JP2539877B2 - Method for preventing tailing of continuous rolling mills - Google Patents

Description

Description: [Industrial field of use] The present invention relates to a reduction leveling control method for preventing tailing of a continuous rolling mill.

[Prior art] In a continuous rolling mill, especially when rolling a thin material (for example, in the case of hot rolling, the sheet thickness is less than 2 mm), the tail end portion meanders when the sheet slips out, causing a drawing phenomenon. I have something to do. Here, the term "drawing" means that the plate comes into contact with the side guide due to meandering to cause buckling, and the plate is folded and rolled. This not only leads to yield loss of the finished product but also deteriorates the roll unit consumption due to flaws on the rolling rolls.
This is a big problem because it also causes a decrease in work rate (increased roll replacement).

The following method (Japanese Patent Laid-Open No. 60-170519) is known as a conventional method for preventing the tail restriction. That is, the ratio of the load difference between the work side (WS) and drive side (DS) and the total rolling load is the load difference ratio ((P _W −P _D ) /
If defined as (P _W + P _D )), this load difference rate will change corresponding to the meandering of the plate. Therefore, based on the load difference rate of the stand at the moment when the plate comes out of the upstream stand,
This is a method in which the amount of change from the standard in the load difference rate that occurs as the plate passes through the stand is regarded as meandering, and the amount of reduction leveling is corrected accordingly.

[Problems to be Solved by the Invention] However, the conventional control method still has the following technical difficulties. That is, since the follow-up type leveling control follows the change in the load difference rate caused by the meandering of the plate, the response is lacking and the effect is small.

The change in the load difference rate caused by slipping out of the plate occurs not only due to the meandering of the plate but also due to the effect of the asymmetrical shape of the tail end, so it is good when the two directions are the same, but in the opposite direction. In some cases, the control may rather lead to the result of promoting the diaphragm.

From the above, conventionally, it has been impossible to expect an effective control effect on the tail end of the plate.

In view of such a background, the present invention provides a tail-drawing prevention method for a continuous rolling mill for preventing a drawing phenomenon that occurs particularly at the tail end of a plate.

[Analysis for Solving Problems] First, the results of the analysis performed by the inventors of the present invention based on the hypothesis described below regarding the tail restriction phenomenon will be described.

It is considered that the mass flow unbalance in the width direction between the adjacent stands largely contributes to the occurrence of tail drawing, but in the steady rolling state, the plate thickness distribution in the width direction due to the self-equilibrium action via the tension between the stands, The distribution of forward and backward rates has changed in the relaxation direction, and the imbalance has not become apparent. However, when slipping out of the buttocks, it is assumed that there will be a reversal of tension, and an imbalance will develop, leading to the buttocks. Based on this hypothesis, there should be a strong correlation between the minute change in the load difference rate and the occurrence of tail restriction when the tension applied state before slipping out of the tail is changed to the non-tension state.

With such an aim, as shown in FIG. 3, the load difference rate (P _df / P) _{1 of the} stand in the tension applied state before slip-out and the plate immediately before the stand stand and the tension disappears. The difference with the load difference rate (P _df / P) _{2 at} the moment when it was released Δ (P _df / P) = (P _df / P) ₂ − (P _df / P) ₁ The fourth
Shown in the figure.

Fig. 4 shows the tail-drawing analysis of a hot-finishing rolling mill consisting of 6 stands for a rolled material with a finishing plate thickness of less than 2 mm and which is likely to cause a drawing phenomenon. (B) shows the case where there is no tail stop. As can be seen from this example, the parameter Δ
(P _df / P) has a strong correlation with the tail diaphragm, and the polarities in the direction of the diaphragm (work side or drive side) are almost the same.

That is, when the tail stop occurs at the F6 stand (Fig. 4 (a)), compared with the case without the tail stop (Fig. 4 (b)), Δ (P _df / P)
When the absolute value of is large and the sign is positive, there is a tendency to narrow to the WS side, and conversely, when the sign is negative, to the DS side. Furthermore, as shown in FIG. 4 (a), the tail stop of the F6 stand is Δ (P _df /
P) is also correlated, and the value of Δ (P _df / P) on the F5 stand is F6
If it is larger in the same sign direction as that of Δ, Δ of F6 stand
Even if the value of (P _df / P) is not so large, there is a tendency that an aperture is likely to occur.

