Screen extruders

Figure 24 The effect of extruder screen pressure on the yield of particles within an acceptable distribution.

Extruder Screen pack Extrusion conditions Zone 1 Zone 2... 

Rotating microscreen batch, fluid loading 3 to 6 L/s m of submerged area usually 66% area submerged solids loading 0.05 to 0.1 g/s m headless 7 to 14 cm to max. of 45 cm. Clean by backwash at 2 to 5 % volumetric throughput capacity. Screen pack downstream of extruders screen pack area directly proportional to rate of extrusion. Cycle time for the screen to blind > time between shutdowns. For example, screen pack area 0.17 m s/kg and screen pack diameter 20 cm s/kg but must be custom selected for the polymer. 

Variable bottle weight Finer extruder screen pack Increase screw cooling Raise rear extruder heats Decrease extruder rate... 

O Connor et al. indicated that the friability of placebo spheres decreased with increasing residence time while the mean particle diameter decreased (24). Erkoboni et al. showed an increase in extruder screen size resulted in reduced friability (21). 

Variable bottle weight 1. Finer extruder screen pack 2. Increase screw cooling 3. Raise rear extruder heats 4. Decrease extrusion rate... 

This approach was adopted for a study of polypropylene used as the filler in the interstices between the cores of some types of three-phase power distribution cables. The cores consisted of a conductor with polymeric insulation and extruded screens which were in turn screened with copper tape. Polypropylene twine is used to pack the interstices as the cable is laid up and then the outer parts of the cable are applied later. Thus the polypropylene is in direct contact with the copper tape. 

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