Cooling single screw

E. Steward W. A. Kramer, Air V5-. Water Cooled Single Screw Extruders, SPE-ANTEC 2003... 

The experiments were conducted on a 2.5 24 L/D Davis-Standard (D-S) water-cooled single-screw extruder. The extruder was instrumented with pressure transducers along the barrel. It contained a 1/2 test head with a valved adapter at the die plate. Both a conventional metering screw of 24 L/D and a barrier screw of 30 L/D were tested. For the 30 L/D barrier screw trials, a 6 L/D barrel extension was added to the end of the barrel. The metering screw had an overall compression ratio of 3.64, while the barrier screw had a compression ratio of 2.53. A rod die was used of 0.5 diameter and 8 length with a... 

Figure 1.2 Schematic of a typical plasticating single-screw extruder. The extruder is equipped with four barrel heating and cooling zones and a combination belt sheave gearbox speed reduction drivetrain (courtesy of William Kramer of American Kuhne)...

Complex profiles require specialty manufacturing skills to build, maintain, and operate extrusion dies as well as cooling and sizing equipment to deliver the exact dimensions required. Cubed compound, where the PVC grains are already broken down, can be run faster on simple single-screw extruders on account of the typical low melt temperatures. 

A special complication is formed by thermal inhomogeneities. The polymer follows a circular path in the cross-channel direction, which implies that only a certain amount of polymer passes the thermal boundary layer where it is cooled directly. Therefore, for deep cut channels the heat of reaction in the middle of the channel is difficult to remove. Janeschitz Kriegl [18] compared the thickness of the thermal boundary layer with the channel depth, and identified a criterion for thermal homogeneity in a single-screw extruder. This can be adapted to twin-screw extruders with m thread starts per screw. It may be concluded that thermal inhomogeneities become important if ... 

Polyimide sulfone resins were melt processed using a single screw extruder with an 80p filter, extruded into strands, cooled, and then cut into pellets. Pellets were injection molded into parts at 370°C to 390°C. The resins in the molded parts showed less than a 30% thermal deterioration in molecular weight. 

Polystyrene foam sheet can be made by a variety of extrusion processes (single screw, twin screw) but is most commonly made using a tandem extrusion process as shown in Figure 11.6. This process uses two extruders in series, which effectively optimize the melting, mixing, and cooling unit operations. The diameters of the extruders currently used in this process are usually 115 mm for the primary extruder and 150 mm for the secondary extruder, with an output capability of 400 kg/h. 

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