FIELD OF THE INVENTION
The invention relates to an improved double strand-four port submerged entry nozzle (SEN) for pouring molten steel into a continuous casting mold to control fluid flow condition inside the mold. More particularly, the invention relates to an improved double strand-four port SEN to introduce the liquid steel to a mold in an effective manner to control and reduce sub meniscus velocity to a desired level.
BACKGROUND OF THE INVENTION
Continuous casting is a process that transforms liquid steel into semi-finished slabs, blooms and billets that can be further processed into finished products. In the continuous casting of steel, liquid steel from a ladle is poured into a large vessel known as a tundish. Tundish has one or more outlets through which the liquid steel flows into mold in which the liquid steel cools and solidifies to form continuously cast solid lengths of the metal.
SEN is located between the tundish and mold. It guides the liquid steel flowing through it from the tundish to the mold. The flow of the liquid steel from the tundish is gravity driven by the pressure difference between the liquid levels of the tundish and that at the top free surface of the mold. Molten metal solidifies in the mold and emerges as a cast metal product which is subsequently moved out of the mold at casting speed.

Many quality problems that originate during continuous casting are directly attributed to poor control of fluid flow conditions inside the mold. Quality of final steel product and productivity of cast depends immensely on liquid steel flow and turbulence associated with gravity feeding of liquid steel into mold. In casting process, during initial solidification of the liquid steel at the meniscus, the top of the solidifying steel shell meets the mold wall and the liquid steel of the mold bath. This is where the surface of the final cast product is created, and defects such as surface cracks can form due to severe level fluctuation occurrence on the liquid surface.
However, it is highly desirable for the SEN to introduce the liquid metal to the mold in a quiescent and smooth manner, without disruption and excessive turbulence particularly at the meniscus, so as to minimize capturing of overlying slag layer by shear actions due to a higher velocity of liquid steel. A smooth, steady discharge facilitates processing and can improve the finished product.
There has been a continuing effort to improve steel flow circulation and reduce turbulence in a continuous casting mold receiving a stream of liquid steel delivered through a SEN. One such prior art (as shown in fig 1) is a bifurcated SEN where a central bore terminates into two exit ports that extend almost horizontally to the central bore. However, although such bifurcated port nozzles cause a certain sub meniscus

velocity within casting molds. But in such cases there exist limitations to reduce it to desired levels. The past SEN designs fail to maintain a calm or still liquid reservoir of molten steel within the mold.
In the mold, a liquid slag layer is formed on the steel meniscus by adding or distributing mold powder into the mold on top of the liquid steel. This liquid slag layer acts as a lubricant between the solidifying steel shell and the mold as the liquid steel solidifies as well as an insulator to the meniscus of the liquid steel. To prevent the freezing of the steel near the meniscus and sufficiently melt mold flux, there must be continuous supply of heat from underneath steel current overcoming heat loss from the meniscus. This is attained in conventional nozzle by creation of a dual roll flow where a part of port-exit flow is directed towards the meniscus. However, the upper roll stream poses danger of dragging mold flux deep into the mold through a higher shear velocity and vortex formation. Consequently, there is an increased risk of formation of surface defects known such as slivers and surface cracks.
It is possible to control and reduce sub meniscus velocity to a desired level by designing an SEN appropriately. Here, a SEN with a feature of double strand-four-port is proposed to achieve the above mentioned goal.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose an improved double strand-four port submerged entry nozzle (SEN) for pouring molten steel into a continuous casting mold to control fluid flow condition inside the mold, which is capable introducing the liquid metal to the mold in a quiescent and smooth manner without disruption and surface turbulence at the meniscus.
Another object of the invention is to propose an improved double strand-four port submerged entry nozzle (SEN) for pouring molten steel into a continuous casting mold to control fluid flow condition inside the mold, which is able to control and reduce sub meniscus velocity to a desired level restricting vortex formation.
A still another object of the invention is to propose an improved double strand-four port submerged entry nozzle (SEN) for pouring molten steel into a continuous casting mold to control fluid flow condition inside the mold, which enables a stable and steady fluid flow inside mold cavity reducing risk of formation of surface defects such as slivers and surface cracks in subsequent steel processing.

SUMMARY OF THE INVENTION
According to a feature of the invention, a SEN includes a structure that has a vertical central straight bore extending to the middle of horizontal bore to which two strands of pipe shaped nozzles are embedded at each end. Each strand of nozzle also incorporates two oppositely directed exit ports in the sidewall of the nozzle where the end of the pipe is closed. The oppositely directed exit ports have slanted lips with angle between 10 to 45 degrees relative to horizontal plane.
A SEN as per the present invention is capable of dividing the incoming flow of liquid steel from tundish into substantially equal portions so that a similar volume and velocity of liquid steel is discharged from each exit port opening into opposite sides of the caster mold under all cast steel flow rates.
The invention provides a SEN having a main transition from central bore (D) of circular cross-section, to two connected distant strands having circular cross sections with condition that twice the cross section area of one strand (2d) internal section is not less than the area of the circular cross-section of central bore (2d > D).
The strands are at a distance of ‘L’ apart where L=3d to 5d where d is the internal diameter of bore of each strand (5a, 5b).

