OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 6 No. 4 2024 rolling temperature (Table 2). The decrease of reductions and increase of specifi c interstand tensions σi−1 and σi to maximal possible values ≤ 60 MPa, as shown by successful experience of implementation at various hot rolling mills in [19, 20], in the rolling direction in the last stands greatly reduce fl uctuations of forces Рi and strip thickness in it. Table 3 presents the process restrictions, new design modes and values of normal contact stresses in the above-mentioned stands No.7, No.9 and No.11. Table 3 is an illustrative example of the effi ciency of the developed method related to redistributing reductions and increasing interstand tensions in the area of contact stresses decrease during hot rolling of 2.1×1,270 mm strip made of 0.1 C-Cr-Si-Ni-Cu steel. The effi ciency of the initial adjustment of hot rolling process modes for low-alloyed structural steel 0.1 C-Cr-Si-Ni-Cu according to the above principle demonstrates the decrease of maximum normal contact stresses in the stand No.11 and up to the safe range of calculated values рхmax = 837.5–838.0 MPa (Table 3). The lifetime of the working rolls of stand No.7 with the increase of reduction to the maximum value εi.max, as shown by calculation of stresses рхmax (Table 3), does not depend on normal contact stresses from the strip contact with the working roll; the decisive factors of the technology are the high temperature of rolling ti, which greatly aff ects thermal deformations and eff ective cooling of working roll bodies [24]. Similar calculations of the maximum contact stresses рхmax and pnmax were done for steels 0.18 CCr-Mn-Ti and 0.14 C-2 Mn-N-V (Table 4) during hot rolling in stands of the fi nishing train from the thickness of 35.5 mm to the thickness of 2.1 mm, to demonstrate the feasibility of using new improved modes compared to the existing ones to increase contact strength of working rolls. Table 4 shows that hot rolling, according to operating modes, of structural steels 0.18 C-Cr-Mn-Ti and 0.14 C-2 Mn-N-V with higher content of carbon and alloying elements, results in increase ofmaximal contact stresses to the values рхmax = 1,095.7–1,245 MPa, which exceed the permissible values [σ] = 1,200 MPa. The results of calculations given in Table 3 and Table 4 lead us to a conclusion that the algorithm of optimization of hot rolling process modes from [19, 20] can be applied to improve the strip rolling technology to ensure high durability of working rolls by reducing of maximum contact stresses to the range of 838–1,023 MPa. Fig. 3. Distribution pattern of normal contact stresses along the length of the deformation zone in rolling stands No.7, No.9 and No.11
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