Analyzing and Troubleshooting Single-Screw Extrusion

The book teaches the fundamentals of single-screw extrusion such that fast troubleshooting and process optimization and design are possible. The fundamental processes that are occurring in the machine are developed from the natural reference point of a rotating screw rather the traditional rotating barrel. These fundamentals are then combined with the chemistry of polymers and the physical properties related to processing to troubleshoot and optimize extrusion processes. Many industrial extrusion problem case studies are presented. In each case study, the root cause of the problem is identified along with the solution. A fundamental view of the processes that occur in a single-screw machine from the natural reference frame; i.e., screw rotation. The theory is discussed and compared to experimental data and to a rotating barrel reference frame. Topics include: polymerization chemistry and degradation mechanisms for polymers, physical properties related to processing (e.g., rheology, heat capacity, dynamic friction, bulk density and pellet compaction, melt density), and 30+ case studies for troubleshooting extrusion problems. A detailed description of the problem and the solution is presented so the reader can implement the solution on their own equipment. 9783446432666%2Efm......Page 1 Preface......Page 6 Acknowledgements......Page 8 Contents......Page 10 1 Single-Screw Extrusion: Introduction and Troubleshooting......Page 21 1.1 Organization of this Book......Page 23 1.2 Troubleshooting Extrusion Processes......Page 25 1.3 Introduction to Screw Geometry......Page 26 1.3.1 Screw Geometric Quantitative Characteristics......Page 28 1.4 Simple Flow Equations for the Metering Section......Page 31 1.5.1 Example 1: Calculation of Rotational and Pressure Flow Components......Page 35 1.5.2 Example 2: Flow Calculations for a Properly Operating Extruder......Page 37 1.5.3 Example 3: Flow Calculations for an Improperly Operating Extruder......Page 38 Nomenclature......Page 40 References......Page 42 2 Polymer Materials......Page 43 2.1 Introduction and History......Page 44 2.1.1 History of Natural Polymers......Page 45 2.1.2 The History of Synthetic Polymers......Page 46 2.2 Characteristics of Synthetic Polymers......Page 48 2.3 Structure Effects on Properties......Page 51 2.3.1 Stereochemistry......Page 54 2.3.2 Melting and Glass Transition Temperatures......Page 55 2.3.3 Crystallinity......Page 57 2.4.1 Condensation Reactions......Page 60 2.4.2 Addition Reactions......Page 63 2.5 Polymer Degradation......Page 66 2.5.1 Ceiling Temperature......Page 69 2.5.2 Degradation of Vinyl Polymers......Page 71 2.5.3 Degradation of Condensation Polymers......Page 73 References......Page 74 3.1 Introduction to the Deformation of Materials......Page 76 3.2 Introduction to Basic Concepts of Molecular Size......Page 77 3.2.1 Size Distribution Example......Page 78 3.2.2 Molecular Weight Distributions for Polymers......Page 79 3.3 Basic Rheology Concepts......Page 82 3.4 Polymer Solution Viscosity and Polymer Molecular Weight......Page 86 3.4.1 Sample Calculation of Solution Viscosity......Page 90 3.5 Introduction to Viscoelasticity......Page 91 3.6.1 Capillary Rheometers......Page 99 3.6.2 Cone and Plate Rheometers......Page 110 3.6.3 Melt Index and Melt Flow Rate......Page 113 3.7 Viscosity of Polymers as Functions of Molecular Character, Temperature, and Pressure......Page 116 3.8 Models for Non-Newtonian Flow......Page 122 Nomenclature......Page 124 References......Page 126 4 Resin Physical Properties Related to Processing......Page 128 4.1 Bulk Density and Compaction......Page 129 4.1.1 Measurement of Bulk Density......Page 130 4.1.2 Measuring the Compaction Characteristics of a Resin......Page 131 4.2 Lateral Stress Ratio......Page 134 4.2.1 Measuring the Lateral Stress Ratio......Page 135 4.3 Stress at a Sliding Interface......Page 137 4.3.1 The Screw Simulator and the Measurement of the Stress at the Interface......Page 138 4.4 Melting Flux......Page 140 4.5 Heat Capacity......Page 142 4.6 Thermal Conductivity and Heat Transfer......Page 143 4.7 Melt Density......Page 144 References......Page 146 5 Solids Conveying......Page 149 5.1 Description of the Solid Conveying Process......Page 150 5.2 Literature Review of Smooth-Bore Solids Conveying Models......Page 152 5.2.1 Darnell and Mol Model......Page 155 5.2.2 Tadmor and Klein Model......Page 156 5.2.3 Clarkson University Models......Page 157 5.2.4 Hyun and Spalding Model......Page 160 5.3 Modern Experimental Solids Conveying Devices......Page 161 5.3.1 Solids Conveying Devices at Clarkson University......Page 162 5.3.2 The Solids Conveying Device at Dow......Page 176 5.4 Comparison of the Modified Campbell-Dontula Model with Experimental Data......Page 186 5.4.1 Solids Conveying Example Calculation......Page 190 5.5 Grooved Bore Solids Conveying......Page 192 5.5.1 Grooved Barrel Solids Conveying Models......Page 196 5.6 Solids Conveying Notes......Page 198 Nomenclature......Page 201 References......Page 203 6 The Melting Process......Page 207 6.1 Compression Ratio and Compression Rate......Page 209 6.2 The Melting Process......Page 211 6.2.1 The Melting Process as a Function of Screw Geometry......Page 212 6.2.2 Review of the Classical Literature......Page 217 6.2.3 Reevaluation of the Tadmor and Klein Melting Data......Page 218 6.3 Theory Development for Melting Using Screw Rotation Physics......Page 221 6.3.1 Melting Model for a Conventional Transition Section Using Screw Rotation Physics......Page 222 6.3.2 Melting Models for Barrier Screw Sections......Page 236 6.4 Effect of Pressure on Melting Rate......Page 245 6.5 One-Dimensional Melting......Page 246 6.5.1 One-Dimensional Melting Model......Page 250 6.6 Solid Bed Breakup......Page 252 6.7 Melting Section Characteristics......Page 256 Nomenclature......Page 258 References......Page 260 7.1 Introduction to the Reference Frame......Page 264 7.2 Laboratory Observations......Page 267 7.3 Literature Survey......Page 271 7.4 Development of Linearized Flow Analysis......Page 276 7.4.1 Example Flow Calculation......Page 291 7.5 Numerical Flow Evaluation......Page 294 7.5.1 Simulation of a 500 mm Diameter Melt-Fed Extruder......Page 296 7.5.2 Extrusion Variables and Errors......Page 298 7.5.3 Corrections to Rotational Flow......Page 304 7.5.4 Simulation of the 500 mm Diameter Extruder Using Fc......Page 309 7.6 Frame Dependent Variables......Page 310 7.6.1 Example Calculation of Energy Dissipation......Page 313 7.7 Viscous Energy Dissipation and Temperature of the Resin in the Channel......Page 314 7.7.1 Energy Dissipation and Channel Temperature for Screw Rotation......Page 320 7.7.2 Energy Dissipation and Channel Temperature for Barrel Rotation......Page 324 7.7.3 Temperature Increase Calculation Example for a Screw Pump......Page 325 7.7.4 Heat Transfer Coefficients......Page 330 7.7.5 Temperature Calculation Using a Control Volume Technique......Page 331 7.7.6 Numerical Comparison of Temperatures for Screw and Barrel Rotations......Page 