BS ISO 3384-2:2012 pdf download – Rubber, vulcanized or thermoplastic — Determination of stress relaxation in compression Part 2: Testing with temperature cycling
7.2 Measurement of dimensions of test pieces
The dimensions of test pieces shall be measured as specified in ISO 23529.
7.3 Number of test pieces
7.4 Time interval between forming and testing
The interval between forming and testing shall be in accordance with ISO 23529.
7.5 Conditioning of test pieces
7.5.1 Prior to testing, the test pieces shall undergo first thermal and then mechanical conditioning as detailed in 7.5.2 and 7.5.3. When using method A at elevated temperature, the thermal conditioning might not be required, as the preheating of the test piece before compression acts as thermal conditioning.
7.5.2 Thermal conditioning shall be carried out by heating the test pieces at 70 °C for 3 h. Following thermal conditioning, the test pieces shall be allowed to stand for a period of not less than 16 h and not more than 48 h at standard laboratory temperature prior to mechanical conditioning or testing. NOTE Some test samples, especially of thermoplastic elastomers, might contain moulding stresses, and thermal conditioning to relieve these stresses might improve the reproducibility of the results.
7.5.3 Mechanical conditioning shall be carried out at one of the standard laboratory temperatures specified in ISO 23529, as follows: Compress the test pieces to the same compression that will be used during the rest of the test and then immediately return them to zero stress; repeat this procedure to give a total of five cycles of deformation and immediate return.
Following mechanical conditioning, the test pieces shall be allowed to stand for a period of not less than 16 h and not more than 48 h at standard laboratory temperature prior to testing. Mechanical conditioning has been found to improve test reproducibility, particularly for compounds containing substantial proportions of filler, but is not always appropriate for finished products and can, therefore, lead to results that are not typical of service. Such conditioning may be omitted provided thermal conditioning is still undertaken. This omission shall be mentioned in the test report.
8 Duration, temperature and test liquid
8.1 Duration of test
The test period begins after the initial compression. If test times longer than one week are used, a logarithmic time-scale shall be employed.
8.2 Temperature of exposure Thetemperatureofexposureshallbechosenfromthelistoftesttemperaturesin ISO 23529.
Temperatures of exposure which cause rapid degradation or evaporation of the test liquid shall be avoided. The temperature shall be kept as constant as possible during the test, with the following tolerances (in accordance with ISO 23529): ±2 °C for standard laboratory temperature (23 ± 2) °C or (27 ± 2) °C, ±1 °C for temperatures up to 100 °C and ±2 °C for temperatures above 100 °C. For subzero temperatures, the tolerance is ±2 °C. For the cyclic tests specified in this part of ISO 3384, one elevated temperature and one subzero temperature shall be chosen.
8.3 Immersion liquids The test liquid shall be chosen according to the particular application, but should preferably be one of those listed in ISO 1817.
9.1 Preparation Carefully clean the operating surfaces of the compression device. When testing in a gas, apply a thin coating of a lubricant having substantially no action on the rubber.
NOTE A silicone or fluorosilicone fluid (having a kinematic viscosity of about 0,01 m 2 /s) and molybdenum disulfide have been found to be suitable lubricants.
9.2 Thickness measurement
9.2.1 Cylindrical test pieces Measure the thickness of each test piece at the central portion with an accuracy of 0,01 mm, after thermal conditioning and before mechanical conditioning, at the chosen standard laboratory temperature, as specified in ISO 23529.
9.2.2 Ring test pieces Measure the axial thickness of each test piece with an accuracy of 0,01 mm at four points approximately 90° apart around the ring after thermal conditioning and before mechanical conditioning, at the chosen standard laboratory temperature, as specified in ISO 23529. Use the average of the measurements to calculate the necessary compression. Individual measurements, on a single test piece, shall not differ by more than 0,05 mm. If they do, discard the test piece.
9.3 Method A 9.3.1 In this method, the test piece is aged at a high temperature, and the temperature is lowered once a week to a low temperature, at which the remaining counterforce is measured. A material or product specification can specify the temperatures and the minimum remaining counterforce (or the minimum value of F tx /F 0 ) (see Clause 10) required at each temperature.