According to another feature of the invention, exit ports of the SEN may be of any general shape including, but not limited to, oval, polygonal or any combination thereof. Conveniently, the general shape of the exit port is substantially rectangular, which has ratio of total port area to bore area in the range of 2 to 3 to ensure the optimal sub meniscus velocity, sufficiently high as to prevent the freezing of the steel and melts sufficient mold flux at the meniscus.
The SEN, according to invention is having horizontal bore which plays as flow divider between the inlet pipe and the outlet ports through two strands. The horizontal bore may suitably be inclined towards both the strands to guide the flow in an equal and hydro-dynamically smooth manner.
Another feature of the invention is to provide a SEN wherein the inertial force of the liquid metal flowing through the nozzle is divided and better controlled by dividing the flow into separate and independent streams by four ports of two strands at exit.
According to another feature of the invention, distance between two strands of nozzle is sufficient to ensure that inter mingling of the jet streaming out of exit-ports is negligible. Generally, it is 3 to 5 times of internal diameter of each strand of nozzle.

According to the invention, the SEN generates sufficient upwards flow in a manner that the temperature near the meniscus is sufficiently high as to prevent the freezing of the steel and melts sufficient mold flux at the meniscus.
According to another feature, the invention ensures that the turbulence at the meniscus is not increased to a point where steel overlying phase is dragged into the mold.
Additional features will become clear and a deeper understanding will be obtained by reading the following detailed description made in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: is a vertical cross-sectional view of a bifurcated submerged entry nozzle
according to Prior Art;
Fig. 2: is a sectioned elevation view of continuous casting system showing
submergence of the SEN in a continuous casting mold;
Fig. 3a, 3b and 3c are three dimensional view of embodiment of the SEN of present invention from different angle;
Fig. 4 is a vertical front cross-sectional view of a SEN constructed in accordance
with the present invention;

Fig. 5 is a side elevation view of the nozzle shown in Figure 4;
Fig. 6 is schematics of experimental setup for water modelling investigation;
Fig. 7 is schematics of experimental setup with vane anemometer to get the sub
meniscus velocity;
Fig. 8 compares water modeling results of the SEN as per the present invention
with a prior art SEN type having a 150 downward ports.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
A submerged entry nozzle for use in a continuous steel casting apparatus is provided between a tundish (not shown) and a mold (10). A lower end portion of the submerged nozzle is immerged in a molten steel (11) in the mold up to the meniscus level (12) as shown in Fig 2.
A SEN as per the present invention is depicted in Fig. 3 to 5 for introducing liquid steel into a slab continuous caster mold. The SEN has appearance of a rigid pipes or tubes and is made of refractory material (1) that has an entry (2) which is connected to a tundish (not shown) at the top.

Fig. 3a, 3b and 3c illustrates an outer view of the submerged entry nozzle, as seen from different angles. The figure shows a circular entry of the SEN as per the disclosed invention where vertical section of the SEN in form of a pipe or tubing leads to horizontal bore in a manner so as to divide the incoming flow of liquid steel through vertical bore equally into two strands of nozzle.
Fig. 4 illustrates a design of two strand SEN with four exit ports. It exemplify a vertically sectioned view of the submerged entry nozzle, showing a vertical straight central bore (3) leading to the middle of horizontal bore (4) to which two strands (5a and 5b) of pipe shaped are embedded at each end, transporting liquid steel from entry (2) of SEN to continuous casting mold. The body of SEN1 is made of refractory material well known to the makers of SENs.
In the preferred embodiment of the invention, the two individually distant connected pipe shaped nozzles (5a and 5b), henceforth called two strands, connect to incoming vertical section (3) of the SEN via horizontal bore (4). The horizontal bore (4) joining vertical section (3) of the SEN and two strand of nozzle (5a and 5b) in a manner so as to divide the incoming flow from vertical section of the SEN equally. The SEN has four exit ports (6) where liquid steel leaves the SEN into the caster mold.

