Barrel Temperature Optimization

To illustrate the barrel optimization process [22], an extrusion process was optimized first for rate and then for discharge temperature. Each of the experiments was conducted at a screw speed of 50 rpm. The initial extruder barrel tempera- 

---

Many standard diagnostic and troubleshooting techniques were tried, including temperature optimization for the feed section of the barrel and changes to the... 

In the injection molding process, setting the temperature involves optimization of the temperature profile of the plasticating unit (extruder barrel), temperatures of the mnners and gates, (aU these determine the molten polymer temperature) as well as the mold temperature. The temperature setpoints depend on the material type (viscosity profile, thermal and shear stability, thermal properties) as well as machine or process considerations (machine capacity to shot size ratio, screw design, mold and part design, cycle time, etc.). Temperatures of the two basic units, the injection system and the mold, should be discussed separately since their selection stems from very different considerations. 

Several injection molding operating parameters must be optimized in order to produce a microfluidic device with a high degree of feature fidelity. Figure 4 presents the impact of the feature fidelity of different micron-sized post features as a function of barrel temperature and injection velocity. It is also important to note that computational modeling can be employed to predict optimal injection molding conditions. 

Starch degradation may reduce radial expansion, which is critically related to product texture. Chinnaswamy (1993) has summarized many factors that affect expansion of starchy materials. Extmsion pressure is a better predictor of expansion than is die nozzle length/diameter ratio. Starches with 50% amylose showed optimal expansion, and barrel temperatures close to 150°C and low feed moistures favor expansion. Irradiation and certain additives were thought to improve expansion, but only sodium chloride proved to be useful. Over a range of amylose contents, 1% NaCl consistently produced more expansion than did the starch alone. 

Figure 5 shows the barrel temperature uniformity varied with position and inspection of Figures 4 and 5 shows it was proportional to the power level and proximity to the material feed. Comparison of the two induction curves in Figure 5 (produced with general purpose and Fusion screws) confirms that melt-stream uniformity may be further optimized by screw design. 

The stress at the interface was measured as a function of temperature and sliding velocity for the resin using the equipment shown in Fig. 4.11, and the data are shown in Fig. 12.33. The stress curve had two maximums the first peak was at the Tg of the resin at 150 °C, and the second peak occurred at a temperature of about 240 °C. In order to maximize solids conveying while maintaining a viable process, the optimal forwarding forces would occur at a barrel surface temperature near 240 °C, and the retarding forces at the screw surfaces would be minimized at temperatures less than about 120 °C. In order to maintain the high rate of this line and the inside barrel wall at a temperature near 240 °C, the first zone of the extruder needed to be maintained at a temperature of 310 °C. 

---