Maddock mixing element

As an extension to the above study, several types of dispersive and distributive mixing elements (26) were evaluated using a single-screw extruder (27) compared with the Maddock mixing element used in the previous study. Elements evaluated included dispersive elements such as straight and tapered Maddock, pineapple and Twente mixers, and distributive elements such as pin and gear... 

Maddock mixing element, is not easily be modeled by 3D FEM mesh. 

In order to demonstrate the hybrid FEM/FDM approach can be easily extended toward the polymer flow in a eomplex serew surfaee without any model modification. Finite element mesh for the barrier screw with a Maddock mixing element is shown in Fig. 7. The polymer is PET. The numerieal pressure profile predicted by hybrid FEM/FDM is shown in Fig. 8. The maximum pressure profile occurs between the end of the compression zone and the start of the metering zone. The numerical solid bed profile SBP predieted by hybrid FEM/FDM is shown in Fig. 

The calculated velocity and pathline in the barrier screw with a Maddock mixing element is shown in Fig. 10. More experimental melting and pumping data for a complex screw surface will be needed More experimental melting and pumping data in a complex screw surface are required to verify the the numerical results in the further. 

Fig. 7. Finite element mesh for the barrier screw with a Maddock mixing element.

Fig. 4.9 Extmsion screw mixing elements. Maddock mixer [55]. Saxton mixers [56]...

Figure 3.10 Maddock (Union Carbide) mixing element.

The barrier screw geometry is shown in Fig. 8.108. The Maddock screw has a fluted mixing element similar to the one shown in the bottom of Fig. 8.108. The CRD screw is a screw with a distributive mixing element that is based on elongational flow rather than shear flow [128-131]. 

Maddock and pin mixing elements can be used, but the more efficient interacting pegs or cavities cannot be used in the same manner as for extrusion described in Chapter 9. The rotor and stator would move completely out of register as the screw reciprocates. Although techniques have been devised, they required greater space than is normally available [1, 2]. 

Preliminary work showed that with the Maddock element screw, the melting/mixing efficiency and output rate of the extruder was very dependent on the temperature profile along the extruder barrel. 

Figure 7.7 Influence of screw temperature profiles on mixing with Maddock element at end of compression zone. Photomicrographs of screw tip channel section. (Reproduced with Permission from G.M. Gale, Masterbatch Flow Patterns in Polyethylene Extrusion, Rapra Members Report No.16, Rapra Technology, Shawbury, Shrewsbury, UK, 1978, Figure 8. 1978, Rapra Technology)...

Conventional screw Mixing screw with Maddock element Temperature (°C) Screw speed (rpm) Concentration of masterbatch (%) Output rate (g/min)... 

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