Lipetsk State Technical University (Lipetsk, Russia):

S. M. Belskiy, Dr. Eng, Prof., Metall Forming Dept., e-mail: belsky-55@yandex.ru
I. I. Shopin, Cand. Eng., Metall Forming Dept.

Cross-section thickness is the most important characteristic of the quality of hot-rolled steel due to the fact that it largely determines the manufacturability of subsequent processing including breaks during cold rolling of hot rolled strips. Cross-section thickness variation is a set of multiple thickness measurements across the width of a hot rolled strip. Such a set is called a strip cross section profile. Therefore, in order to assess the impact on any quantitative characteristics of manufacturability, a small number of parameters should characterize an array of measurements. For this, the cross section profile is approximated with a parabola, most often of the second order. In the scientific and technical literature, a number of similar characteristics of the cross-sectional profile are indicated: convexity, wedge, thickness variation, displacement, coefficient of determination, and wedge in near-rim zones. Recently, a new characteristic of the cross-section profile, the saddle coefficient, has been introduced into scientific use. The key feature of this characteristic is the amplification effect of deviations from the parabolic approximation of the cross-section profile in the near-rim zones of the strip. The article shows a statistically significant effect on the breakage during cold rolling of the transverse thickness variation of the hot rolled strip. As the characteristics of the transverse thickness variation, the saddle coefficient and wedge in near-rim zones are used. The study was conducted by the method of statistical testing of hypotheses by p-value based on regression modeling. In the mathematical model, the probability of strip breakage during cold rolling of a hot rolled strip without preliminary trimming was estimated. Binary logistic regression is best suited for mathematical modeling of the probability of an event occurring (strip breakage). According to the results of statistical analysis, the significance of the influence of the saddle coefficient and wedge in near-rim zones was confirmed. Revealed a strong nonlinearity of the influence of the parameters of the transverse thickness variation on the probability of strip breakage. The optimal ranges of parameters were determined for the saddle coefficient of shape and wedge in near-rim zones in which the probability of breakage strip during cold rolling is minimal.

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