Screw type apparatus for drying moist polymeric materials

In an apparatus for drying moist polymeric material including (a) a processing chamber having an inlet port and an exit port, (b) a compaction worm mounted on a first rotatable shaft disposed within said processing chamber for advancing material to be dried from the inlet port to the exit port while progressively compacting and thereby increasing the pressure of the material as it advances, (c) means for gradually increasing the temperature of the material as it advances through said chamber, the pressure developed due to compaction of the material being sufficient to substantially prevent vaporization of the moisture associated with the material in said processing chamber, and (d) discharge means associated with the exit port for maintaining a suitable back-pressure in said processing chamber and for releasing the material to a relatively low pressure environment as compared to the pressure developed in said processing chamber, the improvement in said discharge means comprising:

• 1. a cylindrical conduit having an inlet port and an exit port, the inlet port of said conduit communicating with the exit port of said processing chamber;
• 2. a second rotatable cylindrical shaft mounted concentrically in said conduit and connected to said first shaft for rotation in unison therewith, said second shaft having diameter substantially less than the inside diameter of said conduit;
• 3. valve means associated with an intermediate portion of said conduit for providing a passageway of controllable cross-sectional area from the portion of said conduit upstream of said valve means to the portion of said conduit downstream of said valve means including:
• 3a. an obstruction mounted on said second shaft, said obstruction having a smooth cylindrical outer surface concentric with said second shaft, the diameter of said obstruction being substantially greater than the diameter of said second shaft but less than the inside diameter of said conduit;
• 3b. at least one valve housing mounted externally of said conduit and containing a valve chamber continuously communicating with the interior of said conduit from a region upstream of said obstruction to a region downstream of said obstruction;
• 3c. a valve member slidably disposed in said valve chamber for radial motion with respect to said conduit for controlling the volume of said valve chamber communicating with said conduit to control the cross-sectional area of said passageway;
• and
• 3d. means associated with said valve member for controlling the position of said valve member in said valve chamber;
• and
• 4. means associated with the portion of said conduit downstream of said valve means for releasing the material exiting from said passageway to said relatively low pressure environment within said downstream portion of said conduit to permit substantially all of the moisture associated with the material exiting from the passageway to immediately vaporize and immediately expand the material to the full extent required for said vaporization, thereby drying the material, and for compacting and advancing the dried material to the exit port of said conduit under pressures sufficiently low to prevent substantial recondensation of the vapor on the dried material including:
• 4a. a plurality of worms spaced longitudinally on said second shaft downstream of said obstruction to form an interrupted compaction worm flight for advancing the dried material to the exit port of said conduit and progressively compacting the dried material as it advances without creating a substantial pressure difference between the exit port of said conduit and the downstream end of said passageway during compaction and advance of the material;
• and
• 4b. a plurality of breakers mounted on said conduit and projecting into the interior of said conduit intermediate at least some of said worms to prevent the dried material from rotating with the worms.