JPS6247101B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method for steel in curved continuous casting equipment.

As is well known, in continuous casting, molten steel stored in a tundish is generally injected into a mold to form a slab with a predetermined cross-sectional shape, which is then continuously pulled downward and solidified to the core of the slab. After that, the steel is manufactured by cutting it to a predetermined length. While the slab is being pulled out of the continuous casting equipment, it solidifies sequentially from the surface, and is transferred to the continuous casting equipment (hereinafter referred to as
The machine length is set so that the core is completely solidified by the end of the continuous casting machine, and the drawing speed, cooling intensity, etc. are controlled.

By the way, when pouring molten steel into the mold, that is, when finishing the casting, the top part of the slab (in the present invention, the top part of the slab refers to the bottom end of the slab that is pulled out from the mold at the end of casting). It is necessary to reliably solidify the material before pulling it out. In other words, if the slab is pulled out when the top of the slab is insufficiently solidified, the solidified shell formed on the slab surface will break in the continuous caster, causing molten steel to flow out and bleed, resulting in equipment damage and damage. A situation that causes a steam explosion may occur, posing a major problem in terms of equipment and safety. Therefore, in conventional continuous casting, the casting speed is greatly reduced toward the end of casting, and in extreme cases, it is common practice to stop drawing and allow the top of the slab to sufficiently solidify before gradually pulling it out. It was hot. For this reason, in the final stage of casting, the productivity was significantly reduced, and the temperature of the slab located in the continuous casting machine was naturally also significantly reduced. In order to solve the above-mentioned problem, a method has been proposed and adopted in which a cold material such as metal scraps or iron plates is charged into the mold.
However, even in this method, the slab cannot be pulled out from the mold until the top part of the slab is solidified, and although it is possible to shorten the time required to drastically reduce the aforementioned drawing speed, it is not possible to change the drawing pattern. Therefore, no satisfactory effect was obtained.

The present invention was developed as a result of repeated various experiments in order to fundamentally solve the problems at the final stage of casting. This invention relates to a method for continuous casting of curved steel, which is characterized by mounting and drawing.

The present invention will be described in detail below based on Examples.

FIG. 1 is a cross-sectional structural diagram of a well-known general continuous casting machine. In the figure, 1 is a pot for storing molten steel 2, and 3 is a tundish. An injection nozzle 4 is attached to the tundish 3, and the injection nozzle 4
The molten steel 2 in the tundish 3 is injected into the mold 5 through the tundish 3. 6 is a slab pulled out from the mold 5; 7
is a cooling device for cooling the slab 6; 8 is a group of guide rolls that continuously pulls out the slab 6, straightens the slab 6 horizontally, and conveys it; 9 is a group of guide rolls that transport the slab 6 to a set length; 10 indicates the steel cut to a predetermined length. In normal continuous casting operations, the molten steel 2 from the tundish 3 is injected into the mold 5 through the injection nozzle 4 to form a slab 6 having a predetermined cross-sectional shape, and the slab 6 is continuously drawn out. The steel 10 is manufactured by cutting the steel 10 to a set length using a cutting device 9 provided near the end of the continuous casting machine. However, when the remaining amount of molten steel 2 in the tundish 3 becomes less than a predetermined amount or becomes zero, for example, the sliding nozzle 30 is closed and casting is completed. Figures 2 and 3 are
FIG. 2 is a perspective view (FIG. 2) and a cross-sectional view (FIG. 3) showing the vicinity of the mold after the injection nozzle 4 has been retracted, and are intended to provide a basic explanation of the present invention at the time of completion of the casting. That is, in the present invention, when the casting is completed, first, an outflow melt receiving fitting (hereinafter referred to as a receiving fitting) 11 is attached to the slab top portion 6a (indicated by a broken line) located in the mold 5. For example, in the embodiment shown in FIGS. 2 and 3, the receiving fitting 11 includes a receiving member 12 formed in the shape of a saucer, a fixing member 13 inserted and fixed into the top portion 6a of the slab in an unsolidified or semi-solidified state, and the above-mentioned. It is composed of a connecting member 14 that connects a receiving member 12 and a fixing member 13. The receiving fitting 11 is attached by inserting the fixing member 13 into the slab top portion 6a. The fixing member 13 also functions as a cold material and accelerates the solidification rate of the slab top portion 6a, thereby firmly holding the receiving fitting 11.
When installing this receiving metal fitting 11, the receiving member 1
2 is mounted so that it is located on the outer surface (hereinafter referred to as F surface) of the curved slab 6. Now, after the fitting 11 has been attached to the slab top portion 6a, the slab 6 is pulled out in the same manner as in normal continuous casting work. That is, in the present invention, the slab 6 is pulled out with the receiving metal fitting 11 attached to the slab top portion 6a.
By the way, in the present invention, the top part 6a of the slab is solidified in the mold 5 from the outer side that contacts the cooled mold wall surface and the part that contacts the fixing member 13, but sufficient solidification is not completed and the mold is left with an unsolidified part. There are many situations in which it is pulled out from 5. Especially slab 6
The solidified shell 6a ₁ (see Fig. 4) formed on the sides of the mold becomes thick enough to have sufficient strength when it comes into contact with the cooled mold wall, but the solidified shell 6a ₂ formed on the top surface is filled with powder and slag. It is often extremely thin because it is covered with On the other hand, in a curved type continuous casting machine, as described above, the slab 6 that has come out of the mold 5 is gradually curved from the vertical direction and finally straightened to be horizontal, and then pulled out.

