Method for improving rolling stability of finishing mill

Abstract

The present application relates to the field of finish rolling mill, a method for improving the stability of finish rolling mill, the steel grade and the thickness after rolling of the steel plate to be rolled by the finish rolling mill are determined, if the steel grade is one of T700L, T600L, TQ700MCD, TQ600MCD (high-strength steel) and the thickness after rolling is less than or equal to 2.5mm (thin specification product), the indirect control of the centering curve of the finish rolling is realized by applying different pressures on both sides of the descaling pinch roll of the finish rolling, so as to improve the stability of the finish rolling.

Description

Technical Field

[0001] This invention relates to the field of finishing mill rolling, and particularly to the field of rolling thin-gauge products of high-strength steel. Background Technology

[0002] Entering 2022, my country's steel industry faced severe overcapacity, widespread losses, and operational difficulties for enterprises. Under these circumstances, producing ordinary steel grades was uncompetitive and resulted in significant losses. High-strength steel in thin specifications was difficult to produce, with low yields, but its high selling price offered profit potential. However, the stability of rolling in the production of this type of steel was not well addressed. Variations in the functional precision of finishing rolling equipment were not fully controlled, leading to high scrap rates, unplanned thickening of rolling mills, and persistently high costs, preventing the realization of the profitability of this steel grade. Therefore, improving the stability of thin-specification high-strength steel production, increasing yields, and achieving stable mass production are of paramount importance and urgently needed. Summary of the Invention

[0003] The technical problem to be solved by this invention is: how to solve the problem of poor production stability of thin-gauge high-strength steel products.

[0004] The technical solution adopted in this invention is: a method for improving the rolling stability of a finishing mill. The method involves determining the steel grade and the thickness of the steel plate to be rolled by the finishing mill. If the steel grade is one of T700L, T600L, TQ700MCD, or TQ600MCD (high-strength steel) and the thickness after rolling is ≤2.5mm (thin specification product), then the finishing mill centering curve is indirectly controlled by applying different pressures to both sides of the finishing mill descaling pinch rolls, thereby improving the rolling stability of the finishing mill.

[0005] When different pressures are applied to both sides of the finishing mill descaling pinch roll, i.e., when the pressure difference between the two sides of the finishing mill descaling pinch roll changes, the pressure difference between the two sides of the finishing mill small vertical roll also changes. The change in the pressure difference between the two sides of the finishing mill small vertical roll directly leads to the change in the finishing mill centering curve. During the rolling process, when the pressure difference between the two sides of the finishing mill small vertical roll exceeds 200KN, the finishing mill centering curve will deviate by more than 20mm, which is very likely to cause misalignment between stands and crush the scrap steel. At this time, it is necessary to adjust the pressure on the drive side of the finishing mill descaling pinch roll. During the adjustment, the pressure difference between the two sides of the finishing mill small vertical roll is less than 180KN by adjusting the pressure on the drive side of the finishing mill descaling pinch roll.

[0006] During each maintenance cycle of the finishing mill, the pressure on the drive side of the finishing mill descaling pinch rolls is adjusted. When the maintenance cycle is less than or equal to 15 days, the rolling stability throughout the entire maintenance cycle can be guaranteed. The adjustment satisfies the formula P. 调整量 =( P 小立辊 -150KN) / 40, where P 调整量 This refers to the pressure adjustment amount on the drive side of the descaling pinch rolls in the finishing mill, measured in kN or P.小立辊 This represents the actual pressure on the drive side of the small vertical roll in the finishing mill, expressed in kN.

[0007] An adjustment function block is added to the PLC control program to realize online adjustment of the pressure on both sides of the finishing mill scale box pinch roll. The PLC display shows the manually input adjustment amount P, the pressure difference between the two sides of the finishing mill small vertical roll, and the actual pressure P small vertical roll on the drive side of the finishing mill small vertical roll.

