AU753291B2

AU753291B2 - Ladle nozzle for continuous casting

Info

Publication number: AU753291B2
Application number: AU92787/98A
Authority: AU
Inventors: Vincent Boisdequin
Original assignee: Vesuvius Group SA
Current assignee: Vesuvius Group SA
Priority date: 1997-10-20
Filing date: 1998-10-14
Publication date: 2002-10-17
Anticipated expiration: 2018-10-14
Also published as: DE69804003D1; CN1276746A; CA2305495A1; EP1028822A1; TR200001045T2; PL187078B1; KR20010031195A; SK5472000A3; AU9278798A; BR9812942A; NZ503979A; WO1999020420A1; FR2769861A1; ES2172919T3; EP1028822B1; JP2001520123A; CN1121919C; ATE213677T1; KR100585245B1; PL340260A1

Abstract

The invention concerns continuous steel casting. It concerns a ladle nozzle for continuous casting comprising, in a downstream zone, a first part (3) with substantially constant cross-section and, upstream of said first part, a second part (4) with substantially divergent cross-section. The invention is particularly applicable to continuous steel casting.

Description

1 LADLE NOZZLE FOR CONTINUOUS CASTING The present invention relates to a ladle nozzle for continuous casting.

Numerous types of nozzles are known, used in continuous casting installations to allow the teeming of the liquid steel between the continuous casting ladle and the distributor. Amongst those most widely used one could cite straight nozzles, convergent nozzles, so-called "Bell Shape" and the nozzles known as "Elephant Foot".

In order to resist the attack by the molten steel these nozzles are made of high-quality refractory materials. The flow of the molten steel in such a nozzle is at one and the same time very unusual and of variable geometry.

One finds in particular at this point that this flow, which takes place in a non-uniform manner, often gives rise to detachment of the boundary layer, even to regions of negative speed, this being at an overall mean speed of the order of metres per second. All this depends on a number of parameters, of which the material configuration at the head of the nozzle (the presence of a valve plug in the ladle in particular), and the detailed geometry of the nozzle. Moreover the dynamic behaviour of the jet on the bottom of the distributor has the effect of giving rise to vibrations, which are all the stronger if the nozzle is convergent. These vibrations produce constraints which, added to the aggressive nature of the medium, can be translated into rupture of the nozzle, especially if the latter is rigidly secured (without any degrees of freedom in rotation) to the valve on the ladle.

Thus, a nozzle which no longer gives satisfactory teeming has to be replaced, which is a delicate operation and expensive in terms of production. It results in considerable practical difficulties.

The invention aims to provide an improved ladle nozzle for continuous casting, avoiding these drawbacks as far as possible.

Furthermore in the installation of each casting ladle, the nozzle has to be able to be placed on the valve of the ladle, which blocks the outlet passage of the ladle towards the nozzle.

Each ladle filled with steel contains a plug mass made of refractory sand which is interposed between the molten steel and the plug, obstructing the pouring hole situated at the base of the ladle. On opening of the plug this plug mass has to be able to escape totally, passing through the plug and the ladle nozzle, and, without the nozzle being blocked, has to avoid any reflection of the pressure wave linked to the start of the teeming of the steel ("blow back").

The aim of the invention is also to allow the plug to be able to be opened when the end of the nozzle is already immersed in the steel of the distributor and that this should take place without a risk of blockage.

More particularly the invention also has the aim of achieving a reduction in the speed of injection of the steel between the ladle and the distributor while at the same time preserving a given flow rate. The applicants have observed that one can thus suppress the momentary dynamic effects resulting from the impact of the jet on the base of the distributor, and thus limit or even eliminate the vibrations of the nozzle itself, and therefore the risk of rupture. Moreover there is also favoured the (beneficial) decantation into the distributor, modifying the structure of the teeming into the heart of the latter. Moreover the shape of the nozzle makes it possible to avoid blockage by the sand which constitutes the plug mass.

With this in mind, the invention has as its subject a ladle nozzle for continuous casting characterised by the fact that it comprises, in a downstream region, a first portion having a substantially constant crosssection and upstream of the said first portion a second portion of section which is relatively divergent towards the downstream region.

One will note in the first place that the first portion, of which the crosssection is substantially constant, could all the same be slightly divergent or convergent. An example will be given below.

As far as the second portion is concerned, its cross-section is relatively divergent, by which is meant that it is more divergent than the first portion.

Its internal transverse cross-section downstream is identical with the upstream internal transverse cross-section of the first portion, such as to form a continuous passage.

V Other features and advantages of the invention will become apparent by a •study of the detailed description which follows, and the accompanying 20 drawings, in which: Figure 1 is a longitudinal section through one particular embodiment of a nozzle according to the invention, and o 25 Figure 2 is a view of the end, looking in the direction of the arrow A, of 0.go oo the nozzle of Figure 1.

The accompanying drawings are, essentially, of a certain character and the invention brings in the matter of shapes. Consequently the drawings can 4 serve not only for a better understanding of the description but also as a contribution to defining the invention, where appropriate.

Figure 1 is an axial section through a ladle nozzle for continuous casting comprising, in a known manner, a collar portion 1 for connecting to the casting ladle and a tubular conduit 2, here of varying circular cross-section.

