The screen cloth is the part of a vibro sifter that actually does the separating, so choosing it well matters more than almost any other specification. A screen that is too fine limits capacity and blinds quickly; one that is too coarse lets oversize material through. This guide explains the terms suppliers use and how to arrive at the right choice for your material.
Mesh number versus aperture
"Mesh" is the number of openings per linear inch of woven wire cloth. A 40 mesh screen has 40 openings across one inch. The size of each opening, however, also depends on the diameter of the wire: the same mesh count woven with a thicker wire has smaller openings and less open area. That is why two "60 mesh" screens from different sources can behave differently.
The figure that really controls separation is the aperture (opening size), normally given in millimetres or microns. Whenever you can, specify the aperture rather than the mesh number. As a rough reference, standard test sieves use these openings:
| Test sieve designation | Nominal opening |
|---|---|
| No. 20 | 850 µm |
| No. 40 | 425 µm |
| No. 60 | 250 µm |
| No. 100 | 150 µm |
| No. 200 | 75 µm |
Production screen cloth is woven with a range of wire diameters, so use the table as a guide and confirm the actual aperture with your supplier.
Start from the job the screen has to do
- Safety or check screening (removing lumps, foreign matter or packaging fragments from an otherwise good product): choose an aperture a little larger than your largest acceptable particle, so good product passes freely and only genuine oversize is retained.
- Grading (splitting a product into size fractions): the aperture of each deck is the cut point between two fractions. Here accuracy matters more than raw throughput.
- De-dusting (removing fines): the aperture sets the upper size of the fines you remove.
Open area, capacity and screen life
Open area is the percentage of the screen surface that is holes. A higher open area passes material faster, but uses thinner wire, which wears out sooner. Abrasive materials such as minerals or metal powders often justify a heavier wire and a slightly larger screen diameter instead of a very fine, fragile cloth.
Watch for near-size particles and blinding
Particles that are almost exactly the size of the aperture tend to wedge in the openings and gradually block the screen ("blinding"). Moist, sticky, fibrous or electrostatic powders make this worse. If your material contains a lot of near-size particles, discuss anti-blinding options and a realistic feed rate before finalising the mesh.
Test with your own material
Bulk density, particle shape, moisture and temperature all change how a powder screens. The most reliable way to choose a mesh is a trial with a representative sample of your product. When you send an enquiry, include the material name, required capacity, the particle size you want to pass and retain, and any hygiene or material-of-construction requirements, and we will suggest a suitable screen configuration.