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GB/T 16920-2015 PDF English


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GB/T 16920-2015: PDF in English (GBT 16920-2015)

GB/T 16920-2015 GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 81.040.01 N 64 Replacing GB/T 16920-1997 Glass - Determination of coefficient of mean linear thermal expansion (ISO 7991.1987, NEQ) ISSUED ON. DECEMBER 31, 2015 IMPLEMENTED ON. JULY 01, 2016 Issued by. General Administration of Quality Supervision, Inspection and Quarantine; Standardization Administration of PRC. Table of Contents Foreword ... 3  1 Scope ... 4  2 Normative references ... 4  3 Terms and definitions ... 4  4 Instruments ... 5  5 Test samples ... 6  6 Procedures ... 7  7 Representation of results ... 8  8 Test of instrument performance ... 10  9 Test report ... 11  Appendix A (Informative) Collimation self-adjusting device for sample and push rod shaft ... 12  Glass - Determination of coefficient of mean linear thermal expansion 1 Scope This standard specifies the method for determining the coefficient of mean linear thermal expansion of elastic solid glass. This standard applies to the determination of the coefficient of mean linear thermal expansion of glass of various materials. 2 Normative references The following documents are essential to the application of this document. For the dated documents, only the versions with the dates indicated are applicable to this document; for the undated documents, only the latest version (including all the amendments) are applicable to this standard. GB/T 1216 External micrometer GB/T 21389 Vernier dial and digital display calipers 3 Terms and definitions The following terms and definitions apply to this document. 3.1 Coefficient of mean linear thermal expansion α (t0; t) Within a certain temperature interval, the ratio of the length change of the specimen to the temperature interval and the initial length of the specimen, expressed by the formula (1). Where. performance. The method is as shown in the calibration and verification of the performance test of instrument. 4.3 Heating furnace The heating furnace shall be matched with the dilatometer device. The upper limit of temperature shall be about 50 °C higher than the expected determined temperature of transformation (t). The working position of the heating furnace as relative to the dilatometer shall have a reproducibility within 0.5 mm in the axial and radial directions. Within the range of test temperature (i.e., the upper limit temperature is 150 °C lower than the highest expected transformation temperature tg, at least the temperature difference between 300 °C and tg is greater than 150 °C, and shall not be lower than 300 °C), throughout the determination interval of the entire specimen length, the furnace’s temperature shall be constantly controlled within ±1 °C. The heating furnace shall be able to meet the control requirements of 5 °C/min ± 1 °C/min. Within the range of the test temperature, the ideal rate of temperature rise is 5 °C/min ± 1 °C/min. 4.4 Temperature measuring device In the temperature range of t0 and t, it may be able to accurately determine the temperature of the specimen, the error is less than ±1 °C. 5 Test samples 5.1 Shape and size The specimen is usually rod-shaped, the shape of which depends on the type of dilatometer used, the length L0 shall be at least 5 × 105 times the resolution of the length measuring device of the dilatometer. Note. For example, the specimen may be a round bar which has a diameter of 5 mm, length of 50 mm ± 1 mm; or according to the structure of the dilatometer, it may also be a square bar which has a section of 5 mm × 5 mm and a length of 25 mm ~ 100 mm. The specimen of other square or rectangular sections shall be able to ensure the accuracy and repeatability of the measurement (see Appendix A). 5.2 Preparation of specimen Select the glass which has no defects such as stones, bubbles, and streaks. Use the mechanical cutting or hot working methods to prepare it into the shape and size required for the specimen, then make it annealed. The annealing difference between the hot joint of the thermocouple and the specimen, the apparent temperature of the specimen shall plus the corrected value. Note. The magnitude of this corrected value depends on the rate of temperature change as well as the rate of heat exchange between the heating furnace and the specimen. Fundamentally, the corrected value is to be determined by comparison with a constant temperature test. 6.4 Constant temperature test At the initial temperature t0, determine the position of the dilatometer. Use this reading as the zero point of the uncorrected amount of change of length ΔLmeas to be measured. Then rise the temperature of furnace to the selected end-point temperature t, keep the furnace’s temperature constantly at ±2 °C. After 20 min, take the reading of ΔLmeas from the dilatometer. Note. Although the temperature-rise test can determine the coefficient α (t0; t) of various temperatures t during the test, if only one end-point temperature t is required, it shall give priority to the constant-temperature test, because this test may provide better accuracy. 7 Representation of results 7.1 Calculation of final length From the measured length variable ΔLmeas, the corrected length L at the temperature t is calculated by the use of formula (2). Where. The correction terms ΔLQ and ΔLB are explained in 7.2 or 7.3, respectively. 7.2 Calculation of expansion of specimen-bearing device (ΔLQ) In the case of a single-pusher-type dilatometer, the correction term ΔLQ in the formula (2) is the thermal expansion of the portion (length = L0) of the specimen- bearing device which is located near the specimen at a temperature of t0. In the case of a differential-pusher-type dilatometer, the correction term ΔLQ is the thermal expansion of the standard bar. The standard bar has a same length as the sample, which is L0 at the temperature of t0. In either case, the correction term ΔLQ is calculated by the use of formula (3). determination of glass. It shall repeat the blank test each time when performing the test of instrument performance in accordance with clause 7. 7.4 Calculation of coefficient of average linear thermal expansion To calculate the coefficient of average linear thermal expansionα (t0; t), substitute the measured values of L0 and ΔLmeas, the correction value as established in accordance with 6.2 and 6.3, the measured value of t0, the t value (if it is the temperature-rise test, use the corrected value) into the formula (4). Calculate α (20 °C; 300 °C) of two specimens (5.3). It may also determine α (20 °C; 200 °C), α (20 °C; 100 °C) or α (20 °C; 400 °C), respectively, as needed. If α (20 °C; t) < 10 x 10-6 K-1, take two significant digits; if α (20 °C; t) ≥ 10 x 10- 6 K-1, take 3 significant digits. If the deviation of the results of the two specimens is not more than 0.2 × 10-6 K-1, take the arithmetic mean. Otherwise, use the other two specimens to repeat the test. 8 Test of instrument performance In order to check whether the entire test device is operating normally, use the standard materials to make samples, follow the provisions of clause 5 and clause 6 to perform test and calculation; the coefficient of average linear thermal expansion of the standard samples is a known standard value. It is recommended to use the following standard materials. - Sapphire standard glass; - Alumina ceramic standard sample; - American standard reference material 731 borosilicate glass (NIST SRM 731); - Pure platinum rods; - Quartz glass that has been annealed in accordance with 5.2. The shape and size of the standard sample shall be similar to the shape and size of the sample that is typically tested in the test device. It shall be ensured that the thermal expansion characteristics of the standard material are not altered by the test. If the standard material is glass, it shall be ......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.