Modeling and development of technological modes for production of grinding balls of increased hardness and impact resistance

In order to substantiate the possibility of producing grinding balls of the 5 th hardness group and to stabilize the production of balls of the 4 th hardness group in an operating ball rolling mill, a series of theoretical and experimental studies were conducted. Based on the results of computer modeling of the production process of grinding balls with a diameter of 60 mm, the authors determined the patterns of formation of the metal stress state during cross-screw rolling of balls made of standard steel Sh2.3 and experimental economically alloyed steel Sh76KhF. A decrease in the temperature of billet discharge from the heating furnace within the permissible range of its change according to current technology (880 – 1000 °C) leads to a significant increase in stress intensity over the entire surface of the balls during rolling, which increases the load on the equipment of the rolling stand and wear of the roller calibers. Additionally, the simulation shows that after the end of rolling, there is a significant (up to 80 °C) temperature unevenness on the balls surface, which, however, is almost completely eliminated after the balls are cooled on the conveyor before quenching. In the case of rolling balls from the billets with a discharge temperature from a heating furnace of less than 980 °C, the balls surface temperature before quenching is lower relative to the recommended range, ensuring the production of products with specified properties, which is confirmed by metallographic and durometric studies. Based on the results of the conducted research, a new mode of grinding balls production was developed with the temperature of billet discharge from the heating furnace increased to 980 – 1030 °C. Pilot testing of the new rolling mode showed that its use guarantees producing grinding balls of the 4 th hardness group according to GOST 7524 – 2015 in their production from standard steel Sh2.3 and producing balls of the 5 th hardness group using the developed economically alloyed steel grade Sh76KhF. At the same time, balls made of both steel grades under consideration have increased impact resistance.