WO2015158439A1

WO2015158439A1 - Submerged entry nozzle for continuous casting

Info

Publication number: WO2015158439A1
Application number: PCT/EP2015/025020
Authority: WO
Inventors: Ronald SCHIMMEL
Original assignee: Tata Steel Ijmuiden B.V.
Priority date: 2014-04-15
Filing date: 2015-04-15
Publication date: 2015-10-22
Also published as: EP3131692B1; EP3131692A1

Abstract

The invention relates to a submerged entry nozzle for use in continuous casting provided with a conduit, distribution zone, two lower and two upper channels and corresponding discharge openings, wherein the geometry of these parts is adapted to maintain the nozzle at all times completely filled with fluid steel resulting in a good control of the jets of fluid steel leaving the nozzle.

Description

SUBMERGED ENTRY NOZZLE FOR CONTINUOUS CASTING

Field of the invention

The invention relates to a submerged entry nozzle used in the continuous casting of steel to guide the flow of molten steel from the tundish into the mould of a continuous casting apparatus.

Background of the invention

Over the years many designs of submerged entry nozzles have been made in order to improve the flow of fluid steel into the bath of molten steel in the mould, to decrease turbulences in the mould and to adapt to a range of mould widths and casting speeds. The development continued from a nozzle with two discharge openings to a nozzle with four discharge openings. The latter nozzle having two central channels directing the fluid flow in jets to the deeper part of the mould and two channels directing the fluid flow in jets in opposite sideward directions. The submerged entry nozzle with four discharge openings has the advantage that the jets to the deeper part of the mould and the jets in sideward direction and up to the meniscus are separate jets resulting among others in that more heat is brought to the meniscus than with a nozzle with two discharge openings. With more heat at the meniscus the mould powder will melt more easily and completely preventing that inclusions in the cast product will arise.

The four jets of molten steel from a nozzle with four discharge openings will also result in four recirculation zones within the steel bath in the mould which will interact with each other and might cause instabilities in the fluid steel in the mould. Such instabilities might have a negative effect on the quality of the cast product.

Other factors that are important in the control of the fluid flow in the mould are the funnel shape of the casting mould and the electromagnetic break means to control the flow velocity in the mould. The geometry of the submerged entry nozzle however, is a dominant factor in controlling the flow in the fluid steel in the mould and the heat transfer to the meniscus. For that reason the geometry of the supply conduit of the nozzle, the distribution zone, the channels, the discharge openings and the dividers in the channels have to be tuned precisely and in relation to each other to realize an optimal flow of fluid steel in the nozzle.

Objectives of the invention

It is an objective of the present invention to provide a submerged entry nozzle that provides a well controlled symmetric flow.

It is another objective of the present invention to provide a submerged entry nozzle that minimizes the recirculation zones of the flow from the different discharge openings.

It is another objective of the present invention to provide a submerged entry nozzle wherein the filling of the subsequent parts of the nozzle is maximized.

It is another objective of the present invention to provide a submerged entry nozzle with a balanced flow ratio between upper and lower discharge openings.

It is another objective of the present invention to provide a submerged entry nozzle with a geometry that it can be manufactured easily.

Description of the invention

According to a first aspect of the invention one or more of the objectives of the invention are realized by providing a submerged entry nozzle for use in continuous casting comprising:

- a conduit with an inlet opening at the feed end and discharge openings at the discharge end,

- a distribution zone at the end of the conduit, wherein the distribution zone connects to the discharge openings at the discharge end, wherein

- the distribution zone comprises a main divider which divides the conduit in two secondary channels and secondary dividers which further divide the secondary channels,

and wherein the distribution zone has a taper seen in downstream direction and perpendicular to an axial plane defined by the longitudinal axis of the secondary channels.

It has turned out that by providing such a taper in the distribution zone that the flow of fluid metal is well guided under all circumstances, that is with different throughputs of fluid metal from the tundish, resulting in a stable flow through the entire nozzle. A stable flow in the conduit, distribution zone, channels and discharge openings results in well defined jets of fluid steel entering the bath of fluid steel in the mould allowing to control the fluid flow in the mould.

According to a further aspect it is provided that the distribution zone has a first tapered part and a second tapered part with the first tapered part upstream of the second tapered part.

It is further provided that each secondary channel is divided in a lower channel and upper channel respectively connecting to a lower discharge opening and an upper discharge opening and wherein the second tapered part starts at or near the highest level of the upper discharge openings. It turned out that this second tapered part contributes substantially to the guidance of the flow and therewith to the control of the flow.

