Control method for improving surface quality of head of hot rolled steel coil

Abstract

The invention provides a control method for improving the surface quality of the head of a hot rolled steel coil, which comprises the following steps of: (1) determining the advance rate of a winding drum and a wrapper roll according to the target thickness of strip steel, and then adjusting the set values of the speed of the winding drum and the speed of the wrapper roll according to the determined advance rate of the winding drum and the determined advance rate of the wrapper roll; (2) adjusting the set value of the pressure of the wrapper roll according to the following formula: the pressure of the wrapper roll = the target thickness of the strip steel * the target width of the strip steel * the thermal yield strength of the strip steel * 0.8, and the minimum pressure of the wrapper roll is 40kN; (3) adjusting the set value of the roll gap of the wrapper roll, wherein the set value of the roll gap of the No.1 wrapper roll is 1.5 times of the target thickness of the strip steel; the set value of the roll gap of the second wrapper roll is 1.3 times of the target thickness of the strip steel; and the set value of the roll gap of the wrapper roll III is 1.1 times of the target thickness of the strip steel. According to the technical scheme, the defects that the head of the hot-rolled strip steel is scratched, folded and the like are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled plate and strip steel, and in particular to a control method for improving the surface quality of a hot-rolled steel coil head. Background Art

[0002] Coiling is the last process of the hot rolling mill. The strip rolled out of the finishing mill enters the down coiler under the bending action of the pinch roller after laminar cooling. The down coiler is mainly composed of a reel and an auxiliary coiling roller. With the assistance of the auxiliary coiling roller, the strip is wrapped around the reel, and finally the coiling of the steel coil is realized under the action of the reel.

[0003] In Siemens' control system, in order to avoid the narrow width phenomenon during the coiling process and the impact of high-speed coiling on the equipment, a smooth coiling mode is adopted, that is, when the strip head enters the coiler, the coil runs at a speed 1.025 times ahead of the final stand of the finishing mill. After the pinch roller bites the steel, it rises to a speed 1.08-1.14 times ahead of the final stand of the finishing mill according to the set acceleration, and the expansion of the coil is completed at the same time. However, for the strip head, in the process of head expansion, in addition to the tension of the finishing mill and the coil, it is also affected by the pressure of the auxiliary coil roller and the expansion of the coil on the strip. Under the coupling of multiple forces, the strip head may slide relatively, and eventually produce defects such as scratches and folds on the head.

[0004] The head defects produced in the steel coil building process can only be detected and discovered during the use of the next process. If the next process is flattening and acid rolling, the defects can be prevented from being missed to the end user by cutting off. If the steel coil is sent directly to the end customer, it will cause quality objections to varying degrees, affecting the company's product image. Therefore, it is urgent to take measures to control it. Summary of the invention

[0005] Based on the above technical problem that the head defects may occur in the hot rolled steel strip during the sheet building process, a control method for improving the surface quality of the head of the hot rolled steel coil is provided.

[0006] The technical means adopted by the present invention are as follows:

[0007] A control method for improving the surface quality of a hot rolled steel coil head, specifically comprising, in a coiling step, optimizing the coiling speed of a coiler and the speed, pressure and roll gap of a coiling auxiliary roller:

[0008] (1) According to the target thickness of the strip, determine the advance rate of the reel and the auxiliary reel roller:

[0009] Strip target thickness / mm Auxiliary roll advance rate / % Roll advance rate / % ≤4.5 8～12 9～11 ＞4.5～9.5 7～10 6～9 ＞9.5 5～8 4～7

[0010] Then, according to the determined advance rate of the reel and the advance rate of the auxiliary winding roller, the set values ​​of the reel speed and the auxiliary winding roller speed are adjusted according to the following formula: reel speed / auxiliary winding roller speed = finishing mill end stand speed * (1+reel advance rate / auxiliary winding roller advance rate); the reel and the auxiliary winding roller are controlled to run at a uniform speed according to the calculated set value;

[0011] (2) Adjust the setting value of the reel roller pressure according to the following formula: reel roller pressure = target strip thickness * target strip width * thermal yield strength of strip * 0.8, and the minimum reel roller pressure is 40 kN;

[0012] (3) Adjust the setting value of the gap between the auxiliary rolls:

[0013] The setting value of the roll gap of the No. 1 auxiliary roll is 1.5 times the target thickness of the strip;

[0014] The setting value of the roll gap of the No. 2 auxiliary roll is 1.3 times the target thickness of the strip;

[0015] The setting value of the roll gap of the No. 3 auxiliary winding roller is 1.1 times the target thickness of the strip.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The control method for improving the surface quality of the head of a hot-rolled steel coil provided by the present invention can significantly improve the occurrence of scratches and folding defects on the head of the hot-rolled strip without increasing costs by optimizing the reel speed, auxiliary reel speed, roll gap and pressure parameters of the coiler, thereby creating higher economic benefits.

[0018] Based on the above reasons, the present invention can be widely promoted in the field of hot-rolled plate and strip steel production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0020] Figure 1 The number of folds at the head of the hot-rolled steel coil before and after the control method of the present invention is adopted in Example 1.

[0021] Figure 2 The scratch length of the head of the hot rolled steel coil before and after the control method of the present invention is adopted in Example 1. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides a control method for improving the surface quality of the head of a hot-rolled steel coil, which specifically includes, in the coiling step, optimizing the reel speed of the coiler and the speed, pressure and roll gap of the auxiliary coiling roller:

[0024] (1) According to the target thickness of the strip, determine the advance rate of the reel and the auxiliary reel roller:

[0025] Strip target thickness / mm Auxiliary roll advance rate / % Roll advance rate / % ≤4.5 8～12 9～11 ＞4.5～9.5 7～10 6～9 ＞9.5 5～8 4～7

[0026] Then, according to the determined advance rate of the reel and the advance rate of the auxiliary winding roller, the set values ​​of the reel speed and the auxiliary winding roller speed are adjusted according to the following formula: reel speed / auxiliary winding roller speed = finishing mill end stand speed * (1+reel advance rate / auxiliary winding roller advance rate); the reel and the auxiliary winding roller are controlled to run at a uniform speed according to the calculated set value;

[0027] (2) Adjust the setting value of the reel roller pressure according to the following formula: reel roller pressure = target strip thickness * target strip width * thermal yield strength of strip * 0.8, and the minimum reel roller pressure is 40 kN;

[0028] (3) Adjust the setting value of the gap between the auxiliary rolls:

[0029] The setting value of the roll gap of the No. 1 auxiliary roll is 1.5 times the target thickness of the strip;

[0030] The setting value of the roll gap of the No. 2 auxiliary roll is 1.3 times the target thickness of the strip;

[0031] The setting value of the roll gap of the No. 3 auxiliary winding roller is 1.1 times the target thickness of the strip.

[0032] There are two main factors that cause embossing at the head of a hot-rolled steel coil. First, during the coil building process, the tension between the finishing mill and the coil is set too high, resulting in a strong compressive stress on the second circle from the head of the strip under the action of the large tension, which leads to embossing. Second, during the coil head forming process, the auxiliary roll exerts a strong pressure on the strip, and under the action of the pressure, the head of the strip produces compressive stress on the second circle, which leads to embossing defects.

[0033] In the speed-up coiling mode in the existing coiling process control system, the coiler runs at an advance rate of 102.5% relative to the final stand of the finishing mill before coiling. When the head of the strip enters the coiler, the coiler speeds up until the set advance speed is reached. During the speed-up process, the auxiliary coiler rolls press against the surface of the strip. At the same time, under the action of the coiler acceleration, the strip tension increases instantly. The superimposed pressure of the auxiliary coiler rolls causes the head of the strip to produce a strong compressive stress on the second circle, thereby producing defects such as folding and scratching. The present invention comprehensively controls the roll gap of the auxiliary coiler roll, the pressure of the auxiliary coiler roll, the auxiliary coiler roll and the speed of the coiler roll, especially optimizes the speed-up coiling of the head of the strip to uniform speed coiling according to the advance speed, which can effectively improve the stress state of the head of the strip when it is being tensioned and reduce the impression of the strip caused by the tension and the pressure of the auxiliary coiler roll.

