Screw mixing Maddock

Union Carbide mixing screw See screw mixing, Maddock. 

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

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

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)... 

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. 

A Maddock solidification experiment was performed using ABS resin at a screw speed of 60 rpm [30]. Like the solidification experiment for the ET screw of Section 14.2.2, the feedstock resin contained 2% Ti02 compounded into the pellets, and a black-colored masterbatch was added at a letdown ratio of about 220 1. The cross-sectional views of the resin solidified in the channels are shown by Eig. 14.15. The white pellets and unmixed resin are visible in the views as white regions. The regions that are well mixed are an evenly colored dark or black color. 

Fig. 9.43 The Union Carbide Maddock Fluted Mixing Screw Section.

B. H. Maddock, A Visual Analysis of Flow and Mixing in Extruder Screws, Tech. Papers, Vol. V, 15th Annu. Tech. Conf., Society of Plastics Engineers, New York, January 1959 also, B. H. Maddock, A Visual Analysis of Flow and Mixing in Extruder Screws, SPE J., 15, 383-389 (1959). 

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