The tubular conduit 2 is made up in itself of a first downstream portion 3 of substantially constant cross-section, at the distributor end, and a second upstream portion 4 which is divergent and at the casting ladle end. The portions 3 and 4 are connected together in a plane 5 where their sections are identical, at least on the inside.

In fact, in the embodiment illustrated, the portion 3 defined as having a substantially constant cross-section, is in this case very slightly divergent with an apex angle of 20. The upstream portion 4 is divergent with an apex angle of 100.

Equally, in the embodiment illustrated, both the portion 3 and the portion 4 have a divergence which is substantially constant and thus have the shape of truncated cones.

As for the internal shape it is possible to envisage other forms having varying divergence: For example instead of the rectilinear generatrix of the truncated cone one could envisage an exponential generatrix, or more generally any other provided that it defines divergence overall.

Moreover the thickness of the wall of the nozzle in the region 3 is preferably substantially constant. Preferably it is the same for the portion 4.

However the external shape of the nozzle could be modified as a function of the requirements, or considerations other than those connected with the teeming.

It should also be noted that upstream of the portion 4 the casting ladle nozzle which is illustrated has another portion 6, adjacent to the collar 1 and which, like the portion 3, has a substantially constant cross-section, in fact it also is very slightly divergent. The portions 4 and 6 are joined together in a plane 7 where the downstream cross-section of the portion 6 is identical with the upstream cross-section of the portion 4, at least on the inside.

Finally the left-hand end of the nozzle is very much preferably enclosed externally in a sheet metal reinforcement which follows its shape.

The portion 3 of the nozzle has a length which is preferably equal to about three times its downstream diameter. For its part the portion 4 has a length which is in particular a function of its angle of divergence and of a desired exit diameter.

The nozzle could be made in particular of graphited alumina or other refractory materials used in steelworks.

The applicants, have observed that the liquid steel entering the nozzle leaves it in a uniform manner with a speed which is lower than the speed of entry. The ratio of the mean speeds of flow is equal to the ratio of the portions and, consequently, equal to the square of the ratio between the diameters since in the present case the nozzle is of round cross-section.

Moreover because of the shape of the nozzle no solid powdered or granulated mass (in particular the plug mass) can become blocked.

The present invention is of particular interest where a plug valve is used in the ladle. The shape of the nozzle is preferably matched to the characteristics of flow at the outlet of this valve.

Although it is possible to envisage manufacturing in a one-piece fashion by isostatic pressing, at least in certain cases, the applicants actually prefer to perform the fabrication of the nozzle in two parts or more, subsequently assembled together in a known manner. Certain, at least, of these portions could be produced by isostatic pressing.

Although the shapes, in particular on the inside, are important, the present invention is not limited to the embodiment described, which could be adapted, in particular in dimensional terms, by a person skilled in the art.

Thus, in the particular embodiment described the said first portion is divergent at an apex angle of the order of 20. However another angle preferably small, in particular zero or convergent, can be envisaged, provided that one is left with a mean angle less than a threshold of the order of More generally, the said second portion is divergent at an apex angle lying between about 10 and about 200, preferably between about 30 and about 140, and in particular between about 60 and about 100.

Furthermore the invention can be applied when the obturating means are other than a ladle valve.

Likewise generalising the dimensions, the said first portion has a length lying between about one and about five times its greatest transverse dimension, preferably between about twice and five times and 7 advantageously between about twice and about four times its greatest transverse dimension.

The shape of the transverse cross-sections of the first and second portions of the nozzle perpendicular to its axis could be anything, with a reservation that they have sufficient continuity. All the same it is preferably substantially oval, for example substantially elliptical or more precisely substantially circular.

Claims

1. Continuous casting nozzle from a ladle to a distributor having a downstream end opening which is substantially oval in transverse cross- section, and designed to operate immersed in the distributor, characterised in that it has, in a downstream region, a first portion of substantially constant cross-section and, upstream of the said first portion, a second portion of section which is relatively divergent towards the downstream region.

2. Nozzle according to claim 1, characterised in that the said first portion has a mean apex angle less than a threshold of the order of 2°.

3. Nozzle according to one of claims 1 and 2, characterised in that the 'said second portion is divergent at an apex angle lying between about 1° a. and about 20°.

4. Nozzle according to claim 3, characterised in that the said second portion is divergent at an apex angle lying between about 3" and about 14°. Nozzle according to claim 4, characterised in that the said second 0100 portion is divergent at an apex angle lying between about 6° and about 10 o o

6. Nozzle according to one of claims 1 to 5, characterised in that the said first portion has a length which is between one and five times its greatest transverse dimension. 9

7. Nozzle according to claim 6, characterised in that the said first portion has a length lying between about twice and about five times its greatest transverse dimension.

8. Nozzle according to claim 7, characterised in that the said first portion is of a length which is between about twice and about four times its greatest transverse dimension.

9. Nozzle according to one of claims 1 to 8, characterised in that at least one of the said first and second portions has a substantially oval transverse section. Nozzle according to one of claims 1 to 8, characterised in that at least one of the said first and second portions has a circular transverse 15 section. *0 0e *S* o 5o *ooo