EP0913219A1 - Method for pouring molten metal in a conduit comprising at least two refractory parts - Google Patents

Abstract

A process in which, during the flow of molten metal in a conduit an inert gas and oil are injected at the position of the joint plane between two refractory parts in such a manner as to prevent the introduction of gases from the atmosphere into this conduit at the position of the joint plane. Apparatus. Advantages: plugging of leaks at the position of the joint plane, lower inert gas consumption absence of degradation of the quality of the molten metal by the inert gas.

Description

The invention relates to a method and a device for sealing the plane. of joint between two adjoining refractory pieces of a flow duct of molten metal.

For the casting of steel from a pocket in an ingot mold, steel is drained from the bottom of the pocket through a flow adjustment drawer, then flows into a distributor through a protective jet tube; steel is then drained from the bottom of the distributor through an internal nozzle, then flows through an external nozzle into the mold.

Along the steel casting circuit, there are then two joint planes of joined refractory pieces: a joint plane between two refractory plates of the pocket drain drawer and a joint plane between the two nozzles internal and external refractories.

A pocket drain flow adjustment drawer has indeed generally two adjoining refractory plates, sliding one on top of the other in a plane perpendicular to the direction of flow of the molten metal, which are each with a hole; by sliding the plates, the surface is adjusted covering the two holes so as to regulate the steel flow.

• dans FR 2 560 085, à proximité du plan de joint des plaques réfractaires, on forme des cavités dans lesquelles on dispose ou on injecte des hydrocarbures (exemple : poix solide, graisse, ou gaz méthane) ; ces hydrocarbures cheminent à travers les pores du réfractaire, notamment jusqu'aux surfaces jointives des plaques et « empêchent ainsi dans une large mesure la pénétration d'acier en fusion entre les plaques » (effet d'étanchéification) « tout en assurant un effet lubrifiant qui évite les détériorations liées au frottement » (page 2, lignes 24 à 30).
• dans FR 2 415 507, par l'intermédiaire d'un canal annulaire pratiqué dans le plan de joint de pièces réfractaires formant un conduit de coulée, on injecte un gaz inerte (argon), afin de régler le débit de coulée de métal (notamment afin de maítriser l'effet de sur-vitesse en début de coulée) ; le gaz injecté se retrouve dans le conduit de coulée.
• dans FR 2 529 493, on rappelle que les plaques réfractaires de ces tiroirs sont généralement en alumine, zircon ou magnésie, généralement graphité, et sont soigneusement imprégnées de goudron sous vide ; on indique que le passage du métal dans le tube de coulée entraíne une aspiration d'air entre les plaques et provoque ainsi une dégradation sensible de la propreté inclusionnaire du métal coulé ; on décrit un dispositif comportant, au niveau du plan de joint entre les pièces réfractaires (« zone à lubrifier et à protéger »), un canal annulaire circulant autour du tube de coulée ; pour améliorer l'étanchéité et limiter les aspirations d'air, on injecte dans ce canal annulaire de la matière « lubrifiante et protectrice » (exemple : brai, dérivé de la distillation du charbon ou du pétrole); cette matière « se répand dans l'interstice entre les plaques » (page 4, ligne18).

The documents FR 2 560 085, FR 2 415 507 and FR 2 529 493 describe drawers for adjusting the drain flow rate:

• in FR 2 560 085, near the joint plane of the refractory plates, cavities are formed in which hydrocarbons are disposed or injected (example: solid pitch, grease, or methane gas); these hydrocarbons travel through the pores of the refractory, in particular to the joining surfaces of the plates and “thus largely prevent the penetration of molten steel between the plates” (sealing effect) “while ensuring a lubricating effect which avoids deterioration linked to friction ”(page 2, lines 24 to 30).
• in FR 2 415 507, via an annular channel formed in the joint plane of refractory pieces forming a pouring duct, an inert gas (argon) is injected, in order to regulate the metal pouring rate (in particular in order to control the effect of overspeed at the start of casting); the injected gas is found in the pouring pipe.
• in FR 2 529 493, it is recalled that the refractory plates of these drawers are generally made of alumina, zircon or magnesia, generally graphite, and are carefully impregnated with tar under vacuum; it indicates that the passage of metal in the pouring tube causes an air suction between the plates and thus causes a significant deterioration of the inclusiveness of the cast metal; a device is described comprising, at the joint plane between the refractory parts (“area to be lubricated and to be protected”), an annular channel circulating around the pouring tube; to improve the seal and limit the air intake, injected into this annular channel "lubricating and protective" material (example: pitch, derived from the distillation of coal or petroleum); this material “spreads in the gap between the plates” (page 4, line 18).

