FR2695848A1 - Metal casting nozzle and methods of manufacturing this nozzle. - Google Patents

Abstract

Casting tube for metal, including a body (22) made from refractory material, in which a flow channel (24) for the molten metal is provided. The tube includes an annular chamber (32) provided in the body (22), arranged around the channel (24) in the vicinity of the periphery of this channel, extending virtually over the entire length of the channel, connected to means (34) for creating a reduced pressure (vacuum) with respect to the environment of the tube. The chamber (32) forms a screen to the migration of gaseous products, such as carbon monoxide, towards the channel. The tube may also include a sleeve (30) made from refractory material interposed between the periphery of the channel (24) and the chamber (32). The tube is used preferably for the continuous casting of steel.

Description

The present invention relates to a metal casting nozzle and

  manufacturing processes for this nozzle. It applies in particular to the continuous casting nozzles of steel, in particular of steel calmed with aluminum. Conventionally, a casting installation

  continuous steel comprises at least one ingot mold

  mented by a distributor of molten steel.

  The molten steel flows into the ingot mold through the channel of at least one nozzle fixed to the bottom of the distributor, in line with the upper opening of the ingot mold. To withstand thermal stresses in contact with molten metal, the nozzles are usually made of a refractory material. The nozzles are also covered with layers of internal and external enamel to prevent oxidation of the refractory material during the usual preheating of the nozzles and also making the material waterproof

  porous refractory during use of nozzles.

  Depending on the grade of the cast steel or the type of

  material constituting the nozzles, there are problems

  mes of degradation of the nozzles by corrosion, or problems of plugging of the nozzles by deposits of oxides on the surface of the steel flow channel These deposits of oxides include for example alumina,

  lime aluminate or alumina titanate.

  It is known to manufacture nozzles in a refractory material of vitreous silica (Si O 2). Nozzles manufactured in this material resist well to thermal shocks and to plugging by deposits of oxides, but resist little corrosion by certain nuances.

  of steel containing, for example, manganese.

  It is also known to manufacture nozzles in a composite material comprising mainly alumina (A 1203) and graphite associated by a carbon bond. These nozzles usually comprise between 20 and 30% by mass of graphite The high graphite content

  promotes the resistance of these nozzles to thermal shocks

  The latter also resist wear well.

  On the other hand, the alumina-graphite nozzles are blocked

relatively quickly.

  The closure of the nozzles is particularly rapid when the cast steel is calmed with aluminum. In this case, deposits of oxides essentially containing alumina are formed in the nozzle channel. This limits the sequence lengths and can lead to when pouring stops in the event of complete clogging of the nozzles. In addition, a certain amount of the deposited oxides is likely to be entrained by the cast steel and therefore to form inclusions degrading the properties.

metallurgical of steel.

  In order to understand the phenomenon of blockage,

three tests were carried out.

  On the one hand, an alumina-carbon rod was immersed for two hours in a bath of XC 38 steel at 15,500 C to which 0.25 * of aluminum was added, in a

  enclosure under controlled atmosphere.

  After two hours, there is the presence of a

  deposit of alumina on the walls of the bar.

  On the other hand, we plunged an alumina bar

  pure, carbon-free in the same bath for two hours.

  After two hours, no deposit is found on

the bar.

  Finally, we immersed an alumina-carbon rod coated with a thick layer of pure alumina in the bath

steel for two hours.

  After two hours, there is a deposit of aluminum.

mine on the bar.

  Given these tests, the idea accepted so far

  whereas while the plugging of the nozzles was due solely to the alumina contained as inclusions in the cast steel which sticks to the refractory wall of the nozzle,

is false.

  In fact, if that were the case, the aluminum bar

  pure mine should have a deposit after two hours like the alumina-carbon bar coated with a thick layer

pure alumina.

  In fact, the plugging of the nozzles is due to two phenomena: the alumina contained as inclusions in the steel sticking to the refractory walls of the nozzle, the aluminum contained in the steel which when it enters contact with the walls of the nozzle oxidizes

  to form alumina A 1203 and germinate against the wall.

  Indeed, by immersing a sample consisting of an alumina graphite rod in a bath of molten steel containing elements eager for oxygen such as aluminum, the chemical equilibria described below are observed. The alumina-graphite sample contains impurities in the form of oxides (Si O 2, Na 2 O, K 20,) which are reduced by the carbon C of the sample to form

carbon monoxide CO gas.

  CO is released on the surface of the sample

  and dissociates into intermediate elements lCl and lOl.

  This dissociation on the surface of the sample locally disturbs the balance between the elements lCl and lOl contained in the steel bath. The oxygen-hungry elements of the bath are then oxidized by the released oxygen and therefore precipitation and growth d on the surface

of the sample.

  In the case of a steel bath calmed with aluminum

  nium, we have in particular: in a region distant from the surface of the sample, the following stable chemical equilibria: 2 lAll + 3 l O l> A 1203 lCl + lOl> CO

  in a region close to the surface of the sea-

  sample, an evolution of the chemical equilibria in the following direction: CO (gas)> lCl + l O l 2 lAll + 3 l O l> A 1203 (precipitate) In the case of a nozzle manufactured with the material A 1203-C , carbon monoxide dissociates on the surface of the steel flow channel and causes on this surface the precipitation of oxides, in particular of alumina, produced from elements contained in the cast steel, in especially aluminum Deposits

  oxides gradually block the nozzle channel.

  In addition, carbon monoxide is formed not only from oxygen from the impurities in the form of oxides contained in the nozzle, but also

  from the oxygen in the air surrounding the nozzle.

  The oxygen in the air infiltrates through the junction of the nozzle and the distributor and through the walls of the nozzle made of porous refractory material The oxygen in the air combines with the carbon contained in the nozzle to form carbon monoxide gas which migrates on the surface of the channel This migration is favored by the depression created in the channel by the flow of steel

liquid.

  The object of the invention is to remedy the clogging of the nozzles made of refractory material comprising in particular alumina-carbon, by avoiding the formation of oxide deposits on the surface of the flow channel for molten metal, this with means simple and easy to put on

in action.

  To this end, the subject of the invention is a metal casting nozzle, in particular of continuous steel casting, comprising a body of refractory material in which is formed a liquid metal flow channel, characterized in that it has an annular chamber

  formed in the body, arranged around the proximal canal

  mite from the periphery of this channel, extending roughly over the entire length of the channel, connected to means for depressurizing relative to the environment of the nozzle, so that the chamber forms a screen for the migration of gaseous products such as monoxide

carbon to the channel.

  According to other characteristics of this invention: the nozzle comprises a jacket, made of refractory material, interposed between the periphery of the channel and the annular chamber, the jacket is made of the same refractory material as the body of the nozzle, or else, the jacket is made of a carbon-free refractory material,

  the body is made of a composite material

  site including alumina and graphite.

  The invention also relates to methods

  manufacturing a nozzle as defined above.

  According to a first manufacturing process: the nozzle is produced by isostatic pressing of a refractory material in which is incorporated a fusible element occupying the volume of an annular chamber which it is desired to provide around a metal flow channel in fusion,

  the whole of the nozzle is cooked at a temperature

  high rature melting the fusible element so as to

  release the volume forming the annular chamber.

  According to a second manufacturing method, a tubular insert and a tubular nozzle body are manufactured separately, by isostatic compression and curing of refractory materials, the insert being intended to delimit a flow channel for the molten metal; the insert is fixed in the body coaxially to the latter so that the free space between the insert and

  the body forms an annular chamber around the canal.

  The invention will be better understood using the

  description which follows, given only as

  example and made with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of part of a continuous steel casting installation comprising a nozzle according to the invention; Fig 2 is a longitudinal sectional view, on a large scale, of the nozzle according to the invention;

  Figs 3 to 5 are sectional views along

  dinal representing elements used for the manufacture-

tion of nozzles according to the invention.

