A method for improving the head wave defect of cold rolled thin strip

Abstract

The present invention relates to a method for improving the wavy shape defects of the head of cold-rolled thin-gauge strip steel, comprising the steps of setting the roller shifting value according to the flatness, adjusting the frame load, and the like. The method for improving the wavy shape defects of the head of cold-rolled thin-gauge strip steel provided by the present invention is based on the existing plate shape control means of cold-rolled UCM equipment. By analyzing the influence of the intermediate roller shifting setting of the finished product frame on the plate shape control, a method for setting the intermediate roller shifting of the finished product frame for the wavy shape of the strip head is designed, as well as a method for resetting the load distribution if the plate shape control ability of the intermediate roller shifting is insufficient. Utilizing the method of the present invention, effective improvement measures can be implemented for the plate shape defects of the head of thin-gauge strip steel that plague production through manual intervention methods, which not only shortens the length of the thin-gauge strip steel with serious plate shape problems that needs to be sheared before entering the subsequent continuous annealing process, thereby improving the yield rate, but also improving the stability of rolling.

Description

Technical Field

[0001] The invention relates to a method for improving the wavy defect of the head of a cold-rolled thin-gauge strip steel, and belongs to the technical field of metal smelting. Background Art

[0002] In addition to mechanical properties, surface quality and thickness accuracy, strip flatness is the most important indicator for cold-rolled sheets and their coated products, as it directly affects the productivity, yield rate, cost and product appearance of downstream companies such as automobiles, home appliances, instruments, and food packaging.

[0003] During the rolling process, if the strip's length is unevenly extended, a transverse internal stress field is generated on the strip's horizontal surface, with the larger portion experiencing compressive stress and the smaller portion experiencing tensile stress. When the internal stress reaches a critical value, the compressive portion buckles, causing the strip to warp and produce the shape defect we see today.

[0004] When rolling strip steel in cold rolling mills, its head is the tail of the hot-rolled material. Due to temperature control during the hot rolling process, the strip is often in an unstable state, making it difficult to control quality factors such as thickness and shape. This can lead to quality defects of varying severity, which in turn affect the stability of the head in the subsequent cold rolling process. Thin strip steel, due to its high total reduction ratio, is already difficult to control in the finished mill. Furthermore, the unstable quality of the incoming material makes it even more difficult to control the wave shape of the head, forcing the head cut to be increased, which reduces the yield rate.

[0005] The UCM rolling mill equipment for cold rolling has a variety of plate shape control methods such as work roll bending, intermediate roll bending and intermediate roll shifting, and its plate shape control capability is greatly improved. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to overcome the shortcomings of the above-mentioned technology, to provide a method based on the existing plate shape control means of cold rolling UCM equipment, to analyze the influence of the intermediate roller shifting setting of the finished product frame on the plate shape control, and to design the intermediate roller shifting setting method of the finished product frame for the wave shape of the strip head.

[0007] In order to solve the above technical problems, the present invention proposes a technical solution: a method for improving the head wave defect of cold-rolled thin strip steel, comprising the following steps:

[0008] Step 1: When rolling a group of strips of the same steel grade and specification using a cold rolling mill having stands S1 to S5, obtain the set value of the intermediate roll shifting and the flatness control target value I of the strip in the S5 stand;

[0009] Step 2: During the rolling process, if there is a flatness defect within the length of 100m in the head of the self-strip steel, calculate the mean IU value within the 100m range. avg , and calculate I avg The difference from the target value ΔI=I avg -I;

[0010] Step 3: Add an increment ΔS to the original roller shift value S; according to the formula Where k = 9 × 10 -5 ×S 2 +2.1×10 -3 ×S+0.3149; Combined with ΔI to determine ΔS;

[0011] Step 4: When a flatness defect occurs during the rolling process, determine the location of the flatness defect on the cross section, specifically whether it is a middle wave or an edge wave. When the flatness defect is an edge wave, the setting of the intermediate roll shifting value S' during the subsequent rolling is: S' = S - △S; when the flatness defect is a middle wave: S' = S + △S;

[0012] Step 5: Set the lower limit of the maximum stroke range of the intermediate roller to -15 mm. If the intermediate roller shifting value S' in step 4 exceeds the lower limit of the maximum stroke range, that is, when S' is less than -15 mm, then S' = -15 mm;

[0013] Step 6: Observe the flatness of the strip head after adjusting the intermediate roll shifting value. If the adjusted △I is higher than 5IU, move part of the load of S5 to the first four stands evenly.

