JPS6319241B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the distribution of the rolling reduction variation amount of each rolling stand when performing strip thickness changing rolling in a continuous rolling mill for rolling strip.

In recent years, hot tandem rolling mills have been used to automatically roll two or more consecutive products from one rolled strip with high accuracy without reducing the rolling speed at all, improving yields and improving fuel efficiency. There is a rapidly increasing need for rolling strips with varying running thicknesses to improve production efficiency and reduce lot surplus material.

Conventionally, the ratio of plate thickness and rolling reduction distribution for each rolling stand in a continuous tandem rolling mill has been determined by taking into consideration the output of the drive motor of each rolling stand, the maximum rolling speed, strip threadability, strip shape, etc. It is a well-known fact that the rolling position, rolling roll speed setting, etc. are determined based on the most suitable schedule. That is, irrespective of the change in plate thickness, operations are carried out in which the rolling reduction ratio of each rolling stand is set to be large on the upstream side of the strip to be rolled and small on the downstream side. This is mainly based on the output constraints of the electric motor driving the rolling mill, the shape of the strip, the runout of the looper angle, and other operational experiences. For example, in conventional rolling, the rolling reduction distribution pattern for each rolling stand in normal rolling is such that even after thickness change rolling, the rolling reduction distribution ratio to each rolling stand is maintained at the same distribution ratio as before the thickness change, and is distributed at a constant percentage. It's changing. If thickness change rolling is carried out using this conventional method, the disturbance in mass flow between the rolling mills on the downstream side where the rolling speed is high will become large, and even though the tension value variation between the rolling stands on the upstream side is small, the Tension fluctuations are concentrated on the side, resulting in an increase in off-gauge length, strip breakage, narrow strip width, and squeezing, resulting in the drawback that stable and accurate strip thickness change rolling cannot be performed.

The primary purpose of the present invention is to stably, accurately, and efficiently change the thickness of a strip during continuous rolling, and to reduce mass flow fluctuations between rolling stands. The present invention relates to a rolling reduction distribution method for distributing the optimum rolling reduction change amount of each rolling stand so that the rolling load is not concentrated on the rolling stands.

In order to achieve the above object, in the present invention,
In a continuous rolling mill equipped with multiple rolling stands, a strip is rolled in between runs without reducing the rolling speed so that the thickness of the finished product after a certain point is completely different from that before that point. When performing so-called running plate thickness change rolling to change the thickness,
The rolling position of each rolling stand with respect to the product thickness after changing the running plate thickness (hereinafter referred to as the second product plate thickness) is calculated as the product plate thickness before changing the running plate thickness (hereinafter referred to as the first finished product plate thickness). When changing the rolling position from the strip thickness, the amount of change in the rolling reduction from the first product to the second product at each rolling stand is determined by focusing on the mass flow disturbance between each rolling stand and the strip tension value fluctuation before and after changing the plate thickness. Adjustments are made so that the same amount of mass flow disturbance occurs between all rolling stands.
In other words, by selecting a large amount of change in the reduction rate as a function of each rolling speed at the upstream rolling stand of the strip and a small change in the downstream side, it is possible to change the strip thickness at a specific rolling stand. To stably and accurately perform strip thickness changing rolling while running without concentrating the mass flow disturbance accompanying the rolling, and without impairing the width accuracy, shape, threadability and operability of the strip to be rolled.

The present invention will be explained in detail below. There are two problems when rolling a strip to change its thickness between runs in two or more continuous tandem rolling mills without reducing the rolling speed at all. The first is to shorten the off-gauge length of the strip where the plate thickness is changed, and the second is to eliminate problems such as strip breakage, narrowing, and squeezing due to rapid changes in strip tension due to changes in mass flow between stands. . In the present invention, the distribution ratio of the rolling reduction change necessary for changing the plate thickness to each rolling stand is optimized by paying attention to the following fact. In the current i rolling stand, the input thickness of the strip is H(i), the output thickness is h(i), the rolling reduction is r(i), the roll circumferential speed, that is, the neutral point speed is V _R (i), and the input side thickness is H(i). The side plate speed is v _i
(i) When the outlet plate speed is v _p (i) and the subscript i is the rolling stand number, the following equation holds true according to the knowledge of rolling theory.

