JPH0470107B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a block-type moving mold for continuously casting thin slabs by moving the block mold.

[Prior art] Recently, for the purpose of high-speed continuous casting of thin-walled slabs, a so-called block casting technology has been developed in which block molds are connected in an endless track and the block molds are continuously cast while moving in the casting direction. It is attracting attention as a next-generation continuous casting technology. In conventional continuous casting, a so-called restraint breakout occurs because the solidified shell slab is forcibly pulled out from a fixed mold, but with block casting, the mold is moved according to the growth rate of the solidified shell, so the restraint breakout occurs. The occurrence of sexual breakouts can be effectively avoided. Therefore, according to block casting, the casting speed can be increased by more than 10 times compared to the conventional method.

In a conventional block type moving mold, a large number of block mold members each having an L-shaped cross section are lined up in an endless track, and similar members are placed facing each other to form a cavity (casting area) having an elongated rectangular cross section.

[Problems to be Solved by the Invention] However, in the conventional block-type moving mold, as shown in FIG. , insufficient cooling of the molten metal occurs at the mutual joint 3 of the block mold parts 2, and a solidification delay occurs along the joint 3. Therefore, shrinkage stress concentrates in this solidification-delayed region, and so-called transverse cracking occurs in which the surface of the slab breaks along the main axis of the dendrite. This transverse cracking occurs even in a normal fixed mold, and mainly occurs on the wide surface of the slab, and in severe cases, it propagates from end to end in the width direction of the slab.

Furthermore, if there are vertical flaws in the casting direction on the inner wall of the mold, there will be insufficient cooling locally at the vertical flaw, resulting in a delay in solidification, which, together with distortion in the width direction of the slab, will cause so-called vertical cracks on the surface of the slab.

These horizontal and vertical cracks can be reduced to some extent by controlling the cooling rate of the slab in the secondary cooling zone after the mold, but they cannot be completely eliminated, and The surface requires surface care by cutting, etc., which lowers yield and increases cost.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a block type movable mold that can prevent the occurrence of defects on the surface of the slab.

[Means for Solving the Problems] The block type movable mold according to the present invention includes a plurality of pairs of block-shaped mold members each having a long side mold and a short side mold in an endless track shape, with opposing surfaces facing in the same direction. In a block-type moving mold that is arranged to move, lattice-shaped grooves are formed in at least a part of the casting wall of the block-shaped mold member, and these lattice grooves are provided in a casting direction and a direction perpendicular thereto. It is characterized by a grid spacing of 5 to 10 mm. Further, in this case, the lattice grooves do not necessarily have to be formed on the entire surface of the casting wall, but may be formed only on the long side surfaces of the mold member.

[Function] In the block-type moving mold according to the present invention, when a solidified shell grows and forms along the casting wall, insufficient cooling of the molten metal occurs at the joints between the block mold members, and solidification delayed regions locally occur. The solidification shrinkage stress concentrates in this region, and transverse cracks tend to occur. Further, a similar solidification delay occurs along vertical flaws in the cast wall, and vertical cracks tend to occur. By the way, lattice-like grooves are formed in the casting wall in the casting direction and in the direction perpendicular to this, and solidification delays occur in these grooves as well, so stress is not concentrated only at the mold member joints and vertical flaws. Shrinkage stress due to delayed solidification is dispersed throughout the cast wall, reducing local stress concentration.

In particular, when casting low carbon aluminum killed steel at high speed, if the groove lattice spacing is 5 to 10 mm,
The occurrence of horizontal and vertical cracks is effectively prevented.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

As shown in FIG. 2, when the molten metal 12 in the tundish 10 is injected into the cavity (molten metal injection area) 27 of the block caster 20 through the nozzle 14, the molten metal comes into contact with the water-cooled casting wall and solidified shell 26.
is formed and a solidified shell has grown to a predetermined thickness.
1 is continuously pulled out from the caster 20.

The block caster 20 is provided to be inclined at a predetermined angle, and a vertical discharge nozzle 14 is inserted into the upper end of the cavity to inject molten metal. The caster 20 is constructed by combining a pair of mold units 22 facing each other. Each unit 22 is formed by arranging a large number of block mold members 23 of the same shape in an endless track, and each member 23 has a pair of gears 28, 29.
Accordingly, it is designed to endlessly drive from the upstream side to the downstream side or from the downstream side to the upstream side. The feeding speeds a and b of the mold members 23 of the upper and lower units 22 and the slab withdrawal speed c are controlled by a computer as appropriate in accordance with changes in the amount of molten metal injected and the level of the molten metal in the cavity.

As shown in FIG.
The cross section perpendicular to the casting direction is L-shaped, and a lattice-like groove 25 is formed in the long side surface 24 of the inner wall. That is, the groove 25 extends along the joint 3 between the mold members from one end of the long side surface 24 in the width direction to the other end, and also extends in a direction perpendicular thereto.

As shown in FIG. 3, the groove 25 has a V-shape in which the groove depth is shallow relative to the groove width. For example, the groove width is 0.5 to 1.0 mm, the groove depth is about 0.5 mm or less, The groove pitch is 5 to 10 mm.

