Method for eliminating flat unilateral waves of cold-rolled sheet with Rm smaller than 340 MPa after cover retreating

Abstract

The invention relates to a method for eliminating flattening unilateral waves of a cold-rolled sheet with Rm smaller than 340 MPa after cover withdrawal, which comprises the following steps of: (1) optimizing planned production scheduling, and ensuring the incoming material temperature of a flattening unit; (2) determining inlet tension and outlet tension of the temper mill unit; (3) controlling the roll bending amount according to the threading rolling force in the speed increasing process of the temper mill unit; (4) controlling the speed of the strip steel; and (5) controlling the plate shape on the premise of ensuring stable output of the strip steel. Under the condition that the incoming material temperature and the outlet tension set value of the leveling unit are proper, the plate shape quality of the leveled strip steel is finally guaranteed by adjusting the roll bending amount and the inclination state of the working roll, and the unilateral wave defect is effectively eliminated.

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 of cold rolling hot rolled steel coils after pickling to remove the oxide scale. The cold rolling production process generally includes raw material preparation, pickling, rolling, degreasing, annealing (heat treatment), finishing, etc., among which the finishing process usually includes inspection, shearing, straightening (flattening), printing, classification and packaging.

[0003] During the cold rolling of the steel strip, it is rolled several times, so that the steel strip is extended and thinned. This deformation causes the work hardening of the steel strip, which is the so-called "cold work hardening". As the reduction rate (deformation) during cold rolling increases, the tensile strength and yield limit of the steel strip also increase, while its elongation and deformation performance decrease significantly. Therefore, the finished cold-rolled steel coil cannot be directly used for cold bending or stamping, and needs to be recrystallized annealed to eliminate the "cold work hardening" of the steel strip. The purpose of the flattening process includes the following three aspects: 1) Eliminate the yield platform of the steel strip after recrystallization annealing to prevent tensile strain during deep processing; 2) Increase the strength limit of the material, reduce the yield limit, 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] The characteristics of cold-rolled strip steel are uniform thickness, beautiful surface, good plate shape, high dimensional accuracy and excellent forming performance. Cold-rolled plates are widely used in the fields of automobiles, light industry, and electrical appliances. The product quality (including appearance quality) directly affects the subsequent use. Plate shape defects will directly affect the yield rate and final quality of the product.

[0005] The single-sided wave defect is the main defect caused by the leveling process. It is mainly caused by severe edge waves of the incoming material, small roll curve or improper adjustment of the bending roll inclination during leveling, which manifests as a single-sided wave on one side of the strip after leveling. For the single-sided wave defect, it is usually eliminated or reduced by adjusting the inclination of the bending roll, 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-sided 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. Under the condition that the incoming material temperature, inlet tension and outlet tension setting values ​​of the flattening unit are ensured to be 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 flat single-side waves of cold-rolled plates with a hood retreat Rm < 340MPa, comprising the following steps:

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

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

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

[0013] (4) Speed ​​control of the strip: During leveling, the speed of the strip is controlled by the step-by-step speed increase method, and the maximum speed of the strip 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 shape meter curve at the outlet side of the flattening unit, observe the state of the flattening liquid on the strip surface at the inlet side of the flattening unit, and adjust the bending amount of the working roll to make the flattening liquid spread evenly 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 the 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 6kN; for every 100mm decrease in strip width, the outlet tension decreases by 4 to 6kN.

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

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

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

[0022] Under the premise of ensuring that the incoming material temperature, inlet tension and outlet tension setting values ​​of the leveling unit 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-sided wave defects is effectively eliminated. DETAILED DESCRIPTION

[0023] From the perspective of pressing deformation, the essence of the leveling process is a secondary cold rolling deformation to adjust the elongation. The normal operating procedures of the leveling unit are as follows:

[0024] The strip enters the mill stand through the entry tensioning roller. Strips with a thickness of more than 1.5 mm can be directly put on the stand without passing through the entry tensioning device. The strip enters the exit side through the rolling line roller and the guide roller, and the strip head is coiled on the exit tension coiler through the strip threading table and the belt auxiliary coiler. After completing 2-3 turns of coiling and establishing tension, the strip threading table shrinks, the buffer roller rises, and the belt auxiliary coiler retracts. The working roll gap is fully closed and the entry tension is established. After all the entry and exit tensions are established, the mill begins to accelerate to the specified rolling speed.

[0025] During the leveling process, the elongation is measured and controlled by encoders installed on the entry tensioning roll and the exit guide roll. In addition, if the rolling force is kept at a preset constant level, the rolling mill can adopt the rolling force control mode. The strip shape is controlled by adjusting the positive and negative bending rolls of the working rolls and the mill guide (tilting) control.

