JPS5970442A - Mold for continuous casting - Google Patents

Abstract

PURPOSE:To decrease the change in the temp. of a billet and a casting mold and to form a strong solidified shell at a uniform thickness by making the cooling power of cooling water for the casting mold higher in the top part of the mold and lower in the bottom part. CONSTITUTION:The wall thickness of casting mold faces 2, 2' is made small in a top part and large in a bottom part in order to make the cooling power for the casting mold in the vertical direction of the mold higher in the top part and lower in the bottom part. In other words, the wall thickness is regulated to t1<t2<...t5. The resistance in extracting heat from the respective mold faces is made such that the opposed faces 2, 2' have an equal wall thickness in the corresponding same height position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting mold for preventing slab defects such as surface cracks in continuously cast slabs and for producing slabs with good surface quality.

The quality of slabs manufactured by continuous casting is influenced by the heat removal conditions of the mold, especially the uniform formation of a solidified shell at the top of the mold, and the heat removal conditions for the progress of solidification after the solidified shell is formed. It is known that

The continuous casting mold has the structure shown in Fig. 1. The surface of the rolling mold +11 that comes into contact with the molten steel and slab is supported by a back amplifier frame (4), and there is a cooling water slit (3) inside. The mold surface is made of a plate of copper or copper alloy with good thermal conductivity and is provided with +21. (2'), (2”), (
2"'). Conventional molds, especially curved molds, are formed by cross-sectional views shown in Fig. 2, Mold surfaces (2), (2') as shown in Figures 3 and 4.

(2″), '(2″'·) thickness Tl, T2.
In T:1 and T4, although they are different, the cooling water drain (3) is connected to the bank amplifier frame (4) on the back of the mold.
), so heat removal from the inner surface of the mold is uneven on all four sides. As a result, the formation of the solidified shell of the molten metal becomes uneven, creating a non-uniform stress state in the slab, which adversely affects the surface quality of the slab, and even becomes one of the factors for the occurrence of breakouts. There is.

The heat removal behavior in such a conventional mold is such that when a solidified shell is formed, the mold surface (21, (2'
), but eventually the mold surface +21. (2') away from the mold surface [21, (2'
) and the surface of the slab (6). Due to the generation of this gap (6), the solidified shell (5) is formed on the mold surface (21, (
The solidified shell (5') is lost due to the static pressure of the molten steel.
) causes a blistering phenomenon and tensile force acts on the surface of the solidified shell. This is thought to be the cause of cracks occurring near the scene, and in conventional molds, it goes to the bottom ← Therefore, although the heat transfer from the slab to the mold becomes smaller, the mold cooling conditions are the same as the upper part. , the slab is strongly cooled, gaps grow, and cracks grow. This is what I mentioned earlier
Coupled with the non-uniform cooling of the planar cross section, this promotes surface cracking of the slab.

The present invention was completed in order to prevent the drawbacks of conventional continuous casting molds in terms of heat removal. To prevent surface cracking, the mold material is cooled to a temperature below the high-temperature softening point temperature, the solidified shell near the surface is thickened while the static pressure of the molten steel is small, and the bottom is warmed and cooled to prevent the mold and slab from forming. While suppressing the generation of gaps, the amount of heat removed from the entire mold is increased, and the temperature difference between the slab and the top and bottom of the mold is reduced, thereby reducing mold stress as well as slab stress, resulting in a uniform solidification system. The purpose of the present invention is to provide a mold that forms a solidified shell, controls the growth process of the solidified shell by the cooling ability of the mold itself, and reduces surface cracks.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIGS. 6 and 7 are longitudinal sectional views of the first embodiment of the mold of the present invention. Each cross section is
Figures 3 and 4, which show cross sections of conventional molds, correspond to each other. In the same figure, the depth of the slit (3) in each horizontal section is adjusted so that the wall thickness of the mold surface (21, (2') is also almost constant), so that each mold surface is uniformly extracted in the horizontal section. In order to obtain a thermal effect, the thickness of the mold surface (21, (2') in each cross section is tl#tllk, tl2=tla HHHtn';
tnl #tn2 #tn3.

In the vertical direction of the mold, the mold surface (2
), (2') is thinner at the top and thicker at the bottom so that tl<t2<...L6+t,,3<ta3
<...153.

The flow of heat into the mold is naturally greater at the top, involving the development of the solidified shell. For this reason, this mold has a structure in which the thickness of the mold surface is adjusted so that the heat extraction resistance (1+) at the top is smaller than the heat extraction resistance (t4) at the bottom.

The heat removal resistance of each mold surface is configured such that the opposing thicknesses of the opposing mold surfaces (21, (2')) are equal at the corresponding same height position.

Adjustment of the vertical thickness of the curved mold can be easily achieved by employing the method shown in FIG.

In order to make the thickness of the mold surface in the vertical direction of the curved part thinner upward and thicker downward, the arc curvature half H ( R), the inner surface (202) of the slit (3) with respect to the center point (0) of Tr).

