KR100627487B1 - Method for controlling thickness of strip - Google Patents

Abstract

The present invention relates to a method for controlling the thickness of a steel sheet for controlling the crown by adjusting the fair cross angle and the bender force of the rolling mill, and after receiving information of the steel sheet to be rolled, setting a target crown thickness according to the information of the steel sheet, Deriving the influence factor of the set target crown thickness, setting the optimum operating conditions for the fair cross angle and the bender force among the derived influence factors, and the optimum operating conditions of the fair cross angle and the bender force set according to the information of the steel sheet. Rolling is performed by applying. This makes it possible to produce low-crown products and to control the thickness of rigid steel sheets.

Pair cross, bender, crown, tolerance range, stand

Description

Thickness Control Method of Steel Sheet {METHOD FOR CONTROLLING THICKNESS OF STRIP}

1 is a schematic configuration diagram of a fair cross rolling machine.

2 is a view showing a roll change in accordance with the application of the bender force.

3 is a block diagram showing a control flow applied to the thickness control method of the steel sheet according to an embodiment of the present invention.

4 is a schematic structural diagram of a logic tree for deriving a potential influence factor for a crown applied in the present invention.

5 is a view showing an analysis process for the influence factor of the crown thickness according to the present invention.

6 is a view showing a result of selecting a detailed influence factor of the crown thickness of the present invention.

7 is a simulation result for setting the optimum conditions of the fair cross angle and the bender force according to the present invention.

8 is a graph showing the thickness control results before and after applying the optimum conditions of the fair cross angle and the bender force set in accordance with the present invention.

Explanation of symbols on the main parts of the drawings

100: upper computer 10: steel plate

20,30: Work roll 40,50: Backup roll

The present invention relates to a method for controlling the thickness of a steel sheet, and more particularly, by adjusting a pair cross angle of a pair cross rolling mill and a bender force of a roll bender facility, a thickness difference between a center portion of a steel sheet and both edge portions thereof. (Hereinafter referred to as 'crown') relates to a thickness control method of a steel sheet for controlling within a set value.

In general, as a facility for controlling the thickness of hot rolled steel sheet in the hot rolling process, a pair cross rolling mill and a roll bender facility are widely used. Controlling the crown by adjusting the fair cross angle of the fair cross rolling mill, and adjusting the bender force of the roll bender to produce the medium wave caused by the difference in the amount of stretching in the longitudinal direction of the steel sheet (when the stretching amount in the center portion is greater than both edge portions) The thickness of the steel sheet is controlled by removing the onion and onion (when the stretching amount in the center portion is smaller than both edge portions).

As shown in FIG. 1, the pair cross rolling machine includes a pair of work rolls 20 and 30 and a backup roll 40 and 50, respectively, having a steel plate 10 interposed therebetween, and the upper work piece. A pair of rolls 20 and a backup roll 40 and a pair of lower work rolls 30 and a backup roll 50 are pair-crossed with each other at a predetermined angle θ. The crown is controlled by rolling the steel sheet in the state. In addition, as shown in Figure 2, by controlling the bender force applied to the upper and lower work rolls (20, 30) to remove the medium or onions of the steel sheet to control the crown of the steel sheet. This application of the bender force is implemented by pressing the chokes 60 for the work rolls 20 and 30 at the upper and lower ends by hydraulic cylinders (not shown), respectively.

In the method of controlling the thickness of the steel sheet using the fair cross rolling mill and the roll bending machine, the setting of the fair cross angle and the bender force for obtaining the target plate thickness is most important. In order to accurately set the fair cross angle and the bender force, Consideration should be given to the conditions (eg roll expansion, steel grade, dimensions, rolling properties in rolling, etc.).

In recent years, the demand for the thickness tolerance of steel sheet is becoming more and more strict, and the thickness control of steel sheets for heavy steel, high carbon steel, high strength steel, etc., has become a big issue. In particular, for automobiles or products requiring high precision, the demand for 1/2 tolerance level of ASTM standard is increasing. Furthermore, domestic automakers are also demanding 20 ~ 30% of the JIS standard for some products.

Although the prior art has produced steel sheets with thickness tolerances in accordance with KS, JIS, and ASTM standards so far, in order to meet more stringent tolerance standards in recent years, the degree of fair cross angle and bender force setting have been insufficient. Due to the lack of proper operating standards for cross angle and bender forces, low-crowned products, ie thick stiff materials (e.g., order thickness tolerances of 1/2 to ASTM or 20 to 30% of JIS standards) Product) was limited.

On the other hand, a method of controlling the shape of the hot rolled steel sheet is presented in Korean Patent Publication No. 1998-0003681. The above-mentioned patent obtains a roll bending force to satisfy a roll bending force and a shape constraint between each stand in order to achieve a target crown shape in the shape control of a plate in a rolling mill having a roll bender, and uses this as a feedback control to form a plate. How to control it. However, even in the case of the prior patent, it does not satisfy the stricter tolerance level of KS, JIS, and ASTM standards for general steel, heavy carbon steel, high carbon steel, high tensile steel, etc. The operating conditions for the fair cross angle and the bender force for each steel type are not presented.

Therefore, the present invention has been proposed to solve the above problems, the thickness control of the steel sheet for setting the operating conditions for the fair cross angle and the bender force for each steel type in order to meet the tolerance level for the thickness strict material of the rolled steel sheet The purpose is to provide a method.

In the thickness control method of the steel sheet according to the present invention for achieving the above object, in the steel sheet thickness control method in a hot rolling facility having a pair cross rolling mill and a roll bender having a plurality of stands in front and rear ends,

A first step of receiving information on a steel sheet to be rolled from a host computer; A second step of setting a target crown thickness according to the information of the steel sheet; Deriving an influence factor of the set target crown thickness; Among the derived influence factors, the fair cross angle and the bender force of the front end portions F1 to F3 stand are set to 0.5 to 1.1 degrees and 50 to 200 kg / cm ² , respectively, and the fair cross angle of the rear end portions F4 to F6 stands. And a fourth step of setting the bender force to 0.3 to 0.9 ° and 80 to 200 kg / cm ² , respectively. And a fifth step of performing rolling by applying the paircross angle and the bender force set according to the information of the steel sheet.

In an embodiment of the present invention, the fourth step sets the pair cross angle and bender force of the front end portions F1 to F3 respectively upward, and the pair cross angle and bender force of the rear end portions F4 to F6 stands. Set each downward.

In an embodiment of the present invention, in the fourth step, when the steel sheet to be rolled is a general steel, the fair cross angle and the bender force of the front end portions F1 to F3 stand are 0.5 to 0.9 ° and 50 to 130 kg / cm ^{2, respectively.} Set the crosscross angle and bender force of the rear end stands (F4 to F6) to 0.3 to 0.7 degrees and 80 to 160 kg / cm ² , respectively.

In an embodiment of the present invention, when the steel sheet to be rolled is a heavy carbon steel, the fair cross angle and the bender force of the front end portions F1 to F3 stand are 0.5 to 0.9 ° and 80 to 150 kg / cm, respectively. Set to ^2, and set the crosscross angle and bender force of the rear end (F4 to F6) stands to 0.4 to 0.8 ° and 130 to 200 kg / cm ² , respectively.

In an embodiment of the present invention, in the fourth step, when the steel sheet to be rolled is high carbon steel, the fair cross angle and the bender force of the front end portions F1 to F3 stand are 0.6 to 1.1 ° and 100 to 200 kg / cm, respectively. Set to ^2, and set the crosscross angle and bender force of the rear end (F4 to F6) stands to 0.4 to 0.8 ° and 130 to 200 kg / cm ² , respectively.

In an embodiment of the present invention, in the fourth step, when the steel sheet to be rolled is a high tensile steel, the pair cross angle and the bender force of the front end stand are set to 0.7 to 1.1 ° and 120 to 200 kg / cm ² , respectively. Set the faircross angle and the bender force of the end stands to 0.4-0.9 ° and 130-200 kg / cm ² , respectively.