[0014] Step 7: Obtain the outlet thickness h1~h5 of the strip of this steel grade and specification at the five stands, and set the inlet thickness of S1 as h0, and the reduction of each of S1~S5 as △h i (1≤i≤5), the total reduction is △h sum , then calculate the pressure reduction of each of the five racks: Δh i =h i-1 -h i , and the total downward pressure: Δh sum =h0-h5;

[0015] Step 8: Assume the relative reduction rate of S1 to S5 is ε i , ε i =△h i / h i-1 ,(0 <i≤5);

[0016] Step 9: Assume the absolute reduction rate of S1 to S5 is E i , E i =△h i / △h sum ,(0 <i≤5);

[0017] Step 10: Average 10% of the absolute reduction rate of S5 to the first four racks, and set the new absolute reduction rate of S1 to S5 to E' i , then the new absolute reduction rates of racks S1 to S5 are as follows:

[0018]

[0019] Step 11: Let the new reduction of S1 to S5 be △h' i , △h' i =△h sum ×E' i ,(0 <i≤5);

[0020] Step 12: Set h' i S1~S5 are the new outlet thicknesses of each rack, h'0 is the inlet thickness of S1, then:

[0021] Step 13: Assume the relative reduction rate of S1 to S5 is ε' i , ε' i =△h' i / h' i ,(0 <i≤5)。

[0022] A further improvement of the above solution is that the cold rolling equipment has the ability to shift the intermediate rolls.

[0023] A further improvement of the above solution is that an interface for manual intervention and adjustment is required for setting parameters during the cold rolling process.

[0024] The above scheme is further improved in that: in the step 3, a finite element simulation software is used to establish a roll system-workpiece coupling calculation model to analyze the flatness control characteristics of the intermediate roll shifting pair; in the roll system-workpiece coupling calculation model, the roll is an elastic material, the upper and lower working rolls are driven to rotate by the rigid surface of the end, and the workpiece is an elastic-plastic material, which is pushed into the roll gap by the rigid surface at a speed slightly lower than the rolling line speed to achieve biting; at least 4 layers of grids are divided in the thickness direction of the strip; each contact setting adopts the direct constraint method, uses the sliding Coulomb friction model, the friction coefficient between the roll and the workpiece is set to 0.05, and the friction coefficient between the rolls is taken as 0.1; by setting different original intermediate roll shifting amounts S and different shifting increments △S as calculation conditions, the changes in △I (IU) in the calculation results are sorted out, and after fitting, k=9×10 -5 ×S 2 +2.1×10 -3 ×S+0.3149.

[0025] The present invention provides a method for improving the head wavy shape defects of thin cold-rolled strip. Based on existing shape control methods for cold-rolled UCM equipment, the method analyzes the impact of intermediate roll shifting settings on shape control in the finished product stand and designs a method for setting intermediate roll shifting in the finished product stand to address the wavy shape of the strip head. Furthermore, a method for resetting the load distribution if the shape control capability of the intermediate roll shifting is insufficient is also designed. The present invention's method allows for manual intervention to effectively improve the head shape defects of thin strip that plague production. This not only shortens the length of thin strip with severe head shape problems that requires shearing before entering the subsequent annealing process, thereby improving the yield rate, but also enhances rolling stability. DETAILED DESCRIPTION

[0026] Example

[0027] The present embodiment's method for improving the head wavy shape defect of thin-gauge cold-rolled strip analyzes the impact of the intermediate roll shifting setting on the strip shape control in the finished product stand. Based on the severity of the head wavy shape defect, a method for setting the intermediate roll shifting of the finished product stand for the strip head wavy shape is designed, as well as a method for resetting the load distribution if the shape control capability of the intermediate roll shifting is insufficient. This method is characterized in that it can utilize the existing shape control means of the cold rolling equipment, and based on the original intermediate roll shifting amount and rolling load distribution settings, manually intervene in the relevant set values, thereby implementing effective improvement measures for the head shape defect of thin-gauge strip that has plagued production. Specific examples are as follows:

[0028] (1) A group of strips of the same steel grade and specification have flatness defects in the form of edge waves at the head during cold rolling. The setting value S of the intermediate roll shifting and the target value I of the edge flatness control of the previous roll of rolled strip in the S5 stand are extracted. The setting value S of the intermediate roll shifting is -5 mm, and the target value I is -3IU.

