JPH03221203A - Method for preventing necking of hot strip - Google Patents

Abstract

PURPOSE:To surely prevent necking by measuring the position of the transformation temp. of the present strip in the direction of line with plural transformation rate sensors and predicting the generating position of necking based on that result. CONSTITUTION:The plural transformation rate sensors 4 are arranged on run out tables 3 to measure the position of transformation temp. of the present strip 5 and the position of transformation temp. of the strip 5 can be measured with these transformation temp. rate sensors 4. And, because the generating position of necking is predicted based on the position in the direction of rolling process line, the generating position of necking can be predicted with high accuracy. Therefore, the generation of necking can be surely prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for preventing necking that occurs in a specific portion of a strip when winding the strip after exiting a final finishing mill during a hot rolling process. Regarding.

[Conventional technology]

In hot rolling, when a rolled strip is wound onto a winding device, the excessive tension generated between the final rolling mill and the winding device at the moment the tip of the strip is wound around the winding device The so-called necking phenomenon, in which a narrow portion occurs at a specific portion in the longitudinal direction of the strip, is known.

Traditionally, the usual method to prevent this necking is to
There is a method in which the width of the strip is uniformly increased by an amount equivalent to necking over the entire length of the strip and then rolled. However, in this method, at least a portion corresponding to the additional amount must be cut on both sides in the next step, resulting in a problem of lower yield.

In recent years, several methods have been disclosed for effectively preventing this necking. In Japanese Patent Publication No. 5143460, the necking position and amount of necking in the strip are predicted from the composition, size, rolling conditions, and winding conditions of the strip, and the plate of the necking portion of the rough bar is prepared in advance on the inlet side of the hot rolling mill. A method is disclosed in which the width is widened to an amount commensurate with the amount of necking by reducing the amount of width loss by edger rolls, and then finish rolling is performed.

Moreover, in JP-A-62-68617, based on the necking prevention method disclosed in JP-A-51-43460, in order to further improve the prediction accuracy of the necking occurrence position and necking amount of the strip, Width gauges, thermometers, etc. are installed at the exit side of the finishing rolling mill and the entrance side of the winding device, and the strip temperature and strip width at the exit side of the finishing rolling mill and the entry side of the winding device are measured by these measuring instruments. The actual values of the amount of width loss due to necking, position, and length are calculated from A method of setting the optimum value by sequentially correcting it through learning is disclosed.

[Problem to be solved by the invention]

However, the known method described in the above publication has the following problems.

In the method described in Japanese Patent Publication No. 51-43460,
The position and amount of necking may change depending on various factors such as the cooling conditions of the rough bar, rolling conditions, and tension fluctuations between the finishing mill and the winding device. It is difficult to predict the amount.

Furthermore, in the method described in JP-A No. 62-68617, measuring instruments such as width gauges are usually optically measured, so they are susceptible to the effects of cooling water vapor on the runout table. Due to the error, it is difficult to accurately grasp the amount of necking that occurs in the strip.

In addition, based on the actual values of width loss, position, and length due to necking, inappropriate data of the prediction model formula for width loss due to necking, position, and length is sequentially corrected by learning. Even if it is set to the optimum value, as described above, the position and amount of necking change depending on various factors at the time, so there is a limit as long as the prediction does not correspond to the current strip being rolled.

Therefore, the main object of the present invention is to provide a method of detecting the line direction position of the current strip transformation point, predicting the necking position of the current strip with high accuracy based on this measurement result, and thereby reliably preventing necking. It's about doing.

[Means to solve the problem]

In order to solve the above problems, the present invention detects the line direction position of the current strip transformation point using a plurality of transformation rate sensors arranged in the line direction on the exit side of the rolling mill on the hot rolling line, and measures the current strip transformation point. This method is characterized by predicting the necking position of the hot strip based on the results and taking measures to prevent necking.

[Effect]

Generally, as shown in Figure 7, the yield stress during high-temperature tensile deformation of carbon steel increases as the material temperature gradually decreases.
It is known that there is a large local decrease in the −α transformation region.

After finish rolling, the strip is gradually cooled on the runout table, and after the γ-α transformation is completed, it is wound up by the winding device. In a range where the generated excessive tensile stress exceeds the yield stress of the strip, plastic deformation occurs, the strip is elongated in the longitudinal direction, and a narrow portion is formed.

