ASTM C336-71(2010)
(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
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) (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 2010)
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
,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 April 1, 2010 Published May 2010. Originally Littleton, J. T., and Roberts, E. H., “A Method for Determining the Annealing
approved in 1954. Last previous edition approved in 2005 as C336 – 71 (2005). Temperature of Glass,” Journal of the Optical Society of America, Vol 4, 1920, p.
DOI: 10.1520/C0336-71R10. 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 (2010)
Accordingly, its usage is widespread throughout of the couple. The cold junction of the thermocouple shall be
manufacturing, research, and development. It can be utilized maintained in an ice bath during tests.
for specification acceptance.
5.2.1 The temperature-indicating instrument, preferably a
potentiometer, shall be of such quality and sensitivity as to
5. Apparatus
permitreadingthethermocoupleemftoanamountcorrespond-
5.1 Furnace—The furnace shall be 368-mm (14 ⁄2-in.) long
ing to 0.1°C (0.2°F), equivalent to about 1 µV for a platinum
and approximately 114 mm (4 ⁄2 in.) in diameter and shall
couple or to about 4 µV for a base-metal couple.
contain a copper core 305 mm (12 in.) long and 29 mm (1 ⁄8
5.2.2 Provision shall be made for reading temperatures
in.) in outside diameter, with inside diameter of 5.6 mm ( ⁄32
accurately at predetermined moments. One means of accom-
in.). It shall be constructed substantially as shown in Fig. 1.
plishing this is to maintain the potentiometer setting at an
5.1.1 Such a furnace will cool naturally at approximately
electromotive force corresponding to a known temperature,
4°C (7°F)/min at 500°C (932°F) and at a rate exceeding 3°C
near the annealing point and inferring the temperature from the
(5.5°F)/min at 400°C (752°F).
deflection of a sensitive galvanometer, previously calibrated
5.2 Temperature Measuring and Indicating Instruments— for the purpose. It is convenient to adjust the galvanometer
For the measurement of temperature there shall be provided a shunt to a sensitivity of about 3°C (5.5°F)/cm of deflection and
thermocouple, preferably platinum-platinum rhodium, inserted to somewhat less than critical damping. This technique for
reading temperature changes is one of the preferred methods;
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 in the following sections it will be assumed that this technique
core. The thermocouple wire shall not be allowed to directly has been used, although any other equally sensitive and precise
contact the copper; this can be ensured by placing a 6-mm method of following the temperature of the thermocouple may
( ⁄4-in.) length of ceramic tube in the bottom of the hole ahead be used.
FIG. 1 Apparatus for Determination of Annealing Point and Strain Point of Glass
C336 − 71 (2010)
5.3 Furnace Control—Suitable means shall be provided for 7. Calibration with Standard Glass
idling the furnace, controlling its heating rate, and, in the case
7.1 Calibration—Prepare at least four fibers of the calibrat-
of very hard glasses, limiting the cooling rate to not more than 2
ing or standard glass, with diameters covering the diameter
5°C (9°F)/min. A variable transformer is a convenient device
range 0.55 to 0.75 mm. In accordance with procedures in
for this purpose. The transformer can also be employed as a
Sections 8 and 9.1, determine the elongation rates at the
switch for interrupting the furnace current.
specified annealing point temperature, and make a calibration
plot as in Fig. 2, of the rate of elongation versus the reciprocal
5.4 Device for Measuring Elongation— The means of
square of the fiber diameter. Then use this calibration plot to
observing the rate of elongation of the fiber should be such as
1 determine the annealing points of unknown glasses with
to indicate reliably over a range of about 6-mm ( ⁄4-in.) change
similar annealing ranges. It is recommended that the apparatus
in fiber length with an uncertainty not greater than about 0.01
be calibrated periodically depending upon usage.
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,
8. Procedure
incorporated in the loading linkage. The fulcrum of the lever
8.1 Method A:
should be mounted on a rigid (but height-adjustable) member,
8.1.1 Long Fiber, Furnace Support—The recommended
substantially free of vibration. With an optical lever arm about
method of fiber support and loading is as shown in Fig. 1,in
38 mm (1 ⁄2 in.) long and a scale distance of about 1 m (40 in.),
which the top of a long fiber is supported on the furnace top
the 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 Long Fiber, Independent Support— An alternative
of curvature at the mirror location. The system may be
long fiber method is that shown in Fig. 3, in which the top of
calibrated by mounting a micrometer screw in place of the
the fiber is supported independently of the furnace. This
platform, L.
method requires the application of a correction for thermal
5.4.1 Any other extensometer arrangement, such as a lin-
expansion.
early variable differential transformer (LVDT) or a travelling
microscope, is suitable for measuring elongation, provided that 8.2 Method B:
length changes are reliably measured as specified.
8.2.1 Short Fiber, Independent Support— The short fiber
method of support and loading is as shown in Fig. 4, in which
5.5 Micrometer Calipers, with a least count of 0.005 mm,
the short fiber is supported independently of the furnace
for measuring specimen fiber d
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