JPS582735B2 - Renzokuchiyuuzou souchiniokaru Chuyuyuhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for pouring molten metal in a continuous casting apparatus, and more specifically, it eliminates turbulence of the metal, entrainment of air and oxides, etc. caused by pouring, and eliminates centerline shrinkage cavities caused by these. The present invention relates to a pouring method for removing ingot defects such as cracks, voids, and inclusions.

The continuous casting equipment to which the method of the present invention is applied is formed by a rotating casting wheel (hereinafter referred to as wheel) having grooves on its circumferential surface and a metal band (hereinafter referred to as belt) that is in contact with the circumferential surface of this wheel. Molten metal is continuously poured into a mold and cast into an ingot (infinite metal rod or ingot), and the method shown in FIG. 1 has conventionally been used as the pouring method.

That is, the molten metal discharged from the holding furnace flows in the groove of the transfer path 1 (hereinafter referred to as gutter), but the molten metal level in the sump 2 is kept constant by a float type flow rate control valve (not shown). automatically controlled.

Next, the molten metal is injected into the mold that is continuously formed by the belt and the groove around the wheel. At this time, the operator constantly monitors the vertical fluctuations of the molten metal level in the mold to keep it constant, and adjusts the handle 9 as appropriate. When activated, the molten metal is discharged from the pouring nozzle 3 into the mold while the flow rate is manually adjusted by the control valve 10.

The molten metal injected into the mold is cooled and solidified through the mold by the cooling water jetted from the cooling water injection nozzle groups 6 and 7 disposed around the outer periphery of the mold, and the mold is released from the vicinity of the mold release point 8. and then guided to the rolling process.

Therefore, the relationship between the pouring nozzle and the mold surface is the second
As shown in FIGS.

In Fig. 2, a cylindrical nozzle 3 is used, and the tip is immersed in melt b that has already been poured and has not yet solidified. is adjusted to the appropriate amount.

In addition, in FIG. 3, molten metal is poured by dropping from above the molten metal b that has already been poured into the same mold as in FIG. 2, using a nozzle 3 or other means.

In these conventional pouring methods, when molten metal is poured, the cross-sectional area a of the pouring nozzle 3 is larger than the mold formed by the circumferential groove d of the casting wheel and the belt f, as shown in FIG. It is considerably smaller than the cross-sectional area A, and the flow velocity V1 of the molten metal discharged from the nozzle 3 is always higher than the descending velocity V2 of the molten metal poured into the mold.

For this reason, the injected hot water creates a vortex as shown in Figure 4A, and the thickness of the crystallized solid phase does not increase uniformly in the longitudinal direction, which causes centerline shrinkage holes as shown in Figure 4A. This phenomenon also has a large effect on the occurrence of cracks.

In the above, the molten metal being injected is adjusted so that the level of the molten metal remains constant within the mold, but this process is extremely difficult and is not necessarily constant, but fluctuates, so fluctuations in the amount of molten metal supplied are the cause of heat inflow and outflow. This disturbs the balance and promotes the occurrence of centerline shrinkage cavities and cracks.Also, the amount of poured molten metal is usually adjusted above the pouring nozzle, and below the adjustment part the molten metal falls freely, so air is removed. If this gets into the ingot, it will become a void.

In the same way, oxides may be entrained, and oxides may also be generated on the surface of the molten metal in the mold, which may also become entrained in the ingot and become inclusions.This tendency is seen in the case of Figure 3. Particularly remarkable.

The present invention was made for the purpose of eliminating defects in the ingot such as centerline shrinkage cavities, cracks, voids, and inclusions in the conventional pouring method. In a continuous casting device that casts an ingot by continuously injecting molten metal into a mold formed by a casting rotating ring with grooves and a metal band in contact with the circumferential surface of the rotating ring, The lower tip of a pouring nozzle for injecting molten metal into the mold is inscribed in the inner surface of the mold, the upper part of the nozzle is connected to a sump, and at least the part of the pouring nozzle that is inscribed in the mold is The pouring nozzle is made of a heat-insulating refractory, and its internal area is approximated to the cross-sectional area of the inner surface of the mold, and the molten metal is sealed from the sump to the inside of the mold. The present invention relates to a pouring method in a continuous casting apparatus, which is characterized by pouring metal into a mold from a pouring nozzle in a laminar flow or in a laminar flow state under static pressure in a reservoir and without exposure to the atmosphere.

A major feature of the present invention is the pouring nozzle, whose cross-sectional shape is inscribed in the mold formed by the belt and the wheel peripheral groove.

Further, the exterior of the nozzle, that is, the part that is inscribed in the mold, is desirably made of a shrinkable and thin heat-insulating refractory.

