Abstract
Abstract. The inline determination of process and product parameters is of great help for the evaluation and optimization of new procedures. Therefore, an ultrasound process tomography system has been developed, which enables the imaging of the local filler distribution in plastic melts. The objects investigated were extruded rods made of polypropylene (PP) with radial filler gradients. During extrusion, sound velocity and attenuation of the plastic melt were determined and processed via a modified reconstruction algorithm according to Radon transform into 2-D sectional images. Despite the challenges of higher attenuation and impedance mismatch of 60 mm filled PP melt compared to water, the resulting images are of good quality. An important factor for the image quality after tomographic reconstruction is the opening angle of the used ultrasound transducers. Furthermore, a simulation environment was developed in Matlab, which serves as a testing platform for the measurement system.
Highlights
1.1 Ultrasound for process monitoringUltrasound (US) waves are mechanical, acoustical – both shear as well as compressive – waves in the frequency range from 20 kHz up to several GHz, depending on the elastic and dissipative properties of the medium
It can be perceived that the tradeoff made during the setup of the measurement system between number and aperture of the transducers leads to tomographic artifacts, such as ring artifacts, shadows, or blurring
We have shown that the examination of the local filler distribution is possible with the Ultrasound process tomography (USPT) system
Summary
Ultrasound (US) waves are mechanical, acoustical – both shear as well as compressive – waves in the frequency range from 20 kHz up to several GHz, depending on the elastic and dissipative properties of the medium. A is the signal amplitude and t1 and t2 are the start and end time of an US pulse. When examining materials with US, advantages can be taken of the frequencydependent attenuation due to viscous losses as well as scattering and thermoelastic effects while sound waves are propagating through a medium. In liquids and plastic melts, US waves propagate mainly in the form of longitudinal waves. The material properties depend on the complex longitudinal modulus M∗, given by Eq (4): c2
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