JPS6149760A - Secondary cooling method of continuously cast steel ingot - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for secondary cooling of continuously cast slabs.

[Prior art and its problems]

Processes in which continuously cast slabs are charged into a heating furnace while still at high temperature and then rolled, or further processes in which they are sent directly to the rolling process without going through a heating furnace and then rolled are being implemented. However, in order to implement these methods, defect-free casting of slabs is required.

It is known that vertical cracks that occur on the surface of a slab are nucleated within the mold and further progress due to non-uniform cooling in the secondary cooling zone. Therefore, in addition to countermeasures against nuclear generation in the mold, various countermeasures have been attempted to prevent uneven cooling in the secondary cooling zone.

Conventionally, water slag cooling has been performed in the secondary cooling zone using flat spray nozzles or full cone nozzles, but since only water is sprayed, the nozzle tip constriction area is extremely small, so the nozzle eye Clogging is likely to occur, and as a result, the cooling ability of the clogged nozzle portion decreases, resulting in uneven cooling.

Therefore, as a countermeasure against uneven cooling in the secondary cooling zone, various gas-liquid cooling methods have been proposed, including the gas-liquid cooling method using hot water in Japanese Patent Publication No. 35-6961. Cooling by cooling methods is being implemented.

However, since the above-mentioned gas-liquid cooling method uses pressurized air to atomize the cooling water and spray it, a large amount of high-pressure air is required, and as the amount of air increases, a large-capacity air compressor, air holder, etc. are required. It becomes necessary.

Furthermore, since the cooling device requires not only cooling water piping but also air piping, the equipment becomes complicated and the amount of equipment increases. Operating costs are also high because the amount of air used is large, which increases the amount of electricity used.

[Purpose of the invention]

In view of the above-mentioned current situation, an object of the present invention is to provide a method for secondary cooling of continuously cast slabs, which can uniformly cool continuously cast slabs.

[Summary of the invention]

The method for secondary cooling of continuously cast slabs of the present invention involves passing hot water at a temperature of 100°C or higher through a pipe provided with a restriction to prevent minute water droplets from flowing through continuously cast slabs pulled from a mold. The method is characterized in that hot water is injected, the hot water cools the slab, and then the slab is water-cooled and/or air-cooled.

[Structure of the invention]

The present inventors previously proposed a method for cooling high-temperature objects using hot water (Japanese Patent Publication No. 57-27926).

This invention was achieved as a result of intensive research into a secondary cooling method for continuously cast slabs that is based on the hot water cooling method described above and can suppress the occurrence of vertical cracks on the slab surface. be.

The present invention will be described in detail below.

FIG. 1 is an explanatory diagram showing one embodiment of the method of the present invention. In FIG. 1, 1 is a mold, 2 is a guide roller that guides a continuously cast slab 3 pulled out from the mold 1;
4 is a hot water cooling zone in which a hot water cooling nozzle 5 is provided between the guide rollers 2 and 2, and 6 is a water cooling zone in which a water cooling nozzle 7 is provided between the guide rollers 2 and 2. The slab 3 is placed in a hot water cooling zone 4 connected to the lower part of the mold 1.
It is cooled by hot water, then cooled by water in a water cooling zone 6 provided following the hot water cooling zone 4, and then cooled by the atmosphere. Note that the slab 3 after being cooled with hot water may be cooled by only one of water cooling and atmospheric cooling. The slab 3 is guided by guide rollers 2 while being cooled by the atmosphere, passes through a straightening machine 8 and a cutting machine 9, and then is transferred to a roller table 1.
0.

The water cooling zone 6 is similar to a water cooling zone provided in a conventional secondary cooling zone, and cools the slab 3 by spraying cooling water from a water cooling nozzle 7 onto the slab 3.

The hot water cooling zone 4 cools the slab 3 by spraying fine water droplets of hot water onto the slab 3 from the hot water cooling nozzle 5. As shown in FIG. 2, a branch pipe 12 equipped with a restrictor 11 is connected to the hot water cooling nozzle 5 arranged therein. The branch pipe 12 is branched from the intermediate header pipe 13, and the intermediate header pipe 13 supplies hot water through a hot water control main pipe 17 in which a flow meter 14, a flow control valve 15, and a cutoff valve 16 are inserted. Hot water main pipe 1
8 is connected.

The branch pipe 12 in which the restrictor 11 is installed extracts hot water in the form of fine water droplets from the hot water at a temperature of 100°C or higher, which is supplied via the hot water main pipe 18, the hot water control main pipe 17, and the intermediate header pipe 13. By passing hot water at a temperature of 100°C or higher through a squeezer 11, a part of it evaporates and expands in volume, and the volumetric expansion breaks it into fine pieces to produce hot water in the form of fine water droplets. That is. The hot water is supplied to the nozzle 5 as a high-speed gas-liquid two-phase flow containing fine water droplets of hot water,
It is injected onto the slab 3. In this invention, in this way, 10
Hot water with a temperature of 0°C or higher is passed through a branch pipe 12 equipped with a restrictor 11.
By passing the hot water through the nozzle 5, the hot water in small droplets t'a is injected from the nozzle 5, so that the slab 3 can be uniformly cooled.

