JPH03106545A - Continuous casting method - Google Patents

Abstract

PURPOSE:To cast a cast slab having good surface characteristic by forming annular gap between outer circumferential wall part of a connecting nozzle set between a tundish and a mold and circumferential wall part in the mold and supplying powdery oxide becoming molten state. CONSTITUTION:The connecting nozzle 9 is set between the water cooled copper mold 2 and the tundish 1. The connecting nozzle 9 is set with a gap of distance D between the outer circumferential part at downstream side and part in the connecting nozzle 9 and the inner circumferential wall face in the mold 2. The gap D is pressurized with a pressure tank 11 so as to supply the powdery flux from a flux supplying tank 10 at the fixed velocity. The flux is brought into contact with molten metal 3 and easily melted to become molten layer 12 of the flux, and on this, the powder layer 13 exists and this is melted in order according to consumption of the molten layer 12. The molten metal 3 flows calmly and the cast slab having good surface characteristic can be cast with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a continuous casting method capable of casting slabs with good surface quality with high efficiency.

(Prior art and its problems) As methods for continuously casting molten metal, the vertical continuous casting method as shown in Figure 3 and the horizontal continuous casting method as shown in Figure 4 are widely adopted. ing.

In the vertical continuous casting method, the molten metal 3 is normally supplied from the tundish 1 to the mold 2 through a submerged nozzle 4, and the tundish 1 and the mold 2 are mechanically separated. .

In FIG. 3, reference numeral 5 indicates a ladle for supplying the molten metal 3 to the tundish 1, 6 indicates a solidified shell whose outer peripheral portion is solidified after being cooled in the mold 2, and 7 indicates a guide roll for guiding the solidified shell 6.

In the case of this vertical continuous casting method, as shown in Figure 5,
The molten metal 3 in the mold 2 has a free surface, and the free surface of the molten metal 3 contains so-called powder 8 mainly composed of oxides.
covered with. This powder 8 prevents oxidation and heat dissipation of the molten metal 3, melts at the part in contact with the molten metal 3, flows into the space between the mold 2 and the slab due to the oscillation of the mold 2 and pulls the slab downward, and is cast. It provides lubrication between the piece and mold 2.

By the way, since the molten metal 3 is supplied from the tundish 1 to the mold 2 through the nozzle hole 4°, which has a much smaller cross-sectional area than the cross-sectional area of the mold 1, the molten metal 3 is supplied from the small-diameter nozzle hole 4°. The discharge flow rate in No. 3 is quite high, and this discharge flow re-melts the solidified shell that has survived near the meniscus, causing cracks on the surface of the slab. In addition, it becomes a factor in the fluctuation of the free surface inside the mold 2, and causes defects in the slab due to the entrainment of the powder 8 on the surface of the slab.

On the other hand, in the case of the horizontal continuous casting method, the tundish l and the mold 2 are mechanically connected by a connecting nozzle 9, as shown in FIG.

That is, in this casting method, the mold 2 and the connecting nozzle 9 are held in close contact with each other, thereby preventing the molten metal 3 from being inserted between the mold 2 and the connecting nozzle 9.

In such a horizontal continuous casting method, as shown in FIG. 4, the free surface of the molten metal 3 is within the tundish l;
The amount of molten metal 3 that is constantly drawn out as a slab is supplied into the mold 2 through the connection nozzle 9. Furthermore, in the case of this casting method, the cross-sectional area of the connecting nozzle 9 is approximately the same as the cross-sectional area of the mold 2, so the supply flow is quiet, and the slabs caused by this supply flow, as in the vertical continuous casting method, are No defects occur.

However, in the horizontal continuous casting method, since the mold 2 and the connecting nozzle 9 are in close contact with each other, it is difficult to supply lubricant between the mold 2 and the slab, which increases the pulling resistance during casting. There is. Furthermore, since the connecting nozzle 9 is cooled by the mold 2, a solidified shell 6 is formed or adhered to the downstream end face of the connecting nozzle 9, as shown in FIG. 6, which causes unstable casting and causes surface flaws. Cause.

Regarding the supply of lubricant between the mold and the slab, see JP-A-53-
There is a method disclosed in Publication No. 40629, but in this method, since the slab is horizontal, there is a slight difference in the static pressure of the molten metal between the top and bottom of the slab, and it is difficult to supply lubricant stably. is difficult. In addition, it is not possible to reduce the adhesion force of the solidified shell on the front surface of the connecting nozzle, and therefore the above-mentioned problems cannot be solved. Furthermore, the formation of a solidified shell on the connecting nozzle results in surface defects, commonly called pull-out marks, which require surface cutting for commercialization.

An object of the present invention is to provide a continuous casting method that can solve the above-mentioned problems.

(Means for Solving the Problems) In order to achieve the above object, the continuous casting method according to the present invention provides a method for continuous casting using a continuous casting device in which a tundish and a mold are vertically and mechanically connected. , a required annular gap is formed between the outer peripheral wall of the downstream end of the connecting nozzle, which is interposed between the tundish and the mold, and the downstream end thereof is inserted into the mold, and the inner peripheral wall of the mold; Casting is carried out by continuously supplying powdered oxide, which easily becomes molten when it comes into contact with molten metal, into the void at a required pressure.

The present invention makes it possible to stably cast slabs with good surface quality by compensating for the drawbacks of vertical continuous casting methods and horizontal continuous casting methods. In other words, by applying the mechanical connection technology between the tundish and mold of the horizontal continuous casting method to the vertical continuous casting method, it is possible to supply hot water with a large cross section, and it is possible to prevent surface flaws on the slab caused by the flow of hot water. It is. Further, by vertically casting, the static pressure of the molten metal is the same in the same cross section at the connection nozzle, so lubricant can be stably supplied to the joint between the connection nozzle, the mold, and the slab.

