JPS5828006B2 - Method for controlling plate crown of rolled material during hot finish rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the crown of a rolled material in hot finish rolling, and in particular, a method for controlling the crown of a rolled material in hot finishing rolling, and in particular, a method for controlling the crown of a rolled sheet in hot finishing rolling, and in particular, determining the target from the mutual relationship between the crown of a hot rolled sheet on the finishing exit side and the humidity on the finishing exit side (hereinafter referred to as FDT). While FDT is set based on prediction so that the plate crown is as desired, the water volume of the scale breaker installed on the inlet side of the finishing rolling mill group and the water volume of the strip coolant in the finishing rolling mill group are controlled to achieve the above-mentioned results. This paper proposes a simple and appropriate method for controlling the FDT plate crown of a rolled material by maintaining the FDT at a set value TK.

In hot finish rolling, the rolling cycle from when the work roll is replaced and the rolling operation is continued until it is replaced again, that is, one rolling cycle, is usually 50 to 15 rolling coils.
However, the crown of the hot rolled sheet within one rolling cycle is approximately 1 coil immediately after the start of the rolling cycle, as shown in Fig. 1 in the case of rolling 80 rolls, for example.
10μ, but gradually decreases to 1 as rolling progresses.
It decreases to about 20μ in the final coil of the rolling cycle.

The main cause of such round variation is that the thermal crown due to thermal expansion of the work roll increases as rolling progresses.

If the crown of the hot-rolled sheet fluctuates significantly as described above, if the sheet thickness accuracy in the width direction is severe, the cutting allowance for the edges increases, resulting in a significant reduction in the end stop.

Furthermore, if the crown of the hot-rolled sheet subjected to cold rolling is not set to a certain appropriate value, it will not only be the biggest cause of deterioration in the widthwise thickness of the rolled product after cold rolling, but also Shape (waving: selvage elongation, middle elongation, etc.)
It can also cause defects.

Another problem is that when a hot-rolled material with a concave crown is cold-rolled, the shape of the edge elongation becomes very poor.

Therefore, it is necessary to always produce a hot rolled sheet with a properly finished exit hot rolled sheet crown.

However, the current method for controlling the change in the crown of a hot-rolled sheet during hot rolling is to preheat the roll before changing the roll using a roll heater, mainly a work roll heater.
In addition to suppressing the change as much as possible during rolling by tightening the thermal crown of the rolls, attempts may be made to vary the total rolling load of all stands during hot finish rolling as rolling progresses. There is a strong momentum to do so.

As a result of conducting research and development to optimize the crown of the finished hot-rolled sheet at the exit side, the inventors found that there is a certain quantitative relationship between the crown of the hot-rolled sheet at the finishing exit side and FDT. I found it.

In addition, this FDT has a certain quantitative relationship between the amount of water in the scale breaker installed on the inlet side of the hot finishing rolling mill and the total amount of water in the strip coolant in the three stands in the front stage of the finishing rolling mill. We found out something from the results of actual rolling experiments.

Therefore, this invention focuses on these relationships and improves the FD of hot rolled material.
A technique has been established for appropriately controlling the crown of the hot-rolled sheet on the finishing exit side by setting T and adjusting the amount of water accordingly.

This will be explained in detail below.

Figure 2 shows the relationship between FDT and the crown of a hot-rolled sheet on the finish exit side, which is obtained by converting the results of development research through actual rolling experiments into a sheet width of 1000 mm, using an example of the case of finish rolling of low-carbon Al-killed steel. In this case, the plate thickness and reduction distribution are shown as parameters.

This relationship can be expressed empirically using a simple linear equation as shown in equation (1).

Ch-a+b T2DT ・・・・・・・・・ (
1) Here, Ch: Crown of rolled plate on finishing exit side)
, T: FDT setting value (°C) a s b
: Set to constant FD'l'.

The constant a varies depending on the steel type, the dimensions of the rolled plate, the reduction distribution, and the rolling mill, and the constant b varies depending on the steel type and rolling mill, but these can be expressed in tables or mathematical formulas for each. For example, as shown in Figure 2. For example, when the plate thickness is 4.5 mm from 26mm with low carbon Ad-killed steel and the reduction rate of the final stand (F7) is 35%, a = 62 (p), b =
-0.6 (p/°C).

Thus, it can be seen that FDT can be an effective means for controlling the crown of the hot rolled sheet on the finishing exit side.

The reason why the hot rolled sheet crown can be controlled by FDT is that (1) the deformation resistance of the rolled sheet changes depending on the temperature, which changes the rolling load and changes the amount of roll deflection. (2) This is because the normal crown of the roll changes depending on the humidity.

For example, when FDT is high, the deformation resistance of the rolled material is small, the amount of deflection of the roll is small, and the thermal crown of the roll, especially the work roll, is large.

Due to this double effect, the crown of the hot rolled sheet becomes smaller.

Next, Figure 3 shows the relationship between the amount of water in the scale flaker on the inlet side of the finishing mill, the total amount of water in the strip coolant in the finishing mill group, especially the three stands in the front stage, and FDT. A simple relationship such as equation (2) accounts for balance.

Where, QTotal The total amount of water in the Niscale breaker and the water amount in the strip coolant in the three stands in the front stage of the finishing rolling mill c, d: Constants (however, it varies depending on the steel type, dimensions, finishing entrance temperature, and rolling mill) Considering the water volume of the strip coolant in the subsequent stands after the 4th stand, the control width of the FDT itself becomes even tighter, but since the control is performed when the plate thickness becomes thinner, the FDT may drop too much due to excessive cooling, or the shape ( waving: selvage extension, middle extension, etc.) This will complicate control.

Usually FDT is 820 to 920°C, preferably 85°C.
Since the control is limited to a range of 0 to 900°C, the sum of the water volume of the scale breaker and the water volume of the coolant in the three front stands is advantageously suited for the control purpose according to the present invention.

Therefore, when the dimensions and rolling reduction schedule for a given hot-rolled coil are determined, first, from the relationship shown in Figure 2, an appropriate FDT is set to obtain the targeted crown of the finished hot-rolled sheet, and then From the relationship shown in Figure 3, the water volume of the scale breaker and the water volume of the coolant in the front 3 stands are determined as follows:
DT is adjusted so that FDT is maintained at its set value T.

This will be explained below using an example.

Fig. 4 shows a preferred example of the control system, 1 and 5 are thermometers, 2
is scale breaker-13 is strip coolant, 4
1 is a plate thickness profile meter, 6 is a computing machine, and 7 is the first three stands of the finishing rolling mill group.

In this case, the finishing entrance temperature (hereinafter referred to as FET) is measured from a thermometer 1 installed on the exit side of the rough rolling mill group, and this is input to the calculator 6 along with the steel type, dimensions, and rolling schedule.

Furthermore, using equation (1) from the target plate crown input to the calculator 6, the corresponding TFD T
Calculate scale breaker 2 and front stage 3 using equation (2).
Determine the amount of water in coolant 3 in stand I, and set the opening degree of each valve (■).

Next, the hot-rolled material rolled in this way is placed on the final stand 8.
The FDT was actually measured using the thermometer 5 installed on the outlet side of the
This is compared with the target FDT, and each water amount is changed according to the difference using equation (2).

Here, FDT is approximately 820 to 92 within the same rolled material.
Supplementary feedback control is performed in the 0°C range.

In addition, the crown of the hot rolled sheet was actually measured using the sheet thickness profile maker 4 installed on the finishing exit side, and this was compared with the target sheet crown.
The DT is corrected and the corrected TFDT is set up for the next coil to be rolled.

FIG. 5 shows the effect of the above rolling control method in comparison with the conventional method.

This shows the change within one rolling cycle of the crown of a hot-rolled sheet with a width of 1000 m4 when low carbon A7 killed steel is rolled from a thickness of 26 mm to a thickness of 4.5 mm.

In the conventional method, within one rolling cycle, 11
A change in the crown of the hot-rolled sheet occurs by approximately 0-20=90μ, but according to the present invention, the change is limited to 70-20=50μ, which is a significant improvement.

Note that the set value of TFDT decreases rapidly after the start of rolling, but stabilizes from around 35 coils, and tends to rise somewhat in the latter half of the coil. However, this can be further improved by slightly preheating the rolls, especially the work rolls, using a roll heater before rolling.

As for the setting method of FDT, since it can be easily estimated from the finishing entrance temperature FET using a conventional method such as the following equation (3), this FET may be used as a control factor in place of FDTO.

FDT=θa+(FET-θa) E xP (-2
aL/ρchfVf)・・・・・・・・・(3) Here, θa: Ambient temperature α: Equivalent heat transfer coefficient L: Distance between the hygrometer for FET measurement and the hygrometer for FDT measurement hf: Final stand exit Side thickness ρ: Density of the rolled material f: Final stand rolling speed C: Specific heat of the rolled material With this invention, the crown of the hot-rolled plate formed after hot rolling can be controlled to be nearly constant within one rolling cycle.
By appropriately selecting the initial crown of the work roll, it is possible to produce hot-rolled coils with plate crowns as close to Oμ as possible, improving the accuracy of shape and dimensions, especially plate thickness, and improving the accuracy of the plate crown. The product finish has improved due to the reduction in cutting allowance.

Furthermore, the number of rolling coils in the (1) cycle is increased, and roll stoppage and rolling efficiency are improved.

In addition, since the crown and shape (waving: edge elongation, mid-elongation, etc.) of a sagging plate after cold rolling are greatly influenced by the crown of the hot rolled plate, the crown and shape of the cold rolled plate are The shape is improved, resulting in improved product quality, improved end-stops, and improved efficiency.

In addition, this invention is based on the total rolling reduction ratio or the same total unit width rolling load in at least three subsequent stands leading to the final stage of the hot rolling finishing process, and the plate crown of the hot rolled material obtained through this rolling process. Using the relationship, rolling is first performed under the rolling schedule for all stands determined using the calculated value of the total rolling reduction rate or total unit width rolling load corresponding to the desired sheet crown, and then In order to correct the difference between the actual value of the hot-rolled plate crown at the finishing exit side and the target plate crown in the case of a hot-rolled plate, the rolling schedule is sequentially corrected using a learning control method. Rather, it is more desirable to use this method in conjunction with a plate crown control method in which the reduction distribution is gradually changed from a preceding high reduction at the beginning of the rolling cycle to a subsequent high reduction as rolling progresses.

[Brief explanation of drawings]

Fig. 1 is a graph showing changes in the crown of a hot-rolled sheet on the finished exit side in one rolling cycle by conventional hot-strength rolling, and Fig. 2 is a graph showing the change in the crown of the hot-rolled sheet on the finishing exit side (sheet width 100).
Figure 3 is a graph showing the relationship between the finishing outlet temperature and the water volume of the scale breaker and the coolant water volume of the three front stands. Figure 4 is an explanation showing an example of the control system. 5 are graphs showing the effect of controlling the crown of a rolled plate by the method of this invention in comparison with the conventional method.

Claims (1)

[Claims] 1. In hot finish rolling, the finished exit side that achieves the target hot rolled sheet crown from the correlation shown in the following equation (1) between the hot rolled sheet crown on the finished exit side and the finishing exit temperature. In addition to setting the temperature, according to the relationship between the amount of water in the scale breaker installed on the inlet side of the finishing rolling mill, the total amount of water in the strip coolant in the group of finishing rolling mills, and the roughness on the finishing outlet side, according to formula (1), The water capacity is set in accordance with the finishing exit temperature set by the above method, and the actual value of the finishing exit temperature measured by a thermometer installed on the exit side of the finishing rolling mill group is compared with the set value of the finishing exit temperature. A method for controlling the plate crown of a rolled material in hot finish rolling, characterized in that the amount of water is changed in proportion to the difference to maintain the finish exit temperature at a set value. Ch in the formula: Crown profile of the hot rolled sheet on the finished exit side) a, b
=Constant TFDT: Set value of finishing outlet temperature ('C)