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Many modern extrusion lines are equipped with data-acquisition systems (DAS). These systems can present extruder operators and process engineers with a large amount of data. There are several critical issues in the proper use of a DAS: • Are the correct process variables measured and monitored? • Is the data collection rate appropriate? • Is operating personnel capable of properly interpreting the data? The first installment ( Jan. '17) focused on the proper use of a DAS. The second installment (Mar. '17) focused on melt temperature. In this third and final installment of this series, the discussion will focus on how process data from a DAS can be used to detect and solve extrusion problems. VARIATION IN STOCK TEMPERATURE Figure 1 depicts a single-screw line extruding tubing. The tempera- ture of the extrudate is measured with an infrared (IR) thermom- eter. Only a short section of the tubing is visible between the die and the calibrator. Process data was captured and plotted (Fig. 2). The trend plot shows temperature measured in 11 locations; it also shows the motor load. There are four extruder zones and five diehead zones. The temper- ature measured in these zones is the temperature of the metal. Polymer melt temperature is measured with an immersion probe in the die and with an IR detector just beyond the exit of the die. In this final installment, learn how process data can be used to identify and fix extrusion issues. How to Collect and Interpret Extrusion Process Data By Chris Rauwendaal Rauwendaal Extrusion Engineering Inc. PART 3 FIG 1 This single-screw tubing line is using an infrared temperature-measurement probe. Process data from the line shown in Fig. 1. The trend plot shows temperature measured in 11 locations, as well as motor load. Note a number of temperatures with a regular sinusoidal variation with the same frequency. The tubing temperature shows the largest variation, which is a problem. The cause? Variation in the feed material entering the extruder. Motor Load, % Melt Temperature 1, C Tubing Temperature, C Extruder Zone 1: Actual Value, C Extruder Zone 2: Actual Value, C Extruder Zone 3: Actual Value, C Extruder Zone 4: Actual Value, C Die-Head Zone 1: Actual Value, C Die-Head Zone 2: Actual Value, C Die-Head Zone 3: Actual Value, C Die-Head Zone 4: Actual Value, C Die-Head Zone 5: Actual Value, C 0 5 10 15 20 25 min Temperature, C → 250 245 240 235 230 225 220 Time (15 sec/unit) → Immersion Probe Melt Temperature IR Stock Temperature Die Temperature—Discharge End 1 9 17 25 33 41 49 57 65 73 81 89 97 Extruded Tubing Extrusion Die IR Dectector Calibrator FIG 2 40 JULY 2017 Plastics Technology PTonline.com Tips and Techniques