Cooling twin-screw

Extrusion. In general, extmsion is the process of forcing a polymer melt through a die (104,105). Typical extmsion appHcations include initial resin pelletization after manufacture and production of film, sheet, pipe, tubing, and insulated wire. The HDPE extmsion temperature is around 150°C, the pressure 40—50 MPa (5800—7250 psi). An extmsion production line usually consists of an extmder (mono- or twin-screw) with a die at the end, a cooling and shaping device, a pulling device (a roUer), and a cutter. 

As with pipe, siding manufacturing is highly optimized for efficient production at high rates and minimal costs. Siding uses powder compounds, twin-screw extmders, and vacuum sizing/cooling. 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

The provision of a separate oil cooler will reduce condenser load by the amount of heat lost to the oil and removed in the oil cooler. This is of special note with twin-screw compressors, where a high proportion of the compressor energy is taken away in the oil. This proportion varies with the exact method of oil cooling, and figures should be obtained from the compressor manufacturer for a particular application. 

Example 3. Hydrolysis in an Extruder.69 PET reactive extrusion experiments were carried out on a 25-mm Berstorff ZE25 corotating twin-screw extruder with a barrel length-to-screw ratio of 28 1. The extruder consisted of six barrel sections equipped for heating, cooling, and controlling the temperature of each section of the extruder. Initially reaction extrusion of PET and water was performed with cold water at room temperature injected into the extruder. Typical operating conditions were reaction temperatures of 230-265° C, extruder speeds... 

Extruded Corn Meal with Thiamin Added. Degerminated yellow corn meal with 0.5% thiamin HC1 was extruded on a Werner Pfleiderer ZSK-30 co-rotating twin-screw extruder. The five heating zones of the barrel were held at 50°C, 76°C, 100°C, 134°C and 172°C, respectively. The product temperature was 180°C, the torque was 46% at 200 RPM and the pressure was 130-172 psi. The extrudate was allowed to cool to room temperature, then stored in glass vessels under nitrogen at 4°C. 

The third type of compounding device is the extruder. Next to its use for fabrication (which will be dealt with in 11.4.2), it is applied as a mixer. In essence, it is a screw pump, in which the mass to be mixed is transported in a heated cylinder by a screw, or, with twin-screw extruders, by two parallel screws. During this transport melting and intensive mixing take place. At the end of the screw the blend is pressed through a number of openings and cooled down in most cases the strands thus obtained are on-line cut into granules. 

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 ... 

Tang et al. (52) fabricated CNT-HDPE composite film by the following technique the first step was the preparation of a precursor material in the form of CNT-HDPE composite pellets. The pellets of neat HDPE and CNTs were combined in a beaker and heated in an oven at 200 °C for 10 min. Then the mixture was mechanically stirred to mix the CNTs into the melt and to form a viscous suspension. The dough-like suspension was then compressed and cooled to form a solid plate. The plate was then chopped into smaller pieces, which were fed into a twin-screw extruder. In the extruder, the temperature was maintained... 

A twin screw feeder unit is used to dose dry blend into the compounder. A discharge screw feeds the melt into a pelletiser unit, which is a multi-hole die plate through which the melt is forced into strands, cut by rotating knives and cooled. Details are available of a range of extruders developed for PVC compounds (34). 

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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