EP0419378A1 - Apparatus for treating a static aluminium bath of large surface area using gases - Google Patents
Apparatus for treating a static aluminium bath of large surface area using gases Download PDFInfo
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- EP0419378A1 EP0419378A1 EP90420406A EP90420406A EP0419378A1 EP 0419378 A1 EP0419378 A1 EP 0419378A1 EP 90420406 A EP90420406 A EP 90420406A EP 90420406 A EP90420406 A EP 90420406A EP 0419378 A1 EP0419378 A1 EP 0419378A1
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- Prior art keywords
- bath
- rotor
- gas
- oven
- furnace
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D27/00—Stirring devices for molten material
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B21/00—Obtaining aluminium
- C22B21/06—Obtaining aluminium refining
- C22B21/064—Obtaining aluminium refining using inert or reactive gases
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
- C22B9/05—Refining by treating with gases, e.g. gas flushing also refining by means of a material generating gas in situ
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
- F27D3/00—Charging; Discharging; Manipulation of charge
- F27D3/16—Introducing a fluid jet or current into the charge
Definitions
- the present invention relates to a device for treatment by means of gas from a large surface aluminum liquid bath maintained in the stationary state in an oven.
- aluminum is understood to mean both aluminum containing the usual impurities at rates which are a function of the quality treated, and the various alloys that this element is capable of forming.
- the word gas refers to both simple elements such as nitrogen, argon and chlorine, for example, as well as their mixtures.
- impurities are mainly constituted by hydrogen and metallic oxides such as alumina which come mainly from the pollution of the metal by the humidity of the environment to which other bodies and in particular other metals can be added, like magnesium for example, when aluminum comes from the remelting of waste.
- impurities will either form inclusions and cause defects in the cast products, or give them unwanted mechanical characteristics. It is therefore essential to treat the aluminum to rid it of these impurities before pouring it.
- This treatment generally consists in introducing into the liquid metal bath, possibly in the presence of a flux, one or more reactive and / or inert gases, the former having the function of reacting with certain impurities, such as magnesium for example, the latter causing the impurities present initially or formed during the reactions towards the surface of the bath where they can be separated by skimming and filtration.
- This treatment can be carried out in ovens, whether it be alloy development ovens, holding ovens where the metal is in a stationary state and / or in pockets in which the metal flows continuously towards the stations of casting.
- ovens almost always have a volume and a bath surface which are more than ten times greater. to those of the pockets and their height is also much greater.
- rotary injectors are generally made of graphite, the only material capable of withstanding the abrasive action of the metal and the corrosive effect of chlorine at temperatures close to 800 ° C; but graphite is relatively fragile.
- a treatment device using gas from a bath (2) of liquid aluminum at rest in an oven (28) where it occupies an area at least equal to 10 m2 including a gantry (21) removable placed above the oven and to which is suspended a set (1) of gas injection and bath stirring which partially plunges into the bath via an opening (3) which is formed in the vault (4) of the oven, said assembly comprising a rotary shaft (5) pierced along its axis by a cavity (6) closed downwards and opening above the oven in (7), said shaft being equipped at its upper part with '' a motor (17) and at its lower part of a rotor (9) provided with blades (10) pierced with channels (11) connected to the cavity, characterized in that at the gantry are suspended at least three sets of length greater than 2 meters, of vertical axis of symmetry which taken two by two are located in different planes, the submerged parts of which are separated from each other only by the bath and that each of the trees is surrounded by a stator (13) extending downwards
- the device according to the invention applies not to pockets of restricted surface where most often the metal circulates, but to ovens where the bath is stationary and occupies an area at least equal to 10 m2.
- ovens are generally closed on the top and their vault is pierced with suitable openings through which the sets are introduced.
- a removable gantry a kind of metal frame which allows, by different mechanical means (pulleys, wheels, jacks, etc.) to move them horizontally from a waiting position to above the openings, simultaneously bring them down into the bath and remove them after treatment of the metal.
- Each of the assemblies is connected to a motor intended to ensure the rotation of the injector and communicates by flexible tubes to the gas inlets. The movements of the gantry, the rotation speed of the motors and the adjustment of the gas flow rates are controlled from a cockpit which simultaneously manages the entire operating chain of the oven.
- the assemblies From the position point of view, the assemblies have their axes located two by two in different planes so as to obtain an offset and to avoid any alignment of more than two assemblies.