Usually, near the end of the γ--α transformation, the tensile stress generated in the strip exceeds the yield stress, and a necking phenomenon of the strip is observed in this area.

Therefore, in the present invention, the actual measurement of the current strip transformation point position is carried out by arranging a plurality of transformation rate sensors on the lunch-out table and measuring the strip transformation point position using the transformation rate sensors, as described later. I can do it.

Furthermore, as described above, the method of the present invention predicts the necking occurrence position based on the line direction position of the current strip transformation point on the rolling process line. Highly accurate prediction can be achieved compared to methods that predict the location where necking occurs.

[Specific structure of the invention]

The present invention will be explained in detail based on the embodiment shown in FIG.

FIG. 1 shows the final step on the hot rolling line. Usually, the strip 5 is finished rolled by finishing stands 1, l...
After the necessary width reduction is performed by the device 2 in order to obtain a predetermined width accuracy, the sheet is water-cooled on a runout table 3, passed through a vinyl roll 6, and wound up by a winding device 7.

In the present invention, a plurality of transformation rate sensors 4, .
will be placed. Regarding the arrangement section of the transformation rate sensors 4, . . ., it is considered sufficient to arrange them, for example, about 20 m before and after the predicted γ→α transformation end position. Further, the arrangement interval is restricted by the table roller interval, and the minimum interval is about 40011Iff1, but since such precision is not required, they are arranged at an interval of about 2 m.

Metamorphosis position data measured by the metamorphosis rate sensors 4, . . . is sent to the computer 8. The computer 8 calculates in advance the position at which the strip width is to be widened based on the mechanical properties of the strip 5, information on the strip thickness, rolling information, etc., and sends a width reduction control signal to the edger device 2. . In the edger device I2, based on the width reduction control signal, the width reduction amount at the expected necking position is made smaller than other parts, that is, by relaxing the width reduction amount at the expected necking position, relatively. The board width in that area can be expanded.

In the above embodiment, the edger device 2 is used as a means to widen the width of the strip 5, but a looper (not shown) between the finishing stand 1, . Since it is known that the width is directly proportional to the width, by adjusting the looper angle, the tension of the strip 5 can be adjusted, and the width of the strip can be relatively increased at that portion.

Regarding the metamorphosis rate sensor 4 adopted in the above embodiment, the third
This will be explained using figures.

Excitation coil 1O111, 12 and detection coil 13.14.1 between table rollers of runner out table 3
5 is arranged. The excitation coils 10,... are excited with alternating current, and by utilizing the fact that the magnetic properties of each phase are different in the temperature range below the magnetic transformation point (TC), changes in the magnetic properties are interpreted as changes in the magnetic flux distribution. can be detected and the metamorphosis rate measured.

According to the above method, it is not affected by strip cooling water;
Metamorphosis rate can be measured.

Next, the method for predicting the necking occurrence position in the method of the present invention will be explained in Figs. 3, 4, and 5 (a), (b) (
A specific explanation will be given based on c).

In FIG. 3, strip 5 is connected to runout table 3.
When passing above, a plurality of metamorphosis rate sensors 4 installed along the strip traveling direction on the runout table 3
．． 4... measures the transformation rate of the strip 5 at that position. Among these actually measured transformation rates, the distance from the transformation rate sensor 4 closest to the finishing rolling mill to the winding device 7 of the transformation rate sensor 4.4 whose transformation rate exceeds 95% is defined as Lt. Once this distance L[ is determined, the necking start position Ls and necking end position Le are determined using the following equations (1) and (2).

L s = L t + 1/2ΔLn
(1) L e = L t-1/2ΔLn
(2) Here, ΔLn is a constant indicating the necking range (hereinafter referred to as necking constant) and is set based on the mechanical properties of the strip 5, the plate thickness, etc.

Regarding this necking constant ΔLn, Fig. 5(a)(bH
This is explained by c).

The strip 5 that has come out of the finishing stand 1 is cooled on the runout table 3, resulting in a temperature gradient state as shown in FIG. 5(a). When setting the transformation region in the strip under this temperature gradient state, the midpoint of the transformation region is determined and set as the point at which the transformation rate is 95% by the method described above, as shown in FIG. 5(b). Ru. It is generally known that the yield stress curve in the transformation region draws a concave curve as shown in FIG. 5(c), and the strength of that part locally decreases. When the line A of the tensile stress of the strip 5 that occurs when it is wound up into the strip 17 is drawn, the yield stress section ΔL below the line A is
At n, the necking phenomenon occurs. Theoretically, it is as explained above, but in practice it is difficult to accurately predict this range, so the above ΔL
n#20m.

