JPH0526569B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a bending control method for setting the amount of bending when straightening the shape of a hot steel plate using a hot leveler equipped with a bending mechanism. [Prior art] When straightening a thin steel plate using a hot leveler, conventionally, the flatness before straightening was exclusively measured,
Based on this data, the amount of bending of the hot leveler was set. [Problems to be Solved by the Invention] However, the conventional method described above has a problem in that even if the flatness is good immediately after straightening, the flatness deteriorates due to shape changes that occur during the cooling process of the steel plate. SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a method for controlling the bending of a hot leveler that also takes into account changes in shape during the cooling process. [Means for solving the problem] In order to achieve the above object, the present invention provides a hot leveler for hot steel plate having a bending mechanism,
In determining the amount of bending, we measure the flatness of the steel plate before straightening and the temperature distribution in the width direction, estimate the shape change during the cooling process after straightening based on the data, and take this shape change into account. It is characterized by setting the bending amount of the hot leveler. Generally, during leveler straightening, a temperature difference ΔT exists between the center and edge of the steel plate. This temperature difference becomes smaller as the steel plate cools, and the temperature distribution becomes uniform. However, during this cooling process, a difference in shrinkage occurs between the center and edges of the steel plate, and this causes ear waves to occur in the steel plate. If the wavelength of this ear wave is 2l _C and the wave height is h, the difference between it and the temperature difference ΔT is ΔT=1/16α(πh/l _c ) ^2where α is the coefficient of linear expansion of the steel plate. Therefore, by measuring the temperature difference ΔT before and after leveler correction, the ear wave height h after cooling can be estimated, and the bending amount can be set by taking this into consideration. [Function] According to the present invention, since distortion caused by temperature distribution in the width direction is also removed, the flatness of the steel plate after cooling can be improved. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the apparatus used in the present invention. In the figure, 1 is a hot thick steel plate flowing on a line, 2 is a flatness meter that measures the flatness before straightening, and 3 is a thermometer that measures the temperature in the width direction of the thick steel plate 1. The data πh/l _C and ΔT obtained from both measuring instruments 2 and 3 are input to the CPU 4, where the shape change after cooling of the steel plate 1 is predicted, and the bending amount is determined so that the flatness after cooling becomes zero. δ is calculated. The bending amount δ feedforward calculated here is given to the hot leveler 5. Next, the theoretical formula for calculating the amount of bending will be explained. If the calculated residual elongation strain difference due to temperature drop is Δε _h (Δε _h > 0), the target residual elongation strain difference after leveling is Δε ₀
= Δε _h . Now, when the steel plate 1 having the elongation strain difference Δε _i is leveled as shown in FIG. 2, if the elongation strain difference Δε ₀ remains, then Δε ₀ =k・(1−ξ)・Δε _i ... ...(1) However, the following relationship holds true: ξ: plastic deformation rate (1-ξ): elongation difference reduction rate k: constant (obtained by experiment). Here, if the difference in elongation strain added to the steel plate due to roll bending is set as Δε _B = AB ₂ − AB ₁ / AB ₁ (2) with reference to Fig. 2, then the elongation in each section is The distortion difference is as shown in Table 1.

[Table] Here, assuming that k=1/2 is obtained from the summation result using the slit model, Δε ₀ =k・(1−ξ)(Δε _i +Δε _B )−Δε _B ……
Substituting k=1/2 into (3), Δε ₀ = (1−ξ)/2(Δε _i +Δε _B )−Δε _B ……
(4) Also, the steepness on the entrance side of the steel plate is λ _i and the steepness on the exit side is λ ₀
Then, Therefore, by substituting these into equation (4), Δε _B
Δε _B =±{1−ξ/1+ξ(π/2λ _i ) ² } +2/1+ξ(π/2λ ₀ ) ² ...(6) is obtained. Here, the meanings of the symbols in item 1 are as follows: +: When the entrance side shape is an ear wave; -: When the entrance side shape is medium elongated. Furthermore, when there is a temperature difference ΔT in the width direction of the steel plate as shown in Fig. 3, the relationship between the strain ε and the temperature difference ΔT between the center and the edge is as explained below, ΔT=ε/α=1/4α (πh/2l _C ) ² ...(7). That is, if the longitudinal direction of the steel plate is taken as the X-axis as shown in Fig. 4, and the wave height direction perpendicular to the X-axis is taken as the Y-axis, the waveform of the edge in the rolling direction is: Y=h/2sinπ/l _C x... ...(8) However, it can be assumed that h: wave height, 2l _c : wavelength. Here, when the length l _E at the edge with respect to the half wavelength i _c at the center is determined by equation (8), the derivation process is as follows under the symbols shown in FIG. l _E =∫ ^lc ₀ √1+′ ² dx Y′=dY／dx Y′=πh／2l _c cosπ／l _c x If θ=π/l _c x, dθ=π/l _c dx, dx=l _c /πdθ

If we take [formula], however,

〔Effect of the invention〕

When an experiment was conducted to compare the present invention and the conventional method, the results shown in FIG. 6 were obtained. From this graph, it can be seen that the flatness is improved after the present invention is implemented, regardless of whether the entrance side shape is medium elongated or ear wave.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus used in the present invention;
Figure 2 is a graph showing the relationship between bending amount and strain, Figure 3 is a graph showing the relationship between temperature difference and cooling distance, and Figure 4 is a graph showing the relationship between temperature difference and cooling distance.
The figure is an explanatory diagram showing the relationship between ear waves and waveforms, and Figure 5 is a graph showing the relationship between temperature difference and ear wave height.
FIG. 6 is a temperature difference-flatness diagram comparing the present invention and the conventional method, and FIG. 7 is an explanatory diagram for deriving the calculation formula. 1... Steel plate, 2... Flatness meter, 3... Thermometer,
4...CPU, 5...Hot leveler.

Claims (1)

[Claims] 1. In a hot leveler for hot steel sheets with a bending mechanism, the flatness of the steel sheet before straightening and the temperature distribution in the width direction are measured, and based on that data, the change in shape during the cooling process after straightening is estimated, and the shape is calculated. A method for controlling the bending of a hot leveler, characterized in that the bending amount of the hot leveler is set in consideration of the change.