- the results of tests carried out with and without offset show that the liquid-gas exchange is better in the offset position.
- the gas injectors are constituted by a rotary shaft connected at its upper end to a drive motor and at its lower end to a rotor, a kind of disc provided on its side wall with blades.
- the shaft is pierced along its axis by a cavity which opens on its wall above the furnace and which is closed down and connected to channels which pass through the blades to open into the bath through the face not adjacent to the rotor. This cavity and these channels serve for the distribution of the gas in the bath.
- stator which extends upwards above the furnace where it is fixed and downwards near the upper face of the rotor where it forms a relatively narrow space of a few millimeters so that the layer of metal therein acts as a hydrodynamic bearing for the rotor and facilitates the rotation of the latter.
- the lateral space which separates the stator from the rotor is filled with metal during the treatment and plays a damping role so that any "whip" effect on the rotor axis and any risk of breakage are eliminated.
- the measurement of this space is preferably between 10 and 30 mm.
- the injectors all rotate in the same direction to avoid eddies liable to hinder the rise of impurities on the surface.
- the axes With identical rotors, which is the most general case, it is preferable to place the axes at equal distances between them. These distances can vary between 2 and 6 times the value of the diameter of the rotors, which is generally between 100 and 500 mm in order to be within a range ensuring at the same time a suitable dimension so as not to excessively multiply the number of injectors and compatible with the mechanical strength of trees.
- the range of rotational speeds enabling good dispersion to be obtained without resorting to excessive torques is between 150 and 600 revolutions / minute.
- the gas flow rate it is preferably between 6 and 12 m3 / h per injector, a lower flow unnecessarily lengthening the duration of the treatment and a higher flow resulting in the formation of too large bubbles which open on the surface of the bath without reacting.
- This gas is preferably distributed by four blades located in planes forming an angle between 3 and 10 degrees relative to the vertical, symmetrically distributed around the rotor and drilled horizontally throughout their width by a channel of diameter from 1 to 3 mm approximately which is connected on one side to the shaft cavity and which opens on the other side at the end of the blade.
- the rotor is preferably placed at a distance from the bottom of the oven between 1/4 and the 1/2 the height of the bath.
- the stator is preferably extended up to a distance from the upper face of the rotor of between 10 and 50 mm.
- the device according to the invention has the following advantages: - very reduced air pollution and therefore improvement of staff working conditions - improvement in the metallurgical quality of the metal due to greater processing efficiency - reduction in the duration of treatment - reduction of gas consumption - reduction in metal loss - increased productivity of the ovens - good mechanical strength of the assemblies.
- FIG. 1 there is a gas injector assembly 1 which partially plunges into the bath 2 via an opening 3 formed in the roof 4 of the oven.
- This assembly comprises a rotary shaft 5 pierced along its axis by a cavity 6 opening below the furnace at 7 through which the next gas is brought 8.
- the shaft 5 is equipped at its lower part with a rotor 9 provided with blades 10 each pierced at their end by a channel 11 connected to the cavity 6 and which injects the gas into the next bath 12.
- the shaft 5 is surrounded by a stator 13 so as to leave a space 14 into which the bath enters.
- This stator extends downwards to a small distance from the face upper rotor to allow the bath to form an annular zone 15 acting as a hydrodynamic bearing; upwards the stator passes through the roof of the furnace to which it is suspended by a collar 16.
- the motor 17 ensures the rotation of the rotor via the shaft.
- FIG. 2 one can see a gantry 21 which rests on rails 22 by means of four wheels 23.
- This gantry is formed by an upper frame 24 to which the axes of the wheels are fixed, by four vertical uprights 25 and of the lower frame 26 removable along the uprights by means of a jack 27. From this lower frame are suspended the four gas injector assemblies 1 which plunge into the bath of the metal to be treated 2 contained in the furnace 28 according to offset positions the one in relation to the other.
- the gantry being in the waiting position A, and the lower frame in the high position, it is brought into position B located above the oven, then the lower frame is lowered to the intermediate position C where the elements are preheated before reaching position D where the elements are immersed in the bath. At this time, the injector engines are started and the gas is sent to the blades.
- the lower frame is gradually raised so as to drain the bath contained in the rotor-stator space. This frame being in high position B is then brought back to position A.
