Internal Mixers Intermeshing

Various new designs of intermeshing rotor internal mixers have been proposed since the 1970s [33, 67 to 69]. In a 1987 patent application, Passoni [69] describes a design wherein the nip distance between the rotors may be varied. This allows the intensity of inter-rotor shearing to be varied during the mixer cycle for any particular compound and the shear intensity to be varied for different compoimd formulations. This machine is manufactured by Techint Pomini. 

It became clear in succeeding years that the intermeshing internal mixer rotors did a better job of controlling the rubber temperature than F. H. Banbury s designs because of their higher metal surface areas. One was less likely to chemically damage expensive specialty elastomers with high temperature. 

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. 

Today in Europe and Japan, intermeshing internal mixers have a dominant position in mixing rubber products for automotive under the hood applications from expensive elastomers (e.g., HNBR). The separated rotor mixers are dominant in the tire industry where larger volumes of compounds are mixed. 

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AEM compounds can be mixed in internal mixers, intermeshing and tangential, or on a mill, with relatively short mix cycles. The guiding principle when mixing AEM compounds is to keep the polymer temperature as low as possible initially to increase mixing times. 

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

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

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). 

Variable Intermeshing Clearance (VIC) Rotor Internal Mixer... 

Internal mixers are made in two types tangential and intermeshing. Banbury mixers are the most popular and they are tangential mixers. ... 

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. 

Internal mixers with a much different mixing chamber design were proposed by Cooke [C17] of Francis Shaw and Company and by Lasch and Stromer [L3] of Werner and Pfleiderer. These internal mixers possess intermeshing counterrotating rotors (Fig. 1.9). In these internal mixers, both rotors must move at the same angular velocity. The Francis Shaw mixer, the Intermix, was marketed first and received considerable attention. In time, the intermeshing mixers dominated the mechanical rubber goods industries in Europe and Japan. 

FIGURE 19 Intermeshing internal mixer design of Cooke. (From Coleman and Noll [C16].)... 

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

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... 

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].

Figure 1.9 Passoni s [55] variable clearance intermeshing internal mixer.

Differences in Behavior Between Internal Mixers with Tangential Rotors and Intermeshing Rotors, as Influenced by the Molecular Structure of EPDM... 

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