Next, a case will be described in which a low carbon aluminum killed steel having a carbon content of about 0.05% by weight is continuously cast using a block moving mold according to an embodiment of the present invention.

A molten metal adjusted to a predetermined composition and a predetermined temperature is charged into a tundish 10 from a ladle (not shown),
The molten metal 12 in the tundish is injected through the nozzle 14 into the cavity 25 into which a dummy bar (not shown) is inserted. At this time, the casting area is previously set to an inert gas atmosphere, and the molten metal is injected while pulling out the dummy bar, and casting is performed with the tip of the nozzle 14 separated from the molten metal surface in the mold. In this way, so-called open casting may be carried out, or instead of this, so-called closed casting may be carried out in which casting is carried out with the nozzle tip immersed in the molten metal in the mold. Further, while accurately adjusting the amount of molten metal injected using a sensor and a control device (not shown) on the tundish side, the endless orbit drive and slab drawing speed of each mold unit 22 are optimally controlled. The casting speed is, for example, 20 m/min or more. When the molten metal contacts the casting wall, an initially solidified shell 26 is formed, and the slab is pulled out at high speed so as to follow the movement of the casting wall.

During the solidification process of the molten metal in the mold, insufficient cooling occurs at the joints 3 and grooves 25, which causes a delay in solidification, and tensile stress occurs in these specific areas during solidification contraction, but the overall surface of the slab Since the stress is dispersed, the degree of stress concentration is alleviated. Moreover, even if a crack should occur, the groove 25 is provided in the direction perpendicular to the crack, so the propagation of the crack is stopped and the crack does not grow into a large crack.

At the exit of the mold, the solidified shell 26 grows to a sufficient thickness and has a predetermined strength, and while it is pulled out, the slab 31 is solidified by spray cooling. In this way, thickness 50mm x
Thin slabs with a width of 1000mm are produced.

Next, with reference to FIG. 4, the quality of slabs manufactured using molds having various grooves will be described.

In Figure 4, the horizontal axis shows the mutual spacing (pitch) of the V-grooves, and the vertical axis shows the crack occurrence frequency and breakout occurrence index, and the groove pitch of the mold is variously changed.
It is a figure which shows the result of quality investigation of the slab casted under substantially the same conditions otherwise. In the figure, black circles plot horizontal cracks, white circles plot vertical cracks, and triangles plot the occurrence of breakouts. In this case, the breakout occurrence index represents an index of the breakout occurrence frequency. As is clear from this figure, the groove pitch is 10mm.
When this value is exceeded, the frequency of occurrence of horizontal and vertical cracks increases rapidly. On the other hand, if the groove pitch is less than 5 mm, the mutual contact between the molten metal and the casting wall will be insufficient, and the molten metal will be insufficiently cooled, so that the breakout occurrence index will increase. Therefore, when casting low carbon aluminum killed steel, it is preferable to set the groove pitch to a range of 5 to 10 mm. In addition, when casting medium carbon steel (carbon content: 0.1 to 0.2% by weight), which is said to be prone to surface cracking of slabs, it is desirable to make the groove pitch smaller than in the above embodiments.

In the above embodiment, the lattice grooves formed on the inner wall of the mold have a V-shaped cross section, but as shown in FIGS.
Various modifications such as the rectangular groove 36 are also possible.

Further, in the above embodiment, the lattice grooves were formed only on the long sides of the mold, but the lattice grooves are not limited to this, and the lattice grooves may also be formed on the short sides. For example, it may be formed only in the peripheral area of the joint between the members.

[Effects of the Invention] According to the present invention, it is possible to effectively prevent the occurrence of horizontal cracks and vertical cracks, and therefore it is possible to significantly reduce the maintenance rate of the slab surface in subsequent processes. Therefore, it is possible to improve the slab yield and reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a part of a block-type moving mold according to an embodiment of the present invention, FIG. 2 is a schematic diagram showing a block caster in which the block-type moving mold according to an embodiment of the present invention is used, Fig. 3 is a partially enlarged view of the cast wall, Fig. 4 is a diagram for explaining the effects of the present invention, and Figs. 5 to 7 are cross sections showing modified examples of lattice grooves formed in the cast wall. Schematic diagram, No. 8
The figure is a schematic cross-sectional view showing a part of a conventional mold during casting. 14... Tandate nozzle, 20... Block caster, 23... Block mold member, 2
4... Long side surface, 25... Groove, 26... Solidified shell, 2
7...Cavity, 28, 29...Gear, 31...
...Slabs.

Claims (1)

[Scope of Claims] 1. A block-type movable mold in which a plurality of pairs of block-shaped mold members each having molds with long side surfaces and short side surfaces are arranged in an endless track so that their opposing surfaces move in the same direction. , lattice-shaped grooves are formed in at least a part of the casting wall of the block-shaped mold member, and these lattice grooves are provided in the casting direction and in a direction perpendicular thereto, and the lattice spacing between the grooves is 5 to 10 mm. A block type moving mold characterized by: 2. The block type movable mold according to claim 1, wherein the groove is formed on a long side surface of the mold member.