Tangential mixers

FIGURE 29.14 Influence of cooling temperature on silanization efficiency in a tangential mixer (mixer volume 3.6 L, open mixer, fill factor 0.6, silanization temperature 145°C, time 150 s). 

It is well known that the cycle time of the mixing process in an industrial-sized internal mixer is limited by the increase of the compound temperamre. For example, typical mixing times on a 400 L tangential mixer with four wing rotors is of the order 200 s as can be derived from Figure 35.2. Especially during the last mixing phase the temperature increase of the compound is approximately l°C/s. 

Pomini reported that their VIC technology combines the fair raw material intake behavior of the tangential mixer with the excellent dispersion and cooling behavior of an intermeshing 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. 

The British equivalent is BS 903-A643 which is identical except for a national foreword and appendix. The foreword points out some of the differences from the previous British standard, which are the inclusion of a second tangential mixer, a miniature mixer and a mould for ring test pieces... 

Over the years various types of mixers have been designed. The most ffeqnently used today are the T-mixers (stopped-flow), four (or more)-jet tangential mixers (ffeeze-qnench), the Berger-ball mixer (stopped-flow) and the coaxial... 

Figure 2 Drawings of commonly used mixers in continuous-flow and stopped-flow devices. Mixing in the four-jet tangential mixers occurs in the orifice of the Pt inlay (MHQ) or in a Teflon gasket (RFQ). Ri and R2 denote reactant 1 and reactant 2, respectively...

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

Fig.1 Rotor geometries of the tangential mixer Werner Pfleiderer GK-2 and the intermeshing mixer Francis Shaw K1 Mark 4 Intermix.

However, the fact that the traces of carbon black dispersion versus temperature are the same in both mixers irrespective of the upswing of carbon black dispersion for polymer E in the intermeshing mixer at 30°C lower than in the tangential mixer must then be explained on the basis of geometrical considerations of the mixers. To compare the fundamentally different geometries of the two mixers is difficult for the two mixers, the following clearances were measured ... 

Use of even-speed therefore tends to be somewhat polarised, with some (but not all) tyre companies favouring even-speed mixing, and some (but again not all) general rubber goods companies favouring conventional friction-ratio tangential mixers. 

Figures 18 and 19 show the basic principle on which tangential mixers work.

Tangential mixer - volumetric effects of fat and thin rotors... 

Layout of tangential mixer operated using two hydraulic drives... 

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