Mesh (scale)
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Mesh material is often used in determining the particle size distribution of a granular material. For example, a sample from a truckload of peanuts may be placed atop a mesh with 5 mm openings. When the mesh is shaken, small broken pieces and dust pass through the mesh while whole peanuts are retained on the mesh. A commercial peanut buyer might use a test like this to determine if a batch of peanuts has too many broken pieces. This type of test is common in some industries, and to facilitate uniform testing methods, several standardized mesh series have been established.

Applicable standards are ISO 565 (1987), ISO 3310 (1999), ASTM E 11-70 (1995), DIN 4188 (1977), BS 410 (1986) and AFNOR NFX11-501 (1987).

Tyler mesh size

One well-known mesh series is the Tyler Equivalent created by the W.S. Tyler screening company^[1] . Tyler mesh size indicates exactly the number of openings per square inch of mesh. For instance, a Tyler number 4 mesh will have 4 openings per square inch, and 16 means it will have 16 openings per square inch. To calculate the size of the openings in a mesh the thickness of the wires making up the mesh material must be taken into account. In practice, mesh openings are determined referring to a chart like the one below.

Variation in mesh openings

Some standards use the mesh designation as the number of wires rather than the size of openings (see Tyler, above). There can be significant differences in particle size passing small laboratory screens versus large heavy-duty industrial screens due to the different wire sizes used. Thicker wire results in a smaller opening size for an equivalent mesh. An example of variation moving between machine sizes is:^[2]

Particle size distribution

Powders and granular materials are sometimes described as having a certain mesh size (e.g. 30 mesh sand). By itself, this type of description is somewhat ambiguous. More precise specifications will indicate that a material will pass through some specific mesh (that is, have a maximum size; larger pieces won't fit through this mesh) but will be retained by some specific tighter mesh (that is, a minimum size; pieces smaller than this will have passed through the mesh). This type of description establishes a range of particle sizes.

One notation for indicating particle size distribution using mesh size is to use + and - designations. A "+" before the sieve mesh indicates the particles are retained by the sieve, while a "-" before the sieve mesh indicates the particles pass through the sieve. This means that typically 90% or more of the particles will have mesh sizes between the two values.

For instance, if the particle size of a material is described as -80/+170 (or could also be written -80 +170), then 90% or more of the material will pass through an 80 mesh sieve and be retained by a 170 mesh sieve. Using the conversion chart below, the resulting particles will have a range of diameters between 0.089 and 0.178 mm (89 and 178 micrometers).

Abrasives

The Federation of European Producers of Abrasives (FEPA) has four sets of standards to denote size of grains coupled with the type of abrasive. The standards indicate a range of grit sizes that may come within any single designator which consists of a letter (F for bonded abrasives and P for coated abrasives) and a number. Within each series are two standards detailing the larger macrogrit (approximately 12 – 240) and smaller microgrit (approximately 230 – 2000 or 2500) sizes and the different process by which sizes are determined (sieving for the larger grits and sedimentation for the smaller).

While following the common practice of smaller designators meaning coarser grits and similar cut-off marks between macro- and microgrit standards, the F and P series are not compatible. While F 12 and P 12 are only about 3% different in size, P 2000 is more than 750% larger than F 2000 (that is, the particles in F 2000 are about 8.5 times as large as those in P 2000).^{[4] [5]}

Sieve size conversion chart

Resources

• Laboratory screen product guide, WS Tyler

References