Method of casting steel into a continuous casting mold and pouring tube for the performance of the aforesaid method

Abstract

A method of casting steel into a continuous casting mold wherein the steel is guided to a level beneath the molten metal pool in the mold, the steel during its departure in the form of a thin coherent pattern is introduced simultaneously towards the bottom as well as laterally into the liquid metal pool. For the practice of the method there is employed a pouring tube having at least one outlet opening which opens into the liquid metal pool in the mold, this outlet opening possessing the shape of a slot which opens downwards and laterally.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a new and improved method of pouring metal, typically steel, into a continuous casting mold, wherein the steel is conducted to a point beneath the level of the liquid metal bath or pool in the mold, and also relates to a new and improved construction of pouring tube for the performance of the aforesaid method.

There are already known to the art techniques in which steel, in the form of lateral flow currents or streams, emerges beneath the level of the molten metal bath in the mold. In this regard there are employed immersible pouring tubes which can have lateral outlet openings possessing round or oval shape. With this technique and when using such type pouring tubes there are directed towards the already solidified strand shell rather massive bundled streams of superheated steel which is then deflected at such location. Owing to the thus prevailing circulation the growth of the solidifying peripheral skin or layer is impaired and there are promoted weakened locations at the edges of the strand, which can lead to transverse fissures. It is particularly disadvantageous when casting rectangular shapes, for instance steel slabs, if streams of superheated steel impinge against the narrow sides of the strand. Furthermore, the steel flow which does not extend deeply into the liquid metal pool in the continuous casting mold promotes the trans-crystalline crystallization and segregation processes.

There are also known to the art techniques and pouring tubes wherein the steel emerges vertically towards the bottom of the mold. The outlet opening in the immersed pouring tube can possess different cross-sectional configurations, for instance can be oval, round or rectangular.

Also known to the art is the use of a pouring block having a circular outlet or discharge channel, the boundary wall of which is slotted by diametrically situated notches. This pouring block does not, however, immerse into the metal bath in the mold. The purpose of the slot in the wall is only to prevent fluttering i.e., to steady the freely falling metal jet.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide an improved method of, and pouring tube for, casting metals into a continuous casting mold which overcomes the aforementioned drawbacks of the prior art casting techniques and the prior art pouring tubes.

A further object of the present invention is to insure for as great as possible undisturbed incipient growth of the frozen layer or shell at the upper portion of the mold, that is to say, at the region of the level of the molten bath in the mold and to promote circulation at the deeper locations of the liquid metal pool in the mold.

Yet a further significant object of the present invention relates to an improved method of, and pouring tube for, the pouring of molten metals into a continuous casting mold which produces a surface and skin at the cast product which is as free as possible of fissures and reduces the possibility of segregation processes from arising during casting.

Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the method aspects of this development contemplate that the molten steel during its outflow or departure in the form of a thin, coherent or bundled-together pattern is introduced into the liquid metal pool in the mold simultaneously downwards as well as also laterally.

The pouring tube which is employed for the practice of the method aspects is manifested by the features that it possesses an outlet opening having the shape of a slot which opens downwardly and laterally.

By virtue of the teachings of the invention there is achieved the result that the superheated steel is uniformly distributed within as large as possible volume of the liquid core of the strand in the mold. As a result the shell or skin of the strand can uniformly grow. Furthermore, the strand shell or skin is subjected to a lesser degree to thermal stresses, reducing the tendency to form fissures.

During casting of slabs at arc-type plants it has been found to be advantageous if the pattern during departure of the steel is retained in a plane inclined towards the inner radius of the strand at an angle with respect to a vertical plane. Owing to this inclination there is insured that the superheated or overheated steel does not come into contact with, or only comes into contact as late as possible with, the solidified wide sides of the strand. Furthermore, the central plane of the pattern advantageously should not approach the surface of the slab at the location of the inner radius closer than about one-quarter of the slab thickness. The width of the slot advantageously does not exceed 25 millimeters, so that the outflowing pattern is relatively narrow. The length of the slot is designed to be advantageously about seven to nine times that of the slot width. As a result, also when casting strands of larger format, for instance having a dimension of 2,000 by 250 millimeters, there can be throughput the required quantity of steel. In the case of arc-type casting plants it is advantageous if the slot at the pouring tube is inclined towards the inner radius in the direction of throughpassage of the strand, wherein the angle of inclination with respect to the vertical should be in the order of 4.degree. to 6.degree.. The machine radius and the thickness of the strand to be cast are decisive for the selection of a suitable angle.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:

FIG. 1 illustrates a mold with a pouring tube immersed in the liquid metal pool or bath in the mold and designed according to the teachings of the present invention;

FIG. 2 is a cross-sectional view of the arrangement of FIG. 1, taken substantially along the line II--II thereof; and

FIG. 3 illustrates a mold and pouring tube having an inclined slot.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Describing now the drawing, in FIG. 1 there is illustrated, by way of example, a rectangular continuous casting mold 1 into which there is infed a molten jet of steel, delivered from a non-depicted casting vessel, for instance a tundish, by means of a pouring tube 2. This pouring tube 2 immerses into the liquid metal pool or core 3 of the strand which is being formed in the continuous casting mold 1. At the top of the metal pool 4 there is a slag layer 5. At the location of the cooled mold walls there is formed a solidified layer or shell 6 having a thickness which increases in the direction of throughpassage of the strand.

