A method for controlling the tension of the looper at the tail of a finishing mill strip

Abstract

This invention discloses a method for controlling the tension of the looper at the tail of a finishing mill strip. The method involves an incrementally increasing deceleration ratio control program for the unloading mill on the upstream stand. Based on the tail-end speed of the mill, a control program and parameters are formulated to achieve stable and continuous effective operation. The purpose of this invention is to provide a method for controlling the tension of the looper at the tail of a finishing mill strip, thereby improving the phenomenon of strip tail slippage and tension loss.

Description

Technical Field

[0001] This invention relates to a method for controlling the tension of the slip loop at the tail of a finishing mill strip. Background Technology

[0002] Currently, customers have increasingly higher requirements for the quality of steel strips. The quality of steel strips mainly involves aspects such as surface, size, and performance. Among these, surface quality is related to surface defects. Generally, the quality of steel strips is determined by identifying surface defects.

[0003] Hot strip mills typically have finishing mill units, usually consisting of 6 to 7 continuous rolling mills. As the most critical finishing mill, the finishing mill plays a decisive role in product quality. A finishing mill unit generally includes small vertical rolls, stands, support rolls, work rolls, roll adjustment devices, guide devices, and loopers. Each stand includes a set of support rolls and a set of work rolls, and guides are installed at each mill inlet and outlet. The looper is located between the two stands before the guides. The looper is used during the finishing continuous rolling process to support the steel strip, store a portion of the roll weight, and maintain a constant flow rate and tension between stands.

[0004] During the rolling of thin strip, there were multiple accidents caused by the strip tail losing tension, resulting in a large number of unplanned accidents and quality issues. The process parameters such as slab exit temperature, R2DT temperature, FET head maximum temperature, and intermediate slab sickle bend were all under normal control. The tracking of the HGC inlet and outlet position sensors on both sides of each stand of the finishing mill was normal. The strip tail exhibited a phenomenon of slippage and loss of tension, resulting in the strip tail losing tension.

[0005] This defect, which has remained unresolved in the hot-rolled region for a long time, severely affects the rolling stability of thin strips and generates numerous roll marks. It results in significant unplanned roll change times, wasting considerable production time, reducing operational efficiency, and causing the strip tail tension curve to resemble... Figure 1 As shown. Summary of the Invention

[0006] Before the steel is ejected from the F4 stand, the rolling is relatively stable. However, starting from the ejection of steel from the F4 stand, the tension of the F6 stand begins to drop from a steady state, causing the strip tail to lose tension, resulting in deviation, tail-wagging, and damage to the rolls. To address this problem, the purpose of this invention is to provide a method for controlling the tension of the looper at the tail of the steel strip in a finishing mill, thereby improving the phenomenon of strip tail looper tension loss.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for controlling the tension of the looper at the tail of a finishing mill strip. The unloading mill on the upstream stand increases the speed reduction ratio control program according to an incremental sequence. Based on the tail-throwing speed of the mill, the control program and control parameters are formulated to achieve stable and continuous effective intervention.

[0009] Furthermore, a fixed reduction value is preset within the program based on experience as a base value. At the same time, an additional value that can be manually adjusted is added to the first-level screen as an adjustable tail reduction value. This value can be changed according to the control situation. The control program does not adopt a step-wise reduction based on the base reduction value, but continuously reduces the speed by increasing the reduction by 0.015-0.025% in each scanning cycle until it reaches the sum of the base value and the dynamically adjusted additional value.

[0010] Furthermore, the scanning speed is continuously reduced by 0.02% per scan cycle.

[0011] Furthermore, this control strategy ensures stable tail angle and tension control, and the tail tension can be adjusted to prevent tail wobble caused by tail tension loss.

[0012] Furthermore, the tension setting of 30MPa at the belt tail can be adjusted from 30MPa to 50MPa.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0014] This invention effectively solves the problem of tail-wagging accidents caused by tail tension loss. The invention provides stable control, does not require frequent replacement and adjustment, and has been verified to be able to operate normally in high-temperature environments, which is very much in line with the actual application and operation in this field.

[0015] This invention effectively improves the problem of tail-end rolling damage caused by tension loss at the tail of thin-gauge steel strips, and significantly reduces the incidence of roll marks. This modification is applicable to steel mills and aluminum plate plants that produce sheet metal using continuous rolling mills, and has strong applicability. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings.

[0017] Figure 1 This refers to the tension loss curve at the tail end of the strip;

[0018] Figure 2 This is the specific control procedure for the strip tail looper tension control method of the present invention;

[0019] Figure 3 The tail tension was improved after adopting the present invention. Detailed Implementation

[0020] A method for controlling the tension of the slip loop at the tail of a finishing mill strip:

[0021] By reviewing the looper control program and observing the observed defects, the team organized discussions, adjusted parameters, and conducted trial rolling. Starting with the steel ejection at the F4 stand, the tension at the F6 stand gradually decreased from approximately 30 MPa to approximately 11 MPa from a steady state, while the looper angle increased from a steady state of 21 degrees to 31 degrees. During this period, methods such as increasing the unit tension and manually reducing the tail speed failed to effectively resolve the issue of strip tail tension loss.