Each strand (5a and 5b) also incorporate two oppositely directed exit ports (6) in the sidewall of the nozzle where the end of the pipe is closed. The oppositely directed exit ports are about 180 degrees apart. Each exit port comprises upper region and lower region, which are partially defined by respective downwardly slanted lips (7, 8) with an angle alpha. According to the invention, the angle alpha can vary between 10 and 45 degrees with respect to horizontal plane. The desired angle may depend on such factors as the size of the nozzle, the casting speed, the submergence depth of the nozzle and other features particular to a caster design. At the end of each strand of nozzle, a small well shaped groove (9) helps to reduce the turbulence.
Four exit ports (6) of the SEN as per the disclosed invention ensure smaller streams introduced into mold cavity in comparison to the prior art where two jets come out of bifurcated ports. This helps in faster reduction of momentum into available liquid steel in the mold cavity thus reducing the velocity near meniscus, therefore, minimizes the likelihood of entraining molten slag into the liquid steel stream.
In Fig. 5, illustrates vertically side internal view of the SEN as per the invention providing a deeper insight into the design feature. Here the two strands (5a, 5b) are shown attached to the vertical section (3) through horizontal bore (4). The body of SEN

pipe (1) extends downwards. The horizontal bore (4) joining vertical section (3) of the SEN and two strands of nozzle (5a, 5b) looks flat from this view.
Experiments were conducted to demonstrate the advantages the SEN as per the present invention over those of the conventional nozzles having bifurcated ports. Water model simulations were performed on a 0.4 scale-down water model caster as per the laws of physical modeling as depicted in Fig 6. The experiments were carried out for a typical caster casting speed of 1.5m/min, slab caster dimension of 1500 x 210 mm2. The time averaged fluid velocity distribution along the mold width direction just under the meniscus was measured as shown in Fig. 7.
Water was used to model steel because it has a similar kinematic viscosity to molten steel enabling the water to exhibit similar flow properties for modeling purposes. In order to achieve the dynamic similarity between the water model and the steel prototype system, the Froude similarity was used,

Where m denotes model (water modeling), and p denotes prototype (molten steel system), U is the characteristic velocity, L is the characteristic length.
For the current study, λ=Lm/Lp=1:2.5, Eq.(1) gives


Thus, the flow rate ratio between the model and the prototype can be calculated by,

The flow rate used in the water modeling can be derived from the casting speed using Eq.(3) and is shown in Table 1. Water modeling experiments were carried out for the steel casting speed of 1.2-1.8 m/min.
Table 1: Flow rate used in the water modeling experiments

Figure 8 compares physical modeling results of the SEN as per the present invention with a prior art SEN type having a 150 downward ports. Fluid velocities along the direction of mold width and slightly below the meniscus were measured using velocity probes to determine the fluid velocity distributions. It was found that the steel velocity near the meniscus is substantially lower for the SEN as per the present invention than it is for the prior art SEN. The two strand nozzle in the disclosed invention is able to direct flow out of the SEN in a desired way. It can be seen from the graph that the peak velocity has shifted away from SEN. This indicates less chances of molten flux being dragged into liquid steel pool due to the vortex formation phenomena near SEN. A

properly designed and controlled upward flow from the SEN as per the present invention gives an optimized performance in terms of heat supply and meniscus behavior. This minimizes disturbances to the meniscus thus reduces the likelihood of entraining particles from upper lying mold molten flux layer into the recirculating liquid steel stream in the mold to avoid defects such as slivers in final steel products. Further, with the use of the nozzle of the present invention, it is possible to improve the quality of a steel product made by using the nozzle, and ensure a stabilized casting process operation.
Although the description of the present invention has been done with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.

WE CLAIM :
1. An improved double strand-four port submerged entry nozzle (SEN) for pouring molten steel into a continuous casting mold to control fluid flow condition inside the mold, the said SEN comprising;
two vertical strands (5a, 5b) in the form of pipes or tubes having an inlet (2) for receiving an incoming flow of liquid steel from a tundish through a vertical bore (3) leading to the middle of a horizontal bore (4) joining the said strands (5a, 5b) closed (10) at the bottom; Characterized in that,
the horizontal bore is configured to join vertical central bore (3) and the two strands (5a, 5b) symmetrically to divide incoming flow of molten metal equally in each strand (5a, 5b),
wherein two oppositely directed exit ports (6) are disposed on each of the strands (5a, 5b) for delivering liquid steel into caster mold, wherein at the end of each strand tube (5a, 5b), a small well shaped groove (9) is disposed for reducing turbulence, wherein
the shape of the exit port (6) is configured horizontal having ratio of total port area to bore area in the range of 2 to 3 for ensuring the optimal sub meniscus velocity sufficiently high as to prevent the freezing of the steel and melts sufficient mold flux at the meniscus.

2. An improved strand-four port SEN as claimed in claim 1, wherein SEN is made of refractory material.
3. An improved strand-four port SEN as claimed in claim 1, wherein each exit port comprising upper region and lower region defined by respective downwardly slanted lips (7, 8) with an angel α (alpha) varying between 10 to 45 degrees with respect to horizontal plane.
4. An improved strand-four port SEN as claimed in claim 1, wherein the distance ‘L’ between the strands is 3 to 5 times of internal diameter ‘d’ of each strand bore that is L=3d to 5d.
5. An improved strand-four port SEN as claimed in claim 1, wherein twice the cross section area (d) of each strand tube (5a, 5b) is greater than that of vertical central straight bore (D) of incoming vertical section (3) that is 2d>D.