1、Designation: C 336 71 (Reapproved 2005)Standard Test Method forAnnealing Point and Strain Point of Glass by FiberElongation1This standard is issued under the fixed designation C 336; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、the 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers
3、the determination of the anneal-ing point and the strain point of a glass by measuring theviscous elongation rate of a fiber of the glass under prescribedcondition.1.2 The annealing and strain points shall be obtained byfollowing the specified procedure after calibration of theapparatus using fibers
4、 of standard glasses having knownannealing and strain points, such as those specified andcertified by the National Institute of Standards and Technology(NIST)2(see Appendix X1).1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsi
5、bility 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:3C 338 Test Method for Softening Point of GlassC 598 Test Method for Annealing Point and Strain
6、Point ofGlass by Beam Bending3. Definitions3.1 annealing pointthat temperature at which internalstresses in a glass are substantially relieved in a matter ofminutes.4,5,6During a test in accordance with the requirementsof this method, the viscous elongation rate is measured by asuitable extensometer
7、 while the specimen fiber is cooling at arate of 4 6 1C/min. The elongation rate at the annealing pointis approximately 0.14 mm/min for a fiber of 0.65-mm diam-eter.63.2 annealing rangethe range of glass temperature inwhich stresses in glass articles can be relieved at a commer-cially desirable rate
8、. For purposes of comparing glasses, theannealing range is assumed to correspond with the tempera-tures between the annealing point (AP) and the strain point(StP).3.3 strain pointthat temperature at which the internalstresses in a glass are substantially relieved in a matter ofhours. The strain poin
9、t is determined by extrapolation of theannealing point data and is the temperature at which theviscous elongation rate is 0.0316 times that observed at theannealing point.4. Significance and Use4.1 This test method provides data useful for (1) estimatingstress release, (2) the development of proper
10、annealing sched-ules, and (3) estimating setting points for seals.Accordingly, itsusage is widespread throughout manufacturing, research, anddevelopment. It can be utilized for specification acceptance.5. Apparatus5.1 FurnaceThe furnace shall be 368-mm (1412-in.) longand approximately 114 mm (412 in
11、.) in diameter and shallcontain a copper core 305 mm (12 in.) long and 29 mm (118in.) in outside diameter, with inside diameter of 5.6 mm (732in.). It shall be constructed substantially as shown in Fig. 1.5.1.1 Such a furnace will cool naturally at approximately4C (7F)/min at 500C (932F) and at a ra
12、te exceeding 3C(5.5F)/min at 400C (752F).5.2 Temperature Measuring and Indicating InstrumentsFor the measurement of temperature there shall be provided athermocouple, preferably platinum-platinum rhodium, inserted1This test method is under the jurisdiction of ASTM Committee C14 on Glassand Glass Pro
13、ducts and is the direct responsibility of Subcommittee C14.04 onPhysical and Mechanical Properties.Current edition approved Sept. 1, 2005 Published October 2005. Originallyapproved in 1954. Last previous edition approved in 2000 as C 336 71(2000).2Available from National Institute of Standards and T
14、echnology (NIST), 100Bureau Dr., Stop 3460, Gaithersburg, MD 20899-3460. Publication 260.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summ
15、ary page onthe ASTM website.4Littleton, J. T., and Roberts, E. H., “A Method for Determining the AnnealingTemperature of Glass,” Journal of the Optical Society of America, Vol 4, 1920, p.224.5Lillie, H. R., “Viscosity of Glass Between the Strain Point and MeltingTemperature,” Journal of American Cer
16、amic Society, Vol 14, 1931, p. 502;“Re-Evaluation of Glass Viscosities at Annealing and Strain Points,” Journal ofAmerican Ceramic Society, Vol 37, 1954, p. 111.6McGraw, D. A. and Babcock, C. L., “Effect of Viscosity and Stress Level onRate of Stress Release in Soda-Lime, Potash-Barium and Borosilic
17、ate Glasses,”Journal of the American Ceramic Society, Vol 42, 1959, p. 330.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.in the upper side hole of the copper core, as indicated in Fig.1, so that its junction is located midway in th
18、e length of thecore. The thermocouple wire shall not be allowed to directlycontact the copper; this can be ensured by placing a 6-mm(14-in.) length of ceramic tube in the bottom of the hole aheadof the couple. The cold junction of the thermocouple shall bemaintained in an ice bath during tests.5.2.1
