Development of On-Line r-value Measurement System for Cold-rolled Steel Sheets by Using Electromagnetic Acoustic Transducer

An on-line measurement system of r-value for cold-rolled steel sheets was developed by measuring the average propagation time of low frequency S0 mode Lamb wave. In this paper, the principle of nondestructive r-value measurement and results of the various experiments are described. In the first experiment, we investigated characteristics of various kinds of EMATs (Electromagnetic Acoustic Transducers) in order to select the optimum EMAT type for on-line measurement. As a results, we developed the on-line measurement system using magnetostrictive type EMATs which measures the r-value with a 3mm gap between the sensor case and the steel sheet. The capability for estimating texture and for measuring r-value was investigated by using a lot of samples. After this analysis, we investigated the effests of measuring conditions such as sheet traveling speed, the sheet temperature and the sensor gap on the measurement accuracy. The on-line test was also done in the continuous annealing line by using test and product coils. Finally it was confirmed that applying this system, the r-value can be measured continuously in the production line with the accuracy of 3σ=0.2.