BS EN ISO 2431:2019 pdf download – Paints and varnishes – Determination of flow time by use of flow cups (ISO 2431:2019)
This document specifies a method for determining the flow time of paints, varnishes and related products that can be used to control consistency. Four flow cups of similar dimensions, but having orifice diameters of 3 mm, 4 mm, 5 mm and 6 mm, are specified. Two methods for checking the flow cups for wear and tear are given (see Annex A). Flow cups with a replaceable jet are not covered by this document as the close tolerances on the supply of the material under test to the jet are not met. Commonly used dipping flow cups are also not covered by this document. NOTE Since the fabrication tolerances for such flow cups are greater than those of the flow cups specified in this document, flow time determinations with dipping flow cups give a precision which is lower than that obtained with the flow cups specified in this document (see Clause 9). The method described in this document is limited to testing materials for which the breakpoint of the flow from the orifice of the flow cup can be determined with certainty. This point is difficult to determine and reproduce for materials with flow times near the upper limit of the measurement range (100 s) due to slowing-down effects.
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 1513, Paints and varnishes — Examination and preparation of test samples
ISO 4618, Paints and varnishes — Terms and definitions
ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
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flow time
time that elapses from the moment when the material under test starts to flow from the orifice of the filled flow cup to the moment when the flow stream of material first breaks off close to the orifice
Newtonian flow
behaviour where the shear viscosity is independent of shear rate, shear stress and time
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
kinematic viscosity
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.