As best seen by referring to FIG. 2, the pouring tube 2 possesses an outflow or discharge opening in the form of a slot 8, this slot 8 being extended upwardly over a longer distance along the wall of the pouring tube 2. Now the steel is introduced into the liquid metal pool 3 in the mold 1 through this slot 8 in the form of an emerging thin, coherent or bunched-together pattern, wherein the steel departs from the pouring tube both laterally as well as downwardly, as indicated by the flow lines 7 of FIG. 1. The central plane 9 of the slot 8, which is vertical in this exemplary embodiment, is located in a vertical plane 11 which extends through the center of the narrow sides 10 of the continuous casting mold 1.

In the case of continuous casting installations or plants having a mold with a curved hollow mold cavity, or a casting plant where the strand after departing from the mold is directly transferred into a curved shape, it is possible to provide a slot 8' (FIG. 3) which is located in a plane 9' which is inclined with respect to the vertical plane 11. Thus, as best seen by referring to such FIG. 3, the central plane 9' of the slot is inclined in the direction of the inner radius of the curved strand 20. This inclination of the slot 8' insures that the superheated steel comes into contact as late as possible with the solidified wide sides of the strand 20 at the outer radius thereof, and will be deflected towards the side of the inner radius, and further, will produce a circulatory movement which penetrates deeply into the pool in the mold, this circulatory movement then reducing segregation effects. For calculating the angle of inclination there is decisive the radius of curvature of the cast strand at the upper portion of the strand where the flow streams of interest are effective as well as the thickness D of the strand 20. During the casting of slabs the minimum spacing 16 of the central plane 9' from the wide side of the strand at the inner radius should be adjusted to be not less than approximately one-quarter of the thickness D of the slab. The angle of inclination 12 advantageously is in a range between 4.degree. and 6.degree.. Thus, for instance, with a slab format of 1,700 by 200 millimeters and an outer machine radius 17 of 12 meters, it has been found to be advantageous to employ an angle of inclination of 5.degree.15'. The inclination of the inflowing pattern also can be adjusted if the pouring tube with vertical oriented slot (FIG. 2) is secured in inclined position to the casting vessel.

In order to realize the desired effect it is necessary to maintain the outflowing metal jet relatively thin, that is to say, the width 14 of the slots 8 and 8' respectively, should be slight and advantageously should amount to no more than 25 millimeters. In order to obtain the required throughput quantity for a certain casting speed the length 15 of each such slot preferably should amount to about seven to nine times the width 14. In order to obtain a compensation of the outflow velocities and therefore the outflow quantities along the entire slot the flow cross-section of the vertical bore 18 of the pouring tube is tapered following the start of the slot in the direction of flow. A similar effect also could be attained by providing different slot widths.

While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

Accordingly, I claim:

1. A pouring tube for pouring steel into a continuous casting mold to form a cast strand, said pouring tube having at least one outlet means capable of opening into the liquid metal pool of the mold for introducing liquid metal into the mold in the form of a thin, coherent pattern, said outlet means having the shape of a downwardly and laterally opening slot of constant width, the width of the slot not exceeding 25 millimeters and the length of the slot being about seven to nine times the slot width.

2. A method of pouring steel into a continuous casting mold, especially during casting of slabs at arc-type casting plants, comprising the steps of conducting the steel to a point beneath the level of the liquid metal pool in the mold, introducing the steel into the mold in the form of a thin, coherent pattern which is directed simultaneously both downwardly as well as laterally into the liquid metal pool in the mold, and directing the pattern, upon outflow of the steel, towards the inner radius of the curved strand in a plane which is inclined at a predetermined angle with regard to a vertical plane.

3. The method as defined in claim 2, wherein the angle of inclination is in a range between 4.degree. to 6.degree..

4. The method as defined in claim 2, wherein the spacing of the central plane of the pattern from the wide side of the inner radius of the strand is adjusted to amount to not less than one-quarter of the thickness of the slab.

5. A pouring tube for pouring steel into a continuous casting mold to form a cast strand, said pouring tube having at least one outlet opening capable of opening into the liquid metal pool of the mold, said outlet opening possessing the shape of a downwardly and laterally opening slot, and wherein the slot is inclined towards the inner radius of the cast strand in the direction of travel of such strand.

6. The pouring tube as defined in claim 5, wherein the angle of inclination of the slot with respect to a vertical plane is in a range of 4.degree. to 6.degree..