1、Designation: C 598 93 (Reapproved 2003)Standard Test Method forAnnealing Point and Strain Point of Glass by BeamBending1This standard is issued under the fixed designation C 598; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the anneal-ing point and the strain point of a glass by measurin
3、g the rateof midpoint viscous bending of a simply loaded glass beam.2However, at temperatures corresponding to the annealing andstrain points, the viscosity of glass is highly time-dependent.Hence, any viscosities that might be derived or inferred frommeasurements by this procedure cannot be assumed
4、 to repre-sent equilibrium structural conditions.1.2 The annealing and strain points shall be obtained fol-lowing a specified procedure after direct calibration of theapparatus using beams of standard glasses having knownannealing and strain points such as those supplied and certifiedby the National
5、 Institute of Standards and Technology.31.3 This test method, as an alternative to Test Method C 336is particularly well suited for glasses that for one reason oranother are not adaptable for flame working. It also has theadvantages that thermal expansion and effective length correc-tions, common to
6、 the fiber elongation method, are eliminated.1.4 The values stated in metric units are to be regarded asthe standard. The values given in parentheses are for informa-tion only.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsib
7、ility 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. Referenced Documents2.1 ASTM Standards:C 336 Test Method for Annealing Point and Strain Point ofGlass by Fiber Elongation43. Terminology
8、3.1 Definitions:3.1.1 annealing rangethe range of glass temperature inwhich stresses in glass articles can be relieved at a commer-cially desirable rate. For purposes of comparing glasses, theannealing range is assumed to correspond with the tempera-tures between the annealing point (A. P.) and the
9、strain point(St. P.).3.1.2 annealing pointthat temperature at which internalstresses in a glass are substantially relieved in a matter ofminutes. During a test in accordance with the requirements ofthis test method, the midpoint rate of viscous deflection of thetest beam is measured by an extensomet
10、er with suitablemagnification during cooling at a rate of 4 6 1C/min. Thenominal deflection rate at the annealing point ideally is asfollows:Deflection rate, cm/min 5 2.67 3 10211L3M!/Ic(1)where:L = support span, cm;M = centrally applied load, g; andIc= cross-section moment of inertia of test beam,
11、cm4(seeAppendix X1).3.1.3 strain pointthat temperature at which internalstresses in a glass are substantially relieved in a matter ofhours. The strain point is determined by extrapolation of theannealing point data and is the temperature at which theviscous deflection rate is 0.0316 times that obser
12、ved at theannealing point.4. Significance and Use4.1 This test method offers an alternate procedure to TestMethod C 336 for determining the annealing and strain pointsof glass. It is particularly recommended for glasses notadaptable to flame working. Also fewer corrections are neces-sary in data red
13、uction.1This 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 Apr. 10, 2003. Published July 2003. Originallyapproved in 1967. Last previous edit
14、ion approved in 1993 as C 598 93.2Hagy, H. E., “Experimental Evaluation of Beam Bending Method of Deter-mining Glass Viscosities in the Range 108to 1015Poises,” Journal of the AmericanCeramic Society, Vol 46, No. 2, 1963, pp. 9597.3NIST Special Publication 260.4Annual Book of ASTM Standards, Vol 15.
