JPH04253563A - Separation of nonmetallic inclusion in molten metal and pouring nozzle - Google Patents

Abstract

PURPOSE:To accelerate the flotation of nonmetallic inclusions and to improve product quality by pouring the discharge flow from an pouring nozzle in such a manner as to strike this discharge flow perpendicularly against the tundish side wall furthest from an outflow port. CONSTITUTION:The bottom of the pouring nozzle is blinded and the discharge port opens to the side wall of the nozzle bottom. The discharge flow having large energy is struck against the wall surface on the opposite side furthest from the outflow port, by which large turbulent flow is formed on the periphery of the wall surface and a stirring region is formed. The coarsening by the entire part among the inclusions is accelerated in this stirring region.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating and removing nonmetallic inclusions in molten metal in a tundish, and a hot water nozzle used therein.

0002

2. Description of the Related Art It is well known that nonmetallic inclusions in molten metal cause defects in products such as steel sheets. In order to promote the flotation and separation of nonmetallic inclusions in a tundish during continuous casting, etc., the molten metal is stirred to promote coalescence and coarsening of the nonmetallic inclusions, and also to promote the flotation of nonmetallic inclusions. For this reason, it is important to control the flow of molten metal in a container such as a tundish. For example, special public service in 1983
Publication No. 27020 discloses that a weir is installed in the tundish to artificially control the flow of molten metal, prevent a short and fast flow from the inlet to the outlet (short circuit), and prevent the separation of non-metallic inclusions. A method of promoting is disclosed.

However, in recent years, there has been an increasing need to reuse hot tundishes for continuous casting of steel to reduce costs, and for this purpose, by tilting the tundish, remaining molten metal and It became necessary to discharge the slag. At this time, if there is a weir inside the container, problems have arisen in that when the remaining molten metal and slag are being discharged, the refractories in the weir may fall, and the remaining molten metal and slag cannot be easily discharged. In addition, the weir portion accounts for a high proportion of the cost of container refractories, and the installation of weirs has been a cause of increased refractory costs.

0004

[Problem to be solved by the invention] In the present invention, the conventional
(1) Difficulty in discharging slag and molten metal remaining at the end of casting, (2) Increased cost of refractories due to the installation of weirs, etc. are solved, and non-metallic inclusions in molten metal in containers such as tundishes are solved. The object of the present invention is to provide a method for promoting the separation of objects more than when installing a weir, and a hot water nozzle for use in the method.

[0005]

[Means for Solving the Problems] The present inventors have proposed that in order to promote floating separation of non-metallic inclusions, the flow velocity when the molten metal is discharged from the hot water supply nozzle is attenuated so that the molten metal flows at high speed at the bottom of the container. We considered it important to prevent short circuits such as underflow. In the conventional method, the distance from the nozzle outlet to the bottom of the container is small, and the reverse flow velocity at the bottom is also large. Therefore, the present inventors discovered that by adjusting the nozzle discharge angle and the distance from the discharge port to the side wall surface in order to apply the discharge flow to the side wall surface of the container, bottom flow due to reverse flow can be prevented, and the present invention has been constructed. I ended up doing it.

That is, the present invention provides a tundish that temporarily receives molten metal from a hot water supply nozzle and discharges it from an outlet, and directs the discharge flow from the hot water supply nozzle to the side wall surface of the tundish that is farthest from the outlet. This is a method for separating non-metallic inclusions in molten metal, which is characterized by pouring the metal at a predetermined distance and hitting it almost perpendicularly to the tundish. This is a nozzle for supplying hot water to a tundish, characterized in that it has a bottom and a discharge port is opened in the side wall of the bottom portion of the nozzle.

[0007]

[Function] When pouring into the tundish, the present invention creates a large turbulent flow field around the wall by hitting the discharge flow with high energy against the wall on the opposite side away from the outlet, creating agitation. forming an area. In this stirring region, coarsening due to coalescence between inclusions is promoted.

[0008] The flow that hits the wall surface forms a reversed flow over a wide range, and this reversed flow spreads over a wide range and becomes a flow approaching a piston flow. Therefore, a short circuit (a short-circuit flow from an inlet to an outlet) which is considered to be the cause of the outflow of large nonmetallic inclusions is prevented, and floating separation of the nonmetallic inclusions is promoted. FIG. 1 is an overall diagram showing the implementation status of the present invention. Further, FIG. 2 is a sectional view illustrating a conventional implementation situation, and FIG. 3 is a sectional view illustrating an implementation situation of the present invention.