334 7.8 Metering Section Characteristics......Page 336 Nomenclature......Page 338 References......Page 342 8 Mixing Processes for Single-Screw Extruders......Page 346 8.1 Common Mixing Operations for Single-Screw Extruders......Page 347 8.1.1 Common Mixing Applications......Page 348 8.2 Dispersive and Distributive Mixing Processes......Page 350 8.3 Fundamentals of Mixing......Page 352 8.3.1 Measures of Mixing......Page 353 8.3.2 Experimental Demonstration of Mixing......Page 355 8.4 The Melting Process as the Primary Mechanism for Mixing......Page 363 8.4.1 Experimental Analysis of the Melting and Mixing Capacity of a Screw......Page 366 8.4.2 Mixing and Barrier-Flighted Melting Sections......Page 369 8.5 Secondary Mixing Processes and Devices......Page 370 8.5.1 Maddock-Style Mixers......Page 371 8.5.2 Blister Ring Mixers......Page 376 8.5.3 Spiral Dam Mixers......Page 378 8.5.4 Pin-Type Mixers......Page 379 8.5.5 Knob Mixers......Page 380 8.5.7 Dynamic Mixers......Page 381 8.5.8 Static Mixers......Page 384 8.6 Mixing Using Natural Resins and Masterbatches......Page 391 8.7 Mixing and Melting Performance as a Function of Flight Clearance......Page 392 8.9 Effect of Discharge Pressure on Mixing......Page 393 8.10 Shear Refinement......Page 394 8.11 Direct Compounding Using Single-Screw Extruders......Page 396 Nomenclature......Page 397 References......Page 399 9 Scaling of Single-Screw Extrusion Processes......Page 404 9.1 Scaling Rules......Page 405 9.2 Engineering Design Method for Plasticating Screws......Page 406 9.3 Scale-Up from a 40 mm Diameter Extruder to an 80 mm Diameter Machine for a PE Resin......Page 410 9.4 Rate Increase for an 88.9 mm Diameter Extruder Running a HIPS Resin......Page 414 Nomenclature......Page 421 References......Page 422 10 Introduction to Troubleshooting the Extrusion Process......Page 424 10.1 The Troubleshooting Process......Page 425 10.2 Hypothesis Setting and Problem Solving......Page 428 10.2.1 Case Study for the Design of a New Resin......Page 429 10.2.2 Case Study for a Surface Blemish......Page 431 10.2.3 Case Study for a Profile Extrusion Process......Page 432 10.3 Equipment and Tools Needed for Troubleshooting......Page 433 10.3.1 Maddock Solidification Experiment......Page 435 10.4.1 Flight Clearance and Hard Facing......Page 436 10.4.2 Barrel and Screw Alignment......Page 438 10.4.3 Extruder Barrel Supports......Page 439 10.4.4 First-Time Installation of a Screw......Page 441 10.4.5 Screw Breaks......Page 442 10.4.6 Protection from High-Pressure Events......Page 444 10.4.8 Particle Seals and Viscoseals......Page 446 10.5 Common Electrical and Sensor Problems......Page 448 10.5.2 Pressure Sensors......Page 449 10.5.3 Electronic Filters and Noise......Page 450 10.6 Motors and Drive Systems......Page 452 10.6.1 Motor Efficiencies and Power Factors......Page 454 10.7 Typical Screw Channel Dimensions......Page 455 10.8.1 Energy Dissipated by the Screw......Page 456 10.8.2 Screw Geometry Indices......Page 457 10.9 Barrel Temperature Optimization......Page 459 10.10 Screw Temperature Profile......Page 462 10.11 The Screw Manufacturing and Refurbishing Process......Page 471 10.12 Injection-Molding Plasticators......Page 479 10.13 New Equipment Installations......Page 481 10.13.1 Case Study: A Large Diameter Extruder Purchase......Page 485 10.13.2 Case Study: Extruder and Line Purchase for a New Product......Page 486 10.13.3 Summary for New Equipment Installations......Page 487 Nomenclature......Page 488 References......Page 490 11.1 Foreign