11.1 Introduction
Rubber is an elastic material and it is often called an ‘elastomer’. It also possesses a
viscous nature, which is manifested in temperature-rises during mixing, i.e., viscous energy
dissipation. Although its viscoelastic nature has been recognised for some time, the
discussion on mixing of rubber often ignores viscoelasticity. One reason for this may lie
in the fact that many people are unfamiliar with viscoelasticity. Another reason may be
that methods for applying viscoelasticity to practical situations are not adequately
developed. The latter concerns the handling of non-linear viscoelasticity in particular. It
also includes fracture behaviour of rubber.
This chapter will discuss the mechanisms of mixing fillers with gum rubbers. It is primarily
concerned with the use of internal mixers.
11.2 Problems associated with internal mixers
In discussing problems associated with internal mixers, we begin with the differences in
operation between the mill and the internal mixer. In the mill operation, it is possible to
observe what is happening, whereas with internal mixers, direct observation is not possible.
In mill mixing, the operator participates in the production process by adjusting mill gap,
cutting and rolling rubber sheet, and recharging. The repeated take-off and recharging
are to give a uniform treatment of the compound. With internal mixers, the gap between
the rotor wing and the chamber wall corresponds to the mill gap. However, the contents
of the mixer do not necessarily pass the gap uniformly; some parts may go through more
times than other parts. Some parts may even remain stagnant. In general, the history of
deformation and fracture of rubber during mixing is non-uniform. The degree of nonuniformity
depends on the rotor configuration and on whether the rotors are intermeshing
or non-intermeshing. In addition, the viscoelasticity of a given gum rubber has a decisive
influence on the uniformity. The uniformity in this discussion primarily concerns the
macroscopic differences but it is indirectly related to microscopic inhomogeneity also.
The fill factor most suitable for the mixing of rubber is about 70-75%, which was
determined through experience. In order for the mixer’s contents to move uniformly, a
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
|