15、02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5. Apparatus5.1 The apparatus shall consist of a furnace, a means ofcontrolling its temperature and cooling rate, a specimen holderand loading rod, and a means of observing the rate
16、of midpointviscous deflection of the glass beam.5.1.1 FurnaceThe furnace shall be electrically heated byresistance-wire windings of either platinum-rhodium or 80-20Ni-Cr alloys. A cutaway drawing of a typical furnace is shownin Fig. 1. Dimensions and details of the furnace constructionare not critic
17、al, but a cylindrical furnace of height of 255 mm(10 in.), outside diameter of 230 mm (9 in.), and insidediameter of 130 mm (5 in.) with a removable top plug isrecommended. The temperature distribution shall be such thatdifferences in temperature greater than 2C shall not result overthe length of th
18、e specimen beam and along the axis of thefurnace from the undeflected beam plane to a point 13 mm (12in.) below.5.1.2 Temperature Measuring and Indicating InstrumentsFor the measurement of temperature, there shall be provided acalibrated Type R or S thermocouple. The thermocouple shallbe housed in a
19、 double-bore alumina tube with its junctionplaced within 5 mm of the specimen near the axis of thefurnace. It is recommended that the thermocouple be refer-enced to 0C by means of an ice bath and its emf measuredwith a calibrated potentiometer having a sensitivity of 61Vand an accuracy of 65 V. Prec
20、autions shall be taken to ensurethat the ice bath is maintained at 0C throughout the test.5.1.3 Furnace ControlSuitable means shall be providedfor idling the furnace, controlling the heating rate, and, in thecase of very hard glasses, limiting the cooling rate to not morethan 5C/min. Although commer
21、cially available programmingequipment provides excellent control, a variable transformerwith manual control is an inexpensive and adequate technique.5.1.4 Specimen Holder and Loading RodA ceramic sup-port stand and a ceramic loading rod shall be provided forsupporting the specimen and applying the l
22、oad to the specimen,respectively. The thermal expansion characteristics of bothstand and rod materials must be very similar so as to minimizemotion of the loading rod on cooling as a result of expansiondifferences (see Appendix X2). A rectangular alumina mufflemakes a suitable support stand (Note 1)
23、. The side walls of thismuffle can be notched to define specimen position. Thesupporting surfaces of these notches shall be flat and lie in aplane perpendicular to the axis of the furnace. The inside edgesAAlumina muffle support stand ELinearly variable differential transformerBSpecimen beam (LVDT)C
24、Thermocouple FZero-adjust mechanism for LVDTDLoading rod GWeightHLaboratory jackFIG. 1 Cutaway Drawing of Beam-Bending ApparatusC 598 93 (2003)2of these supporting surfaces define the support span once thespecimen beam starts to deflect. A support span of about 50mm is recommended. A suitable loadin
25、g rod can be providedby a single-crystal sapphire rod flame bent at one end in theform of a shepherds crook.5The arrangement is shown in Fig.1.NOTE 1Vitreous silica is a suitable material for both support standand loading rod. It is not recommended for temperatures above 900C.5.1.5 Extensometer for
26、Measuring MidpointDeflectionThe means of observing the rate of midpointdeflection of the beam should be such as to indicate reliablyover a range of at least 2.5 mm. The graduated scale of theextensometer shall permit direct reading to 0.025 mm andestimates of 0.0025 mm. Its accuracy shall be such th
27、at theerror of indication will not exceed 60.005 mm for any lengthchange. To ensure this accuracy, the extensometer shall beprecalibrated. A linearly variable differential transformer(LVDT) is suitable for this purpose but any device (optical,capacitative, or other) may be used, provided that length
28、changes are reliably measured as specified. The arrangementwith the LVDT is shown on Fig. 1. The core of the LVDT isattached to the end of the loading rod, whereas the coils areattached to the leg of the furnace platform. A screw arrange-ment is provided in the coil attachment assembly to move theco
29、ils vertically for zeroing purposes.5.1.6 Micrometer Calipers, with an accuracy of at least 0.01mm, for measuring specimen dimensions.6. Preparation of Test Specimen6.1 Specimens may either be flame drawn or centerlessground into cylindrical form or diamond-saw cut and millground into rectangular fo
30、rm. Nonuniformity of any dimensionalong the length of the specimen shall not exceed 2 %. For asupport span of 50 mm, the cross-section moment of inertiashall be between 2 3 104cm4and 10 3 104cm4.7. Calibration and Measurement with Standard Glass7.1 CalibrationDetermine the deflection rates at the an
31、-nealing point using test beams of a calibrating glass6whichcover a range of cross-section moments of inertia. Determinethe deflection rates by following the standard proceduredescribed in Section 8 and in 9.1. The range of cross-sectionmoments of inertia shall bracket the expected operating rangebu
32、t be limited to the maximum permissible variation asspecified in Section 6. Carry out tests keeping load, span, andcooling rate constant. Make a linear calibration plot as shownin Fig. 2. Then use this calibration plot to determine thedeflection rates at the annealing points of unknown glasseshaving
