Method for improving yield of thick plate

Abstract

According to the method for improving the yield of the thick plate, in the thick plate rolling process section, production line optimization of the rolling process section is established, and the rolled steel plate is in a concave special shape with the head and the tail being roughly symmetrical. According to the method for improving the yield of the thick plate, a scheme with universality for improving the yield is provided, the limitation of other schemes in the prior art is overcome, and the method has the value of universal popularization.

Description

Technical Field

[0001] The invention belongs to the field of thick plate production, and in particular relates to a method for improving the yield rate of thick plates. Background Art

[0002] The optimization of the yield rate runs through the entire process from coking, ironmaking, steelmaking to rolling. That is, the improvement of the yield rate can be achieved by establishing corresponding measures in any of these process stages. In the rolling process stage, some medium and thick plate production lines are equipped with vertical roller mills, which are arranged very close to the main rolling mill. Some are arranged in front of the main rolling mill, and some are arranged behind the main rolling mill. Figure 1 , 2 The vertical roller mill is mainly used to control the plane shape of the steel plate, correct the uneven width that is easy to occur in the forming and widening stages, and perform vertical roller edge rolling in the length direction after forming and the width direction after widening to reduce the uneven deformation of the steel plate in the length and width directions and reduce the shearing amount of the rolled steel plate.

[0003] The specific process of the existing common thick plate plane shape control is as follows: first, the target thickness of the steel plate in the rolling stage (forming, widening and finishing stage) is calculated according to the instructions of the production control system (L3 system) (rolling method, slab size, steel plate size). If there is a vertical roller mill, the effective width reduction amount of the steel plate required by the vertical rollers in the forming stage and the widening stage is calculated at the same time; then, this width reduction amount is taken into account in the process of determining the final thickness of the widening stage, and the steel transfer thickness is adjusted so that the width of the steel plate after the widening is expected to be the rolling target width + the expected width reduction amount. The vertical rollers perform side rolling according to the expected width reduction amount to ensure that the steel plate reaches the rolling target width. The above adjustments are automatically completed by the mathematical model in the process control system (L2 system).

[0004] The shortcomings of the existing general technology are that, although there are plane shape control models and vertical roll rolling models, the plane shapes of steel plates after rolling are very different, and it is impossible to truly roll out rectangular steel plates, but only close to rectangles. There are three reasons: 1) The size of the slab is limited, while the size of the corresponding rolled steel plate is infinite, and the model calculation accuracy is not enough; 2) Due to the difference in deformation along the rolling direction, there are differences between the head and tail of the rolled steel plate; 3) There are differences between the head and tail of the steel plate after horizontal rolling after the vertical roll rolling side. For these shortcomings, the actual improvement schemes are usually the following two: one is to improve the accuracy and reliability of the mathematical modeling of the model and improve the calculation accuracy, and the other is to control the abnormalities of the process manually. However, the improvement scheme based on the model usually has extremely high limitations and is not universally compatible; and the scheme based on manual control abnormalities often cannot be prepared to grasp the angle of regulation, which will cause the width of the rolled steel plate to be greater than the target width once the angle control is too large, thereby causing the problem that the final length of the rolled steel plate is insufficient.

[0005] The invention application with application number: CN2011102061684 discloses "a thick plate rolling method", including a forming rolling stage, a widening rolling stage and a finishing rolling stage. Through three rotations, the slab uses forming MAS rolling once and widening MAS rolling once to control the planar shape of the slab during the rolling process, which greatly improves the planar shape of the steel plate and makes the shape of the steel plate after rolling close to a rectangle, thereby improving the steel plate yield rate.

