A method for improving the edge finishing defects of pickled steel plates

Abstract

This invention discloses a method for improving the edge finishing defects of pickled steel strips, belonging to the field of hot-rolled pickled steel strip production. The improvement method includes controlling the convexity of the hot-rolled strip cross-section, controlling the roll shape of the leveling mill, and controlling the bending roll force matching. The leveling mill rolls adopt a concave design, with a flat roll in the middle and symmetrical sinusoidal curves on both sides. Addressing the current issue of bright edge defects easily appearing after leveling hot-rolled pickled steel strips, affecting product delivery, this invention designs the roll shape inwardly concave. This effectively compensates for the convex portion in the middle of the hot-rolled strip, allowing for better contact between the leveling mill work rolls and the hot-rolled strip surface, thereby solving the problem of insufficient contact between the strip on both sides during leveling roll operation and resolving the edge finishing defects.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled pickled steel plate production, and more specifically, relates to a method for improving the edge finishing defects of pickled steel plates. Background Technology

[0002] For products manufactured by the four-roll leveling unit of the hot-rolled pickling line, the edge finishing defect generally refers to a "bright edge band" defect appearing within 100mm of the strip edge after pickling and leveling, affecting product delivery. With increasingly stringent user quality requirements, complaints about "bright edge bands" in hot-rolled pickled sheets are on the rise, primarily concerning products with a width of 1380mm or more that require flat delivery.

[0003] Typically, the crown (C40) of hot-rolled strip is controlled within the range of 20-60μm. The actual thickness of the strip cross-section shows a significant thinning trend within 200mm of the edge, with the thinning becoming more pronounced closer to the edge, especially within 50mm, where the actual thickness decreases sharply, often exceeding 100μm. The lower rolling pressure of the leveling mill in the pickling line results in less harmful bending of the rolls, leading to insufficient leveling force on the steeply sloping edges of the hot-rolled raw material, making it prone to "under-leveling." Therefore, the significant difference in harmful contact between the rolls, causing a mismatch between the shape of the gap between the hot-rolled raw material and the pickling and leveling rolls, is the main reason why the edges of hot-rolled pickled coils are prone to "under-leveling."

[0004] A search revealed existing technologies for improving the bright strip phenomenon in steel strips. For example, patent CN102248003A provides a method for improving the bright strip defect in hot-rolled steel strips, including controlling the target value of the strip crown and the local high and low points. The target crown value is controlled between 40±13μm and 50±13μm, and the height of the local high and low points is ≤10μm. By controlling the target crown value and the height of the local high and low points, the transverse stress difference of the strip is reduced, thereby improving the cross-sectional shape of the hot-rolled steel strip. Patent CN111957752A discloses a production method for eliminating bright stripes and additional waviness defects on the surface of hot-rolled low-carbon mild steel. This method achieves elimination of bright stripes and additional waviness through three control stages: a descaling control stage before finishing rolling, a local high-point control stage in the middle of the finished strip cross-section, and a coiling pinch roll and tension control stage. During the strip coiling stage, by reducing the unit tension during stable coiling and lowering the pinch roll pressure, the occurrence rate of bright stripes in low-carbon mild steel is ultimately reduced, mitigating the associated waviness defects to some extent and reducing losses from steel coil cutting and repeated leveling. The above designs provide optimization directions for hot-rolled steel strip production technology, and there is still room for further improvement in practice. The industry is continuously researching effective ways to alleviate edge bright strip defects. Summary of the Invention

[0005] 1. The problem to be solved

[0006] In response to the current situation where hot-rolled pickled steel sheets are prone to edge bright band defects, which affect product delivery, this invention provides a method to improve the edge finishing defects of pickled steel sheets. This method can alleviate the bright band defects to a certain extent, significantly improve product quality, and meet the higher requirements of production for product quality.

[0007] 2. Technical Solution

[0008] To solve the above problems, the present invention adopts the following technical solution.