The radius of curvature of the arc toward (202') is the inner surface of the mold (201
), (201') Same as the arc curvature radius (R).

Tr), the respective center points (0') and (0'') are the center of the arc of the mold inner surface (201) and (201') (
0), it can be easily manufactured by moving it up and down, respectively. The thickness of the vertical mold can be adjusted by making the slits taper, as shown in FIG. Through such processing, it is possible to create a structure that increases the cooling capacity at the top, reduces the cooling capacity at the bottom, and increases the heat removal capacity as a whole. At the same time, this mold/mold is more advantageous than conventional molds in terms of modifying the copper plate. Conventional molds have a meniscus (scene) with large heat transfer from molten steel to the mold.
The slit depth is determined by taking into account the yield strength of the copper plate, and since the slit depth is constant from top to bottom, the copper plate remaining on the (reference side) is placed at the thinnest curvature (R) - of the steel plate thickness. The modification limit is determined from the thickness (steel plate thickness - slit depth). On the other hand, in the mold of the present invention, the residual thickness of the copper plate increases from the meniscus toward the lower end, so it is also advantageous for modification.

The means for changing the top and bottom of the cooling capacity by adjusting the thickness of the mold surface described above is suitable for a four-sided assembled plate mold.

Furthermore, as a means for changing the cooling capacity of the cooling water passing through the cooling water passage, it is also possible to achieve this by changing the passage speed of the cooling water within the mold. Figures 9 to 11 show, as specific implementation means, that the cooling water passage is narrowed at the top to increase the cooling water flow rate at the top, thereby increasing the cooling capacity at the top of the mold. Show the structure. Each mold surface (21), (21'
) Cooling water passage (41) passing through the inner surface of (41
), cooling channel forming plate (31), (31”)
By making the top narrower and the bottom wider, the cooling water flow rate is changed. A structure in which the cooling ability of the top and bottom of the mold is changed by changing the flow rate of cooling water is suitable for tubular molds or block molds.

Of course, the cooling capacity can be changed by changing the flow rate of the cooling water to increase the heat removal capacity at the top, by changing the thickness of the mold surface as shown in FIGS. 6 and 7, or by changing the thickness of the mold surface as shown in FIGS. This is also possible by arbitrarily combining changes in wall thickness such as surface treatment.

FIG. 12 shows aspects of heat removal in a conventional mold and the present invention, with the solid line showing the case of the conventional mold and the dotted line showing the case of the present invention.

In the present invention, the cooling capacity of each surface is made more uniform than that of conventional molds, and in the vertical direction, the cooling capacity of the cooling water of the mold in the horizontal cross section is increased at the top of the mold and softened at the bottom. The difference in the amount of heat removed between the top and the bottom is reduced (and the temperature change of the slab and mold is reduced. Moreover, the amount of heat removed from the entire mold is increased.
A strong solidified shell with uniform thickness can be formed in the mold.
This makes it possible to manufacture high-quality slabs.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the external appearance of a curved continuous casting mold, and FIGS. 2 to 4 are lines nm and m in FIG. 1, respectively.
Figure 3 shows a cross-section of a conventional mold along line -m and line IV-IV. FIG. 5 is a longitudinal cross-sectional view showing the state of formation of a solidified shell during casting. 6 and 7 are longitudinal sectional views showing one embodiment of a continuous casting mold according to the present invention. FIG. 8 shows a design procedure when the present invention is applied to a curved mold. FIG. 9 is a longitudinal sectional view showing another embodiment of the present invention. Figures 10 and 11 are ■-■ and ■-■ of Figure 9.
The cross-sectional view along the line and FIG. 12 show the difference in heat removal status between the conventional continuous casting mold and the continuous casting mold according to the present invention. +1) Mold +21. (2'), (2''), (2''')
Mold surface (3) Slit (4) Bank up frame (21) , (21”) Mold surface Patent applicant
Mishima Kosan Co., Ltd. agent Masu Tebori (and 2 others) 0 JP-A-59-70442 (4) JP-A-59-70442 (6) Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 1 Tomoheat amount, K size

Claims (1)

[Claims] 1. The cooling capacity of each mold surface in the horizontal cross section is made uniform, and in the vertical direction, the cooling capacity of the top part is increased, and the cooling capacity of the bottom part is made gentler than that of the top part. A continuous casting mold characterized by: 2. Changes in cooling capacity due to cooling slits on each surface in the horizontal section are made uniform by adjusting the thickness of each mold surface, and in the vertical direction, the thickness of the mold surface is thinner at the top.
2. The continuous casting mold according to item 1, wherein the mold has a thick bottom. 3. Changes in cooling capacity due to cooling slits on each surface in the horizontal section are made uniform by adjusting the thickness of each mold surface, and the cooling flow path at the top portion is configured to be narrower than the bottom portion in the vertical direction. 2. The continuous casting mold according to item 1, characterized in that: