JPH06328207A - Deformation preventing belt mold for casting thin cast slab - Google Patents

Abstract

PURPOSE:To stably produce a sound cast slab by attaching linear or spotted recessed parts or projecting parts on a belt surface. CONSTITUTION:One pair of shifting belts 10 are rotated and molten metal is supplied between the belts to continuously cast the thin cast slab. Then, by attaching the linear or the spotted recessed parts or the projecting parts on the belt surface, the deformation of the belt 10 generated with heat transfer from the molten metal is prevented. For example, by changing the depth (d) and the interval (w) of grooves 14 having 100mum width as parallel in the casting direction applied on the back surface (cooling liquid side) of the belt 10, the deforming quantity L of the belt 10 is obtd. In this result, by forming the groove 14 at narrower interval (w) and deeper depth (d), the effect for reducing the deforming quantity L of the belt is made to be large. By this method, the generation of surface defect can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of belt-type continuous casting, in which a thin ingot having a thickness of 100 mm or less is obtained by continuous casting from molten metal (hereinafter referred to as "molten steel"). In particular, the present invention relates to a belt mold for casting a thin slab for producing a slab with a good surface quality without cracks when carrying out this technique.

[0002]

2. Description of the Related Art Conventionally, as one of continuous casting methods, for example, some regions of a traveling route are provided with a predetermined interval as disclosed in, for example, JP-A-58-107255 and JP-A-1-293956. A pair of endless metal belts facing each other facing each other, a metal belt sandwiched between the metal belts, and a pair of blocks that move synchronously with the thin slab form a cross-sectional shape corresponding to the desired slab, and the metal The belt and block group are guided and supported by guide rolls and guide rails so as to rotate along a predetermined movement path, and a jet nozzle and a cooling pad are arranged on the backside of the metal belt between the guide rolls. The metal belt is cooled by a fluid film formed by ejecting a cooling fluid onto the metal belt, while molten steel is injected from above the casting space through an injection nozzle. , A so-called "belt caster" configured to generate a solidified shell along the wall of the metal belt or block group and to draw out a slab generated by the growth of the solidified shell from the lower end through a guide roll from the casting space. A belt-type continuous casting machine, which is called as, has been proposed. In such a belt type continuous casting machine, it is necessary to uniformly cool the metal belt and the slab with a cooling fluid in the casting width direction and the casting direction in order to normally form a solidified shell and protect the metal belt. . To that end, in the case of supplying a constant cooling fluid, it is essential that the film thickness of the cooling fluid is constant and the flow velocity of the cooling fluid between the jet nozzle / cooling pad and the metal belt is uniform. It is a condition, and usually, the belt water cooling device is devised to realize such a state.

[0003]

DISCLOSURE OF THE INVENTION The present invention cannot be solved only by devising a uniform flow velocity of the cooling fluid of the belt cooling device which occurs when casting is performed using such a belt type continuous casting machine. The aim is to overcome such points. That is, even if the belt is cooled uniformly and is kept smooth without deformation before the start of casting, once the molten steel is injected, the belt temperature rises due to the transfer of heat from the molten steel, Thermal expansion of the belt occurs in both the width direction and the width direction. Normally, the belt is pulled with a constant tension in the casting direction via the tension control tension pulley, so that the thermal expansion (elongation) in this direction can be absorbed. However, with regard to the elongation in the width direction, the belt is strongly adhered and constrained to the short side blocks at both ends, so it cannot be fully absorbed, and as a result, a long period wavy belt deformation with some peaks and valleys is generated. Occur. When such deformation occurs, it becomes difficult to keep the film thickness of the cooling liquid, which is the above-mentioned essential condition, constant and to make the flow velocity of the cooling fluid between the jet nozzle / cooling pad and the metal belt uniform. Causes uneven cooling in the direction. As a result, there is a problem in that the slab surface defects such as vertical cracks occur due to nonuniformity of the solidified shell thickness.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by adding linear or dot-like irregularities to the belt surface to cause some peaks and valleys due to the thermal expansion of the belt. By distributing the long-cycle large waviness belt deformation into short-cycle fine deformation, cooling unevenness in the belt width direction can be greatly reduced, and a thin casting with a sound casting surface without surface defects such as vertical cracks. It is possible to stably cast the piece.

