A novel measurement technique for the study of wire coating instabilities

A new non-intrusive investigation technique developed especially for the study of liquid film instabilities occurring in the wire coating process is presented. A laser-sheet-based probe assures high spatial resolution and high frequency response, along with robustness to wire movements and vibrations. Moreover, the calibration is easy and fast, since the calibration curve is linear. The post-processing procedure allows the detection and measurement of the most important wave characteristics, such as wavelength, wave amplitude, wave velocity, and amplification (damping) factor. Results obtained with this technique are compared with existing theories, showing good agreement. More than one wave is detected and it is found that short waves dominate at low entrainment speeds, whereas long waves dominate for high speeds, with a smooth transition from the former behavior to the latter. The trend of the amplification factor follows that predicted by the theory. Due to its simple implementation and automatic data analysis, this technique seems to be very promising, not only for research purposes, but also for industrial applications. Among those, the most straightforward would be in the control of the final surface properties during the wire coating process, in order to ensure the desired characteristics.