JP3408127B2 - Tundish for continuous casting and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tundish for continuous casting having an injection nozzle for performing open injection in which a molten metal stream is exposed to a surrounding atmosphere when the molten metal is injected into a mold for continuously casting molten metal. is there.

[0002]

2. Description of the Related Art Molten metal typified by molten steel is cast by a continuous casting method after completion of refining in a converter, an electric furnace or the like to obtain a slab. The molten metal that has undergone refining is stored in a ladle, then poured into a continuous casting mold through an intermediate container called a tundish, and solidification proceeds from four rounds in the process of being drawn below the mold, and finally solidification occurs. It becomes a completed slab. The reason for using tundish is
In order to distribute the molten metal to a plurality of strands at the same time, and in continuous casting, the casting is not interrupted even when the casting for one heat of the ladle is completed, and the casting is continued over a plurality of heats of the ladle. This is because it functions as an intermediate container for preventing the supply of the molten metal to the mold from being interrupted when the ladle is replaced.

A tundish is a container for intermediately containing molten metal, the inner surface of which is covered with a refractory material, and a refractory injection nozzle for pouring the molten metal into a continuous casting mold is provided at the bottom. . In a multi-strand mill in which casting is performed by a large number of molds at the same time, there are as many tundish injection nozzles as there are molds. In each injection nozzle, a refractory stopper or sliding nozzle corresponding to a valve for opening / closing the injection flow path and controlling the flow rate of the injection flow is usually installed.

In a slab continuous casting apparatus or a bloom continuous casting apparatus having a large slab cross-section size, an injection nozzle extends into the continuous casting mold and uses a dipping nozzle for immersing in a molten metal bath in the mold. It prevents the molten metal from coming into contact with the surrounding atmosphere and proceeding with the oxidation.
However, in a billet continuous casting device with a small cross section, it is difficult to load the immersion nozzle into the mold because the mold has a small cross-sectional size, and the injection flow from the injection nozzle at the bottom of the tundish into the mold below. Open implants are commonly used where the is exposed to the surrounding atmosphere.

When performing open injection, it is essential that the injection flow be stable and rectified. The injection flow is not rectified,
In the case of splashing, the surface quality defect of the produced slab increases due to the progress of oxidation from the surface of the droplet and the destabilization of the surface of the molten metal in the mold. Further, when the droplets adhere to and grow on the wall surface of the mold, the solidified shell is broken immediately below the mold, causing a breakout in which the molten metal inside leaks to the outside. Also, due to the adherence of droplets to the wall surface of the mold, the melt surface level fluctuation due to the malfunction of the melt surface level detector in the mold increases, and the liquid level at the upper end of the slab falls out of the lower end of the mold. Becomes

When performing open injection, it is generally difficult to use a stopper or a sliding nozzle for controlling the injection flow rate. This is because if the injection flow rate is controlled by narrowing the injection flow path using a stopper or a sliding nozzle, the injection flow is not rectified and scattering occurs. Therefore, when performing open injection, the stopper is used only for opening and closing the injection nozzle, and during injection, the stopper is fully opened and the injection flow rate is not controlled by the stopper. Therefore, the injection flow rate into the mold is determined only by the static pressure of the molten metal in the tundish and the cross-sectional area of the injection nozzle. In a multi-strand continuous casting machine, the static pressure of the molten metal in the tundish affects the injection flow rate of all strands and is therefore usually kept constant. Therefore, the cross-sectional area of the through hole of the injection nozzle needs to be kept constant, and the melt loss of the inner wall of the through hole of the injection nozzle during injection must be minimized.

Alumina graphite is usually used as the refractory material for the injection nozzle. However, since alumina graphite cannot sufficiently prevent the progress of melting loss due to molten metal, it is essential to use a zirconia (ZrO ₂ ) refractory material that has minimal melting loss due to molten metal when performing open injection. . The injection nozzle made of zirconia refractory has a length of 22 mm due to the limitation of the manufacturing method of the zirconia refractory.
It is difficult to manufacture a refractory having a thickness of more than 0 mm, and if it is forcibly manufactured, it causes an increase in casting cost due to an increase in cost. On the other hand, the thickness of the refractory at the bottom of the tundish is
In order to prevent deformation of the tundish iron skin due to thermal strain, 300 mm is usually required. Therefore, conventionally, as shown in FIG. 5A, the upper end of the injection nozzle 2 is located at a position lower than the surface of the tundish bottom refractory 6 and the molten metal pool 18 is present above the injection nozzle. It was supposed to be done.

