DS/ISO 2431:2019

Paints and varnishes - Determination of flow time by use of flow cups

1.1 This document specifies a method for determining the flow time of paints, varnishes and related*products that can be used to control consistency.*1.2 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 International Standard 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 International Standard. In general,*the fabrication tolerances for such flow cups are greater than those of the flow cups specified in this*International Standard. Therefore flow time determinations with dipping flow cups give a precision*which is lower than that obtained with the flow cups specified in this International Standard (see*Clause 9).*1.3 The method 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.*1.4 Flow times are reproducible only for products of Newtonian or near-Newtonian flow properties.*This effectively limits their practical use. Nevertheless, for checking purposes, these flow cups do serve*a useful purpose. Furthermore, the measurement of flow time is often used to confirm the application*consistency.*Paints often contain flow-arresting agents to confer increased viscosity. Such paints exhibit non-*Newtonian flow properties. Their viscosity during application can only be properly assessed using*viscometers such as that described in ISO 3219.*Resins and varnishes can exhibit Newtonian or near-Newtonian flow at much higher viscosities than*most paints and, where this applies, flow cups can provide a useful means of controlling the consistency.*To meet this requirement, this International Standard provides flow cups suitable for viscosities up to*about 700 mm2/s.*With thixotropic materials, stirring or other such mechanical disturbance immediately before testing*will reduce the flow time compared with that for an unstirred sample. With such materials, uncertain*and variable flow time values are obtained with all the flow cups. The repeatability and reproducibility*limits given in Clause 9 cannot be achieved in the determination of the flow time of such materials.