The joining surface of two internal and external refractory nozzles poses the same sealing problems as the two refractory plates adjoining a drain drawer; like the external nozzle, made of material refractory, must be able to be changed during casting (using a nozzle exchange device), this nozzle therefore has a joint plane or contiguous surface with the internal nozzle.

If the seal is not sufficiently ensured between two elements joined refractories of the liquid metal circuit, the depression created in the pouring duct by the flow of liquid steel causes, at the level of joint planes of the refractory parts of the circuit, of the external gas aspirations.

To prevent certain gases from the atmosphere, such as oxygen or nitrogen, do not penetrate at this level in the molten metal circuit, we inject generally, at the contiguous surface, an inert gas, such as argon ; the injected gas is therefore found in the molten metal circuit.

Thus, at the joint planes where contiguous surfaces of parts successive refractories of a liquid metal casting circuit, provision is made generally an annular inert gas diffusion channel going around the liquid metal conduit at this location.

This annular channel is connected to a through feed pipe towards the outside of the nozzles; it is itself connected to means for injecting inert gas.

During the pouring of liquid metal, we therefore maintain, in this channel annular, a flow of inert gas intended to be aspirated at the level of the joins refractory pieces of said circuit, so as to avoid at this location gas infiltration from the atmosphere into the liquid metal circuit.

The flow of inert gas is even generally high enough to that part of the inert gas escapes even towards the outside of the joint plane, ie towards the atmosphere.

The disadvantage of such a process is that it consumes quantities significant inert gas.

Another disadvantage is caused by the inert gas in the metal flow liquid: this gas can have harmful effects on the solidification of the metal (especially in the mold), which is detrimental to the quality of the metal got.

Furthermore, to improve the sealing of the joint plane and limit the air aspirations in the pouring tube, one can also inject into the joint plane of a material as described in FR 2,529,493.

To carry out this injection, circulation means are then used practiced in one of the refractory elements so as to reach the plane of joint or interface between the refractory elements and means for sending this matter through these means of circulation.

The disadvantage of the device described in FR 2 529 493 is that it clogs quickly and that, in the event of blockage of the circulation means of the injected material, air may again be sucked in large quantities in the pouring tube.

The invention aims to avoid the aforementioned drawbacks.

To this end, the subject of the invention is a process for casting liquid metal. through a conduit comprising at least two adjoining refractory pieces in which, during the flow of said liquid metal in said conduit, it is injects a gas, inert with respect to said liquid metal, at the joint plane between the two said refractory pieces so as to avoid the introduction of gases coming from the atmosphere in said conduit at said joint plane, characterized in that oil is propelled or injected at the level of said plane joint using said inert gas.

• la température de craquage ou de décomposition de ladite huile est inférieure à la température dudit plan de joint à l'endroit où l'on injecte ledit gaz inerte ; de la sorte, les résidus solides de craquage ou de décomposition colmatent ledit plan de joint pour en améliorer l'étanchéité.
• ladite huile contient des particules de carbone, notamment du graphite et/ou du noir de fumée ; ces particules solides renforcent l'effet de colmatage du plan de joint.
• on injecte l'huile de manière intermittente par « doses » de volume prédéterminé ; le gaz inerte propulse chaque dose d'huile dans le plan de joint ; on diminue encore les risques de bouchage des circuits d'injection de gaz.
• si l'on injecte ledit gaz dans un canal annulaire pratiqué autour dudit conduit dans ledit plan de joint, de préférence ledit volume de dose d'huile est supérieur au volume dudit canal annulaire.
• on régule l'injection ou la propulsion d'huile en fonction de l'évaluation du niveau d'étanchéification dudit plan de joint ; on peut même supprimer complètement l'injection d'huile quand on estime avoir atteint un niveau suffisant d'étanchéité et re-déclencher l'injection d'huile quand le niveau d'étanchéité se dégrade à nouveau ; cette régulation permet de maintenir à un niveau minimum la consommation de gaz inerte et permet aussi de limiter les risques de bouchage.
• on régule l'injection d'huile en modifiant la fréquence d'injection des doses d'huile.
• on évalue ledit niveau d'étanchéification en fonction de la pression d'injection du gaz inerte ou en fonction du débit d'injection du gaz inerte ; à débit donné, une pression faible est l'indice d'une mauvaise étanchéité ; à pression donnée, un débit élevé est l'indice d'une mauvaise étanchéité.

