Mixing in Single Screw

Transcription

1 A Mixing in Single Screw Extrusion Martin Gale TECHNISCHE INFORM ATiQIMSBIOLIQTHEK UNIVERSITATS3IBUOTMEK HANNOVER J m ismithers z'smithers - Smithers Group Company Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0) Fax: +44 (0) TIB/UB Hannover X

2 ontents Preface 1 1 The Need for Good Mixing in Single Screw Extrusion Examples of Mixing Problems Polyethylene Pipes and Cables Blow Moulded Bottles Chalk Filled Polypropylene Pipe Blown Film Industrial Blow Mouldings Production Scrap Re-use Agglomerates and Gels in Thin Extrusions Transparent Polycaprolactone/SAN Blends Decorative Wood Grain Effects 15 References 16 2 Dispersive and Distributive Mixing Definitions and Illustrations Dispersive Mixing Dispersive Mixing Mechanisms Dispersive Mixing of Additive Powders Such as Pigments Distributive Mixing Laminar Shear Flow Mixing Measurement of Distributive Mixing Achieved by Laminar Shearing 32 i

3 Mixing in Single Screw Extrusion Limitations of Lamina Flow Mixing Eliminating Laminar Striations 36 References 55 3 Measurement of Mixing The Need for Measurement of Mixing Striatum Thickness Measurement Agglomerate Measurement Microscopy Examination of Thin Samples Agglomerate Count for Blown Film Screen Pack Filtration Test Influences of Mixing on Product Properties Preparation of Thin Sections for Optical Microscopy Assessment 69 References 69 4 Single Screw Extruder Stages: Effects on Mixing 71 References 75 5 Pellet Handling: A Source of Variable Composition Introduction Hopper Design Mass Flow Hopper Non-mass Flow Hopper Round Hoppers Square and Rectangular Hoppers Ledges and Corners Composition Variations Example Example Example 3 82 ii

4 Contents Other Systems Measurement of Particulate Properties Hopper Flow Tests 84 References 85 6 Solids Conveying in the Feed/Transport Zone Smooth Feed Zones Grooved Feed Zones Particulate Friction Measurements Friction in the Feed Zone 99 References Melting Melting Mechanism Variations in Melting Rate Solids Bed Break-up Melting Devices Barrier Flight Melting Screws The Barrier Screw Concept Maillefer Barrier Screw North American Barrier Screws Combined Barrier Screws and Grooved Feed Zones Barrier Screw Developments Other Melting Screws Double Wave Screw Barr Energy Transfer Screws Stratablend Mixing Screw Shear-Ring Screw ' 127 iii

5 Mixing in Single Screw Extrusion 7.7 Barrier Flight Screws versus Conventional Screws 127 References Screw Channel Mixing and the Application of Mixing Sections Striations: Their Formation and Mixing in the Screw Channel Mixing During Melting Mixing in the Melt Filled Screw Channel Residence Time Distribution (RTD) Concentration Smoothing Variation of Residence Time with Channel Position Implications of Pressure/Drag Flow Effects Mixing Sections Maddock Mixer Pins and Slots Mixer Evaluation Using an Independent Drive 152 References Interacting Rotor/Stator Mixers Overview Turbine Mixing Heads Stanley (ICI) Mixer Other Turbine Mixers Woodroffe Key Slot Mixers Gerber (Metal Box) Mixer Renk (Barmag) Mixer Rounded Cavity Mixers Rapra Cavity Transfer Mixer Reifenhauser Staromix 184 References 186 iv

6 Contents 10 Floating Ring Mixing Devices Introduction Injection Moulding Check-ring Mixers Adaption of the Check Ring Mixer to Extrusion 193 References Static (or Motionless) Mixers Mixing Mechanism Static Mixers Used in plastics extrusion Helical Mixers Honeycomb Mixers Application in Heat Exchangers Disadvantages 200 References Incorporation of Liquid Additives and Dispersions by Direct Addition Viscosity Differences Incorporating Liquid Additives Some Examples of Liquid Injection Processes Polybutene in Pallet-wrap and Silage-wrap Film Injection of Liquid Colours (General) Wire Insulation Colouring Fibre Extrusion Skin Colouring Pipes and Profiles Crosslinking Polyethylenes Silicone Lubricant Injection Extrusion Foaming 220 References 227 v

7 Preparation Mixing in Single Screiv Extrusion 13 Dispersive Mixing of Fillers and Pigments Formation of Agglomerates Starved Feeding to Avoid Agglomerate Formation Dispersive Mixing Using Polymer Powders Dispersive Mixing Using Polymeric Waxes 239 References Dispersive Mixing Applied to Polymer Blending Polymer Blends Polymer Scrap Polymer Waste Blending Immiscible Viscous Fluids Polymer Blending Mechanisms in a Single Screw Extruder Break-up of Fibrils into Droplets Polymer Blending in Single Screw Extrusion: Overall Mechanism Mixing by Controlled Continuous Chaotic Advection Blending Mixed Polymer Waste: Comparison of Twin Screw and Single Screw Extruders Elongational Flow Mixing Elimination of Gels 262 References Compounding with Single Screw Extruders 269 References Appendix of Microtome Sections for Assessment of Dispersive and Distributive Mixing 273 Flattening Sections 273 VI

8 Contents Trimming the Block 274 Flattening the Rolled Sections 276 Holey Sections 276 Brushing Flat 276 Distortion 276 Washing and Mounting 277 Abbreviations 279 Index 281 vii