JPH05123830A - Dummy bar chuck for casting hollow cast billet and method for starting hollow cast billet casting using same - Google Patents

Abstract

PURPOSE:To surely make the bottom part of a cast billet be caught to a dummy bar chuck by forming the outer diameter at the lower part of the dummy bar chuck to the specific size and the outer diameter at the upper biting part to smaller than the outer diameter of the hollow cast billet, arranging the specific condition of the biting projections and forming the whole height higher than the height of a pouring basin part at the initial stage. CONSTITUTION:The outer diameter at the lower part of the dummy bar 1 is made smaller than the inner diameter of the mold in an infected hollow cast billet casting apparatus by 5-10mm and the biting part is arranged at the upper part so as to surround the outer periphery, and the outer diameter of this biting part is made smaller than the outer diameter of the casting hollow cast billet and also the thickness from the apex of projections 2 to the inner diameter in the biting part is made to >=10mm, and the height of the projection in the biting part is made >=5mm and the number is arranged to >=4 and the whole height is higher than the height of the molten metal pouring basin part at the initial stage in the objected hollow cast billet casting apparatus. The bottom part of the cast billet can surely be caught to the dummy bar chuck and the solidified shell is not restricted by a core before casting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dummy bar chuck for hollow slab casting and a method for starting hollow slab casting using the dummy bar chuck.

[0002]

2. Description of the Related Art Heretofore, in a continuous casting method for hollow cast pieces using a water-cooled columnar core, there has been no particular mention of a casting start method and a dummy bar chuck for joining a bottom portion of the cast piece to a dummy bar. However, a representative example thereof is Japanese Patent Application No. 02-62777 proposed by the present inventors. FIG. 5 shows an overall view of the device. Reference numeral 43 is a dummy bar chuck, and 44 is a dummy bar.

This device has a pool 11 for opening upward, a cooling mold 18 arranged below the pool, and a columnar core 24 penetrating the pool and reaching the inside of the cooling mold. The cooling mold 18 is provided while supplying the molten metal M from the pool to the cooling mold by the immersion nozzle 41.
It is a continuous casting device for thin-walled hollow slab P that pulls out the slab 42 from. 27 is a water pipe, 15 is an uncooled mold, 33 is an induction heating device, and 34 is an induction heating coil.

In this method, the inner and outer surfaces of the slab are formed by a columnar core and a cooling mold, respectively. Therefore, like this method, when casting the inner surface of the slab using a columnar core that is water-cooled, a negative taper is applied to the columnar core in the casting direction in order to avoid trapping a and b of the solidified shell. ..

This causes problems. That is, in the conventional casting start method, after setting the tip of the dummy bar chuck at a position below the preset molten metal surface position during casting, the cylinder formed by the mold and the columnar core that form the outer surface of the cast slab The molten metal was poured into the hollow space, and the drawing was started after the molten metal reached the preset molten metal position during casting.

FIG. 6 shows the change over time in the load acting on the columnar core when such a casting start was carried out. The core load was measured by the load cell above the core. From FIG. 6, it can be seen that a large load is applied before the start of drawing.

In particular, when the initial pouring speed is low, or when the distance from the tip of the dummy bar chuck to the preset molten metal surface position during casting at which drawing is started is too long, and solidification like stainless steel occurs. When casting a steel type with a large shrinkage, a heavy load was applied to the core, and the casting had to be stopped.

This phenomenon is understood as follows. Since the shrinking direction of the solidified shell formed on the side of the columnar core is the direction in which it is constrained by the core, the columnar core is given a negative taper in the casting direction. On the other hand, before the start of casting, the molten metal rises without being pulled out. Therefore, the solidified shell is constrained around the columnar core, and therefore, the load increases as the weight of the solidified shell constrained by the core increases.

Moreover, in such a casting start method, since sticking to the core of the solidified shell, that is, sticking, is apt to occur, sticking bleeding and lateral cracking are observed on the inner surface of the slab and the yield is reduced. There is a problem of doing.

Conventionally, as shown in FIG. 5, the tip of the dummy bar chuck 43 is flat. However, when casting a thin hollow slab, defective welding between the slab and the tip of the dummy bar chuck is likely to occur, and if the solidified shell is constrained to the core too much, it may be impossible to pull out.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and is capable of achieving stable casting in continuous casting of hollow slabs in which the inner surface of the slab is formed by a water-cooled columnar core, and a dummy bar chuck and casting. Provide a starting method.

