Double wave mixing screw

Mixing screws — S-shaped kneader, Eagle mixing. Turbine mixing, Cohen double-wave, or Maillefer screws with pin-, blister ring-, fluted-, barrier-screw. Dynamic Extentional Flow Mixer (DEEM), etc. 

Some of the more widely used high-performance screws include the Energy Transfer (ET) screw [19], the Variable Barrier Energy Transfer (VBET) screw [20], the Double Wave screw [21], Stratablend [22] and Stratablend II [23] screws, and the Unimix [24] screw. Other devices can, however, act as a trap for solid materials from the melting section. These devices include Maddock-style mixers [25], spiral dams, and blisters. They will be briefly discussed in this section as many of them have been the subject of many articles on secondary mixing processes. 

The double wave screw (Fig. 5.17 ) provides both distributive and dispersive mixing. This screw has a second flight in the metering zone. The depth of both channels alternately increases and decreases. When the channel depth is shallow, melt is sheared and can be transferred into the adjacent channel. 

Dispersive mixing also occurs in the double wave mixing screw see Fig. 8.81. 

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. 

In variable depth mixers, the channel depth of the mixer is varied to obtain improved mixing. An example of a variable depth mixer is the double wave screw shown in Fig. 8.81 and the energy transfer screw see Fig. 12.23. Another example is the Pulsar mixing section shown in Fig. 8.103. 

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