A method for eliminating flat single-side waves of cold-rolled plate with cover setback Rm<340MPa

Abstract

The present invention relates to a method for eliminating single-edge wave during the flattening of cold-rolled steel sheets with a hood backlash Rm < 340 MPa, comprising the following steps: (1) optimizing production planning to ensure the incoming material temperature of the flattening mill; (2) determining the inlet tension and outlet tension of the flattening mill; (3) controlling the amount of roll bending according to the strip-threading rolling force during the speed increase of the flattening mill; (4) controlling the speed of the strip; and (5) controlling the strip shape while ensuring stable strip output. While ensuring that the incoming material temperature and outlet tension of the flattening mill are set to appropriate values, the present invention adjusts the amount of roll bending and the tilt state of the working rolls, ultimately ensuring the quality of the strip shape after flattening and effectively eliminating the occurrence of single-edge wave defects.

Description

Technical Field

[0001] The invention relates to the field of cold rolling technology, in particular to a method for eliminating single-side waves of a cold-rolled plate with a tensile strength Rm less than 340 MPa after hood withdrawal. Background Art

[0002] Cold rolling is a process that uses hot-rolled steel coils as raw material, pickling to remove the oxide scale, and then cold rolling. The cold rolling production process generally includes raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), and finishing. The finishing process usually includes inspection, shearing, straightening (flattening), printing, sorting and packaging.

[0003] During cold rolling, the steel strip undergoes several rolling passes, which causes the strip to stretch and become thinner. This deformation causes the steel strip to undergo work hardening, which is the so-called "cold work hardening". As the reduction rate (deformation amount) during cold rolling increases, the tensile strength and yield point of the steel strip also increase, while its elongation and deformation properties decrease significantly. Therefore, the finished cold-rolled steel coil cannot be used directly for cold bending or stamping, and needs to undergo recrystallization annealing to eliminate the "cold work hardening" of the steel strip. The purpose of the leveling process includes the following three aspects: 1) Eliminate the yield platform that exists in the steel strip after recrystallization annealing to prevent tensile strain during deep processing; 2) Increase the strength limit of the material, reduce the yield point, and expand the range of plastic processing; 3) Make the surface of the steel strip obtain the required roughness and gloss, and correct the shape of the plate.

[0004] Cold-rolled strip is characterized by uniform thickness, aesthetically pleasing surface, good shape, high dimensional accuracy, and excellent formability. It is widely used in the automotive, light industry, and electrical industries. Its product quality (including appearance) directly impacts subsequent use. Shape defects can directly impact the product's yield and final quality.

[0005] The single-side wave defect is the main defect produced in the leveling process. The main reason for its occurrence is that the incoming material has serious side waves, the roll curve is small during leveling, or the bending roll inclination is improperly adjusted, which manifests as a single-side wave on one side of the strip after leveling. For the single-side wave defect, it is usually eliminated or alleviated by adjusting the bending roll inclination, adjusting the bending roll, or increasing the roll curve.

[0006] At present, the shape of cold-rolled strip is mainly controlled by the operator's experience, and the shape adjustment methods of different operators vary greatly, resulting in uneven shape control levels, which directly affects product quality and causes an increase in single-side wave defects after leveling, bringing unnecessary economic losses to the company. Summary of the Invention

[0007] The present invention provides a method for eliminating single-side waves in the flattening of cold-rolled plates with a hood retreat Rm < 340MPa. While ensuring that the incoming material temperature, inlet tension and outlet tension setting values ​​of the flattening unit are appropriate, the bending roll amount and the inclination state of the working rolls are adjusted to ultimately ensure the plate shape quality of the strip after flattening and effectively eliminate the occurrence of single-side wave defects.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for eliminating flattening single-side waves of cold-rolled plates with a hood setback Rm < 340 MPa, comprising the following steps:

[0010] (1) Optimize production planning to ensure the incoming material temperature of the skin-pass mill; after the cold-rolled strip is annealed in a bell-type furnace, it is naturally cooled to 40-45°C before entering the skin-pass mill;

