Double-stage (cascade system) granulating lines in the plastic recycling are intended for granulation of shredded in the form of films and plastic scrap, strongly printed (highly contaminated) and higher humidity of plastic waste such as: PP, PE, LLDPE, LDPE, PS or ABS. Depending on the materials being processed, the double-stage lines may have different equipment configurations.

The cascade system of the granulating line consists in a special arrangement of 2 connected extruders and its configuration in one system with the other devices of the granulation line. The specificity of granulation in this system assumes a milder treatment of the material to obtain better quality granules in respect of plasticity, purity and humidity. This becomes possible by equipping the second extruder with a clearly lower motor power and shorter screw length of the plasticizing system and thus achieving a longer material path extrusion at a lower coagulation rate.

Unlike a conventional single-screw extruder line, better quality parameters in the use of double-stage granulating lines are achieved by using multiple (from 3 to 5) vacuum degassing systems. A special part for them is the degassing chamber, which is installed at the transition between extruders and is adapted to work with a much larger surface area of the material than in a standard degassing system in the extruder. The appropriate purity of the processed material is also obtained by using double filtration in the form of 2 screen changers, installed both at the transition between extruders and at the outlet from the second extruder.

Configuration table for double stage granulating lines.

Model KLT-Z100 KLT-Z120 KLT-Z160 KLT-Z180
Extruder 1 motor power [kW] 110 160 – 200 200 – 355 355 – 500
Extruder 2 motor power [kW] 55 70 – 90 110 – 132 132 – 160
Compactor motor power [kW] 90 110 200 – 250 250 – 280
Screw diameter of extruder 1 [mm] 100 120 160 180
Screw diameter of extruder 2 [mm] 120 150 180 200
Screw length of extruder 1 [L/D] 44 : 1 44 : 1 44 : 1 44 : 1
Screw length of extruder 2 [L/D] 23 : 1 23 :1 23 : 1 23 : 1
Total output [kg/h] 350 – 450 500 – 700 850 – 1100 1000 – 1500

    Advantages of double-stage (cascade system) granulating lines include:

  • high output (up to 2500 kg/h);
  • high quality of obtained granules in respect of plasticity level, purity and humidity;
  • material preheating and condensing for processing by a compactor;
  • multi-stage (from 3 to 5) degassing system;
  • use of a special degassing chamber at the transition between extruders;
  • double-stage material filtration (2 systems of screen changers);
  • use of a cutting die in water ring;
  • extruder control by the HMI operator panel;
  • innovative use of moving elements subjected to natural wear in the plasticizing system;
  • possibility of drying granules through a dewatering vibrating screen;
  • convenient granules collection system.
    Double-stage granulating lines are intended for extrusion:

  • strongly printed, shredded plastic waste in the form of films: PE, LLDPE, LDPE, HDPE;
  • strongly printed, shredded plastic waste in the form of plastic scrap: PP, ABS, EPS, PS.