Control method for improving head mark of hot-rolled coil head

Abstract

The invention relates to the technical field of hot-rolled coil production, in particular to a control method for improving a hot-rolled coil head mark. According to the control method for improving the head mark of the hot-rolled coil, the set value of the thermal yield strength is optimized according to different steel types, different thicknesses and different rolling processes, and the stepping pressure control threshold value of the wrapper roll is reduced; the initial roll gap and the stepping roll gap of the wrapper roll are optimized, roll gap control is more reasonable, the steel stacking risk is reduced, and meanwhile stepping force increase caused by the too small roll gap is avoided; the combination of different time modules and servo valve integral values is cooperatively controlled, and the response time of the wrapper roller is optimized. According to the control method for improving the hot-rolled coil head mark, for steel types with different strengths and different thicknesses, the length and depth of the head mark after coiling are improved, the product quality of the hot-rolled coil is effectively improved, the product reject ratio caused by the head mark problem is reduced, and remarkable economic benefits and social benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of hot rolled coil production, and in particular to a control method for improving the head mark of a hot rolled coil. Background Art

[0002] In the production process of hot rolled coils, the head mark of the strip is a common problem that affects product quality. The head mark is formed when the strip head enters the coiler and the coiler squeezes the adjacent layers of strip steel layer by layer after the strip head is impacted during the stepping process. It usually appears in the inner circle of the steel coil. There will be obvious indentations and slight waves on the strip with the head mark. During the spinning process after punching, the user will cause the spinning head to jump frequently due to the uneven surface of the steel plate, affecting the spinning quality and product dimensional accuracy. In severe cases, the spinning head will be damaged. The strip with serious head mark cannot be used by the user and can only be scrapped, causing great waste and huge losses to the user.

[0003] In order to solve the problem of hot-rolled strip head marks, various countries have successively developed auxiliary roll step control technologies similar to AJC. The core logic is: when the strip head approaches the auxiliary roll, the roll gap is temporarily increased to "avoid", and the fitting setting is restored after passing. It is necessary to balance "avoidance to prevent indentation" and "fitting to maintain coil shape", otherwise it will cause serious strip head marks, loose coils and steel piling. From the current technical level, the control of strip head marks using auxiliary roll step control technologies similar to AJC mainly focuses on adjusting a single parameter, such as adjusting only the roll gap or auxiliary roll pressure. However, since the various parameters in the hot-rolled coil production process are interrelated and affect each other, adjusting a single parameter is not feasible. It is difficult to achieve the ideal control effect, and it is impossible to effectively solve the problem of strip head marks on steels of different strengths and thicknesses. Moreover, with the intensification of market competition, higher requirements are placed on the cost and product quality of manufacturers. The higher the output of strip steel, the lower the production cost. For hot rolling mills, the most effective way to increase output is to increase the rolling speed. However, after the rolling speed is increased, the strip steel is prone to tensile deformation under the action of tension, resulting in uneven interlayer pressure of the strip steel after coiling, and coil defects such as tower shape and loose coiling. In severe cases, steel piling accidents may occur. In addition, as long as there is a strip head mark, it means waste and increased cost for users. Summary of the Invention

[0004] The purpose of the present invention is to provide a control method for improving the head mark of hot-rolled coils. By synergistically optimizing multiple parameters such as the roll gap, thermal yield strength, and the response time of the auxiliary coil, the length and depth of the head mark after coiling can be effectively reduced for steel grades of different strengths and thicknesses, thereby improving the quality of hot-rolled coil products.

[0005] The solution of the present invention provides a control method for improving the head mark of a hot-rolled coil, comprising the following steps: Step 1: Based on the strip strength and target thickness, the initial roll gap value of the winding roller is set in the secondary system. For different steel grades, combined with their chemical composition and rolling process, the hot yield strength setting is optimized in the secondary system. Step 2: The strip head enters the No. 1 auxiliary winding roller, the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller in sequence to complete one circle of winding; Step 3: After the strip head completes one circle of winding, the strip head approaches the No. 1 auxiliary winding roller again, and the No. 1 auxiliary winding roller starts the first jump step. The roller gap value of the first jump step is a limited value; In step 4, after the strip head passes through the No. 1 auxiliary winding roller, it approaches the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller in turn. The No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller start to jump, and the jump roller gap value is consistent with the jump roller gap value in step 3.

