The hydrostatic extrusion behavior of polyoxymethylene (POM) is described. Extrusions were performed at 164°C for a range of different molecular weight grades. Excellent unflawed lengths of extrudate were obtained with axial Young's moduli, measured at room temperature, reaching values as high as 24 GPa. The extrusion characteristics are discussed in terms of the very strong dependence of the flow stress of POM on strain and strain rate and pressure. In addition to measurements of Young's modulus over a wide temperature range, data for shear modulus and transvers modulus are also presented. A limited amount of other structural measurements is presented.

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Ultrasonic velocity measurements provide process related information to complement conventional temperature and pressure measurements, since velocity varies with material type and with temperature and pressure conditions. The technique is non-invasive, can be applied directly to the process, and results are available in real time. An ultrasonic virtual instrument has been used on industrial scale extruders in house. Experimental results are presented, showing ultrasonic velocity to be a powerful tool for improving knowledge of polymer melt bulk temperature during extrusion.PRC/1608

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