JPS6247619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the quality of a bottom slab by improving the sealing operation in a cutting mold in a continuous casting method.

In continuous casting, the slab at the initial stage of casting as shown in Fig. 1 is called the bottom part, and is located in the bottom crop 3.
and bottom slab 4. The bottom part is
It contains many nonmetallic inclusions, refractory fragments and fine powder in the tundish, and coolant for initial solidification in the mold, which flow into the mold together with the molten steel at the early stage of casting. Therefore, conventionally, bottom crop 3 was 500 mm.
It had been truncated as a degree of scrap. In addition, the bottom slab 4 also contains more non-metallic inclusions than a steady slab (a slab that is not affected by the dirt that flows into the mold in the early stage of casting) due to the influence of the dirt diffusion mentioned above. They were demoted to low-grade products or scrapped, leading to lower yields.

By placing a box-shaped jig on the dummy bar head during casting preparation work, the present invention can contain the non-metallic inclusions and dirt that are present in large quantities in the bottom part as a bottom crop within the necessary minimum range. The purpose is to prevent dirt from spreading to the bottom slab and improve the quality to the same level as a regular slab. In addition, by creating a non-oxidizing atmosphere in the mold at the initial stage of casting by injecting inert gas such as Ar gas, the generation of oxides in the mold is suppressed and the increase in non-metallic inclusions of Al ₂ O ₃ is prevented. At the same time, the purpose is to prevent nitrogen in the air from dissolving into molten steel. Another effect of the present invention is that mold sealing work, which conventionally required about 10 minutes, can be completed in a few seconds by using a box-shaped jig.

Next, a specific example of the mold initial sealing operation in the present invention will be described.

First, in the conventional mold initial sealing operation, as shown in FIG.
In order to prevent the bottom part from sticking, nail scrap 7 is spread several centimeters thick. Furthermore, more than ten pieces of coolant 8 (a steel material with a rectangular cross section of several centimeters) are placed to promote initial solidification. and,
After that, casting begins.

On the other hand, in the mold expiry sealing operation of the present invention, as shown in FIG. Install the tool 10.

When starting casting, from the inert gas blowing hole 15,
After blowing inert gas through the pipe 11 to create a non-oxidizing atmosphere, the immersion nozzle 9 is inserted through the jig upper hole 16 to start casting. Figure 4 shows
This figure shows one example of a box-shaped jig used in the present invention. This box-shaped jig is composed of a mesh steel plate 12 at the bottom, an upper steel plate 13 having an inert gas blowing hole 15, and an immersion nozzle insertion hole 16, and a main column steel bar 14 that supports the upper steel plate 13. The reticulated steel plate 12 at the bottom is processed to have irregularities in accordance with the shape of the dummy bar head 1. The main pillar is
The length is set so that the immersion nozzle discharge port is slightly below the upper steel plate 13 at the start of casting.
The size of the upper steel plate 13 is such that when it is placed on the dummy bar in the mold, it maintains a clearance of about 10 mm with the mold copper plate. The immersion nozzle insertion hole 16 of the upper steel plate 13 has a diameter approximately 10 mm larger than the outer diameter of the immersion nozzle. In addition, the inert gas is blown at a rate of 200 to 300/min for 2 minutes or more.

By using the box-shaped jig described above,
Dirt and inclusions that flow into the mold during the initial stage of casting are trapped between the dummy bar and the box-shaped jig, preventing them from spreading to the bottom slab, and improving the quality of the bottom slab. In addition, after the slab drawing starts, the box-shaped jig will be lowered together with the dummy bar, and the nozzle discharge port will be
The box-shaped jig comes out above the upper steel plate, so the rest is normal casting work. Also, the area between the dummy bar head and the upper steel plate of the box-shaped jig where dirt is concentrated is cut off as a bottom crop. By shortening the vertical height of the box-shaped jig to, for example, 350 mm, the rate of obtaining good continuous slabs in one continuous casting operation is improved (0.3% increase as an example), and the yield is improved. The present invention is useful for this purpose.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the bottom part of the slab, Figure 2 is a sectional view in the longitudinal direction of the mold using the conventional initial sealing method, and Figure 3 is a diagram showing the bottom part of the slab.
The figure is a sectional view in the longitudinal direction of the mold for the initial sealing method of the present invention, and FIG. 4 is a diagram showing an example of a box-shaped jig used in the present invention. 1...Dummy bar head, 2...Jig for connecting the dummy bar and slab, 3...Bottom crop, 4
...Bottom slab, 9...Immersion nozzle,
10... Box-shaped jig, 15... Inert gas blowing hole, 16... Immersion nozzle insertion hole.

Claims (1)

[Claims] 1. When starting continuous casting work, place a box-shaped jig with an immersion nozzle insertion hole and an inert gas injection hole in the upper part on the dummy bar head,
A method for cleaning a bottom slab in a continuous casting method, characterized by sequentially inserting an immersion nozzle, blowing inert gas into the box-shaped jig, and injecting molten steel from the immersion nozzle.