[Means for Solving the Problems] The present invention made based on the findings obtained above predicts the tail restriction based on the value of the parameter Δ (P _df / P), and feed-forwards the reduction leveling. This is a control method in which tail correction is prevented by making corrections. That is, the method for preventing the tail reduction in the continuous rolling mill of the present invention, in the rolling leveling control for suppressing the bending and meandering of the plate in the continuous rolling mill, regarding the trailing edge of each stand, is close to the trailing edge. The load difference ratio (value obtained by dividing the load difference between the work side and the drive side by the total rolling load) at the stage where the plate has not been pulled out from the upstream stand just before and the rear tension exists between the stands and It is characterized in that the tail throttle of the stand is predicted based on the difference in the load difference rate at the moment when the plate passes through the upstream stand and the rear tension disappears, and the reduction leveling control of the stand is performed based on this prediction.

According to FIG. 4, when predicting the tail stop of the F6 stand, it can be done only by the magnitude of Δ (P _df / P) of F6 (for example, Δ (P _df / P of the vertical axis of F6
If P) is large on the positive side, it is easy to narrow down to the work side), and more accurate diaphragm prediction can be expected by patterning the information of multiple stands (for example, F5 and F6).
Specifically, the larger the value of F5 stand Δ (P _df / P), the value of the F6 Δ (P _df / P) is to produce a diaphragm be not so large in the same direction, contrary to the F5 If the absolute value of Δ (P _df / P) is small, the aperture is likely to occur when the value of (P _df / P) of F6 is large. If this is expressed in a table, it will be as shown in Table 1.

If you predict the aperture with this pattern recognition method,
Since the direction of the throttle can be specified, the tail leveling can be prevented by performing feed-forward correction control of the reduction leveling of the stand, that is, by performing the leveling correction that tightens the pressure reduction on the side of the predicted aperture direction.

FIG. 1 is a schematic representation of the control method of the present invention, in which Δ (P _df /
The pattern (P) indicates that the tail stop of the stand is predicted and the reduction leveling of the stand is corrected.

The control method of the present invention has the following advantages over the conventional method. That is, (1) The plate is pulled out of the upstream stand by magnifying and monitoring a minute load difference rate change Δ (P _df / P) that has not been considered in the past during the transition from the tension application state to the tension disappearance state. At that moment, the tail throttling tendency of the stand can be predicted, and the reduction leveling control by feedforward can be performed, which is advantageous in terms of responsiveness as compared with the conventional feedback control.

(2) The parameter Δ (P _df / P) is a parameter that does not depend on the asymmetrical shape of the tail end portion, so it is unlikely that the aperture direction is erroneous depending on the tail end shape as in conventional control. .

FIG. 2 shows an embodiment of the present invention. In the hot strip rolling mill comprising the F1 to F6 stands, a slight change in load difference rate Δ (from the tension applied state of the F5 and F6 stands to the transition to the tension disappearance state Δ ( Aperture control (F6 based on P _df / P)
An example of modification of the stand-down leveling is shown. That is, in this example, the load difference rate change of F5: large and the load difference rate change of F6: medium pattern, and it is predicted that tail restriction will occur at the F6 stand. The F6 stand aperture control output is performed at. As a result of performing such aperture control, the aperture generation rate could be reduced to almost half that of the conventional one.

[Effects of the Invention] As described above, the present invention is an invention that can prevent drawing at the time of strip trailing in a continuous rolling mill and contribute to improvement in product yield, improvement in work rate, and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a control method of the present invention, FIG. 2 is a diagram showing a load difference rate change of F5 and F6 stands and an F6 stand throttle control output in the embodiment of the present invention, and FIG. 3 is a load difference rate. Fig. 4 is a correlation diagram with Δ (P _df / P) as a pattern and the tail stop.

Claims (1)

(57) [Claims] 1. In a rolling leveling control for suppressing bending and meandering of a plate in a continuous rolling mill, regarding the slip-out of each stand, the plate is slipping out of the upstream stand which is close to the slip-out but is just before. Without the load difference rate (value obtained by dividing the load difference between the work side and the drive side by the total rolling load) when there is rear tension between the stands and the plate immediately past the upstream stand, there is no rear tension. A method for preventing tail restriction of a continuous rolling mill, which comprises predicting tail restriction of the stand based on a difference in load difference rate at a given moment, and performing reduction leveling control of the stand based on the prediction.