JPH0366964B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for controlling tension when changing plate thickness during running in a tandem rolling mill, and in particular, to a tandem rolling mill that continuously rolls a strip-shaped rolled material including a plate thickness change point without stopping rolling. This invention relates to an improvement in the tension control method when changing the running plate thickness. Conventionally, when rolling metal strips, rolling was carried out by setting (set-up) the roll gap of each stand of a tandem rolling mill for each coil, but with this method, (A) rolling was stopped each time the set-up was performed; (B) Many people are required to thread the strip into the rolling mill; (C) The roll unit consumption deteriorates due to scratches on the rolls that occur during threading. (D) Yield is reduced due to the presence of a defective plate thickness at the tip and rear end of the coil; and other problems have occurred. Therefore, in order to alleviate these problems, a completely continuous tandem rolling method has been developed in which each coil is welded and connected and rolled one after another without stopping rolling. In this case, when the thickness of the strip metal material changes, it is essential to change the thickness between runs, and this has conventionally been done using the following method. That is, when the plate thickness change point comes to the i-th stand, the roll gap of the i-th stand and the roll rotation speed upstream from this are changed. Figure 1 shows the stage at which the plate thickness change point P passes the i-th stand.
This figure shows how the running plate thickness is changed using the conventional method. In the figure, h is the material plate thickness (mm), T is the total tension between the stands (tons), , is the pass schedule, and the lower right subscripts i-2 to i+1 are the stand numbers, respectively. Focusing on the total tension T here, the pass schedule is set between the 1st to i-th stands, and the pass schedule is set between the i-th and i+1-th stands downstream of the i-th stand, but the i-th and i+1 The total tension between the th stands is the value Ti determined by the pass schedule.
[ ]. That is, the total tension T was changed to that of the pass schedule after the i-th stand. The i-th stand has both pass schedules,
Since it does not belong to any of the above, it is called a transient stand. This conventional control method is
This has the effect of reducing plate thickness defects (off-gauge) at the rear end of the front coil. Further, when changing the plate thickness from a thin material to a thick material as shown in FIG. 1A, the problem of excessive unit tension does not occur because the total tension of the thin material is set to be low. However, as shown in Figure 1B, when the plate thickness is changed from a thick material to a thin material, the total tension of the pass schedule for the thick material Ti[] (ton)
hangs on the thin material as it is, and the unit tension of the thin material (Kg
f/mm ² ) becomes high. In other words, in tandem rolling, the rolling operation is generally controlled to be performed with a nearly constant unit tension (Kgf/mm ² ) regardless of whether the material is thick or thin. In thin parts, a unit tension that is higher than the normal set unit tension by an amount inversely proportional to the plate thickness ratio is applied, so there is a problem that there is a risk of material breakage due to slight tension fluctuations. It is something that The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is to provide a method for controlling the tension when changing the running plate thickness in a tandem rolling mill without increasing the unit tension and causing no risk of breakage or the like. The present invention provides a strip-shaped rolled material including a plate thickness change point,
In the tension control method when changing the running plate thickness in a tandem rolling mill that rolls continuously without stopping rolling, among the above plate thickness change points, the plate thickness change point where the plate thickness is changed from thick to thin. When passing through the i-th stand, the total tension between the i-th stand where the plate thickness change point exists and the i+1-th stand downstream from it is calculated as follows: By changing the roll gap and roll speed, the above object is achieved by changing the running plate thickness while setting a tension that does not destroy the strip-shaped rolled material. Note that the same method as the conventional method can be used for detecting that the plate thickness change point has passed through a specific rolling stand. For example, since each rolling stand is provided with a load cell to control the amount of rolling reduction, if a sudden change in the detection value of this load cell is detected, it is possible to detect the passing of a specific stand at a plate thickness change point. Detection can also be made by tracking the movement of the plate thickness change point based on the rolling speed and elapsed time based on a certain specific position and time. An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 2 shows a schedule pattern corresponding to one embodiment of the present invention. In this example, between the stands including the plate thickness change point P, the set tension Ti in the pass schedule of the next coil with a thin plate
[] is used for rolling. In this case, since the rear tension of the i+1-th stand is changing, the settings of the roll gap and roll rotation speed are also changed for this stand. That is, in this case, the i+1th stand becomes the transient stand. Tables 1 and 2 show how to change the specific pass schedule settings at each stand. Table 1 shows the conventional method, and Table 2 shows the method of this embodiment. In these tables, S shows the roll gap, V shows the roll speed, and O shows the transient schedule, respectively.