[0026] The amount of reduction during flattening is very small (only micrometer level), and the thickness deviation of the strip steel at the outlet and inlet sides of the flattening unit can hardly be measured by a thickness gauge. Therefore, the elongation of the strip steel is usually measured as an equivalent value for measuring its thickness change. Elongation adjustment is an important part of the quality control of the flattening process. Elongation is the only deformation index of flattening rolling, and plays an important role in ensuring the mechanical properties of the strip steel and meeting user requirements.

[0027] The method for eliminating the flattening single-side wave of the cold-rolled plate with a hood retreat Rm < 340MPa described in the present invention adopts the following measures in the flattening process of the cold-rolled 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 of 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 of the leveling unit (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 type 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 within 45°C. When the incoming material temperature is higher than 45°C, the flattened strip steel 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 30-45 kN, and the outlet tension is controlled at 30-65 kN.

[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 middle 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 strip width increases, outlet tension also increases, and conversely, as strip width decreases, outlet tension decreases; specifically: for every 100mm increase in strip width, outlet tension increases by 4 to 6kN; for every 100mm decrease in width, outlet tension decreases by 4 to 6kN.

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

[0036] During the speed increase 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 increase can be effectively controlled.

[0037] (4) Speed ​​control of the strip: During leveling, the strip speed is controlled by the step-by-step speed-up 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-up method, which is conducive to adjusting the plate shape.

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

[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 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 spread the leveling liquid flat on the strip surface by adjusting the bending amount of the working roll.

[0040] During the process of adjusting the plate shape, we should always pay attention to the actual running state of the steel plate, ensure that the strip surface is stably output in the direction of the leveling unit outlet, and the edge of the strip has no obvious shaking. Through the actual running state of the steel plate, the plate shape meter curve is used for comparison, and the leveling liquid aggregation state is observed, dynamic adjustments are made to ensure the plate shape after leveling.

[0041] When the strip is stabilized at the maximum speed, observe the actual plate shape at the exit side of the leveling unit and compare it with the plate shape meter curve. The plate shape meter curve reflects the elongation distribution defect along the transverse unit length of the strip. If the plate shape meter curve is high on the left and low 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 working roll needs to be tilted more toward the operating side, that is, the inclination value of the working roll is increased to make the inclination value positive; if the plate shape meter curve is high on the right and low 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 working roll needs to be tilted more toward the transmission side, that is, the inclination value of the working roll is reduced to make the inclination value negative; if the plate 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, and the bending amount of the working roll is reduced; if the plate 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, and the bending amount of the working roll is increased; refer to the plate shape meter curve when reducing and increasing the bending amount until the plate shape meter curve is adjusted to be symmetrical on the left and right and close to coincide 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 accumulation of leveling liquid 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 single-sided wave defects can be effectively eliminated.

[0044] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for eliminating the flattening of single-side waves of cold-rolled plates with cover retreat Rm<340MPa, characterized in that: The process includes the following: (1) Optimize production planning and ensure the incoming material temperature of the leveling mill; after the cold-rolled strip is annealed in a bell furnace, it enters the leveling mill when it is naturally cooled to 40-45°C; (2) Determine the inlet tension and outlet tension of the leveling unit; the inlet tension is controlled at 30-45 kN, and the outlet tension is controlled at 30-65 kN; (3) During the speed increase of the skin-pass unit, the amount of roll bending is controlled according to the threading rolling force; if the threading rolling force F≤2.5MN, the amount of roll bending is controlled at 8% to 12% during the speed increase; if the threading rolling force 2.5MN<F<4MN, the amount of roll bending is controlled at 45% to 55% during the speed increase; if the threading rolling force F≥4MN, the amount of roll bending is controlled at 95% to 100% during the speed increase; (4) Speed ​​control of the strip: During leveling, the speed of the strip is controlled by the step-by-step speed increase method, and the maximum speed of the strip 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 shape meter curve at the outlet side of the flattening unit, observe the state of the flattening liquid on the strip surface at the inlet side of the flattening unit, and adjust the bending amount of the working roll to make the flattening liquid spread evenly 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 the 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 6kN; for every 100mm decrease in strip width, the outlet tension decreases by 4 to 6kN.

3. 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 (4), the step speed increase 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 within the range of 90-110m / min; within the range of 50m<L≤100m, the strip steel speed is controlled within the range of 180-220m / min; within the range of 100m<L≤200m, the strip steel speed is controlled within the range of 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. 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 (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 coincident with the horizontal line.

5. 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 (5), the state of the leveling liquid after spraying on the surface of the strip is observed in the frame at the inlet side of the leveling unit; if there is no obvious accumulation of the leveling liquid on the surface of the strip, 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.

Images