Conveying capability

The drag flow or volumetric conveying capability, for the plastic melt is dependent only on screw speed, IV, and the geometry, 4, of the screw ... 

The solids conveying capability of the extruder is also determined by its geometrical design. For this, there are some basic rules supported by experimental and operating experience ... 

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 multi-element kneading blocks are assembled of discs of different thickness (to adjust the ratio of dispersive to distributive mixing) and displacement angle (see Table 9.10). Blocks constmcted from the same number of elements, but of different thickness also behave differently. Wide discs provide mach greater sharing action than the narrow ones, i.e., the former provides dispersive mixing while the latter the distributive one. As the disc thickness in the block decreases its conveying capability increases. 

The properties of the conveyed material have a major influence on the conveying capability of a pneumatic conveying system. It is the properties of the material that dictate whether the material can be conveyed in dense phase in a conventional conveying system, and the minimum value of conveying air velocity required. For this reason the conveying characteristics of several different materials are presented in order to illustrate the importance and significance of material properties. 

PIAB (2006) outlines procedures for the selection of both standard and customised conveyors on its website. These procedures based on recommended values and should only be used as a guide for system specification. It is recommended that the material to be conveyed is tested by the supplier or independently for its pneumatic conveying capability before committing to a conveyor system specification. 

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