Extrusion International 6-2022

49 Extrusion International 6/2022 ical reasons, throughputs achievable with one unit are approx. 1,000 kg/h. Connection of several units in parallel enables larger amounts of material to be easily separated. In the separation of ABS-PS mix- tures, for example, the ABS is sepa- rated as a high purity fraction in a first separation stage. The PS is also recovered as a pure fraction in a subsequent second separation stage. Due to the special electro- static charging unit, it is also pos- sible to simultaneously separate a filled polypropylene fraction, as it is in the same density range as ABS and PS. Foreign substances in a good product When processing PS and ABS from car shredders or electronic scrap, it is found that after passing through the various separation stages, there are still small amounts of unwanted foreign substances such as wood or rubber in the ground material. It is essential to separate these substanc- es to ensure subsequent processing into high grade compounds or even directly into products. While wood can be separated by melt filtration, rubber or other elastomer frac- tions pose more serious problems. Especially at high pressure in an ex- truder, these elastomers are pressed through the melt filters and lead to a reduction in the quality of the fin- ished product. Wood separation Wood is usually moist and there- fore conductive. For this reason, wood present in plastic can easily be separated with the help of an elec- trostatic separator of the “conduc- tor/non-conductor separator” type, such as the hamos KWS equipment. A highly concentrated conductive fraction is obtained, which also con- tains rubber particles, cardboard and other unwanted conductive residues. Rubber separation Separation of an unwanted rub- ber fraction is more difficult. Since this fraction also contains silicones, chlorinated rubbers and other elas- tomers, special attention must be paid here to separating these for- eign substances as completely as possible. The “hamos RSS rubber separator” is used for this purpose. This equipment succeeds in separat- ing the undesired rubber fraction almost completely from ground ma- terial. Due to the physical character- istics of electrostatic separation, the rubber is mainly collected in the PS fraction, whereas the ABS fraction is already rubber-free after electro- static separation. Therefore, only the PS fraction needs to be re-sepa- rated. Summing up it is possible to separate pure and very clean PS, ABS and PP fractions with a com- bination of wet and dry processing methods, even from very complex mixtures of different hard plastics. Our customers running the hamos recycling systems for the separa- tion of ABS, PS and PP already for many years. Author Selinda Sliz, Head of Marketing, hamos GmbH hamos GmbH Recycling- und Separationstechnik Im Thal 17, 82377 Penzberg, Germany www.hamos.com Picture 6: hamos customer plant for mixed plastics Picture 7: Fraction wood