The invention may also have one or more of the following characteristics:

• the cracking or decomposition temperature of said oil is lower than the temperature of said joint plane at the point where said inert gas is injected; in this way, the solid cracking or decomposition residues clog said joint plane to improve the seal.
• said oil contains carbon particles, in particular graphite and / or smoke black; these solid particles reinforce the sealing effect of the joint plane.
• the oil is injected intermittently in “doses” of predetermined volume; inert gas propels each dose of oil into the joint plane; the risk of blockage of the gas injection circuits is further reduced.
• if said gas is injected into an annular channel formed around said conduit in said joint plane, preferably said volume of oil dose is greater than the volume of said annular channel.
• the injection or propulsion of oil is regulated according to the evaluation of the level of sealing of said joint plane; it is even possible to completely suppress the oil injection when it is deemed to have reached a sufficient level of tightness and to re-trigger the oil injection when the tightness level degrades again; this regulation makes it possible to keep the consumption of inert gas at a minimum level and also makes it possible to limit the risks of blockage.
• oil injection is regulated by modifying the frequency of injection of the oil doses.
• said sealing level is evaluated as a function of the injection pressure of the inert gas or as a function of the injection rate of the inert gas; at a given flow rate, a low pressure is an indication of poor sealing; at a given pressure, a high flow rate indicates poor sealing.

• au moins deux pièces réfractaires successives et jointives formant une portion de conduit pour le métal liquide,
• des moyens de circulation de fluide pratiqués dans l'une au moins des pièces réfractaires pour atteindre le plan de joint desdites deux pièces réfractaires,
• des moyens d'injection de gaz inerte dans lesdits moyens de circulation,

   lesdits moyens de circulation et lesdits moyens d'injection de gaz étant adaptés pour éviter l'introduction de gaz provenant de l'atmosphère dans ledit conduit au niveau dudit plan de joint,
   caractérisé en ce qu'il comporte des moyens pour injecter ou propulser de l'huile dans lesdits moyens de circulation de gaz.The subject of the invention is also a device for pouring liquid metal capable of being used to implement the method according to the invention, of the type comprising:

• at least two successive and adjoining refractory pieces forming a portion of conduit for the liquid metal,
• fluid circulation means used in at least one of the refractory parts to reach the joint plane of said two refractory parts,
• means for injecting inert gas into said circulation means,

said circulation means and said gas injection means being adapted to prevent the introduction of gas from the atmosphere into said conduit at said joint plane,
characterized in that it comprises means for injecting or propelling oil into said gas circulation means.

According to a variant of this device, said circulation means comprise an annular channel formed around said duct in the plane of joint of said two refractory pieces and a supply duct for said channel annular opening to the outside and connected to said gas injection means.

The invention will be better understood on reading the description which will follow, given by way of nonlimiting example, and with reference to the case of junction between two adjoining refractory nozzles in a casting circuit continuous steel.

On the steel casting circuit, there is a pocket, a distributor and a ingot mold; the liquid steel of the distributor is emptied by an integral internal nozzle from the bottom of the distributor which communicates with an external refractory nozzle whose lower end dips below the level of liquid metal in the ingot mold.

The two successive refractory pieces that are the internal nozzle and the external nozzle therefore form a casting conduit element for steel liquid.

The junction plane or contiguous surface of these two parts includes a annular channel around said conduit and a supply conduit of said annular channel opening outwards.

By suitable connection means, said supply conduit is connected to inert gas injection means.

On the inert gas supply circuit, a suitable device is added to inject oil into this circuit up to the level of the annular channel.

This oil injection device can be an injection device or a device for periodic intermittent injections of "doses" oil.

As a continuous oil injection device, it is possible in particular to use a device for spraying oil droplets into the inert gas, or still an “oiler” of the type that we conventionally implant on compressed air supply circuits for pneumatic cylinders.

