Extruders conveying elements

Geometry of the Co-Rotating Extruders Conveying, and Kneading Elements... 

Conveying elements take the product to be metered - pellets, powder, ground product, melt, etc. - into the extruder and transport it downstream to the first processing section where it may be compressed. Then, the product is transported through processing sections,... 

Conveying elements are supplied with different pitches and lengths. They almost always wipe the barrel with small clearances to prevent leakage flows over the tips. This means that only single- and double-flighted elements can be used in extruders with a D()/D, ratio of more than 1.36. 

Conveying elements with single or double-flighted self-wiping profiles and undercut profiles differ substantially regarding certain factors relevant to the extruder conveying capability, i.e., free volume and conveying efficiency (Fig. 12.13). 

The conveying efficiency of the screw element varies with the product characteristics and the extruder s operating conditions. A conveying element with a pitch that is too small will not actively convey but will act as a flow resistance. It has to be overrun by the conveying element located upstream. 

A schematic representation of the tracking of color particles is shown in Figure 22.10. The flow situation being described in this figure corresponds to the flow in fully filled conveying elements of a corotating intermeshing twin screw extruder. In essence, what happens in the depicted flow problem is that a polymeric flow takes place in... 

Table 7.1 Main characteristics of conveying elements and kneading blocks of twin-screw extruders ((a) and (b) should not be directly compared) [44].

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