Extrusion Dies for Plastics and Rubber E-Book

Christian Hopmann

• Herausgeber: Carl Hanser Verlag GmbH & Co. KG
• Kategorie: Fachliteratur
• Sprache: Englisch
• Veröffentlichungsjahr: 2017

Seitenzahl: 646

Beschreibung

This definitive book provides a comprehensive account of the full range of dies used for extrusion of plastics and elastomers. The distinctive features of the various types of dies are described in detail. Expert advice on the configuration of dies is given, and the possibilities of computer-aided design, as well as its limitations, are demonstrated.

Fundamentals and computational procedures are clearly explained so that no special prior knowledge of the subject is required. The mechanical configuration, handling, and maintenance of extrusion dies are described. Calibration procedures for pipes and profiles are also discussed.

This book was written for plastics engineers who need daily support in their practical work in industry and science, as well as for students preparing for their professional life.

The 4th edition is brought up to date with several important additions, including coverage of multilayer (>15 layer) dies, melt encapsulation, and simulation tools (rheological/thermal CFD simulations).

Leseprobe

Christian Hopmann Walter Michaeli

Extrusion Dies for Plastics and Rubber

Design and Engineering Computations With Contributions by Dr.-Ing. Ulrich Dombrowski • Dr. Ulrich Hüsgen • Dr.-Ing. Matthias Kalwa • Dr.-Ing. Stefan Kaul • Dr.-Ing. Michael Meier-Kaiser • Dr.-Ing. Boris Rotter • Dr.-Ing. Micha Scharf • Dr.-Ing. Claus Schwenzer • Dr.-Ing. Christian Windeck • Nafi Yesildag, M.Sc.

4th Edition

The authors:

Prof. Dr.-Ing. Christian Hopmann, Head of the Institute of Plastics Processing (IKV) at RWTH Aachen University, Aachen, GermanyProf. Dr.-Ing. Dr.-Ing. E.h. Walter Michaeli, former Head of the Institute of Plastics Processing (IKV) at RWTH Aachen University, Aachen, Germany

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Print-ISBN 978-1-56990-623-1 E-Book ISBN 978-1-56990-681-1