Here, for each steel grade of each steel plate, the pair cross angle of the center part F3 stand is set smaller than the pair cross angle of the front end stand, and the bender force of the last stand F7 is smaller than the bender force of the rear end stand. Or set equal to

Further, in an embodiment of the present invention, the second step is to set the target crown thickness of the steel sheet to 40㎛, and to set the target plate thickness and upper and lower management tolerances of the hot rolled steel sheet according to the set target crown thickness Steps.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

3 is a block diagram showing a control flow applied to the thickness control method of the steel sheet according to an embodiment of the present invention. Referring to FIG. 3, in a hot rolling apparatus having a pair cross rolling mill and a roll bender having a plurality of stands at front and rear ends, information on steel type, thickness, and width of the steel sheet 10 to be rolled from the host computer 100 is provided. The target crown thickness and the upper and lower tolerance ranges according to the received information of the steel sheet 10 are set (200). Deriving the influence factor of the set target crown thickness (300), and setting the optimum operating conditions for the pair cross angle and the bender force among the derived influence factors (400), the pair set according to the information of the steel sheet 10 The rolling is performed by applying the optimum operating conditions of the cross angle and the bender force (500).

Referring to Figure 3, the annual rolling facility according to the present invention is provided with seven stands (F1 ~ F7). For convenience of description, F1 to F3 are defined as the front end stand, F4 to F6 as the rear end stand, F3 as the center stand, and F7 as the last stand. Each stand can be set with a pair cross rolling mill as needed among the said F1-F7 stands. This can be appropriately set in consideration of the plate-flowability of the rolled steel sheet.

Various information including the steel type, thickness, and width of the steel sheet 10 to be rolled is managed from the host computer 100. The host computer 100 performs all the management related to the rolling, but will be described with respect to the information of the steel sheet related to the present invention. The host computer 100 manages information of a product required by the demand price. For example, the host computer 100 manages the type, thickness, width, length, serial number, and the like of the steel sheet to be rolled. Here, the types of steel sheets include ordinary steel, bicarbonate steel, high carbon steel, high tensile steel, and the like.

Receiving the information on the steel sheet from the upper computer 100, and sets the target crown thickness and the upper and lower tolerance range according to the information of the steel sheet (200). The target crown thickness is adjusted downward to ensure a low crown steel sheet product. Preferably, the target crown thickness for the thickness stiffener is currently set at 60 μm to 40 μm. Thereby, the total target plate | board thickness and upper and lower management tolerances of a hot rolled sheet steel are set. The plate thickness of the steel sheet is measured using X-rays. The overall target plate thickness and the upper and lower limit management tolerances of the steel sheet for managing the plate thickness measured by the X-ray to the target plate thickness are set using the following Equation 1.

[Equation 1]

Target plate thickness of steel sheet (T) = TT + (U0 + L0) / 2 + Ci / 2

Upper limit management tolerance (U) = (U0-L0-Ci) / 2-S

Lower control tolerance (L) = (L0-U0 + Ci) / 2 + S

(TT is the pre-set hot rolling target thickness (mm), U0, L0 is the upper and lower tolerances (μm), Ci is the target crown thickness of the steel sheet (μm), S is the crown inverse deviation set value)

For example, if the target crown thickness for low crown products is set to 40 µm, the hot rolled target thickness of the steel sheet is 1.506 if the order thickness of the demand is 1.499 mm and the acceptance tolerance is L0 = 0, U0 = 150 µm. mm (= 1.499 + (1 + 0.5 / 100)), so that the overall target plate thickness (T) for X-ray management is 1.601 mm (= 1.506 + (0.15-0) / 2 + 0.04 / 2 )to be. In addition, the upper limit management tolerance U is -0.035mm (= (0-0.15-0.04) / 2-0.02), and the lower limit management tolerance is 0.035mm (= (0.15-0-0.04) / 2-0.02).

