ASTM C336-71(2015)
(Test Method)Standard Test Method for Annealing Point and Strain Point of Glass by Fiber Elongation
Standard Test Method for Annealing Point and Strain Point of Glass by Fiber Elongation
SIGNIFICANCE AND USE
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.
SCOPE
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.
1.2 The annealing and strain points shall be obtained by following the specified procedure after calibration of the apparatus using fibers of standard glasses having known annealing and strain points, such as those specified and certified by the National Institute of Standards and Technology (NIST)2 (see Appendix X1).
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.
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Designation: C336 − 71 (Reapproved 2015)
Standard Test Method for
Annealing Point and Strain Point of Glass by Fiber
Elongation
This standard is issued under the fixed designation C336; 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 3. Definitions
3.1 annealing point—that temperature at which internal
1.1 This test method covers the determination of the anneal-
stresses in a glass are substantially relieved in a matter of
ing point and the strain point of a glass by measuring the
4,5,6
minutes. During a test in accordance with the requirements
viscous elongation rate of a fiber of the glass under prescribed
of this method, the viscous elongation rate is measured by a
condition.
suitable extensometer while the specimen fiber is cooling at a
1.2 The annealing and strain points shall be obtained by
rate of 4 6 1°C/min.The elongation rate at the annealing point
following the specified procedure after calibration of the
is approximately 0.14 mm/min for a fiber of 0.65 mm diam-
apparatus using fibers of standard glasses having known
eter.
annealing and strain points, such as those specified and
3.2 annealing range—the range of glass temperature in
certified by the National Institute of Standards and Technology
which stresses in glass articles can be relieved at a commer-
(NIST) (see Appendix X1).
cially desirable rate. For purposes of comparing glasses, the
1.3 This standard does not purport to address all of the
annealing range is assumed to correspond with the tempera-
safety concerns, if any, associated with its use. It is the
tures between the annealing point (AP) and the strain point
responsibility of the user of this standard to establish appro-
(StP).
priate safety and health practices and determine the applica-
3.3 strain point—that temperature at which the internal
bility of regulatory limitations prior to use.
stresses in a glass are substantially relieved in a matter of
hours. The strain point is determined by extrapolation of the
2. Referenced Documents
annealing point data and is the temperature at which the
2.1 ASTM Standards:
viscous elongation rate is 0.0316 times that observed at the
C338 Test Method for Softening Point of Glass
annealing point.
C598 Test Method for Annealing Point and Strain Point of
Glass by Beam Bending
4. Significance and Use
4.1 This test method provides data useful for (1) estimating
stress release, (2) the development of proper annealing
This test method is under the jurisdiction of ASTM Committee C14 on Glass
schedules, and (3) estimating setting points for seals.
and Glass Products and is the direct responsibility of Subcommittee C14.04 on
Physical and Mechanical Properties.
Current edition approved May 1, 2015. Published May 2015. Originally Littleton, J. T., and Roberts, E. H., “A Method for Determining the Annealing
approved in 1954. Last previous edition approved in 2010 as C336 – 71 (2010). Temperature of Glass,” Journal of the Optical Society of America, Vol 4, 1920, p.
DOI: 10.1520/C0336-71R15. 224.
2 5
Available from National Institute of Standards and Technology (NIST), 100 Lillie, H. R., “Viscosity of Glass Between the Strain Point and Melting
Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov. Publi- Temperature,” Journal of American Ceramic Society, Vol 14, 1931, p. 502;
cation 260. “Re-Evaluation of Glass Viscosities at Annealing and Strain Points,” Journal of
For referenced ASTM standards, visit the ASTM website, www.astm.org, or American Ceramic Society, Vol 37, 1954, p. 111.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM McGraw, D. A. and Babcock, C. L., “Effect of Viscosity and Stress Level on
Standards volume information, refer to the standard’s Document Summary page on Rate of Stress Release in Soda-Lime, Potash-Barium and Borosilicate Glasses,”
the ASTM website. Journal of the American Ceramic Society, Vol 42, 1959, p. 330.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C336 − 71 (2015)
Accordingly, its usage is widespread throughout contact the copper; this can be ensured by placing a 6 mm
manufacturing, research, and development. It can be utilized ( ⁄4-in.) length of ceramic tube in the bottom of the hole ahead
for specification acceptance. of the couple. The cold junction of the thermocouple shall be
maintained in an ice bath during tests.
