Flow Surging for a PC Resin Extrusion Process

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. 

To verify that the cooling water was the root cause for the flow surging, the cooling water flow was turned off and on several times. As expected, the stability of the extruder was acceptable when the cooling water was on and unacceptable when it was off. The line was operated for about a month with the cooling water on, and the line has operated stably. Thus, the level of cooling for this system was acceptable and major modifications to the extrusion process were not required. 

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. 

F energy flux produced via frictional dissipation at a polymer-metal interface 

V relative sliding velocity between a resin and metal surface X independent position variable for the cross-channel direction z independent position variable for the downstream channel direction 

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