Lipetsk State Technical University (Lipetsk, Russia):

Belskiy S. M., Dr. Eng., Prof., e-mail: belsky-55@yandex.ru

The shape of the cross section of a hot-rolled strip has a significant impact on strip’s shaping during the subsequent cold rolling. Defects such as local edge thickenings lead to the edge waviness of the strip in cold rolling. The shape of the cross-section is represented by a set of strip thickness values along its width, the number of measurements depending on the width of the rolled strip — the wider the strip, the greater the measured cross-sectional shape values. The convexity of the shape of the cross section is estimated from the approximating parabola, which is constructed from the measured values of the strip thickness along the strip width. Approximation is produced by a least-squares method. The accuracy of the coincidence of the approximating parabola with the actually measured cross-section shape of the hot-rolled strip is characterized by the determination coefficient R2. In the process of hot rolling an increased wear of working rolls appear in places of more cold strip’s edges therefore local thickenings of the edge areas appear on a strip. Further cold rolling of such strips leads to formation of an edge waviness and violation of admissible level of non-flatness of a rolled strip. It is shown that the determination coefficient is not able to estimate the magnitude of the edge thickenings of the hot-rolled strip. The necessity of developing of an additional parameter which characterizes the edge thickenings of the cross-section shape of hot-rolled strips is shown. For this purpose, a simplifi ed mathematical model of the profile of the cross-section of the hot-rolled strip has been developed, which consists of the middle parabolic part and the edge sections, the thickenings of which are modeled by rectangles. With the help of the developed mathematical model, it is possible to determine the coefficients of the approximating parabola and the determination coefficients of the modeled cross sections. The article gives an example of two cross sections with the same determination coeffi cients and identical parameters of approximating parabolas, one of the sections having obviously designated edge thickenings.

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