We will now describe the liquid metal casting process according to the invention.

In a manner known per se, steel is poured into the dispatcher; the steel contained in the distributor then flows by gravity into the mold through the conduit formed by the two refractory nozzles.

During the flow of the liquid metal in this conduit, one feeds in inert gas, for example argon, the supply duct of the annular channel, so that, if there are leaks in the junction plane of the two nozzles, only the inert gas enters the liquid metal and any risk of pollution from liquid steel by reactive gases such as oxygen or nitrogen from the atmosphere.

It should be noted that these leaks depend on the machining defects of the planes joint of the nozzles and the wear of these joint planes, resulting for example from positioning of the external nozzle when changing the nozzle.

In the case of drawers at the outlet of a pocket, these leaks depend on the wear of the two sliding plates of the drawer.

The rate of injection of inert gas into the joint plane of the nozzles therefore depends on the level of these leaks and is adapted in a manner known in itself to avoid any risk of pollution of liquid steel by gases reagents like oxygen or nitrogen.

According to the invention, using the suitable device already mentioned, therefore injecting the oil in the inert gas supply circuit so as to drive it into the annular canal and distribute it evenly over the entire circumference of this channel, from where it is then sucked or pushed, with the inert gas, through leakage interstices all around the joint plane of two nozzles on the one hand towards the center of the conduit where the liquid metal flows on the other hand towards the outside of said duct.

Like the joint plane area, especially the area between the annular channel and the inner wall of the duct, is at a very high, the oil entrained in this joint plane breaks down into particles solids which agglomerate and gradually accumulate in the interstices leak until they are completely sealed.

Gradually, this leads, thanks to the invention, to a improved if not complete sealing of the joint plane, which allows significantly reduce the consumption of inert gas; moreover, since the oil injection circuit is common to the gas injection circuit, we decrease considerably the risks of blockage encountered in the device described in FR 2,529,493; in case of insufficient clogging of the joint plane, the injection inert gas still prevents air from being drawn into the casting.

It can be seen that sealing is carried out more quickly when injects doses of oil with a volume greater than that of the annular canal and then injects these doses of oil intermittently.

There is also an improvement in the quality of the cast steel according to the invention, in particular because the amount of inert gas entrained in the liquid metal is much weaker.

Preferably, to implement the invention, an oil is chosen whose the cracking or decomposition temperature is lower than the normal temperature prevailing in the annular canal when pouring from metal in the duct.

Preferably, to implement the invention, oils are used containing suspended carbon particles, which facilitates clogging leaks.

The following examples illustrate the invention.

Example 1 :

The purpose of this example is to illustrate the method according to the invention applied to clogging of the joint plane between two steel casting nozzles.

• diamètre interne du conduit de coulée d'acier : 70 mm ;
• diamètre de l'anneau du conduit annulaire d'injection de gaz inerte : 120 mm;
• conduit annulaire de section approximativement demi-cylindrique : largeur 5 mm, hauteur 3 mm (le volume total du conduit annulaire atteint donc environ 4 cm3) ;
• nature du gaz inerte : argon ;
• nature de l'huile utilisée pour l'injection : huile référencée « TELLUS 22 » de la Société SHELL ;

The characteristics of the device at the joint plane are as follows:

• internal diameter of the steel pouring duct: 70 mm;
• diameter of the ring of the annular inert gas injection duct: 120 mm;
• annular duct of approximately semi-cylindrical section: width 5 mm, height 3 mm (the total volume of the annular duct therefore reaches approximately 4 cm3);
• nature of the inert gas: argon;
• nature of the oil used for injection: oil referenced "TELLUS 22" from the company SHELL;

The oil injection device is suitable for injecting so intermittent doses of oil with a volume much greater than that of the canal annular and so that these doses of oil are propelled by the inert gas to distribute evenly throughout the volume of the channel annular; an inert gas overpressure may be necessary for this purpose when a dose of oil is injected.

During the casting of the steel in the casting conduit, while one injects inert gas into the annular channel in a manner known per se to prevent reactive gases from entering the casting circuit, oil is therefore also injected into the inert gas circuit using the oil injection device.

Preferably, the operation of the oil injection device is controlled. so as to stop the injections as soon as the required level of sealing is reached and resume as soon as the evaluated level of sealing is no longer considered sufficient.

