Farrel Continuous® Mixer

The throughput rate of intermeshing twin-screw extruders (Fig. 18-56) and the Farrel continuous mixer (Fig. 18-51) is scaled up with diameter to about the 2.6 power. 

Counter-rotating TSEs are applied in PVC compounding and processing. This concept has been used by Farrel for mbber mixing and they call this aggregate the Farrel Continuous Mixer. ... 

Other common continuous mixers involve substantial modification of single and twin screw extruders, aimed at improving distributive mixing capability in particular, and leading to the development of continuous mixers such as the Transfermix (50) and the Buss Ko-Kneader (51). Another approach in continuous mixer development is to transform batch mixers into continuous ones. Thus, the roll-mill can be converted into a continuous mixer by feeding raw material on one side and continuously stripping product on the other side. In addition, the Banbury mixer was imaginatively transformed into the Farrel Continuous Mixer (FCM) by Ahlefeld et al. (52), and, later, two similar continuous mixers were developed by Okada et al. (53) at Japan Steel Works and by Inoue et al. (54) at Kobe Steel. 

The continuous mixer (CM) is a counterrotating, nonintermeshing twin-rotor machine. The Farrel Continuous Mixer (FCM) was the first CM developed (1964) by Ahlefeld et al. (8). It has rotor designs along the principles of the Banbury3 high-intensity batch mixer. 

Fig. 10.6 The single-stage FCM. (a) Size 15 FCM with chamber opened and rotated hydraulically (b) top view of staged apex twin rotors and the axial zones for carrying out the solids feed handling and the melting and mixing elementary steps (c) cross-sectional view of two rotor orientations, tip-to-tip (cx) and tip-to-flat (c2). [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Farrel Continuous Mixer Systems for Plastics Compounding, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

Fig. 10.47 The effect of the Power Law index in the Carreau model, and the melt-pool size for a characteristic model wedge with e/h — 3 and ot= 15° on the non-Newtonian qp/qd parameters. [Reprinted hy permission from L. N. Valsamis and E. L. Canedo, Mixing in the Farrel Continuous Mixer in Mixing and Compounding of Polymers, I. Manas-Zloczower and Z. Tadmor, Eds., Hanser, Munich, 1994.]...

As the result of the departure from geometric similarity, the throughput rate of single-screw extruders scales up with the diameter to 2.0 to 2.5 power, instead of the diameter cubed, at constant length-to-diameter and screw speed. The throughput rates of twin-screw extruders (Fig. 18-57) and the Farrel continuous mixer (Fig. 18-58) are scaled up with the diameter to about the 2.6 power. 

Although commercial twin-screw extruders can be as large as 300 mm size, capable of compounding up to 40 ton/hr, the acmal type and size of the equipment used depends on the type of the polymer blend and the production volume. Normally, for engineering polymer blends, twin-screw extmders of about D = 90 mm size (L/D = 30 to 40) and capable of compounding at 700 to 1000 kg/hr, are used. For blending PVC or elastomer blends other types of compounding equipment are used, e.g. Farrell continuous mixer (FCM), Buss co-kneader, or a batch mixer, such as Banbury. 

Another class of mixers for producing fluxed formulations are continuous mixers, examples of which are the Farrell Continuous Mixer (FCM) (121 the Buss Kneader (131), or compounding extruders such as the Kombiplast(132). 

Continuous mixers can also be preceded by low intensity ribbon blenders but if the materials are not sufficiently dispersed in the blender, the final tluxing in the Farrell Continuous Mixer should be designed to overcome this. 

Figure 9.33 Farrell continuous mixer with 15 type rotor ...

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