Table of Contents

Title page

Copyright page

Table of Contents

Preface

Preface to the Third Edition

Preface to the Second Edition

Preface to the First Edition

1 Introduction

2 Properties of Polymeric Melts

2.1 Rheological Behavior

2.1.1 Viscous Properties of Melts

2.1.2 Determination of Viscous Flow Behavior

2.1.3 Viscoelastic Properties of Melts

2.2 Thermodynamic Behavior

2.2.1 Density

2.2.2 Thermal Conductivity

2.2.3 Specific Heat Capacity

2.2.4 Thermal Diffusivity

2.2.5 Specific Enthalpy

3 Fundamental Equations for Simple Flows

3.1 Flow through a Pipe

3.2 Flow through a Slit

3.3 Flow through an Annular Gap

3.4 Summary of Simple Equations for Dies

3.5 Phenomenon of Wall Slip

3.5.1 Model Considering the Wall Slip

3.5.2 Instability in the Flow Function - Melt Fracture

4 Computation of Velocity and Temperature Distributions in Extrusion Dies

4.1 Conservation Equations

4.1.1 Continuity Equation

4.1.2 Momentum Equations

4.1.3 Energy Equation

4.2 Restrictive Assumptions and Boundary Conditions

4.3 Analytical Formulas for Solution of the Conservation Equations

4.4 Numerical Solution of Conservation Equations

4.4.1 Finite Difference Method

4.4.2 Finite Element Method

4.4.3 Comparison of FDM and FEM

4.4.4 Examples of Computations of Extrusion Dies

4.5 Consideration of the Viscoelastic Behavior of the Material

4.6 Computation of the Extrudate Swelling

4.7 Methods for Designing and Optimizing Extrusion Dies

4.7.1 Industrial Practice for the Design of Extrusion Dies

4.7.2 Optimization Parameters

4.7.3 Optimization Methods

4.7.4 Practical Applications of Optimization Strategies for the Design of Extrusion Dies

5 Monoextrusion Dies for Thermoplastics

5.1 Dies with Circular Exit Cross Section

5.1.1 Designs and Applications

5.1.2 Design

5.2 Dies with Slit Exit Cross Section

5.2.1 Designs and Applications

5.2.2 Design

5.3 Dies with Annular Exit Cross Section

5.3.1 Types

5.3.2 Applications

5.3.3 Design

5.4 Formulas for the Computation of the Pressure Loss in Flow Channel Geometries other than Pipe or Slit

5.5 Dies with Irregular Outlet Geometry (Profile Dies)

5.5.1 Designs and Applications

5.5.2 Design

5.6 Dies for Foamed Semifinished Products

5.6.1 Dies for Foamed Films

5.6.2 Dies for Foamed Profiles

5.7 Special Dies

5.7.1 Dies for Coating of Profiles of Arbitrary Cross Section

5.7.2 Dies for the Production of Profiles with Reinforcing Inserts

5.7.3 Dies for the Production of Nets

5.7.4 Slit Die with Driven Screw for the Production of Slabs

6 Coextrusion Dies for Thermoplastics

6.1 Designs

6.1.1 Externally Combining Coextrusion Dies

6.1.2 Adapter (Feedblock) Dies

6.1.3 Multimanifold Dies

6.1.4 Layer Multiplication Dies

6.2 Applications

6.2.1 Film and Sheet Dies

6.2.2 Blown Film Dies

6.2.3 Dies for the Extrusion of Parisons for Blow Molding

6.3 Computations of Flow and Design

6.3.1 Computation of Simple Multilayer Flow with Constant Viscosity

6.3.2 Computation of Coextrusion Flow by the Explicit Finite Difference Method

6.3.3 Computation of Velocity and Temperature Fields by the Finite Difference Method

6.3.4 Computation of Velocity Fields in Coextrusion Flows by FEM

6.4 Instabilities in Multilayer Flow

7 Extrusion Dies for Elastomers

7.1 Design of Dies for the Extrusion of Elastomers

7.2 Fundamentals of Design of Extrusion Dies for Elastomers

7.2.1 Thermodynamic Material Data

7.2.2 Rheological Material Data

7.2.3 Computation of Viscous Pressure Losses

7.2.4 Estimation of the Peak Temperatures

7.2.5 Consideration of the Elastic Behavior of the Material

7.3 Design of Distributor Dies for Elastomers

7.4 Design of Slotted Disks for Extrusion Dies for Elastomers

7.4.1 Computation of Pressure Losses

7.4.2 Extrudate Swelling (Die Swell)

7.4.3 Simplified Estimations for the Design of a Slotted Disk

8 Heating of Extrusion Dies

8.1 Types and Applications

8.1.1 Heating of Extrusion Dies with Fluids

8.1.2 Electrically Heated Extrusion Dies

8.1.3 Temperature Control of Extrusion Dies

8.2 Thermal Design

8.2.1 Criteria and Degrees of Freedom for Thermal Design

8.2.2 Heat Balance of the Extrusion Die

8.2.3 Restrictive Assumptions in the Modeling

8.2.4 Simulation Methods for Thermal Design

9 Mechanical Design of Extrusion Dies

9.1 Mechanical Design of a Breaker Plate

9.2 Mechanical Design of a Die with Axially Symmetrical Flow Channels

9.3 Mechanical Design of a Slit Die

9.4 General Design Rules

9.5 Materials for Extrusion Dies

10 Handling, Cleaning, and Maintaining Extrusion Dies

11 Calibration of Pipes and Profiles

11.1 Types and Applications

11.1.1 Friction Calibration

11.1.2 External Calibration with Compressed Air

11.1.3 External Calibration with Vacuum

11.1.4 Internal Calibration