[0011] (2) Determine the inlet tension and outlet tension of the leveling unit; the inlet tension is controlled at 30-45kN, and the outlet tension is controlled at 30-65kN;

[0012] (3) During the speed increase of the skin-pass mill, the roll bending amount is controlled according to the strip-threading rolling force; if the strip-threading rolling force F≤2.5MN, the roll bending amount is controlled at 8% to 12% during the speed increase; if the strip-threading rolling force is 2.5MN<F<4MN, the roll bending amount is controlled at 45% to 55% during the speed increase; if the strip-threading rolling force F≥4MN, the roll bending amount is controlled at 95% to 100% during the speed increase;

[0013] (4) Speed ​​control of the strip steel: the speed of the strip steel is controlled by the step-by-step speed increase method during leveling, and the maximum speed of the strip steel is controlled within 800 m / min;

[0014] (5) Control the strip shape while ensuring stable output of the strip; when the strip reaches and stabilizes at the maximum speed, adjust the inclination value or bending amount of the working roll by comparing the flatness meter curve at the outlet side of the leveling unit, observe the leveling liquid state on the strip surface at the inlet side of the leveling unit, and adjust the bending amount of the working roll to spread the leveling liquid flat on the strip surface.

[0015] In the process (2), the outlet tension of the leveling unit is determined according to the material and thickness of the incoming material, as shown in the following table:

[0016]

[0017] The numerical unit of outlet tension in the above table is kN. The relationship between strip width and outlet tension is: as the strip width increases, the outlet tension also increases; conversely, as the strip width decreases, the outlet tension decreases. Specifically, for every 100mm increase in strip width, the outlet tension increases by 4 to 6 kN; for every 100mm decrease in strip width, the outlet tension decreases by 4 to 6 kN.

[0018] In the process (4), the step-by-step speed-up method is specifically as follows: along the running direction of the strip, within the length range of L≤50m, the strip speed is controlled at 90-110m / min; within the range of 50m<L≤100m, the strip speed is controlled at 180-220m / min; within the range of 100m<L≤200m, the strip speed is controlled at 380-420m / min; within the range of 200m<L≤300m, the strip speed is controlled at 580-620m / min; within the range of L>300m, the strip speed is controlled at 780-800m / min.

[0019] In the process (5), if the shape meter curve is higher on the left and lower on the right, it means that the elongation on the transmission side is greater than the elongation on the operating side. At this time, the inclination value of the working roll is increased to make the inclination value positive; if the shape meter curve is higher on the right and lower on the left, it means that the elongation on the transmission side is less than the elongation on the operating side. At this time, the inclination value of the working roll is reduced to make the inclination value negative; if the shape meter curve is convex upward, it means that the elongation in the middle of the strip is greater than the elongation on both sides. At this time, the bending amount of the working roll is reduced; if the shape meter curve is convex downward, it means that the elongation on both sides of the strip is greater than the elongation in the middle. At this time, the bending amount of the working roll is increased; when reducing and increasing the bending amount, refer to the shape meter curve until the shape meter curve is adjusted to be symmetrical on the left and right and nearly coincides with the horizontal line.

[0020] In the process (5), the state of the leveling liquid after spraying on the strip surface is observed in the frame on the inlet side of the leveling unit; if there is no obvious accumulation of leveling liquid on the strip surface, the bending amount of the working roll is increased; if the leveling liquid accumulated on the strip surface fluctuates violently, the bending amount of the working roll is reduced until the leveling liquid is evenly spread on the strip surface.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] While ensuring that the incoming material temperature, inlet tension and outlet tension setting values ​​of the leveling mill are appropriate, by adjusting the bending roll amount and the inclination state of the working roll, the plate shape quality of the strip after leveling is ultimately guaranteed, and the occurrence of single-side wave defects is effectively eliminated. DETAILED DESCRIPTION