- the operating conditions were as follows: - distance from the bottom of the rotors to the bottom of the oven: 0.20 m - rotation speed 260 rpm - gas used: 95% by volume of argon and 5% of chlorine - gas flow: 10 m3 / h per injector - quantity of chlorine introduced: 0.06 kg / tonne - duration: 20 min.
- a sample of metal thus treated was subjected to the telegas analysis method to determine the hydrogen content.
- the amount found was 0.10 ⁇ g / g of metal.
Abstract
Description
La présente invention est relative à un dispositif de traitement au moyen de gaz d'un bain liquide d'aluminium de grande surface maintenu à l'état stationnaire dans un four.The present invention relates to a device for treatment by means of gas from a large surface aluminum liquid bath maintained in the stationary state in an oven.
On entend ici par aluminium à la fois l'aluminium contenant les impuretés habituelles à des taux qui sont fonction de la qualité traitée, et les différents alliages que cet élément est susceptible de former. De même, le mot gaz se rapporte aussi bien aux éléments simples tels que l'azote, l'argon et le chlore, par exemple, qu'à leurs mélanges.Here, aluminum is understood to mean both aluminum containing the usual impurities at rates which are a function of the quality treated, and the various alloys that this element is capable of forming. Similarly, the word gas refers to both simple elements such as nitrogen, argon and chlorine, for example, as well as their mixtures.
L'homme de l'art de la fonderie de l'aluminium sait que le métal qu'il met en oeuvre contient des impuretés. Ces impuretés sont constituées principalement par l'hydrogène et des oxydes métalliques tels que l'alumine qui proviennent surtout de la pollution du métal par l'humidité de l'environnement auxquels peuvent s'ajouter d'autres corps et notamment d'autres métaux, comme le magnésium par exemple, quand l'aluminium provient de la refusion de déchets. Ces impuretés vont soit former des inclusions et provoquer des défauts dans les produits coulés, soit leur conférer des caractéristiques mécaniques non souhaitées. Il est donc indispensable de traiter l'aluminium pour le débarrasser de ces impuretés avant de le couler.Those skilled in the art of aluminum smelting know that the metal they use contains impurities. These impurities are mainly constituted by hydrogen and metallic oxides such as alumina which come mainly from the pollution of the metal by the humidity of the environment to which other bodies and in particular other metals can be added, like magnesium for example, when aluminum comes from the remelting of waste. These impurities will either form inclusions and cause defects in the cast products, or give them unwanted mechanical characteristics. It is therefore essential to treat the aluminum to rid it of these impurities before pouring it.
Ce traitement consiste généralement à introduire dans le bain de métal liquide, éventuellement en présence de flux, un ou plusieurs gaz réactifs et/ou inertes, les premiers ayant pour fonction de réagir avec certaines impuretés, comme le magnésium par exemple, les seconds entraînant les impuretés présentes initialement ou formées au cours des réactions vers la surface du bain où elles peuvent être séparées par écrémage et filtration. Ce traitement peut être effectué dans les fours que ce soit les fours d'élaboration d'alliages, les fours de maintien où le métal est dans un état stationnaire et/ou dans des poches dans lesquelles le métal s'écoule en continu vers les postes de coulée.This treatment generally consists in introducing into the liquid metal bath, possibly in the presence of a flux, one or more reactive and / or inert gases, the former having the function of reacting with certain impurities, such as magnesium for example, the latter causing the impurities present initially or formed during the reactions towards the surface of the bath where they can be separated by skimming and filtration. This treatment can be carried out in ovens, whether it be alloy development ovens, holding ovens where the metal is in a stationary state and / or in pockets in which the metal flows continuously towards the stations of casting.
