Striations Their Formation and Mixing in the Screw Channel

1 Striations Their Formation and Mixing in the Screw Channel 

Striation formation is an essential part of the distributive mixing process. In Chapter 2 it was shown diagrammatically how an individual pellet was transformed into a striation in a simple laminar shear field - the mechanism available for mixing in single screw extruders. 

It was also explained that the orientation in the direction of shear resulted in the decreasing effectiveness of the flow field in reducing striation thickness. 

The overall mixing requirement is to reduce the striation thickness to a value which represents an overall acceptable product whether visually or with respect to its physical properties. Clearly this is not always achievable a wide range of striation problems were described in Chapter 1 and many examples have been described in published articles [1, 2]. 

Experiments carried out using a 38 mm extruder with a screw jacking facility verified that individual masterbatch pellets were transformed into individual finite striations during melting [3]. 

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