Single-Flighted Extruder Screws

It is normal practice to have screws double flighted under the feed section. This is mainly because a single flight, working in conjunction with the feed roll, does not effectively pull in the feed strip in a consistent manner. In some extruder constructions the double flight continues down the length of... 

All single-screw extruders have several common characteristics, as shown in Figs. 1.1 and 1.2. The main sections of the extruder include the barrel, a screw that fits inside the barrel, a motor-drive system for rotating the screw, and a control system for the barrel heaters and motor speed. Many innovations on the construction of these components have been developed by machine suppliers over the years. A hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or metered (starve-fed) through the hopper to the screw flights. The resin can be in either a solid particle form or molten. If the resin feedstock is in the solid form, typically pellets (or powders), the extruder screw must first convey the pellets away from the feed opening, melt the resin, and then pump and pressurize it for a down-... 

Figure 12.3 Measured pressure profiles with rotation for a 63.5 mm diameter extruder running an ABS resin at 30 rpm, a conventional single-flighted screw, and with a positive downstream pressure gradient in the metering section [dP /dz >0)...

Devolatilizing Screw Extruder A 150-mm-diameter, square-pitched, single-flighted screw extruder, with screw channel depth of 25 mm and 20-mm flight width is used to devolatilize a 1000-kg/h stream with 0.78-g/cm3 density at 200° C and 125 torr. (a) At what frequency of screw rotation will the channel be 30% or less full (b) With water injection, if density is halved by formation of 1-mm bubbles, how much surface area (per meter length) is created (c) How does... 

This simple model is schematically represented for single flighted screws in Fig. 10.28. The model is based on the overall balances for enthalpy, mass, and concentration that can be derived for each individual chamber moving through the extruder. Assuming constant density, the preceding equation reduces to... 

Technical requirements may sometimes mean switching between elements with different numbers of threads along an extruder. This always requires transfer elements, spacers in the simplest case, otherwise a slight axial movement of the screw shafts towards one another will cause them to collide. Figure 5.11 shows this for the transition between triple- and single-flighted screw elements. 

Erdmenger s patent for single-flighted and double-flighted self-cleaning kneading discs is considered to be the basic patent of the twin screw extruder. The patent describes the eccentric disc as well as the traditional profiles. 

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