  FIG. 1 shows a part of a continuous steel casting installation designated by the

  general reference 10, intended for example for the manufacture

  cation of metallic semi-finished products such as blooms or

slabs.

  Conventionally, the installation comprises a distributor 12 of molten steel supplying an ingot mold 14 comprising an upper mold 16 and rollers 18 for driving and guiding the semi-finished product during solidification. The distributor 12 is itself supplied with molten steel by a ladle not shown in the figure. The molten steel flows by gravity into the ingot mold 14, passing through at least one nozzle 20 according to the invention, fixed, by known means, on the bottom of the distributor 12 in line with the upper opening.

of the mold 14.

  We will now describe in more detail the nozzle

20 with reference to FIG. 2.

  The nozzle 20 comprises a nozzle body 22, of generally tubular shape, made of a material

  refractory, preferably a composite material

  mainly from alumina (A 1203) and graphite

(VS).

  The body 22 comprises a channel 24 for the flow of

  molten steel The channel has an upper end

  lower 26 intended to be connected, by known means, to a steel flow orifice of the distributor, and a lower end 28 forming two branches 28 A,

  28 B opening to the outside of the nozzle by orifices

these diametrically opposite.

  The periphery of channel 24 is delimited over almost the entire length of the latter by the surface

  internal of a cylindrical jacket 30, made of refractory material

  shut up, fixed in the nozzle body 22 by means and

  processes which will be described later.

  An annular chamber 32, coaxial with the channel 24, surrounds the outer surface of the jacket 30 extending approximately over the entire length of the latter. The wall of the chamber 32 has a small thickness compared to

  to the thickness of the wall of the nozzle body 22.

  The end branches 28 A, 28 B of the channel, are also surrounded by corresponding parts of the

shirt 30 and chamber 32.

  The chamber 32 is arranged in the vicinity of the periphery of the channel 24, being separated from this channel by the wall of the jacket 30 interposed between the periphery of the

canal and bedroom.

  Conventionally, the internal and external surfaces of the nozzle are covered with layers of enamel, not shown in the figures, so as to preserve the nozzle against oxidation and to waterproof the

  porous surfaces of refractory materials.

  Chamber 32 is connected via an orifice 34 to a vacuum source of known type, not shown in the figures, for the depression of

  the chamber in relation to the environment of the nozzle.

  Also shown in Fig 2, a ring 36, conventionally arranged around the body 22

  nozzle, consisting of a refractory product, generally

  graphite zirconia ral, intended to resist corrosion

by the mold powder.

  In the example described, the nozzle 20 has an external diameter of 100 mm, the channel 24 has a diameter of mm, the wall of the jacket 30 has a thickness of 4 mm and the wall of the annular chamber 32 has a thickness of 2 mm. Room 32 allows, on the one hand, to collect

  gaseous products, in particular carbon monoxide

  ne, forming in the refractory material of the nozzle body 22 and migrating towards the channel 24, and, on the other hand,

  to evacuate these gaseous products through orifice 34.

  According to a first embodiment of the in-

  vention, the jacket 30 is made of a refractory material, identical to that of the body 22 of nozzle, comprising alumina and graphite In this case, the shirt 30 may have come in one piece with the body 22 and

form a single block with it.

  In addition, the amount of carbon monoxide

  which forms in the wall of the jacket 30 is neglected

corn.

  According to a second embodiment of the in-

  vention, the jacket 30 is made of a carbon-free refractory material comprising, for example, alumina, zirconia, aluminum nitrides (Al N) or boron (BN), spinels, magnesia, of

  borides, in particular zirconium (Zr B 2).

  Thus, in the absence of carbon, there is no formation of carbon monoxide in the wall of the

  jacket 30 separating the chamber 32 from the channel 24.

  We will now describe two manufacturing processes.

  cation of a nozzle according to the invention, opposite the

Figures 3 to 5.

  The first manufacturing process makes it possible to produce a nozzle in which the jacket 30 has come integrally with the body 22 and forms a single block with this

  last This process includes the following steps.