[0009] This invention provides a method for improving the edge finishing defects of pickled strip, including controlling the convexity of the hot-rolled strip cross-section, controlling the roll shape of the leveling mill, and controlling the bending force matching. The leveling mill rolls adopt a concave design, with a flat roll in the middle and symmetrical sinusoidal curves on both sides. The formula for the sine curves on both sides is:

[0010] y = A*SIN(W*x+Ψ)+K;

[0011] Where x is the axial position coordinate of the roll, in millimeters; y is the relative deviation of the roll radius at coordinate x, in micrometers; A is the crown influence coefficient, determined by the target crown of the hot-rolled strip; and W, Ψ, and K are the position influence coefficients, respectively.

[0012] Furthermore, the crown of the hot-rolled strip is controlled at 30±15μm.

[0013] Furthermore, the length of the middle flat roll of the leveling machine's working roll is the same as the length of the curved roll section on each side.

[0014] Furthermore, the total length of the working rolls of the leveling machine is 1800mm, the length of the middle flat roll is 600mm, and the length of the single-sided curved roll section is 600mm.

[0015] Furthermore, the formula for the sine curves on both sides is:

[0016] When -900mm≤x≤-300mm, y=A*s in(x*π / 2400-3*π / 8)+A;

[0017] When -300mm < x < 300mm, y = 0;

[0018] When 300mm≤x≤900mm, y=A*s in(x*π / 2400-5*π / 8)+A.

[0019] Furthermore, the range of values ​​for A is determined by the target crown of the hot-rolled strip. When the target crown of the hot-rolled strip is in the range of [15, 45], the value of A is [51.21, 153.64].

[0020] Furthermore, based on the actual strip shape, adjust the bending force of the working rollers of the leveling machine. When the strip width is ≤1380mm, the bending force is 10±5 tons; when 1380mm < strip width ≤1480mm, the bending force is 15±5 tons; when 1480mm < strip width ≤1580mm, the bending force is 20±5 tons; and when 1580mm < strip width ≤1380mm, the bending force is 25±5 tons.

[0021] 3. Beneficial effects

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] In traditional techniques, the mismatch between the thinning of the strip itself and the roll shape leads to significantly less stress on the edges of the strip compared to the center during leveling. In severe cases, the roll edges may detach from the strip, resulting in a noticeable difference between the edge and center morphologies. The improved method of this invention aims to effectively compensate for the central bulge of the hot-rolled strip by controlling the crown of the hot-rolled strip and employing concave rolls with appropriate reverse crown on the pickling and leveling machine, along with reasonable roll bending control. The roll shape is designed to be concave inwards. This allows for better contact between the leveling machine's work rolls and the hot-rolled strip surface, solving the problem of insufficient contact between the sides of the strip during leveling, addressing edge finishing defects, and ultimately achieving the goal of mass production of wide-width, leveled pickled sheets. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the roller curve in this invention;

[0025] Figure 2 This is a schematic diagram showing the effect of grinding the leveling work roller in this invention;

[0026] Figure 3 This is a schematic diagram of the outline of the hot-rolled pickling plate in this invention;

[0027] Figure 4 This is a schematic diagram of the contact state between the flat roller and the plate surface in traditional technology;

[0028] Figure 5 This is a schematic diagram showing the contact state between the roller and the plate surface designed in this invention.

[0029] In the diagram: 1. Strip steel; 2. Traditional flat roll; 2a. New roll. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Example

[0032] Currently, the pickling and leveling process in the industry is a subsequent processing step. Traditionally, the rolls used in this process are usually flat rolls or convex rolls to facilitate strip shape control and rolling stability. However, the inventors discovered through long-term practice that the mismatch between the strip's own side thinning and the roll shape leads to significantly less stress on the strip's edges than on the center during leveling. In severe cases, the roll edges may detach from the strip, resulting in a significant difference between the edge and center morphologies. This embodiment aims to solve the edge-finishing defects by controlling the crown of the hot-rolled strip, using concave rolls with appropriate reverse crown on the pickling and leveling machine, and coordinating with reasonable bending roll control, ultimately achieving the goal of mass production of wide-width, leveled pickled sheets for delivery.

