What is a Test Sieve
A test sieve is an instrument that is used for the measurement of particle size. In its most common form, it consists of a woven wire screen, with square apertures, rigidly mounted in a shallow cylindrical metal frame. For coarse sieving, a perforated plate screen with square or round holes may be used in place of wire mesh. Square hole perforated plate sieves range down to 4 mm and round hole sieves down to 1 mm aperture.
The sizes of solid particles from 125 mm down to 20 µm can be measured rapidly and efficiently by means of standard test sieves. Special sieves with apertures smaller than 20 µm are available, but it should be appreciated that the finer a screen is, the more easily will certain types of particulate solids tend to block or blind the apertures. Nevertheless, ‘micro’ sieving can be carried out down to 5 µm using special techniques.
Particle size, as measured by test sieving, may be specified simply by quoting two sieve sizes, one through which the particles have passed, and the other on which they are retained.
However, the most frequent use of test sieving is for measuring the size spread, i.e., the particle size distribution.
Test sieving is not the only method available for particle size analysis, but it is certainly the most widely used and probably the most important. A shortlist of some of the more common methods, together with their effective size ranges, is given in Table 1.
|Method||Measuring range [µm]|
|Microscopy (electron)||0.005 – 1|
|Liquid sedimentation (centrifugal)||0.05 – 5|
|Optical microscopy||0.25 – 50|
|Liquid sedimentation (gravity)||1 – 20|
|Dynamic Image Analysis||1 – 30 000|
|Electrical sensing zone (Coulter)||1 – 200|
|Laser light scattering (Fraunhofer)||1 – 1 000|
|Air elutriation||5 – 50|
|Test sieving||5 – 125 000|
The table shows two important characteristics of sieving: first, it covers a very wide range of particle size – this very range is the one which happens to be of considerable industrial importance. Secondly, it meets little or no serious competition from the other methods
Advantages of Sieving
Perhaps the biggest advantage of test sieving is that it so frequently happens to be the only suitable method of size analysis for a particular purpose. However, even when there is a choice of method, test sieving generally proves to be the most convenient one.
It is a quick and reliable method of size analysis, equally suited to accurate scientific research work or routine analysis under industrial conditions. Tests can be performed at almost any location.
No complicated apparatus is demanded. A nest of sieves and a simple laboratory balance will suffice in most cases. In fact, rapid size checks can often be made on-site at a particular plant with the aid of a rough pair of scales.
The technique of test sieving is basically simple. No specialized knowledge or skill is needed; care and diligence are the main requirements. Process operators can easily be trained to carry out sieve tests.
When the size distribution of a sample has been determined by test sieving, the material becomes separated into several fractions. This is another important attribute. These fractions are not contaminated, nor have their chemical or physical properties been altered. They are, therefore, available for further inspection or independent analysis if required.
For a selection of sieves and systems, please see our selection from Endecotts.