JPH02108442A - Block type moving mold - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a block-type moving mold that continuously casts 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 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 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 a rectangular cross-section are arranged in an endless track, and similar members are faced 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. 8, the molten metal 4 comes into contact with the mold, and the solidified shell 5
When the molten metal grows at a substantially constant rate, insufficient cooling of the molten metal occurs at the mutual seam 3 of the block mold member 2, and a delay in solidification occurs along the seam 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.

In addition, 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, causing a delay in solidification, which, combined 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 must be cleaned with a solvent or the like, which lowers the yield and increases costs.

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 surface flaws in the slab.

[Means for Solving the Problems] A block-type movable mold according to the present invention includes a plurality of pairs of block-shaped mold members each having a mold having a long side surface and a short side surface in an endless track shape, with opposing surfaces facing in the same direction. In a block-type mobile mold provided to be movable, at least a portion of the mold of the block-shaped mold member is formed with a lattice-like groove, and these lattice grooves are provided in a casting direction and a direction perpendicular thereto. It is characterized by In this case,
Preferably, the lattice spacing of the grooves is 5 to 10IIIll. Furthermore, in this case, the lattice grooves do not necessarily need to be formed on the entire surface of the mold, but may be formed only on the long side surfaces of the mold member.

[Operation] In the block-type moving mold according to the present invention, when a solidified shell grows and forms along the mold, insufficient cooling of the molten metal occurs at the joints between the block mold members, and solidification delayed regions are locally formed. The solidification shrinkage stress concentrates in this area, and transverse cracking tends to occur.

Further, a similar solidification delay occurs along the vertical flaws of the mold, and vertical cracks tend to occur. By the way, the mold has lattice-like grooves formed in the casting direction and in the direction perpendicular to this, and solidification delays also occur in these grooves, so solidification can be achieved without stress concentration only at the mold member joints and vertical flaws. Shrinkage stress due to the delay is dispersed throughout the mold, reducing local stress concentration.

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

As shown in FIG.
When the molten metal is injected into the cavity (molten metal injection region) 27 of the block caster 20 through the nozzle 14, the molten metal contacts the water-cooled mold to form a solidified shell 26, and a slab 31 with the solidified shell grown to a predetermined thickness. is adapted to be continuously pulled out from the caster 20.

The block caster 20 is provided to be inclined at a predetermined angle, and the tandate nozzle 1 is installed on the upper end side of the cavity.
4 is inserted, and molten metal is injected. 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 is moved from the upstream side to the downstream side or from the downstream side to the upstream side by a pair of gears 28 and 29. It is designed to run infinitely. In addition, the upper and lower units 2
The feeding speeds a and b of the second mold member 23 and the slab withdrawal speed C are controlled by a computer as appropriate in accordance with the amount of molten metal injected and the fluctuation of the molten metal level in the cavity.

As shown in FIG. 1, the block mold member 23 has an L-shaped cross section perpendicular to the casting direction, and has a long side surface 2 of its inner wall.
A lattice-shaped groove 25 is formed in 4. That is, full 2
5 extends along the joint 3 between the mold members from one end to the other in the width direction of the long side surface 24, 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, the groove depth is approximately 0.5 mm or less, and the groove pitch is 5 to 10IIIll.

Next, a case will be described in which a low carbon aluminum guild 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.

The molten metal adjusted to a predetermined composition and temperature is charged from a ladle (not shown) into the tundish canister 10, and the molten metal 12 inside the tundish canister is injected through the nozzle 14 into the cavity 25 into which a dummy bar (not shown) is inserted. do. At this time,
The casting area is previously set to an inert gas atmosphere, the molten metal is injected while the dummy bar is pulled out, and casting is performed with the tip of the nozzle 14 separated from the molten metal surface in the mold. So-called oven casting may be carried out in this manner, or alternatively, so-called closed casting may be carried out in which casting is performed 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 track 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 mold, an initially solidified shell 26 is formed, and the slab is pulled out at high speed so as to follow the movement of the mold.

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, since the groove 25 is provided in the direction perpendicular to the crack, the crack will stop propagating and will 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, a thin slab having a thickness of 50a+m and a width of 1000a+rA is manufactured.

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

Figure 4 shows the mutual spacing (pitch) of V-grooves on the horizontal axis, and the crack occurrence frequency and breakout occurrence index on the vertical axis, with the groove pitch of the mold being variously changed, and other conditions being substantially the same. FIG. In the figure, black circles plot horizontal cracks, white circles plot vertical cracks, and triangles plot the occurrence of breakouts. Note that 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 1011II11
When this value is exceeded, the frequency of occurrence of horizontal and vertical cracks increases rapidly. On the other hand, when the groove pitch is less than 5 squares, the mutual contact between the molten metal and the mold becomes insufficient, resulting in insufficient cooling of the molten metal, resulting in an increase in the breakout occurrence index. Therefore, when casting low carbon aluminum killed steel, the groove pitch should be 5 to 1.
It is preferable to set it in the range of 0IIIIIIl. 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 example. .

In the above embodiment, the lattice grooves formed on the inner wall of the mold had a V-shaped cross section, but as shown in FIGS. Various modifications such as a U-shaped groove 35 and a 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, the generation of horizontal cracks and vertical cracks can be effectively prevented, so that the maintenance rate of the slab surface in subsequent steps can be significantly reduced. Therefore, it is possible to improve the slab yield and reduce manufacturing costs.

[Brief explanation of drawings]

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, and FIG. 3 is a partially enlarged view of the mold, FIG. 4 is a diagram for explaining the invention in detail, and FIGS. 5 to 7 are schematic cross-sectional views showing modifications of the lattice grooves formed in the mold, respectively. FIG. 8 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, 24; Long side surface, 25; Groove, 26; Solidified shell, 27: Cavity, 28.29. Gear, 31; Patent attorney and agent for slab applicant Takehiko Suzue u-4P-◇Goma H! ! Cape leprosy (9 months, ε)

Claims (3)

[Claims] (1) In a block-type movable mold in which a plurality of pairs of block-shaped mold members each having a long-side surface and a short-side mold are arranged in an endless track shape so that their opposing surfaces move in the same direction, the block-shaped A block-type movable mold characterized in that lattice-shaped grooves are formed in at least a portion of the mold of the mold member, and these lattice grooves are provided in the casting direction and in a direction orthogonal thereto. (2) The block-type movable mold according to claim 1, characterized in that the lattice spacing of the grooves is 5 to 10 mm. (3) The block-type movable mold according to claim 1, wherein the groove is formed on the long side surface of the mold member.