James L. White / Helmut Potente (Editors)

Screw Extrusion Science and Technology

With Contributions from

U. Berghaus, E. Bürkle, H. Potente, H. Recker, K. Schäfer, V. Schöppner, J.L. White, G. Wiegand, M. Wtlrtele

HANSER Hanser Publishers, Munich

Hanser Gardner Publications, Inc., Cincinnati

Contents

1 Introduktion 1 1.1 Overview 1 1.2 Historical Development 2

1.2.1 Early Period 2 1.2.2 1920 to 1945 3 1.2.3 1946 to 1959 4 1.2.4 1960 to Present 5

1.3 Earlier Books on Screw Extrusion 7 References 9

2 Fundamentals 13

2.1 Introduction 13 2.2 Pumping Mechanisms 13

2.2.1 General 13 2.2.2 Positive Displacement Pumps 14

2.2.2.1 Ram Extruders 14 2.2.2.2 Rotary Positive Displacement Pumps 15

2.2.3 Drag Flow Pumps 19 2.2.4 Normal Stress Pump 23

2.3 Specifications of Screws 24 2.4 Single Screw Pumps 27

2.4.1 Principles 27 2.4.2 Simple Screw Design Features 30

2.5 Counter-Rotating Twin Screw Machine 31

2.5.1 Tangential 31 2.5.2 Intermeshed 32

2.6 Co-Rotating Twin Screw Machine 34 2.7 Multiple-Screw Extrusion 35 References 37

3 Screw Extrusion Technology 41 3.1 Rubber Extrusion 41

3.1.1 Introduction 41 3.1.2 Extruder Technology 41

3.1.2.1 Hot-Feed and Cold-Feed Extruders 41 3.1.2.2 Special Screw Designs for Cold-Feed Extruders 42

3.1.2.2.1 Plastication and Homogenization 42 3.1.2.2.2 Vacuum Extruders 48

3.1.2.3 Overall Screw Extruder Design 50 3.1.3 Basic Experimental Studies 51

3.1.3.1 General 51

3.1.3.2 Plasticating and Homogenization Screws 54 3.1.3.3 Pin Barrel Extruders 54 3.1.3.4 Vacuum Extruders 55

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3.1.4 Flow Simulations 56 3.1.4.1 Rheological Properties of Rubber Compounds 56 3.1.4.2 Simple Screws 57 3.1.4.3 Screw Sections with Slices 58 3.1.4.4 Pin Barrel Extruders 58

3.1.5 Multilayer Extrusion Lines 58 3.1.6 Continuous Vulcanization Lines 60

References 61 3.2 Extrusion of Thermoplastics 63

3.2.1 Trends in the Development of Single-Screw Extruders 63 3.2.1.1 High-Speed Extruders with Melt Pumps 64 3.2.1.2 Grooved Feed Extruders with 30D or 33D Screws 64 3.2.1.3 Feed Section Design 66 3.2.1.4 Screw Designs 67 3.2.1.5 Increased Output Without Increase in Wear 67 3.2.1.6 Homogenizing, In-Line Dispersion 68

3.2.1.7 Barrier Screw 72 3.2.1.8 Vented Extruders with 33D or 36D Screws 73 3.2.1.9 Reduced Wear as a Result of Appropriate Material Selection . . . 74

3.2.2 Single Screw Extrusion Technologies 76 3.2.2.1 Blown Film - A Classic Product with Good Properties 76 3.2.2.2 Double-Bubble Process for Biaxially Oriented Blown Film . . . . 78 3.2.2.3 Cast Films-Quality of the Highest Standard 79 3.2.2.4 Extrusion Coating - Improved Quality for Composites 83 3.2.2.5 Plastic Sheets and Thermoforming Sheets - In Highest Quality for a

Host of Applications 85 3.2.2.6 Plastic Pipes and Profiles - The Ideal Components for Civil

Engineering and Technological Applications 88 3.2.2.7 Synthetic Filaments - Monofilaments, Slit Film Tapes, and Strapping

Tapes 90 3.2.2.7.1 Monofilaments 90 3.2.2.7.2 Slit Film Tapes 90 3.2.2.7.3 Stapping Tapes 91

