Degassing extruder

A single screw degassing extruder for thermoplastic materials, comprising:

• an elongated extruder housing defining a feed section in which a feed inlet is provided for feeding material to the extruder, and an outlet section for increasing the pressure of the material, said outlet section having a material outlet opening for discharging molten material under pressure from the extruder,
• an extruder screw having a screw core and a helical flight, said screw being mounted for rotation in said housing about the longitudinal axis of said screw, said housing and said screw core defining therebetween a processing chamber, and means for driving said screw,
• said housing further defining a pin-barrel section in which at least one row of pins extend radially inwardly of the housing through the processing chamber toward the core of said screw, said helical flight of said screw being interrupted in the regions of said pins so as to accommodate rotation of said screw in such region.
• a transfer section defined by said housing longitudinally adjacent said pin-barrel section, said transfer section having an inlet region and an outlet region the helical flight of said screw in said transfer section being constructed so that thread depth of the areas between adjacent flight sections first decreases toward zero and then increases, and wherein said housing in said transfer section is also formed with a helical flight generally aligned with the helical flight of said screw, said helical flight of said housing defining between adjacent flight sections thereof grooves which vary in depth and which are radially aligned with the areas between adjacent flight sections of said screw, the depth of said grooves between adjacent flight sections of said housing first increasing in said inlet region of said transfer section to a maximum thread volume and then decreasing in said outlet region of said transfer section, and being generally inversely proportional to the thread depth between radially adjacent flight sections of said screw,
• a plurality of radially adjustable throttling pins disposed in the region of maximum thread volume of the housing threads and protrudable through the housing into the housing threads and processing chamber, and means for radially adjusting the protrusion depth of said throttle pins, and
• a degassing section disposed downstream of said transfer section, said extruder in said degassing section having a reduced number of threads, and said extruder housing in said degassing section being formed with a degassing opening through which degassed constituents are discharged.