According to the method of the present invention, the cross-sectional area of the inner surface of the pouring nozzle is approximated to the cross-sectional area of the inner surface of the mold over the entire length of the pouring nozzle, so that the flow of the molten metal poured from the nozzle into the mold is undisturbed. Guided in laminar flow or a state close to this,
In addition, the nozzle always slides at a constant position relative to the rotating wheel, and the part corresponding to the molten metal level in the mold in the conventional method is always at a constant position.Therefore, fluctuations in the molten metal level in the mold cannot occur. It is possible to maintain the balance of heat in and out of the molten metal in the mold without requiring any means for adjusting the level of the molten metal in the mold.

As a result, the method of the present invention can prevent the occurrence of centerline shrinkage cavities and cracks caused by turbulence in the hot water and changes in the amount of heat supplied, and also has the advantage of omitting the need for adjusting the hot water level in the mold, which requires delicate adjustment. be.

Furthermore, as a result, the molten metal is introduced into the mold in a sealed state from the molten metal sump in the molten metal sump to the inside of the mold, with the flow velocity hardly changing and in a state close to laminar flow.

Since the hot water in the nozzle and the hot water in the mold are always under constant static pressure from the molten metal in the sump, air is not entrained and no voids are formed in the ingot. Furthermore, since the hot water does not come into contact with the atmosphere from the sump to the inside of the mold, it has the advantage that there are no inclusions caused by entrainment of oxides.

The present invention will be explained below with reference to embodiments shown in the drawings.

First, FIG. 5 shows a cross section of the pouring nozzle used in the method of the present invention, and the thickness t of the exterior heat-insulating refractory (3-1)
1 is 4 to 5 mm, the thickness t of the interior heat-resistant steel (3-2)
2 is about 1 mm, and both are bonded together with a heat-resistant adhesive.

Further, its cross-sectional dimension is slightly larger than the mold internal cross-sectional dimension l1.

For example, when the cross-sectional area of the inner surface of the mold is 2000 to 3000 mm, if the difference t3 is about 1 to 2 mm, the pouring nozzle will slide closely against the inner surface of the mold, and the poured molten metal will not leak.

FIG. 6 shows a state in which the pouring nozzle configured as described above is attached to a continuous casting machine having a belt and a wheel, and pouring and casting.

The pouring nozzle 3 is directly connected 13 to the bottom of the sump 2, and its tip is inserted into the mold approximately 50 mm from the point 9 where the belt 4 and wheel 5 come into contact to form the mold, and slides closely against the inner surface of the rotating mold. There is.

The molten metal produced in the melting furnace and holding furnace is transferred to the sump 2 through the gutter 1.
The water level in the water reservoir is adjusted by the float type flow rate control valve 10 so that the water level in the water reservoir remains at a constant position.

Furthermore, since the surface area (cross-sectional area) of the hot water reservoir 2 is large, the vertical fluctuation of the hot water level is about ±1 mm, and a macroscopically constant static pressure can be obtained with this degree of fluctuation.

Therefore, the molten metal is introduced into the mold under a constant static pressure in a laminar flow or a nearly laminar flow state.

The molten metal thus filled into the mold is cooled and solidified into an ingot 12 by the cooling systems 6 and 7, similar to the conventional method.

In the above embodiment, the molten metal is poured horizontally, but the molten metal may be poured vertically, diagonally, or from below to above, as described below.

FIG. 1 is a schematic diagram showing another embodiment of the present invention, in which a pouring nozzle 3 is connected to a sump 2, and the outer periphery of its tip is the inner surface of the mold, which is formed by the circumferential grooves of a wheel 5 and the pelt 4. The nozzle 3, which is in close contact with the wheel 5 and slides on its inner surface as the wheel 5 rotates, is made of a heat-insulating refractory material that can withstand this sliding, and has a thin wall thickness to reduce its inner cross-sectional area. be as close as possible to that of the mold.

Therefore, the molten metal in the sump 2 passes through the inner hole of the nozzle 3 and is introduced into the mold without changing its flow rate.

Next, the effects of the method of the present invention will be further clarified by comparing them with those of the conventional method.

(1) Regarding the vortex in the mold.

In the conventional method, the molten metal is injected through a nozzle whose cross-sectional area is much smaller than the internal cross-sectional area of the mold, so the flow velocity at the time of discharge is always greater than the speed at which the molten metal in the mold descends along the wheel.

For this reason, the discharged molten metal generates a vortex in the mold, which causes discontinuous growth of the solid phase and the formation of centerline convergence cavities, which also causes cracking.