[0006] The invention application with application number: CN201310295698.X discloses "a method for controlling the width of the head and tail of a steel plate with a large aspect ratio". The method includes a forming stage, a widening stage and a longitudinal rolling stage. The forming stage has one rolling pass, the reduction is 15 to 35 mm, the step reduction depth h is calculated by h = 2.3 × (B / B'), and the rolling speed V is calculated by V = (ba) × (VHGC / h) / 2. The method controls the reduction, step thickness curve and rolling speed of the rough rolling forming pass. When rolling a steel plate with a large aspect ratio, the method can improve the followability of the step thickness curve in the forming stage with the set curve while maintaining a high rolling rhythm of the rough rolling mill, and reduce the difference between the width of the head and tail and the width of the middle of the steel plate with a large aspect ratio, thereby reducing the edge trimming amount of the steel plate and improving the yield rate of the steel plate.

[0007] The invention application with application number: CN2018114501418 discloses "a method for controlling the head and tail width of a steel plate with a large width ratio". The method includes the following steps: after heating and descaling the right-angle continuous casting billet, vertical-flat rollers are used for longitudinal pre-forming rolling, so that the full roller indentation line on the narrow surface of the continuous casting billet is flipped to the upper and lower surfaces through widening, and then the steel is turned for transverse widening rolling. After the widening is completed, the steel is turned again for longitudinal forming rolling.

[0008] The invention application with application number: CN202210963990.3 discloses "a method for improving the rectangularity of the transverse section of a wide and thick steel plate", comprising: (1) using a wide and thick plate rolling mill with a roughing mill and a finishing mill as the double frames, and completing the widening rolling of the steel plate on the roughing mill; (2) when the slab is out of the furnace, the temperature difference between the upper and lower surfaces does not exceed 30°C; (3) the diameter of the upper working roll of the roughing mill is 25 to 40 mm larger than that of the lower working roll; (4) when the steel plate is rolled in the widening stage, the bite speed is set to 0.5 m / s and the bite length is set to 0.5 m; the linear speed of the lower working roll in the steel plate bite stage is 3% to 8% faster than the linear speed of the upper working roll; (5) when the steel plate is rolled in the widening stage, descaling is performed 1 to 2 times, and the descaling method is positive descaling; (6) when the steel plate is rolled in the widening stage, the torque is set to 80% of the designed rated torque of the rolling mill. Summary of the invention

[0009] In order to solve the above problems, a universal solution for improving the yield rate is provided. The present invention provides a method for improving the yield rate of thick plates, and the technical solution thereof is specifically as follows:

[0010] A method for improving the yield rate of thick plates,

[0011] In the thick plate rolling process section, by optimizing the production line of the rolling process section, the steel plate is formed into a concave shape that is roughly symmetrical at the head and tail after rolling.

[0012] Further,

[0013] The above-mentioned production line optimization for the rolling process section specifically includes the following steps:

[0014] S1: For the situation of setting up rollers in the finishing section, the pitting process parameter setting is issued before the current type of slab enters the rolling mill for rolling;

[0015] S2: After the slab has completed the rolling of the forming section and the rolling of the widening section in sequence, it enters the finishing section in a manner such that the widening end position is controlled on the opposite side of the vertical roll.

[0016] Further,

[0017] The control of the end position of the widening at the opposite side of the vertical roller in step S2 is achieved by establishing an optimized distribution of the pass reduction, as follows:

[0018] The optimal distribution of reduction is established with the minimum reduction as the constraint condition. When the reduction after the optimal distribution does not meet the constraint condition, the end position of widening is controlled on the opposite side of the vertical roller by adding an empty pass after widening. Otherwise, the end position of widening is controlled on the opposite side of the vertical roller through pass optimization.

[0019] The method of improving the yield rate of thick plates of the present invention firstly directs the improvement method to the thick plate rolling process section, and secondly, by establishing the production line optimization of the rolling process section, a universal solution for improving the yield rate is established, which overcomes the limitations of other previous solutions and has the value of universal promotion. The production line optimization further directs to the finishing section, which is achieved by controlling the widening end position on the opposite side of the vertical roller by establishing the pit digging control coordination under the premise of setting the vertical roller in the finishing section. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 , 2 It is a schematic diagram of the layout of the vertical rolling mill and the main rolling mill in the background technology of the present invention;

[0021] in,

[0022] Figure 1 It is a schematic diagram of the layout of the proximity vertical roll mill arranged in front of the main rolling mill;

[0023] Figure 2 It is a schematic diagram of the layout of the proximity vertical roll mill arranged behind the main rolling mill;

[0024] Figure 3 It is a schematic diagram of the steps of establishing production line optimization for the rolling process section in the present invention. DETAILED DESCRIPTION

[0025] Below, a method for improving the yield rate of thick plates of the present invention is further described in detail according to the accompanying drawings and specific implementation methods of the specification.

