Foreign objects in the plastic melt are a problem in extrusion. SKZ researchers have now succeeded in developing an adapter to connect terahertz sensors directly to the extruder and thus examine the melt inline for foreign objects. The challenge was to guide the THz waves into the melt, since pressures of up to 300 bar and temperatures of up to 300°C can prevail in extruders. In addition, the extruder housing is made of metal, which is not transparent to THz waves. Not only different plastics were examined at different temperatures and pressures, but also foreign objects such as glass beads in the melt. In the next step, a measuring head for measuring in reflection will be developed, which can be used at any point on the extrusion line
The optoNCDT 1760-1000 long-range laser sensor by Micro-Epsilon also measures at distances of up to 2m with up to 7.5kHz.