JP5862907B2 - Method and apparatus for cooling coiled hot-rolled steel sheet - Google Patents

Description

  The present invention relates to a cooling method and a cooling device for cooling a hot-rolled steel sheet wound in a coil shape after hot rolling without causing rust.

  As shown in FIG. 2, in order to manufacture a hot-rolled steel sheet, a slab is heated to a predetermined temperature in a heating furnace 1, and the heated slab is rolled with a roughing mill 2 to form a rough bar. In a continuous hot finishing rolling mill 3 composed of a plurality of rolling stands, a hot rolled steel sheet 4 having a predetermined thickness is obtained. The hot-rolled steel sheet 4 coming out from the finish rolling mill 3 is cooled by supplying cooling water from above and below with a cooling device 5 installed on the run-out table, and then wound up with a winder 6 and coiled hot-rolled steel sheet. 7

  The coiled hot-rolled steel sheet (hereinafter also simply referred to as “coil”) after winding has a temperature of about 500 to 650 ° C., and is thus transported and shipped after being cooled to room temperature in a coil place in a hot-rolling factory. Is done. A large amount of coils are cooled in the coil storage area, and since the high temperature coils are placed around the high temperature coils, the temperature around each coil becomes high and the cooling efficiency is lowered. It takes 5 days. Therefore, there arises a problem that a vast site for placing the coil is required, a period until shipment becomes long, and an inventory increases.

  In order to shorten the coil cooling time, various methods for spraying cooling water have been proposed. However, if the cooling water is sprayed in a state where the coil surface temperature is 100 ° C. or less, the cooling water hardly evaporates, the coil surface gets wet with water, and if left as it is, rust is generated on the steel sheet surface. If rust occurs, the appearance will be damaged and shipping will not be possible.

  For this reason, conventionally, as described in Patent Document 1, a water cooling method has been proposed in which the temperature and humidity around the coil are measured and the spray amount is controlled so that the steel sheet surface does not get wet. Also, as described in Patent Document 2, a cooling method has been proposed in which one end of each width direction of one coil is cooled from both sides using a cooling nozzle.

JP-A-57-134207 Japanese Patent Application Laid-Open No. 5-177240

  However, the method of Patent Document 1 has a problem that cooling cannot be efficiently performed because the cooling water is sprayed from a distance from the ceiling of the coil storage area and the cooling capacity is low. Further, as in Patent Document 2, a cooling nozzle is provided for each coil on each side in the coil width direction and both end faces of the coil are cooled, so that a micro droplet (hereinafter referred to as “mist”) is used. )) Does not spread sufficiently, and it is difficult to cool the entire coil, and the cooling efficiency is low.

  In order to improve the water cooling capacity, it is important to increase the injection flow rate per unit area of the mist (hereinafter referred to as “water density”). However, when the water density is increased, the mist is less likely to evaporate due to an increase in humidity or a decrease in coil surface temperature, and droplets are likely to adhere to the coil. In particular, when the coil surface temperature is less than 100 ° C., the attached droplets are difficult to evaporate, so that the coil surface tends to get wet.

  A mist having a small droplet particle size is effective for preventing wetting of the coil surface during water cooling. This is because the smaller the particle size of the droplet, the smaller the amount of heat necessary for evaporation, and the easier it is to evaporate. However, even when the droplet particle size is small, it is difficult to evaporate when the humidity is high, and it is necessary to suppress an increase in humidity.

  As described above, it has been difficult in the past to achieve both suppression of wetting of the coil surface and improvement of the cooling capacity. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cooling method and a cooling device that do not generate rust in a coil and perform cooling with high efficiency.

In order to solve the above-mentioned problems, the method for cooling a coiled hot-rolled steel sheet according to the present invention is coiled by being wound on a coiling machine installed in a hot rolling line and then placed on a cooling floor. A method for cooling a hot-rolled steel sheet,
The coiled hot rolled steel sheet on the cooling floor is sprayed with a mist (cooling water made into fine droplets) as a refrigerant on both end faces in the width direction, and the coil shape is obtained by intermittent cooling (a cooling method in which injection and stop are repeated) While cooling the hot-rolled steel sheet,
The combination of the mist injection time and the stop time is changed in accordance with the surface temperature of the coiled hot-rolled steel sheet on the cooling bed.

Moreover, in order to solve the above-mentioned problem, the cooling device for a coiled hot-rolled steel sheet of the present invention is a cooling device used in the cooling method,
A mist nozzle that blows the mist onto both end faces in the width direction of the coiled hot-rolled steel sheet on the cooling floor;
A temperature sensor for measuring the surface temperature of the coiled hot-rolled steel sheet on the cooling floor;
Mist injection control means for changing the combination of the mist injection time and the stop time based on the surface temperature of the coiled hot-rolled steel sheet measured by the temperature sensor;
It is characterized by comprising.

  By using the cooling method and the cooling device of the present invention, water cooling that prevents wetting of the surface of the coiled hot-rolled steel sheet is possible. As a result, it is possible to prevent the occurrence of rust and to achieve high-efficiency cooling. Coiled hot-rolled steel sheets can be shipped.

The coiled hot-rolled steel sheet cooling device of the present invention used in one embodiment of the coiled hot-rolled steel sheet cooling method of the present invention applied to a coil group consisting of a plurality of coils stacked in two stages on a coil storage site. It is a perspective view which shows the outline of one Embodiment. It is a block diagram which shows the outline of a normal hot rolling line. One of the cooling apparatus of the coiled hot-rolled steel sheet of this invention used for one Embodiment of the cooling method of the coiled hot-rolled steel sheet of this invention applied to the coil group which consists of a plurality of coils placed flat in the coil place. It is a perspective view which shows the outline of embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, FIG. 1 shows the coil shape of the present invention used in one embodiment of the method for cooling a coiled hot-rolled steel sheet of the present invention applied to a coil group consisting of a plurality of coils stacked in two stages on the coil storage. It is a perspective view which shows the outline of one Embodiment of the cooling apparatus of a hot-rolled steel plate.

  The coil place here is divided into a plurality of blocks, and the coils 7 are stacked in two stages as shown in FIG. 1, and the cooling device of this embodiment includes a header pipe 8 in which a plurality of mist nozzles 9 are arranged. These are installed in the vicinity of the plurality of coils 7 to be cooled placed for each block. This is because the mist having a minute droplet particle diameter is difficult to reach far away, and is used to spread the mist on the entire coil 7 stacked in two stages by utilizing the rising air flow generated by the heat of the coil 7.

  Further, in the coil storage area, it is necessary to cool the coil 7 without wetting the surface of the coil 7 to 50 ° C. that is the cooling completion temperature of the coil 7. As a result of examining the relationship between the droplet particle diameter and the wetting occurrence temperature, the present inventor has found that the droplet particle diameter should be 40 μm or less in order to prevent wetting from occurring up to 50 ° C. It was also found that the droplet particle size of 20 μm or less has a high evaporation efficiency and is more suitable. Therefore, in the cooling method of this embodiment using the cooling device, water droplets having a particle diameter of 40 μm or less, preferably 20 μm or less are used for the mist. It was practically difficult to make the droplet particle size smaller than 10 μm.

  In cooling using mist, when the surface temperature of the coil 7 is 200 ° C. or higher, the mist is easily evaporated by heat from the coil 7. Therefore, in the cooling method of this embodiment, the mist is continuously sprayed to continuously cool, or the mist is not always sprayed, but the mist spraying and stopping are alternately repeated (hereinafter, intermittently). (Referred to as cooling) to suppress an increase in humidity and perform effective cooling.

As for the surface temperature of the coil 7 when complete | finishing continuous cooling, 150-250 degreeC is preferable. If it is higher than 250 ° C., the effect of shortening the cooling time is small, and if it is lower than 150 ° C., rust is generated. In this case, the water density in the continuous cooling and the intermittent cooling (spray water amount / coil width end surface cooling area) is preferably ^{2 to} 6 liters (L) / m ² · min (min). If the water density is less than ² L / m ² · min, the effect of shortening the cooling time is small, and if it is more than 6 L / m ² · min, rust is generated. It is desirable to increase the water density as the surface temperature of the coil 7 is higher.

  When the surface temperature of the coil 7 is lower than 150 ° C., the mist is hardly evaporated. As a countermeasure, intermittent cooling is performed in the cooling method of this embodiment. As the intermittent cooling pattern, the mist injection time is desirably 60 seconds (s) or less. When the spraying time is longer than 60 s, the humidity greatly increases. The stop time is preferably 0.25 to 1.5 times the injection time. If the stop time is less than 0.25 times the injection time, the evaporated mist is not transported far enough, and the humidity suppressing effect is reduced. On the other hand, if it is longer than 1.5 times, the cooling time shortening effect becomes small. The end temperature of these suitable conditions is preferably 100 to 150 ° C. If it is higher than 150 ° C., the effect of shortening the cooling time is small, and if it is lower than 100 ° C., rust is generated.