As shown in FIG. 2, in the case of a conventional straight nozzle, the molten metal has a discharge flow of v0. On the other hand, in the method of the present invention, as shown in Fig. 3, the discharge part of the nozzle

0010

[Math 1]

The discharge flow velocity decreases to [0011], and by the time it hits the side wall, v2 = v1 (b・d/x) (where x is the distance from the nozzle to the wall, b is the potential core length≒2,
d is the discharge hole diameter). That is, in the method of the present invention, by changing the distance x from the nozzle to the wall surface and the nozzle discharge angle that changes the branching loss coefficient ξ, the flow velocity of the molten metal when it hits the wall surface can be adjusted.
It is possible to stir the molten metal near the wall surface and suppress the reverse flow necessary for floating inclusions.

Note that FIG. 5(a) is a sectional view of the hot water supply nozzle of the present invention, and FIG. 5(b) is a sectional view of the vicinity of the bottom of a conventional hot water supply nozzle.

[0013]

EXAMPLE 100 tons of low carbon aluminum killed steel was poured from a molten steel ladle into a continuous casting mold through a tundish shown in FIG. The pouring nozzle is a conventional straight type (inner diameter 60 mm) as shown in FIG. 5(b), and the present invention shown in FIG. 5(a) has a bottom with a bottom and a discharge port opens laterally on the side wall of the bottom. Comparison was made using two types (inner diameter 60 mm).

As an example of the present invention, two cases were conducted in which the horizontal distance L between the inlet nozzle and the outlet nozzle was 1800 mm and 1200 mm. The angle α of both nozzles is 5° downward. Further, a conventional straight type nozzle was used at the position shown by 8 in FIG. 4, and experiments were also conducted with a weir installed. The amount of molten steel passing through is 1.1 tons/
min, which is constant for each experiment. The amount of nonmetallic inclusions was evaluated by cutting out a 1/4 thickness position of the slab where nonmetallic inclusions tend to accumulate, and using a slime extraction method.

Table 1 summarizes the amount of nonmetallic inclusions extracted from the slab under each condition. From this, it can be seen that whether L is 1200 mm or 1800 mm, the amount of nonmetallic inclusions in the slab is smaller than when installing a conventional weir.

[0016]

[Table 1]

[0017]

Effects of the Invention According to the present invention, the flow of molten metal within the tundish can be controlled and the floating separation of non-metallic inclusions can be promoted. This effect reduces defects caused by nonmetallic inclusions in products and improves product quality. In addition, by not using a weir, it is easier to remove the molten metal and slag that remain in the container at the end of casting, allowing hot reuse of the container. Additionally, by not using a weir, it has become possible to reduce the cost of refractories associated with weir installation.

[Brief explanation of the drawing]

FIG. 1 is an overall diagram showing the implementation status of the present invention.

FIG. 2 is a conceptual diagram schematically showing the flow of molten metal in a conventional method.

FIG. 3 is a conceptual diagram schematically showing the flow of molten metal in the method of the present invention.

FIG. 4 is an auxiliary diagram for explaining the embodiment.

FIG. 5(a) is a vertical cross-sectional view of a nozzle of the present invention and FIG. 5(b) is a conventional nozzle.

[Explanation of symbols]

1 Ladle 2 Tundish 3 Hot water nozzle 4 Outflow nozzle 5 Molten metal 6 Undercurrent (short circuit) 7 Nozzle (at the time of example experiment) 8 Nozzle (during comparative example experiment) 9 Weir (during comparative example experiment)

Claims (2)

[Claims] Claim 1: In a tundish that temporarily receives molten metal from a hot water supply nozzle and discharges it from an outlet, the flow discharged from the hot water supply nozzle is directed to the side wall surface of the tundish furthest from the outlet at a predetermined distance. A method for separating non-metallic inclusions in molten metal, which is characterized by pouring the metal so that it hits the metal almost vertically. 2. A nozzle for supplying hot water to a tundish, characterized in that the bottom of the nozzle is closed, and the discharge port is opened in a side wall of the bottom of the nozzle.