Grooved feed section

Peiffer [52, 53] developed an empirical relationship between the geometry of the grooved feed section and rate as follows ... 

Schematic diagram of the grooved feed section of a single screw extruder.

The adjustable grooved feed extruder developed at Rauwendaal Extrusion Engineering [246] uses a grooved feed section in which the depth of the grooves can be continuously adjusted while the extruder is in operation. Parallel developments have taken place in Poland at the Technical University of Lublin [244, 245). Earlier concepts have been developed [247], however, due to the complexity of the adjustment mechanism, these have not been applied on a wide scale. 

Some bulk materials are very difficult to handle for instance, post consumer reclaim (PCR) usually has a wide particle size distribution and a low bulk density. As a result, special extruders have been developed to handle this bulk material efficiently. These machines can have larger diameters in the feed section than in the metering section they may also use crammer feeders to achieve steady flow of material into the extruder. In some cases, a grooved feed section is used to improve the feeding of low bulk density material. 

Pig. 34. Grooved feed section with adjustable groove depth. 

This chapter provides a description of the solids conveying process and the theoretical models in the literature. The literature models will be presented before the experimental solids conveying data because only recently has experimental data become available for this process section. That is, the early theoretical models were developed without actual solids conveying data. Data will be presented regarding the temperature and forces that are associated with solids conveying of different polymers. Next, a comparison of the models with the experimental data will be provided. Both smooth bore and grooved barrel feed sections will be presented. The field experiences of the authors, however, are dominated by smooth bore extruders. 

The Potente-Schoppner model provides evidence for why extruders over 150 mm in diameter are not designed with grooved barrel feed sections. In general, resin... 

Sikora, J.W., The Effect of the Feed Section Groove Taper Angle on the Performance of a Single-Screw Extruder, Polym. Eng. ScL, 41, 1636 (2001)... 

Within the feed section, as well as elsewhere in the extruder, friction between the plastic and the barrel is responsible for conveying the plastic forward. Without this friction, the plastic would simply rotate with the screw, staying in place rather than moving forward. Grooving of the feed section of the barrel is sometimes used... 

When the rubber is slippery, as in dewatering rubber extruders, the feed section of the barrel is grooved to prevent slipping along the barrel surface or the barrel I.D. may be fitted with pins. This significantly improves the conveying action of the extruder. The same technique has been applied to the thermoplastic extrusion, as discussed in Section 1.4 and Section 7.2.2.2. 

Extruders equipped with grooved barrel sections often have a specially designed feed throat section to accommodate this grooved section. A schematic feed throat section is shown in Fig. 3.12, where the effective length of the grooves may range from three to five diameters. 

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