[0006] Preferably, in step 1, a roll gap setting model is established according to the strength and thickness of the steel grade; for low-strength steel grades with the same strength grade as 380CL, the roll gap setting value is appropriately reduced according to different thicknesses, and the roll gap setting value is reduced by 3%-8% compared with the original value; for high-strength steel grades with the same strength grade as 490CL, the roll gap setting value is reasonably increased according to different thicknesses under the premise of considering the rolling force and equipment load capacity, and the roll gap setting value is increased by 2%-5% compared with the original value; by accurately controlling the roll gap value, the strip steel can obtain more uniform rolling process. The deformation of the strip can be reduced, and the strip head mark caused by unreasonable roll gap can be reduced; for low-strength steel grades with the same strength grade as 380CL, the hot yield strength setting is adjusted from the conventional 220-240MPa to 210-225MPa during rolling; for high-strength steel grades with the same strength grade as 490CL, the hot yield strength setting value is adjusted from the conventional 320-350MPa to 330-345MPa during rolling; the hot yield strength is reasonably reduced to make the plastic deformation of the strip more sufficient during the coiling process, reducing the depth and length of the strip head mark.

[0007] Preferably, in step 1, the roll gap setting value of the low-strength steel with the same strength grade as 380CL and a thickness of less than 5 mm is reduced by 7%-8% compared with the original value; the roll gap setting value of the low-strength steel with the same strength grade as 380CL and a thickness of 5-10 mm is reduced by 5%-6% compared with the original value; the roll gap setting value of the low-strength steel with the same strength grade as 380CL and a thickness greater than 10 mm is reduced by 3%-4% compared with the original value; the roll gap setting value of the high-strength steel with the same strength grade as 490CL and a thickness less than 10 mm and a thickness equal to 10 mm is increased by 2%-3% compared with the original value; the roll gap setting value of the high-strength steel with the same strength grade as 490CL and a thickness greater than 10 mm is increased by 4%-5% compared with the original value; the hot yield strength of the low-strength steel with the same strength grade as 380CL is set to 210-220 MPa; the hot yield strength of the high-strength steel with the same strength grade as 490CL is set to 320-340 MPa.

[0008] Preferably, in step 2, after the auxiliary winding roller bites the steel, the pressure sensor detects the actual pressure value of the auxiliary winding roller and compares the actual pressure value with the set pressure value. When the actual pressure value exceeds the set pressure value, the roller gap value of the auxiliary winding roller gradually increases until the actual pressure of the auxiliary winding roller reaches its set pressure value. At the same time, in order to improve the response time of the auxiliary winding roller, the time module and the servo valve integral value are optimized.

[0009] Preferably, in step three, the skipping process is as follows: after the strip completes one circle of winding in step two, the head of the strip approaches the No. 1 auxiliary roller again. When the head of the strip approaches the No. 1 auxiliary roller, it will be detected by the laser detector, and the No. 1 auxiliary roller will be lifted by the hydraulic servo system to avoid the incoming steel plate. The lifted roller gap value is a set value. After the strip head passes, the No. 1 auxiliary roller will be pressed down quickly to make the strip tightly wound on the roller of the No. 1 auxiliary roller; the lifted roller gap value is 2H+fH, H is the thickness of the product, and f is a coefficient; by optimizing the auxiliary roller control response time module and the servo valve integral parameters, the auxiliary roller response time is significantly shortened. After receiving the winding instruction, the auxiliary roller can move faster, reducing the impact when the strip head contacts the auxiliary roller, thereby reducing the probability and degree of head mark formation. The time module is selected from T2-T3, and the servo valve integral is selected from 25-35.

[0010] Preferably, in step four, the skipping process is specifically as follows: when the strip head approaches the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller, it will be detected by the laser detector, and the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller will be lifted by the hydraulic servo system to avoid the incoming steel plate. The lifted roller gap value is a set value. After the strip head passes, the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller will be quickly pressed down to make the strip tightly wound on the rollers of the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller; the lifted roller gap value is 2H+fH, H is the thickness of the product, and f is a coefficient; by optimizing the auxiliary winding roller control response time module and the servo valve integral parameter, the auxiliary winding roller response time is significantly shortened. After receiving the winding instruction, the auxiliary winding roller can move faster, reducing the impact when the strip head contacts the auxiliary winding roller, thereby reducing the probability and degree of strip head mark formation, the time module is selected from T2-T3, and the servo valve integral is selected from 25-35.