[0026] In order to form a clearer understanding of this technical solution, the technical principle and process of this technical solution are explained as follows. Figure 3 conduct.

[0027] Factors affecting the yield rate include the transverse rolling ratio (i.e., width ratio), longitudinal rolling ratio in the length direction, reduction ratio, contact arc length of the deformation zone, etc. The transverse rolling ratio and the rolling ratio in the length direction are ultimately projected as the edge shear amount and head and tail shear amount of the steel plate. So, in other words, the shear amount and reduction ratio of the steel plate, the contact arc length of the deformation zone, etc. are factors affecting the yield rate. Among these influencing factors, the head and tail shear amount accounts for a large proportion, and under normal circumstances, the head and tail plate shapes generally present two types of concave and convex shapes. The reasons for the difference in these two shapes point to the width ratio and rolling extension ratio. The influence of the width ratio and rolling extension ratio on the plate shape follows the following principle: when the width ratio is large and the rolling ratio in the length direction is small, the head and tail ends of the rolled piece are concave, and the edges are convex; when the width ratio is small and the rolling ratio in the length direction is large, the head and tail ends of the rolled piece are convex, and the edges are concave. Under such circumstances, how to establish a solution that is similar to a production line upgrade to form a solution that breaks through technical limitations and achieves universal applicability to improve the yield rate is the original intention and starting point of this technical solution. To achieve this goal, this technical solution first optimizes the rolling process section, and then uses the production line with vertical rollers in the finishing section to determine the optimization plan as follows: first establish pit control to solve the convexity problem of the head and tail of the steel plate; then control the end position of the widening of the slab after the widening process section to the opposite side of the vertical roller. Through the cooperation of the two, the head and tail shapes of the steel plate are controlled to be roughly symmetrical concave, thereby reducing the shearing amount of the head and tail, serving the improvement of the yield rate.

[0028] In order to control the shape of the strip, a pit control is established for the forming section and the width extension section, so that there is a thickness deviation along the rolling length direction of the steel plate after the forming stage and the width extension stage, which is called pitting. It is divided into pitting in the length direction and pitting in the width direction. The pitting in the length direction is used to control and reduce the edge pattern, and the pitting in the width direction is used to solve the head and tail convexity. The pitting of this technical solution is directed at the control of the head and tail strip shape. The end position of the width extension mentioned above is on the opposite side of the vertical roll, which means that: if the vertical roll is set in front of the horizontal roll, the end position of the width extension is controlled to be behind the rolling mill, and if the vertical roll is set behind the horizontal roll, the end position of the width extension is controlled to be in front of the rolling mill. The rolling mill here refers to a rolling mill internally equipped with a forming rolling section, a width extension rolling section and a finishing rolling section. The end position of the width extension after the slab passes through the width extension process section is controlled on the opposite side of the vertical roll, which is completed by establishing an optimal distribution of the reduction per pass. However, a problem of the minimum reduction per pass constraint will be encountered here. Therefore, the specific optimal distribution plan is established under the constraint of the minimum reduction per pass. Specifically, when the reduction per pass after the optimal distribution does not meet the constraint conditions, the end position of the width extension is controlled on the opposite side of the vertical roll by adding an empty pass after the width extension. When the reduction per pass after the optimal distribution meets the constraint conditions, the end position of the width extension is controlled on the opposite side of the vertical roll through pass optimization. It should be noted that although this technical solution is set with the original intention and purpose of breaking through limitations and achieving universal applicability, there are still limitations in the applicable occasions, and these limitations are reflected in the following two aspects: 1. It is only applicable to production lines with vertical rolls in the finishing section; 2. It is only applicable to rolling production lines with a width extension stage. The specific implementation process is as follows:

[0029] Before the current type of slab enters the rolling mill for rolling, the pitting process parameters are set, and the distribution of the reduction per pass and the setting of the rolling passes are completed. The rolling process formed accordingly is divided into the following two types:

[0030] 1. The pass optimization can be completed through the optimal distribution of the reduction per pass, so that the end position of the width extension of the slab is on the opposite side of the vertical roll. The rolling process at this time is as follows: First, the rolling in the length direction is completed through the forming stage; then it rotates 90 degrees to enter the width extension stage, and the formed rolled piece is width extended and rolled to obtain the rough edge width of the finished steel plate; then it rotates 90 degrees back to the original length direction, and the steel plate reaches the thickness required for the finished steel plate through the finishing section.

[0031] 2. The pass optimization cannot be completed by the optimized distribution of the reduction amount, so that the end position of the slab width expansion is on the opposite side of the vertical rolls. The rolling process at this time is as follows: First, the rolling in the length direction is completed through the forming stage; then it rotates 90 degrees to enter the width expansion stage, and the formed rolled piece is width-expanded to obtain the rough edge width of the finished steel plate. After the width expansion pass is completed, an empty pass operation is carried out to control the end position of the width expansion on the opposite side of the vertical rolls; then it rotates 90 degrees back to the original length direction, and the steel plate reaches the required thickness of the finished steel plate through the finishing rolling section.

[0032] Embodiment

[0033] Suppose a vertical roll mill in a heavy plate plant is in front of the horizontal mill, and the slab dimensions and the rolled steel plate dimensions are as follows:

[0034] Slab dimensions: 250*1900*2881mm;

[0035] Steel plate dimensions: 16.51*2.54*32000mm.

[0036] The calculation results of the unoptimized rolling passes are as follows:

[0037] The number of forming rolling passes: 1;

[0038] The number of width expansion rolling passes: 3, the pit depth: 4.71mm, and the end position of the width expansion is on the same side of the vertical roll mill.

[0039] The vertical rolls are used for one pass, the additional width of the vertical rolls: 13.36mm, the abnormal length of the head of the rolled steel plate: 381mm, and the abnormal length of the tail: 492mm.

[0040] After optimization:

[0041] The number of forming rolling passes: 1;

[0042] The number of width expansion rolling passes: 4, the pit depth: 3.7mm, and the end position of the width expansion is on the opposite side of the vertical roll mill.

[0043] The vertical rolls are used for one pass, the additional width of the vertical rolls: 13.36mm, the abnormal length of the head of the rolled steel plate: 291mm, and the abnormal length of the tail: 320mm.

Claims

1. A method for improving the yield rate of thick plates, Features: In the thick plate rolling process section, by optimizing the production line of the rolling process section, the steel plate is formed into a concave shape that is roughly symmetrical at the head and tail after rolling.

2. A method for improving the yield rate of thick plates according to claim 1, Features: The above-mentioned production line optimization for the rolling process section specifically includes the following steps: S1: For the situation of setting up rollers in the finishing section, the pitting process parameter setting is issued before the current type of slab enters the rolling mill for rolling; S2: After the slab has completed the rolling of the forming section and the rolling of the widening section in sequence, it enters the finishing section in a manner such that the widening end position is controlled on the opposite side of the vertical roll.

3. A method for improving the yield rate of thick plates according to claim 2, Features: The control of the end position of the widening at the opposite side of the vertical roller in step S2 is achieved by establishing an optimized distribution of the pass reduction, as follows: The optimal distribution of reduction is established with the minimum reduction as the constraint condition. When the reduction after the optimal distribution does not meet the constraint condition, the end position of widening is controlled on the opposite side of the vertical roller by adding an empty pass after widening. Otherwise, the end position of widening is controlled on the opposite side of the vertical roller through pass optimization.

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