[0012]

The present invention has the following structures.

The first one is a dummy bar chuck for hollow cast slab casting, in which the outer diameter of the lower part is made smaller than the inner diameter of the mold of the hollow slab caster intended to be 5 to 10 mm, and the upper part is bited so as to surround the outer periphery. And the outer diameter of the biting portion is made smaller than the outer diameter of the hollow slab for casting, and the wall thickness from the top of the peak of the biting portion to the inner diameter is 10
mm or more, the height of the ridge of the biting part is 5 mm or more,
Further, the dummy bar chuck for hollow cast slab casting is characterized in that the number of the slabs is four or more, and the total height of the dummy bar chuck is set higher than the initial pool height of the hollow cast slab casting apparatus.

The second point is that the outer diameter of the lower portion is made smaller by 5 to 10 mm than the inner diameter of the mold of the hollow cast product casting apparatus, and the upper portion is provided with a biting portion so as to surround the outer circumference, and the biting portion outer diameter. Is smaller than the outer diameter of the hollow slab for casting, and the wall thickness from the apex of the bite portion to the inner diameter is 10 mm or more. The height of the bite portion is 5 mm or more, and Four or more were provided, and the total height was made higher than the initial pool height of the hollow slab casting apparatus,
The method for starting casting of hollow slab is characterized in that the top of the dummy bar chuck for hollow slab casting is set above a preset molten metal surface position, and then molten metal is injected to start casting.

[0015]

First, the first structure of the present invention will be described.

According to the present invention, the diameter of the upper portion of the dummy bar chuck is reduced and the indented portion is provided in order to facilitate the hugging of the slab. FIG. 1 shows a vertical sectional view of an example of the dummy bar chuck 1 of the present invention. 2 is the bite part, and 3
2 is a female screw into which a bolt 4 for connecting the dummy bar chuck 1 and the dummy bar 5 is fitted, as shown in FIG.

The outer diameter of the lower part of the dummy bar chuck is 5 to 10 mm smaller than the diameter of the mold in order to move up and down in the mold and at this time so as not to damage the mold, while the inner diameter is the core of the molten metal surface position during casting. It is designed to be 5 to 10 mm larger than the diameter. If the space between the dummy bar chuck and the core or the mold is too large, the sealing performance will deteriorate.
Can be said to be appropriate.

The portion where the slab holds the slab is designed to have a wall thickness of at least 10 mm or more so as to have sufficient strength. The shape of the hugging portion may be such that the diameter gradually decreases upward. Further, a structure having bolts or the like may be used in order to strengthen the bonding between the cast slab and the dummy bar chuck by the top portion.

It is desirable that the indented portion is at least 5 mm or more so that molten steel can be surely infiltrated. Further, it has been clarified from an experiment that the number of the bite portions 2 may be four or more.

Next, the second structure of the present invention will be described.

In the casting start method of the present invention, in order to prevent the molten steel initially poured into the mold from coming into contact with the core cooled by water before the start of drawing, the dummy bar chuck covers the molten metal surface position during casting. To do. By this method,
It became possible to avoid the restraint of the solidified shell to the core in the early stage of casting, which is the only one in the casting that is accompanied by a large rise in the molten metal level.

Therefore, as shown in FIG. 2, when the dummy bar chuck 1 and the dummy bar 5 of the present invention are fastened together by the female screw 3 and the bolt 4, the height of the dummy bar chuck 1 of the present invention and the bottom of the dummy bar 5 are reached. The total length L of the heights is required to be equal to or longer than the immersion length of the core in the conventional method.

As will be described in detail in the examples, a stable casting start can be achieved by the dummy bar chuck having the bite portion and the casting start method of covering the core to the molten metal surface position during casting.

[0024]

EXAMPLE A thin-walled hollow slab was cast using a mold whose upper portion shown in FIG. 5 was induction-heated by an induction heating coil 34.

In this method, when the core is covered with the dummy bar chuck from preheating to a preset molten metal surface position during casting, the dummy bar chuck is affected by the magnetic field and is induction-heated.

