Mixers to Break Up the Solid Bed

The CRD mixer described above is normally designed to break up agglomerates into much smaller aggregates or even individual particles the final size is typically at the micron or submicron level. However, the same principle can be applied to break up large clusters of unmelted polymer particles into smaller clusters or individual particles (usually pellets) at the millimeter level. A number of variations of the CRD mixer have been developed with the specific objective to break up clusters of unmelted particles-these mixers are called the Cluster Buster or CB mixer [89]. An example of the CB mixer is shown in Fig. 8.94. 

Other mixing screws have been developed in the past to disrupt the solid bed and mix unmelted with melted material. The double wave screw shown in Fig. 8.80 breaks up the solid bed and mixes the material by forcing a cross-channel flow by the cyclic variation in channel depth. The principle of the double wave screw was used by Barr in his energy transfer (ET) screw [90]. The ET section is basically a double wave section with occasional undercuts in both flights to force a cross-channel mixing between the two channels. Modeling of the ET mixer is discussed in Section 12.4.3.2 see also Figs. 12.23 to 12.25. 

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