That is, according to the present invention, a pair of slabs for supporting the short side surface of the slab and a group of short side blocks that move in synchronism with each other face each other for supporting the long side surface of the slab, and The casting space is composed of a metal belt that rotates and moves in synchronization,
In a continuous casting method in which molten steel is poured into this space through a dipping nozzle and thin-walled slabs are pulled out from below, belt-type thin-walled slab casting belt molds characterized by adding linear or dot-like irregularities to the belt surface Is provided.

[0006]

The function of the present invention will be described below. The present invention provides a short undulation due to a large undulating deformation in the belt width direction due to thermal expansion, which is difficult to avoid during casting. Since it is possible to change the deformation mode for a fine cycle deformation, it is possible to obtain a thin slab with a sound casting surface free of surface defects such as vertical cracks. In other words, in a smooth belt with no surface processed, the stretch in the width direction caused by thermal expansion due to contact with molten steel is attempted to absorb the stretch because both ends of the belt are constrained. Usually, it exhibits a deformation behavior with a long period and a large amplitude as shown in FIG. However, for example, when the belt surface (in this case, the belt cooling surface side) is processed as shown in FIG. 2A, a small amplitude with an extremely short cycle as shown in FIG. 2B is obtained. It turns out that it transforms into a transformation that it has. That is, it is considered that if the unevenness which is the starting point of the deformation is provided on the belt surface, the deformed state of the belt can be controlled, and if it can be optimized, the slab surface defects such as vertical cracks can be prevented.

By the way, as a method of applying a deformation starting point to the belt, both a surface in contact with molten steel (hereinafter referred to as "front surface") and a surface in contact with cooling liquid (hereinafter referred to as "rear surface") It is conceivable to carry out at the same time or only on one of the front and back surfaces. The present inventors have already tried or studied those methods. As a result, any method is effective for controlling the deformation of the belt itself, and in particular, it is more effective to add the starting points of the deformation to both the front surface and the back surface as compared with the case where the deformation is performed on only one surface. all right. However, as another problem, a new fact is revealed that if the surface of the belt, that is, the side in contact with molten steel where the solidified shell is formed, is processed, fine cracks will occur depending on the processing method. Became.

Therefore, as means for avoiding the above-mentioned restrictions and problems when the belt surface is processed, the present inventors devised a method of controlling the belt deformation by processing only the back surface of the belt. did. According to this method, no matter what shape of processing is applied to the belt surface, there is no fear that fine cracks will start from that point, and effective processing can be arbitrarily performed by belt deformation control. Was confirmed.

[0009]

The present invention will be described in more detail based on the following examples. Normal low carbon aluminized steel composition with temperature 15
A twin-belt continuous casting machine capable of producing a slab with a width of 1200 mm and a thickness of 50 mm whose molten steel at 70 ° C. is schematically shown in FIG. 3 (only one side is shown in detail for left and right) has the shape shown in FIG. Width 1500mm with the processing on the back side (cooling liquid side),
Casting was performed at a pouring speed of 10 m / min using a steel belt having a thickness of 1.2 mm.

The results obtained in this casting test are shown in FIGS. 4 and 5. FIG. 4 shows the amount of deformation of the belt when the depth d and the interval w of the groove having a width of 100 μm and parallel to the casting direction applied to the belt shown in FIG. It is the figure which shows the actually measured distance L) between the peak and the valley shown in FIG. Further, FIG. 5 shows the relationship between the belt deformation amount and the surface defect (vertical crack) generation amount observed in the cast slab.