[0011] The strip head mark is formed when the strip head enters the coiler and the coiler squeezes the adjacent layers of strip layer by layer after the strip head is impacted during the stepping process. It usually appears in the inner 1-3 circles of the steel coil. Therefore, to improve or even eliminate the strip head mark, it is necessary to reduce the impact force or stepping force on the strip head.

[0012] Appropriately reducing the thermal yield strength of thick steel grades and reducing the threshold value of the winding roller step pressure control without affecting the coil shape can allow the winding roller to start pressure control at a lower pressure and reduce the step force.

[0013] For the traditional 1580mm hot rolling production line, affected by the working conditions and working characteristics of the coiler, the impact is relatively large when the equipment is in operation. The actual roll gap will be smaller than the set roll gap during the stepping process. The impact of thick-gauge stepping will be even greater. When the deviation between the set roll gap and the actual roll gap of the auxiliary coiling roller is too large, the stepping pressure control will fail. The auxiliary coiling roller will not open when the strip head passes through it. Excessive impact without any buffering will increase the stepping force and aggravate the degree of strip head mark.

[0014] The time module is essentially a set of signal processing logic parameters for the control system. The larger its value, the longer the delay in the system processing instructions. The T1 module adopts the shortest signal processing path and priority scheduling strategy, and has the shortest time. The T5 module adopts a conservative control strategy, setting multiple safety confirmation and state synchronization mechanisms, and has the highest total delay. The servo valve integral link compensates for the speed by adjusting the valve core displacement. Its integral value is nonlinearly positively correlated with the opening speed of the auxiliary winding roller. The combination of different time modules and servo valve integral values ​​presents a complex synergistic effect, which jointly affects the response time of the auxiliary winding roller.

[0015] The overall idea of ​​the present invention is: to optimize the set value of hot yield strength according to different steel grades, different thicknesses, and different rolling processes, and to reduce the threshold value of the step pressure control of the winding roller; to optimize the initial roll gap and the step roll gap of the winding roller, so that the roll gap control is more reasonable, reducing the risk of steel piling while avoiding the increase in step force caused by too small a roll gap; to coordinate the control of different time modules and the servo valve integral value combination to optimize the response time of the winding roller.

[0016] Compared with the prior art, the present invention has the following beneficial effects: through the control method of the present invention, for steel grades of different strengths and thicknesses, the length and depth of the head mark after coiling are improved, thereby effectively improving the product quality of the hot-rolled coil and reducing the product failure rate caused by the head mark problem, thereby having significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A printed photo of the steel strip head produced by the existing technology; Figure 2 This is a photo of the steel strip head produced by the control method for improving the head mark of hot-rolled coils according to the present invention. DETAILED DESCRIPTION

[0018] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the technical solutions in the specific implementation methods of the present invention are clearly and completely described below to further illustrate the present invention. Obviously, the specific implementation methods described are only part of the implementation methods of the present invention, rather than all styles.

[0019] Example 1 A control method for improving the head mark of a hot-rolled coil comprises the following implementation steps.

[0020] Step 1: Set the initial roll gap value of the auxiliary roll in the secondary system based on the strength and target thickness of the strip. Optimize the hot yield strength setting in the secondary system for different steel grades, taking into account their chemical composition and rolling process. The strip used is 380CL steel with a thickness of 10 mm. The initial roll gap is set to 12.2 mm, the hot yield strength is set to 215 MPa, the time module is set to T2, and the servo valve integral is set to 35.

[0021] In step 2, the strip head enters the No. 1 auxiliary winding roller, No. 2 auxiliary winding roller and No. 3 auxiliary winding roller respectively to complete one circle of winding; after all the auxiliary winding rollers bite the steel, the pressure sensor detects the actual pressure value of the auxiliary winding roller and compares the actual pressure value with the set pressure value. In this embodiment, because the roller gap is reasonably set, the actual pressure value is not much different from the set pressure value.

