ISO 2431:2019 pdf free
ISO 2431:2019 pdf free.Paints and varnishes – Determination of flow time by use of flow cups
With the orifice closed by a finger, fill the flow cup with the well stirred, bubble-free sample, pouring slowly to avoid the formation of air bubbles. If bubbles are formed, allow them to rise to the surface and remove them.
NOTE If the flow cup has been properly levelled, the sample will overflow evenly over the rim into the gallery.
Remove any meniscus formed either by drawing the straight-edge scraper (see 5.2.4) over the entire rim of the flow cup or by sliding over the rim a flat glass plate with rounded edges so that no air bubbles form between the glass and the surface of the sample, subsequently drawing this plate horizontally across the rim of the flow cup so that, when the plate is removed, the level of the sample coincides with the top rim of the flow cup.
Place a suitable receiver under the flow cup so that the distance between the orifice of the flow cup and the surface of the received sample is never less than 100 mm. Remove the finger from the orifice and simultaneously start the timing-device (5.2.5), stopping it as soon as the first break occurs in the stream of sample close to the orifice. Record the rounded flow time to the nearest 0,5 s.
Carry out a second determination on another portion of the originally prepared sample and check carefully that the temperature of testing is within the prescribed limits. Record the flow time to the nearest 0,5 s. Calculate the mean of the two determinations.
If the two determinations differ by more than 5 %，carry out a third determination. If the third determination and either of the previous determinations do not differ by more than 5 %, discard the outlier. Calculate the result as the mean of the two accepted determinations.
If the third determination does not provide this measure of agreement, the method of test is unlikely to be suitable because of non-Newtonian flow behaviour, and consideration shall be given to other methods of test, e.g. to measuring the viscosity using a rotational viscometer.ISO 2431 pdf free download.