19、 The temperature-indicating instrument, preferably apotentiometer, shall be of such quality and sensitivity as topermit reading the thermocouple emf to an amount correspond-ing to 0.1C (0.2F), equivalent to about 1 V for a platinumcouple or to about 4 V for a base-metal couple.5.2.2 Provision shall
20、be made for reading temperaturesaccurately at predetermined moments. One means of accom-plishing this is to maintain the potentiometer setting at anelectromotive force corresponding to a known temperature,near the annealing point and inferring the temperature from thedeflection of a sensitive galvan
21、ometer, previously calibratedfor the purpose. It is convenient to adjust the galvanometershunt to a sensitivity of about 3C (5.5F)/cm of deflection andto somewhat less than critical damping. This technique forreading temperature changes is one of the preferred methods;in the following sections it wi
22、ll be assumed that this techniquehas been used, although any other equally sensitive and precisemethod of following the temperature of the thermocouple maybe used.5.3 Furnace ControlSuitable means shall be provided foridling the furnace, controlling its heating rate, and, in the caseof very hard gla
23、sses, limiting the cooling rate to not more than5C (9F)/min. A variable transformer is a convenient devicefor this purpose. The transformer can also be employed as aswitch for interrupting the furnace current.5.4 Device for Measuring Elongation The means ofobserving the rate of elongation of the fib
24、er should be such asto indicate reliably over a range of about 6-mm (14-in.) changein fiber length with an uncertainty not greater than about 0.01mm (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 linkag
25、e. The fulcrum of the levershould be mounted on a rigid (but height-adjustable) member,substantially free of vibration. With an optical lever arm about38 mm (112 in.) long and a scale distance of about 1 m (40 in.),FIG. 1 Apparatus for Determination of Annealing Point and Strain Point of GlassC 336
26、71 (2005)2the multiplying factor is about 50. Readings can be made to 0.5mm on the scale and, if the scale is 508 mm in length, asufficient range is attained. The scale is curved with its centerof curvature at the mirror location. The system may becalibrated by mounting a micrometer screw in place o
27、f theplatform, L.5.4.1 Any other extensometer arrangement, such as a lin-early variable differential transformer (LVDT) or a travellingmicroscope, is suitable for measuring elongation, provided thatlength changes are reliably measured as specified.5.5 Micrometer Calipers, with a least count of 0.005
28、 mm,for measuring specimen fiber diameters.6. Test Specimen6.1 Drawing the FiberDraw a suitable fiber from 2 cm3(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 othersuitable material, such as refractory or metal, and then wor
29、k itinto a ball, using a flame adjustment found suitable for theparticular kind of glass. When the ball is in a uniform state ofproper temperature, and while it is still in the fire, slightlyelongate it into a pear shape. Then, remove the ball from thefire, and draw it down to a convenient length.6.
30、2 Measurement of Fiber Dimensions Measure the fiberwith micrometer calipers at 51-mm (2-in.) intervals, and selecta 508-mm (20-in.) length that is substantially circular in crosssection, 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 inM
31、ethod B of this test procedure may be between 102 mm (4in.) and 203 mm (8 in.) in length; once established, such a shortfiber specimen length must be maintained within6 2mmforall further calibration and testing.6.3 Fiber PreparationPrepare the selected length of fiberfor the test by melting both its
32、 ends down into spherical formabout 2.5 mm (0.1 in.) in diameter, taking care that the balls arecentered on the fiber axis. Starting 25.4 mm (1 in.) from oneend, which is thereafter to be regarded as the top end,remeasure the fiber for diameter at 1 in. intervals over theremaining fiber length or up
33、 to a maximum of 305 mm (12 in.).Record the average diameter for subsequent calculations.7. Calibration with Standard Glass7.1 CalibrationPrepare at least four fibers of the calibrat-ing or standard glass,2with diameters covering the diameterrange 0.55 to 0.75 mm. In accordance with procedures inSec
34、tions 8 and 9.1, determine the elongation rates at thespecified annealing point temperature, and make a calibrationplot as in Fig. 2, of the rate of elongation versus the reciprocalsquare of the fiber diameter. Then use this calibration plot todetermine the annealing points of unknown glasses withsi
