JPH0716607A - Method for continuously hot rolling billet - Google Patents

Abstract

PURPOSE:To execute stable continuous hot rolling by drastically suppressing thickness variation and tension fluctuation due to local temp. drop that are generated at the time of joining billets. CONSTITUTION:After the rear end of a preceding billet and the tip part of the following billet are butt joined, the billets are fed to rolling equipment and, when hot finish rolling is continuously executed and at time of rolling down at least the joined part between the preceding and follwing billets and its vicinity, variable control of the rigidity of rolling mill is executed at the tuning rate of 0.8-1.0 under the control cycle of <=1/1000 of the period of temp. disturbance that is generated at the time of joining the billets.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous hot rolling method for a steel strip, such as a sheet bar, a slab, a billet, or a bloom, which is continuously rolled over several or dozens of steel strips. It is intended to avoid local dimensional variation or plate breakage caused by rolling down the joint and the vicinity thereof.

[0002]

2. Description of the Related Art Conventionally, in a hot rolling line for billets, the billets to be rolled are individually heated, rough-rolled and finish-rolled to finish a hot-rolled sheet having a desired thickness. Such a rolling method has an unavoidable disadvantage of stopping the line due to defective biting of the rolled material in finish rolling, and also lowering the yield due to defective shape of the leading end and the trailing end of the rolled material. It was

For this reason, recently, a continuous hot rolling method has been adopted in which the rear end portion and the front end portion of the steel pieces to be rolled are joined prior to finish rolling, and this is continuously supplied to a hot rolling line for rolling. It has been adopted. Regarding this point, reference is made to JP-A-5-42306.

[0004]

By the way, the above continuous hot rolling method has some problems as described below when joining steel slabs, and its solution has been desired.

That is, in this type of rolling method, in order to perform positioning when joining steel pieces to each other, the end regions of the steel pieces are clamped and supported by clamps and heated to a temperature at which they can be joined in this state. Although it was customary to raise the temperature and press it (welding, forging, and fitting methods are used as the joining method for steel pieces), especially in the pressing step of steel pieces, a corresponding clamping force and time are required. Therefore, it is unavoidable that the temperature is lowered (a stepwise low temperature region is generated in the longitudinal direction of the steel slab) in the region clamped and supported by the clamp. And, since this deformation region has a high deformation resistance, it becomes a disturbance that causes an increase of rolling load in the subsequent rolling process or causes a tension variation between stands, and the sheet thickness locally varies or the sheet breaks. There was a problem.

In particular, in hot finish rolling of a steel slab, which is the object of the present invention, unlike the cold rolling, the precision of the finish rolling temperature is strict, so that the rolling speed cannot be reduced, and at the same time, including the joint portion. Since changes in rolling conditions in the vicinity are much steeper than changes in rolling conditions in cold rolling, it is necessary to perform rapid strip thickness control.
The conventional strip thickness control system in hot rolling has a disadvantage that it cannot follow such a steep disturbance because its control period is long.

By the way, if the pressing force required to press steel pieces against each other to join them is about 100 to 300 tons, the clamping force of the clamp needs to be several times as large as that of the clamp. The greater the clamping force, the greater the amount of heat transfer that flows out through the clamp when the temperature of the billet is increased.
Even if the heating time is only 5 to 10 seconds, the difference in temperature between the part and the region excluding the part becomes 50 ° C or more.

An object of the present invention is to propose a rolling method capable of solving the above-mentioned conventional problems which were inevitable in a continuous hot rolling method in which steel pieces are butt-joined and then hot rolled. It is in.

[0009]

[Means for Solving the Problems] When a portion of a steel slab having a changed size or temperature distribution is rolled, the rolling load changes, and the sheet thickness distribution after rolling also changes accordingly. During continuous hot rolling of a billet, for example, when a low temperature part is rolled down by an i stand,
The rolling load of the i-stand will increase, and along with this, the output side plate thickness will increase and the output side plate speed will decrease. And such a situation also disturbs the mass flow balance between the i to i + 1 stands, increases the tension between the stands, and causes the plate to break (when the high temperature part is pressed down, the low temperature part is pressed down. Conversely, the tension between stands decreases.).

According to the present invention, the rigidity of a rolling mill is variably controlled with respect to a steep temperature disturbance generated during the joining of steel slabs, and the apparent rolling mill rigidity coefficient is changed (the roll gap of the rolling mill is controlled at high speed). By this, fluctuations in plate thickness due to fluctuations in load during rolling are suppressed, tension fluctuations are reduced by maintaining a mass throw balance between stands, and breakage of plates at joints is avoided.

That is, according to the present invention, after butt-joining the trailing end of the preceding steel slab and the leading end of the trailing steel stake, they are fed to rolling equipment and continuously hot-finish rolled, and at least the preceding steel is 1 / of the temperature disturbance cycle that occurred during the joining of the steel pieces during the reduction of the joint between the steel piece and the trailing steel piece and its vicinity
This is a continuous hot rolling method for billets, which is characterized by performing variable control of rolling mill rigidity at a tuning rate of 0.8 to 1.0 under a control cycle of 100 or less.

[0012]

It is generally known that the rolling force P and the plate thickness h of the steel plate have a linear relationship as shown below.

H = (P / M) + S ₀ (1) S ₀ : Set roll gap at no load M: Rolling mill rigidity

The above equation (1) can be expressed as follows by transforming it into an equation of a differential amount that handles a variation amount from a reference value at a certain time.

Δh = (ΔP / M) + ΔS (2) Δh: Variation of plate thickness ΔP: Variation of rolling force ΔS: Variation of gap

The value ΔP obtained by subtracting the set rolling load from the rolling load at the present time is added to the coefficient α / M (α: tuning rate)
When rolling is performed by setting a roll gap change amount that satisfies the following equation by multiplying by, rolling thickness variation due to load variation can be suppressed.

ΔS + (α / M) ΔP = 0 (3)

Further, the following equations are established from the above equations (2) and (3).

ΔP / Δh = M / 1−α = M ′ (4)

Here, M ′ in the above equation (4) is an apparent rolling mill rigidity coefficient, and the tuning rate α in the control system is
The apparent rolling mill stiffness coefficient M ′ can be changed arbitrarily by changing the value of ω, and this control is defined as rolling mill stiffness variable control (variable mill constant control).

FIG. 1 schematically shows a control system suitable for carrying out the present invention. The load detector 1 such as a load cell continuously detects the current rolling load P, and the calculator 2
At, the deviation between the rolling load P and the set rolling load P ₀ is calculated.

Then, the timing at which the joint or the steady portion of the steel piece reaches the rolling mill is judged by the tracking signal T _r of the joint, and the switching device 3 is operated to make the coefficient (α '/ M) from the coefficient unit 4. Alternatively, a reduction position control signal considering (α / M) is output to the reduction cylinder 5 to adjust the gap of the work roll r.

FIG. 2 shows the temperature distribution in the longitudinal direction of the steel slab after joining. A temperature disturbance in which the temperature fluctuates abruptly occurs particularly in the section x of the clamping pressure support portion L by the clamp, but if the rolling mill rigidity variable control as described above is performed,
Fluctuations in plate thickness due to the reduction of the pressure in this region and fluctuations in tension between the stands due to the fluctuations are extremely small.

FIG. 3 shows the relationship between the sampling number of the temperature disturbance cycle and the plate thickness deviation in the rigidity variable control of the rolling mill. Here, the temperature disturbance cycle in the present invention corresponds to the section x (1/4 cycle) in the example of FIG. 2 above (in FIG. 2, there are four temperature disturbances (4x is one cycle)). Yes,
The temperature disturbance cycle and the control cycle have the following relationship.

Control cycle = temperature disturbance cycle / sampling number

In the present invention, the control period is set to be 1/100 or less of the temperature disturbance period, because the reason is that, in the general hot rolling, at least in the region where the temperature of the billet rapidly changes. This is because it is difficult to reduce the plate thickness fluctuation unless the control cycle is set to allow sampling of 100 points or more.