[0023] From the perspective of compression deformation, the essence of the skin-pass process is a secondary cold rolling deformation to adjust the elongation. The normal operating procedures of the skin-pass mill are as follows:

[0024] The strip enters the mill stand over the entry tensioning rollers. Strip thicker than 1.5 mm can be loaded directly onto the stand without passing through the entry tensioning device. The strip passes through the pass line rollers and guide rollers to the exit side, where it is wound by a threading table and belt winder, and then coiled onto the exit tension winder. After two or three turns of winding are completed and tension is established, the threading table retracts, the buffer rollers rise, and the belt winder retracts. The work roll gap closes completely, and entry tension is established. Once full entry and exit tension is established, the mill accelerates to the specified rolling speed.

[0025] During the skin-passing process, encoders mounted on the entry tensioning roll and exit guide rolls measure and control the elongation. Furthermore, if the rolling force is maintained at a predetermined constant level, the mill can operate in a rolling force control mode. Strip shape is controlled by adjusting the positive and negative bending of the work rolls and the mill's guide (tilting) control.

[0026] The reduction during tempering is so small (only micrometers), that thickness gauges can barely measure the strip thickness deviation between the exit and entry sides of the tempering mill. Therefore, measuring strip elongation is often used as an equivalent measure of thickness variation. Elongation regulation is a crucial aspect of tempering process quality control. Elongation is the sole deformation indicator in tempering rolling and plays a crucial role in ensuring the strip's mechanical properties and meeting customer requirements.

[0027] The method for eliminating single-side wave in cold-rolled steel sheet with hood retreat Rm < 340 MPa described in the present invention adopts the following measures in the flattening process of cold-rolled steel strip:

[0028] (1) Optimize production planning to ensure the incoming material temperature of the leveling mill; after the cold-rolled strip is annealed in a bell-type furnace, it enters the leveling mill when it is naturally cooled to 40-45°C.

[0029] The incoming materials to the leveling unit are usually strip steel that has been annealed in a bell furnace and cooled at ambient temperature. The present invention requires that the temperature of the incoming materials to the leveling unit (the cooled strip steel) cannot be lower than 40°C. If the incoming material temperature is lower than 40°C, the plasticity of the strip steel will be greatly reduced, the deformation amount will be reduced, the elimination of the wave shape will be adversely affected, and the possibility of roller marks will be increased. At the same time, the present invention controls the upper limit of the incoming material temperature of the leveling unit to within 45°C. When the incoming material temperature is higher than 45°C, the strip steel after leveling is prone to thermal folding, and this defect will not be eliminated after re-leveling. Therefore, the temperature of the strip steel when entering the leveling unit should be controlled between 40 and 45°C.

[0030] (2) Determine the inlet tension and outlet tension of the leveling unit; the inlet tension is controlled at 30~45kN, and the outlet tension is controlled at 30~65kN.

[0031] The inlet tension and outlet tension of the leveling unit should not be too large, because the strip cannot reflect the true plate shape under excessive tension. At the same time, excessive tension will stretch the strip and produce mid-wave defects that are difficult to eliminate.

[0032] The relationship between the material and thickness of the incoming material and the outlet tension of the leveling unit is shown in the following table (the unit of outlet tension is kN):

[0033]

[0034] The relationship between strip width and outlet tension is: as the strip width increases, the outlet tension also increases, and conversely, as the strip width decreases, the outlet tension decreases; specifically: for every 100mm increase in strip width, the outlet tension increases by 4 to 6kN; for every 100mm decrease in width, the outlet tension decreases by 4 to 6kN.