[0034] The method of the present invention was applied to the Xichang Steel and Vanadium hot rolling line to control the surface quality of the head of the hot rolled steel coil from July of a certain year. The comparison results before and after the application are as follows: Figure 1-2 As shown, after applying the method of the present invention, that is, from July to December, the average values ​​of the number of folds and the length of scratches on the head of the hot-rolled steel coils were significantly lower than those in the previous 6 months, which proves that the method of the present invention has significant improvements on the folds and scratches on the head of the hot-rolled steel coils; and the method of the present invention can create higher economic benefits: based on the average weight of the steel coils of 26 tons and an average agreed price reduction of 100 yuan per ton, the annual economic benefits can be: (18.85-7)*26*100*12=369,700 yuan.

[0035] Example 1

[0036] When producing strip steel with a specification of 3.75*1500mm, the method described in the present invention is adopted, and the roll gaps of No. 1, No. 2 and No. 3 auxiliary winding rollers are set to 5.625mm, 4.875mm and 4.125mm respectively, the advance rate of the auxiliary winding rollers is set to 10%, the advance rate of the reel is set to 9%, the set pressure of the auxiliary winding rollers is set to 63kN, and after coiling, there is a slight fold at the head of the strip steel, and the length is about 3 meters. However, if the method described in the present invention is not adopted, there will be 3 folds at the head of the strip steel after coiling, and the length is about 9 meters.

[0037] Example 2

[0038] When the production specification is 2.5*1250mm strip steel, the method described in the present invention is adopted, and the roller gaps of No. 1, No. 2 and No. 3 auxiliary winding rollers are set to 3.75mm, 3.25mm and 2.75mm respectively, the advance rate of the auxiliary winding rollers is set to 11%, the advance rate of the reel is set to 10%, and the set pressure of the auxiliary winding rollers is 54kN. After coiling, the head of the strip steel has 2 slight folds and a length of about 6 meters. If the method described in the present invention is not adopted, the head of the strip steel has 5 folds and a length of about 14 meters after coiling.

[0039] Example 3

[0040] When producing strip steel with a specification of 5.25*1600mm, the method described in the present invention is adopted, and the roll gaps of No. 1, No. 2 and No. 3 auxiliary winding rollers are set to 7.875mm, 6.825mm and 5.775mm respectively, the advance rate of the auxiliary winding rollers is set to 9%, the advance rate of the reel is set to 8%, the set pressure of the auxiliary winding rollers is 76kN, and after coiling, there is a slight fold at the head of the strip steel, with a length of about 3 meters. However, when the method described in the present invention is not adopted, there are 3 folds at the head of the strip steel after coiling, with a length of about 10 meters.

[0041] Example 4

[0042] When the production specification is 13.75*1500mm strip steel, the roll gaps of No. 1, No. 2 and No. 3 winding rollers are set to 20.625mm, 17.875mm and 15.125mm respectively, the leading rate of the winding rollers is set to 8%, the leading rate of the reel is set to 7%, the setting pressure of the winding rollers is 157kN, and there is no fold mark on the strip after coiling, while one fold mark appears at the head after coiling without using the method described in the present invention, and the length is about 3 meters.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for improving the surface quality of a hot-rolled steel coil head, characterized in that: In the winding step, optimize the winder's reel speed as well as the speed, pressure and roll gap of the auxiliary winding rollers: (1) According to the target thickness of the strip, determine the advance rate of the reel and the auxiliary reel roller: Then, according to the determined advance rate of the reel and the advance rate of the auxiliary winding roller, the set values ​​of the reel speed and the auxiliary winding roller speed are adjusted according to the following formula: reel speed / auxiliary winding roller speed = finishing mill end stand speed * (1+reel advance rate / auxiliary winding roller advance rate); the reel and the auxiliary winding roller are controlled to run at a uniform speed according to the calculated set value; (2) Adjust the setting value of the reel roller pressure according to the following formula: reel roller pressure = target strip thickness * target strip width * thermal yield strength of strip * 0.8, and the minimum reel roller pressure is 40 kN; (3) Adjust the setting value of the gap between the auxiliary rolls: The setting value of the roll gap of the No. 1 auxiliary roll is 1.5 times the target thickness of the strip; The setting value of the roll gap of the No. 2 auxiliary roll is 1.3 times the target thickness of the strip; The setting value of the roll gap of the No. 3 auxiliary winding roller is 1.1 times the target thickness of the strip.

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