JPS6339321B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method when changing the pass schedule during rolling to change the thickness of the finished product. The present invention relates to a control method that stably changes the schedule without disturbing the mass flow balance as much as possible by aligning the response and speed response.

The technology of changing the pass schedule during rolling and changing the thickness of the finished product (hereinafter referred to as changing thickness during rolling) has already been introduced in cold tandem mills. This, combined with continuous rolling technology, has led to significant improvements in productivity.

On the other hand, although the use of continuously cast slabs is increasing in hot strip mills, it is not easy to change the slab size in continuous casting, and the technology to roll products of various sizes from the same slab size is lacking. Rolling multiple coils from a single slab is desirable and advantageous in terms of productivity, and the technology is being developed.

Thickness change rolling while running in a tandem mill is carried out by changing a pre-given post-thickness change pass schedule at the timing when the thickness change start point is reached. At this time, the important point is not only how to find the pass schedule that will achieve the target thickness, but also how to maintain the mass flow balance from the start point of the thickness change to the end point of the thickness change. So, the question is whether to change the pass schedule while keeping inter-stand tension fluctuations small.

By the way, recent hot strip mills have a configuration in which a hydraulic rolling down device with a high speed rolling response is installed downstream of the finishing stand, and a normal electric rolling down device is placed upstream, in order to achieve highly accurate and efficient plate thickness control. Even if planned and equipped with an all-stand hydraulic or all-stand electric down-down system, the response speed of each stand's down-down system is usually different, and this causes the normal running time to be It has been found that changing the thickness of a steel sheet disrupts the mass flow balance, which is a major factor that impedes stable operations.

Now γi: Reduction rate of i-stand, Hi: Inlet side plate thickness of i-stand εi: 〃 Reverse rate i: 〃 Assuming advance rate, γi = Hi - Hi + 1 / Hi ...... (1) εi = E (Hi, Hi + 1) ≒ E′(γi) ………(2) i = F(Hi, Hi+1) ≒F′(γi) ………(3) There is a relationship as follows, and if the rolling reduction rate γi changes, the advancing rate i and the backward rate εi It also fluctuates, especially the reverse rate fluctuation.

FIG. 1 shows the relationship between the rolling reduction rate γi, the advance rate i, and the backward rate εi. Note that in equations (2) and (3), E
(・), E′(・), F(・), and F′(・) mean functions.

On the other hand, a control device suitable for the conventional rolling control method for changing strip thickness during running shown in FIG. 2 will be explained as follows.

That is, in order to ensure the responsiveness of plate thickness control in the rolling down devices 2a and 2b, it is assumed that the responsiveness of the rolling down device 2b is considerably higher than that of the rolling down device 2a.

When the plate thickness change starting point reaches the rolling stand 1a, a new rolling roll gap correction set value Sa after the pass schedule change, which has been previously determined by the arithmetic unit 4, is set as a step input to the rolling reduction control device 2a. On the other hand, as the roll gap of the rolling stand 1a changes, the advancing rate a and the backward rate εa also change, which disturbs the mass flow. Therefore, when the pass schedule determined in advance by the arithmetic unit 4 is changed, the amount of rolling speed correction is made to maintain the mass flow balance. is step inputted into the rolling speed control device 3a.

Next, when the plate thickness change point reaches the rolling stand 1b, the roll gap correction set value Sb and the rolling speed correction amount, which have been determined in advance by the calculation device 4, are set by the rolling control device 2b and the rolling speed control device 3a. The step is input to 3b.

The reason why the mass flow is disturbed when such an operation is performed will be explained with reference to FIG.

Now, as shown in Fig. 3a, the entrance side plate thickness Ha entering the rolling stand 1a is assumed to be constant, and at the timing when the plate thickness change starting point reaches the rolling stand 1a, the roll gap correction set value ΔSaε is set as shown in Fig. 3b. Set in steps. At this time, the pressure reduction control device 2
The roll gap changes by the set roll gap correction amount according to the response speed of
As shown in Figure C, the roll gap changes slowly,
Accordingly, as shown in FIG. 3d, the sheet thickness ha at the exit side of the rolling stand 1a also gradually changes from the sheet thickness _ha1 before the pass schedule change to the sheet thickness _ha2 after the pass schedule change.

Therefore, the plate thickness Hb at the entrance to the rolling stand 1b
However, since the response speed of the rolling-down control device 2b of the rolling stand 1b is considerably faster than that of the rolling-down control device 2a, as shown in FIG. 3, f and g. After the plate thickness change point reaches the rolling stand 1b, the roll gap follows with a quick response up to the set roll gap correction amount ΔSb. Therefore, the thickness hb of the sheet exiting from the rolling stand 1b is as shown in FIG. 3h.

In this way, rolling stand 1a and rolling stand 1
Due to the difference in the rolling response speed of rolling stand 1b, the plate thickness change pattern for the entrance and exit side of the rolling stand 1b is different, so as shown in Figure 3i, in the rolling stand 1b, The rolling reduction ratio does not change linearly and gently from the rolling reduction ratio γ ₁ to the rolling reduction ratio γ ₂ after changing the pass schedule, but fluctuates greatly from the plate thickness change start point to the plate thickness change end point.

On the other hand, as shown in equations (2) and (3), the advancing rate and retreating rate ε of the stand change depending on the rolling reduction rate, so
The plate speed also oscillates greatly from the plate thickness change start point to the plate thickness change end point. Fig. 3j shows the plate speed Vb entering the rolling stand 1b, which oscillates greatly from the plate speed Vb ₁ before the plate thickness change starts to the plate speed Vb ₂ after the plate thickness change ends.

On the other hand, since the exit speed of the plate from the rolling stand 1a can be considered to be constant while the plate thickness is being changed in the rolling stand 1b, the mass flow balance between the stands will be greatly disrupted. Actually, in order to compensate for this mass balance collapse, a rolling speed correction amount is set in the rolling speed control device 3a, but the rolling speed control device 3a also has a specific response speed, and the response speed does not necessarily match that of the rolling reduction control device. is not matching,
The step-like setting cannot compensate for disturbances in mass flow, as can be seen by comparing FIGS. 3j and 3k.

As described above, in the conventional rolling control method for changing plate thickness during running, the mass flow between the stands is greatly disturbed, and it is difficult to ensure stable operation.

The present invention provides a control method that improves the drawbacks of the conventional methods described above.

FIG. 4 is a block diagram for explaining one embodiment of the present invention, and FIG. 5 is a diagram for explaining its operation. The features of the present invention will be explained in detail below with reference to this figure.

When the plate thickness change point reaches the rolling stand 1a, the plate thickness change is started by the reduction control device 2a, but instead of setting the roll gap correction amount ΔSaε given by the calculation device 4 as a direct step input as in the conventional case, a ramp signal is generated. A ramp-like input rising at time T is set as shown in FIG. 5b through the device 5a. The slope of the ramp should be such that all rolling devices and rolling speed control devices can follow it. By doing this, the plate thickness can be changed in a ramp-like manner approximately in time T as shown in FIG. 5d. Next, when the plate thickness change point reaches the rolling stand 1b, the roll gap correction amount ΔSb similarly given by the calculation device 4 is transmitted to the ramp signal generator 5b for the same time T as shown in FIG. 5f.
A ramp-shaped roll gap correction setting input rising at is applied to the roll-down control device 2b. At this time, Figure 5 e
As shown in FIG. 5, since the entrance side plate thickness Hb is also changed in a ramp-like manner at approximately time T, the exit side plate thickness hb is also changed in a substantially ramp-like thickness as shown in FIG. 5h.

Therefore, as shown in FIG. 5i, the rolling reduction γ in the rolling stand 1b varies linearly and gently from the rolling reduction γ ₁ before changing the pass schedule to the rolling reduction γ ₂ after changing the pass schedule. The entrance plate speed also changes in a ramp-like manner with time T, as shown in FIG. 5j.

On the other hand, a rolling stand 1a for maintaining the inter-stand mass flow balance given by the calculation device 4
Similarly, the rolling speed correction amount ΔVa is changed by applying a ramp-like input Δa that rises at time T to the rolling speed controller 3a through the ramp signal generator 6a, so that the rolling stand 1 is changed as shown in FIG.
The exit side plate speed Va has almost the same value as the input side plate speed Vb of the rolling stand 1b shown in FIG. 5J at any given time, and the mass flow balance between the stands can be maintained.

It goes without saying that the mass flow balance will be disrupted even if the advanced ratio changes caused by changing the plate thickness, but this can be compensated for by the method described above.

Furthermore, it goes without saying that increasing or decreasing the overall rolling speed after changing the plate thickness as a pass schedule can be done by effectively utilizing the successive characteristic.

When performing strip thickness change rolling in this way, if the response speed of the reduction control device at each stand is different, it is necessary to use a ramp signal that can sufficiently follow the roll gap correction signal, and at the same time at each stand. A ramp signal with a slope that ends the plate thickness change is used, and the rolling speed is corrected to compensate for disturbances in mass flow caused by changing the pass schedule.By performing the same ramp correction as for rolling, the mass flow balance between stands is maintained. It is possible to perform stable and smooth plate thickness changes while maintaining the

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the rolling reduction rate, advance rate, and reverse rate; Fig. 2 is a block diagram of a control device to which a conventional rolling control method for changing plate thickness during running is applied; Fig. 3 a to k.
is a characteristic diagram for explaining the operation of FIG. 2, FIG. 4 is a block diagram of a control device to which an embodiment of the present invention is applied, and FIGS. 5 a to 1 are characteristic diagrams for explaining FIG. 4. It is. 1a and 1b are rolling stands, 2a and 2b are rolling control devices, 3a and 3b are rolling speed control devices, 4 is a calculation device, and 5a, 5b, 6a, and 6b are ramp signal generators. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a rolling control method for changing plate thickness during running, in which the plate thickness is changed when the plate thickness change point of a single rolled material rolled by a rolling mill having multiple stands reaches a specific stand, If the response speed of the roll-down control device is not equal to the response speed of the roll-down control device of another stand, each of the roll-down control devices can follow the roll gap correction signal sent to each of the roll-down control devices, and the roll-gap correction signal sent to each of the roll-down control devices can be followed by the same time on each stand. A ramp signal of a gradient at which the thickness change ends at , and a ramp signal at which the rolling speed change ends at the same time as the roll gap correction signal is used as a rolling speed correction signal for each stand. Control method.