r(i)=H(i)-h(i)/H(i)...(1) v _i (i)=V _R (i) [1-r(i)]・[1+f(i)
]
...(2) v _p (i)=V _R (i)・[1+f(i)] ...(3) Here, f(i) is the advance rate at rolling stand i, and the above rolling reduction rate r(i ) can also be expressed by the following approximate formula.

f(i)=α·r(i) (4) However, α is a proportionality constant, and according to the knowledge of rolling theory, it generally takes a value of 0.25.
From the above equations (2), (3) and (4), the strip entry speed and exit speed of the i rolling stand are v _i (i)≒V _R (i) [1-(1-α)・r(i )〕
...(5) v _p (i)≒V _R (i) [1+α・r(i)] ...(6), and the distance between the (i-1)th rolling stand and the i-th rolling stand in the steady rolling state is The following equation holds true from the relationship between the loop amount of the strip (the length of the strip) L(i-1, i).

v _p (i-1)=v _i (i) ...(7) By the way, the roll circumferential speed at each rolling stand [V _R
(i), i=1...N] is already determined by the rolling schedule. When changing the running plate thickness of a strip during rolling, when changing the rolling reduction ratio at each rolling stand, the change ΔL in the loop amount of the rolled strip between each rolling stand is expressed by the following equation.

ΔL (i-1, i) = V _R (i-1)・αΔr-(i-1) +V _R (i)・(1-α)Δr(i) ...(8) Here, ΔL(i- 1, i) indicates the amount of change in the loop amount of the strip between the (i-1)th rolling stand and the i-th rolling stand, and ΔL(i-1, i) is the i
- The amount of change in the loop amount L (i-1, i) due to the change in the exit side plate speed due to the change in plate thickness at the -1 stand,
This is the sum of the loop amount change due to the change in the entrance plate speed due to the change in plate thickness at the i-stand. ΔL(i-
As 1, i) increases, the tension in the strip between the i-1 and i stands decreases, causing sag, and as it decreases, the tension increases. Excessive tension will cause the strip to become narrow and break. Δr(i
-1) and Δr(i) each represent the amount of change in the rolling reduction in the (i-1)th rolling stand and the i-th rolling stand. In the derived equation (8), the first term is due to the change in the advance rate of the upstream rolling stand of the strip being rolled, and the second term is due to the change in the backward rate of the rolling stand downstream of the strip being rolled. It is something. Furthermore, as mentioned earlier, α=0.25
And α<(1-α). In addition, in a continuous rolling mill, since V _R (i-1)<V _R (i), the above
Since the second term on the right side of equation (8) is larger than the first term, this second term almost determines the change in the loop amount of the strip. In addition to this,
-1) and changes in the roll circumferential speed of the i-th rolling stand ΔV _R (i-1), ΔV _R (i) There are changes in the mass flow amount of the strip being rolled, but compensation called successive control is usually used. This discussion does not take into account the mass flow disturbances (changes in loop amount) that occur due to changes in the thickness of the strip being rolled. What this equation (8) means is that the change in the loop amount of the strip between each rolling stand is uniquely determined as the product of the rolling speed of the relevant rolling stand and the amount of change in rolling reduction, and usually the first term It is also characteristic that the second term does not occur at the same time, but rather at different timings. That is, if the rolling reduction rate change is the same in each rolling stand, it is clear that disturbances in the mass flow amount will be concentrated on the downstream stand where the roll circumferential speed is high.

In the present invention, based on the above results derived from equation (8), the amount of change in rolling reduction is set large at the rolling stand upstream of the strip where the roll circumferential speed is slow, and the rolling reduction is increased at the downstream side of the strip where the roll circumferential speed is fast. By selecting a small rate change amount, disturbances in the mass flow of the strip at a particular rolling stand are not concentrated, and when controlling the mass flow of the strip, the strip tension value between the rolling stands can be maintained at a good value to improve strip width accuracy. , it is possible to realize rolling with a change in plate thickness during running without reducing the rolling speed, without impairing the shape, threadability or operability at all.

Furthermore, according to the present invention, the amount of change in rolling reduction at each rolling stand is selected to be approximately the inverse ratio of the roll circumferential speed, but the output of the drive motor of each rolling stand,
The effect is also great when this is carried out within the range permitted by the maximum rolling speed and other conditions.

Next, simulation results of continuous rolling to which the present invention is applied will be described with reference to FIGS. 1 and 2.

