What's So Complicated About Sieve Testing?

By: Arthur Gatenby Click author's name for more of his/her articles

Sieving in its most elemental definition is the separation of fine material from coarse material by means of a meshed or perforated surface. The technique was used as far back as the early Egyptian days as a way to size grains. These early sieves were made of woven reeds and grasses. Today the sieve test is the technique used most often for analyzing particle-size distribution.

Although at first look the sieving process appears to be elementary, in practice, there is a science and art involved in producing reliable and consistent results. In order to better understand sieving, there are several areas of sieve specifications that should to be explained, including:

The first sieve testing standards were developed by W.S. Tyler Company before 1920. This original work predated any published activity by the standards organizations and the Tyler designation is the de facto standard in many industries. In 1925, ASTM International prepared the official standard for Test Sieve Size, Test Sieve Construction, and Test Sieve Mesh in the United States. European Standards were developed by a German university group in 1977 and are known by the designation DIN 4188. These were followed by British Standards (BS 410). The International Standards (ISO 565) were developed by the International Standards Organization in Europe. This was designed to be the universal international standard. However, in practice, all of the standards are in operation.

Sieve testing standards relate to the construction of the sieve frame and mesh mounting as well as the tolerances allowed in the variability of mesh openings. Basic principles are common to all of the standards and variations in terminology and in details are small. These small differences, however, can often lead to confusion. The following is a synopsis of the principles behind these standards.

Test sieve frame standards include the following:

1.Rigid construction

2.Cloth (mesh) mounted without distortion, looseness, or waviness

3.Joint between mesh and frame to be filled or constructed so that particles will not be trapped

4.Frame will be of non-corrosive material and seamless

5.Bottom of the frame sized to easily slide into the top of same sized sieve, thus enabling stacking

6.Cloth opening to be a minimum of 0.5 inches less than nominal diameter

The wire cloth (mesh) standards include the following list of nominal size openings in inches, millimeters (microns), and sieve number. The following specific dimensional examples come from the ASTM E11 Standard:

1.Permissible variation of average openings (depending on opening size and ranges from ± 2.9% of nominal size for 125 mm mesh to ± 15% for 20µ mesh)

2.Not more than 5 % of the openings can exceed 1.04 times the nominal size for 125 mm mesh to 1.45 times the nominal opening for 20µ mesh

3.Maximum individual opening (for any opening) ranges from 1.0472 times the nominal size for 125 mm mesh to 1.75 times the normal mesh for 20µ mesh

4.Wire diameters are specified and range from 8 mm for 125 mm mesh to 0.020 millimeters for 20µ mesh

More recently, methods based on laser and energy technologies, sedimentation techniques, image analysis, and centrifuge-type methods have gained acceptance. However, procedures using test sieves are still widely used. The sieve-test result remains the basis or standard against which newer techniques are checked. In addition, the equipment cost for the test sieve procedure is significantly lower than the capital investment needed for newer methods.

Copyright (c) 2009 CSC Scientific Co

Article Source: ABC Article Directory

About The Author: Arthur Gatenby has been involvedin measurement and control for more than 30 years. Art is President of CSC Scientific. CSC specializes in the production and distribution of equipment used to measure moisture, www.cscscientific.com/html/sieves.html particle size and surface tension.