Mixing, Maddock

Union Carbide mixing screw See screw mixing, Maddock. 

FIG. 18-48 Mixing enhancers for single-screw extruders a) Maddock (straight), (h) Maddock (tapered), (c) pineapple, (d) gear, (e) pin,... 

The melting process is the primary mode for mixing in single-screw machines. This concept can be observed from Maddock solidification experiments. Melting as a method for mixing is presented in Section 8.4. 

Figure 8.21 Schematic for Maddock-style mixers a) a mixer with the flutes aligned in the axial direction, and b) a cross-sectional view perpendicular to the screw axis showing the clearance for the mixing flight (courtesy of Jeff A. Myers of Robert Barr, Inc.)...

Maddock, B.H., An Improved Mixing-Screw Design, SPEL, 23, 23 (1967)... 

Maddock-styie mixer 25.2 2 0.51 mm undercut on the mixing flight... 

Although the full history of this screw is unknown, the mixing pins appeared to have been added to the screw after the screw failed to mix and homogenize the extrudate. Pin mixers have been retrofitted to screws for many years as a way to improve the distributive mixing for an extruder. Here the pin mixers would distribute the solid polymer fragments evenly in the extrudate, hut the mixers lacked the ability to trap and disperse them. Pin mixers were clearly the wrong type of mixer to use for this application. Instead, a dispersive mixer such as a Maddock-style mixer would be preferred see Section 8.5.1. 

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