Barrel zones

Figure 2. Sketch of cylindrical extruder barrel zone used in mathematical model.

Figure 5.15 Outside barrel zone temperature measurements for a solids oonveying experiment using HIPS resin and a sorew speed of 50 rpm and a disoharge pressure of 1 MPa...

Figure 10.20 Zone 3 screw temperature response to changes in screw speed. The barrel zones were 200, 220, and 240 °C for Zones 1,2, and 3, respectively...

The modified screw was placed back into the injection-molding press and evaluated for performance. The barrel temperatures were maintained at 245, 255, 260, and 260 °C for the feed zone through the last barrel zone, respectively. This temperature setting was lower than that used for the original screw. The screw was rotated at a speed of 235 rpm, and the back pressure was set so that the pressure at the tip was 10 MPa. The 0.244 kg part and runner system was plasticated in 4.2 s for a specific rate of 0.89 kg/(h-rpm). All parts produced were completely free of the splay defect. The modifications were able to eliminate the bubbles and the unmelted material. 

In order to reduce the cooling level to the barrel zone, a metering valve was placed in the water line upstream of the solenoid valve as shown in Fig. 12.8(b). Now when the controller opens the solenoid valve, a much lower quantity of water and thus cooling is available to the barrel zone. Prior to this modification, the barrel temperatures oscillated 10 °C about the set point temperature. After the modification, the temperature oscillations were reduced to about 3 °C, and the profitability of the process was improved due to the minimization of resin consumption. 

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Figure 12.14 Screw speed, extrudate temperature, and barrel zone temperatures for a large-diameter extruder running stably and unstably...

Figure 12.22 Barrel zone temperatures for stable ABS resin extrusion...

A portable electronic data acquisition system was transported to the plant site and connected to the extruder panel. All available instrument outputs from the panel were connected in parallel with the acquisition system. Data collected included barrel zone temperatures, screw speed, motor current, pressure at the entry to the pump, transfer line temperature, and gear pump temperature. Process data were collected at a frequency of once every five seconds. 

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