Filter Discs for Sieving Contaminant

Filter discs, used in most extruders, are usually square mesh. The purpose of filter discs is to filter out contaminants and also to build up pressure in the extruder.

Typically, the filter discs are supported on a breaker plate, a perforated steel disk that prevents the discs from being pushed into the head and die and serving as a seal between the head section and the extruder barrel.

The exception to the square mesh is Dutch weave, where one direction uses fewer and thicker wires than the other.

This arrangement results in a stronger screen with rectangular openings. In most extrusions, a filter disc is used, which is made from several mesh: a 20 mesh is put up against the breaker plate, then perhaps a 40 mesh.

In case of extreme levels of filtration required, an 80 mesh is used after the 40 mesh. Some very critical applications such as fibers, filaments and thin film use even finer screens, such as 200-350 mesh.

Most filter discs are assembled with the heaviest screen next to the breaker plate, as heavier screens support the finer ones and prevent their blowing through from the differential pressure.

In the reverse arrangement, the coarser mesh will catch most of the contamination and the pressure drop across the finest one will stay low, preventing a blow-through.