A processor recently sent me a video of a control panel from an extruder that was surging badly, asking me to diagnose the problem. The digital meters were a blur of flashing numbers, and after reviewing the video several times I could not detect any discernible pattern. This reminded mc of what I consider a step backward in modern extruder control systems: the use of digital meters for amps, pressure, and screw speed on the extruder and melt pump. In the "old days," many extrusion problems could be clarified using analog meters. By comparing the easily interpreted movement of the dial indicator, you could troubleshoot problems such as surging, feed restrictions, poor temperature profiles, melt-pump-related instability and even external inconsistencies. For example, by merely observing the ammeter and head pressure you could trouble-shoot melt-channel plugging, poor feeding, and lack of fill. Even un melt can sometimes be detected on an analog pressure meter located at the end of the barrel.
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