JPH05277541A - Method for cooling hot-rolled steel sheet - Google Patents

Abstract

PURPOSE:To provide a cooling method for hot-rolled steel sheet by which coiling temp. can precisely be measured and trace of water wetting on the surface of the hot-rolled steel sheet is not left as pattern. CONSTITUTION:In the cooling method for the hot-rolled steel sheet after rolling, a thermometer on the outlet of the finish rolling mill, plural upper water spraying headers and lower water spraying headers, draining spray and coiling thermometer are arranged in this order between the hot finish rolling mill and a coiler and the water is sprayed from the upper water spraying headers and the lower water spraying headers. Further, at the time of coiling the hot- rolled steel sheet having <=400 deg.C coiling temp. and <=4mm sheet thickness, the water spraying from the upper water spraying headers in proximity to the coiling thermometer is stopped and the water spraying only from the lower water spraying header is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cooling a hot-rolled steel sheet after rolling in a hot-rolling facility. More specifically, a hot-rolled coil capable of accurately measuring a winding temperature and having an excellent surface property is provided. The present invention relates to a method for cooling a hot-rolled steel sheet for obtaining the same.

[0002]

2. Description of the Related Art FIG. 3 shows each equipment from a hot finish rolling mill to a winding machine. A hot rolled steel sheet 8 rolled by a hot finish rolling mill 1 has a finish rolling mill outlet side thermometer 5 The temperature is measured at, and water is poured from the upper water injection header 3 and the lower water injection header 4 to a predetermined winding temperature based on the measured temperature and cooled. The hot-rolled steel sheet 8 that has been cooled to a predetermined winding temperature is blown off the cooling water on the hot-rolled steel sheet by the draining spray 7, and then the winding temperature is measured by the winding thermometer 6 and the winding machine. It is wound up by 2 and becomes a hot rolled coil.

The high temperature hot rolled steel sheet which has been finish rolled has a winding temperature determined in accordance with the required mechanical properties.
It is cooled to a predetermined temperature before being wound up by the winder. The cooling method also includes the temperature measured by the output side thermometer of the finish rolling mill, the value measured by the strip thickness gauge (not shown), the actual measurement of the rolling speed of the final stand of the hot finish rolling mill, and the temperature of the cooling water. And
The required cooling water injection amount is calculated, water is injected by the cooling equipment shown in FIG. 4, and the water is cooled to a predetermined winding temperature.

Usually, the hot rolled steel sheet is accelerated, so that the water injection amount increases in accordance with the acceleration. In this increasing method, the cooling equipment shown in FIG. 4 is divided every 3 to 8 m in the running direction of the hot-rolled steel sheet, the upper water injection header 3 and the lower water injection header 4 are paired, or the upper water injection header 3 and the lower water injection header 3 are used. The header 4 is alternated to increase the water injection amount.

[0005]

Since the hot-rolled hot-rolled steel sheet is poured and cooled from the upper and lower water injection headers as described above, the injected cooling water is on the upper surface of the hot-rolled steel sheet. Will remain. In order to remove this cooling water, a draining spray is usually installed in front of the winding thermometer.

The cooling water injected from the upper water injection header runs on the table together with the hot-rolled steel sheet while riding on the hot-rolled steel sheet, but in a region where the surface temperature of the hot-rolled steel sheet is high,
The cooling water on the hot-rolled steel sheet evaporates immediately. In addition, since the water drops are formed without immediate evaporation, the water can be blown off with a water spray.

However, when the surface temperature of the hot-rolled steel sheet becomes low, it takes time for the cooling water on the hot-rolled steel sheet to evaporate,
Further, the cooling water is changed from a water drop shape to a flat surface and wets the upper surface of the hot-rolled steel sheet. Therefore, even if the draining spray is operated, the cooling water is not blown off from the hot-rolled steel sheet but is taken up by the winder together with the hot-rolled steel sheet.

When the cooling water is present on the hot-rolled steel sheet, the winding temperature cannot be accurately measured, so that the accuracy of controlling the winding temperature is significantly deteriorated, and it becomes impossible to secure the predetermined mechanical properties. Furthermore, when the hot-rolled steel sheet is wound into a coil while being wet with cooling water, traces of water-wetting remain on the surface of the hot-rolled steel sheet as a pattern, and the surface quality is significantly impaired.