When the surface temperature of the coil 7 is 100 ° C. or lower, the mist is more difficult to evaporate. As a countermeasure, in the cooling method of this embodiment, water density is suppressed and intermittent cooling is performed. In this case, the water density is preferably 4 L / m ² · min or less. If the water density is higher than 4 L / m ² · min, rust is generated. As an intermittent cooling pattern, the mist injection time is desirably 60 seconds or less. When the spraying time is longer than 60 seconds, the humidity increases greatly. The stop time is preferably 1 to 4 times the injection time. When the stop time is less than 1 time of the injection time, the evaporated mist is not transported far enough, and the humidity suppressing effect is reduced. On the other hand, if it is longer than four times, the effect of shortening the cooling time is reduced.

  In order to carry out the cooling method of this embodiment, in the cooling device of this embodiment shown in FIG. 1, the cooling water supply pipe 10 connected to the header pipe 8 and the cooling water source 13 having a predetermined pressure are connected in series for each block. Further, an electromagnetic on-off valve 11 and an electromagnetic flow control valve 12 as mist injection control means are inserted, and the operation of these electromagnetic on-off valve 11 and electromagnetic flow control valve 12 is also used as mist injection control means. And one or a plurality of infrared cameras 15 as temperature sensors for measuring the surface temperature of the entire widthwise end faces of the plurality of coils 7 placed in the coil place. Input measurement data from.

  The computer 14 operates based on a program given in advance, and the lowest surface temperature in each block among the surface temperatures of the plurality of coils 7 placed in the coil place for each block based on the measurement data from the infrared camera 15. Based on the lowest surface temperature, continuous cooling and intermittent cooling of the coil 7 are performed for each block based on the reference temperature under the above-described conditions.

  FIG. 3 shows a coiled hot-rolled steel sheet according to the present invention, which is used in an embodiment of a method for cooling a coiled hot-rolled steel sheet according to the present invention, which is applied to a coil group consisting of a plurality of coils placed flat on a coil place. It is a perspective view which shows a part of one Embodiment of a cooling device, The cooling device of this embodiment also has the header pipe | tube 8 which has arrange | positioned the plurality of mist nozzles 9 for every block similarly to what is shown in FIG. The mist injection control means is installed in the vicinity of the plurality of coils 7 to be cooled and is connected in series between a cooling water supply pipe 10 connected to the header pipe 8 and a cooling water source 13 of a predetermined pressure (not shown) for each block. The electromagnetic on-off valve 11 and the electromagnetic flow control valve 12 (not shown) are inserted, and the operation of the electromagnetic on-off valve 11 and the electromagnetic flow control valve 12 is operated as a normal compile (not shown) as mist injection control means. One or a plurality of infrared cameras 15 (not shown) serving as temperature sensors that measure the surface temperature of the entire widthwise end faces of the plurality of coils 7 placed in the coil storage area. The measurement data from is input.

  The computer 14 operates based on a program given in advance, and is the lowest in each block among the surface temperatures of the plurality of coils 7 placed in the coil place for each block based on the measurement data from the infrared camera 15. The surface temperature is judged, and the continuous cooling and intermittent cooling of the coil 7 are performed for each block under the above-described conditions with the lowest surface temperature as a reference. Each header pipe 8 is provided with three types of mist nozzles 9 having different droplet particle diameters (particle diameters) of the mist to be ejected, and switching of the cooling water supply pipe 10 connected to each of them causes the mist particles. The diameter can be changed. Further, during the continuous cooling, the coil 7 is surrounded by mist-like mist, so when measuring the surface temperature with the infrared camera 15 during that time, spraying is stopped for a few seconds to sweep the mist-like mist. It is desirable.

  Hereinafter, as shown in FIG. 3, invention examples (examples) and comparative examples in which a plurality of coils 7 placed flat on a coil place in a hot rolling factory are cooled using the cooling device of this embodiment are shown. explain. The cooling start temperature of the coil 7 is 600 ° C., the weight of the single unit is 25 ton, the temperature of the coil place is 45 ° C., the cooling water temperature is 30 ° C., and the surface temperature of the coil 7 is 50 ° C. The cooling conditions and results are shown in Tables 1 and 2.