[0035] (3) During the speed increase of the skin-pass mill, the roll bending amount is controlled according to the strip-threading rolling force; if the strip-threading rolling force F≤2.5MN, the roll bending amount is controlled at 8% to 12% during the speed increase; if the strip-threading rolling force is 2.5MN<F<4MN, the roll bending amount is controlled at 45% to 55% during the speed increase; if the strip-threading rolling force F≥4MN, the roll bending amount is controlled at 95% to 100% during the speed increase;

[0036] During the speed-up process of the leveling mill, attention should be paid to the changes in the leveling rolling force. By controlling the bending amount in combination with the threading rolling force, the edge waves caused by the increase in rolling force during the speed-up process can be effectively controlled.

[0037] (4) Speed ​​control of the strip; during leveling, the strip speed is controlled by the step-by-step speed-increasing method, and the maximum speed of the strip is controlled within 800 m / min; during the leveling process, the speed of the strip is controlled by the step-by-step speed-increasing method, which is conducive to adjusting the plate shape.

[0038] The specific steps of the step speed increase method are as follows: along the running direction of the strip, the strip speed is controlled at 90-110m / min within the length range of L≤50m, the strip speed is controlled at 180-220m / min within the length range of 50m<L≤100m, the strip speed is controlled at 380-420m / min within the length range of 100m<L≤200m, the strip speed is controlled at 580-620m / min within the length range of 200m<L≤300m, and the strip speed is controlled at 780-800m / min within the length range of L>300m.

[0039] (4) Control the flatness and leveling liquid state under the premise of ensuring stable output of the strip; when the strip reaches and stabilizes at the maximum speed, adjust the inclination value or bending amount of the working roll by comparing the flatness meter curve on the outlet side of the leveling unit, observe the leveling liquid state on the strip surface on the inlet side of the leveling unit, and adjust the bending amount of the working roll to make the leveling liquid spread flat on the strip surface.

[0040] During the flatness adjustment process, the actual operating status of the steel plate must be constantly monitored to ensure a stable strip surface at the exit of the leveling mill and no noticeable edge jitter. Dynamic adjustments are made by combining the actual operating status of the steel plate, comparing it with the flatness meter curve, and observing the leveling fluid concentration to ultimately ensure the flatness of the finished strip.

[0041] After the strip stabilizes at maximum speed, observe the actual strip shape at the exit of the skin-pass mill and compare it with the shape meter curve. The shape meter curve reflects the distribution of elongation defects per unit length along the transverse direction of the strip. If the shape meter curve is higher on the left and lower on the right, it indicates that the elongation on the drive side is greater than that on the operating side. In this case, the work rolls need to be tilted more toward the operating side, that is, the tilt value should be increased to a positive value. If the shape meter curve is higher on the right and lower on the left, it indicates that the elongation on the drive side is less than that on the operating side. In this case, the work rolls need to be tilted more toward the drive side, that is, the tilt value should be reduced to a negative value. If the shape meter curve is convex upward, it indicates that the elongation in the center of the strip is greater than that on the sides. In this case, the work roll bending amount should be reduced. If the shape meter curve is convex downward, it indicates that the elongation on the sides is greater than that in the center. In this case, the work roll bending amount should be increased. When reducing and increasing the roll bending amount, refer to the shape meter curve until the shape meter curve is symmetrical and nearly coincides with the horizontal line.

[0042] While observing the plate shape at the outlet side of the leveling machine, also observe the plate shape at the inlet side of the leveling machine at the same time; observe the state of the leveling liquid after spraying on the strip surface into the frame at the inlet side of the leveling machine; if there is no obvious leveling liquid accumulation on the strip surface, increase the bending amount of the working roll; if the leveling liquid accumulated on the strip surface fluctuates violently, reduce the bending amount of the working roll until the leveling liquid is evenly spread on the strip surface.

[0043] By taking the above technical measures, the occurrence of unilateral wave defects can be effectively eliminated.