[0008]

When continuous casting of molten metal is performed by open pouring using the tundish having the pouring nozzle corresponding to the above open pouring, the pouring flow is not rectified and scattering occurs. Could not be completely prevented. The problem caused by the scattering is as described above. An object of the present invention is to provide a tundish that prevents the occurrence of such scattering and rectifies the injection flow of open injection, and a method for manufacturing the tundish.

[0009]

As a result of the inventors' research on the relationship between the flow of molten metal in the tundish and the turbulence of the injection flow, the results in FIG.
There is a flow of molten metal as shown in (b), and the molten metal flow 19 from the ladle through the long nozzle 10 collides with the tundish wall and becomes a molten metal flow 20 along the bottom of the tundish. As the flow 20 hits the pool 18 at the top of the injection nozzle, the vortex 21 inside the pool 21
It was found that the vortex 21 caused the turbulence of the injection flow.

The present invention has been made on the basis of the above research results, and its gist is to perform open pouring in which a molten metal flow is exposed to a surrounding atmosphere when pouring the molten metal into a mold for continuously casting molten metal. A continuous casting tundish having an injection nozzle for performing, characterized in that a refractory rectifying tube having a length of 50 mm or more and having a through hole is provided on an upper portion of the injection nozzle. is there.

In the tundish for continuous casting,
The inner diameter of the through hole of the flow straightening cylinder is preferably 15 mm or more and 50 mm or less. Further, the upper end of the flow straightening cylinder may be above the bottom refractory surface near the injection nozzle of the tundish by 5 mm or more. A straightening cylinder has an alumina content of 6
It is preferably made of a cast refractory material of 0% by weight or more. The difference between the inner diameter of the through hole at the lower end of the flow straightening cylinder and the inner diameter of the through hole at the upper end of the injection nozzle is preferably 10 mm or less.

The tundish for continuous casting described above is characterized in that a preformed straightening cylinder is installed above the injection nozzle before the refractory constituting the refractory constituting the bottom of the tundish is constructed. The manufacturing method, and the method for manufacturing the tundish for continuous casting described above, characterized in that the straightening cylinder and the injection nozzle are joined to form an integrated nozzle, and the integrated nozzle is incorporated into the tundish.

As a result of arranging the flow straightening cylinder 1 above the injection nozzle 2, the flow of injection into the continuous casting mold was very good. It is considered that as a result of arranging the flow straightening cylinder, the molten metal pool portion 18 at the upper part of the injection nozzle disappears and the generation of the vortex 21 which causes the turbulence of the injection flow disappears.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of the tundish bottom has an outer skin, which is an outer skin, on which a heat insulating board intended for heat insulation is arranged, and on which a perma brick is arranged. Wear bricks are placed on top and coated refractories are placed on top. The thickness of the refractory at the bottom of the tundish excluding the iron skin is about 300 mm. An injection nozzle 2 made of zirconia refractory for open injection is arranged at the bottom of the tundish as shown in FIG. In the case of open pouring, since the slab cross-sectional area is small, the pouring amount per unit time is small, and the inner diameter of the through hole 5 of the pouring nozzle is 14 to 19 mm.
It will be around φ. Further, the height of the injection nozzle 2 is around 100 to 150 mm based on the manufacturing restrictions of the zirconia refractory.

A refractory rectifying cylinder 1 having a through hole 4 is arranged above the injection nozzle 2 as shown in FIG. The height of the rectifying cylinder is 5 in order to fully exert the rectifying effect.
It must be 0 mm or more. If the upper end of the flow straightening cylinder is lower than the surface of the refractory at the bottom of the tundish and a large step is created, a hot water pool is formed on the upper part of the straightening steam, and harmful vortices are generated there, causing the injection flow to scatter. It is necessary to arrange the flow straightening cylinder so that a large step is not formed between the upper end of the flow straightening cylinder and the refractory surface of the tundish bottom portion.