The level of sealing between the two nozzles is evaluated by example by measuring the supply pressure of the annular channel under flow constant, or for example by measuring the feed rate under pressure constant.

When there are leaks at the joint plane to the outside of the pouring pipe, the quantity of oil sprayed outwards into the atmosphere at the time of the injections ignites spontaneously at the level of the joint plane.

After implementing the invention, the carbon contents were analyzed of the steel obtained and no carbon recovery of this steel was observed, this which clearly indicates that the process according to the invention does not pollute carbon liquid metal.

It was indeed feared that solid particles resulting from the decomposition of the oil to be entrained in the metal during the setting of the invention.

Example 2 :

• soit de 10% en poids de graphite (granulométrie : 70% de passage au tamis de maille égale à 100 µm).
• en « noir de fumée » d'une qualité utilisée habituellement dans la « poudre de moule », c'est à dire pour la lubrification de l'acier dans les lingotières de coulée continue ; cette poudre est fournie par la Société DENAIN ANZIN MINÉRAUX.

Other conclusive tests were carried out under the same conditions as in Example 1 with the same oil, but loaded:

• or 10% by weight of graphite (particle size: 70% passage through a mesh sieve equal to 100 μm).
• in “smoke black” of a quality usually used in “mold powder”, that is to say for the lubrication of the steel in the continuous casting molds; this powder is supplied by DENAIN ANZIN MINÉRAUX.

Example 3 :

The purpose of this example is to illustrate a variant implementation of the casting method according to the invention in the case where “doses” are injected oil periodically in the inert gas supply circuit, in the case where inert gas supply means are available which can be regulated in flow and in the case where the injection of oil and inert gas is regulated according to a “target” sealing level.

• on fixe une valeur « haute » et une valeur « basse » de débit d'alimentation en gaz inerte ; la valeur « basse » peut être égale à 10% de la valeur « haute ».
• à partir de ces valeurs, on détermine et on fixe une valeur « plancher » et une valeur « plafond » de pression d'alimentation du canal annulaire ;
• on fixe également le volume de chaque « dose » injectée, la période d'injection de cette dose et un nombre maximal de doses d'étanchéification ; de préférence, ce volume est largement supérieur au volume du canal annulaire.
• on alimente le canal annulaire en gaz inerte selon un débit de gaz inerte établi à ladite valeur « haute » et, pendant la coulée du métal, on mesure la pression d'alimentation dudit canal ;
• puis, tant que la pression dans ce canal n'atteint pas le « plafond » de pression prédéterminé, à chaque période d'injection, on injecte une « dose » d'huile dans le circuit de gaz inerte de manière à propulser la dose d'huile dans le canal annulaire et à la répartir uniformément dans le volume de ce canal ; la propulsion de la dose d'huile peut nécessiter un surpression instantanée de gaz inerte.

According to this variant:

• a “high” value and a “low” value of inert gas supply flow are fixed; the “low” value can be equal to 10% of the “high” value.
• from these values, a “floor” value and a “ceiling” value for the supply pressure of the annular channel are determined and fixed;
• the volume of each “dose” injected, the period of injection of this dose and a maximum number of sealing doses are also fixed; preferably, this volume is much greater than the volume of the annular channel.
• the annular channel is supplied with inert gas according to an inert gas flow rate established at said “high” value and, during the casting of the metal, the supply pressure of said channel is measured;
• then, as long as the pressure in this channel does not reach the predetermined pressure “ceiling”, at each injection period, a “dose” of oil is injected into the inert gas circuit so as to propel the dose d oil in the annular channel and to distribute it uniformly in the volume of this channel; propelling the dose of oil may require an instantaneous overpressure of inert gas.

When the pressure measured is low, at constant flow, this means that the level of leakage is high at the joint plane of the nozzles.

• si la pression dans ce canal atteint ensuite ledit « plafond » de pression, on réduit le débit de gaz inerte qui alimente le canal annulaire à ladite valeur « basse » ;
• si ultérieurement la pression vient à chuter en dessous du « plancher » de pression, on ré-augmente le débit de gaz inerte au niveau de la valeur « haute »;
• si la pression dans ce canal n'atteint pas ledit « plafond » de pression lorsqu'on a atteint le nombre maximal de doses d'injection d'huile, on cesse les injections d'huile et on maintient le débit de gaz inerte à sa valeur « haute » ;

When the pressure measured is high, at constant flow, this means that the leaks are plugged or almost plugged.

