ISO-7991-1987.pdf
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1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXjJYHAPOjJHAR OPrAHM3AMR IlO CTAH/JAPTkl3AMM 1 d 1 1 , j b : .y 2. ,- : n*.P* B .i , _, -;_ , i.i.j i,*:f s *:L i t) : The ratio of the change in length of a specimen within a tempera
2、ture interval to that temperature interval, related to the initial specimen length. It is given by the following equation: I - I, cd,; t) = f x - . . . 0 t - to to is the initial or reference temperature; t is the actual (constant or variable) specimen tem- perature; I, is the length at temperature
3、to of the specimen of glass under test (usually a rod made from the glass); I is the specimen length at temperature t. For the purposes of this International Standard, the nominal reference temperature, to, is 20 OC; therefore the coefficient of mean linear thermal expansion is denoted by a(20 YZ; t
4、). 4 Apparatus 4.1 Device for measuring the specimen length, to an ac- curacy of 0,l %. 4.2 Push-rod dilatometer, capable of determining changes in length of the specimen of 2 x 10e5 L, (i.e. 2 pm per 100 mm). The contact force of, the extensometer should not exceed 1 N. That force shall act through
5、 contacts of planes with spherical faces the radii of curvature of which shall be not less than the rod diameter of the specimen. In some special assemblies (see figure I) parallel planes are needed. The specimen-holding assembly shall ensure that the specimen is held firmly in position and shall pr
6、event even small changes in its alignment with respect to the push-rod axis throughout the test (see examples given in the annex). If the specimen-holding assembly is made of vitreous silica, see the precautions given in 7.2. From time to time, a performance test shall be carried out using a referen
7、ce material (see clause 8). 4.3 Furnace, compatible with the dilatometer assembly, for temperatures up to 50 “C above the expected transformation temperature. The working position of the furnace relative to the dilatometer assembly shall be defined with a repeatability of 0,5 mm in both the axial an
8、d the radial directions. Within the range of testing temperatures (i.e. up to tempera- tures about 150 OC below the highest expected transformation temperature, ty and at least up to 300 Cl, the furnace shall be capable of marntaining a constant temperature to + 2 OC over the whole specimen length.
9、4.4 Furnace control device, suitable for the desired rate of increase in temperature up to (5 + I) OC/min within the test range (see 6.1) and for a cooling rate of (2 + 0,2) “Urnin for the annealing procedure according to 5.2. 1 Copyright International Organization for Standardization Provided by IH
10、S under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 00:30:01 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 7991 : 1967 (El 4.5 Temperature-measuring device (e.g. a thermocouple of type E, J or K in accordance with IEC 684
11、-11, capable of determining the temperature of the specimen to f 2 OC in the temperature range between to and t. 5 Test specimen 5.1 Shape and size The test specimen is usually in the form of a rod. Its shape depends on the type of dilatometer used. The length I, shall be at least 5 x lo4 times the
12、resolution of the dilatometer s measuring device for the change in length. NOTE - The specimen may be, for example, a rod either with a cir- cular cross-section having a diameter of 5 mm or with a square cross- section 5 mm x 5 mm, and between 25 and 100 mm in length. In cer- tain cases, a cross-sec
13、tion of at least 100 mm2 is more convenient (see the annex). 5.2 Preparation The test specimen shall be annealed before the test by heating it to about 30 YZ above the transformation temperature and then cooling it to about 150 OC below the transformation temperature at a rate of (2 + 0,2) Wmin, fol
14、lowed by further cooling to room temperature in draught-free air. 5.3 Number The test shall be carried out with two test specimens (see also 7.4). 6 Procedure 6.1 Choice of the test range In accordance with clause 3, the nominal reference temperature is 20 OC. For practical reasons, however, the mea
15、surement may be started between 18 and 28 OC. The preferred final actual temperature is 290 OC 10 x 10-a K-l. If the results for the two test specimens differ by not more than 0,2 x low6 K-l, take the arithmetic mean. If the difference is larger, repeat the test with two other test specimens. 8 Perf
16、ormance test In order to check that the whole test device is functioning cor- rectly, the test procedure and calculation laid down in clauses 6 and 7 shall be carried out on a specimen of a reference material, the value of the coefficient of mean linear thermal expansion of which is certified. I) Re
17、commended reference materials are as follows : - vitreous silica annealed according to 7.2; - sapphire single crystal; - chemically pure platinum. NOTE - Sintered alumina fAl203) as a reference material is very insen- sitive to the thermal treatment applied in the test procedure laid down in this In
18、ternational Standard. However, the values of the mean linear thermal expansion coefficient differ from one rod to another. The shape and dimensions of the reference specimen shall be similar to those of the specimens usually tested in the test device. Care shall be taken to ensure that the thermal e
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