The inner diameter of the through hole 4 of the straightening cylinder is preferably 1
It is set to 5 mm or more and 50 mm or less. If the inner diameter of the through hole is less than 15 mm, the injection flow rate into the mold cannot be substantially secured, and if the inner diameter of the through hole exceeds 50 mm, the through hole becomes a basin and harmful vortices are generated therein. Because. When a stopper 8 made of a refractory material is arranged above the flow straightening cylinder and the on / off control of the injection flow is performed by opening / closing between the stopper 8 and the flow straightening cylinder 1, the through hole of the flow straightening cylinder is the through hole of the injection nozzle. One that is slightly thicker than the inner diameter of
It has the advantage that the injection can be stably resumed when the stopper is opened again.

Since the inner diameter of the through hole of the injection nozzle used for open injection is small, if foreign matter falls into the injection nozzle before the molten metal is injected into the tundish, the injection from the injection nozzle may not be possible. is there. As shown in FIG. 3, by disposing the upper end of the flow straightening cylinder 1 at least 5 mm above the surface of the bottom refractory 6 near the injection nozzle of the tundish, foreign matter is present near the injection nozzle at the bottom of the tundish. Even in this case, it is possible to prevent the foreign matter from falling into the injection nozzle, and it is possible to prevent an abnormal injection accident due to clogging of the injection nozzle.

The refractory forming the straightening cylinder does not need to be a fired brick or a costly manufacturing method such as mechanical tamping, and it is made of cast refractory, and the refractory is used as a mold. It is manufactured by pouring and has sufficient performance. The material preferably has an alumina content of 60% by weight or more. As a result, it is possible to secure sufficient durability as the rectifying cylinder. By selecting such a refractory material, it is possible to obtain the effect of reducing the manufacturing cost while maintaining the sufficient function and durability of the flow straightening cylinder.

The inner diameter of the through hole 5 of the injection nozzle and the inner diameter of the through hole 4 of the rectifying cylinder above it need not necessarily match. However, it is preferable that the inner diameters of the two through holes are close to each other in the contact portion between the two in order to alleviate the step difference in the molten metal inflow passage and to straighten the injection flow. Specifically, the difference between the inner diameter of the through hole at the lower end of the flow straightening cylinder and the inner diameter of the through hole at the upper end of the injection nozzle is preferably 10 mm or less. The inner diameter difference is 10
If it exceeds mm, the flow is turbulent at the level difference between the flow straightening cylinder and the injection nozzle, which causes the instability of the injection flow.

The rectifying cylinder and the injection nozzle are separately manufactured, and each is incorporated into the tundish when the tundish refractory is constructed. In the type in which the straightening cylinder and the injection nozzle as shown in FIG. 1 are inserted from above the tundish, first, the injection nozzle is inserted, then the straightening cylinder is inserted in the upper part thereof, and then the fire resistant material constituting the tundish bottom part and the wall surface. Fill the material including the circumference of the straightening cylinder.

The flow straightening cylinder and the injection nozzle can be bonded and integrated before being assembled in the tundish. As a result, the rectifying cylinder and the injection nozzle can be attached to the tundish after being accurately aligned and bonded to each other, so that the misalignment between the two can be prevented. In addition, it is possible to simplify the process for hot maintenance of the tundish nozzle.

The surface where the flow straightening cylinder and the injection nozzle are in contact with each other may not be a flat surface, but a step may be provided as shown in FIG. As a result, it becomes easy to mount the two so that their centers are accurately aligned.

A stopper for on / off control of the injection flow may be arranged above the injection nozzle. When the straightening cylinder of the present invention is arranged, the other side which comes into contact with the tip of the stopper and blocks the injection flow is the straightening cylinder. Therefore, it is necessary that the upper end of the through hole of the flow straightening cylinder has a curved surface with a curvature to ensure smooth contact with the tip of the stopper and prevention of damage to the contact surface. Even if the flow straightening cylinder is provided with such a contact function with the stopper, the flow straightening cylinder must have sufficient durability as a refractory material in a cast refractory having an alumina content of 60% by weight or more. Has been confirmed.