The top solidified shell _6a2 of the slab top portion 6a accelerates solidification while being pulled out from the mold 5 in a substantially vertical direction, and its thickness increases. However, when the slab top portion 6a reaches a curved portion as shown in FIG. 4, the top surface _6a3 is inclined, and static pressure from the unsolidified molten steel 2 inside the slab is applied to the solidified shell _6a2 . If there is a portion of the solidified shell _6a2 that is thin and weak in strength, it will break, causing a phenomenon in which unsolidified molten steel, that is, the molten material 100 referred to in the present invention, flows out. The present invention makes it possible to continue the continuous casting operation without reducing the drawing speed by receiving such flowed melt 100 in the aforementioned receiving fitting 11.

Next, a specific example in which a slab 6 having a thickness of 250 mm and a width of 950 mm was manufactured based on the present invention will be described.

In this embodiment, the metal holder 11 having the structure shown in FIGS. 2 and 3 was used. The fixing member 13 of this receiving bracket 11 is composed of six ordinary steel plates with a thickness of 9 mm, a width of 30 mm, and a length of 250 mm.
It was stuck almost in the center.

The connecting member 14 is made of a round bar with a diameter of 16 mm and a length of 190 mm, and the receiving member 12 is fixed to the rear end. The receiving member 12 is a 5mm thick iron plate with a flange height of h50.
It is shaped like a saucer with a length of 200 mm and a width of 950 to 1250 mm. The bottom of the receiving member 12 has a diameter of 2 to 5 mm.
An appropriate number of drain holes 15 are provided. This drain hole 15 allows the cooling water stored by water spraying to be efficiently discharged before the melt 100 flows into the receiving member 12, and also prevents the highly viscous melt 100 from flowing out. It is effective in preventing steam explosions. FIG. 5 is a diagram showing the change in drawing speed (hereinafter referred to as drawing speed pattern) at the final stage of casting in this example. The fifth
The solid line a in the figure shows the drawing speed pattern based on the present invention, and is an example in which the final stage of casting was reached while casting work was being performed at a drawing speed of 1.6 m/min. In FIG. 5, x indicates the end of casting, and in this example, the drawing speed is reduced to 0.2 m/min at the same time as the end of casting, and the above-mentioned receiving fitting 11 is attached to the slab top part 6a in this low speed state. did. The time required for the mounting was about 10 to 20 seconds, and immediately after the mounting was completed, the drawing speed was increased to 1.6 m/min, and drawing was carried out in the same manner as in normal casting work. In this example, prior to the end of the casting, the drawing speed is reduced from 45 seconds before the end of the casting, and the casting is ended with the drawing speed controlled at 1.0 m/min to ensure separation of the slag. Speed down control to the extremely low speed of 0.2 m/min was performed smoothly.

