1、Designation: C 338 93 (Reapproved 2003)Standard Test Method forSoftening Point of Glass1This standard is issued under the fixed designation C 338; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This test method covers the determination of the soft-ening
3、point of a glass by determining the temperature at whicha round fiber of the glass, nominally 0.65 mm in diameter and235 mm long with specified tolerances, elongates under its ownweight at a rate of 1 mm/min when the upper 100 mm of itslength is heated in a specified furnace at the rate of 5 61C/min
4、.1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Significanc
5、e and Use2.1 This test method is useful to determine approximatelythe temperature below which the glass behaves as a rigid solidin glass-forming operations and for a control test to indicatechanges in composition. It has been found useful for specifi-cation acceptance and for providing information i
6、n researchand development work with glass.3. Apparatus3.1 The apparatus for determining the softening point ofglass shall consist essentially of an electrically heated resis-tance furnace, a furnace stand, a device for controlling theheating rate of the furnace, equipment for measuring thetemperatur
7、e of the furnace, and equipment for measuring theelongation rate of a fiber of glass suspended in the furnace.3.1.1 FurnaceThe furnace shall conform in all essentialrespects to the requirements shown in Fig. 1.3.1.2 Furnace StandA means shall be provided for sup-porting the furnace so that the fiber
8、 hangs below it. This standmust be provided with a leveling device such as three screws.The stand shown in Fig. 1 is convenient when used with eithera cathetometer or a telescope and scale.3.1.3 Heating Rate ControllerSuitable controls shall beprovided for maintaining the furnace heating rate at 5 6
9、1C/min.NOTE 1A continually adjustable transformer has proved effective forcontrolling the heating rate.3.1.4 Temperature-Measuring EquipmentThe furnacetemperature shall be measured with a calibrated Type R or Sthermocouple and a calibrated potentiometer capable of mea-suring the true temperature of
10、the furnace within 60.2C. Thecold junction shall be maintained at 0C by means of an icebath. An alternative acceptable means of temperature measure-ment is the use of a potentiometer to oppose the thermocoupleelectromotive force. This potentiometer shall be set at astandard setting for the type of g
11、lass being measured, andgalvanometer deflection shall serve as a means of obtainingrelative temperatures, the deflection of the galvanometer hav-ing been calibrated. Also acceptable for temperature measure-ment is a solid-state digital thermometer that is capable of theaccuracy specified.3.1.5 Fiber
12、-Elongation Measurement EquipmentThe fi-ber elongation shall be measured by a device capable ofmeasuring the position of the end of the fiber within 0.02 mmthroughout the entire elongation period.NOTE 2Suitable devices that have proved effective for measuring theelongation are cathetometers, project
13、ion magnifiers, and telescope andscale combinations.3.1.6 TimerA timing device with a least count and accu-racy of 1 s shall be used.4. Preparation of Test Specimens4.1 The fiber specimen used for the test shall meet thefollowing requirements:4.1.1 It shall be round.4.1.2 It shall be smooth and shal
14、l contain no void spots orforeign matter.4.1.3 Its average diameter shall be 0.65 6 0.10 mm and themaximum diameter shall not exceed the minimum diameter bymore than 0.02 mm over the entire length of the fiber.4.1.4 It shall be 235 6 1 mm in length, not including the topbead. Test fibers conforming
15、to these requirements may bedrawn by attaching a clean sample of the glass under test1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Products and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Nov.
16、 15, 1993. Published January 1994. Originallyapproved in 1954. Last previous edition approved in 1998 asC 338 73 (Reapproved 1988)e1.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.FIG. 1 Details of Softening Point FurnaceC 338 93 (2
17、003)2between two infusible rods (such as platinum-group alloys,porcelain, or fused silica) and flame-working the sample untilthe glass is sufficiently fluid to be drawn into a fiber. If thesample is in long stick cane form, it may be flame-workeddirectly without attaching it to a handle. Acceptable
18、fibersections may then be broken from the fiber and a bead formedon one end of the fiber section by fusing in the flame. Theopposite end shall then be broken to the specified length andthe tip may be fire-polished if desired.5. Calibration with Standard Glass5.1 Calibration of the apparatus shall be
19、 done by measuringin duplicate the softening point of appropriate calibrating orstandard glass(es),2the softening points of which are near tothat of the test glass. Compute the difference between theaverage measured softening point and the certified softeningpoint for the standard glass(es), and the
20、 average of thesedifferences. If the average difference is greater than 1C fromthe certified values, add or subtract this difference as acorrection factor to the measured softening points of theunknown glasses.6. Procedure6.1 To equalize the heat distribution of the furnace, heat thefiber furnace to
21、 about 30C above the expected softening pointof the glass under test. Then cool the furnace to about 20Cbelow the expected softening point and determine the settingson the heating rate controller that will give a heating rate of 56 1C/min.6.2 Again, cool and hold the furnace about 20C below theexpec
22、ted softening point and insert the fiber in the furnace byplacing the bead end in the furnace sample holder. Check thefiber to be certain it is hanging free in the center of the furnaceand relevel the furnace if necessary. Standardize the potenti-ometer and adjust the elongation measuring equipment.
23、6.3 Set the furnace control for a heating rate of 5 61C/min. Observe the fiber as the furnace heats, and when itbegins to elongate at the rate of approximately 0.1 mm/min,start recording the fiber length to within 0.02 mm. Take alength reading at the end of each minute and take thetemperature of the
24、 furnace at each12 -min point. Continue toread and record the length and the temperature until theelongation becomes 1.2 mm or greater in a 1-min period. Whenthe elongation exceeds 1.2 mm in a 1-min interval, remove thefiber and cool the furnace for a duplicate run. An alternativeacceptable method i
25、s to read the length at 1- and12 -min points,and the temperature at the14 - and34 -min points, continuingto read and record length and temperature until the elongationbecomes 0.6 mm or greater in a12 -min period.7. Calculation7.1 Determine the temperature at which the elongation is 1mm/min. This may
26、 be done by any reliable method, one ofwhich is as follows. Plot the data on semi-log paper, thepotentiometer or temperature readings on the uniform scale,and the difference between length readings per unit time on thelog scale. The point at which a straight line drawn through thepoints crosses the
27、1.0-mm/min line shall be taken as theindicated softening point. Make the calibration corrections asspecified in Section 5 if necessary.8. Report8.1 Report the following information:8.1.1 Designation of the material, name of the manufacturer,and identifying production data, when known,8.1.2 Identific
28、ation of the softening point apparatus used,8.1.3 Average softening point temperature, and8.1.4 Date of test and name of operator.9. Precision and Bias9.1 This test method in general will yield softening pointswithin 1C on duplicate checks. The accuracy of results shouldbe checked by determining the
29、 softening point of appropriatestandard glasses2as indicated in the calibration procedure(Section 5).ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that det
30、ermination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved o
31、r withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel th
32、at your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints
33、 (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).2Calibrating glasses known as standard reference materials (SRMs) are availablefrom the National Institute of Standards and Technology (NIST). See Table 1 ofNIST Special Publication 260, SRM Program, NIST, Gaithersburg, MD 20899.Glass SRMs available and their certified values are listed in the back of Vol 15.021999 Annual Book of ASTM Standards.C 338 93 (2003)3
