Intermeshing Rotor Mixers

In the 1930s, there was a major innovation in the rubber industry with the invention of intermeshing rotor internal mixers. A June 1934 British patent 

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Fig. 8 Motor power versus mixing time, intermeshing rotor mixer.

B. Difference Between the Tangential and Intermeshing Rotor Mixers... 

As a function of specific mixing energy, about three times the amount is needed to reach the same amount of carbon black dispersion in the intermeshing rotor mixer, irrespective of the type of EPDM. 

The shift of the carbon black dispersion to a lower-temperature regime, going from tangential to intermeshing rotor mixers, can be explained in terms of Tokita regimes in relation to the differences in clearances between rotors and mixer walls for both type mixers. 

In more recent years. Parrel Inc. has purchased Francis Shaw and Company. Intermeshing rotor mixers are also marketed by Techint Pomini and Krupp Gummitechnik, the successor company to Werner and Pfleiderer in producing internal mixers. Intermeshing rotor internal mixers are also made in Japan by Hitachi and Mitsubishi Heavy Industries. 

The Intermix (Figure 12), developed during the early 1930s, appears to have been the first commercially successful intermeshing rotor mixer. It was designed and constructed at Francis Shaw and Company of Manchester to the basic design of an unknown engineer of the ITS Rubber Company. 

As may be expected, the mixing behaviour of tangential and intermeshing rotor mixers is very different. An attempt is made below to describe the mixing actions of the different concepts of machine in layman s terms, there being many learned texts published by various educational institutions which may be read by those wishing to explore this interesting subject further. 

Table 2. Observations on mixing behaviour in tangential and intermeshing rotor mixers ...

The number of temperature control zones is usually recommended by the mixer manufacturer, with three being quite common, one each for rotors, mixing chamber sides and drop door. Where the door top is profiled to the mixer shape, as is often seen in intermeshing rotor mixers, two zones are commonly adequate, one for the mixing chamber sides and ram, if this is temperature controlled, and one for the rotors and drop door. 

A comparative study was made of the effidency of two intermeshing rotor mixers, one with fixed clearance and the other a VIC 165 variable intermeshing clearance mixer (Techint-Pomini), in the mixing of NR, EPDM and polyepichlorohydrin compounds. The results showed that the variable clearance mixer gave reduced cycle times with equal quality of the compounds produced, and that higher fill factors were possible with this mixer. The cost advantages of the VIC 165 were also analysed. 

Figure 8 Internal mixer rotor designs (a) tangential rotor, (b) intermeshing rotor.

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. 

Basically two rotor types are applied in the internal mixer The tangential rotor type and the intermeshing rotor type. The latter one interferes with the adjacent rotor and turns at the same rotor speed compulsory. In the drop door or through the side plates a thermocouple is mounted to record the temperature of the mbber. 

FI CU RE 35.12 Typical fingerprint of a masterbatch mixing process on an intermeshing internal mixer (GK 320E (Harburg Freudenberger) with PES5 rotors styrene-butadiene rubber/carbon black [SBR/CB] tread compound). 

The variable intermeshing clearance rotor mixer is designed to allow a variable clearance between the intermeshing rotors of the mixer. 

In the case of the intermeshing rotor machine the majority of the mixing action takes place between the rotors with the shearing action being created by the rotor design. Unlike the tangential mixers where the rotors revolve at different speeds, the rotors in intermeshing machines run at the same speed. 

Figure 1-5 Intermeshing Rotors from Internal Mixer...

The factory system based on internal mixers, screw extruders, calenders, and vulcanization presses has remained basically unchanged in the past half-century. Internal mixers have had major improvements, e.g., intermeshing rotors proposed by Francis Shaw and Company [C16] and Werner and Pfleiderer [L3], and variable intermeshing clearance rotors [PI] proposed by Pomini-Farrel SpA. Sophisticated computer control systems have been introduced. The early single hot-feed extruders have been replaced by cold-feed extruders with increasingly sophisticated design including pin barrel extruders [G7, H12, H13, M18, W16] as well as complex control systems. 

FIGURE 4.30 Schematic of internal mixers with tangential or intermeshing rotors. 

Figure 1.6 Cook s June 14 1934 British patent application drawing for an internal mixer with intermeshing rotor. From Reference [43].

There have also been new designs of internal mixer rotors, notably by MiDauer [53] of Werner Pfleiderer (Figure 1.8a) and Johnson et td. [54] of Francis Shaw (Figure 1.8b). Passoni [55] of Pomini has described a completely new design of intermeshing rotor internal mixer in which the rotor inter-axial distances may be... 

Figure 1.8 Post-Cooke intermeshing internal mixer rotors (a) Millauer[53] (b) Johnson etal. [54].

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