3.2.2.8 Nonwoven Textiles - The Cost-Effective Alternative 92 3.2.2.9 Outlook 94

3.2.2.9.1 Design Conditions 94 3.2.2.9.2 Processing Conditions 95

References 95 3.3 Screw Design 96

3.3.1 Introduction 96 3.3.2 Evaluation and Specification 97

3.3.2.1 Specification of the Input Variables 97 3.3.2.1.1 Material 97 3.3.2.1.2 Drive 98 3.3.2.1.3 Temperature Control 98 3.3.2.1.4 Downstream Equipment 100

3.3.2.2 Quality Criteria of the Output Values 100 3.3.2.3 Quality Criteria Within an Extruder 101 3.3.2.4 Quantification of the Quality Criteria 101

3.3.3 Subdivision into Operating Zones and Types of Construction 105

Contents xi

3.3.3.1 Feeding Section 105 3.3.3.1.1 Smooth Barrel Extruder 105 3.3.3.1.2 Grooved-Barrel Extruder 105

3.3.3.2 Melting Section 106 3.3.3.2.1 Transition Zone 106 3.3.3.2.2 BarrierZone 107 3.3.3.2.3 Dispersive Melting 108

3.3.3.3 Metering Zone 108 3.3.3.4 Torpedoes 109

3.3.3.5 Mixing Sections 110 3.3.3.6 Special Geometries 110

3.3.3.6.1 Combination of a Metering Zone with Shear or Mixing Elements 110

3.3.3.6.2 Mixing Screws 112 3.3.3.6.3 Dynamic Mixers 112

3.3.3.7 Screw Construcion Types and Applications 113 3.3.3.7.1 Plasticating Extruders 113

3.3.3.7.1.1 Three-Section Screw 113 3.3.3.7.1.2 Barrier Screw with Mixing Section 113 3.3.3.7.1.3 Srew with Torpedo and Mixing Section 113 3.3.3.7.1.4 Barrier Screw with Torpedo and

Mixing Section for Grooved-Barrel

Exruders 114 3.3.3.7.2 Melt Extruders 114 3.3.3.7.3 Vented Extruders 114

3.3.4 Geometrical Design 115 3.3.4.1 Design Strategy and Means 115 3.3.4.2 Definition of an Appropriate Specific Throughput 120 3.3.4.3 Optimization of the Single Function Zones 123

3.3.4.3.1 Feeding Zone 123 3.3.4.3.2 Melting Zone 124 3.3.4.3.3 BarrierZone 124

3.3.4.3.3.1 Pitches, Flight and Channel Width 124

3.3.4.3.3.2 Zone Length, Feed, and Outlet Design . . . . 126 3.3.4.3.3.3 Channel Depth 126 3.3.4.3.3.4 Metering Zone 128 3.3.4.3.3.5 Spiral Torpedo Section 128 3.3.4.3.3.6 Faceted Mixing Torpedo 129

3.3.4.4 Series Design 130 3.3.5 Example: Extruder 090mm for 300 kg/h PET IV 0.8 133

References 139 3.4 Machine Design and Construction 140

3.4.1 Extruder Size 140

3.4.2 Components of a Single Screw Extruder 141

3.4.2.1 Frame 141 3.4.2.2 Extruder Drive 143 3.4.2.3 Transmission and Clutch 144 3.4.2.4 GearUnit 144 3.4.2.5 Feeding Section 146 3.4.2.6 Hopper 148

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3.4.2.7 Barrel 148 3.4.2.8 Barrel Heating and Cooling Equipment 149

3.4.2.8.1 Heating 149

3.4.2.8.2 Extruder Cooling 151 3.4.2.9 Screw 152

3.4.3 Special Designs 154 3.4.3.1 Spinning Extruder 154 3.4.3.2 Adiabatic Extruder 154 3.4.3.3 Vented Extruder 156 3.4.3.4 Metering Extruder 157 3.4.3.5 Tandem Extruders 158

3.4.3.6 Vertical Extruder 158 3.4.3.7 Extruder with Conical Feed Zone 160

References 160 3.5 Measurement and Open-Loop and Closed-Loop Control Engineering 161

3.5.1 Temperature Measurement and Closed-Loop Control 162 3.5.1.1 Wall Temperature 162 3.5.1.2 Melt Temperature 162 3.5.1.3 Surface Temperature 164 3.5.1.4 Closed-Loop Temperature Control 165

3.5.2 Measurement and Closed-Loop Control of Pressure 167 3.5.2.1 Melt Pressure 167 3.5.2.2 Open-Loop Pressure Control 168 3.5.2.3 Closed-Loop Pressure Control 168 3.5.2.4 Closed-Loop Thickness Control with the Aid of Pressure and Temperature Measurements 169