[0044] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for eliminating unilateral wave of cold-rolled plate with cover retreat Rm<340MPa, characterized in that: The process includes the following: (1) Optimize production planning to ensure the incoming material temperature of the skin-pass mill; after the cold-rolled strip is annealed in a bell-type furnace, it is naturally cooled to 40-45°C before entering the skin-pass mill; (2) Determine the inlet tension and outlet tension of the leveling unit; the inlet tension is controlled at 30-45kN, and the outlet tension is controlled at 30-65kN; (3) During the speed increase of the skin-pass mill, the roll bending amount is controlled according to the strip-threading rolling force; if the strip-threading rolling force F≤2.5MN, the roll bending amount is controlled at 8% to 12% during the speed increase; if the strip-threading rolling force is 2.5MN<F<4MN, the roll bending amount is controlled at 45% to 55% during the speed increase; if the strip-threading rolling force F≥4MN, the roll bending amount is controlled at 95% to 100% during the speed increase; (4) Speed ​​control of the strip steel: the speed of the strip steel is controlled by the step-by-step speed increase method during leveling, and the maximum speed of the strip steel is controlled within 800 m / min; (5) Control the strip shape while ensuring stable output of the strip; when the strip reaches and stabilizes at the maximum speed, adjust the inclination value or bending amount of the working roll by comparing the flatness meter curve at the outlet side of the leveling unit, observe the leveling liquid state on the strip surface at the inlet side of the leveling unit, and adjust the bending amount of the working roll to spread the leveling liquid flat on the strip surface.

2. A method for eliminating single-side waves of cold-rolled sheet with cover retreat Rm < 340MPa according to claim 1, characterized in that: In the process (2), the outlet tension of the leveling unit is determined according to the material and thickness of the incoming material, as shown in the following table: The numerical unit of outlet tension in the above table is kN. The relationship between strip width and outlet tension is: as the strip width increases, the outlet tension also increases; conversely, as the strip width decreases, the outlet tension decreases. Specifically, for every 100mm increase in strip width, the outlet tension increases by 4 to 6 kN; for every 100mm decrease in strip width, the outlet tension decreases by 4 to 6 kN.

3. The method for eliminating single-side wave of cold-rolled plate with cover retreat Rm<340MPa according to claim 1, characterized in that: In the process (4), the step-by-step speed-up method is specifically as follows: along the running direction of the strip steel, within the range of length L≤50m, the strip steel speed is controlled at 90-110m / min; within the range of 50m<L≤100m, the strip steel speed is controlled at 180-220m / min; within the range of 100m<L≤200m, the strip steel speed is controlled at 380-420m / min; In the range of 200m<L≤300m, the strip speed is controlled at 580~620m / min; in the range of L>300m, the strip speed is controlled at 780~800m / min.

4. The method for eliminating single-side wave of cold-rolled plate with cover retreat Rm < 340MPa according to claim 1, characterized in that: In the process (5), if the shape meter curve is higher on the left and lower on the right, it means that the elongation on the transmission side is greater than the elongation on the operating side. At this time, the inclination value of the working roll is increased to make the inclination value positive; if the shape meter curve is higher on the right and lower on the left, it means that the elongation on the transmission side is less than the elongation on the operating side. At this time, the inclination value of the working roll is reduced to make the inclination value negative; if the shape meter curve is convex upward, it means that the elongation in the middle of the strip is greater than the elongation on both sides. At this time, the bending amount of the working roll is reduced; if the shape meter curve is convex downward, it means that the elongation on both sides of the strip is greater than the elongation in the middle. At this time, the bending amount of the working roll is increased; when reducing and increasing the bending amount, refer to the shape meter curve until the shape meter curve is adjusted to be symmetrical on the left and right and nearly coincides with the horizontal line.

5. The method for eliminating single-side wave of cold-rolled plate with cover retreat Rm < 340MPa according to claim 1, characterized in that: In the process (5), the state of the leveling liquid after spraying on the strip surface is observed in the frame on the inlet side of the leveling unit; if there is no obvious accumulation of leveling liquid on the strip surface, the bending amount of the working roll is increased; If the leveling liquid gathered on the strip surface fluctuates violently, reduce the bending amount of the working roll until the leveling liquid is evenly spread on the strip surface.

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