[0008] The beneficial effects of this invention are: the method of this invention effectively improves the rolling stability of high-strength steel thin specifications rolled by finishing mill, and the scrap rate of finishing mill line is reduced from 1.95% to 0.60%. Attached Figure Description

[0009] Figure 1 This is a centering curve diagram of a finishing mill that did not employ the method of this invention;

[0010] Figure 2 This is a centering curve diagram of the finishing mill using the method of this invention;

[0011] Among them, 1. Pressure curve of the drive side of the small vertical roll of the finishing mill, 2. Monotonic curve, 3. Finishing mill deviation curve. Detailed Implementation

[0012] Since Shanxi Taiyuan Iron & Steel Co., Ltd. began producing high-strength steel thin grades (T700L / T600L / TQ700MCD / TQ600MCD, etc., thickness ≤2.5mm) on its 2250 production line, the finishing rolling process has consistently been unstable, with over 15 pieces of scrap steel produced annually and a scrap rate exceeding 1.2%. During production, the finishing mill requires two operators (one for normal grades), while three others monitor the plate shape to prevent waviness and misalignment between stands, making production extremely difficult.

[0013] Technical problems that need to be solved:

[0014] When it is not possible to quickly improve the functional accuracy of the finishing mill equipment, improve the rolling stability of the finishing mill and solve the problem of scrap steel deviation during the rolling process.

[0015] Technical solution:

[0016] By establishing a research team, conducting on-site monitoring during the production process, verifying actual production data and various rolling parameters and equipment parameter curves, and combining the good rolling stability of high-strength, difficult-to-roll stainless steel materials, the team conducted analysis and research, and found that the key point affecting the deviation problem of high-strength carbon steel precision rolling mill is the pinch roll of the precision rolling descaling box.

[0017] Preliminary trials

[0018] During the initial production trial, when producing the T700L thin specification, the pressure on both sides of the finishing mill descaling box was adjusted manually using the control buttons on the table. The actual pressure of the finishing mill small vertical roll and the actual position of the finishing mill centering curve were observed and recorded.

[0019] Data Statistical Analysis

[0020] In one embodiment, such as Figure 1 As shown in Figure 1, the pressure curve on the drive side of the finishing mill small vertical roll increases from 171.4 kN to 205.5 kN. The finishing mill deviation curve 3 deviates from the working side by 35.3 mm. The operator is forced to adjust the monotonous 20th track to avoid deviation of the scrap steel.

[0021] Statistical analysis of several experimental data revealed that when the pressure difference between the two sides of the finishing mill's small vertical roll exceeds 200 kN, the finishing mill alignment curve will deviate by more than 20 mm, easily leading to misalignment between stands and crushing of scrap steel. Increasing the pressure on the drive side of the finishing mill's scale box pinch rolls can reduce the pressure on the drive side of the finishing mill's small vertical rolls. When the pressure is reduced to below 180 kN, the overall curve can be controlled within ±20 mm. For every 10 kN adjustment of the pressure difference in the finishing descaling pinch rolls, the pressure of the finishing mill's small vertical rolls can change by 30-50 kN. In one embodiment, such as... Figure 2 As shown in Figure 1, the pressure curve on the drive side of the small vertical roll in the finishing mill is controlled within 200KN, and the deviation curve of the finishing mill is within ±20mm. The operator does not need to intervene during the rolling process, and the rolling is stable.

[0022] Develop control functions

[0023] Manual adjustments are prone to error, increasing labor costs and potentially leading to unstable scrap steel production during finishing milling if the adjustment is too large or too small. Therefore, an automatic adjustment function needs to be developed. This function should allow for real-time and rapid modification of the finishing mill descaling pinch roll pressure parameters, enabling precise control of the pressure difference between the two sides.

[0024] Implementation details: Each overhaul involves replacing the finishing mill support rolls and performing periodic maintenance on the finishing mill equipment. The rolling status of the finishing mill will change. For the first production of this type of steel grade, the actual pressure on both sides of the small vertical rolls is observed on the monitoring screen, and the adjustment amount of the finishing mill descaling pinch rolls is calculated and adjusted in real time in the program to basically ensure the stability of rolling throughout the entire overhaul cycle (approximately 15 days).