[0033] Combination Figures 1-5 As shown, this embodiment provides a method for improving the edge finishing defects of pickled steel strips, including: control of the cross-sectional crown of hot-rolled strip, control of the roll shape of the leveling mill, and control of the bending roll force matching; each of these aspects will be analyzed and explained in detail below:

[0034] Control of cross-sectional crown of hot-rolled strip: The crown of hot-rolled strip is controlled within 30±15μm;

[0035] Leveling mill roll shape control: The purpose of designing the leveling mill roll shape is to compensate for the hot rolling edge drop. Based on the bright edge morphology and hot rolling plate shape profile, the roll shape curve adopts a three-segment fitting method. The middle part uses a flat roll, and the curves on both sides use symmetrical sine curves. The intersection points of the curve and the straight line are smoothly transitioned to ensure the grinding effect of the roll shape.

[0036] The formula for the sine curves on both sides is:

[0037] y = A*SIN(W*x+Ψ)+K;

[0038] Specific combination Figure 1 and Figure 2 As shown, x represents the axial position coordinate of the roll (in millimeters); y represents the relative deviation of the roll radius at coordinate x (in micrometers); A is the crown influence coefficient, determined by the target crown of the hot-rolled strip; W, Ψ, and K are position influence coefficients. W is determined by the length of the roll curve portion and the period of the trigonometric function it occupies; Ψ is determined by the position of the roll curve on the X-axis; and K is determined by the position of the roll curve on the Y-axis. Ψ and K together determine the position of the roll curve on the coordinate axes.

[0039] In this embodiment, the length of the middle flat roll of the leveling machine's working roll is the same as the length of the curved roll section on each side. In practice, the total length of the leveling machine's working roll is 1800mm. Based on the actual measured width of the bright edge, the distance from the edge is usually 0-100mm. According to the roll shape transition, the length of the single-sided curve is determined to be 600mm. Since the bright edge is symmetrical on both sides, the length of the middle flat roll is also 600mm.

[0040] Because the curved section and the flat roller section need to transition smoothly, that is, tangent at the intersection point, when the x-axis is equal to 300 and -300, we can find that y = 0 and SIN(W*x + Ψ) = -1. Therefore, we can find that A = K.

[0041] Considering the stress concentration at the edge of the roll, the slope should not be too large. 1 / 8 of the period of the sine function is used as the roll curve. Since the length of the curved roll is 600mm, using 600mm as 1 / 8 of the sine function period, the complete period length is 4800mm. The sine function W = π / 2400 can be obtained.

[0042] Based on the positions of the curves on the coordinate axes [-900≤x≤-300] and [300≤x≤900], substitute (-300,0) and (300,0) into the formula y=A*SIN(x*π / 2400+Ψ)+A to determine the value of Ψ in the sine function. For curve 1: Ψ=-3*π / 8, and for curve 3: Ψ=-5*π / 8.

[0043] The final roller profile curve is as follows:

[0044] Curve 1: y=A*s in(x*π / 2400-3*π / 8)+A[-900≤x≤-300];

[0045] Curve 2: y = 0 [-300 < x < 300];

[0046] Curve 3: y=A*s in(x*π / 2400-5*π / 8)+A[300≤x≤900];

[0047] The purpose of designing the roll shape of the leveling mill is to compensate for the edge drop of the hot-rolled strip. Therefore, the range of A is determined by the crown of the hot-rolled strip. When the crown of the hot-rolled strip is in the range of [15, 45], A takes the value of [51.21, 153.64].

[0048] Based on the actual shape of the sheet, adjust the bending force of the working rollers on the leveling machine. The basic adjustment range for bending roller control is as follows:

[0049] Bending roll force range: 0-30 tons. Adjust the bending roll according to the strip shape. When the strip width is ≤1380mm, the bending roll force is 10±5 tons; when the strip width is 1380mm<1480mm, the bending roll force is 15±5 tons; when the strip width is 1480mm<1580mm, the bending roll force is 20±5 tons; when the strip width is 1580mm<1380mm, the bending roll force is 25±5 tons.

