Recycling process and apparatus for the production of polymer from thermoplastic polycondensate

Apparatus for producing polymer from plastic polycondensate comprising a dual screw extruder including a housing having overlapping longitudinal bores therein and two rotatable screws in said bores having threads tightly meshing with one another, said extruder having three successive zones arranged longitudinally thereof, the first of said zones being a conveyor zone having an inlet for plastic polycondensate, which is heated to a temperature in said first zone which is lower than the melting point of the polycondensate, said screws conveying the polycondensate through the three zones of the extruder, said housing having a degassing opening in said first zone, the polycondensate being heated in the second of said zones to a temperature above its melting point to produce a polymer melt, said conveyor screws including a first set of kneading disks in a region of said second zone to knead the polymer melt during its advance in the extruder, two further sets of kneading disks spaced longitudinally in said extruder in said second zone downstream of the first set of kneading disks, said further sets of kneading disks being arranged in said housing so as not to produce advance of said melt in said extruder, said housing having a degassing outlet between said further sets of kneading disks at which a vacuum is applied, the third of said zones being downstream of the second zone and having an outlet for discharge of the polymer melt from the extruder, and a mixing tank in direct communication with said extruder at the outlet of said third zone for receiving the polymer melt therefrom, said mixing tank comprising a vertical housing, rotatable, spiral mixing blades in said housing which engage one another and walls of said housing to clean the same of polymer melt, drive means for rotating said mixing blades in the housing of the mixing tank, and a melt pump connected to said housing of the mixing tank for pumping the melt from said housing of the mixing tank, said spiral mixing blades having a direction of spiral winding and being driven by said drive means in a direction related to the direction of spiral winding to urge polymer in said mixing tank upwardly against the action of gravity, said housing of said mixing tank having a longitudinal axis, said spiral mixing blades being rotatable around respective axes of rotation offset from said longitudinal axis.

Apparatus for producing polymer from plastic polycondensate comprising a dual screw extruder including a housing having overlapping longitudinal bores therein and two rotatable screws in said bores having threads tightly meshing with one another, said extruder having three successive zones arranged longitudinally thereof, the first of said zones being a conveyor zone having an inlet for plastic polycondensate, which is heated to a temperature in said first zone which is lower than the melting point of the polycondensate, said screws conveying the polycondensate through the three zones of the extruder, said housing having a degassing opening in said first zone, the polycondensate being heated in the second of said zones to a temperature above its melting point to produce a polymer melt, said conveyor screws including a first set of kneading disks in a region of said second zone to knead the polymer melt during its advance in the extruder, two further sets of kneading disks spaced longitudinally in said extruder in said second zone downstream of the first set of kneading disks, said further sets of kneading disks being arranged in said housing so as not to produce advance of said melt in said extruder, said housing having a degassing outlet between said further sets of kneading disks at which a vacuum is applied, the third of said zones being downstream of the second zone and having an outlet for discharge of the polymer melt from the extruder, and a mixing tank in direct communication with said extruder at the outlet of said third zone for receiving the polymer melt therefrom, said mixing tank comprising a vertical housing, rotatable, spiral mixing blades in said housing which engage one another and walls of said housing to clean the same of polymer melt, drive means for rotating said mixing blades in the housing of the mixing tank, and a melt pump connected to said housing of the mixing tank for pumping the melt from said housing of the mixing tank, said housing of said mixing tank including an upper conical portion which narrows upwardly, a lower conical portion which narrows downwardly, and a cylindrical portion interconnecting said conical portions, said third zone of said housing of said extruder being connected to said cylindrical portion with said outlet of said third zone directly opening into the interior of said housing of said mixing tank at said cylindrical portion.