High purity thermoplastics insulation esp. for high voltage cables - is extruded from final extruder after sieving from preliminary extruder

摘要

An appts. comprising an extruder for thermoplastics, esp. for polyolefin-based insulation for high voltage cables, has the supply to this extruder provided by a straining extruder equipped with fine-mesh sieves on it outlet side. Specifically, the straining extruder and final extruder are combined in one very long extruder assembly, the ratio of screw length to dia. >=30 and the sieve being approximately in the middle of the screw. The sieve may be composed of a number of replaceable sieves, the smallest mesh size being 50 mu. Used where extremely high purity of the extruder material is required, partic. for the insulation of high voltage cables. The use of an upstream extruder equipped with fine sieves on its outlet side ensures that the material entering the final extruder is extremely pure.