3.5.3 Measuring Specific Product Properties 169 3.5.3.1 Dimensioning 169 3.5.3.2 Surface Defect Recognition on Panels and Films 171 3.5.3.3 Surface Inspection of Profiles 171

3.5.4 Process Control on the Extruder 172 3.5.4.1 Automation System Structures 173

3.5.4.1.1 Centralized System Structure 173 3.5.4.1.2 Networked Automation Systems 173

3.5.4.2 Material Metering 174 3.5.4.3 Closed-Loop Startup Control 174 3.5.4.4 Process Control for Selected Extrusion Methods 175

3.5.4.4.1 Tubular Film Plants 175

3.5.4.4.2 Flat Film Plants 176 3.5.4.4.3 Pipe and Profile Plants 176

References 177

4 Technology of Single Screw Extrusion with Reciprocating Screws 179 4.1 Screw Injection Molding 180

4.1.1 Particularities Regarding the Transition from the Continuous to the Discontinuous Method of Operation 180 4.1.1.1 Feed Zone 183 4.1.1.2 Transition Section 188

4.1.1.2.1 Melting Process During the Metering Period 188

Contents xiii

4.1.1.2.2 Melting Process During Injection 189

4.1.1.2.3 Screw Idle Time 189 4.1.1.3 MeteringZone 191 4.1.1.4 Mixing Zone 192

4.1.2 Size Transposition 193 4.1.3 Considering the Plasticizing Unit as a Whole 193

4.1.3.1 Feed Performance 194 4.1.3.2 Air Entrapment 194 4.1.3.3 Swept Volume 195 4.1.3.4 Feed Problems 197 4.1.3.5 Melting Section 201 4.1.3.6 Mixing Quality 205

4.1.3.6.1 Homogeneity and Melt Temperature 205 4.1.3.6.2 Influence of Processing Parameters on the Mixing

Quality | 206 4.1.3.7 Residence Time 208

Nomenklature 209

References 211 4.2 Buss Kneader 212

4.2.1 Introduction 212

4.2.2 Machine Technology 213 4.2.2.1 Earlier Related Machines 213 4.2.2.2 Origins of the Kneader 213 4.2.2.3 Development of the Kneader 215 4.2.2.4 Modern Kneader 218

4.2.3 Basic Experimental Studies 219 4.2.4 Flow Simulations 220

4.2.4.1 General 220 4.2.4.2 Flow Due to an Oscillating Screw 220 4.2.4.3 Flux Patterns and Pumping Characteristics of Kneader

Elements 222 4.2.4.4 Theory of Composite Modular Machines 223

4.2.5 Applications 225 References 225

5 Single Screw Extruder Analysis and Design 227 5.1 Melt Conveying Section Analysis 227

5.1.1 Isothermal Analysis 227 5.1.1.1 Melt Conveying 227 5.1.1.2 Power Consumption 237

5.1.2 Nonisothermal Analysis 241 5.1.2.1 Melt Conveying 241 5.1.2.2 Temperature 243 5.1.2.3 Power Consumption 249

5.1.2.4 Melts That Slip at the Wall 249 5.1.2.4.1 One-Dimensional Treatment 249 5.1.2.4.2 Two-Dimensional Treatment 254

5.2 Melting Analysis 256 5.2.1 Starting Point 256 5.2.2 Melting 258

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5.2.2.1 Requirements for the Mathematical Treatment 258 5.2.2.2 Mathematical Tratment Regardless of the Leakage Flow Across the

Screw Flight 260 5.2.2.2.1 Velocity Profile in the Melt Film at the Barrel Wall . . . 260 5.2.2.2.2 Melting Velocity 262 5.2.2.2.3 Temperature in the Melt Film at the Barrel Wall . . . . 263 5.2.2.2.4 Heat Flows at the Boundary Layer Between the Melt film

and the Soldid Bed 263 5.2.2.2.5 Determination of the Exponent с and the Melt Film

Thickness 8„ 264 5.2.2.2.6 Solid Bed Profile and Melting Length Regardless of the

Melting Film at the Screw 265 5.2.2.3 Mathematical Treatment in Consideration of the Leakage Flow Across

the Screw Fligth 268 5.2.2.4 Mathematical Treatment of Melting During the Screw Downtime at