Subsequently, a plurality of influence factors influencing the set target crown thickness are derived 300. In the present invention, a logic tree is used to derive a potential influence factor on the crown. 4 is a schematic structural diagram of a logic tree for deriving a potential influence factor for a crown applied in the present invention. Referring to FIG. 4, the factors affecting the crown are largely classified into machine / method, material, and man, and the influence factors are detailed in FIG. 4 as shown in FIG. 4. A total of 29 influence factors were classified.

For these 29 influence factors, potential major influence factors through multi-voting were selected as shown in Table 1 below.

Table 1

Influence Factor Importance Multi-Voating Controllability Indication A B C D E system RA / Bender Poor Learning 7 7 5 5 7 31 U Improved learning Inappropriate RA / Bender settings 9 9 9 9 9 45 C RA / Bender value Improper manual installation 5 5 7 9 7 33 C Minimize manual setting ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ ㆍ Understanding of abnormal work 5 5 7 7 5 29 U Standard setting Understanding of coil quality characteristics 9 7 7 7 7 37 U Recognition of quality characteristics by coil

(Where importance is 1 = Normal, 3 = Slightly important, 5 = Important, 7 = Very important, 9 = Absolute, C is Controllable, U is Uncontrollable.

As shown in the above table, the potential major influence factors are selected through multi-voting as shown in Table 2 below.

[Table 2]

Major Influence Factor Control Indication Remarks (Integrated Factor) Improper pair cross angle setting C Fair Cross Angle Inappropriate setting of vendor power C Bender power Thickness Control Tolerance U Rolling Control Tolerance Automatic modification of thickness control tolerance when changing crown design-> Possible to integrate Crown Goal Design U Crown design value Extraction temperature C Extraction temperature Rough rolling temperature C RDT Same influence factor-> can be integrated Filament rolling temperature C FTO set change U set change Unit combination (the number of heads) Understanding of coil quality characteristics C Recognition of quality characteristics by coil

In Table 2 above, the technical characteristics between potential major influence factors are similar or identical.

Subsequently, a detailed influence factor of the nine main influence factors shown in Table 2 was analyzed. Data mining (Decision Tree analysis, Regression analysis, Variable Seletion) analysis was used as an analysis tool. This analysis process is shown in FIG. 5, and the selection result of the detailed influence factors is shown in FIG. 6. Referring to FIG. 5, it can be seen that a low crown is formed when the pair cross angle is large, and a low crown is formed when the bender force value is large. Also, in the analysis result of Decision Tree analysis in FIG. 5, a pair of F1 and F4 stands is shown. The cross angle and the bender of the F3 and F5 stands were selected as the influencing factor, the pair cross angle of the F1 and F4 stands and the bender of the F3 and F4 stands were selected as the influencing factor in the regression analysis results, and the F1 in the variable seletion analysis result. The pairing angle of the F4 stand and the bender of the F3 and F5 stands were selected as the influencing factors. As shown in FIG. 6, the detailed influence factors on the crown thickness were selected as the pair cross angle, the bender force, the set number, and the like, in particular, the pair cross angles of the first, third and fourth stands, and the third, fourth and fifth stands. Vendor power was selected as the main key influencer. The set number is not a factor that can be managed in the operation, and it can be seen from the beginning of the set change that the faircross angle and the bender force control are important.

As such, the results of selecting and verifying the major influence factors affecting the crown thickness are shown in Table 3 below.

Table 3
division Quantitative factors Qualitative Factors Process factors Major Influence Factor 1.Fair cross angle 2.Bender force Quality characteristic factor by coil 1. Crown design target-X-ray target thickness-Thickness control tolerance 2. Process change

delete

When the crown target thickness is changed, the rolling x-ray target value and thickness control tolerances are changed, and the crude root and extraction temperatures, which are potential root influencing factors, were excluded from the verification phase.