Preferably the second tapered part is limited to the lower channels. These lower channels guide the largest part of the flow and widen in the axial plane defined by the longitudinal axis of the secondary channels and in the direction of the lower discharge openings. The combination of the second taper and the widening of the lower channels provides that the fluid flow remains fully controlled over the entire length of the lower channels.

The lower channels are designed to have a flow rate of 60-80% of the total flow rate of the lower and upper channels. The second tapered part is adapted to that flow rate and has a taper ratio in the range of 0.70-0.94 and preferably in the range of 0.76-0.88.

In order to have complete control over the fluid flow in the nozzle guiding of the flow should be controlled over the length of the nozzle starting in the conduit of the nozzle preceding the distribution zone. To that end it is provided that the conduit has a straight part followed by a tapered section connecting to the distribution zone and wherein the tapered section widens in downstream direction and parallel to the axial plane defined by the longitudinal axis of the secondary channels. In prior art nozzles this part of the conduit is divided in the same plane in parts with different tapers wherein the transition to a wider part of the conduit results in a disturbance of the flow and therewith a disturbance in the control of the flow. According to a further aspect of the invention the tapered section narrows in downstream direction and perpendicular to the direction in which the single tapered part widens with a first and second tapered part, wherein the first tapered part has a larger angle than the second tapered part. The angle of the second tapered part is < 2° and preferably < 1°. The combination of widening parallel to said axial plane and narrowing perpendicular to that direction provides that the filling of the tapered section and therewith the control of the flow in the conduit remains unaffected.

In order to avoid disturbances in the control of the fluid at the transition from the conduit to the distribution zone it is provided that the tapered section connects in the axial plane with the upper discharge openings with a continuous curvature. This curvature runs in said axial plane from the conduit to the very end of the upper channel, that is the discharge opening. The combination of the curvature and the side of the secondary divider facing the curvature define to a large extent the geometry of the upper channels. The resulting geometry is such that a complete filling of the upper channel is obtained along the whole length of the channel. This in turn results in a well defined yet into the fluid steel in the mould and therewith a good control over recirculation in the mould.

The division of the flow in upper and lower channels by means of a main divider and secondary dividers is an important feature in the geometry of the nozzle. In order to maintain control over the fluid flow in the nozzle it is provided that the main divider starts below the highest level of the upper discharge openings and that the secondary dividers start below the highest level of the main divider.

A further feature is that the secondary dividers seen in the axial plane widen in downstream direction wherein at least one of the sides of one of the secondary dividers has a curvature over part of the length of the side and wherein the side with a curvature is facing a side of the main divider. Although the curvature continues over a relatively short distance with a radius of curvature that is of the same order as the continuous curvature that runs from the conduit to the very end of the upper channel, that is to the discharge opening, it is an important feature in guiding the flow from the distribution zone into the lower channel.

This curvature of the secondary dividers is followed by a straight part up to the lower discharge opening. The straight parts of the sides of each of the secondary dividers enclose an angle in the range of 32-36° and the angle between the side of a secondary divider facing the curvature of the upper discharge opening and the central axis of the nozzle is in the range of 56-60°. This results in a geometry of the lower channels such that a complete filling of the lower channel is obtained along the whole length of the channel. This in turn results in a well defined yet into the fluid steel in the mould and therewith a good control over recirculation in the mould.

Brief description of the drawings

The invention will be further explained on hand of the example shown in the drawing, in which:

Fig.1 shows the lower part of the submerged entry nozzle, and

Fig.2 shows the distribution zone with the upper and lower channels in more detail.

Detailed description of the drawings

In fig. 1 the lower part of the submerged entry nozzle 1 is shown with part of the tapered section of the conduit 2 connecting to the distribution zone 3. The acute angle between the sides of the tapered section seen in the plane of the drawing enclose an angle in the range of 6-10°. The distribution zone is provided with a main divider 4 dividing the fluid flow in two channels which each are divided by means of secondary dividers 5,6 in upper channels 7,8 with discharge openings 9,10 and lower channels 11,12 with discharge openings 13,14. The sides of the tapered part of the conduit run with a continuous curve 16 to the upper part of the discharge openings 9,10 of upper channels 7,8.