Contaminants in the Extrudate......Page 493 11.1.1 Melt Filtration......Page 494 11.1.2 Metal Fragments in the Extrudate......Page 498 11.1.3 Gas Bubbles in a New Sheet Line......Page 499 11.2 Gels in Polyolefin Resins......Page 500 11.2.1 Protocols for Gel Analysis......Page 501 11.3 Resin Decomposition in Stagnant Regions of a Process......Page 507 11.4 Improper Shutdown of Processing Equipment......Page 509 11.5 Equipment Purging......Page 510 11.7 Flight Radii Size......Page 512 11.8 Drying the Resin......Page 515 11.9 Color Masterbatches......Page 516 11.10.1 Intermittent Crosslinked Gels in a Film Product......Page 517 11.10.2 Small Gels in an LLDPE Film Product......Page 523 11.10.3 Degassing Holes in Blow-Molded Bottles......Page 526 11.11.1 Splay Defects for Injection-Molded Parts......Page 529 11.12.1 Injection-Molded Parts with Splay and Poor Resin Color Purge......Page 532 11.12.2 Black Color Streaks in Molded Parts: Case One......Page 536 11.12.3 Black Streaks in Molded Parts: Case Two......Page 541 11.12.4 Silver Streaks in a Clear GPPS Resin Injection-Molded Packaging Part......Page 545 11.12.5 The Injection-Molding Problem at Saturn......Page 552 Nomenclature......Page 553 References......Page 554 12 Flow Surging......Page 557 12.1.1 Relationship Between Discharge Pressure and Rate at the Die......Page 558 12.2 Troubleshooting Flow Surging Processes......Page 559 12.3 Barrel Zone and Screw Temperature Control......Page 560 12.3.1 Water- and Air-Cooled Barrel Zones......Page 561 12.4 Rotation- and Geometry-Induced Pressure Oscillations......Page 562 12.5 Gear Pump Control......Page 564 12.7.1 Poor Barrel Zone Temperature Control......Page 567 12.7.2 Optimization of Barrel Temperatures for Improved Solids Conveying......Page 570 12.7.3 Flow Surging Due to High Temperatures in the Feed Section of the Screw......Page 572 12.7.4 Flow Surging Due to High Temperatures in the Feed Casing......Page 579 12.7.5 Flow Surging Due to a Poorly Designed Barrier Entry for GPPS Resin......Page 581 12.7.6 Solid Blockage at the Entry of a Spiral Mixer......Page 584 12.7.7 Flow Surging Caused by a Worn Feed Casing and a New Barrel......Page 590 12.7.8 Flow Surging for a PC Resin Extrusion Process......Page 599 Nomenclature......Page 603 References......Page 604 13 Rate-Limited Extrusion Processes......Page 606 13.1 Vent Flow for Multiple-Stage Extruders......Page 608 13.2 Screw Wear......Page 610 13.4.1 Rate Limitation Due to a Worn Screw......Page 612 13.4.2 Rate Limitation Due to Solid Polymer Fragments in the Extrudate......Page 613 13.4.3 Rate Limited by the Discharge Temperature for a Pelletizing Extruder......Page 618 13.4.4 Large Diameter Extruder Running PS Resin......Page 625 13.4.5 Rate Limited by Discharge Temperature and Torque for Starch Extrusion......Page 629 13.4.6 Vent Flow for a Two-Stage Screw Running a Low Bulk Density PS Feedstock......Page 632 13.4.7 Increasing the Rate of a Large Part Blow-Molding Process......Page 634 Nomenclature......Page 638 References......Page 639 14 Barrier and High-Performance Screws......Page 640 14.1 Barrier Screws......Page 642 14.2.1 Double Wave Screw......Page 648 14.2.2 Energy Transfer Screws......Page 650 14.2.3 Variable Barrier Energy Transfer Screws......Page 656 14.2.4 Distributive Melt Mixing Screws......Page 660 14.2.5 Fusion Screws......Page 664 14.3.1 Stratablend Screws......Page 665 14.3.2 Unimix Screws......Page 667 Nomenclature......Page 668 References......Page 669 15.1 Simulation Methods......Page 672 15.2 Compounding Processes......Page 673 15.2.1 Common Problems for Melt-Fed Extruders on Compounding Lines......Page 675 15.3 Large-Diameter Pumping Extruders......Page 676 15.3.1 Loss of Rate Due to Poor Material Conveyance in the Feed Section......Page 685 15.3.2 Operation of the Slide Valve......Page 687 15.3.3 Nitrogen Inerting on Vent Domes......Page 688 15.4 Secondary Extruders for Tandem Foam Sheet Lines......Page 689 15.4.1 High-Performance Cooling Screws......Page 693 Nomenclature......Page 696 References......Page 697 Appendix A1 Polymer Abbreviation Definitions......Page 699 A3.1 Capillary Rheometer......Page 701 A3.2 Cone and Plate Rheometer......Page 705 References......Page 707 A4.1 Shear Stress at a Sliding Interface for Select Resins......Page 709 A4.2 Melting Fluxes for Select Resins......Page 713 References......Page 716 A5.1 Channel Dimensions, Assumptions, and Basic Force Balances......Page 719 A5.2 Campbell-Dontula Model......Page 721 A5.2.1 Modified Campbell-Dontula Model......Page 722 A5.3 Hyun-Spalding Model......Page 724 A5.4 Yamamuro-Penumadu-Campbell Model......Page 726 A5.6 The Complete Dow Solids Conveying Data Set......Page 728 References......Page 733 A6.1 Derivation of the Melting Performance Equations for a Conventional Channel......Page 735 References......Page 746 A7.1 Transformed Frame Flow Analysis......Page 747 A7.1.1 x-Directional Flow......Page 749 A7.1.2 z-Directional Flow......Page 750 A7.1.3 z-Directional Flow for Helix Rotation with a Stationary Screw Core and Barrel......Page 756 A7.1.4 z-Directional Flow Due to a Pressure Gradient......Page 758 A7.2.1 Viscous Energy Dissipation for Screw Rotation: Generalized Solution......Page 763 A7.2.2 Viscous Energy Dissipation for Screw Rotation for Channels with Small Aspect Ratios (H/W < 0.1)......Page 769 A7.3 Viscous Energy Dissipation for Barrel Rotation......Page 771 A7.3.1 Viscous Energy Dissipation for Barrel Rotation: Generalized Solution......Page 772 A7.3.2 Viscous Energy Dissipation for Barrel Rotation for Channels with Small Aspect Ratios (H/W < 0.1)......Page 775 References......Page 776 Author......Page 777 Subject......Page 783 Prior extrusion books are based on barrel rotation physics—this is the first book that focuses on the actual physics of the process—screw rotation physics. In the first nine chapters, theories and math models are developed. Then, these models are used to solve actual commercial problems in the remainder of the book. Realistic case studies are presented that are unique in that they describe the problem as viewed by a typical plant engineer and provide the actual dimensions of the screws. Overall, there is not a book on the market with this level of detail and disclosure. The new knowledge in this book will be highly useful for production engineers, technical service engineers working with customers, consultants specializing in troubleshooting and process design, and process researchers and designers that are responsible for processes that running at maximum rates and maximum profitability.Contents:oIntroduction & TroubleshootingoPolymer MaterialsoIntroduction to Polymer Rheology for ExtrusionoResin Physical Properties Related to ProcessingoSolids ConveyingoThe Melting ProcessoFluid Flow in Metering ChannelsoMixing Processes for Single-Screw Extruders oScaling of Single-Screw Extrusion ProcessesoIntroduction to Troubleshooting the Extrusion ProcessoContaminations in the Finished ProductoFlow Surging oRate-Limited Extrusion Processes oBarrier and High-Performance ScrewsoMelt-Fed Extruders