Ce qu'on recherche dans le traitement, c'est évidemment l'efficacité, c'est-à-dire l'obtention de la meilleure purification dans le temps le plus court avec la quantité de gaz la plus faible possible. Ce dernier paramètre est particulièrement important dans le cas où on utilise pour le traitement un gaz comme le chlore. En effet, il est bien connu que ce gaz est un élément toxique pour l'homme et qui, de plus, a des propriétés corrosives vis à vis des métaux courants comme le fer, le cuivre, etc... Donc, si une fraction du volume de chlore introduit ne réagit pas avec le bain, certes l'efficacité du traitement diminuera mais elle aura des conséquences fâcheuses sur le plan de la sécurité du personnel et de la pollution de l'environnement. D'où la mise en oeuvre de techniques permettant d'obtenir une efficacité plus ou moins grande.What we are looking for in the treatment is obviously efficiency, that is to say obtaining the best purification in the shortest time with the smallest amount of gas possible. This last parameter is particularly important in the case where a gas such as chlorine is used for the treatment. Indeed, it is well known that this gas is a toxic element for humans and which, moreover, has corrosive properties with respect to common metals such as iron, copper, etc ... So, if a fraction of the volume of chlorine introduced does not react with the bath, of course the effectiveness of the treatment will decrease, but it will have unfortunate consequences in terms of personnel safety and environmental pollution. Hence the implementation of techniques to obtain more or less efficiency.
Ces techniques peuvent être regroupées en deux familles :
- les techniques par injection dans un four comme l'introduction de composés chlorés gazéifiables tels que l'hexachloroéthane ou de gaz à partir d'injecteurs fixes tels que des bouchons poreux, cannes ou lances. Dans ce cas, seule une fonction injection de gaz dans le bain est exercée;
- les techniques d'injection en poche "in-line" où on utilise des ensembles tournants qui jouent à la fois les fonctions d'injection de gaz dans le bain et de brassage dudit bain.These techniques can be grouped into two families:
- techniques by injection into an oven such as the introduction of gaseous chlorinated compounds such as hexachloroethane or gas from fixed injectors such as porous plugs, rods or lances. In this case, only a gas injection function in the bath is exercised;
- In-line bag injection techniques where rotary assemblies are used which play both the functions of injecting gas into the bath and of mixing said bath.
Les lois classiques du génie chimique montrent que l'efficacité d'un traitement par injection de gaz dans du métal liquide dépend en première approximation :
- d'un coefficient d'échange gaz-métal liquide de nature physico-chimique;
- de la surface spécifique des bulles qui, pour des bulles supposées sphériques, est inversement proportionnelle à leur diamètre;
- de la fraction volumique de gaz, c'est-à-dire du quotient de la division du volume total qu'occupent les bulles par le volume total du métal.The classical laws of chemical engineering show that the effectiveness of a treatment by injection of gas into liquid metal depends as a first approximation:
- a gas-liquid metal exchange coefficient of a physico-chemical nature;
- of the specific surface of the bubbles which, for supposedly spherical bubbles, is inversely proportional to their diameter;
- the volume fraction of gas, that is to say the quotient of the division of the total volume occupied by the bubbles by the total volume of the metal.
A débit de gaz constant, plus l'agitation est grande et les bulles petites et dispersées, plus l'interface gaz-métal liquide est importante et meilleure est l'efficacité du système.
C'est le principe des injecteurs rotatifs qui allient à l'injection un effet important d'agitation du volume de bain traité.
Cependant, lorsqu'on augmente le débit de gaz en présence d'une agitation donnée, la fraction volumique de gaz croît puis, au-dessus d'une certaine valeur du débit de gaz, l'agitation n'est plus assez efficace pour disperser les bulles qui coalescent : leur diamètre croît alors fortement et l'efficacité du traitement diminue rapidement.
Ceci est a fortiori vrai lorsqu'il y a injection de gaz sans agitation concomittante comme c'est le cas avec les dispositifs classiques tels que l'hexachlororéthane, les bouchons poreux, les cannes ou les lances d'injection.
C'est pourquoi lorsqu'on veut obtenir une efficacité maximum, il est préférable d'utiliser des injecteurs rotatifs.At constant gas flow, the greater the agitation and the bubbles Small and dispersed, the larger the gas-liquid metal interface, the better the efficiency of the system.
This is the principle of rotary injectors which combine injection with a significant agitation effect on the volume of bath treated.
However, when the gas flow is increased in the presence of a given agitation, the volume fraction of gas increases then, above a certain value of the gas flow, the agitation is no longer effective enough to disperse bubbles which coalesce: their diameter then increases sharply and the effectiveness of the treatment decreases rapidly.
This is a fortiori true when there is injection of gas without concomitant agitation as is the case with conventional devices such as hexachloroethane, porous plugs, canes or injection lances.
This is why when you want to obtain maximum efficiency, it is preferable to use rotary injectors.