Further, in the present invention, the above-mentioned tuning rate is set in the range of 0.8 to 1.0, because the thickness variation and the inter-stand tension caused by rolling the local temperature drop area are set. This is because, as shown in FIG. 4, the fluctuation can be made extremely small by setting the tuning rate in the range of 0.8 to 1.0 (increasing the apparent rolling mill rigidity coefficient).

When rolling the steady portion, if the tuning rate is set in the above range due to the characteristics of the rolling mill, interference with other control systems, etc., there may occur variations in strip thickness (in rolling of the steady portion. Is about 0.6), so it is desirable to set the tuning ratio to 0.8 to 1.0 only during rolling of the joint (including its vicinity) where the priority is to keep the mass flow balance to prevent the plate from breaking.

[0029]

Example: The temperature of the joint is 250 ° C higher than the ambient temperature,
85 ° C lower clamping support by clamps (length x along the longitudinal direction of the steel slab in the temperature fluctuation part: 250 mm x 4 locations)
Continuously hot-rolling the joined sheet bar with the temperature distribution shown in Fig. 1 (biting speed of the first rolling mill: 1000 mm /
S, time for temperature disturbance to pass through rolling mill (total): 1 second,
Control cycle: 5 msec (1/200 of temperature disturbance cycle), Tuning rate during rolling of steady part: 0.6, Tuning rate during rolling in the vicinity including the joint: 0.9) The fluctuation situation of tension was investigated. The results were obtained when the sheet thickness was not controlled during hot finish rolling of the sheet bar and when the control cycle was 20 msec.
5a-c and 6a-c together with the results when the gauge meter plate thickness control that becomes (1/50 of the temperature disturbance period) is performed
Shown in.

As is apparent from FIGS. 5 and 6, when the rolling is performed according to the present invention, the variation of the plate thickness is greatly reduced and the mass flow balance between the stands is maintained, so that the rolling can be performed in other rolling. By comparison, it was confirmed that the fluctuation in tension was small and that the plate could be rolled without the risk of breaking from the joint.

[0031]

EFFECTS OF THE INVENTION According to the present invention, it is possible to significantly suppress the plate thickness variation and the tension variation due to the local temperature drop that occurs during the joining of steel slabs, and it is possible to carry out stable continuous hot rolling. .

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a rolling procedure according to the present invention.

FIG. 2 is a diagram showing a temperature distribution along a longitudinal direction of a steel slab.

FIG. 3 is a graph showing the relationship between the sampling number of the temperature disturbance cycle and the plate thickness deviation of the clamp part.

FIG. 4 is a graph showing a relationship between a tuning rate and a plate thickness deviation of a clamp part.

FIG. 5 shows the variation of the strip thickness in the longitudinal direction of the strip in the case where a is the variable control of the rolling mill rigidity, b is the case without strip thickness control, and c is the case with the gauge meter strip thickness control. It is the figure which showed the result.

FIG. 6 is a graph showing a change in the tension of the plate between the final stands in the case where a is the variable control of the rolling mill rigidity, b is the case where the plate thickness control is not performed, and c is the case where the gauge meter plate thickness control is performed. It is the figure which showed the result.

[Explanation of symbols]

 1 load detector 2 arithmetic unit 3 switching device 4 coefficient unit 5 reduction cylinder r work roll

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunio Isobe, 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Iron & Steel Co., Ltd. Technical Research Headquarters (72) Sadayuki Miyoshi 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd.Chiba Works

Claims (1)

[Claims] 1. A butt joint between the trailing end of a preceding steel slab and the leading end of a trailing steel slab, which is then fed to a rolling facility for continuous hot finish rolling, at least the preceding steel slab and the trailing steel. During rolling down of the joint of the steel slab and its vicinity, the temperature disturbance cycle generated during the welding of the steel slab
A continuous hot rolling method for billets, characterized by performing variable control of rolling mill rigidity at a tuning rate of 0.8 to 1.0 under a control cycle of 1/100 or less.