11.1.5 Precision Extrusion Pullforming (the Technoform Process)

11.1.6 Special Process with Movable Calibrators

11.2 Thermal Design of Calibration Lines

11.2.1 Analytical Computational Model

11.2.2 Numerical Computational Model

11.2.3 Analogy Model

11.2.4 Thermal Boundary Conditions and Material Data

11.3 Effect of Cooling on the Quality of the Extrudate

11.4 Mechanical Design of Calibration Lines

11.5 Cooling Dies, Process for Production of Solid Bars

Preface

In January 2003, this book was published in its 3rd edition in English. Since then, an unrelenting demand for the book has been observed, both for the German and English versions. In order to meet this demand, it is our pleasure that Hanser now publishes this 4th edition. With this edition, “Extrusion Dies” has for the first time two editors: In April 2011 Prof. Dr.-Ing. Christian Hopmann succeeded Prof. Dr.-Ing. Dr.-Ing. E. h. Walter Michaeli as holder of the Chair of Plastics Processing and Head of the Institute of Plastics Processing (IKV) at RWTH Aachen University, Aachen, Germany. We are very pleased that this book with its long history with Hanser is continued into the next IKV generation.

This update will continue to help you in your work and life while hopefully also providing pleasure in reading. We have retained the structure of the book, which has proven itself over many years and received much positive resonance from readers.

When we say “we”, we particularly refer to Dr.-Ing. Christian Windeck, former head of the IKV extrusion department, and his successor Nafi Yesildag, M.Sc., who have critically analyzed, checked, and supplemented the contents, equations, and reference lists. We would like to express our special thanks to both of them.

We further thank Mark Smith and Jörg Strohbach of Hanser for their support in the publication of our work.

Once again, suggestions obtained from the plastics and rubber industry were taken up and addressed in this fourth edition. We thank all those who provided their suggestions and help. Many research and development efforts of the IKV form the fundament of some of the facts described in this book. Against this background, we thank the Federal Ministry for Economic Affairs and Energy (BMWi), Berlin, for the promotion of many industrial research projects through the German Federation of Industrial Research Associations (AIF e. V.), Cologne, the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad Godesberg, the Federal Ministry of Education and Research (BMBF), Bonn, and the European Commission, Brussels, with respect to extrusion dies.

Walter Michaeli

Christian Hopmann

Preface to the Third Edition

During my last visit to Medellin, Colombia, on occasion of the 10th anniversary of the ICIPC, a thriving plastics and rubber research institute, I met many young and eager students who knew my name because they had studied the book on extrusion die design. They asked many questions and I could not say good-bye without being photographed showing me at the center of their group. I enjoyed that for two reasons: first, this event showed that the book has reached acceptance even far away from my hometown. Second, it was important to learn that those young men and women enjoyed studying the book on their way to qualify for their professional life. But this book has also been written for the people who need daily support in their practical work applications in industry and science. Twelve years have gone by since the second edition of this book was published, years with visible changes and innovations in the field of extrusion and die design. For example, spiral mandrel dies have existed for more than three decades, but some functionalities have changed. Today, we place the spiral on a flat surface and feed it from the side. And when we pile a couple of those systems on top of each other, the result is the so-called stack die, which provides several advantages over classical coextrusion dies with annular slits. We incorporated this new development in Chapter 5.

It may be the dream of an extrusion die designer to process all of the material, processing, and geometrical data of the final product with a computer and end up with a fully designed flow channel which facilitates the optimum flow distribution. In studying this book, the reader will realize that finite element analysis is a key to fulfilling this dream, but the proper description of the viscoelastic properties of the extruded materials is still a challenge for rheologists and engineers. Nevertheless, significant steps have been made in this direction. For viscous flow, that goal has almost been reached. Therefore, a new chapter on optimization of extrusion die performance with computers was integrated into this third edition.