In fig. 2 the distribution zone 3 is shown in more detail wherein the distribution zone starts at horizontal line 15 with a first tapered part which continues to about the highest level of the discharge openings 9,10 in the upper channels 7,8. From that level a second tapered part starts which continues over part or the complete length of the lower channels 11,12. Preferably the second tapered part continues over only part of the length of the lower channels 11,12 wherein the larger part of the channels 11,12 downstream of the second tapered part have flat opposite sides. Both tapered parts run in a plane perpendicular to the plane of the drawing. The tapered parts are very effective in keeping the distribution zone and the channels well filled with fluid steel. A taper ratio in the range of 0.70 - 0.76 for the first tapered part and in the range of 0.85 - 0.95, preferably in the range of 0.87 - 0.91 for the second tapered part show good results in this respect. The taper ratio's of the first and second tapered part and the length of the first and second tapered parts are preferably tailored such that the first and second tapered part have the same taper angle.

As with the lower channels 11,12 a part of the upper channels 7,8 downstream of the first tapered up to the discharge openings 9,10 have flat opposite sides.

The secondary dividers have a straight side 17 facing the continuous curvature 16 and at the opposite side a curvature 18 followed by a straight side 19. The straight sides enclose an angle a which is in the range of 32-36°. The angle β enclosed by the central axis 20 of the nozzle and straight side 17 of the secondary divider is in the range of 56-60°. This geometry of upper and lower channels with the specific angles including the tapered parts are important measures to keep the channels well filled and results in a stable flow and defined jets entering the fluid steel in the mould.

The main divider 4 is provided with inclined sides 21,22 connecting to discharge openings 13,14 to prevent that the fluid jets coming from the lower channels 11,12 would merge into another.

Claims

1 . Submerged entry nozzle for use in continuous casting comprising:

characterized in that,

the distribution zone has a taper seen in downstream direction and perpendicular to an axial plane defined by the longitudinal axis of the secondary channels.

2. Nozzle according to claim 1, wherein the distribution zone has a first tapered part and a second tapered part with the first tapered part upstream of the second tapered part.

3. Nozzle according to claim 2, wherein each secondary channel is divided in a lower channel and upper channel respectively connecting to a lower discharge opening and an upper discharge opening and wherein the second tapered part starts at or near the highest level of the upper discharge openings.

4. Nozzle according to claim 3, wherein the second tapered part is limited to the lower channels.

5. Nozzle according to one or more of claims 1-4, wherein the conduit has a straight part followed by a tapered section connecting to the distribution zone and wherein the tapered section widens in downstream direction and parallel to the axial plane defined by the longitudinal axis of the secondary channels.

6. Nozzle according to claim 5, wherein the tapered section narrows in downstream direction perpendicular to the direction in which the single tapered part widens.

7. Nozzle according to claim 6, wherein the tapered section narrows in downstream direction with a first and second tapered part, wherein the first tapered part has a larger angle than the second tapered part.

8. Nozzle according to one or more of claims 5-7, wherein the tapered section connects in the axial plane with the upper discharge openings with a continuous curvature.

9. Nozzle according to one or more of claims 5-8, wherein the main divider starts below the highest level of the upper discharge openings.

10. Nozzle according to claim 9, wherein the secondary dividers start below the highest level of the main divider.

1 1 . Nozzle according to one or more of claims 1-10, wherein the secondary dividers seen in the axial plane widen in downstream direction wherein at least one of the sides of one of the secondary dividers has a curvature over part of the length of the side.

12. Nozzle according to claim 11, wherein the side with a curvature is facing a side of the main divider.

13. Nozzle according to claim 11 or 12, wherein the sides of each of the secondary dividers enclose an angle in the range of 32-36°.

14. Nozzle according to claim 13, wherein the angle between the side of a secondary divider facing the curvature of the upper discharge opening and the central axis of the nozzle is in the range of 56-60°.

15. Nozzle according to one or more claims 3-14, wherein the distance between the highest part of the upper discharge opening and the lowest part of the lower discharge opening is in the range of 128-136 mm.

16. Nozzle according to one or more claims 7-15, wherein the radius of the curvature of the upper discharge opening is in the range of 105-111 mm.

17. Nozzle according to one or more claims 5-16, wherein the angle of the tapered section is in the range of 6- 10° .

18. Nozzle according to one or more claims 2-17, wherein the taper ratio of the second taper is in the range of 0.85 - 0.95, preferably in the range of 0.87 - 0.91.