatesunderitsown
3.1.2 Furnace Stand—A means shall be provided for sup-
weight at a rate of 1 mm/min when the upper 100 mm of its
porting the furnace so that the fiber hangs below it. This stand
length is heated in a specified furnace at the rate of 5 6
must be provided with a leveling device such as three screws.
1 °C⁄min.
The stand shown in Fig. 1 is convenient when used with either
1.2 The values stated in SI units are to be regarded as
a cathetometer or a telescope and scale.
standard. No other units of measurement are included in this
3.1.3 Heating Rate Controller—Suitable controls shall be
standard.
provided for maintaining the furnace heating rate at 5 6
1.3 This standard does not purport to address all of the
1 °C⁄min.
safety concerns, if any, associated with its use. It is the
NOTE 1—A continually adjustable transformer has proved effective for
responsibility of the user of this standard to establish appro-
controlling the heating rate.
priate safety, health, and environmental practices and deter-
3.1.4 Temperature-Measuring Equipment— The furnace
mine the applicability of regulatory limitations prior to use.
temperature shall be measured with a calibrated Type R or S
1.4 This international standard was developed in accor-
thermocouple and a calibrated potentiometer capable of mea-
dance with internationally recognized principles on standard-
suring the true temperature of the furnace within 60.2 °C. The
ization established in the Decision on Principles for the
cold junction shall be maintained at 0 °C by means of an ice
Development of International Standards, Guides and Recom-
bath.An alternative acceptable means of temperature measure-
mendations issued by the World Trade Organization Technical
ment is the use of a potentiometer to oppose the thermocouple
Barriers to Trade (TBT) Committee.
electromotive force. This potentiometer shall be set at a
standard setting for the type of glass being measured, and
2. Significance and Use
galvanometer deflection shall serve as a means of obtaining
2.1 This test method is useful to determine approximately
relative temperatures, the deflection of the galvanometer hav-
the temperature below which the glass behaves as a rigid solid
ing been calibrated. Also acceptable for temperature measure-
in glass-forming operations and for a control test to indicate
ment is a solid-state digital thermometer that is capable of the
changes in composition. It has been found useful for specifi-
accuracy specified.
cation acceptance and for providing information in research
3.1.5 Fiber-ElongationMeasurementEquipment—The fiber
and development work with glass.
elongation shall be measured by a device capable of measuring
the position of the end of the fiber within 0.02 mm throughout
3. Apparatus
the entire elongation period.
3.1 The apparatus for determining the softening point of
NOTE 2—Suitable devices that have proved effective for measuring the
glass shall consist essentially of an electrically heated resis-
elongation are cathetometers, projection magnifiers, and telescope and
tance furnace, a furnace stand, a device for controlling the
scale combinations.
3.1.6 Timer—A timing device with a least count and accu-
1 racy of 1 s shall be used.
This test method is under the jurisdiction of ASTM Committee C14 on Glass
and Glass Products and is the direct responsibility of Subcommittee C14.04 on
Physical and Mechanical Properties. 4. Preparation of Test Specimens
Current edition approved Aug. 1, 2019. Published August 2019. Originally
4.1 The fiber specimen used for the test shall meet the
approved in 1954. Last previous edition approved in 2013 as C338 – 93 (2013).
DOI: 10.1520/C0338-93R19. following requirements:
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C338 − 93 (2019)
FIG. 1 Details of Softening Point Furnace
C338 − 93 (2019)
4.1.1 It shall be round. 6.2 Again, cool and hold the furnace about 20 °C below the
4.1.2 It shall be smooth and shall contain no void spots or expected softening point and insert the fiber in the furnace by
foreign matter. placing the bead end in the furnace sample holder. Check the
4.1.3 Its average diameter shall be 0.65 6 0.10 mm and the fiber to be certain it is hanging free in the center of the furnace
maximum diameter shall not exceed the minimum diameter by and relevel the furnace if necessary. Standardize the potenti-
more than 0.02 mm over the entire length of the fiber.
...

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1.1 This practice covers the determination of the viscosity of glass above the softening point through the use of a platinum alloy spindle immersed in a crucible of molten glass. Spindle torque, developed by differential angular velocity between crucible and spindle, is measured and used to calculate viscosity. Generally, data are taken as a function of temperature to describe the viscosity curve for the glass, usually in the range from 1 to 106 Pa·s.  
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SIGNIFICANCE AND USE
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SCOPE
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4.1 The Knoop indentation hardness is one of many properties that is used to characterize glasses. Attempts have been made to relate Knoop indentation hardness to tensile strength, grinding speeds, and other hardness scales, but no generally accepted methods are available. Such conversions are limited in scope and should be used with caution, except for special cases where a reliable basis for the conversion has been obtained by comparison tests.
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1.1 This test method covers the determination of the Knoop indentation hardness of glass and the verification of Knoop indentation hardness testing machines using standard glasses.  
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3.1 Stress-optical coefficients are used in the determination of stress in glass. They are particularly useful in determining the magnitude of thermal residual stresses for annealing or pre-stressing (tempering) glass. As such, they can be important in specification acceptance.
SCOPE
1.1 This test method covers procedures for determining the stress-optical coefficient of glass, which is used in photoelastic analyses. In Procedure A the optical retardation is determined for a glass fiber subjected to uniaxial tension. In Procedure B the optical retardation is determined for a beam of glass of rectangular cross section when subjected to four-point bending. In Procedure C, the optical retardation is measured for a beam of glass of rectangular cross-section when subjected to uniaxial compression.  
1.2 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.  
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4.1 This test method provides data useful for (1) estimating stress release, (2) the development of proper annealing schedules, and (3) estimating setting points for seals. Accordingly, its usage is widespread throughout manufacturing, research, and development. It can be utilized for specification acceptance.
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1.1 This test method covers the determination of the annealing point and the strain point of a glass by measuring the viscous elongation rate of a fiber of the glass under prescribed condition.  
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