Dewatering extruders

For the manufacture of turning pastes, the paste slip is dewatered with filter presses to water contents of 20 to 25% by weight, comminuted in a sieve kneader and formed in vacuum extruders into suitably sized slugs. 

Rotary press dewater and handle flocculated solids. Particle size 1-50 pm feed solids 0.1-25% w/w. Related to extruders. Section 9.11 and expellers. Section 5.17. 

When the rubber is slippery, as in dewatering rubber extruders, the feed section of the barrel is grooved to prevent slipping along the barrel surface or the barrel I.D. may be fitted with pins. This significantly improves the conveying action of the extruder. The same technique has been applied to the thermoplastic extrusion, as discussed in Section 1.4 and Section 7.2.2.2. 

A twin-screw extruder is fed with dry fluff-pulp and the phosphoric acid solvent. The first cooled zone mixes the cellulose into the solvent and reduces the particle size, the second hotter zone starts the dissolution, and the third zone provides further blending and dissolution time, its temperature being controlled to achieve the desired reduction in cellulose DP. A final low pressure zone allows deaeration and dewatering (or the injection of additives) as necessary, and filters remove particles before spinning. 

Coarse materials are dewatered and washed on fine mesh screens and stockpiled for further processing. Metallics may simply be melted in a pot or standard lead kettle or can be melted in a short rotary furnace, with some collection of a htharge slag to separate antimony and arsenic and produce a soft lead. Separator plastics are usually disposed of in landfill but polypropylene is thoroughly washed, and extruded as pellets for sale to battery manufacturers for new case production. 

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