I would like to thank my co-workers, Dr.-Ing. Boris Rotter, head of the IKV extrusion department, and Dipl.-Ing. Stefan Kaul, research engineer in this department, for their support and active help in reviewing and improving this book with their expertise. Many of the results presented in this book were produced by students at the Institute during the research for their diplomas.

Much gratitude also goes to those who provided many suggestions and help; in particular, the members of the IKV advisory committees: Extrusion, Blow Molding, and Rubber Technology. Many research and development projects of IKV form the basis of some of the relations documented in the book. They were made possible by the cooperative research between the industry and the IKV, by the support and funding of the Arbeitsgemeinschaft industrieller Forschungsvereinigungen Otto von Guericke e.V. (AiF) in Cologne, the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad Godesberg, and the Federal Ministry for Education, Research and Technology (BMBF) in Berlin, respectively Bonn and the European Commission, Brussels.

Last but not least, I woud like to thank Dr. Wolfgang Glenz of Hanser, Munich, for so many years of excellent and active cooperation and for his vital insight. Such insight is appreciated by technical authors like myself, who have a rather challenging job, which at least nourishes our families, parallel to writing books. All of these contributing factors make things easier to write a book like this.

Walter Michaeli

Preface to the Second Edition

Ten years after the publication of the first edition of this book it is appropriate to start anew by reviewing and documenting the new developments and applications in the area of designing and manufacturing of extrusion dies. That is the purpose of this new, revised edition. Although the basic principles pertaining to extrusion dies are the same, there have been, in the meantime, many developments and refinements in this area due to continuously growing demands for improved quality and increased productivity, as well as emerging new polymers and novel products. For example, coextrusion has gained importance recently and the polymers based on liquid crystals represent an entirely new class of materials which will, without doubt, require new concepts in extrusion die design. That means development will continue and, therefore, this second edition can summarize the current state of technology. Particular attention is given here to the theoretical tools, such as the finite element method, which have been greatly developed in the last decade and which can provide solutions to many current problems.

The basic goal of this book, as already stated in the preface to the first edition, will not change under any circumstances; it is written for the practitioner, to help him in his daily work and for the student, to introduce him to the complex world of extrusion dies and provide him with an extensive orientation and thorough education. The response to the first edition of this book was very positive. Nevertheless, as with everything, it can be further improved and this is what we are attempting with this second edition. The chapter about the design of dies for the extrusion of elastomers was added; the area of coextrusion dies was expanded considerably; and all other chapters were subjected to substantial revisions.

When I say “we”, I refer to my coworkers at the Institut fuer Kunststoffverarbeitung (IKV) at the Rheinisch-Westfaelische Technische Hochschule in Aachen. Those are Messrs. Dr. U. Dombrowski, Dr. U. Huesgen, Dr. M. Kalwa, Dr. M. Meier and Dr. C. Schwenzer. They took part in the work on this book and dedicated many hours of their personal time. This is also true for Mrs. N. Petter and Mrs. D. Reichelt, who transcribed the text and for Mrs. G. Zabbai and Mr. M. Cosier who assured the good quality of the illustrations. Many special and personal thanks to all of them.

Many of the results presented in this book were produced by students at the Institute during their studies and research leading to diplomas. They also deserve sincere thanks.

Suggestions obtained from the plastics and rubber industry were taken up and dealt with in this second edition. Many thanks go also to those who provided the suggestions and help, in particular the members of the advisory committees Extrusion, Blow Molding and Rubber Technology of the IKV.

Many research and development efforts of the IKV form the basis of some of the relations described in this book. They were made possible by the cooperative research between the industry and IKV, by the support of the Arbeitsgemeinschaft Industrieller Forschungsvereinigungen (AIF) in Cologne, of the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad Godesberg and the Federal Ministry for Research and Technology (BMFT) in Bonn as well as by the Volks wagen werk Foundation in Hannover.

Aachen, in November 1991

Walter Michaeli

Preface to the First Edition

In this book an attempt is made to present to the practitioner and to the student a broad picture of all extrusion dies for plastics. In pursuing that objective the various types of dies and their specific features are discussed, guidelines for their design given and approaches to computational engineering analyses and its limitations demonstrated. This is even more important in view of the increasing efforts made by the industry as well as academia, starting in the recent past and continuing in the present, to model the transport phenomena (flow and heat transfer) in the extrusion die mathematically. These important projects are motivated primarily by the demand for higher productivity accompanied by better product quality (i. e. dimensional accuracy, surface quality) of the extruded semifinished goods. Purely empirical engineering methods for extrusion dies are becoming unacceptable at an increasing rate because of economical considerations.

The design of the flow channel takes a focal position in the engineering process of extruder dies. This book starts by identifying and explaining the necessary material data for designing the flow channel.

The derivation of basic equations permits estimates to be made of pressure losses, forces acting on the flow channel walls, velocity profiles, average velocities etc. in the flow channel. The simple equations that are useful for practical applications are summarized in tables. For the majority of extrusion dies these equations are sufficient to arrive at a realistic design based upon rheological considerations.

Approaches to calculating the velocity and temperature fields using finite difference and finite element methods (FEM) are also discussed because of their increasing importance in the design of extrusion dies.

The various types of single and multiple layer extrusion dies and their specific features are highlighted in detail in Chapters 5 and 6, followed by a review of the thermal and mechanical design considerations, and comments pertinent to the selection of material for extrusion dies and to their manufacture. A discussion of handling, cleaning and maintenance of extrusion dies as well as of devices for sizing of pipes and profiles concludes the book. At the end is a comprehensive list of references.

The book was written during my activity as head of the Extrusion and Injection Molding Section at the Institut fuer Kunststoffverarbeitung (IKV) at the Rheinisch-Westfaelische Technische Hochschule Aachen (Institute for Plastics Processing at the Aachen Technical University, Aachen, West Germany, Director: Prof. Dr.-Ing. G. Menges). I had access to all important results of the research at the IKV in the field of engineering of extrusion dies. I wish to extend my thanks to my former and present colleagues at the IKV, in particular Messrs. J. Wortberg, A. Dierkes, U. Masberg, B. Franzkoch, H. Bangert, L. Schmidt, W. Predoehl, P.B. Junk, H. Cordes, R. Schulze-Kadelbach, P. Geisbuesch, P. Thienel, E. Haberstroh, G. Wuebken, U. Thebing, K. Beiss and U. Vogt whose research work was essential in the preparation of the text and also to all other colleagues who contributed and to the students and graduate students of the Institute. But foremost, I wish to thank Prof. Dr.-Ing G. Menges for encouraging me to prepare this book and for his ceaseless help, promotion and support which made it possible for me to complete it.

Further thanks are extended to a number of representatives of the plastics industry, in particular to the members of the Section Extrusion and Extrusion Blow Molding of the Advisory Board of the Foerdervereinigung (Sponsors Society) of the IKV.

Many of the research and development projects of the IKV which are referred to in this book and which became the basis for some of the facts presented in it, were only made possible financially by the joint research between industry and the IKV, support by the Arbeitsgemeinschaft Industrieller Forschungsvereinigungen (AIF), Cologne, the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad Godesberg and the Ministry for Research and Technology (BMFT), Bonn.

This book was first published in German in 1979. The book in your hands is the first English translation based on this slightly revised 1979 edition. We have added an alphabetic index and checked the list of references to make sure that the most important references in English are easily identified.

‘Life goes on’ ‒ also in extrusion tooling ‒ so the list of references is completed by publications since 1979. I wish to thank all who made the English version possible: The Society of Plastics Engineers (SPE) for sponsoring this book, Dr. Herzberg for translating, Dr. Immergut and Dr. Glenz of Hanser for coordinating, Dr. Hold of Polymer Processing Institute ‒ Stevens Institute of Technology, Hoboken, New Jersey, for being the technical editor, and Hanser for publishing.

Heppenheim, W. Germany August 1983

Walter Michaeli

1Introduction

In the extrusion of thermoplastics into semifinished products, two units occupy a central position: the extrusion die (also known as the extruder head), which shapes the melt, and the former or calibrator, usually mounted adjacent to the extrusion die, whose function is to guide the molten semifinished product while maintaining the desired dimensions and providing the specified degree of cooling (Figs. 1.1 and 1.2).

Conversely, when extruding elastomeric materials, the dimensions of the product are essentially determined by the geometry of the extrusion die. Only when vulcanization follows the extrusion some geometrical changes occur, mainly due to the crosslinking of the material, especially when the extrudate is allowed to shrink freely.

A sufficiently large, pulsation-free, reproducible, and thermally and mechanically homogeneous melt stream is expected from the extruder. Subsequently, the extrusion die and the calibration unit determine the dimensions of the semifinished products. In this connection, it must be taken into consideration that the rheological and thermodynamic processes in the die and in the calibrator, as well as any stretching processes that may be present between the die and the calibrator or in connection to both, have a decisive effect on the quality of the extruded semifinished products (such as the surface and the characteristic mechanical properties). In order to design the extrusion die and the calibration unit in a manner that is appropriate from a process engineering point of view, it is necessary to take into consideration the flow, deformation, and temperature relationships in both parts of the production line. If an analytical description of the physical processes is selected, the empirical portion in the design of the die and of the forming stage can be reduced, because changes, such as in the geometry of the channels of the die, in the operating conditions, or in the rheological and the thermodynamic material values of the polymer being processed, can be evaluated directly with regard to shaping and cooling of the extruded semifinished products. This leads to a more reliable design of extrusion die and of calibration unit.

Figure 1.1 Diagram of an extrusion line for profiles, left to right: dumping chute (storage), cutter, take-up, cooling section, calibration, die, and extruder

Figure 1.2 Functional sections of a die and a calibrator [Reifenhäuser]

It is therefore an objective of this book to provide a comprehensive description of the processing and engineering methods used in extrusion dies and calibration units, with attention being focused on a description of the extrusion die. Rules are derived for their design, and simple mathematical aids are given that conform to practical needs. Moreover, reference is made to the special features of different designs for the die and the calibration unit. Specific differences between dies used for the extrusion of elastomeric materials and those used for thermoplastics are pointed out.

Rheological, thermodynamic, mechanical, manufacturing, and operational points of view arise in the design and engineering of extrusion dies and calibration units [1].

The operational aspects include, for example, an adequate mechanical stiffness of the extrusion die, in order to keep changes in the cross section of the outlet that are due to the action of melt pressure to a minimum; the ease of installation and dismantling of the die and calibration unit; and the ease of cleaning the die. In addition to that, as few as possible well-sealed surfaces in the dies and a readily detachable and tight connection between the extruder and the die are important [1]. Manufacturing points of view must be given consideration in the design of the individual die and calibration unit components to achieve the lowest manufacturing costs, such as using die materials that lend themselves to machining, polishing and, if necessary, tempering and employing established manufacturing methods.

When considering rheological aspects, the question must be asked [1]: How should the dimension of the flow channel in the die be selected so that

a specified throughput is achieved for a given extrusion pressure? (This question may also be reversed.)

the melt emerges at the same average rate from the whole of the outlet cross section?

the desired extrudate geometry is achieved for semifinished products without axial symmetry? (This is, among other things, on the basis of visco-elastic effects.)

the surface of the extrudate or the interfaces of different melt layers remain smooth even at high throughputs? (At high shear rates, melt fracture may arise.)

stagnations and decompositions of the extruded material, which are partly associated with stagnations, are avoided? (This is a question of the residence times of the material in the die as well as of the temperatures existing there.)

In the thermodynamic consideration of the problem, which is closely associated with the rheological aspects, information must be obtained concerning the maximum temperatures occurring in the melt stream in the die on the basis of existing heat transmission and dissipation relationships, especially in view of the heat-sensitive polymeric materials. In addition, the homogeneity of temperatures within the melt is of importance because local temperature variations directly change the materials' viscosity, and throughput deviations may arise. This topic also includes the realization of a uniform and controllable temperature in the die and the calibrator.

As a rule, not all of the subjects addressed here can be realized simultaneously with the same success when designing an extrusion die as well as a calibrator. For this reason, priorities must be established. For example, in designing a pelletizer die (perforated plate for pelletizing), every effort is made to obtain as high a throughput as possible, while in wire coating a smooth surface has a high priority [1].

In these considerations, however, it is necessary to pay attention to the fact that the extruder and the extrusion die interact in their operating behavior. This is the case particularly when using a conventional single-screw extruder with a smooth cylinder and an extruder screw with three sections. As can be seen from Fig. 1.3, increased extrusion die resistance at a constant screw speed can lead to a clear reduction in the throughput in this case. The pressure drop in the extrusion die is therefore important in the mechanical design of the die body and of the bolts that hold the die together, as well as for the throughput that can be achieved. (Note: In many cases, the throughput of an extrusion line is not limited by the die or by the extruder that has been selected, but rather by the attainable rate of cooling in the region of the calibrating and cooling stages. For instance, thick-walled rods are manufactured with extruders having a small screw diameter.) Moreover, under adiabatic conditions, the temperature increases in the extrusion die, which results from internal friction of the melt (dissipation) correlated with this pressure drop according to the well-known equation

(1.1)

ΔT

Temperature difference

Δp

Pressure loss

Density

cp

Specific heat capacity

Fig. 1.3 Performance graph of a conventional extruder

With regard to the design of the extrusion die, the pressure drop is of primary importance.

The aspects addressed, which must be taken into consideration in designing an extrusion die, are presented in the following diagram (Fig. 1.4). The input data for designing an extrusion die (Fig. 1.4, Step I) are as follows:

the geometry of the semifinished product to be extruded (e. g., pipe, flat film, any profile) and whether this is also designed in conformity with the needs of the polymer processed;

the manner in which the die is fed and whether several semifinished products are to be manufactured simultaneously (Fig. 1.5);

the material or the combination of materials to be processed in the case of coextrusion; and

the operating point (or the operating region) of the extrusion die (the operating point is understood to be the throughput and the temperature in the die).

This is followed in Step II by the selection and design of the flow channel, as well as by the calculation of the pressure drop on the basis of the information provided in Step I. Moreover, the position of the heaters relative to the flow channel can be given, with minimum clearances being taken into consideration.

In Step III, the basic dimensions of the die are established. However, the sequence of the steps to be considered can be changed.

The exact design of the die takes place in Step IV. If necessary, control calculations can be carried out for the structural details.

Fig. 1.4 Flow diagram of the development of an extrusion die from design to acceptance

Fig. 1.5 Types of extrusion dies

The manufacture (Step V) is followed by the initial operation of the die (Step VI) with the material (or material combination) selected for the design and under the operating conditions aimed for in later use (see Step I). Several die corrections can also become necessary here.

If the result is satisfactory, the die is then finally accepted (Step VII) and is ready for production.

Symbols and Abbreviations

cp

Specific heat capacity

k

Die resistance

n

Screw speed

p

Pressure

Δp

Pressure difference

T

Temperature

ΔT

Temperature difference

Volume flow

Density

Reference of Chapter 1

1. Röthemeyer, F.: Bemessung von Extrusionswerkzeugen. Maschinenmarkt76 (1970) 32, pp. 679‒685

2Properties of Polymeric Melts