【table】

[Table] Next, in Figure 3, two coils of low carbon hot rolled steel strips having the plate thickness and plate width shown in Table 3 (1) and (2) are connected and 5
The results of comparing the state of tension change when rolling with a cold tandem rolling mill on a stand and changing the running plate thickness at the welding point using the conventional method and the method of this example are shown.

[Table] The figure shows changes in the total tension and unit tension between the fourth and fifth stands when the plate thickness change point P passes between the fourth and fifth stands. In the conventional method, the total tension between the stands where the plate thickness change point P exists is a high value corresponding to the pass schedule of the previous coil of thick material, so during this time the unit tension of the next coil of thin material is About 2 of the example law
It has doubled to 30Kgf/mm ² , indicating that the risk of material breakage is extremely high. On the other hand, in the method of this embodiment, the change in plate thickness is started at the fourth stand, and the total tension between the stands is changed to a low value corresponding to the pass schedule of the next coil of thin material. Therefore, while the plate thickness change point P exists during this period, the unit tension of the front coil of the thick material is half the value. That is, it can be seen that according to the method of this embodiment, even when coils having greatly different thicknesses are continuously rolled, a tension exceeding the normal set unit tension is not generated. As a result, constraints on the process are significantly relaxed, such as almost no need to implement welding restrictions based on plate thickness. The method of the present invention attempts to control the total tension between the i-th to i+1-th stands where the plate thickness change point P exists, and as shown in the above embodiment, the total tension is controlled by the path of the next coil. Matching the total tension setting value Ti[] in the schedule is just one example. That is, for example, the plate thickness change point P
When rolling a material where the welding point overlaps with the plate thickness, the welding force is weak, and there is a high risk of breakage, the plate thickness change point P
The total tension between the stands where P is the plate thickness change point P
Set the pass schedule to a lower value that is different from the value specified by the pass schedule determined corresponding to the front and rear plate thicknesses, or set the pass schedule to a lower value that is different from the value specified by the pass schedule determined corresponding to the front and rear plate thicknesses, or The method of the present invention also includes setting the value to an intermediate value between the values specified by the schedule. The "total tension" in the invention is essentially the roll gap of the stand upstream from the i+1st stand,
It is sufficient to set the tension to such a value that the strip-shaped material to be rolled does not break by changing the roll speed. As explained above, according to the present invention, even when the plate thickness change point from thick to thin passes through each stand, the unit tension can be kept low at all times, and the rolling This has the effect of preventing material breakage due to tension fluctuations inside.

[Brief explanation of drawings]

Figures 1A and 1B show an example of a schedule diagram using a tension control method when changing plate thickness during running in a conventional tandem rolling mill. In this case, B indicates the case where the plate thickness is changed from thick to thin, and B indicates the case where the plate thickness is changed from thick to thin.
The figure is a schedule diagram corresponding to FIG. 1B showing an example of the tension control method when changing the running strip thickness in a tandem rolling mill according to the present invention, and FIG. 3 shows the tension when changing the running strip thickness. FIG. 3 is a diagram comparing measurement results of changes between a conventional example and the above-mentioned example. P... Plate thickness change point, i-1, i, i+1... Stand number, ,... Pass schedule, h... Plate thickness,
T...Total tension.

Claims (1)

[Scope of Claims] 1. In a method for controlling tension when changing plate thickness during running in a tandem rolling mill that continuously rolls a strip-shaped rolled material including a plate thickness change point without stopping rolling, the method comprises: Among the plate thickness change points, when the plate thickness change point from thick to thin passes through the i-th stand, the i-th stand where the plate thickness change point exists and the i+1-th stand downstream from this By changing the roll gap and roll speed of the i+1st stand and the stands upstream from it, the plate thickness is changed while running while setting the total tension between the stands to a tension that does not destroy the strip-shaped rolled material. A method for controlling tension when changing strip thickness in a tandem rolling mill, characterized by: