JPH0734932B2 - Temperature control method for rolled material in hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a method for adjusting the temperature of a material to be rolled in hot rolling.

(Prior Art) Generally, in the hot rolling of a sheet bar such as a steel strip,
As shown in the drawing, the sheet bar B that has passed through the rough rolling mill A is transferred by the transport table roller C, passes through the crop shear D, and then enters the finishing rolling mill group E.
At this time, in the sheet bar B waiting for finish rolling, heat dissipation progresses with the passage of time toward the rear end portion compared to the front end portion,
The temperature drops significantly.

In order to solve such a problem, for example, Japanese Patent Publication No. 50-300
28, Japanese Patent Sho 51-26317, Japanese Patent Sho 52-45304, Japanese Sho 53-16380
As shown in FIG. 3, the sheet bar B is once wound into a coil in front of the finishing rolling mill group E to obtain its heat retention effect, and then rewound to finish the rolling mill group E. It is disclosed that a sheet bar winding / unwinding device F (hereinafter referred to as a coil box) for rolling is provided.

By using the coil box, heat dissipation of the sheet bar on the entry side table of the finish rolling mill can be prevented, and drop of the finish rolling mill entry side temperature (F, E, T) due to the progress of rolling can be prevented. Fig. 4 shows an example of F, E, T when the coil box is used and when it is not used. However, the deformation resistance does not rise because F, E, T does not drop when the coil box is used. Since the rolling load does not increase, the power consumption of the main engine is reduced.

(Problems to be Solved by the Invention) In the prior art using the coil box, when accelerated rolling is performed by a finish rolling mill, F, E, and T do not fall over the entire length of the strip. , The surface temperature of the slip rises excessively and the finish outlet temperature (F,
There is a problem that D, T) rises, and as a result, scale grows between the finishing stands, which is pushed into the strip during rolling by the next stand and becomes a surface defect of the final product. The occurrence of this surface defect tends to concentrate on the back surface where the cooling capacity of the strip between the finishing stands is low. Therefore, when the coil box is used, there is a drawback that accelerated rolling cannot be performed and rolling efficiency cannot be increased.

In order to solve these problems, it is an object of the present invention to provide a method for preventing the generation of scale by cooling only the surface of the sheet bar upstream of the coil box of the hot rolling line.

[Structure of the Invention] (Means for Solving Problems) Focusing on the fact that when a coil box is used, the strip front and back surfaces are inverted by a finishing rolling mill, and the scale occurs on the finishing back surface. In order to achieve the object, in the method of adjusting the temperature of the material to be rolled by providing a winding and rewinding device for the sheet bar on the upstream side of the hot finish rolling mill, the temperature of the sheet bar on the upstream side of the winding and rewinding device. Is measured, the finish rolling outlet side temperature of the material to be rolled is predicted from the temperature and rolling conditions, and the upstream side of the take-up and rewinding device until the finish rolling outlet side temperature becomes equal to or lower than the scale flaw occurrence limit temperature of the material to be rolled. The side is characterized in that the surface of the seat bar is cooled by water injection.

(Example) An example of the present invention will be described in detail with reference to FIG.

The sheet bar 2 exiting the rough final rolling mill 1 is a coil box 3
Is once wound into a coil and then rewound to finish rolling mill group 4
To be sent to.

The cooling device 5 is installed above the seat bar 2 on the entrance side of the coil box 3. Then, the temperature of the sheet bar 2 is measured by a thermometer 6 installed on the outlet side of the rough final rolling mill 1, and the processing type processor for predicting the finishing outlet temperature by storing the steel type, size, and rolling schedule of the sheet bar in advance. 7, the required amount of water injection and the timing of water injection are calculated by this arithmetic processing unit 7, and a command is sent to the water injection control device 8, and from the water injection control device 8 to the surface of the seat bar 2 from the cooling device 5. Pour water and cool the seat bar 2.

It is sufficient to cool the seat bar 2 to a level at which scale flaws can be prevented.

FIG. 2 shows a temperature chart, in which the broken line shows the conventional uncontrolled state, and the winding temperature is uniform over the entire length.

Therefore, the finishing inlet temperature is also uniform over the entire length. In this case, in order to increase the rolling efficiency, the finishing rolling speed is increased during the rolling process. (In the initial stage of normal rolling, the material tip to be rolled at a lower speed is used to stabilize the threading. The timing of leaving the stand,
(Alternatively, the temperature is increased at the timing when it reaches the winder.) As the rolling speed increases, the amount of temperature drop during finish rolling decreases, and F, D, and T increase, and the scale flaw limit is exceeded. .

Since F, D, and T complete rolling in an austenite single phase, the lower limit is usually about 830 ° C. On the other hand, the occurrence of scale defects generally sharply increases when F, D, and T exceed 860 ° C. Pass the tip of the seat bar at 770 mpm and
When accelerated to around mpm, the finish outlet temperature increases by about 100 ° C. Therefore, if 830 ° C is secured at the tip, it will enter the scale flaw risk area after completion of acceleration. The timing at which the acceleration of finish rolling starts and the amount of acceleration are determined by the steel grade and product dimensions. Therefore, the amount of temperature rise due to acceleration is also determined by this.

In this example, the prediction calculation of the finish outlet temperature is performed based on the information on the steel type, dimensions, rolling schedule, rough mill final stand outlet temperature of the rolled material. Which part of the steel sheet exceeds the scale flaw occurrence limit by about ℃ In order to make F, D, and T within the scale flaw occurrence limit,
By determining and controlling the water injection timing and the number of water injections for each cooling header installed in front of the coil box, it is possible to obtain the temperature distribution in the longitudinal direction as shown by the solid line in FIG.

That is, the heat retaining effect of the coil box is sufficiently exerted,
In addition, the rolling efficiency is not reduced, and the increase in the rate of scale defects can be prevented.

In the conventional method, all the coils exceed the scale flaw generation limit, and as a result, the rate of product degradation due to scale flaws reaches 40% or more. On the other hand, according to the present embodiment, this number can be suppressed to 1% or less.

[Effects of the Invention] F by the coil box without reducing the rolling efficiency,
The effect of preventing E and T from falling is sufficiently exerted, and the occurrence of scale flaws can be prevented.

[Brief description of drawings]

FIG. 1 is a front view of an apparatus used for carrying out a method for controlling the temperature of a material to be rolled in hot rolling according to the present invention, FIG. 2 is a temperature flowchart, FIG. 3 is a front view of a conventional method, and FIG. It is a figure which shows the relationship between the temperature of the finishing rolling mill entrance side, and the progress of rolling. 1 ... Coarse final stand, 2 ... Sheet bar, 3 ... Coil box, 4 ... Finishing mill group, 5 ... Cooling device, 6
…… Thermometer, 7 …… Processor, 8 …… Water injection control device.

Claims (1)

[Claims] 1. A method for adjusting the temperature of a material to be rolled by providing a sheet bar winding and rewinding device on the upstream side of a hot finish rolling mill, wherein the temperature of the sheet bar on the upstream side of the winding and rewinding device is adjusted. Measured, predicting the finish rolling outlet side temperature of the rolled material from the temperature and rolling conditions, until the finish rolling outlet side temperature is below the scale flaw occurrence limit temperature of the rolled material A method for adjusting the temperature of a material to be rolled in hot rolling, which comprises cooling the surface of a sheet bar with water.