definitions & history

manufacture

hydration

classification

types

TESTS

field examination

lab tests

Different Test sieves are just like different individuals. Being fabricated of a woven mesh material, variations in the weave are common. The chances of locating two sieves with an identical distribution of opening sizes are extremely remote. Due to these variations, the reproducibility of test results between sieves can be adversely affected.

The stringent standards imposed by ASTM, ISO or other regulating bodies have established tolerance factors which allow for the permissible variations in the weave while striving to maintain a level of uniformity in the performance of the 'test grade' sieve cloth.

With this variation of opening sizes present, some smaller than the nominal and some larger, the time interval of the sieve analysis becomes extremely important. If, for example, a sieve has several openings far above the nominal opening size for the particular mesh size, and the test is run for 30 minutes, the probability of larger-than-nominal particles finding those oversize openings is much greater than if the test was run for only 15 minutes. Similarly, if the sample of powder contains a large percentage of elongated or needlelike particles, a longer test interval would provide a greater likelihood that the elongated particles will orient themselves 'on end' and pass through the openings. If the sieving cloth has a wide range of opening sizes, the sieving of this type of material has a compounded error.

Therein lies the significance of specifying the sieving time.