[0022] Step 3: After the strip head completes one circle of winding, it approaches the No. 1 auxiliary winding roller again, and the No. 1 auxiliary winding roller starts the first jump step. The setting value of the roller gap of this jump is 24mm, the time module is T2, and the servo valve integral is 35.

[0023] In step 4, after the strip head passes through the No. 1 auxiliary winding roller, it approaches the No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller in turn. The No. 2 auxiliary winding roller and the No. 3 auxiliary winding roller start to jump, and the jump roller gap value is basically the same as the jump roller gap value in step 3.

[0024] Example 2 A control method for improving the head mark of a hot-rolled coil is provided, according to the manufacturing method of Example 1, except that the thickness of the steel strip is 12 mm, the initial roll gap value is set to 14.9 mm, the thermal yield strength is set to 213 MPa, the time module is T1, and the servo valve integral is 25.

[0025] Example 3 A control method for improving the head mark of a hot-rolled coil is provided, according to the manufacturing method of Example 1, except that the thickness of the steel strip is 14 mm, the initial roll gap value is set to 17.6 mm, the thermal yield strength is set to 212 MPa, the time module is T1, and the servo valve integral is 35.

[0026] Example 4 A control method for improving the head mark of a hot-rolled coil is provided, according to the manufacturing method of Example 1, except that the thickness of the steel strip is 16 mm, the initial roll gap value is set to 19.3 mm, the thermal yield strength is set to 210 MPa, the time module is T2, and the servo valve integral is 25.

[0027] Example 5 A control method for improving the head mark of a hot-rolled coil is provided, according to the manufacturing method of Example 1, except that the strip steel used is 490CL steel with a thickness of 10 mm, the initial roll gap value is set to 13.4 mm, the thermal yield strength is set to 325 MPa, the time module is T2, and the servo valve integral is 35.

[0028] Example 6 A control method for improving the head mark of a hot-rolled coil is provided, according to the manufacturing method of Example 1, except that the strip steel used is 490CL steel with a thickness of 12 mm, the initial roll gap value is set to 16.6 mm, the thermal yield strength is set to 323 MPa, the time module is T2, and the servo valve integral is 25.

[0029] Example 7 A control method for improving head print of hot-rolled coil, according to the manufacturing method of embodiment 1, except that the steel strip is 490CL steel with thickness of 14mm, the initial roll gap value is set to 19.8mm, the hot yield strength is set to 322 Mpa, the time module is T3, and the servo valve integration is 35.

[0030] Embodiment 8 A control method for improving head print of hot-rolled coil, according to the manufacturing method of embodiment 1, except that the steel strip is 490CL steel with thickness of 14mm, the initial roll gap value is set to 19.8mm, the hot yield strength is set to 322 Mpa, the time module is T3, and the servo valve integration is 35.

[0031] Table 1 Process parameters and head print of each embodiment

[0032] Figure 1 The photo of head print of the head of the steel strip produced by the prior art shows that the head print is obvious, Figure 2 The photo of the head of the 10mm opened 380CL steel strip produced by embodiment 1 shows that the head print is only one, and the depth is 0.20mm, which basically does not affect the processing and use of the end user.

[0033] According to the results of the above eight embodiments, the hot-rolled coil produced according to the present application has a head print length of basically not more than 5 meters, and the number of head prints is one, and the depth of the head print is controlled to be within 0.30mm, which basically does not affect the processing and production of the downstream enterprises, and compared with the prior art (the head print is more than 10 meters, and the depth is more than 0.5mm), the length and depth of the head print are significantly reduced.

[0034] From the perspective of steel type, the depth of the strip mark with high strength is relatively deeper, indicating that there is room for further optimization in coordinated control. After setting the appropriate thermal yield strength and roll gap value, adjusting different winding roller response times will result in different strip mark depths. From Examples 1 and 2, the effects achieved by time module T2, servo valve integral 35 and time module T1, servo valve integral 25 are similar. The T1 module optimizes the signal processing flow, reduces unnecessary time delays, and shortens processing time for signal acquisition, logical judgment, and other links. However, this may also lead to system instability and cause accidents such as steel piling. From actual production cracking, increasing the rolling speed and selecting the T1 module does indeed lead to an increase in steel piling accidents. Therefore, the present invention does not recommend selecting the time module as T1. Selecting the time module T1 and the servo valve integral 35 at the same time actually deepens the strip mark depth. This may be because the overly strong integral effect in the T1 mode can easily cause system overshoot, causing the winding roller to start quickly and then oscillate due to overshoot and retreat, resulting in increased impact force on the strip head and a deeper strip mark.