[0022] An attempt was made to add an automated speed reduction function for unloading the upstream stand to prevent tail looper tension loss. An adjustment window was added to the primary screen, and upstream stand unloading was implemented from stands F4 to F7. The current stand initially reduced its speed at a fixed ratio. However, the effect was poor. Initially, the looper angle decreased and tension increased, but as the rolling strip speed was adjusted, the looper experienced slippage and tension loss, resulting in extremely unstable tail control (severe fluctuations in angle and tension). Multiple attempts to optimize the steel-throwing speed reduction function failed to achieve stable control of the tail angle and tension.

[0023] Based on the strategy of unloading the mill at a fixed speed in the upstream stand, a control program was invented to increase the deceleration ratio of the mill by an incremental sequence. After multiple debugging sessions, the control program and control parameters were formulated according to the mill tail-out speed to achieve stable and continuous effective intervention.

[0024] Within the program, a fixed deceleration value is preset as a base value based on experience. Simultaneously, an adjustable additional value is added to the primary screen as an adjustable tail deceleration value, which can be changed according to control conditions. The control program does not perform step-wise deceleration based on the base deceleration value, but continuously decelerates by increasing the deceleration by 0.02% per scan cycle until the sum of the base value and the dynamically adjusted additional value is reached. The specific control program is as follows: Figure 2 As shown.

[0025] After implementing this control strategy, the tail angle and tension control are stable, and the tail tension can be adjusted (the tension setting is 30MPa, and the tail tension can be adjusted from 30MPa to 50MPa), eliminating the tail-wagging problem caused by tail tension loss. The measures of this invention are effective. The improvement in tail tension is as follows: Figure 3 .

[0026] This invention effectively solves the tail-wagging accident caused by tail tension loss through innovative control program. The control is stable and does not require frequent replacement and adjustment. It has been verified that it can operate normally in high-temperature environments, which is very suitable for practical applications and operations in this field.

[0027] This invention effectively improves the problem of tail-end rolling damage caused by tension loss at the tail of thin-gauge steel strips, and significantly reduces the incidence of roll marks. This modification is applicable to steel mills and aluminum plate plants that produce sheet metal using continuous rolling mills, and has strong applicability.

[0028] Application effects and benefits:

[0029] Statistics show that on average, approximately three unplanned work roll replacements are required per month due to strip tail tension loss during thin strip rolling. Each incident lasts about 45 minutes, resulting in an unplanned loss of approximately 310 tons of strip. Each roll damage incident costs approximately 90,000 yuan. Based on this calculation, an annual reduction of 3.07 million yuan in losses can be achieved. The detailed calculation process is as follows:

[0030] (1) Based on a monthly reduction of 0.75 hours of accident time, an average coil weight of 22 tons for low-alloy high-strength thin strip, a rolling rate of 33 coils per hour, and a profit of 300 yuan per ton of steel, the annual profit increase is approximately 1.52 million yuan. Profit increase = 0.75 * 22 * ​​33 * 300 * 12 = 1.9602 million yuan.

[0031] (2) Defective steel coils are judged to have defects and the flattening and re-inspection is carried out. The flattening processing fee is 42 yuan / ton. The average coil weight of low alloy high strength thin strip is 22 tons. Each accident produces 3 coils. The annual efficiency increase is 33,000 yuan per month. Efficiency increase = 3 * 22 * ​​42 * 12 = 33,000 yuan.

[0032] (3) The cost of each millimeter of the roll is about 5,000 yuan. Each accidental roll needs to be ground by about 3mm. Assuming that the accident caused by the belt tail loss is reduced by 3 times per month, and each time a set of F7 rolls is replaced, the annual efficiency can be increased by about 900,000 yuan. Efficiency increase = 2*3*5000*3*12 = 1,080,000 yuan.

[0033] In summary, the combined annual profit increase from these three items is approximately RMB 3.07 million.

[0034] This invention has a novel and unique structure, and a simple and practical program structure, which is very beneficial to actual production needs and has a certain degree of applicability.

[0035] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for controlling the tension of the slip loop at the tail of a finishing mill strip, characterized in that, The upstream stand unloading mill increases the deceleration ratio according to an incremental sequence for program control. Based on the mill tail-throwing speed, the control program and control parameters are formulated to achieve stable and continuous effective intervention. Within the program, a fixed reduction value is preset as a base value based on experience. At the same time, an additional value that can be manually adjusted is added to the first-level screen as an adjustable tail reduction value. The additional value is changed according to the control situation. The control program continuously reduces the speed by 0.02% in each scanning cycle until the sum of the base value and the manually adjusted additional value is reached.

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