On the other hand, in the present invention, there is not much difference between the cross-sectional area of the nozzle and the cross-sectional area within the mold, and therefore the flow rate of the molten metal during discharge is approximately equal to the descending speed of the wheel, so no vortex is generated in the molten metal within the mold.

The flow of the molten metal is close to a laminar flow, and discontinuities in solid phase growth due to vortices do not occur as in the conventional method, which prevents defects such as centerline shrinkage cavities and cracks.

(2) Regarding fluctuations in hot water level.

In the conventional method, the operator uses the handle 9 in FIG. 1 to adjust the level of molten metal in the mold so that it remains constant, but it is difficult to make it completely constant and in reality it constantly fluctuates.

In continuous casting, in order to perform stable casting, it is necessary that heat supply and heat extraction are always in a constant balance.

However, in the conventional method, heat supply is not constant due to fluctuations in the hot water level, which is another factor causing the discontinuity in solid phase growth mentioned above.

Furthermore, although the temperature of the ingot should gradually decrease in the longitudinal direction of the mold, fluctuations in the heat supply as described above can cause high-temperature areas to form in some areas, which may encourage cracks to occur in these areas. become.

In contrast, in the present invention, the tip of the pouring nozzle always slides at a constant position relative to the heat extraction system, so the position where the molten metal starts contacting the mold (corresponding to the molten metal surface in the mold) is always constant. Therefore, the heat supply is stable and there are no obstacles like in the conventional method.

(3) Regarding air entrainment.

In the conventional method, the amount of molten metal is adjusted at the position of the control valve 10 shown in FIG. Inside the tank, the pouring metal simply falls freely, and the pressure tends to be below atmospheric pressure.

In addition, the molten metal amount adjusting part and the nozzle part are usually not integrated, but have a combined structure, and there is a small gap, which can cause air to be drawn in. This drawn-in air flows into the mold and becomes trapped during solidification. There is an inconvenience that it becomes a void.

On the other hand, in the method of the present invention, everything from the sump to the mold is sealed and is constantly under hydrostatic pressure, so air entrainment may occur, which is not the drawback of the conventional method.

(4) Concerning oxide film entrainment.

In the conventional method, the mold surface is always in contact with the atmosphere, and an oxide film is formed.

On the other hand, the surface layer of the molten metal in the mold constantly flows downward and solidifies as the wheel rotates, and at this time, the oxide film formed on the surface also flows and solidifies.

Most of this solidified material is trapped on the surface of the ingot and does not pose a major problem, but some of it gets inside and becomes inclusions.

In contrast, in the method of the present invention, the molten metal is in a closed system from the sump to the mold, and there is no problem as described above.

(5) Regarding workability.

The conventional method required the difficult work of adjusting the pouring while observing the hot water level, but according to the present invention, such adjustment work is completely unnecessary.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the pouring method in a conventional continuous casting device, Figs. 2 and 3 are explanatory diagrams of the operation of the conventional pouring method, Fig. 4 A, the opening is from the nozzle in the method of Fig. 2. The flow of the injected molten metal creates a vortex in the molten metal that has already been injected, and this shows the process by which the discontinuous growth of the solid phase leads to defects. FIG. 5 is an illustrative cross-sectional view of a pouring nozzle used in the pouring method in the continuous casting apparatus of the present invention, FIG. 6 is an exemplary diagram of the pouring method of the present invention, and FIG. 1 is an exemplary diagram of the pouring method of the present invention. It is another illustrative diagram of. DESCRIPTION OF SYMBOLS 1... Transfer path, 2... Hot water reservoir, 3... Molten pouring nozzle, 4... Belt, 5... Wheel, 6, 7... Cooling water injection nozzle, 8... Separation Type point, 9...handle,
10... Control valve, 11... Mold internal cross-sectional dimension, 12.
... Ingot, 13... Direct connection point.

Claims (1)

[Claims] 1 Continuous casting into an ingot by continuously injecting molten metal into a mold formed by a rotating casting ring with grooves on its circumferential surface and a metal band in contact with the circumferential surface of the rotating ring. In a casting device, a lower tip of a pouring nozzle for injecting molten metal into the mold is inscribed in the inner surface of the mold, an upper part of the nozzle is connected to a sump, and at least the tip of the pouring nozzle is connected to the mold. The inscribed part is made of a heat-insulating refractory, and the inner area of the pouring nozzle is made to approximate the cross-sectional area of the inner surface of the mold, so that the molten metal is sealed from the sump to the inside of the mold. pouring in a continuous casting device characterized by pouring molten metal from a pouring nozzle into a mold in a laminar flow or in a laminar flow state, under static pressure in a sump and without contact with the atmosphere. Method.