  In Tables 1 and 2, the cooling time indicates that it has a shortening effect of 2.5 days or more, and ○ indicates that it has a shortening effect of 2 days or more, compared to the case of cooling to the atmosphere. △ indicates that there is a shortening effect between 1 and 2 days, and x indicates that there is a shortening effect of 1 day or less. As for rust, ○ indicates that rust does not occur in the entire length and width, △ indicates that rust occurs in an area of 10% or less of the entire length and width, and × indicates the area of the entire length and width. Of these, rust is generated in an area of 30% or more. The part shown by the thick frame shows a part different from that on the basis of the first invention example.

  Table 1 shows Invention Examples (Examples) 1 to 27. Table 2 shows the case of cooling in the atmosphere as Comparative Example 1 and the case of cooling with mist as Comparative Examples 2-33. In Invention Examples 1 to 27, rust was not generated, and a sufficient cooling time was shortened, and a coil with good quality could be shipped in a short time. On the other hand, in Comparative Example 1, although it took 105 hours to complete the cooling, no rust was generated on the surface of the coil 7. In Comparative Example 2 and after, cooling with mist was performed according to the conditions of Table 2. However, since the cooling conditions were inappropriate, the effect of shortening the cooling time was small or rust was generated.

  In this embodiment, the cooling start temperature of the coil 7 is set to 600 ° C., but the effect of the present invention does not change greatly depending on the cooling start temperature. The cooling water temperature is 30 ° C., but the cooling effect is higher as the cooling water temperature is lower. On the other hand, when the cooling water temperature exceeds the cooling stop temperature of 50 ° C., the cooling water temperature is preferably 40 ° C. or lower because the cooling water temperature cannot be cooled to the cooling stop temperature.

  Although the present invention has been described based on the illustrated examples, the present invention is not limited to the above-described examples and can be appropriately changed within the scope of the claims. For example, a thermocouple or the like can be used instead of the infrared camera 15. A contact-type temperature sensor may be used. Further, instead of the electromagnetic on-off valve 11 or the electromagnetic flow control valve 12, a motor-operated on-off valve or a flow control valve may be used.

  Thus, according to the cooling method and the cooling device of the present invention, water cooling that prevents wetting of the surface of the coiled hot-rolled steel sheet is possible, and as a result, generation of rust and high-efficiency cooling are possible, and in a short time. Coiled hot-rolled steel sheets can be shipped.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Coarse rolling mill 3 Finishing rolling mill 4 Hot-rolled steel plate 5 Cooling device 6 Winding machine 7 Coiled hot-rolled steel plate (coil)
8 Header pipe 9 Mist nozzle 10 Cooling water supply pipe 11 Electromagnetic on-off valve 12 Electromagnetic flow control valve 13 Cooling water source 14 Computer 15 Infrared camera

Claims (5)

In the method for cooling a coiled hot-rolled steel sheet placed on a cooling bed, after being coiled by a winder installed in a hot rolling line,
Injecting mist as a refrigerant to both end surfaces in the width direction of the coiled hot rolled steel sheet on the cooling floor, cooling the coiled hot rolled steel sheet by at least intermittent cooling,
A method for cooling a coiled hot-rolled steel sheet, wherein the combination of the mist injection time and the stop time is changed according to the surface temperature of the coiled hot-rolled steel sheet on the cooling floor. Cooling of the coiled hot rolled steel sheet due to the injection of the mist, the surface temperature of the coiled hot-rolled steel sheet is 150 to 250 ° C., it continuously from the continuous cooling for injecting a mist in which switching to the intermittent cooling The method for cooling a coiled hot-rolled steel sheet according to claim 1. The cooling of the coiled hot-rolled steel sheet by the mist injection is characterized in that the surface temperature of the coiled hot-rolled steel sheet is 100 ° C. or less, and the water density is suppressed together with the intermittent cooling. The cooling method of the coiled hot-rolled steel sheet according to claim 2. In the cooling device used for the cooling method of any one of Claim 1 to 3,
A mist nozzle that blows the mist onto both end faces in the width direction of the coiled hot-rolled steel sheet on the cooling floor;
A temperature sensor for measuring the surface temperature of the coiled hot-rolled steel sheet on the cooling floor;
Mist injection control means for changing the combination of the mist injection time and the stop time based on the surface temperature of the coiled hot-rolled steel sheet measured by the temperature sensor;
An apparatus for cooling a coiled hot-rolled steel sheet. The mist injection control means includes an on-off valve and a flow control valve inserted in series between a header pipe having the mist nozzle and a cooling water source, and a computer for controlling the operation of the on-off valve and the flow control valve. The cooling apparatus for a coiled hot-rolled steel sheet according to claim 4, comprising:

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