EXTRUSION: Twin-Screw Extruder In ‘Direct to Sheet’ Set Up

System combines compounding and sheet processing in one step.

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Leistritz, Somerville, N.J., will demonstrate its ZSE-27 Maxx “direct-to-sheet” system for in-line compounding and production of prototype sheet samples. Benefits of direct sheet extrusion include one less heat/shear history and cost savings through bypassing the pelletization step. The system will be among the machinery Leistritz will display next month at NPE2015 in Orlando.

The system utilizes a ZSE-27 Maxx co-rotating, twin-screw extruder with 40/1 L/D and LSB-26 side stuffer for filler/fiber introduction. It will be accompanied by a gear pump, 14-in. flat die with push/pull flex-lip design, and a three-roll stand with rolls of 8 in. diam. x 16 in. wide, driven rotary shear edge-trimming, dual unwinds for extrudate lamination/encapsulation utilizing magnetic-particle brakes, integral, center driven rewind with automatic gap control and closed loop tension control, and air expanding chucks on rewind and unwind shafts.

The ZSE-27 Maxx extruder and downstream lamination system each have their own PLC and operator interface. These two systems can operate independently or together via an Ethernet communications link to allow fully integrated system sharing of recipe, data acquisition, and logic/alarming.

Newer features include a PLC distributive-processing control architecture. Distributive processing refers to when sub-processes are controlled by a discrete PLC while a master PLC manages the overall system and consolidates recipe management and data acquisition. This is particularly important when integrating systems from multiple suppliers with distinctly different technologies.

Also new is the pressure-control algorithm. Typically the gear pump RPM is locked to set a constant volumetric rate to the die. The tuning algorithm in the PLC analyzes the inputs from key points in the system, makes numerical calculations, and applies corrections to the extruder screw RPM and feed rate to maintain the gear pump inlet pressure at setpoint.