[0025] P 调整量 =( P 小立辊 -150) / 40

[0026] in:

[0027] P 调整量 The pressure adjustment of the descaling pinch roll drive side in the finishing mill can be input as a parameter in the program.

[0028] P 小立辊 The actual pressure of the precision rolling mill vertical roll can be monitored in real time during production.

[0029] After the invention was officially put into application in September 2022, it effectively improved the rolling stability of high-strength steel thin specifications rolled by the finishing mill. The number of scrap steel blocks in the finishing mill decreased from 1.33 blocks / month to 0.57 blocks / month, and the scrap rate of the finishing mill line decreased from 1.95% to 0.60%.

[0030] 1. Based on a monthly output of 1,500 tons of high-strength steel thin-gauge (thickness ≤ 2.5mm) and a price difference of 2,500 yuan / ton between scrap steel and finished product, the annual cost savings would be 1,500 * (1.95% - 0.60%) * 2,500 * 12 = 607,500 yuan.

[0031] 2. For high-strength steel thin-gauge (thickness ≤ 2.5mm) difficult-to-roll materials, based on the calculation that each scrap steel failure time is 1 hour, the machine output is 710 tons, and the profit per ton is 500 yuan, the annual increase in production and profit is 710*1*(1.33-0.57)*12*500=3.2376 million yuan.

[0032] 3. For high-strength steel thin-gauge (thickness ≤ 2.5mm) difficult-to-roll materials, each scrap steel loss on the finishing mill rolls results in a steel content of 1.2mm for F1-F4, with a single millimeter weight of 175.29Kg / mm and a single millimeter price of 25 yuan / Kg; and a single millimeter weight of 2mm for F5-F7, with a single millimeter weight of 141.42Kg / mm and a single millimeter price of 12 yuan / Kg. The annual savings in roll consumption costs are: (8*1.2*175.29*25+6*2*141.42*12)*(1.33-0.57)*12 = 569,400 yuan.

[0033] The total annual profit generated is: 60.75 + 323.76 + 56.94 = 441.45 million yuan.

Claims

1. A method for improving the rolling stability of a finishing mill, characterized in that: Determine the steel grade and thickness of the steel plate to be rolled in the finishing mill. If the steel grade is one of T700L, T600L, TQ700MCD, or TQ600MCD and the thickness after rolling is ≤2.5mm, the finishing mill centering curve can be indirectly controlled by applying different pressures to both sides of the finishing mill descaling pinch rolls, thereby improving the stability of the finishing mill rolling process. When different pressures are applied to both sides of the finishing mill descaling pinch rolls, i.e., when the pressure difference between the two sides of the finishing mill descaling pinch rolls changes, the pressure difference between the two sides of the finishing mill small vertical rolls will also change. The change in the pressure difference between the two sides of the finishing mill small vertical rolls directly leads to… The centering curve of the finishing mill changes. During the rolling process, when the pressure difference between the two sides of the finishing mill's small vertical roll exceeds 200 kN, the centering curve will deviate by more than 20 mm, which can easily lead to misalignment between stands and damage to the scrap steel. In this case, it is necessary to adjust the pressure on the drive side of the finishing mill's descaling pinch rolls. During adjustment, the pressure difference between the two sides of the finishing mill's small vertical roll should be less than 180 kN. The pressure on the drive side of the finishing mill's descaling pinch rolls should be adjusted during each maintenance cycle of the finishing mill. When the maintenance cycle is less than or equal to 15 days, stable rolling can be guaranteed throughout the maintenance cycle, and the adjustment should satisfy formula P. 调整量 =( P 小立辊 -150KN) / 40, where P 调整量 This refers to the pressure adjustment amount on the drive side of the descaling pinch rolls in the finishing mill, measured in kN or P. 小立辊 The actual pressure on the drive side of the finishing mill's small vertical roll is expressed in kN. An adjustment function block is added to the PLC control program to achieve online adjustment of the pressure on both sides of the descaling box pinch rolls. The manually input pressure P is displayed on the PLC monitor. 调整量 Pressure difference between the two sides of the finishing mill vertical roll, and actual pressure P on the drive side of the finishing mill vertical roll. 小立辊 .

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