The diaphragm 11 is not a rounded diaphragm with low flow resistance as seen in conventional spray nozzles, but a diaphragm with sharp edges. A diaphragm 11 with such sharp edges
For example, an oriswiss plate can be used, and branch pipe 1
In order to install the orifice plate 2, as shown in FIG.
o should be inserted between the 7 langes 19 and 19 and fixed with bolts. By making the diaphragm 11 a diaphragm with sharp edges, when hot water passes through the diaphragm 11, a low-pressure region is generated to promote the generation and growth of bubble nuclei, and to prevent microscopic water droplets from being formed by the hot water. To stably perform flushing of a piece 3.

As the hot water cooling nozzle 5, for example, a ring nozzle 21 as shown in FIG. 4(a) can be used. The nozzle 21 consists of an annular gib 23 in which a plurality of nozzle holes 22 are provided at intervals on the inner surface facing the slab 3, and the outer surface of the pipe 23 has a plurality of nozzle holes 22 arranged at intervals. Two branch pipes 12 supplying hot water in droplets are attached tangentially.

As shown in FIG. 4(b), the nozzle hole 22 has a surface 23a perpendicular to the annular pipe 23, and a flow direction A in the pipe 23 of a gas-liquid two-phase flow containing fine water droplets of hot water. On the downstream side, there is a notch on two surfaces, a surface 23b forming an acute angle, for example, 45 degrees, with respect to the surface 23a. According to such a ring nozzle 21, the spray characteristics in the circumferential direction of the nozzle are improved, and hot water in the form of fine water droplets can be sprayed uniformly in the circumferential direction of the nozzle. , is suitable.

In order to supply hot water to the hot water main pipe 18, a hot water supply facility as shown in FIG. 5, for example, can be used. Fifth
In the figure, 24 is a hot water tank to which a main hot water pipe 18 is connected, and this hot water tank 24 has a water supply pipe 26 installed with a water supply control valve 25 for supplying water into the tank 24, and a steam A heating steam pipe 28 equipped with a flow control valve 27 for supplying heating steam to heat the water in the tank 24
are connected. An exhaust pipe 30 equipped with a pressure control valve 29 is provided at the top of the hot water tank 24, and a drain pipe 32 equipped with a blow water control valve 31 is provided at the bottom.

In this hot water supply equipment, the temperature of the hot water in the hot water tank 24 is controlled by controlling the pressure of steam in the tank 24. The pressure of steam in the hot water tank 24 is controlled by detecting the pressure of steam in the tank 24 with a pressure detector 33, and controlling the steam flow rate control valve 27 of the heating steam pipe 28 and the pressure control valve 29 of the exhaust pipe 30. This is done by adjusting the opening of the valve. Therefore, the hot water in the hot water tank 24 is saturated water corresponding to the water vapor pressure in the tank 24. The water level of the hot water in the hot water tank 24 is controlled by detecting the water level of the hot water in the tank 24 with a water level detector 34, and controlling the water supply control valve 25 of the water supply pipe 26 and the blow and water control valve of the drain pipe 32. This is done by adjusting the valve opening degree with respect to 31.

In this invention, as described above, when performing secondary cooling of the continuously cast slab 3 drawn from the mold 1, hot water with a temperature of 100° C. or more is passed through the branch pipe 12 provided with the drawing sheath 11. By this, hot water cooling can be performed by spraying fine water droplets of hot water onto the slab 3 in advance to uniformly cool the slab 3.
Since the slab 3 is first cooled and then the slab 3 is subjected to normal water cooling and/or air cooling, the secondary cooling of the slab 3 can be performed more uniformly.

It goes without saying that steam generated in the boiler equipment may be used as the steam supplied to the hot water tank 24 of the hot water supply equipment shown in Fig. 5 through the heating steam pipe 28, but energy saving is also possible. Therefore, it is preferable to recover the heat radiated from the slab 3 into the atmosphere during the secondary cooling of the slab 3 and use it as a heat source. That is, the slab 3 is pulled out from the mold 1 and cooled from a temperature of about 1300°C to a temperature of about 700°C while being delivered to the cutting machine 10, and the heat of the slab 3 corresponding to this temperature difference is Part of the heat is consumed to raise the temperature of the cooling water in the hot water cooling zone 4 and the water cooling zone 6, and the remaining heat is consumed.