In conventional rolling methods, the rolling reduction rate at each rolling stand is generally calculated based on a rolling schedule in which the rolling reduction rate at each rolling stand is larger at the upstream rolling stand and smaller at the downstream side, depending on the strip threadability, shape, output constraints of the rolling stand drive motor, and other conditions. has been done. When rolling to change the running plate thickness, case 1 is the conventional method in which the rolling plate thickness is changed by changing the rolling reduction ratio at each rolling stand by a certain percentage compared to before the plate thickness change. Case 2 is a case in which the plate thickness is changed using the method according to the present invention, that is, the rolling reduction ratio of each rolling stand is determined by optimizing the amount of change in the rolling reduction ratio of each rolling stand. Figures 1 and 2 show the logical formulas and models that describe the rolling phenomena for the conventional method (Case 1) and the method according to the present invention (Case 2), as well as computer simulation results including the inter-rolling stand loop amount control function. . Figure 1 shows the rolling reduction values at each rolling stand before and after the plate thickness change rolling. In Case 1, which represents the conventional method, each plate thickness after the plate thickness change is changed by a certain percentage with almost the same reduction rate distribution as before the plate thickness change. In case 2, which is a method to which the present invention is applied, the rolling reduction ratio distribution of the rolling stands is shown, and in case 2, the amount of change in the rolling reduction ratio of each rolling stand is calculated according to the equation (8) above, so that the mass flow is the same between all rolling stands before and after changing the plate thickness. By averaging and distributing the turbulence, the distribution of rolling reductions to each rolling stand after the thickness change is set to a value that is much wider on the upstream side of the strip and closer to the value on the downstream side than before the thickness change. It is characterized by the presence of

As a result of simulating the case where the rolling reduction ratio distribution of each rolling stand is optimized by the method applying the present invention and the case using the conventional method, an example of the variation of the inter-stand tension value at the time of changing the strip thickness is shown. Shown in Figure 2. In this simulation example, the disturbance due to the skid mark of the strip with a plate thickness change rate of 30% is a -30°C triangular wave. As is clear from Fig. 2, in Case 1 using the conventional method, the strip tension value fluctuations between the downstream rolling stands are extremely large, whereas in Case 2 where the present invention is applied, the strip tension fluctuations between each rolling stand are extremely large. The effect of averaging and dispersing the tension fluctuations between each rolling stand while avoiding concentration is clearly demonstrated, and the fluctuation of the strip tension value between the downstream rolling stands is much smaller than in the conventional method.

As is clear from the above-mentioned simulation results, the present invention not only greatly improves the width accuracy, shape, operability, and threadability of the strip in strip thickness changing rolling, but also improves the strip thickness. This has the effect of further shortening the off-gauge length.

Furthermore, the scope of application of the present invention can be expanded to include a cold tandem continuous rolling mill equipped with a strip tension value control mechanism between each rolling stand and a hot tandem continuous rolling mill equipped with a looper mechanism, without changing the gist of the present invention in any way. It is also effective for continuous tandem rolling mills that do not have a looper control mechanism. In addition, if there is a response difference inherent in the looper control tension control between each rolling stand, the method according to the present invention which takes into account the quality of the response and determines the distribution of the amount of change in rolling reduction at each rolling stand can be applied again. Needless to say, it can be expected to significantly improve operational efficiency in line with actual rolling.

[Brief explanation of the drawing]

FIG. 1 shows an example of the distribution of the rolling reduction ratio of each rolling stand before and after changing the plate thickness in the conventional method, and a simulation result of an example of the rolling reduction ratio distribution of each rolling stand before and after changing the plate thickness optimized by applying the present invention. FIG. 2 is a graph showing the simulation results of the amount of variation in tension value of the strip between each rolling stand and its peak value when the conventional method and the present invention are applied.

Claims (1)

[Claims] 1. When changing the thickness of the same strip during continuous rolling, the rolling reduction ratio for each rolling stand is determined individually, and the rolling ratio for the upstream rolling stand is determined from the rolling ratio for the downstream rolling stand. A rolling reduction distribution method in continuous rolling, in which the rolling reduction ratio is set to be large, and the rolling reduction ratio is set so that the same amount of mass flow disturbance occurs in each rolling stand before and after the plate thickness is changed.