THE ROLE OF THE

5
5.1 IntroductIon
Manufacturing and
Process Technology
This book was written from the perspective of the OEM (original equipment manufacturer)
chemist. Thus, manufacturing or processing for various plastics, elastomers,
or metals is not discussed in detail, although some time should be devoted to it.
Often, the OEM chemist or material engineer is required to interface with raw material
suppliers and chemists from tier one or tier two suppliers regarding processing
and how best to manufacture the product of interest. We will briefly touch on some
of the most important and useful technologies for the chemist today. The discussion
centers on some of the key processes and technologies within this book.
5.2 rubber ProcessIng
Rubber processing can be considered to take place in four steps: mixing, forming, storing,
and molding. During the mixing process, heat applied to the rubber will cause the
rubber to go through various states of flow. Below the T g (the glassy region), the polymer
chains are frozen in place. The material is highly elastic and molecular motion is
limited to bending and stretching. At the glass transition region (T g), rotational motion
increases and the polymer is very viscous. In the rubbery region, the polymer is highly
elastic and rubber like, which will allow for elongation. In this region, chains develop
entanglements that act like cross-links. Finally, in the flow region, at the highest temperatures,
resistance to translational motion decreases and the chains slip easily past
one another. Viscous flow is now possible, dimensional stability is lost, and the material
can be compounded using mixers, rubber calendar machines, and curing presses.
Finished products will no longer flow because they are now cross-linked.
Rubbers must first be mixed. They consist of various components that provide a
specific function to the compound. A typical rubber compound has the components
listed in Table 5.1. To mix the components, a Banbury mixer is often used. These
types of mixers have been in use since 1916 [1]. A Banbury will have two spiral
blades held within a housing and is considered an internal mixer. The two blades
of the mixer will have channels for heating and cooling if necessary. Between the
blades is a ridge or space for the material to be mixed. The invention of the Banbury
resulted in the removal of roller milling in rubber production [2]. Figure 5.1 shows
a rough schematic of the internal Banbury type mixer. For a typical tire batch of
225 kg, a Banbury mixer has a gross capacity of around 270 L and operates at up to
2,000 hp [3].
67