5. Apparatus
5.2.1 The temperature-indicating instrument, preferably a
5.1 Furnace—The furnace shall be 368 mm (14 ⁄2-in.) long potentiometer, shall be of such quality and sensitivity as to
and approximately 114 mm (4 ⁄2 in.) in diameter and shall
permitreadingthethermocoupleemftoanamountcorrespond-
contain a copper core 305 mm (12 in.) long and 29 mm
ing to 0.1°C (0.2°F), equivalent to about 1 µV for a platinum
(1 ⁄8 in.) in outside diameter, with inside diameter of 5.6 mm
couple or to about 4 µV for a base-metal couple.
( ⁄32 in.). It shall be constructed substantially as shown in Fig.
5.2.2 Provision shall be made for reading temperatures
1.
accurately at predetermined moments. One means of accom-
5.1.1 Such a furnace will cool naturally at approximately
plishing this is to maintain the potentiometer setting at an
4°C (7°F)/min at 500°C (932°F) and at a rate exceeding 3°C
electromotive force corresponding to a known temperature,
(5.5°F)/min at 400°C (752°F).
near the annealing point and inferring the temperature from the
deflection of a sensitive galvanometer, previously calibrated
5.2 Temperature Measuring and Indicating Instruments—
For the measurement of temperature there shall be provided a for the purpose. It is convenient to adjust the galvanometer
shunt to a sensitivity of about 3°C (5.5°F)/cm of deflection and
thermocouple, preferably platinum-platinum rhodium, inserted
in the upper side hole of the copper core, as indicated in Fig. to somewhat less than critical damping. This technique for
1, so that its junction is located midway in the length of the reading temperature changes is one of the preferred methods;
core. The thermocouple wire shall not be allowed to directly in the following sections it will be assumed that this technique
FIG. 1 Apparatus for Determination of Annealing Point and Strain Point of Glass
C336 − 71 (2015)
has been used, although any other equally sensitive and precise remaining fiber length or up to a maximum of 305 mm (12 in.).
method of following the temperature of the thermocouple may Record the average diameter for subsequent calculations.
be used.
7. Calibration with Standard Glass
5.3 Furnace Control—Suitable means shall be provided for
7.1 Calibration—Prepare at least four fibers of the calibrat-
idling the furnace, controlling its heating rate, and, in the case
ing or standard glass, with diameters covering the diameter
of very hard glasses, limiting the cooling rate to not more than
range 0.55 to 0.75 mm. In accordance with procedures in
5°C (9°F)/min. A variable transformer is a convenient device
Sections 8 and 9.1, determine the elongation rates at the
for this purpose. The transformer can also be employed as a
specified annealing point temperature, and make a calibration
switch for interrupting the furnace current.
plot as in Fig. 2, of the rate of elongation versus the reciprocal
5.4 Device for Measuring Elongation—The means of ob-
square of the fiber diameter. Then use this calibration plot to
serving the rate of elongation of the fiber should be such as to
determine the annealing points of unknown glasses with
indicate reliably over a range of about 6 mm ( ⁄4-in.) change in
similar annealing ranges. It is recommended that the apparatus
fiberlengthwithanuncertaintynotgreaterthanabout0.01mm
be calibrated periodically depending upon usage.
(0.0004in.).AconvenientmethodisshowninFig.1,wherethe
arm of the optical lever, N, bears upon a platform, L, incorpo-
8. Procedure
rated in the loading linkage.The fulcrum of the lever should be
8.1 Method A:
mounted on a rigid (but height-adjustable) member, substan-
8.1.1 Long Fiber, Furnace Support—The recommended
tially free of vibration. With an optical lever arm about 38 mm
method of fiber support and loading is as shown in Fig. 1,in
(1 ⁄2 in.) long and a scale distance of about 1 m (40 in.), the
which the top of a long fiber is supported on the furnace top
multiplying factor is about 50. Readings can be made to 0.5
itself and the fiber extends entirely through the furnace to the
mm on the scale and, if the scale is 508 mm in length, a
lever platform, L, or to the attachment of the load.
sufficient range is attained. The scale is curved with its center
8.1.2 LongFiber,IndependentSupport—Analternativelong
of curvature at the mirror location. The system may be
fiber method is that shown in Fig. 3, in which the top of the
calibrated by mounting a micrometer screw in place of the
fiber is supported independently of the furnace. This method
platform, L.
requires the application of a correction for thermal expansion.