This is the atmospheric cooling zone between the water cooling zone 6 and the cutting machine 10, where the heat is dissipated into the atmosphere.For example, as shown in FIG. A heat insulating material 36 is installed inside the supporting member 35 on the moving path of the slab 3.
A heat exchanger 38 with an annular heat transfer tube 37 fixed thereto is installed, and by passing the slab 3 through the heat exchanger 38, boiler water that is circulated and supplied from the boiler 39 to the heat exchanger 38 is heated. It is preferable that the heat radiated from the slab 3 be recovered. Steam generated within the boiler 39 is sent to the hot water tank 24 via the heating steam pipe 28.

As described above, by recovering the heat dissipated from the slab 3 and using it as a heat source for hot water used in the hot water cooling zone 4, it is possible to save energy used in the heat source. In terms of slab temperature, it is also advantageous because the heat radiation of the slab 3 is suppressed and maintained at a high temperature compared to when the heat of the slab 3 is dissipated into the atmosphere. The consumption economy will decline.

Next, the present invention will be explained using examples.

Length 1.4mK from just below the mold of billet continuous casting machine
The cooling zone is divided into two, and as shown in FIG. 6(a) FC, the upper half following the mold 1 is a hot water cooling zone 4, and the lower half is a water cooling zone 6 similar to the conventional water cooling zone. , the slab 3 pulled out from the mold 1 is cooled with hot water, then water cooled, then air cooled, and while secondary cooling is performed, the slab 3 is test cast. Vertical cracks that occurred on the surface were investigated. For comparison, we will compare a case where all the cooling zones are water cooling zones (comparative example 1) and a case where the hot water cooling zone 4 and the water cooling zone 6 are replaced with the 6th cooling zone as shown in FIG. Vertical cracks that occurred on the surface of the slab 3 were similarly examined for the case where the slab 3 was installed in the opposite direction to that shown in Figure (a) (Comparative Example 2).

In the hot water cooling nozzle 5 of the hot water cooling zone 4: FIG. 4(a),
The ring nozzle 21 shown in (b) was used. In addition, the water cooling nozzle 7 of the water cooling zone 6 is provided with a slab 3 of an annular pipe.
A plurality of spray nozzles were installed at equal intervals in the circumferential direction on the inner surface facing the .

Table 1 shows casting conditions such as slab size and hot water cooling conditions such as hot water flow rate. Furthermore, the occurrence of vertical cracks in the slab 3 is shown in Fig. 7.

As is clear from FIG. 7, in the method of the invention, the vertical crack that occurred in the slab 3 was 1.4 m in length just below the mold.
Approximately half of Comparative Example 1 in which the entire cooling zone extending over □ was cooled as a water cooling zone, and the upper half of the cooling zone was a water cooling zone,
Approximately '6' in Comparative Example 2 where the lower half was cooled with hot water and cooling zone
It was worth it.

〔Effect of the invention〕

As explained above, according to the method of the present invention, the continuously cast slab pulled out from the mold can be uniformly secondary cooled, thereby eliminating the vertical cracks that had occurred on the slab surface due to uneven secondary cooling. can be reduced.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of the method of the present invention, Fig. 2 is a piping diagram showing the piping of the hot water cooling zone used in the method of Fig. 1, and Fig. 3 is a piping diagram showing the piping of the hot water cooling zone used in the method of Fig. 2. Fig. 4 (a) is a plan view showing the hot water cooling nozzle used in the hot water cooling zone of Fig. 2; Figure 4 (A) is a plan view showing the nozzle hole portion of the hot water cooling nozzle; Figure 5 is an explanatory diagram showing the hot water supply equipment that supplies hot water to the hot water cooling zone in Figure 2;
Figure (a) is a configuration diagram showing a part of the secondary cooling zone used in the example of this invention, and Figure 6 (b) is a configuration diagram showing a part of the secondary cooling zone used in Comparative Example 2. Figure 7 is a graph showing the occurrence index of vertical cracks generated on the slab surface by the methods of Examples and □ Comparative Example 1.2, and Figure 8 is a graph showing the occurrence index of vertical cracks generated on the slab surface by the methods of Examples and □ Comparative Example 1.2. It is a figure showing one preferred aspect of a collection device. In the drawings, 3"...mold, 2...guide roller, 3...slab, 4...hot water cooling zone,
5... Hot water cooling nozzle, 6... Water cooling zone, 7...
... Water cooling nozzle, 11 ... Restriction, 12 ... Branch pipe, 19 ... 7 langes, 20 ... Orifice plate, 21 ... Ring nozzle, 22 ... Nozzle hole, 23 ...・Annular / Guib.

Claims (1)

[Claims] Hot water at a temperature of 100° C. or higher is passed through a pipe equipped with a throttle to spray hot water in the form of fine water droplets onto the continuously cast slab that has been pulled out of the mold. A method for secondary cooling of a continuously cast slab, characterized in that the slab is cooled by cooling the slab, and then the slab is water-cooled and/or air-cooled.