35、milar annealing ranges. It is recommended that the apparatusbe calibrated periodically depending upon usage.8. Procedure8.1 Method A:8.1.1 Long Fiber, Furnace SupportThe recommendedmethod of fiber support and loading is as shown in Fig. 1,inwhich the top of a long fiber is supported on the furnace t
36、opitself and the fiber extends entirely through the furnace to thelever platform, L, or to the attachment of the load.8.1.2 Long Fiber, Independent Support An alternativelong fiber method is that shown in Fig. 3, in which the top ofthe fiber is supported independently of the furnace. Thismethod requ
37、ires the application of a correction for thermalexpansion.58.2 Method B:8.2.1 Short Fiber, Independent Support The short fibermethod of support and loading is as shown in Fig. 4, in whichthe short fiber is supported independently of the furnacebetween two metal rods. This method requires a larger fu
38、rnacebore than Method A and application of a correction for thermalexpansion.58.2.2 Short Fiber, Furnace SupportIn this method theshort fiber is joined to the two metal rods as in 7.2.1, exceptthat the upper metal rod is supported by the furnace, beingseated in the stainless steel support disk, J,in
39、Fig. 1.8.3 Assembly of Specimen in Apparatus With the furnaceat least 25C (45F) below the estimated annealing point, insertthe bottom end of the sample in the top of the furnace (Note).Put the support disk, J (Fig. 1), around the shaft of the sampleand place it in its proper location in the top of t
40、he furnace.Lower the sample to seat its upper ball in the support disk.Attach the loading linkage, L and M, apply a 1-kg load, andbring the optical lever arm to bear on the platform, L. Adjustthe lever base, N, vertically to bring the scale reading near thelower end of the scale.NOTE 1Caution: Ensur
41、e that the bore of the furnace is vertical.Position the fiber so as to be centered as well as possible to avoid contactwith the copper core.FIG. 2 CalibrationFIG. 3 Apparatus Assembly for Independent Support of SampleFiberC 336 71 (2005)38.4 HeatingAdjust the position of the extensometer to thelower
42、 end of its measuring range. Start heating the furnace ata convenient rate, preferably at about 5C/min. Stop heatingand establish a cooling rate of 4 61C/min when the elonga-tion rate reaches about 0.60 mm/min, or when the furnacetemperature is no more than 25C above the estimated anneal-ing point.8
43、.5 Immediately after cooling has been established, takereadings of both the extensometer and potentiometer alter-nately at 30-s intervals so that each shall be read at 1-minintervals. Continue readings until the elongation rate is 0.1mm/min.9. Calculation9.1 Plotting DataTake the change in extensome
44、ter read-ings during each 1-min interval as the rate of elongation at thetemperature recorded for the middle of that minute. Plot itlogarithmically against its corresponding temperature, usingstandard-form three-cycle graph paper with 85-mm (313-in.)length cycles and linear scale 381 mm (15 in.) lon
45、g with 300divisions. The relation should be substantially linear; draw astraight line to represent the plotted points as in Fig. 5, givingmore weight to the higher temperature data points.9.2 Annealing PointSelect from the calibration plot inFig. 2 the elongation rate of the calibrating glass having
46、 thesame diameter as the test glass. Using the elongation rate thusobtained, select corresponding potentiometer reading from theplot of the glass under measurement. This potentiometerreading indicates the annealing point temperature of the glassunder test.9.3 Strain PointObtain the strain point by e
47、xtrapolation ofthe straight-line plot of Fig. 5. Divide the elongation rate at theannealing point by 31.6 to obtain the elongation rate at thestrain point. From the plot in Fig. 5, select the potentiometerreading corresponding to this elongation rate. This potentiom-eter reading indicates the strain
48、 point temperature of the glassunder test.10. Report10.1 Report the following information:10.1.1 Identification of the glass tested,10.1.2 Manufacturing source and 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
49、and Bias11.1 Method A in general will yield annealing points to astandard deviation of 62C. For higher precision with MethodA and for Method B it is necessary to apply a correction forthermal expansion, which must be determined empirically forthe apparatus in use by calibrating with NIST standard refer-ence glasses of known thermal expansion and contraction andcertified annealing points.4A rigid test of the apparatus is tocalibrate with one NIST standard glass and then measure otherNIST standard glasses based on this calibration.
