Screw cooling

Figure 10.8 Schematic of screw cooling at a viscoseal for a tandem foam sheet line...

Lead length, flight width, and flight clearance were 203.2, 23.9, and 0.20 mm, respectively, in all sections of the screw. A 28.7 mm diameter screw cooling hole was drilled in the shank end of the screw, and it extended 3.8 diameters into the feed section. The first 2.5 diameters of the screw were inside a water-cooied feed casing. The specific rotationai rate of the first-stage metering section was caicuiated at 20 kg/(h-rpm). 

Figure 12.16 Screw speed, pressure at the entry to the first-stage meter (PI), and discharge pressure for the screw cooling experiment...

Figure 12.31 Operation of the extruder at a constant rate of 1720 kg/h with and without screw cooling for a PC resin...

Lead length, flight width, and flight clearance were 203.2, 20, and 0.20 mm, respectively, in all sections of the screw. A 38 mm diameter screw cooling hole was drilled in the shank end of the ... 

The feed zone has the most effects on solid conveying of the resin. Three coefficients of friction take place, namely friction between barrel and pellet, between pellet and pellet, and between root of the screw and pellet. Solid conveying is the process wherein the material must stick to the barrel and slip on the screw. Hence, cooling root of screw will reduce the coefficient of friction between the screw and the plastic pellets. Screw cooling should be installed in the core of the screw in the feed section to give another zone of temperature control on the extruder. 

In some cases, screw cooling is used to improve the pressure-generating capability of the screw. The screw is cooled all the way into the metering section. The colder screw surface freezes the polymer close to the screw or, at least, significantly increases the viscosity of the polymer melt close to the screw surface. This reduces the effective channel depth of the extruder screw and can result in improved pressure-generating capacity if the screw was cut too deep to begin with. Therefore, if... 

The viscous dissipation is a specific power consumption, i.e., power per unit volume. In S.I. units it is expressed in Watts per cubic meter [W/m ]. The heat fiux away from the polymer melt is determined by the heat fiux from the melt to the barrel and screw. If the screw is neutral the heat fiux to the screw is usually small and can be assumed to be negligible. If screw cooling is used, this assumption will not be correct. The heat fiux (heat flow per unit cross-sectional area) for cooling the polymer melt is determined by Fourier s law of conductive heat transport ... 

Variable bottle weight Finer extruder screen pack Increase screw cooling Raise rear extruder heats Decrease extruder rate... 

Figure 9.18 shows a fragment of a multi-cavity mould for a feeder made of PR The long nozzle (1) is located in a bushing (2) with a double screw cooling channel leading right up... 

Screw cooling. Generally the centres of extruder screws are hollow. This allows cooling fluid to be passed along the screw in order to cool the screw at various points. The commonest areas to cool are ... 

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