Buss Ko-Kneaders

Extrusion compounders such as the Buss Ko-Kneader have been used for mixing phenolic resins. It is elaimed that they produce in some respects a better produet and are more eeonomical to use than mill-mixers. 

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. 

Depending on the nature of the filler distribution within the matrix, the morphology of the nanoeomposites can evolve from the so-called intercalated structure where a regular alternation of the layered silicates and polymer monolayers is observed, to the exfoliated (delaminated) structure where the layered silicates are randomly and homogeneously distributed within the polymer matrix. The easiest and technically most attractive way to produce these types of materials is to knead the polymer in the molten state with a modified layered silicate, such as montmorillonite. Compounding on different machines, such as a Buss ko-kneader or mills, still produces essentially the same morphology in the resulting nanoeomposites. 

The performance of two compounds was compared one made from 65 wt% ATH and 35 wt% EVA with 28% vinyl acetate content and a second from 60 wt% ATH, 5 wt% organoclays, and 35 wt% EVA with 28% vinyl acetate content. Both compounds were prepared on a BUSS Ko-kneader (46-mm screw diameter, L/D 11). Both were investigated... 

Whilst most early work was carried out in solution French workers have developed solid state methods where the anhydride is added to the rubber either on a 2-roll mill or, as later developed, in an extrusion compounder such as a Buss Ko-kneader. A typical reaction in such a device took 8-15 minutes at 200-250°C. 

Typical examples of the single screw kneader are the Buss Ko-kneader and the Baker-Perkins Ko-kneader. 

FIGURE 7.11 Heat release rates for cable compound 2A with the filler blends of MWC-NTs and organoclays by twin-roll miU and Buss Ko-kneader. Heat flux = 35 kW/m. (From Ref. 62, copyright 2005, John Wiley Sons, Ltd., with permission.)... 

Plastication by kneading is done in variable shear roll mixers, in rotor mixers of the Banbury or Wemer-Pfleiderer type, or in twin-screw extruders or in special mixers. Plastication made in two-roll mixers is not economical and it is used mainly for batch production or to mix substances of different natures. For continuous line production, single or twin-screw extruders or a Buss KO-Kneader are used. These mixers or extruders operate in a friction mode this friction is obtained by a horizontal backward and forward motion of the screw. The screw may have threads or flights of regular width or of lai ger width and slantly cut in the rotational direction (see Fig. 14.10). Homogenization in these machines is so efficient that even fish-eyes present in PE and suspension polymerized PVC can be disaggregated [8]. 

Figure 7.5 Reciprocating single screw extruder (Buss, Ko-kneader)...

There are several methods of densification. In one method, the heated powder is formed into strips by passing through the nip of a two-roll mill. The strips are then powdered into tiny flat flakes in a hammer mill. Other processes involve agglomeration of the powder by heating in an internal mixer at about 100°C or by treatment with water or steam and subsequent drying. Continuous compounders, such as the Buss Ko-Kneader, are also used. 

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