[0024]

EXAMPLES The present invention was applied to a steel billet continuous casting apparatus. The continuous casting apparatus is an 8-strand mill, the slab size is 130 mm x 130 mm, and the casting speed is 2.6.
Casting was performed under the condition of -3.2 m / min. The tundish 3 is as shown in FIG. 2, the tundish capacity is 33 tons, the molten steel refined by the converter refining method is received in a ladle with a capacity of 240 tons, and the tundish 3 is fed from the ladle 9. Molten steel is injected into the via a long nozzle 10. A refractory stopper 8 is disposed above a part of the injection hole that serves as a discharge hole for the injection flow 12 into the mold 13, and ON / OFF control of the injection flow is performed.

As the injection nozzle 2 and the flow straightening cylinder 1 of the present invention, three types (invention examples No. 1, No. 2 and No. 3) shown in FIGS. Moreover, what was shown in FIG.5 (a) was used as a comparative example. Each of the injection nozzles of the examples of the present invention has a height of 135 mm, an inner diameter of the through hole through which the injection flow passes, and is made of zirconia refractory. The straightening cylinder has a height of 150 mm, and the inner diameter of the through hole is No. 1 and No. 3 is 25 mmφ, No. 3 2 is 50m
mφ, and the through hole of the injection nozzle is tapered so that no step is formed at the joint between the rectifying cylinder and the through hole of the injection nozzle. The shape of the through hole at the upper end of the flow straightening cylinder is rounded to 30 mmR in order to make good contact with the stopper. As the flow straightening cylinder, a cast refractory having an alumina content of 75% by weight was used. The injection nozzle of the comparative example has a height of 135 mm and an inner diameter of the through hole of 17.
The diameter of the through hole is 5 mm, and the shape of the through hole at the upper end of the injection nozzle has a roundness of 30 mmR like the straightening cylinder.

Both the injection nozzle 2 and the flow straightening cylinder 1 were inserted into the installation site from above the tundish 3. In the example of the present invention, the refractory on the outermost surface of the bottom of the tundish is constructed by a spraying method, and is sprayed after the straightening cylinder 1 is installed. Inventive Example No. 1, No. In No. 2, the upper end of the rectifying cylinder 1 and the surface of the tundish bottom refractory were made to have the same height. Inventive Example No. In No. 3, the upper end of the flow straightening cylinder 1 was set at a position 5 mm higher than the surface of the tundish bottom refractory as shown in FIG. In the comparative example, since the upper end of the injection nozzle 2 is located 150 mm lower than the surface of the tundish bottom refractory, a casting refractory is used near the injection nozzle as the tundish bottom refractory, as shown in FIG. A tapered pool of water having the shape shown was formed.

In continuous casting, one ladle 4 heats is 1 on average.
Each cast was made into a tundish refractory, and at the timing of refractory maintenance, the injection nozzle and rectifying cylinder were replaced.

The results of continuous casting are shown in Table 1. The present invention No. 1-No. In No. 3, all the injection flows achieved rectification, and the injection flows were not scattered into the mold. On the other hand, in the comparative example, the injection flow into the mold is disturbed and scattering occurs, and as a result, the occurrence rate of surface defects of the slab is higher than that of the present invention, and the occurrence rate of breakout is also high. It became a result. The frequency of occurrence of casting failure accidents caused by falling foreign matter into the injection nozzle is determined by the invention example N.
o. 3 was the lowest, and the comparative example was the highest.

[0029]

[Table 1]

Next, the invention sample No. 4, an integrated nozzle 1 in which an injection nozzle and a rectifying cylinder are bonded as shown in FIG.
5 was manufactured, and this was incorporated into a tundish to perform continuous casting. The total length of the integrated nozzle 15 was 300 mm. The length of the injection nozzle part 17 made of zirconia refractory was 150 mm and the inner diameter of the through hole was 17.5 mmφ. The straightening tube portion 16 was made of a cast refractory material having an alumina content of 75% by weight, and the through hole inner diameter was 40 mmφ. The integral nozzle was manufactured by separately molding the injection nozzle and the flow straightening cylinder and joining them with an adhesive.

