Screens and Screen Changers

The screens before the breaker plate are generally incorporated to filter out contaminants. The coarsest screen (lowest mesh number) is usually placed against the breaker plate for support, with successively finer screens placed against it. A typical screen pack is one 100-mesh screen followed by one 60-mesh and one 30-mesh screen, with the 30-mesh placed against the breaker plate. Some extrusion operations use as many as twenty 325-mesh screens backed up by coarser screens, as reported by Flathers [10]. 

There are three important types of metallic filter medium wire mesh, sintered powder, and random fiber. Wire mesh comes in a square weave or Dutch twill (woven in parallel diagonal lines). The different filter media do not perform equally with respect to their ability to hold contaminant, capture gels, etc. [11, 12]. A relative performance comparison is shown in Table 3.7. 

Gel capture Poor Fair Good Very good 

Contaminant capacity Fair Good Fair Very good 

Permeability Very good Poor Fair Good 

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