BS EN ISO 305:2019 pdf download – Plastics – Determination of thermal stability of poly(vinyl chloride), related chlorine- containing homopolymers and copolymers and their compounds – Discoloration method 8 Method B: Oven method 8.1 Apparatus 8.1.1 Forced-air-circulation oven, having the following additional features: 8.1.1.1 The temperature of the oven shall be controlled by a thermostat capable of maintaining it to within ±0,5 °C of the temperature selected. 8.1.1.2 The oven shall be equipped with a calibrated thermometer and the proper system correction shall be applied to the temperature measurement. 8.1.1.3 The air flow in the oven shall be adjusted to provide a temperature which is sufficiently uniform throughout the test area of the oven that specimens of uniform colour are produced (see 8.1.2, second paragraph). This will usually require an air flow of 0,3 m 3 /min. 8.1.1.4 Prior to the test, the uniformity of the temperature within the oven shall be verified. Temperature uniformity is usually verified by placing thermocouples near each corner and at the centre; checks are made at 5 min intervals. It may also be done by inserting, at the test temperature, a rack with 8 to 10 specimens from the same sample distributed over the test area and exposing them until an early stage of discoloration is reached. The formulation shall be such as to cause a sharp change in colour within 45 min to 60 min under the test conditions. A non-uniform temperature distribution, as indicated by differences in the colours of the exposed specimens, shall be corrected before proceeding with the test. 8.1.1.5 The inside of the oven shall be free of contamination and surface deposits. Use stainless-steel oven liners to reduce corrosion due to extended exposure to decomposition gases. 8.1.2 Specimen supports, made of new, clean aluminium foil laid on a removable oven rack (grille). If an oven equipped with a rotating specimen-holder is employed, the specimens shall be supported so that no appreciable elongation or necking down of the test specimens occurs during the test, since this would alter the specimen dimensions, and especially the thickness. In this case, the uniformity of the oven temperature shall be checked with the specimen holders mounted on the rotating device. 8.1.3 Timing device, for example a stopwatch, with an accuracy of 0,5 min or better. 8.2 Procedure 8.2.1 Prepare, for each exposure time envisaged, a specimen support (8.1.2) of sufficient size to hold one...
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