(Example) The method of the present invention will be explained based on an example shown in FIGS. 1 and 2.

FIG. 1 is a conceptual diagram of the present invention, and FIG. 2 is a drawing showing details of a connection nozzle, a mold, and a joint portion of a slab.

In these FIGS. 1 and 2, the same numbers as in FIGS. 3 to 6 indicate the same or corresponding parts.

First, the structure of the continuous casting apparatus used in the method of the present invention will be explained based on FIG.

The connecting nozzle indicated by 9 connects the water-cooled copper mold 2 and the tundish 1.
It is interposed between them and is in close contact with the tundish l. The connection nozzle 9 is made of a refractory material mainly composed of Si3N4, for example, and the downstream end outer circumference of the connection nozzle 9 is placed a distance D apart from the inner circumference wall surface of the mold 2.

Powdered Franx is supplied to this gap D from a Franx supply tank 10 provided at an appropriate position outside the mold 2 at a constant speed. Also,
This flanx is supplied with a pressure corresponding to the static pressure (corresponding to the height L) of the molten metal 3 by a pressurized gas such as N2 supplied from a pressure tank 11, and the molten metal 3 is
This prevents it from being inserted into the gap.

The molten metal 3 supplied from the tundish 1 is pulled downward by the mold 2 and pinch rolls (not shown).

Next, the function of adding Franks will be explained based on FIG.

The molten metal 3 is held at the downstream end of the connection nozzle 9 in a balance between the static pressure of the molten metal 3 and the gas pressure of the flux.

By the way, flux is supplied to the gap between the connection nozzle 9 and the mold 2 as described above, but this flux comes into contact with the molten metal 3 and easily melts. Then, a Franks powder layer 13 is formed on this molten layer 12 of flux, and this powder layer 13 of flux is sequentially melted as the amount of molten layer 12 is consumed.

Meanwhile, the molten metal 3 is cooled by the mold 2 to form a solidified shell 6.

Therefore, in this case, the tip of the coagulation shell 6 is connected to the connection nozzle 9.
It is necessary to ensure a gap D that does not extend to the outer circumferential surface of the downstream end. According to the experimental results of the present inventors, this gap D was required to be 5 am or more. By providing this gap D, the tip of the solidified shell 6 comes into contact with the molten layer 12 of flux, so that it does not become a resistance during drawing of the slab. Further, the molten layer l2 of flux flows between the solidified shell 6 and the mold 2 as the slab is drawn out, and performs a lubricating action between the solidified shell 6 and the slab.

Note that the gas pressure acts to help the molten layer 12 flow into the gap. Further, in the present invention, as shown in FIG. 2, since the connecting nozzle 9 is not in contact with the mold 2, there is no cooling of the downstream end of the connecting nozzle 9, and a solidified shell is formed in the connecting nozzle 9. Nor.

Incidentally, a larger gap is advantageous from the viewpoint of preventing cooling, but if it is too large, the cross-sectional area on the inner circumference side of the connecting nozzle 9 becomes small and the difference with the cross-sectional area of the mold 2 becomes large, which reduces the flow of hot water. This disturbs the molten metal in the mold 2 and deteriorates the surface quality of the slab. In the casting results of the present inventors, the gap D
It has been confirmed that 5M is sufficient to prevent the cooling. Next, in order to confirm the effects of the method of the present invention, the results of experiments conducted under the conditions shown in Table 1 below will be explained.

As a result of a casting test conducted under the conditions shown in Table 1, the surface quality of the slab was extremely smooth and the depth of the pull-out mark was reduced to less than 1/3 compared to the conventional case where no flux was used. , it was possible to obtain a rolled product without cutting the surface of the slab.

In addition, no problems were observed during operation, and the project was completed easily.

In addition, in this casting experiment, the amount of flux consumed was 500 mm.
The amount was approximately 150 g/m of slab when using a mold with a width of 1,000 mm, and approximately 200 g/m of slab when a mold with a width of 1,000 mm was used.

(Effects of the Invention) As explained above, according to the method of the present invention, the drawbacks of the conventional vertical continuous casting method and horizontal continuous casting method can be solved, and slabs with good surface properties can be cast with high efficiency. It has the great effect of being able to.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the configuration of the continuous casting apparatus used in the method of the present invention, Fig. 2 is a detailed view of the vicinity of the connecting nozzle, Figs. 3 to 6 are explanatory diagrams of the conventional method, and Fig. 3 5 is an explanatory view of the vertical continuous casting method, FIG. 5 is an enlarged view of the main parts thereof, FIG. 4 is an explanatory view of the horizontal continuous casting method, and FIG. 6 is an enlarged view of the main parts thereof. 1 is a tundish, 2 is a mold, 3 is a molten metal, 9 is a connecting nozzle, 11 is a pressure tank, 12 is a molten layer of flux, and 13 is a powder layer of flux. Figure 1

Claims (1)

[Claims] (1) When performing continuous casting using a continuous casting device in which a tundish and a mold are vertically and mechanically connected, a connection that is interposed between the tundish and the mold and whose downstream end is inserted into the mold. A required annular gap is formed between the outer circumferential wall of the downstream end of the nozzle and the inner circumferential wall of the mold, and powdered oxide, which easily becomes molten when it comes into contact with molten metal, is applied to this annular gap under the required pressure. A continuous casting method characterized by casting while continuously supplying.