5.4.1 Any other extensometer arrangement, such as a lin-
8.2 Method B:
early variable differential transformer (LVDT) or a travelling
8.2.1 Short Fiber, Independent Support—The short fiber
microscope, is suitable for measuring elongation, provided that
method of support and loading is as shown in Fig. 4, in which
length changes are reliably measured as specified.
the short fiber is supported independently
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C336 − 71 (Reapproved 2010) C336 − 71 (Reapproved 2015)
Standard Test Method for
Annealing Point and Strain Point of Glass by Fiber
Elongation
This standard is issued under the fixed designation C336; 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
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.
1.2 The annealing and strain points shall be obtained by following the specified procedure after calibration of the apparatus
using fibers of standard glasses having known annealing and strain points, such as those specified and certified by the National
Institute of Standards and Technology (NIST) (see Appendix X1).
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.
2. Referenced Documents
2.1 ASTM Standards:
C338 Test Method for Softening Point of Glass
C598 Test Method for Annealing Point and Strain Point of Glass by Beam Bending
3. Definitions
4,5,6
3.1 annealing point—that temperature at which internal stresses in a glass are substantially relieved in a matter of minutes.
During a test in accordance with the requirements of this method, the viscous elongation rate is measured by a suitable
extensometer while the specimen fiber is cooling at a rate of 4 6 1°C/min. The elongation rate at the annealing point is
approximately 0.14 mm/min for a fiber of 0.65-mm0.65 mm diameter.
3.2 annealing range—the range of glass temperature in which stresses in glass articles can be relieved at a commercially
desirable rate. For purposes of comparing glasses, the annealing range is assumed to correspond with the temperatures between
the annealing point (AP) and the strain point (StP).
3.3 strain point—that temperature at which the internal stresses in a glass are substantially relieved in a matter of hours. The
strain point is determined by extrapolation of the annealing point data and is the temperature at which the viscous elongation rate
is 0.0316 times that observed at the annealing point.
4. Significance and Use
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.
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.
Current edition approved April 1, 2010 Published May 2010May 2015. Originally approved in 1954. Last previous edition approved in 20052010 as C336 – 71 (2010).
(2005). DOI: 10.1520/C0336-71R10.10.1520/C0336-71R15.
Available from National Institute of Standards and Technology (NIST), 100 Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov. Publication 260.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Littleton, J. T., and Roberts, E. H., “A Method for Determining the Annealing Temperature of Glass,” Journal of the Optical Society of America, Vol 4, 1920, p. 224.
Lillie, H. R., “Viscosity of Glass Between the Strain Point and Melting Temperature,” Journal of American Ceramic Society, Vol 14, 1931, p. 502; “Re-Evaluation of
Glass Viscosities at Annealing and Strain Points,” Journal of American Ceramic Society, Vol 37, 1954, p. 111.
McGraw, D. A. and Babcock, C. L., “Effect of Viscosity and Stress Level on Rate of Stress Release in Soda-Lime, Potash-Barium and Borosilicate Glasses,” Journal
of the American Ceramic Society, Vol 42, 1959, p. 330.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C336 − 71 (2015)
5. Apparatus
1 1
5.1 Furnace—The furnace shall be 368-mm368 mm (14 ⁄2-in.) long and approximately 114 mm (4 ⁄2 in.) in diameter and shall
1 7
contain a copper core 305 mm (12 in.) long and 29 mm (1 ⁄8 in.) in.) in outside diameter, with inside diameter of 5.6 mm ( ⁄32
in.). in.). It shall be constructed substantially as shown in Fig. 1.
5.1.1 Such a furnace will cool naturally at approximately 4°C (7°F)/min at 500°C (932°F) and at a rate exceeding 3°C
(5.5°F)/min at 400°C (752°F).
5.2 Temperature Measuring and Indicating Instruments—For the measurement of temperature there shall be provided a
thermocouple, preferably platinum-platinum rhodium, inserted in the upper side hole of the copper core, as indicated in Fig. 1, so
that its junction is located midway in the length of the core. The thermocouple wire shall not be allowed to directly contact the
copper; this can be ensured by placing a 6-mm6 mm ( ⁄4-in.) length of ceramic tube in the bottom of the hole ahead of the couple.