  Firstly, the nozzle is produced by isostatic pressing of a refractory material in which is incorporated a fusible element 32 A occupying the volume of the annular chamber 32 which it is desired to provide in the

nozzle (see Fig 3).

  The 32 A fuse element is manufactured for example

  made of a polymer material or wax.

  The whole is then baked at a high temperature of around 10,000 melting the polymer. The molten polymer flows through the wall of porous refractory material and releases the volume which it originally occupied. This volume forms an annular chamber around

of the nozzle channel.

  A nozzle 20 is then obtained as shown substantially in FIG. 2, the jacket 30 being

coming of matter with the body 22.

  The second method of manufacturing the nozzle

includes the following steps.

  A tubular insert 30 and a tubular body 22 of nozzle, as shown in FIGS. 4 and 5 respectively, are produced separately by isostatic pressing and curing of refractory materials, according to a

known process.

  The insert 30 is then fixed in the body 22 coaxially with the latter, for example with a cement of known type, so that the free space between the insert 30 and the nozzle body 22 forms an annular chamber.

around the nozzle channel.

  As can be seen in Fig 4, the insert and manufactured in three parts, a first part 30 A,

  coaxial with the body being introduced by the upper end

  body and the other two parts 30 B, 30 C, forming the branches of the insert, being introduced by

the lower holes of the body.

  The invention is not limited to the modes of

realization described.

  The nozzle body and the inner liner can be made from a variety of refractory materials.

  The nozzle can be used in instal-

  continuous or discontinuous casting lations and can supply

  lie in molten metal ingot molds of various types.

  The invention has many advantages.

  The clogging of a conventional nozzle being done

  by oxidation of the carbon contained in the material

  fractional, the annular depression chamber of a nozzle according to the invention makes it possible to avoid migration of the

  carbon monoxide gas in the nozzle channel.

  By manufacturing the inner jacket of the nozzle in a carbon-free refractory material, the formation of gaseous carbon monoxide is avoided at the periphery of the channel and, in the case of a continuous casting of very

  low carbon content, unwanted transfer is avoided

  ble of carbon in the steel passing in the channel of the nozzle.

Claims (6)

RESELL I CAT IONS   1 metal casting nozzle, in particular of continuous steel casting, comprising a body (22) of refractory material in which is formed a liquid metal flow channel (24), characterized in that it comprises an annular chamber (32) formed in the body (22), disposed around the channel (24) near the periphery of this channel, extending almost over the entire length of the channel (24), connected to means (34) depression in relation to the environment of the nozzle, so that the chamber (32) forms a screen for the migration of gaseous products such as carbon monoxide carbon towards the channel (24).   2 nozzle according to claim 1, character-   risée in that it comprises a jacket (30), of refractory material, interposed between the periphery of the channel (24) and the annular chamber (32).   3 nozzle according to claim 2, characterized in that the jacket (30) is manufactured in the same   refractory material as the nozzle body (22).   4 nozzle according to claim 2, character-   laughed at in that the shirt (30) is made in a   carbon-free refractory material.   Nozzle according to any one of claims 1 to 4, characterized in that the body (22) is   made of a composite material comprising aluminum mine and graphite.   6 A method of manufacturing a metal casting nozzle, in particular of continuous steel casting, characterized in that: the nozzle is produced by isostatic pressing of a refractory material in which is incorporated a fusible element (32 A) occupying the volume of an annular chamber (32) which it is desired to provide around a flow channel for the molten metal, the entire nozzle (22) is baked at a high temperature melting the fusible element so as to release a volume forming the annular chamber (32).   7 A method of manufacturing a metal casting nozzle, in particular of continuous steel casting, characterized in that: a tubular insert is manufactured separately   (30) and a tubular body (22) of nozzle, by compression   isostatic sion and baking of refractory materials, the insert (30) being intended to delimit a channel (24) for the flow of molten metal; the insert (30) is fixed in the body (22) coaxially with the latter so that the free space between the insert (30) and the body (22) forms a chamber   annular (32) around the channel (24).