33、 similar annealing points. It is recommended that theapparatus be recalibrated periodically depending upon inci-dence of usage.7.2 Annealing Point MeasurementMeasure the deflectionrate of the glass under test in accordance with the standardprocedure as described in Section 8. Obtain a plot as in Fig
34、. 3by following the procedure described in 9.1. Select from thecalibration plot in 7.1 the deflection rate of the calibrating glasshaving the same cross-section moment of inertia as the testglass. Using the deflection rate thus obtained, determine thecorresponding temperature from the plot of the gl
35、ass undermeasurement. This temperature is the annealing point of theglass under test.5Flame bent sapphire hooks, available from Insaco Inc., PO Box 422, Quaker-town, PA, 18951, have been found suitable for this purpose.6Calibrating glasses known as standard reference materials (SRMs) are availablefr
36、om the National Institute of Standards and Technology (NIST). See Table 1 ofNIST Special Publication 260, SRM Program, NIST, Gaithersburg, MD 20899.Glass SRMs are available and their certified values are listed in the back of Vol15.02, 1999 ASTM Annual Book of Standards.FIG. 2 Graphical Calibration
37、Plot of Deflection Rate VersusReciprocal of Moment of Inertia of Standard Glass Test BeamsFIG. 3 Graphical Method of Analyzing Deflection Rate-Temperature DataC 598 93 (2003)37.3 Strain Point DeterminationObtain the strain point byextrapolation of the straight-line plot in 7.2. (See Fig. 3.)Divide t
38、he midpoint deflection rate at the annealing point by31.6 to obtain the midpoint deflection rate at the strain point.From the plot in 7.2 (Fig. 3), select the temperature corre-sponding to this deflection rate. This temperature is the strainpoint of the glass under test.8. Procedure8.1 With the furn
39、ace at least 25C (45F) below the esti-mated annealing point, remove the top plug and place thespecimen beam across the support stand at the notch points.Carefully engage the loading rod to the specimen and center itusing long calipers. Replace the top plug.8.2 Apply a weight to the hook on the end o
40、f the LVDT coreas shown in Fig. 1. Adjust the total applied load consisting ofthe loading rod, LVDT core, hooks and fixtures, and weightaccording to the cross-section moment of inertia of the testspecimen. The appropriate total load may be approximatedfrom Fig. 4, which shows this load plotted as a
41、function ofcross-section moment of inertia.8.3 Adjust the position of the extensometer to the lower endof its measuring range. Then start heating the furnace at aconvenient rate, preferably at about 5C/min. Stop heating andestablish a cooling rate of 4 6 1C/min when the specimenmidpoint deflection r
42、ate in centimetres per minute reaches:4 3 10210L3M!/Ic(2)Reset the extensometer to the lower end of its range.NOTE 2This deflection rate, corresponding to a viscosity of 1012P,guarantees erasure of previous thermal history.8.4 Immediately after cooling has been established, takereadings of both the
43、extensometer and potentiometer alter-nately at 30-s intervals so that each will be read at 1-minintervals. Continue readings until the temperature is 10Cbelow the annealing point. Such a temperature will generallybe reached when the extensometer indicates a deflection ratethree times less than that
44、expected at the annealing point. If theextensometer goes off range during the test, reset it to the lowerend of the range by means of the vertical zeroing screw. Totalbeam deflections greater than 10 mm are excessive.9. Interpretation of Results9.1 Plotting DataTake the change in extensometer read-i
45、ngs during each 1-min interval as the rate of midpointdeflection at the temperature recorded for the middle of thatminute. Plot it logarithmically against its corresponding tem-perature, using standard-form 3-cycle graph paper with 85-mm(3.33-in.) length cycles and linear scale 381 mm (15 in.) longw
46、ith 300 divisions. The relation should be substantially linear;draw a straight line to represent the plotted points as in Fig. 3.9.2 Annealing and Strain PointsDetermine the midpointviscous deflection rate of the test beam corresponding to theannealing and strain points as described in Section 7. Fr
47、om thegraph relating deflection rate to temperature, determine thetemperatures corresponding to these deflection rates. Thesetemperatures will be the annealing and strain points.10. Report10.1 Report the following information:10.1.1 Identification of the glass tested,10.1.2 Manufacturing source and
48、date,10.1.3 Calibration reference,10.1.4 Annealing point,10.1.5 Strain point, and10.1.6 Date of test and name of operator.11. Precision and Bias11.1 This procedure in general will yield annealing points to62C (standard deviation) of standard values. A rigid test ofthe apparatus is to calibrate with
49、one NIST SRM and thenmeasure other NIST SRMS based on this calibration. If theother standard glasses values are within 2C of certification,excellent performance has been established. If errors arise thatincrease as the difference in annealing points increases, atemperature measurement or distribution problem may exist.This should be corrected. If attempts to correct such a situationare unsuccessful, an unknown glass should never be measuredwithout calibration with a standard reference glass as close aspossible in annealing point.FIG. 4 Rec
