TWIN SCREW EXTRUSION SYSTEMS TO PROCESS BIO- BASED ...

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HSEI Twin screw extruders process materials bounded by screw flights and barrel walls. Screws are segmented and assembled on high torque splined shafts. Barrels are also modular and utilize liquid cooling, which is particularly beneficial for heat sensitive formulations. A typical process length to diameter ratio (L/D) is 32 to 48 to 1 L/D, with up to 60 to 1 L/D’s being possible to facilitate reactive processing and/or multi-stage devolatilization. The motor inputs energy into the process via rotating screws that impart shear into the materials. HSEI twin screw extruder process section with multiple vents & downstream side stuffing Segmented screws/barrels, in combination with the controlled pumping and wiping characteristics of the screws, allows screw/barrel geometries to be matched to the process tasks. Solids conveying and plastication occurs in the first part of the process section. Screw elements for mixing and devolatilization are then utilized as dictated by the process. Discharge elements finally build and stabilize pressure to a die. Screw designs can be shear intensive or passive. Co-rotating intermeshing twin screw extruder screw set HSEI twin screw extruders are starve fed, which means the output rate is determined by the feeder(s), which meter pellets, liquids and fibers into the process section. The extruder screw RPM is independent from the feed rate and is used to optimize compounding efficiencies. Because the pressure gradient is controlled, and zero for much of the process, materials can be introduced into downstream barrels sections. For instance, a twin screw side stuffer can “push” high filler loadings, such as a starch or natural fiber, into the extruder screws after melting has already occurred. Downstream
side stuffing can be beneficial to obtain high filler loadings, to decrease the abrasive wear in the extruder process section, and when processing shear sensitive materials. The controlled pressure profile also facilitates venting. Factors that effect devolatilization efficiencies include residence time of the melt under the vent(s) (longer RT = better devol), the surface area of the melt pool (smaller melt pool = higher surface area = better devol) and the surface renewal of the melt pool (higher renewal = better devol). Vacuum pump system that interfaces to HSEI twin screw extruder for devolatilization Front end design: The front-end design of the HSEI twin screw extruder is critical to the overall success or failure when processing many bio-based products, as this is where degradation often occurs. Adapters and front-end attachments should be designed to minimize dead areas that can/will result in high pressures and/or flow stagnation. If filtration is a requirement, the adapter should facilitate a low volume, streamlined transition to the breaker plate. In many cases an oval breaker plate is used and the screws are extended from the extruder to minimize the distance from the screw tips to the breaker plate. Options include a simple breaker plate that holds screens in the front-end adapter, slide-plate (discontinuous) screen changers and continuous screen changers of various designs. The throughput of the system, level of contamination and degree of filtration are all selection factors. It is worth noting that high-volume, nonstreamlined melt flow paths associated with some of the continuous model screen changers will preclude usage with some bio-based formulations.
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Page 5 and 6: Pelletization: Pelletizing systems,
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TWIN SCREW EXTRUSION SYSTEMS TO PROCESS BIO- BASED ...

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