[0035] The embodiment of the present invention has a good coil shape and almost no head mark, which greatly reduces the user's scrap rate. The present invention only adjusts by optimizing parameters and does not require additional equipment. The product quality is stable and is suitable for large-scale industrial production of traditional 1580 hot rolling production lines. It has good promotion and applicability.

[0036] Obviously, the above embodiment is only an example for clear explanation and is not limited to this example. Different forms of changes made in this field are not listed here, so the derived changes are all within the scope of protection of the present invention.

Claims

1. A control method for improving the head mark of hot rolled coil, characterized in that: The following steps are involved: Step 1: Based on the steel grade strength, target thickness, chemical composition, and rolling process of the strip, the initial roll gap of the reeling rollers is set in the secondary system and the hot yield strength is optimized. Step 2: The strip head enters the No. 1-3 auxiliary winding rollers in sequence. The actual pressure value of the auxiliary winding roller is detected in real time by the pressure sensor and compared with the set pressure value. If the actual pressure value exceeds the set value, the roller gap is dynamically increased until the actual pressure reaches the set value. Step 3: After the strip completes one turn, when the head approaches the No. 1 auxiliary roll again, the laser detector triggers the No. 1 auxiliary roll to perform a jump action. The gap between the raised rolls is within the preset range, and the strip head passes through the rear auxiliary roll and is quickly pressed down. Step 4: When the strip head approaches the No. 2 auxiliary roll and the No. 3 auxiliary roll in sequence, the skipping action is performed in the same manner as in step 3.

2. The method for improving the head mark of hot rolled coil according to claim 1, characterized in that: In step 1, the thermal yield strength is selected as: The hot yield strength of low-strength steel grades is set at 210-225 MPa; The hot yield strength of high-strength steel grades is set at 330-345 MPa.

3. The method for improving the head mark of hot rolled coil according to claim 2, characterized in that: In step 1, the thermal yield strength is selected as: The hot yield strength of 380CL steel grade is set at 210-220 MPa; The hot yield strength of 490CL steel grade is set at 320-340MPa.

4. The method for improving the head mark of a hot rolled coil according to claim 2, characterized in that: In step 1, a roll gap setting model is established based on the strength and thickness of the steel grade; For low-strength steels with the same strength grade as 380CL, the roll gap setting value is reduced according to different thicknesses. The roll gap setting value is reduced by 3%-8% compared to the original value. For high-strength steels of the same strength grade as 490CL, the roll gap setting value is increased according to different thicknesses. The roll gap setting value is increased by 2%-5% compared to the original value. The hot yield strength of low-strength steel grades is set at 210-220 MPa; The hot yield strength of high-strength steel grades is set at 320-340 MPa.

5. The method for improving the head mark of hot rolled coil according to claim 2, characterized in that: The roll gap setting value of low-strength steel with thickness less than 5mm is reduced by 7%-8% compared with the original value; The roll gap setting value of low-strength steel with a thickness of 5-10mm is reduced by 5%-6% compared with the original value; For low-strength steel grades with a thickness greater than 10 mm, the roll gap setting value is reduced by 3%-4% compared to the original value; The roll gap setting value of high-strength steel with thickness ≤10mm is increased by 2%-3% compared with the original value; The roll gap setting value for high-strength steel grades with a thickness greater than 10mm is increased by 4%-5% compared to the original value.

6. The method for improving the head mark of hot rolled coil according to claim 1, characterized in that: In steps 3 and 34, the calculation formula for the raised roller gap value is: S=2H+fH Among them, S is the roll gap value, H is the strip thickness, and f is the compensation coefficient.

7. The method for improving the head mark of hot rolled coil according to claim 1, characterized in that: In steps 3 and 34, the response time is shortened by optimizing the winding roller control response time module and the servo valve integral parameters: The response time module is selected from the T2-T3 gear; The servo valve integral value is set to 25-35.

8. The method for improving the head mark of a hot-rolled coil according to claim 1, characterized in that: In step 2, the real-time pressure regulation process simultaneously optimizes the time module and the servo valve integral value to shorten the roller response time.

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