Kneading zone

These benefits resulted in the USP [21] with priority 1959 for R. Erdmenger. The modular design is illustrated in Fig. 2.14 below with a combination of different consecutive screw and kneading zones and in Fig. 2.15 as a modular assembly diagram. 

The previous chapters have shown how screw machines are comprised of successive zones that perform specific process tasks. The most common process task is a combination of transporting materials and generating pressure. At the head of the machine, higher pressure needs to be applied, in particular, where typically an extrusion die or a nozzle plate is attached however, most mixing and kneading zones are also pressure consumers that require pressurization of the melt. 

The nozzle (5) and the back-feeding kneading block (3) are obstacles to flow that generate a drop in pressure. The screw sections upstream of this must build up the pressure needed to overrun the obstacle. The back-feeding kneading block (3) ensures that at least a part of the kneading zone is wholly filled, which promotes the mixing effect. 

Figure 2.20 shows an example of the pressure profile in a screw, consisting of transport elements, followed by pressure buildup elements, a kneading zone, transport elements, and finally pressure buildup elements before the die. At location A the material is pressureless and the channel is not necessarily fully filled. This location can be used, for instance, for devolatilization or for an easy feeding of an extra component. However, it should be realized that at increasing throughput the filling of the extruder increases and the pressureless zone will disappear. 

First, Figs. 7.24 and 7.25 illustrate the experimental results when monitoring the morphology development in the case of a maleated polypropylene (mPP)-polyamide (PA) binary reactive blending system (where A-1 1st kneading zone, A-2 intermediate, A-3 2nd kneading zone, A-4 die exit). 

As mentioned already, the powdered rubber initially has a certain particle size distribution. This distribution changes as the particles break. The probability of the breaking of a particle is influenced by the transport and exchange of material to and from the kneading zone, the cut-back zone, and the milling zone. 

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