7 is a DOE simulation diagram for setting the optimum conditions of the fair cross angle and the bender force according to the present invention. Referring to FIG. 7, a simulation in which an optimal level and an optimal direction of the fair cross angle and the bender force are derived through the DOE is illustrated. As an example, the simulation of FIG. 7 was performed 16 times at the level of 4 factor 2 through the Full-Factorial Design for general steel. Here, the four factors are the face cross angle and the bender force of the front and rear end stands of 0.2 °, 0.6 °, 20kg / cm ² and 120kg / cm ² , respectively. Looking at the conditions of the fair cross angle and the bender force of the front and rear end stands in response to the simulation result of FIG. 7, the edge flatness of the roll flat increased due to the reduction of the edge was reduced by the pair cross and the bender force of the front end stand. It is necessary to eliminate the edge thickness by reducing the cross-cross angle and bender force of the rear end stand, and to control the sinusoidal crown. In addition, it is necessary to reset the medium wave by excessive control of the fair cross angle of the central stand F3 and the experimental plan technique for onion control in the last stand F7.

The inventors have carried out the working conditions for the fair cross angle and the bender force of the front and rear end stands by steel type and thickness through the experimental design technique for a long time. As a result, the fair cross angle of the front end stand is adjusted upward and the rear end stand is We found the need to set the faircross angle of to be adjusted downward. In addition, the inventors have found the necessity of adjusting the bender force of the front end stand upward and adjusting the bender force of the rear end stand downward. Specifically looking, the steel plate in this case general lecture pair cross angle of the front end portion a pair cross angle of the stands are set to 0.6 - 0.8 °, and the rear end stand and to 0.5 ~ 0.6 ^°, vendor force of the front end stand is 100 and We found the need to set 150 kg / cm ² and the bender of the rear end stand to 80-120 kg / cm ² . At this time, the necessity of setting the faircross angle of the center stand F3 to 0.6 ° and setting the bender force of the last stand F7 to 80 kg / cm ² was found.

In the case of high strength steel, the fair cross angle of the front end stand is set to 0.7 to 0.9 °, the fair cross angle of the rear end stand is set to 0.6 to 0.8 °, and the bender force of the front end stand is 150 to 200 kg / cm. ^It was found that it was necessary to set ² and the bender force of the rear end stand was set at 80 to 150 kg / cm ² . At this time, the necessity of setting the fair cross angle of the center stand F3 to 0.7 ° and the bender force of the last stand F7 to 80 kg / cm ² was found.

Furthermore, the present inventors set the optimum operating conditions for the front cross and the back cross angle and bender force of the front and rear end stands by thickness and width for the general steel, the heavy carbon steel, the high carbon steel, and the high tensile steel through more experiments. Are shown in Tables 4-7, respectively.

Table 4

Table 5

Table 6

Table 7

As such, when the optimum conditions for the facrose angle and the bender force, which are the influence factors of the crown thickness, are set (400), rolling is performed by applying the optimum operating conditions of the paircross angle and the bender force set according to the information of the steel sheet 10. Perform 500.

8 is a graph showing the thickness control results before and after applying the optimum conditions of the fair cross angle and the bender force set in accordance with the present invention. Referring to FIG. 8, it can be seen that thickness control is better after the application of the fair cross angle and the bender force set in accordance with the present invention for the general steel and the high tensile strength steel.

The detailed description and the contents of the drawings described above exemplarily describe a preferred embodiment of the thickness control method of the steel sheet according to the present invention, but the present invention is not limited thereto. In particular, the selection technique, verification technique, etc. applied in the present invention can be applied to various techniques within the scope not departing from the technical spirit of the present invention as an example. Accordingly, the scope of the present invention should not be determined by the above description and drawings, but should be determined by the appended claims.

According to the present invention, a steel plate of low crown can be produced with respect to a thickness strict material, and the operator can roll the steel sheet according to a preset fair cross angle and operating conditions of the bender force, thereby increasing production efficiency.

In addition, it is possible to significantly reduce the product defects by removing the edge onion, medium wave due to securing the low crown products, it is possible to provide a product that meets the demand of the demand.

