Plastics Technology

JUL 2017

Plastics Technology - Dedicated to improving Plastics Processing.

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barrel zones. When the tuning was corrected, the barrel-temper- ature variation reduced to normal levels and the pressure varia- tion reduced from ±10% to about ±0.7%. PROCESS OPTIMIZATION Data-acquisition systems are also very useful for process optimi- zation. For instance, barrel temperatures can be optimized to achieve the lowest pressure fluctuation. This can be done by changing the setpoint and following the transient response of the extruder. Figure 8 shows the transient response of changing the setpoint of barrel zone 1 from 100 C to 175 C (212 to 347 F). This figure shows the pres- sure vs. the actual tempera- ture of zone 1. This figure shows clearly that the pressure fluctua- tion reaches a minimum at a temperature of about 130-135 C (266-275 F). These results indicate that the optimum temperature of barrel zone 1 is around 130-135 C. Since the pressure versus temperature can be displayed in graphical form, determination of the optimum temperature is quite easy. These examples show that a DAS is very helpful in detecting process problems and in troubleshooting these problems. A DAS is also very helpful in process optimization, as the example indicates. ABOUT THE AUTHOR: Dr. Chris Rauwendaal is a well-known author, lecturer, researcher, entrepreneur, and consultant in the field of extru- sion. He holds numerous patents and has written more than 200 articles and seven books related to extrusion, mixing, injection molding, and statistical process control. A Fellow of the Society of Plastics Engineers (SPE), he is the developer of the CRD, VIP, and ASM mixing technologies that utilize strong elongational flow to improve mixing in extrusion and molding. Rauwendaal also developed the HHT (high-heat-transfer) extruder screw designed to improve cooling in foam tandem and other extrusion operations. In 1990 he founded and is still president of Rauwendaal Extrusion Engineering. Contact: (530) 269-1082; chris@rauwendaal.com; rauwendaal.com. The pressure pulsing of the teeth of a gear pump can be reduced by using helical gears rather than straight gears. 250 225 200 175 150 125 100 FIG 6 The discharge pressure on a new extruder just put into service showed a regular sinusoidal variation. FIG 7 The barrel temperatures also showed a regular sinusoidal variation. The trend plot shows that the variation in barrel temperature is much too large, suggesting poor tuning of the temperature controllers for the barrel zones. FIG 8 Barrel temperatures can be optimized to achieve the lowest pressure fluctuation. This can be done by changing the setpoint and following the transient response of the extruder. This shows the transient response from changing the setpoint of barrel zone 1 from 100 C to 175 C. This figure shows the pressure vs. the actual temperature of zone 1 150 125 100 75 50 25 0 Time, min → 0 15 30 Pressure, bar → Time, min → 0 15 30 Temperature, C E1 E2 E3 Temperature, C → Pressure, MPa → Optimum 100 125 150 175 18 16 14 12 10 @plastechmag 43 Plastics Technology E X T R U S I O N

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