ISO 2431:2011 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 in an annex.
Flow cups with a replaceable jet are not covered by ISO 2431 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 ISO 2431. In general, the fabrication tolerances for such flow cups are greater than those of the flow cups specified in ISO 2431. Therefore flow time determinations with dipping flow cups give a precision which is lower than that obtained with the flow cups specified in ISO 2431.
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.
