Maddock-Style Mixers

Numerous mixing sections are available commercially from many manufacturers. Only the most commonly used mixers will be discussed in this section. 

---

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.)...

Figure 10.29 Photograph of screw in a vertical milling machine a) the mill is cutting the flow channel for a Maddock-style mixer, and b) the keyway is being cut into the shank of the screw (courtesy of Jeffrey A. Kuhman of Glycon Corporation)...

Maddock-style mixer 2 1.5 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. 

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. 

---