Single and twin screw extruders with ultrasound horns for decrosslinking and devulcanization

A process for decrosslinking crosslinked plastic or devulcanizing vulcanized rubber comprising the steps of:

• feeding crosslinked plastic or vulcanized rubber to a twin screw extruder having a first screw and second screw in a barrel, the first screw having a first axis and the second screw having a second axis;
• advancing the crosslinked plastic or vulcanized rubber, by rotation of the first screw and the second screw, to an ultrasonic treatment zone in the barrel, the ultrasonic treatment zone including:
• a body including:
• a first bore through the body, the first bore having a bore axis that is coaxial with the axis of the first screw,
• a second bore through the body, the second bore having a bore axis that is coaxial with the axis of the second screw, the first bore and second bore overlapping to create a twin bore, and
• a horn passage communicating with both the first bore and the second bore of the twin bore,
• a first cylindrical shaft associated with the first screw to rotate therewith, the first cylindrical shaft rotating in the first bore of the body and providing no threads such that the crosslinked plastic or vulcanized rubber is not advanced by rotation of the first cylindrical shaft, but rather is advanced by rotation of the first screw and second screw forcing the crosslinked plastic or vulcanized rubber into the ultrasonic treatment zone,
• a second cylindrical shaft associated with the second screw to rotate therewith, the second cylindrical shaft rotating in the second bore of the body and providing no threads such that the crosslinked plastic or vulcanized rubber is not advanced by rotation of the second cylindrical shaft, but rather is advanced by rotation of the first screw and second screw forcing the crosslinked plastic or vulcanized rubber into the ultrasonic treatment zone, the first cylindrical shaft and second cylindrical shaft contacting one another,
• an ultrasonic horn extending into said horn passage, the ultrasonic horn being aligned over both the first shaft and second shaft and having a distal end spaced from the first shaft and the second shaft, the distal end being shaped complementary to the first shaft and the second cylindrical shaft to define a portion of a double-arcuate ultrasonic treatment flow path;
• advancing the crosslinked plastic or vulcanized rubber through the double-arcuate ultrasonic treatment flow path;
• and
• ultrasonically treating the crosslinked plastic or vulcanized rubber at the double-arcuate ultrasonic treatment flow path by ultrasonic waves generated by the ultrasonic horn.