Injection Molding 270 5.2.2.5 Computation of the Melted Material 271 5.2.2.6 Premelting 273 5.2.2.7 Approaches for the Computation of the Melt Films at the Screw 276

5.2.3 Pressure-Throughput Behavior and Power Comsumption in the Melting Zone . 277 5.3 Solid Conveying 283

5.3.1 Smooth-Barrel Feed Zone 283 5.3.1.1 Throughput 283 5.3.1.2 Power Consumption 292

5.3.2 Grooved Feed Section 293 5.3.2.1 Throughput 293 5.3.2.2 Power and Torque 299

5.3.3 High-Speed Conveying 299 5.4 Composite Extruder Models 302

5.4.1 Integral Treatment 302 5.4.1.1 Throughput Behavior of Smooth-Barrel Extruders with Melt-

Dominated Conveying 302 5.4.1.2 Throughput Behavior of Grooved Barrel Extruders 306 5.4.1.3 Throughput Behavior of Ventintg Extruders 307 5.4.1.4 Power Input 309

5.4.2 Coupling the Models of the Function Zones 310 5.5 Scale-Up 317

5.5.1 Principle of Similarity 317 5.5.2 General Formulation of the Scale-Up Rules 317 5.5.3 Treatment by Zones 319

5.5.3.1 Melt Conveying Zone 319 5.5.3.2 Plasticating Zone 322 5.5.3.3 Solid Conveying 328

5.5.3.3.1 Smooth-Barrel Extruder 328 5.5.3.3.2 Grooved-Barrel Extruder 329

5.5.4 Summary 338 5.5.4.1 Scale-Up Rules for Melt and Smooth-Barrel Plasticating Machines 338 5.5.4.2 Scale-Up Rules for Grooved-Barrel Extruders 343

Nomenklature 346 References 349

Contents xv

6 Twin and Multiscrew Extrusion 353 6.1 Introduction 353 6.2 Intermeshing Co-Rotating Twin Screw Extrusion 354

6.2.1 Technology 354 6.2.2 Geometry 363 6.2.3 Experimental Studies 364

6.2.3.1 Early Studies to 1975 364 6.2.3.2 Flow Visualization Including Solid Conveying and Melting . . . . 365 6.2.3.3 Residence Time Distributions 367 6.2.3.4 Pumping Characteristics 368 6.2.3.5 Heat Transfer 369 6.2.3.6 Mixing 370

6.2.4 Flow Modeling 374 6.2.4.1 General 374 6.2.4.2 Flow Pumping in Modules 374

6.2.4.2.1 Screw Elements 374 6.2.4.2.2 Kneading Disc Blocks 383

6.2.4.3 Composite Modular Machine Behavior 386 6.2.4.4 Melting and Composite Pumping Model 388 6.2.4.5 Mixing 390 6.2.4.6 Reactive Extrusion 392

6.2.5 Applications 393

6.3 Intermeshing Counter-Rotating Twin Screw Extrusion 393

6.3.1 Technology 393 6.3.2 Experimental 397

6.3.2.1 Flow Visualization 397 6.3.2.2 Residence Time Distributions 397 6.3.2.3 Pumping Characteristics 399 6.3.2.4 Melting 400 6.3.2.5 Mixing 400

6.3.3 Modeling 400 6.3.3.1 General 400 6.3.3.2 Leaking C-Chamber Models 404 6.3.3.3 FAN Analysis of Flow 405 6.3.3.4 Three-Dimensional Solutions 407 6.3.3.5 Composite Pumping Model 407

6.3.4 Screw Bending 409 6.3.5 Applications 409

6.4 Tangential Counter-Rotating Twin Screw Extruders 409

6.4.1 Technology 409 6.4.2 Experimental 410

6.4.2.1 Flow Visualization 410 6.4.2.2 Screw Pumping Characteristics 411

6.4.3 Modeling 413 6.4.3.1 General 413 6.4.3.2 Analytical Flow Models 413 6.4.3.3 Quantitative Flow Models 413

6.4.3.4 Composite Modular Pumping Modeling 418 6.4.4 Applications 419

6.5 Continuous Mixers 419

xvi Contents

6.5.1 Technology 419 6.5.2 Experimental 424 6.5.3 Modeling 425 6.5.4 Applications 427

References 427

Subject Index 435

Name-Author Index 438