wpc extrusion 1-28-08 - EXTRUSION OF WOODPLASTIC COMPOSTES...

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1 EXTRUSION OF WOOD- PLASTIC COMPOSTES Douglas J. Gardner Professor of Wood Science University of Maine OVERVIEW • WPC Feeding Equipment - Rob Edwards • WPC Extrusion Machinery-Dave Murdock
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2 PROCESSING EXTRUSION UNIT OPERATIONS • Conveying Systems – Vacuum – Screw (Flexicon) • Wood Feeding –D ry ing – Feeding • Polymer Feeding – Powders – Pellets • Compounded Pellets • Extruder(s) •D i e ( s )
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3 Pneumatic Conveying Systems Screw Conveying Systems
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4 MOISTURE REMOVAL Fiber must be dried to < 1% to obtain maximum output rate Dried fiber cannot be stored for very long (CONVENTIONAL SYSTEMS) Monomolecular layer of water on wood at ~ 6% moisture content. Preheaters Feeding ?, Removal of Moisture? High Intensity Mixers Expensive Hot air dryers Most Common - Fire Potential if not designed properly Rotary Furnace MOISTURE REMOVAL D-S NOTE: WOOD-DUST IS A STRONG TO SEVERE EXPLOSIVE HAZARD IF DUST “CLOUD” CONTACTS AN IGNITION SOURCE (CONVENTIONAL SYSTEMS)
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5 Historic Feeding Practice DRYER MIXER EXTRUDER WEIGH HOPPER STORAGE PREBLEND COMPONENTS DOWNSTREAM ADDITIVE TRANSPORT SYSTEM COLOR FEEDER RESIN FEEDER PREBLEND FEEDER WOOD FLOUR Limitations of Historic Practice ± Large inventory of preblend ± Low formulation flexibility ± Preblend transport with segregation risk ± Formulation inconsistency at process point ± Density variations uncompensated at process point ± High error cost ± Manual recipe control ± Significant delay between wood flour drying and use ± Inferential material use data due to volumetric proportioning
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6 Gain-in-Weight Preblend: a Closer Look Major Components Weighing Minor Components Weighing Sequential Addition Off-line Formulation Segregation Inventory Drying Fixed resolution of weigh hopper Manual Requires mixing Requires transport system High risk Large; High error cost Delay before use Parameter Disadvantage Flow Measurement Density Variations Linearity Errors Drift Calibration No-Flow Detection Throughput Inferential (motor speed) No detection or compensation No compensation No detection or compensation Regularly required Optional Inferred Parameter Volumetric On-Line Volumetric Blending: a Closer Look
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7 Continuous On-line Gravimetric Blending Advantages of Continuous On-Line Weigh Blending ± Minimum inventory of preblend ± High formulation flexibility ± No transport or segregation ± High formulation accuracy ± Mass flow control of all components at process point ± Low error cost ± Automatic recipe control ± Short interval between wood flour drying and use ± Measured material use data
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wpc extrusion 1-28-08 - EXTRUSION OF WOODPLASTIC COMPOSTES...

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