As is apparent from FIG. 4, by forming grooves on the back surface of the belt, the belt deformation amount L is greatly reduced, and it is more effective to narrow the groove intervals and increase the depth. I understand. Further, in the figure, the groove spacing is important for reducing the belt deformation amount, and the depth is 200 μm.
It shows that the effect is not so remarkable even if the depth is deeper than m.

The inventors of the present invention also conducted a test for changing the width t of the groove in the range of several tens μm to several hundreds μm,
Analysis was performed. As a result, it was confirmed that the influence of the groove width was extremely small, and that there was almost no difference in the range of several tens of μm to several hundreds of μm from the result shown in FIG. Therefore, in order to reduce the amount of belt deformation from the industrial viewpoint by using this method, it is important to optimize the groove spacing w, and the depth and width must be about several hundreds of μm. Can be said to be sufficient.

By the way, from the results shown in FIG. 5, in order to prevent vertical cracks caused by belt deformation, it is necessary to suppress the amount of deformation to 2 mm or less.
From this, it was found that it is important to set the interval between the grooves provided on the back surface of the belt to be at least several millimeters or less.

Although the present inventors have not described in detail as an example, the present invention also examined belts having various processes shown in FIGS. 6 to 8 and confirmed that similar results could be obtained. Was done.

[0015]

As described above, the present invention reduces the belt deformation due to thermal expansion, which is a problem in casting a belt type thin cast slab, by the method of performing a simple processing on the back surface of the belt, and causes it. Since surface defects are prevented, stable and sound production of cast pieces is possible, and the industrial effect thereof is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a belt thermal deformation having a large amplitude of a long cycle, which is observed in a smooth belt having a surface which is not processed in the present invention.

FIG. 2 is a schematic diagram (a) of a belt used to reduce the amount of thermal deformation used in the present invention and a diagram (b) showing thermal deformation of a belt having a short period and a small amplitude.

FIG. 3 is a schematic view of a continuous casting apparatus used in the present invention.

FIG. 4 is a diagram showing a relationship between belt deformation amounts when the groove interval and the depth of the belt processed into the shape shown in FIG. 2A are changed.

FIG. 5 is a diagram showing a relationship between a belt deformation amount and a cast slab vertical crack generation amount obtained by a test conducted by the present inventors.

FIG. 6 is a view showing another surface processing belt which is not shown in the examples tested by the present inventors, and is an example by a combination of straight lines.

FIG. 7 is a diagram showing another surface-treated belt not shown in the examples tested by the present inventors, which is an example by a combination of curves.

FIG. 8 is a diagram showing another surface-treated belt not shown in the examples tested by the present inventors, which is an example of a combination of dots. In (c) and (d) of the figure, dot-shaped concaves or convexes are not regularly arranged as in (a) and (b),
This is an example of randomly (that is, disorderly) arrangement, and (c) is the same diameter, while (d) is the diameter itself.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tundish 2 ... Sliding nozzle 3 ... Injection nozzle 4 ... Jet cooling nozzle 5 ... Pad cooling nozzle 6 ... Jet cooling piping 7 ... Pad cooling water piping 8 ... Cooling water piping 9 ... Cooling water 10 ... Metal belt 11 ... Top pulley 12 ... Tension pulley for tension control of metal belt 13 ... Foot roll 14 ... Groove formed on belt AA ... Belt cross section

Continuation of the front page (72) Inventor San-ichi Yoshino Ikujin Oita-shi Oita-city Oita-shi, Nishinosu 1 Nippon Steel Co., Ltd. Oita Works (72) Inventor Junkichi Yoneda 4-chome Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima No. 6-22 Mitsubishi Heavy Industries Ltd. Hiroshima Works

Claims (1)

[Claims] 1. In a method for continuously casting a thin cast piece by supplying molten metal to a pair of rotating moving belts, in order to prevent belt deformation caused by heat transfer from the molten metal, a linear or dot-shaped belt surface is formed. A belt mold for producing thin-walled slabs, characterized by adding concaves or convexes.