The present invention has been made in order to solve the above-mentioned problems, and by stopping the water injection from the upper water injection header in the vicinity of the winding thermometer and by supplying water only from the lower water injection header, An object of the present invention is to provide a method for cooling a hot-rolled steel sheet, which enables accurate temperature measurement and does not leave a pattern of water-wetting traces on the surface of the hot-rolled steel sheet.

[0010]

A first aspect of the present invention is to provide a finish rolling mill outlet thermometer, a plurality of upper and lower water injection headers, a lower water injection header, a draining spray, and a winding machine between a hot finish rolling mill and a winding machine. Disposing the take-up thermometer in order, in the cooling method of the hot-rolled steel sheet after rolling by pouring water from the upper water-pouring header and the lower water-pouring header, stop pouring water from the upper water-pouring header in the vicinity of the winding thermometer, This is a cooling method for hot-rolled steel sheets, in which water is injected only from the lower water injection header.

According to a second aspect of the present invention, a finishing rolling mill outlet side thermometer, a plurality of upper and lower water injection headers, a lower water injection header, a draining spray and a winding thermometer are arranged in this order between the hot finish rolling mill and the winding machine. Then, in the cooling method of the hot-rolled steel sheet after rolling by pouring water from the upper water-pouring header and the lower water-pouring header, the winding temperature is 400 ° C or less and the sheet thickness is 4 m.
When winding a hot-rolled steel sheet having a length of m or less, cooling of the hot-rolled steel sheet is performed by stopping the water injection from the upper water injection header near the winding thermometer and injecting water only from the lower water injection header.

[0012]

In the present invention, by the time the hot-rolled steel sheet after finish rolling reaches the upper water injection header near the winding thermometer,
Cool down to almost the specified winding temperature, stop water injection from the upper water injection header near the winding thermometer,
Only pour water from the bottom pour header. In the case of a hot-rolled steel sheet with a thin plate that can be cooled to the coiling temperature only by cooling water from the lower cooling header, stop cooling water from the upper cooling header close to the winding thermometer and Actively inject water from the header. As a result, the winding temperature can be accurately measured, and the pattern of water wetting does not remain on the surface of the hot-rolled steel sheet.

The reason why the winding temperature is limited to 400 ° C. or lower in the second invention is as follows. Winding temperature is 400
In the range exceeding ℃, no significant change was observed in the winding temperature, and no visual observation showed that the hot-rolled steel sheet was wet with water, nor was there a pattern of water-wetting traces on the product. But,
When the coiling temperature is 400 ° C or less, the cooling water on the hot-rolled steel sheet does not evaporate immediately, it becomes flat from water droplets, and this cooling water can be blown off from the hot-rolled steel sheet even if a draining spray is operated. It was not possible to do so, and a large fluctuation was recognized in the winding temperature. Further, since the hot-rolled steel sheet was wound into a coil in a state of being wet with cooling water, a pattern of water-wetting traces was observed on the product. As described above, it is considered that the time required for the evaporation of the cooling water on the hot-rolled steel sheet changes drastically when the temperature of the normal hot-rolled steel sheet is 400 ° C.

Further, the reason for limiting the winding plate thickness to 4 mm or less is that when the plate thickness exceeds 4 mm, the amount of water injection increases, and in the case of water injection only from the lower water injection header, the hot-rolled steel sheet is transferred from the back surface to the surface. It becomes difficult to cool it evenly,
This is because predetermined mechanical properties cannot be secured. Therefore, the winding temperature is 400 ℃ or less, and the winding plate thickness is 4m.
Limited to m or less.

It is preferable to stop the water injection from the upper water injection header in a region where the calculated temperature on the surface of the hot-rolled steel sheet between the finish rolling mill outlet side thermometer and the winder is 500 ° C. or less.
Further, as shown in FIG. 2, water is injected from the lower water injection header toward the outside in the plate width direction of the hot rolled steel sheet so that the water injection from the lower water injection header does not get on the hot rolled steel sheet. As a result, cooling water does not exist on the hot-rolled steel sheet, the temperature measurement accuracy of the winding temperature is improved, and the surface quality of the product is improved.

