Unlike traditional austenitic rolling, there is phase transformation during hot finishing rolling for thin gauge and high strength steel or non-oriented electrical steel. The transverse differences of temperature and asynchronous phase transformation result in uneven distribution of material property of rolled strip, further change the buckling behavior of strip during hot finishing rolling. By replacing the elastic modulus constant in the traditional buckling model with the distribution function of tangent modulus obtained by multiphase compression experiments and multifield coupling simulation, the effect of uneven distribution of material property on the critical buckling stress and buckling wave length are analyzed. The results show that for the global longitudinal wave, the critical buckling stress at the exit of stand is greater than that at the entry. But the opposite is true for the local longitudinal wave. Under the effect of uneven distribution of material property, the critical buckling stress and buckling wavelength of global and local center waves change little. The critical buckling stress of global edge wave is almost unchanged, but the buckling wavelength decreases slightly. The critical buckling stress and buckling wavelength of local edge wave are reduced obviously, and the buckling wavelength is decreased by about 10%. It means that the existence of soft ferrite at the strip edge easily makes the wave mode develop to "fragmented edge wave", which is consistent with the actual phenomenon.
Quarter wave defects often occur in high-strength steel production in wide rolling mills, which seriously affect product quality and production stability. The existing shape control actuators, such as roll bending, roll shifting, and CVC roll shape, can not adjust the high-order wave, and the upgraded CVCplus roll shape also has limited effects on the quarter wave. Therefore, the MVCplus roll shape is developed based on the superposition principle in order to realize the local roll shape modification at the wave position. Two cosine curves are superposed on the CVC roll shape within the strip width to decrease the reduction at the quarter of the strip width, and maximum reduction is achieved at the position of maximum wave height. The new roll shape can significantly reduce the quarter wave defects in practical application, and has little effect on the adjustment characteristics of the original CVC roll shape.
Good profile is one of the important control objectives in hot rolling of aluminum plate. However, M-shaped profile defect often appears for wide aluminum plate and W-shaped profile defect often appears for narrow aluminum plate. In order to reveal the formation mechanism of the two typical profile defects, the evaluation indexes of the M-shaped profile defect and W-shaped profile defect are proposed, and the roll-plate coupling deformation model and the roll thermal expansion model are established. The effects of rolling force, bending force and work roll thermal expansion on the profile are analyzed using these models. The results show that the rolling force and bending force has little effect on M-shaped profile defect, and the main reason for this problem is the uneven thermal expansion of work roll. Meanwhile, the W-shaped profile defect is produced under the combined action of the roll thermal expansion and large roll deflection, and the roll thermal expansion is the necessary condition for the formation of W-shaped profile defect. The greater the thermal crown of the roll, the smaller the rolling force and the greater the bending force, the more obvious the W-shaped profile defect. Based on the above conclusions, industrial tests were carried out. By increasing the cooling flow in the middle of the roll, the frequency of M-shaped profile defect decreases from 29.4% to 9.0%. Meanwhile, by increasing the positive shifting of CVC rolls, reducing the bending force, and decreasing the cooling flow of work roll at the edge of the plate, the frequency of W-shaped profile defect decreases from 42.1% to 14.1%. The profiles of the hot rolled aluminum plates are effectively improved by the developed control strategies.
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