[0029] (2) Calculate the mean IU value of the head of the previous strip within 100m along the length direction. avg =16IU, and calculate the difference △I from the target value; △I=I avg -I=16-(-3)=19IU;

[0030] (3) According to the results of the analysis of the flatness control characteristics of the intermediate roll shifting based on the roller system-workpiece coupling finite element calculation model, the increment of the intermediate roll shifting value setting in this case is calculated. According to the relationship between the k value and the original roll shifting setting value S:

[0031] k = 9 × 10 -5 ×S 2 +2.1×10 -3 ×S+0.3149=9×10-5 ×(-5) 2 +2.1×10 -3 ×(-5)+0.3149=0.30665;

[0032] The original setting value of the intermediate roller shifting is S = -5mm, k = 0.312, then the setting increment of the intermediate roller shifting is:

[0033] △S=k×△I=0.30665×19=5.82635mm;

[0034] (4) The flatness defect that occurs during this rolling process is specifically manifested as edge waves. Therefore, when rolling the next coil, the setting of the intermediate roll shifting value S' is: S' = S-ΔS = -5-5.82635 = -10.82635 mm;

[0035] For ease of setting, take out the next roll and set the middle roller shifting value to -11mm;

[0036] (5) Observe the flatness of the strip head after adjusting the intermediate roll shifting setting. According to calculation, it is found that after adjustment, △I = 7IU, which is still greater than 5. Then, by adjusting the load distribution, part of the load of S5 is evenly shifted to the first four stands to ensure the flatness of the strip in the finished product stand.

[0037] (6) Extract the outlet thickness h1~h5 of the original five stands of this steel grade and set the inlet thickness of S1 as h0 and the reduction of S1~S5 as △h i , the total reduction is △h sum , then calculate the compression of the 5 racks and the total compression, the calculation formula and results are as follows:

[0038]

[0039] i 0 1 2 3 4 5 <![CDATA[h0(μm)]]> 2000 1196 698 452 299 202 <![CDATA[△h i ]]> - 804 498 246 153 97

[0040] Then △h sum =h0-h5=2000-202=1798μm;

[0041] (7) Let the relative reduction rate of S1 to S5 be ε i , calculate the relative reduction rate of each rack, the calculation formula and results are as follows: ε i =△h i / h i-1 ,(0 <i≤5);

[0042] i 1 2 3 4 5 <![CDATA[ε i ]]> 40.20％ 41.64％ 35.24％ 33.85％ 32.44％

[0043] (8) Assume that the absolute reduction rate of S1 to S5 is E i, calculate the absolute compression rate of each rack, the calculation formula and results are as follows: E i =△h i / △h sum ,(0 <i≤5);

[0044] i 1 2 3 4 5 <![CDATA[E i ]]> 44.72％ 27.70％ 13.68％ 8.51％ 5.39％

[0045] (9) Move up 10% of the absolute reduction of S5 and average it to the first four racks. Let the new absolute reduction rate of S1 to S5 be E' i , then the new absolute reduction rates of racks S1 to S5 are as follows:

[0046]

[0047] i 1 2 3 4 5 <![CDATA[E' i ]]> 44.85％ 27.83％ 13.82％ 8.64％ 4.86％

[0048] (10) Let the new reduction of S1 to S5 be △h' i , then the new reduction of racks S1 to S5 is as follows:

[0049] △h' i =△h sum ×E' i ,(0 <i≤5);

[0050]

[0051] (11) Let h' i S1~S5 are the new outlet thickness of each rack (h'0 is the inlet thickness of S1), then the new outlet thickness of S1~S5 is:

[0052]

[0053] i 0 1 2 3 4 5 <![CDATA[h' i (μm)]]> 2000 1194 693 445 289 202

[0054] (12) Let the relative reduction rate of S1 to S5 be ε' i , then the new relative reduction rates of the S1 to S5 stands are as follows:

[0055] ε' i =△h' i / h' i ,(0 <i≤5);

[0056] i 1 2 3 4 5 <![CDATA[ε' i ]]> 40.32％ 41.93％ 35.84％ 34.95％ 30.18％

[0057] (13) So far, all the relevant parameters of the new load distribution after the S5 part load is evenly moved up to S1~S4 are obtained;

[0058] (14) So far, the above is a complete method for improving the flatness defect of the head of cold-rolled strip steel. When the next roll is rolled, the corresponding setting parameters can be manually adjusted.

