Improving dynamic regime of rolling for increasing durability of ball-rolling mill rolls

One of the important reasons for the downtime of ball rolling mills is replacement of rolls due to their wear and tear. The degree and zones of critical wear of ball rolling rolls are investigated in the article, where the greatest wear is observed over the flanges in zone of billet capture. Conditions necessary to capture the blank and to perform rolling process are analytically determined. Variable frequency method of roll rotations is proposed as a progressive technology for blank supply. The results of tests for its variations in accordance with linear and quadratic law are presented. Known formulas determining average strain rate at rolls rotational speed change are converted for linear and quadratic dependences. Experimental studies have been carried out in conditions of EVRAZ Nizhnetagilsky Metallurgical Plant ball rolling mills during rolling of 60mm ball made of Sh-3G steel. Ex-periments were performed for given parameters of manual change in rolls rotation speed at blank capture by rollers. The results have shown a significant effect of change in rotational speed on average specific pressure during blank capture. Evaluation of torque-time and average contact pressure for calculated and experimental data are presented. Empirical characteristics are also described at variable rotational speed of rolls according to linear and quadratic law. Acceptable convergence of results of calculated and empirical characteristics is determined. Engineering solution has been proposed for that task. It consists in installation of a thyristor converter. This solution allows reduction of rolls speed before blank capture. Also, this solution will increase frequency to the nominal value according to the given law after blank capture. As an obtained result, there is uniform distribution of average contact pressure over the entire length of the roll under different operating conditions of mill in automatic mode. Application of this technique will reduce wear degree of the rolling tool. At the same time, productivity of ball rolling mill will be maintained. Rolls consumption and number of rolls change will decrease due to rolls wear. © 2018, National University of Science and Technology MISIS. All rights reserved