Standard Test Method for Softening Point of Glass

SIGNIFICANCE AND USE
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 This standard does not purport to address all of the safety problems, 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 .

General Information

Status
Historical
Publication Date
14-Nov-1993
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ASTM C338-93(2003) - Standard Test Method for Softening Point of Glass
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:C338–93 (Reapproved 2003)
Standard Test Method for
Softening Point of Glass
This standard is issued under the fixed designation C 338; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3.1.3 Heating Rate Controller—Suitable controls shall be
provided for maintaining the furnace heating rate at 5 6
1.1 This test method covers the determination of the soft-
1°C/min.
ening point of a glass by determining the temperature at which
a round fiber of the glass, nominally 0.65 mm in diameter and
NOTE 1—A continually adjustable transformer has proved effective for
235mmlongwithspecifiedtolerances,elongatesunderitsown controlling the heating rate.
weight at a rate of 1 mm/min when the upper 100 mm of its
3.1.4 Temperature-Measuring Equipment—The furnace
length is heated in a specified furnace at the rate of 5 6
temperature shall be measured with a calibrated Type R or S
1°C/min.
thermocouple and a calibrated potentiometer capable of mea-
1.2 This standard does not purport to address all of the
suring the true temperature of the furnace within 60.2°C. The
safety concerns, if any, associated with its use. It is the
cold junction shall be maintained at 0°C by means of an ice
responsibility of the user of this standard to establish appro-
bath.An alternative acceptable means of temperature measure-
priate safety and health practices and determine the applica-
ment is the use of a potentiometer to oppose the thermocouple
bility of regulatory limitations prior to use.
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-Elongation Measurement Equipment—The fi-
and development work with glass.
ber elongation shall be measured by a device capable of
measuring the position of the end of the fiber within 0.02 mm
3. Apparatus
throughout 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.
heating rate of the furnace, equipment for measuring the
3.1.6 Timer—A timing device with a least count and accu-
temperature of the furnace, and equipment for measuring the
racy of 1 s shall be used.
elongation rate of a fiber of glass suspended in the furnace.
3.1.1 Furnace—The furnace shall conform in all essential
4. Preparation of Test Specimens
respects to the requirements shown in Fig. 1.
4.1 The fiber specimen used for the test shall meet the
3.1.2 Furnace Stand—A means shall be provided for sup-
following requirements:
porting the furnace so that the fiber hangs below it. This stand
4.1.1 It shall be round.
must be provided with a leveling device such as three screws.
4.1.2 It shall be smooth and shall contain no void spots or
The stand shown in Fig. 1 is convenient when used with either
foreign matter.
a cathetometer or a telescope and scale.
4.1.3 Its average diameter shall be 0.65 6 0.10 mm and the
maximum diameter shall not exceed the minimum diameter by
This test method is under the jurisdiction of ASTM Committee C14 on Glass
more than 0.02 mm over the entire length of the fiber.
and Glass Products and is the direct responsibility of Subcommittee C14.04 on
4.1.4 It shall be 235 6 1 mm in length, not including the top
Physical and Mechanical Properties.
bead. Test fibers conforming to these requirements may be
Current edition approved Nov. 15, 1993. Published January 1994. Originally
approved in 1954. Last previous edition approved in 1998 as
drawn by attaching a clean sample of the glass under test
e1
C 338 – 73 (Reapproved 1988) .
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C338–93 (2003)
FIG. 1 Details of Softening Point Furnace
C338–93 (2003)
between two infusible rods (such as platinum-group alloys, 6.3 Set the furnace control for a heating rate of 5 6
porcelain, or fused silica) and fl
...

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