Claims (10)

In the steel sheet thickness control method in a hot rolling facility having a fair cross rolling mill and a roll bender having a plurality of stands at the front and rear ends, A first step of receiving information on a steel sheet to be rolled from a host computer; A second step of setting a target crown thickness according to the information of the steel sheet; Deriving an influence factor of the set target crown thickness; Among the derived influence factors, the fair cross angle and the bender force of the front end portions F1 to F3 stand are set to 0.5 to 1.1 degrees and 50 to 200 kg / cm ² , respectively, and the fair cross angle of the rear end portions F4 to F6 stands. And a fourth step of setting the bender force to 0.3 to 0.9 ° and 80 to 200 kg / cm ² , respectively. And A fifth step of performing rolling by applying a fair cross angle and a bender force set according to the information of the steel sheet; Steel plate thickness control method comprising a. The method of claim 1, wherein the fourth step, Steel plate thickness control characterized by setting the fair cross angle and the bender force of the front ends F1 to F3 stand upward, and setting the fair cross angle and the bender force of the rear ends F4 to F6 stands downward, respectively. Way. The method of claim 1, wherein the fourth step, If the steel sheet to be rolled is a general steel, the fair cross angle and the bender force of the front end (F1 ~ F3) stand is set to 0.5 ~ 0.9 ° and 50 ~ 130kg / cm ² , respectively, and the rear end (F4 ~ F6) of the stand Steel sheet thickness control method characterized in that the fair cross angle and the bending force is set to 0.3 ~ 0.7 ° and 80 ~ 160kg / cm ² , respectively. The method of claim 1, wherein the fourth step, When the steel sheet to be rolled is a hard carbon steel, the fair cross angle and the bender force of the front end (F1 ~ F3) stand is set to 0.5 ~ 0.9 ° and 80 ~ 150kg / cm ² , respectively, the rear end (F4 ~ F6) stand Steel sheet thickness control method, characterized in that the fair cross angle and the bender force of 0.4 ~ 0.8 ° and 130 ~ 200kg / cm ² respectively. The method of claim 1, wherein the fourth step, If the steel sheet to be rolled is a high carbon steel, the fair cross angle and the bender force of the front end (F1 ~ F3) stand is set to 0.6 ~ 1.1 ° and 100 ~ 200kg / cm ² , respectively, Steel sheet thickness control method characterized by setting the fair cross angle and the bender force to 0.4 ~ 0.8 ° and 130 ~ 200kg / cm ² , respectively. The method of claim 1, wherein the fourth step, When the steel sheet to be rolled is high tensile steel, the fair cross angle and the bender force of the front end stand are set to 0.7 to 1.1 ° and 120 to 200 kg / cm ² , respectively, and the fair cross angle and the bender force of the rear end stand are 0.4 to respectively. Steel plate thickness control method characterized in that set to 0.9 ° and 130 ~ 200kg / cm ² . The method according to any one of claims 3 to 6, A steel sheet characterized by setting the fair cross angle of the stand of the center part F3 to be smaller than the fair cross angle of the front end stand, and setting the bender force of the last stand F7 to be smaller than or equal to the bender force of the rear end stand. Thickness control method. The method of claim 1, wherein the second step is A steel plate thickness control method, wherein the target crown thickness of the steel sheet is set to 40 μm. The method of claim 1, wherein the second step, And setting the target plate thickness and the upper and lower limit management tolerances of the hot rolled steel sheet according to the set target crown thickness. The method of claim 9, A steel plate thickness control method, characterized in that the target plate thickness and the upper and lower management tolerances of the steel sheet are set using the following equation. [expression] Target plate thickness of steel sheet (T) = TT + (U0 + L0) / 2 + Ci / 2 Upper limit management tolerance (U) = (U0-L0-Ci) / 2-S Lower control tolerance (L) = (L0-U0 + Ci) / 2 + S (TT is the pre-set hot rolling target thickness (mm), U0, L0 is the upper and lower tolerances (μm), Ci is the target crown thickness of the steel sheet (μm), S is the crown inverse deviation set value)

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