The cold junction of the thermocouple shall be maintained in an ice bath during tests.
5.2.1 The temperature-indicating instrument, preferably a potentiometer, shall be of such quality and sensitivity as to permit
reading the thermocouple emf to an amount corresponding to 0.1°C (0.2°F), equivalent to about 1 μV for a platinum couple or to
about 4 μV for a base-metal couple.
5.2.2 Provision shall be made for reading temperatures accurately at predetermined moments. One means of accomplishing this
is to maintain the potentiometer setting at an electromotive force corresponding to a known temperature, near the annealing point
and inferring the temperature from the deflection of a sensitive galvanometer, previously calibrated for the purpose. It is convenient
to adjust the galvanometer shunt to a sensitivity of about 3°C (5.5°F)/cm of deflection and to somewhat less than critical damping.
This technique for reading temperature changes is one of the preferred methods; in the following sections it will be assumed that
this technique has been used, although any other equally sensitive and precise method of following the temperature of the
thermocouple may be used.
FIG. 1 Apparatus for Determination of Annealing Point and Strain Point of Glass
C336 − 71 (2015)
5.3 Furnace Control—Suitable means shall be provided for idling the furnace, controlling its heating rate, and, in the case of
very hard glasses, limiting the cooling rate to not more than 5°C (9°F)/min. A variable transformer is a convenient device for this
purpose. The transformer can also be employed as a switch for interrupting the furnace current.
5.4 Device for Measuring Elongation—The means of observing the rate of elongation of the fiber should be such as to indicate
reliably over a range of about 6-mm6 mm ( ⁄4-in.) change in fiber length with an uncertainty not greater than about 0.01 mm
(0.0004 in.). A convenient method is shown in Fig. 1, where the arm of the optical lever, N, bears upon a platform, L, incorporated
in the loading linkage. The fulcrum of the lever should be mounted on a rigid (but height-adjustable) member, substantially free
of vibration. With an optical lever arm about 38 mm 38 mm (1 ⁄2 in.) long and a scale distance of about 1 m (40 in.), the multiplying
factor is about 50. Readings can be made to 0.5 mm on the scale and, if the scale is 508 mm in length, a sufficient range is attained.
The scale is curved with its center of curvature at the mirror location. The system may be calibrated by mounting a micrometer
screw in place of the platform, L.
5.4.1 Any other extensometer arrangement, such as a linearly variable differential transformer (LVDT) or a travelling
microscope, is suitable for measuring elongation, provided that length changes are reliably measured as specified.
5.5 Micrometer Calipers, with a least count of 0.005 mm, for measuring specimen fiber diameters.
6. Test Specimen
6.1 Drawing the Fiber—Draw a suitable fiber from 2 cm (more or less) of glass in any form such as a fragment, cane, flat strip,
or tubing. Stick the piece to handles of glass or other suitable material, such as refractory or metal, and then work it into a ball,
using a flame adjustment found suitable for the particular kind of glass. When the ball is in a uniform state of proper temperature,
and while it is still in the fire, slightly elongate it into a pear shape. Then, remove the ball from the fire, and draw it down to a
convenient length.
6.2 Measurement of Fiber Dimensions—Measure the fiber with micrometer calipers at 51-mm51 mm (2-in.) intervals, and select
a 508-mm508 mm (20-in.) length that is substantially circular in cross section, has a diameter of 0.65 6 0.10 mm (0.025 6 0.004
in.), and is uniform to 0.015 mm (60.0006 in.). The fiber used in Method B of this test procedure may be between 102 mm (4
in.) (4 in.) and 203 mm (8 in.) in length; once established, such a short fiber specimen length must be maintained within6 2 mm
for all further calibration and testing.
6.3 Fiber Preparation—Prepare the selected length of fiber for the test by melting both its ends down into spherical form about
2.5 mm (0.1 in.) in diameter, taking care that the balls are centered on the fiber axis. Starting 25.4 mm (1 in.) from one end, which
is thereafter to be regarded as the top end, remeasure the fiber for diameter at 1 in. intervals over the remain
...
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