THE ACQUISITION AND FREQUENCY ANALYSIS OF DIGITAL DATA FROM A SINGLE SCREW EXTRUDER

The primary aim of this research has been to measure, display and analyze instabilities involved in a single screw extrusion process. A fairly broad spectrum of conditions was examined including crystalline and amorphous polymer extrusions at three different screw speeds for three different screws.; The three different screw speeds cover almost the entire range of speeds possible for the 2 1/2 inch extruder used in this study and, in addition, this is a common range for industrial extruders in use today. The three screw designs investigated also are both common and represent the most widely used feed screw designs.; In order to accurately study the process, detection systems were designed and built to monitor screw speed and input and output flow rates. These systems were combined with commercial pressure detection systems and an infrared fiber optic detection system to isolate the extrusion process so that fluctuations occurring within the extruder during "stady state" operation could be recorded and analyzed.; In order to calibrate these measuring elements, reliable appatus, techniques and computer programs were developed. These systems were used to check both the static and dynamic characteristics of the transducers.; A digital data acquisition system was developed, tested and used to collect and store the data and a frequency analysis package was developed based on an IBM shared library fast Fourier transform program to analyze the data.; The data collected have been presented in their entirety in graphical form. In addition, important statistical quantities have been calculated and presented. These data are composed of fast data recorded at the rate of 20 Hertz and slow data recorded at the rate of 2 Hertz. The variables examined included six pressures, flow rates into and out of the extruder, screw speed and temperature.; Frequency analysis results indicate that periodic and non-periodic fluctuations continuously occur during the extrusion process. Fluctuations occurring at 1/2 the screw speed frequency appear to be caused by the asymmetrical geometry of the solids conveying section of the extruder. Other frequencies at 1/4 and 3/4 that of the screw appear in many of the runs. Although the 3/4 frequency apparently is linked to the rotation of the polymer helix, no plausible explanation could be determined for the 1/4 screw speed frequency.; Frequency analysis techniques were also shown to be useful for (1) Filtering data (2) Determining flow rates of instabilities and the solid bed (3) Determining acceleration in the solid bed (4) Determining residence times in specific sections of the extruder.; Finally, the study was also designed to evaluate in a qualitative manner the usefulness of the infrared fiber optic probe for temperature measurement. The fiber optic probe response was shown to be sensitive to pressure fluctuations within the extruder as well as temperature differences including those between the solid and melt.