• if the pressure in this channel then reaches said "ceiling" of pressure, the flow of inert gas which feeds the annular channel is reduced to said "low"value;
• if the pressure subsequently drops below the pressure "floor", the inert gas flow rate is re-increased to the "high"value;
• if the pressure in this channel does not reach said pressure “ceiling” when the maximum number of doses of oil injection has been reached, the oil injections are stopped and the flow of inert gas is maintained at its "high"value;

Periodic injection of large doses of oil and their application uniform throughout the volume of the annular canal prevents fouling of the annular channel, which is necessary to be able to maintain the tightness of the joint plane and restore it if necessary, especially after a change of external nozzle.

• valeur « haute » de débit de gaz inerte : 5 N.l/min. (normo-litre par minute) ;
• valeur « basse » de débit de gaz inerte : 0,5 N.l/min.
• valeur « plancher » » de pression d'alimentation : 0,2 . 10⁵ Pa.
• valeur « plafond » de pression d'alimentation : 1 . 10⁵ Pa.
• volume « nominal » d'une dose d'injection d'huile : 50 cm³.
• période d'injection d'huile : 5 minutes.
• nombre maximal de doses d'injection d'huile : 5.

If this variant is applied to the installation described in example 1 or 2, the following values can be chosen for example:

• "high" value of inert gas flow: 5 Nl / min. (normo-liter per minute);
• "low" value of inert gas flow: 0.5 Nl / min.
• supply pressure “floor” value: 0.2. 10 ⁵ Pa.
• supply pressure "ceiling" value: 1. 10 ⁵ Pa.
• “nominal” volume of an oil injection dose: 50 cm ³ .
• oil injection period: 5 minutes.
• maximum number of oil injection doses: 5.

During the implementation of the method according to the invention, it is noted that the argon supply pressure in the supply channel of the annular channel progressively passes from 0.3 10 ⁵ Pa. To 2 10 ⁵ Pa., This which indicates a good clogging of the joint plane of the two refractory nozzles.

It can be seen that the change in pressure following the injections oil can spread over several minutes.

Claims (10)

Method for casting liquid metal through a conduit comprising at least at least two adjoining refractory pieces in which, during flow of said liquid metal in said conduit, a gas is injected, inert with respect to said liquid metal, at the joint plane between the two said refractory pieces so as to avoid the introduction of gases from the atmosphere into said conduit at said joint plane, characterized in that one propels or one injects oil at said joint plane using said inert gas. Method according to claim 1 characterized in that the temperature cracking or decomposition of said oil is below the temperature of said joint plane at the place where said inert gas is injected. Method according to any one of the preceding claims characterized in that said oil contains carbon particles, in particular graphite and / or smoke black. Method according to any one of the preceding claims characterized in that the oil is injected intermittently by "doses" of predetermined volume. The method of claim 4 wherein said gas is injected into an annular channel formed around said conduit in said joint plane characterized in that said oil dose volume is greater than the volume of said annular channel. Method according to any one of the preceding claims characterized in that the injection or propulsion of oil is regulated as a function of the evaluation of the level of sealing of said joint plane. Method according to claim 6 depending on any of Claims 4 to 5, characterized in that the injection of oil is regulated modifying the frequency of injection of said doses. Process according to either of Claims 6 and 7, characterized in in that said level of sealing is evaluated as a function of pressure inert gas injection or depending on the inert gas injection rate. Liquid metal pouring device capable of being used to implement the method according to any one of the preceding claims, of the type comprising: at least two successive and adjoining refractory pieces forming a portion of conduit for the liquid metal, fluid circulation means used in at least one of the refractory parts to reach the joint plane of said two refractory parts, means for injecting inert gas into said circulation means, said circulation means and said gas injection means being adapted to prevent the introduction of gas from the atmosphere into said conduit at said joint plane,
characterized in that it comprises means for injecting or propelling oil into said gas circulation means. Device according to claim 9 characterized in that said circulation means comprise an annular channel formed around said conduit in the joint plane of said two refractory pieces and a conduit supplying said annular channel opening outwards and connected to said gas injection means.