BS EN ISO 2431:2019 pdf – Paints and varnishes – Determination of flow time by use of flow cups (ISO 2431:2019).
3.2 Newtonian flow behaviour where the shear viscosity is independent of shear rate, shear stress and time 3.3 non-Newtonian flow behaviour where the shear viscosity is dependent either on shear rate and shear stress or on shear rate, shear stress and time 3.4 kinematic viscosity ν ratio of shear viscosity and density Note 1 to entry: The kinematic viscosity υ has the unit square metres per second (m 2 ⋅s −1 ). 4 Temperature considerations Temperature and humidity are important parameters affecting test results. Deviations from the requirements specified can lead to results that are not comparable. However, the interested parties may agree upon alternative parameters and these parameters shall be reported. The effect of temperature on flow time is highly significant with respect to application properties and varies with the type of product. For reference purposes, (23,0 ± 0,5) °C is specified as the test temperature in this document. However, it might be more convenient to carry out comparative testing at some other agreed temperature (for example, 25 °C) because of prevailing temperature conditions (see also Annex B). For control by flow time, the test sample and flow cup shall be conditioned to an agreed or specified temperature and it shall be ensured that the temperature variation does not exceed 0,5 K during testing. The flow cup shall be in a place which is free from draughts. If testing is conducted in a fume cupboard and the air suction is left on, this shall be noted in the test report.
5 Apparatus 5.1 Flow cups 5.1.1 Dimensions The dimensions of the ISO flow cups and the tolerances allowed in manufacture shall be as shown in Figure 1. NOTE The most critical tolerance is the internal diameter of the jet of the flow cup, because the flow time is inversely proportional to the fourth power of this dimension. 5.1.2 Material The jet of the flow cup shall be made of stainless steel or sintered carbide, and the body of the flow cup shall be made of a material which is corrosion-resistant and is not affected by the products to be tested. 5.1.3 Construction The dimensions not specified, such as wall thickness, shall be such that no distortion of the flow cup can occur in use. The external shape should preferably be as shown in Figure 1, but may be modified for convenience of use, or manufacture, provided that the protruding jet of the flow cup is protected from accidental damage as far as possible by an external protective sleeve. Such a protective sleeve shall not be immediately adjacent to the jet, so as to prevent any capillary action when the material under test flows out. Flow cups having an additional jacket for temperature control are preferred. 5.1.4 Finish The interior surfaces of the flow cups, including the orifice, shall be smooth and free from turning marks, crevices, ledges and burrs which might cause random flow or trap sample or cleaning material. The standard of finish required is equivalent to a maximum roughness Ra (as defined in ISO 4287) of not more than 0,5 µm.
5.2 Supplementary apparatus 5.2.1 Thermometer, graduated at intervals of 0,2 °C or finer. 5.2.2 Stand, suitable for holding the flow cup and provided with levelling screws. 5.2.3 Spirit level, preferably of the circular type. 5.2.4 Flat glass plate with rounded edges or straight-edge scraper. 5.2.5 Stopwatch, or other suitable timing-device, with scale divisions of 0,2 s or finer. 5.2.6 Temperature-controlled room or enclosure, capable of maintaining the flow cup and sample at a recommended, constant temperature (see Clause 4). NOTE This will not be needed if the flow cup has a jacket for temperature control. 6 Sampling Take a representative sample of the material to be tested, as described in ISO 15528. Examine and prepare the sample for testing, as described in ISO 1513. A sample of 150 ml is sufficient for carrying out one test. Take care to mix the material thoroughly, while at the same time avoiding, as far as possible, loss of solvent by evaporation.