Therefore, in this embodiment, the amount of the aforementioned melted material 100 flowing out from the slab top portion 6a is at most 20 kg.
It was confirmed that the melt 100 that flowed out was efficiently received by the receiving member 12, and not only the flowed melt 100 but also the slab 6 solidified while being pulled out of the guide roll group 8, and that steel could be manufactured without any problems. On the other hand, in FIG. 5, the broken line b shows the general drawing speed pattern at the end of casting in the conventional casting method, which extends over a long period of time from about 3 to 5 minutes before the end of casting to about 5 to 8 minutes after the end of casting. It was common practice to perform extraction at low speeds. Therefore, the time required for pulling the slab top portion 6a from the mold 5 to the cutting device 9 in this embodiment was extremely short at 23 minutes, which is two-thirds of that in the conventional method. As a result, the productivity of the steel 10 has been greatly improved, and in addition, it has become possible to significantly reduce the temperature drop in the slab 6. FIG. 6 is a diagram showing the temperature drop at a portion 40 mm from the side surface of the slab 6 corresponding to the embodiment shown in FIG. 5. In FIG. 6, the solid line c corresponds to the solid line a in FIG. 5, that is, the embodiment of the present invention, and the broken line d corresponds to the broken line b in FIG. 5, that is, the conventional method.
/Kg. As can be seen from FIG. 6, it was confirmed that the casting method of this example could maintain an extremely high temperature immediately before the cutting device 9 compared to the conventional method. This is especially effective in direct rolling, which has been actively adopted in recent years, in which the slab 6 is directly fed to the rolling process without being cooled. That is, in order to carry out the above-mentioned direct rolling, it is important to prevent the temperature drop of the slab 6 as much as possible and to feed it to the rolling process at as high a temperature as possible. Therefore, the slab 6 manufactured according to the present invention at the final stage of casting is also
Alternatively, it has become possible to carry out direct rolling with only slight heating.

As described above, in the present invention, by attaching the receiving fitting 11 to the top part 6a of the slab at the end of casting and performing the drawing, the reduction in the drawing speed at the end of casting is minimized, and troubles caused by molten steel flowing out can be effectively prevented. This solution enabled safe and efficient continuous casting work.

Incidentally, the receiving fitting 11 is not limited to the above-mentioned embodiment, and may be used depending on the size of the slab 6 to be manufactured, the structure of the mold 5, other equipment, operating conditions, etc., as long as it can perform the above-mentioned functions. It may be designed and used as appropriate. FIG. 7 is a perspective view showing an embodiment of a receiving fitting that can be attached even when the injection nozzle 4 is not retracted. In the receiving fitting 110 in this embodiment, the receiving member 120 is divided approximately at the center. Even if the fixing member 130 and the connecting member 140 are configured to protrude from the receiving member 120, the receiving member 120 can be easily attached to the slab top portion 6a by taking the receiving member 120 from both sides of the injection nozzle 4 and joining them. Can be done.

As described in detail above, although the present invention has a simple configuration, its practical effects are very large.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a well-known general curved continuous casting machine, Fig. 2 is a perspective view showing an embodiment of a receiving fitting based on the present invention, Fig. 3 is a cross-sectional view of Fig. 2, and Fig. 3 is a cross-sectional view of Fig. 2; Fig. 4 is a drawing diagram of the curved part of the top of the slab according to the present invention, Fig. 5 is a diagram showing an example of the drawing speed pattern at the final stage of casting, and Fig. 6 is a diagram showing the temperature corresponding to the drawing speed pattern of Fig. 5. FIG. 7 is a diagram showing the changing situation, and is a perspective view showing another embodiment of the receiving fitting based on the present invention. 1: pot, 2: molten steel, 3: tundish, 4:
Injection nozzle, 5: Mold, 6: Slab, 7: Cooling device, 8: Guide roll group, 9: Cutting device, 10:
steel, 11,110: receiving metal fitting, 12,120: receiving member, 13,130: fixing member, 14,140: connecting member, 100: molten material.

Claims (1)

[Claims] 1. A method for continuous casting of curved steel, characterized in that at the end of casting, a fitting for receiving molten metal is attached to the top of the slab and then the slab is pulled out.