[0059] The present invention is not limited to the above embodiments. Any technical solutions formed by equivalent replacement fall within the protection scope required by the present invention.

Claims

1. A method for improving the head wave defect of cold-rolled thin strip steel, characterized in that: The steps include: Step 1: When rolling a group of strips of the same steel grade and specification using a cold rolling mill having stands S1 to S5, obtain the set value of the intermediate roll shifting and the flatness control target value I of the strip in the S5 stand; Step 2: During the rolling process, if there is a flatness defect within the length of 100m in the head of the self-strip steel, calculate the mean IU value within the 100m range. avg , and calculate I avg The difference from the target value ΔI=I avg -I; Step 3: Add an increment ΔS to the original roller shift value S; according to the formula Where k = 9 × 10 -5 ×S 2 +2.1×10 -3 ×S+0.3149; Combined with ΔI to determine ΔS; Step 4: When a flatness defect occurs during the rolling process, determine the location of the flatness defect on the cross section, specifically whether it is a middle wave or an edge wave. When the flatness defect is an edge wave, the setting of the intermediate roll shifting value S' during the subsequent rolling is: S' = S - △S; when the flatness defect is a middle wave: S' = S + △S; Step 5: Set the lower limit of the maximum stroke range of the intermediate roller to -15 mm. If the intermediate roller shifting value S' in step 4 exceeds the lower limit of the maximum stroke range, that is, when S' is less than -15 mm, then S' = -15 mm; Step 6: Observe the flatness of the strip head after adjusting the intermediate roll shifting value. If the adjusted △I is higher than 5IU, move part of the load of S5 to the first four stands evenly. Step 7: Obtain the outlet thickness h1~h5 of the strip of this steel grade and specification at the five stands, and set the inlet thickness of S1 as h0, and the reduction of each of S1~S5 as △h i (1≤i≤5), the total reduction is △h sum , then calculate the pressure reduction of each of the five racks: Δh i =h i-1 -h i , and the total downward pressure: Δh sum =h0-h5; Step 8: Assume the relative reduction rate of S1 to S5 is ε i , ε i =△h i / h i-1 ,(0 <i≤5); Step 9: Assume the absolute reduction rate of S1 to S5 is E i , E i =△h i / △h sum ,(0 <i≤5); Step 10: Average 10% of the absolute reduction rate of S5 to the first four racks, and set the new absolute reduction rate of S1 to S5 to E' i , then the new absolute reduction rates of racks S1 to S5 are as follows: Step 11: Let the new reduction of S1 to S5 be △h' i , △h' i =△h sum ×E' i ,(0 <i≤5); Step 12: Set h' i S1~S5 are the new outlet thicknesses of each rack, h'0 is the inlet thickness of S1, then: Step 13: Assume the relative reduction rate of S1 to S5 is ε' i , ε' i =△h' i / h' i ,(0 <i≤5)。 2. The method for improving the head wave defect of cold-rolled thin strip according to claim 1, characterized in that: The cold rolling mill has the ability to shift the intermediate rolls.

3. The method for improving the head wave defect of cold-rolled thin strip according to claim 1, characterized in that: For the setting parameters during the cold rolling process, an interface for manual intervention and adjustment is required.

4. The method for improving the head wavy defect of cold-rolled thin strip according to claim 1, characterized in that: In the step 3, a roller system-workpiece coupling calculation model is established using finite element simulation software to analyze the flatness control characteristics of the intermediate roller shifting pair; in the roller system-workpiece coupling calculation model, the roller is an elastic material, the upper and lower working rollers are driven to rotate by the rigid surface of the end, and the workpiece is an elastic-plastic material, which is pushed into the roller gap by the rigid surface at a speed slightly lower than the rolling line speed to achieve biting; at least 4 layers of grids are divided in the thickness direction of the strip; each contact setting adopts the direct constraint method, uses the sliding Coulomb friction model, the friction coefficient between the roller and the workpiece is set to 0.05, and the friction coefficient between the rollers is taken as 0.1; by setting different original intermediate roller shifting amounts S and different shifting increments △S as calculation conditions, the change of △I in the calculation results is sorted out, and after fitting, k=9×10 -5 ×S 2 +2.1×10 -3 ×S+0.3149.

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