ISO 23766:2022 pdf – Thermal insulating products for industrial installations — Determination of the coefficient of linear thermal expansion at sub-ambient temperatures.
1 Scope This document specifies the equipment and procedures for determining the coefficient of linear thermal expansion at sub-ambient temperatures (−196 °C to 25 °C), subject to the possible temperature limitation of the test specimens. It is not applicable to products which experience dimensional changes during the test due to the loss of hydration water or which undergo other phase changes. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 9229, Thermal insulation — Vocabulary ISO 18099, Thermal insulating products for building equipment and industrial installations — Determination of the coefficient of thermal expansion 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 9229, ISO 18099 and the following apply. ISO and IEC maintain terminology databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https:// www. iso. org/ obp — IEC Electropedia: available at https:// www .electropedia. org/ 3.1 sub-ambient temperature temperature from −196 °C to 25 °C at which the thermal insulation product is used to reduce heat flow 4 Method A — Optical method 4.1 Principle The changes in a product’s linear dimensions, as its temperature is changed, are measured and characterized by the optical measurement method (See Figure 1 for an example).
4.2.4 Temperature-measuring instruments Calibrated thermocouples suitable for the test with an accuracy of ± 0,5 K. The thermocouples are connected to a stepwise recording device. If only the mean coefficient of linear thermal expansion, α m , between two temperatures is needed, the measurements shall only be carried out at these temperatures. If the full curve over a temperature range is needed, it shall be done in a continuous way. 4.2.5 Equipment to prepare the test specimen Suitable saw or thin-walled steel tube to prepare the test specimen. The thin-walled steel tube is a steel tube with a thin wall, and one side is sharp, which can be used to cut a cylinder-shaped specimen. 4.3 Test specimen 4.3.1 Dimensions of test specimens The dimensions shall be appropriate for the dimensions of the apparatus and smaller than the width of the light beam, usually 10 mm to 30 mm. Because of its small dimensions, the test specimen should be carefully selected to be representative of the product being tested. The shape of the specimen can be a cylinder or cuboid. If a cuboid is used, the trapezoidal transversal surface is in favour of avoiding the influence of deviation of the position, where the topline will not influence the measurement of baseline. For anisotropic materials, the direction should be marked and recorded. The material tested can be rigid or flexible material, except the transparent materials. 4.3.2 Preparation of test specimens Any skins, facings, and/or coatings shall be removed. Test specimens shall be sawn or cut from the product with a thin-walled steel tube in the direction in which the measurement of the coefficient of linear thermal expansion shall be made and in which the linear dimensions are to be recorded. Special requirements for preparation such as annealing or drying under specified conditions shall be indicated where relevant in the product standard. For anisotropic products, the measurements shall be carried out both in the direction of the length and of the width.
4.5 Procedure Clean the test specimen and position it in the centre of the light beam area in the chamber, making sure that the end surfaces are perpendicular to the light beam. Measure its length at (23 ± 2) °C which shall be considered as the reference temperature. Place the thermocouples in a hole, which is on the backside of the light beam of the specimen, or in good contact with the test specimen in which emissivity of the test specimen and thermocouples should be matched. Close the test chamber and cool the system to the lowest temperature needed. Then heat the chamber, making sure that the temperature gradient given in the relevant product standard is respected. If no information is available, do not exceed 3 K/min and 1 K/min for the last 50 °C interval to target temperature. Stabilize the temperature at temperature intervals over a time sufficient to obtain a uniform temperature within the test specimen. Usually, 30 min is sufficient. Measure the temperature and the test specimen length when stable temperature is recorded (±1 K). Record the length variation/temperature curves continuously. When the temperature returns to the reference value, remeasure the length. If irreversible changes have occurred, repeat the cycles until only reversible changes occur, and the irreversible changes should be reported as a whole for information. The result shall be calculated from the readings of the reversible changes.