Since the injection nozzle and the flow straightening cylinder are joined in advance separately from the tundish maintenance, the centers of the through holes of both can be easily aligned. Since this integrated nozzle is incorporated in the tundish, the tundish can be easily maintained as compared with the method of separately incorporating the injection nozzle and the flow straightening cylinder in the tundish. Regarding the casting results such as product surface quality or breakout occurrence rate, the invention example No. 1-No. The result equivalent to 2 was able to be obtained.

[0032]

EFFECTS OF THE INVENTION By realizing a tundish in which a rectifying cylinder is arranged above the injection nozzle of continuous casting that performs open injection, rectification of the injection flow is realized, the surface quality of the slab is improved, and the breakout frequency And the fluctuation of the molten metal surface level in the mold has been reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a tundish rectifying cylinder and an injection nozzle of the present invention. FIG. 1A is an example in which the inner diameter of the through hole of the rectifying cylinder is thin, and FIG. 1B is an example in which the inner diameter of the through hole of the rectifying cylinder is large. is there.

FIG. 2 is a sectional view showing the overall arrangement of a tundish, a ladle, and a mold of the present invention.

FIG. 3 is a sectional view showing a rectifying cylinder and an injection nozzle of the tundish of the present invention.

FIG. 4 is a sectional view showing an integrated nozzle of a tundish of the present invention.

5A and 5B are cross-sectional views showing an injection nozzle of a conventional tundish, FIG. 5A is a cross-sectional view showing a state of an injection nozzle incorporated in a tundish, and FIG. 5B is a vortex of molten metal in a conventional example. It is sectional drawing which shows an occurrence condition.

[Explanation of symbols]

1 straightening cylinder 2 injection nozzle 3 tundish 4 Through hole of straightening cylinder 5 Through hole of injection nozzle 6 refractories 7 iron skin 8 stopper 9 ladle 10 long nozzle 11 Molten metal 12 injection flow 13 Mold 14 Slab 15 integrated nozzle 16 Rectifying cylinder 17 Injection nozzle 18 Hot water pool 19 Molten metal flow 20 Molten metal flow 21 Vortex

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-39064 (JP, A) JP-A-7-63484 (JP, A) JP-A-6-328208 (JP, A) JP-A-2- 63677 (JP, A) JP-A-2-46958 (JP, A) JP-A-51-116119 (JP, A) Actually open 49-117316 (JP, U) Actually open 4-70251 (JP, U) Actually open 1-84858 (JP, U) Actually open 1-17-1868 (JP, U) Actually open 63-41354 (JP, U) Actually open 57-32749 (JP, U) Special table 2000-505727 ( (58) Fields surveyed (Int.Cl. ⁷ , DB name) B22D 11/10 330 B22D 11/10 310 B22D 41/50 520

Claims (5)

(57) [Claims] 1. A continuous casting tundish having an injection nozzle for performing open injection in which a molten metal stream is exposed to a surrounding atmosphere when the molten metal is injected into a mold for continuously casting molten metal . It is made of a refractory having an inner diameter of 14 mm or more and a length of 50 mm or more and a through hole in the upper portion of the injection nozzle, and the inner diameter of the through hole is 15 mm or more and 50 mm or less and the inner diameter of the through hole at the lower end. Through hole at the upper end of the injection nozzle
A tundish for continuous casting, which has a rectifying cylinder having a difference from the inner diameter of 10 mm or less . 2. The tundish for continuous casting according to claim 1 , wherein the upper end of the flow straightening cylinder is located 5 mm or more above the surface of the bottom refractory near the injection nozzle of the tundish. 3. A continuous casting tundish of claim 1乃<br/> optimum 2, wherein the gas flow-guide cylinder is made of refractory cast over 60 wt% alumina content. 4. A claim, characterized in placing the preformed flow-guide cylinder before construction of the refractory constituting the surface of the tundish bottom refractory at the top of the injection nozzle 1 to 3
The method for producing a tundish for continuous casting according to item 1. 5. an integral nozzle by joining flow-guide cylinder and the injection nozzle, the manufacturing method of the continuous casting tundish according to claim 1, wherein the incorporation of the integral nozzle to the tundish.