Extrusion International 1-2017

28 Extrusion International 1/2017 MEASUREMENT the eccentricity of the products. Thereby, in addition to the quality control andprocess optimization, the savingof plastic material and cost reduction play an essential role. Conven- tionally available technologies are, for example, based on ultrasound technology. This method is suitable for the basic measurement of the wall thickness of single layer products but reaches its limits due to its function and dependence on material properties, the plastics temperature and the cou- plingmedium. A precisemeasurement of all product param- eter without the dependence on environmental or material influences is nowadays ensured by the X-ray technology. Ultrasound technology The ultrasound technology is only partly suitable for on- line quality control of hoses and tubes. For example, the ultrasound is not able to penetrate the aluminum layer that is used as a vapor barrier in composite pipes and is therefore not applicable for this application. Measuring rubber hoses, the ultrasound signals are largely absorbed by the porosity and absorption of the rubber so that they are also not reliably measurable. Furthermore, multi-layer rubber hoses contain typical fabric reinforcements, which divert the ultrasound echo and make a measurement im- possible. The ultrasound measurement is usually realized in a water bath as the water is used as a coupling medium for the transmission of the sound. A precise temperature compensation is necessary as the propagation speed of the ultrasound, which is used for the calculation of the eccen- tricity, depends on temperature and material. This tech- nology requires a calibration. Further, an estimation of the wall thickness is typically only possible by combining the ul- trasonic technique with an additional gravimetric system. X-ray technology The X-ray technology is based on an imaging principle. The X-ray technology does not require an adaptation to Pic. 4: X-ray measuring system installed in a hose extrusion line Pic. 5: The measuring system based on millimeter waves technology for the determination of the diameter, wall thickness and the sagging based on the time difference analysis of reflected signals