[0050] By measuring the crown value of the hot-rolled pickled plate and taking an average value of 30.3 μm, corresponding to a length of 900 mm on both sides of the roll, and substituting (-900, 30.3) and (900, 30.3) into the above roll profile curve, A = 103.5 is obtained, and the roll profile curve is as follows:

[0051] Curve 1: y=103.5*s in(x*π / 2400-3*π / 8)+103.5[-900≤x≤-300];

[0052] Curve 2: y = 0 [-300 < x < 300];

[0053] Curve 3: y=103.5*s in(x*π / 2400-5*π / 8)+103.5[300≤x≤900];

[0054] After the work roll of this roller curve grinding is put into operation, combined with the bending roll control of the leveling machine, the problem of bright edges on both sides of the pickling plate has been effectively alleviated in practice.

[0055] Combination Figure 4 and Figure 5 As shown, when the leveling machine is working, the work rolls improve the surface morphology of the strip by directly contacting it. The outline of the hot-rolled strip is a convex shape with a high center and low sides. Figure 4 The process involves using a traditional flat roller 2 to process the strip 1. Since the traditional flat roller 2 does not contact both sides of the strip 1, bright edges are generated on both sides. Figure 5 In order to use the new roll 2a designed in this embodiment for processing, the roll shape is designed to be concave inward, which can effectively compensate for the convex part in the middle of the hot-rolled strip 1, so that the new roll 2a of the leveling machine and the surface of the hot-rolled strip 1 can make better contact, thereby solving the problem that the two sides of the flat roll cannot contact the strip when it is working.

[0056] The examples described herein are merely preferred embodiments of the invention and are not intended to limit the concept and scope of the invention. Any modifications and improvements made by those skilled in the art to the technical solutions of the invention without departing from the design concept of the invention should fall within the protection scope of the invention.

Claims

1. A method for improving edge finishing defects in pickled steel plates, characterized in that: This includes control over the crown of hot-rolled strip, the shape of the work rolls in the leveling mill, and the matching control of bending force. The work rolls in the leveling mill feature a concave design, with a flat roll in the middle and symmetrical sinusoidal curves on both sides. The formula for the symmetrical sinusoidal curves on both sides is: y = A * SIN(W * x + Ψ) + K; Where x is the axial position coordinate of the roll, in mm; y is the relative deviation of the roll radius at coordinate x, in μm; A is the crown influence coefficient, determined by the target crown of the hot-rolled strip; W, Ψ, and K are the position influence coefficients, respectively; W is determined by the length of the roll curve portion and the period of the trigonometric function it occupies; Ψ is determined by the position of the roll curve in the X-axis; K is determined by the position of the roll curve in the Y-axis; Ψ and K together determine the position of the roll curve in the coordinate axes. The crown of hot-rolled strip steel is controlled at 30±15μm; The length of the middle flat roll of the leveling machine's working roll is the same as the length of the curved roll section on each side; The formula for the sine curves on both sides is: When -900mm≤x≤-300mm, y=A*sin(x*π / 2400-3*π / 8)+A; When -300 mm < x < 300 mm, y = 0; When 300 mm≤x≤900 mm, y=A*sin(x*π / 2400-5*π / 8)+A; The range of values ​​for A is determined by the target crown of the hot-rolled strip. When the crown value of the hot-rolled strip is in the range of [15, 45], the value of A is [51.21, 153.64]. Based on the actual strip shape, adjust the bending force of the working roller of the leveling machine. When the strip width is ≤1380mm, the bending force is 10±5 tons; when the strip width is 1380mm<1480mm, the bending force is 15±5 tons; when the strip width is 1480mm<1580mm, the bending force is 20±5 tons.

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