Mixers, internal general

Silica compounds are generally processed in conventional internal mixers, preferably with intermeshing rotors. These mixers are designed and optimized for carbon black-fiUed compounds in which mixing is based only on physical processes. When a silica-silane reinforcing system is used, additionally a chemical reaction, the sUanization, occurs. One of the main influencing factors of the silanization reaction is the concentration of ethanol in the compound as well as in the mixer [25,26]. As the silanization finally reaches an equilibrium, low concentrations of ethanol in the compound are expected to enhance the reaction rate. 

All types of split-recombine mixers generally have high volume flows (e.g. 1001 h and more at moderate pressure drops) at favorable pressure drops (not exceeding 5 bar) as their internal micro structures can be held large [41,42,48,49]. 

In general a rotating part of a machine in the mbber industry the term refers particularly to the contoured rolls of an internal mixer and to the mushroom-shaped rotor of the Mooney Viscometer. 

The tolerance allowed on mass of ingredients is fairly tight at 1% generally but down to 0.02g for sulphur and accelerators. For miniature internal mixers this reduces even further to 0.002g. There are limits on the difference between the sum of the masses of the ingredients and the final mass of the mixed batch of between + 0.5% and - 1.5%. Carbon black is required to be conditioned before use to remove moisture but it seems curious that this is not required for other fillers. 

Outline procedures are given for using both mill and internal mixers which provide a very sound basis for obtaining reproducible mixes provided the detailed schedule for any particular mix is properly standardised and adhered to. This is all that can be hoped for considering that, in general, the results from laboratory mills and mixers are not identical with those obtained with full-sized factory equipment. 

In some cases, the curing agent is added during the milling operation, generally in the form of a master batch. This practice is used for peroxides that decompose at a lower temperature, to reduce the risk of accidental curing in the internal mixer, when localized temperature can be very high. 

Since internal mixers can be opened for material feed and compound removal, these are generally simpler to clean when compared to screw-type mixers. It is a common practice to run natural rubber or special high-tack, cohesive compounds through a mixer as a final stage of cleaning. Further, the first batch of compound is typically sacrificed or saved for experimental work following clean-out. 

Compared with E-SBR, the curing rate of S-SBR grades is faster by about 10-20%. Generally, the processing of S-SBR compounds is the same as for E-SBR. The difference is that the molecular chain of S-SBR cannot be broken in the internal mixer with high power therefore, all the components can be added into the mixer simultaneously without precalendering. 

In general, the masticated NR and EPDM were mixed together with other ingredients including compatibilizers and homogenizing agents in an internal mixer or open mills. The rubber compound is cured in an electrically heated press at 160 °C for optimum cure time, which is determined by rheometer. In order to study the... 

Mixing The general methods for incorporating compounding ingredients into dry natural rubber involve the use of either a two roll mill or an internal mixer (e.g. Banbury mixer). Both in the open mill and in the internal mixer, a definite time, temperature, and order of addition of ingredients should be followed for each batch. [59]... 

Polymers are first broken down in an internal mixer where, in addition to the polymer, a peptizer may also be added. This stage is essentially a polymer molecular weight reduction phase. After initial breakdown of the polymer, carbon black, rubber chemicals, and oils can be added to the polymer at intervals to complete the compound formulation. Polymer breakdown and mixing generally occur at a high temperature, up to 180°C. 

There are three basic procedures for mixing rubber compounds in an internal mixer namely, the conventional method, the rapid oil addition method, and the upside-down mix method. Many variations of these three methods are also used to suit the special characteristics of individual formulations and equipment. It is, in general, necessary to add particulate fillers early in the mixing cycle, so that good dispersion is achieved as a result of the high shear stress and high viscosity at the lower temperatures then prevailing. Similarly, the oils and plasticizers which reduce viscosity should be added later. Upside-down procedures and variants of it are attempts to implement these ideas in practice. 

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