[0016]

EXAMPLES Examples of the present invention will be described below.
A hot-rolled steel plate having a plate thickness of 3 mm and a plate width of 1235 mm was rolled, cooled by the conventional method and the method of the present invention, and wound on a winder at a target winding temperature of 350 ° C. The cooling of the present invention is performed in front of the winding thermometer.
Water injection from the top water injection header from 30m to immediately before was stopped. During this time, water was injected only from the lower water injection header. In this case, the surface temperature of the hot-rolled steel sheet in the water injection stop region from the upper water injection header was 500 ° C or lower.

An example of the temperature measurement results by the winding thermometer of the conventional method and the method of the present invention is shown in the form of a temperature chart in FIGS. 1 (a) and 1 (b). In Fig. 1 (a), because of the conventional method, cooling water exists on the hot-rolled steel sheet, and this cooling water influences the temperature measurement result, and the temperature measurement result fluctuates greatly. Further, this product could not be shipped as a product because a pattern due to water wetting was observed.

FIG. 1 (b) shows that, because of the method of the present invention, there is no cooling water on the hot-rolled steel sheet, there is no large change in the temperature measurement result, and the temperature measurement result is the original winding of the hot-rolled steel sheet. Take temperature 3
It shows 50 ° C. In addition, no pattern due to water wetting was observed in the product, and the surface quality was good.

[0019]

Industrial Applicability According to the present invention, a hot rolling mill output side thermometer, a plurality of upper and lower water injection headers, a lower water injection header, a draining spray, and a winding thermometer are sequentially arranged between a hot finish rolling mill and a winding machine. In the cooling method of the hot-rolled steel sheet after rolling, which is performed by pouring water from the upper water pouring header and the lower water pouring header, the water pouring from the upper water pouring header close to the winding thermometer is stopped, and the water is pouring only from the lower water pouring header. According to the method of the present invention, which is a method for cooling a hot-rolled steel sheet, the winding temperature can be accurately measured, so that predetermined mechanical properties can be ensured, and the surface of the hot-rolled steel sheet is wet with water. The pattern disappears and the surface quality of the hot rolled steel sheet can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of temperature measurement results by a winding thermometer of a conventional method and a method of the present invention.

FIG. 2 is a diagram showing a direction of water injection from a lower water injection header.

FIG. 3 is an explanatory diagram of each equipment from a hot finish rolling mill to a winding machine.

FIG. 4 is an explanatory diagram of a cooling facility including an upper water injection header and a lower water injection header.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hot finishing rolling mill, 2 ... Winding machine, 3 ... Upper water injection header, 4 ... Lower water injection header, 5 ... Finishing rolling machine outlet side thermometer, 6 ... Winding thermometer, 7 ... Draining spray, 8 ... Hot-rolled steel sheet, 9 ... Top water injection, 10 ... Bottom water injection.

Claims (2)

[Claims] 1. An exit side thermometer, a plurality of upper water injection headers and lower water injection headers, a water draining spray, and a winding thermometer are arranged in this order between the hot finish rolling mill and the winder, and In the cooling method of the hot-rolled steel sheet after rolling by pouring water from the upper water injection header and the lower water injection header,
A method for cooling a hot-rolled steel sheet, characterized in that water injection from an upper water injection header close to a winding thermometer is stopped and water is injected only from a lower water injection header. 2. A finish rolling mill outlet side thermometer, a plurality of upper and lower water injection headers, a lower water injection header, a draining spray and a winding thermometer are arranged in this order between the hot finish rolling mill and the winder, and In the cooling method of the hot-rolled steel sheet after rolling by pouring water from the upper water injection header and the lower water injection header,
When rolling a hot-rolled steel sheet with a coiling temperature of 400 ° C or less and a plate thickness of 4 mm or less, stop the water injection from the upper water injection header close to the winding thermometer and inject water only from the lower water injection header. Steel plate cooling method.