As explained above, the section where necking occurs is the section of L e - L s shown by (1) and (2), but the edger device 2 sets the sheet width in advance for this section. Since it is being widened,
Thickness of strip 5 at device 2 position and winding device 7
It is necessary to correct the necking position based on the ratio of the thickness at the position where the sheet is wound. Therefore, the starting position distance Lo (s) and the ending position distance Lo (
e) is expressed by the following formula.

Lo(s)=Le−Hr/hr−Lm (3)L
o(e)-Ls-Hr/hr-Lm (4
) Here, LO: distance from the tip of the strip to the final finishing stand, Hr: thickness of the strip 5 at the edger device 2 position, hr: thickness at the position where it is wound up by the winding device 7, Lm: final finishing stand It is the distance from l to the edger device 2.

As shown in FIG. 6, the edger device 2 performs a preliminary widening of the plate width by an amount ΔS corresponding to the amount of necking in the section ΔL shown by the above equation, but the preliminary widening amount ΔS is determined based on the winding conditions, material properties and shape of the strip 5, etc. Hereinafter, the above ΔS
A specific example of quantity determination will be described.

Board thickness 2.3+ui, board width 1000II11. [C)
%-0.03% strip under the following conditions, the opening change amount ΔS of the work/sodger device 2 is determined.

〔conditions〕

・Strip speed 700mpm ・Finish outlet temperature 900°C ・Down coiler mandrel lead rate 10% Mandrel motor torque tension σv = 1.8kg/m1 Mandrel inertia tension a M = 1.7kg/r11m" Tension application time t = 0. 4 sec strip temperature 8
The formula for calculating the amount of packing at 70°C is: ε-Elongation rate K = 12.3-38 [C] [C]≦0.06%
=10.3-4.6[C] When calculated under the condition that [C]>0.06% or more, ε=2.46x103.

Therefore, the amount of necking ΔW is ΔW=1000xε=2.46m.

On the other hand, the board width adjustment efficiency η of the edger installed between the finishing stands is η#0.25 (when the rough thickness is 35M1 and the rough width is 1000cm), so the opening change amount ΔS of the finishing stands is ΔS = 2 -4610.25=9.8 m.

By the way, the transformation zone of the strip 5 measured by the transformation rate sensor 4 is usually the same as that of the strip 5 because the advancing speed of the strip 5 and the cooling conditions for the strip are kept constant until the start of the strip winding. It is assumed that there will be no change until the start.

In the above-described specific example, the edger device 2 was placed just in front of the final finishing stand, but this position can also be placed further upstream (to the left in FIG. 4).

〔Effect of the invention〕

As explained above in detail, the following effects can be achieved by the present invention.

In the present invention, the position of the current strip transformation point in the line direction is measured using a plurality of transformation rate sensors arranged on the runout table, and the necking position of the hot strip is predicted based on this measurement result. Accuracy can be achieved, and necking can be prevented reliably and without waste.

[Brief explanation of drawings]

FIG. 1 is a rolling process line diagram for explaining the present invention in detail, FIG. 2 is a diagram for explaining the transformation rate measuring method in an embodiment of the present invention, and FIGS. 3 and 4 are diagrams showing occurrence of necking in the present invention. Figure 5 (a), (b), and (c) are diagrams for explaining the necking constant ΔLn in the method for predicting the necking occurrence position. Figure 6 is a diagram for explaining the necking occurrence position prediction method. FIG. 7 is a diagram showing the expansion of the strip width, and a diagram showing the decrease in yield stress during high-temperature tensile deformation of carbon steel in the γ-α transformation region. ■... Finishing stand, 2... Edger device 3...
・Runner table 4... Metamorphosis rate sensor 5... Strip 6...
Vinci roll, 7... Winding device 8... Computer 1O111, 12... Excitation coil 13.14.15... Detection coil diagram

Claims (1)

[Claims] (1) On the exit side of the rolling mill on the hot rolling line, the position of the current strip transformation point in the line direction is detected by multiple transformation rate sensors arranged in the line direction, and necking of the hot strip is performed based on the measurement results. A method for preventing necking of hot strips, which is characterized by predicting the occurrence position and taking measures to prevent necking.