Extruder feedback-control system

The dynamic behavior of an extruder is significantly determined by the temperature control system on the extruder. It is, therefore, important to understand the basic characteristics of the various temperature control systems. Most control systems are closed-loop or feedback systems. The variable to be controlled is measured and this information is sent to a control unit. From the control unit a signal is sent to an actuator that adjusts the process such that the control variable is as close as possi-... 

The most important component of the feed system in a flood-fed extruder is the feed hopper with possible stirrer and/or discharge screw. A mechanical malfunction of this system can be determined by visual Inspection. If the feed hopper is equipped with a discharge screw (crammer feed), constancy of the drive should be checked. For proper functioning of a crammer feeder, the drive of the crammer feeder should have a torque feedback control to ensure constant feeding and to avoid overfeeding. 

The usual way to do this is by moving the mandrel in an axial direction relative to the die (Fig. 10.33). If both the die and the mandrel are provided with conical outlet features, this movement will increase or decrease the annular die gap between the two. The mandrel movements are controlled by a servo system acting on a preprogrammed thickness profile. The system may include a feedback loop to adjust parison profiling in response to screw speed variations in the extruder. 

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