Therefore, the dummy bar chuck is made of non-magnetic stainless steel and cuts the induced current.
As shown in FIGS. 3A and 3B, the slit 6 is formed in the vertical direction.
I put it in. On the other hand, in order to suppress the leakage of molten steel from the slit portion, water glass was filled in the slit portion before the dummy bar chuck was set on the dummy bar. In addition,
It has been found that the length of the slit is preferably such that it includes at least the entire induction heating coil, and the number of slits is preferably 3 to 4 in order to keep the strength while cutting the induction current. ..

Thus, as shown in FIG. 3A, before casting, the dummy bar chuck 1 was placed in a region where induction heating was not performed, and immediately before casting, the dummy bar chuck 1 was raised to the molten metal surface position during casting to cover the core. .. And inject the molten metal,
The dummy bar chuck was lowered, and casting was started as shown in FIG.

FIG. 4 shows the change over time in the core load during casting using such a dummy bar chuck. From this, it can be seen that the heavy load before the start of drawing as shown in FIG. 6 disappeared and a stable casting start was performed.

Further, the bottom portion of the cast piece was securely held by the dummy bar chuck, and the molten steel that had been initially poured into the bite portion 2 was surely infiltrated into the gap. There was no evidence of molten steel infiltrating between the dummy bar chuck and the core or mold. Further, no sticking bleeding or lateral cracking was observed on the inner surface of the slab, which was good.

[0030]

The present invention configured as described above has the following effects.

By using the dummy bar chuck of the present invention and selecting the casting start method for covering the core to the molten metal surface position during casting, it is possible to securely hold the bottom portion of the slab with the dummy bar chuck. It became possible to achieve a stable casting start without the solidified shell being restricted by the core before casting.

By this method, not only the casting was stabilized, but also the inner surface of the bottom was excellent without sticking bleeding or lateral cracking, and the yield was improved.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of an example of a dummy bar chuck of the present invention.

FIG. 2 is a schematic vertical cross-sectional view of an example in which the dummy bar chuck and the dummy bar of the present invention are coupled by tightening a bolt and a female screw.

3A and 3B are schematic vertical cross-sectional views showing an example of the relationship between the position of the slit and the position of the induction heating coil of the dummy bar chuck of the present invention.

FIG. 4 is a graph showing the change over time in the core load when cast, which is an example of the present invention.

FIG. 5 is a vertical cross-sectional explanatory view of a continuous apparatus for hollow cast slabs.

FIG. 6 is a graph showing changes with time in core load when casting is performed by a conventional method.

FIG. 7 is a schematic vertical sectional explanatory view of a dummy bar chuck used in a conventional method.

DESCRIPTION OF SYMBOLS 1 Dummy bar chuck of the present invention 2 Bite part 3 Female screw 4 Bolt 5 Dummy bar 6 Slit 11 Hot water pool 15 Uncooled mold 18 Cooling mold 24 Columnar core 27 Water guide pipe 33 Induction heating device 34 Induction heating coil 41 Immersion nozzle 42 Cast slab 43 Dummy bar chuck 44 Dummy bar M Molten metal P Hollow cast slab a, b Solidified shell L Total height

Claims (2)

[Claims] 1. A hollow bar slab casting dummy bar chuck, the outer diameter of the lower part of which is made smaller than the inner diameter of the mold of a hollow slab casting apparatus by 5 to 10 mm, and the upper part has a biting part so as to surround the outer periphery. And the outer diameter of the biting part is smaller than the outer diameter of the hollow slab to be cast, and the wall thickness from the apex of the bite of the biting part to the inner diameter is 10 mm or more. A dummy bar chuck for hollow cast slab casting, wherein the dummy bar chuck for hollow cast slab casting has a size of 5 mm or more and four or more thereof, and the total height of the dummy bar chuck is set higher than the initial pool height of the hollow slab casting apparatus. 2. The hollow outer diameter of the lower part is made smaller than the inner diameter of the mold by 5 to 10 mm, and the upper part is provided with a biting part so as to surround the outer periphery, and the biting part outer diameter is cast. It is smaller than the outer diameter of the hollow slab, and the wall thickness from the top of the crest of the biting part to the inner diameter is 10 m.
m or more, the height of the ridges of the biting part is 5 mm or more, and the number of ridges is 4 or more, and the total height is higher than the initial pool height of the hollow slab casting apparatus A method for starting the casting of a hollow slab, which comprises setting the top of a dummy bar chuck for casting above a preset molten metal surface position, injecting molten metal, and then starting casting.