C. Rauwendaal – Polymer Extrusion (5th edition)

Автор: C. Rauwendaal
Название книги: Polymer Extrusion (5th edition)
Формат: PDF
Жанр: Химия
Страницы: 944
Качество: Изначально компьютерное, E-book

Bridging the gap between theory and practice, the fifth edition of Polymer Extrusion continues to serve the practicing polymer engineer and chemist, providing the theoretical and practical tools for successful extrusion operations. In its revised and expanded form, this book incorporates many new developments in extrusion theory and machinery.

The extruder is indisputably the most important piece of machinery in the polymer
processing industry. To extrude means to push or to force out. Material is extruded
when it is pushed through an opening. When toothpaste is squeezed out of a tube, it
is extruded. The part of the machine containing the opening through which the
material is forced is referred to as the extruder die. As material passes through the
die, the material acquires the shape of the die opening. This shape generally changes
to some extent as the material exits from the die. The extruded product is referred to
as the extrudate.
Many different materials are formed through an extrusion process: metals, clays,
ceramics, foodstuffs, etc. The food industry, in particular, makes frequent use of
extruders to make noodles, sausages, snacks, cereal, and numerous other items. In
this book, the materials that will be treated are confined to polymers or plastics.
Polymers can be divided into three main groups: thermoplastics, thermosets, and
elastomers. Thermoplastic materials soften when they are heated and solidify when
they are cooled. If the extrudate does not meet the specifications, the material can
generally be reground and recycled. Thus, the basic chemical nature of a thermoplastic
usually does not change significantly as a result of the extrusion process.
Thermosets undergo a crosslinking reaction when the temperature is raised above a
certain temperature. This crosslinking bonds the polymer molecules together to
form a three-dimensional network. This network remains intact when the temperature
is reduced again. Crosslinking causes an irreversible change in the material.
Therefore, thermosetting materials cannot be recycled as can thermoplastic materials.
Elastomers or rubbers are materials capable of very large deformations with
the material behaving in a largely elastic manner. This means that when the deforming
force is removed, the material completely, or almost completely, recovers. The
emphasis of this book will be on thermoplastics; only a relatively small amount of
attention will be paid to thermosets and elastomers Materials can be extruded in the molten state or in the solid state. Polymers are
generally extruded in the molten state; however, some applications involve solidstate
extrusion of polymers. If the polymer is fed to the extruder in the solid state
and the material is melted as it is conveyed by the extruder screw from the feed port
to the die, the process is called plasticating extrusion. In this case, the extruder
performs an additional function, namely melting, besides the regular extrusion
function. Sometimes the extruder is fed with molten polymer; this is called melt fed
extrusion. In melt fed extrusion, the extruder acts purely as a pump, developing the
pressure necessary to force the polymer melt through the die.
There are two basic types of extruders: continuous and discontinuous or batch type
extruders. Continuous extruders are capable of developing a steady, continuous flow
of material, whereas batch extruders operate in a cyclic fashion. Continuous extruders
utilize a rotating member for transport of the material. Batch extruders generally
have a reciprocating member to cause transport of the material.

This book will primarily deal with plasticating extrusion in a continuous fashion.
Chapters 2, 3, and 4 deal with a description of extrusion machinery. Chapter 5 will
briefly review the fundamental principles that will be used in the analysis of the
extrusion process. Chapter 6 deals with the polymer properties important in the
extrusion process. This is a very important chapter, because one cannot understand
the extrusion process if one does not know the special characteristics of the material
to be extruded. Understanding just the extrusion machinery is not enough.
Rheological
and thermal properties of a polymer determine, to a large extent, the
characteristics of the extrusion process. The process engineer, therefore, should be
a mechanical or chemical engineer on the one hand, and a rheologist on the other
hand. Since most engineers have little or no formal training in polymer rheology, the
subject is covered in Chapter 6, inasmuch as it is necessary for the analysis of the
extrusion process.
Chapter 7 covers the actual analysis of the extrusion process. The process is analyzed
in discrete functional zones with particular emphasis on developing a quantitative
understanding of the mechanisms operational in each zone.
The theory developed in Chapter 7 is applied to the design of extruder screws in
Chapter 8 and to the design of extruder dies in Chapter 9. Chapter 10 is devoted to
twin screw extruders. Twin screw extruders have become an increasingly important
branch of the extrusion industry. It is felt, therefore, that any book on extrusion cannot
ignore this type of extruder. Troubleshooting extruders is covered in Chapter 11. This is perhaps the most critical and most important function performed in industrial
operation of extruders. Extrusion problems causing downtime or off-spec products
can become very costly in a short period of time: losses can often exceed the
purchase price of the entire machine in a few hours or a few days. Thus, it is very
important that the process engineer can troubleshoot quickly and accurately. This
requires a solid understanding of the operational principles of extruders and the
basic mechanisms behind them. Therefore, the chapter on troubleshooting is a practical
application of the functional process analysis developed in Chapter 7.
The final chapter of the book, Chapter 12 on modeling and computer simulation was
added in the fourth edition. This chapter was written by Paul Gramann, Bruce Davis,
and Tim Osswald; three workers who have made substantial contributions to the
development of this branch of polymer processing. Computer aided engineering
(CAE) is now an integral part of extrusion engineering and a current book on extrusion
would not be complete without dealing with this important subject.
The book is therefore divided in four main parts. The first part deals with the hardware
and /or mechanical aspects of extruders: this is covered in Chapters 2, 3, and 4.
The second part deals with the process analysis: this is covered in Chapters 5, 6,
and 7. The third part deals with practical applications of the extrusion theory: this
is covered in Chapters 8, 9, 10, and 11. Part four is the chapter on modeling and
computer simulation. Parts I, II, and IV can be studied independently; Part III, however,
cannot be fully appreciated without studying Part II