Sachant par ailleurs que la pureté du métal à la sortie des poches est fonction de la pureté à l'entrée, on conçoit l'importance de pouvoir disposer dans les fours de moyens de traitement les plus efficaces possible.Knowing moreover that the purity of the metal at the outlet of the bags is a function of the purity at the inlet, we understand the importance of being able to have in the ovens the most effective treatment means possible.
Or, dans l'état actuel de nos connaissances, on constate que si les injecteurs rotatifs équipent maintenant la plupart des poches de traitement in-line, il n'en est pas de même dans le cas des fours où l'hexachloroéthane, les bouchons poreux et les cannes prévalent encore. Alors, pourquoi les injecteurs rotatifs ne sont ils pas utilisés dans les fours ?However, in the current state of our knowledge, we note that if rotary injectors now equip most of the in-line processing bags, it is not the same in the case of ovens where hexachloroethane, plugs porous and canes still prevail. So why are rotary injectors not used in ovens?
La demanderesse, aussi bien expérimentée dans le domaine des poches que dans celui des fours, explique cet état de fait de la manière suivante d'une part, les fours ont presque toujours un volume et une surface de bain qui sont plus de dix fois supérieurs à ceux des poches et leur hauteur est également beaucoup plus grande. D'autre part, les injecteurs rotatifs sont généralement réalisés en graphite, seul matériau capable de résister à l'action abrasive du métal et corrosive du chlore à des températures voisines de 800°C; mais le graphite est relativement fragile.The Applicant, both experienced in the field of pockets and in that of ovens, explains this state of affairs in the following manner, on the one hand, ovens almost always have a volume and a bath surface which are more than ten times greater. to those of the pockets and their height is also much greater. On the other hand, rotary injectors are generally made of graphite, the only material capable of withstanding the abrasive action of the metal and the corrosive effect of chlorine at temperatures close to 800 ° C; but graphite is relatively fragile.
Dans ces conditions, on conçoit mal la transposition de tels injecteurs rotatifs à des fours. En effet, pour qu'ils agissent convenablement dans l'ensemble du bain, il faudrait augmenter notablement le diamètre des rotors et de ce fait le couple important nécessaire à leur rotation conduirait à des efforts incompatibles avec la résistance mécanique du graphite.
De plus, en raison de la distance relativement grande qui sépare le niveau du bain de la voûte du four, il faudrait placer les rotors au bout d'arbres de plus de deux mètres de long qui produiraient inévitablement le phénomène de "fouet", c'est-à-dire une tendance à s'écarter de la verticale, sollicitation à laquelle ne peut répondre le graphite du fait de sa faible élasticité et qui se traduirait par une rupture de l'arbre. En outre, l'introduction d'un tel injecteur dans un four nécessiterait la réalisation d'ouvertures convenables, aménagement difficilement réalisable et en tout cas très coûteux sur les fours existants.Under these conditions, it is difficult to imagine the transposition of such rotary injectors to ovens. In fact, in order for them to act properly throughout the bath, the diameter of the rotors would have to be appreciably increased, and therefore the significant torque necessary for their rotation would lead to forces incompatible with the mechanical strength of the graphite.
In addition, because of the relatively large distance separating the bath level from the oven roof, the rotors should be placed at the end of trees more than two meters long which would inevitably produce the phenomenon of "whip", c 'is to say a tendency to deviate from the vertical, a stress which graphite cannot respond to due to its low elasticity and which would result in a rupture of the shaft. In addition, the introduction of such an injector into an oven would require the production of suitable openings, an arrangement which is difficult to achieve and in any case very expensive on existing ovens.
Certes, on a également pensé mettre en oeuvre plusieurs injecteurs rotatifs du type utilisé dans les poches, mais au problème de la longueur qui se posait toujours s'ajoutait celui des effets contraires que chacun d'eux peut développer au sein d'un même volume de bain et qui se traduit alors par une diminution globale de l'efficacité.
Ce handicap qui apparaît déjà dans des poches de volume relativement grand a été surmonté par l'emploi de cloisons intermédiaires.
Un tel type de poches est décrit dans l'USP 3870511. Mais une telle solution ne peut être envisagée dans un four car elle conduirait à des difficultés énormes de construction, d'exploitation et de maintenance.Admittedly, we have also thought of implementing several rotary injectors of the type used in the bags, but to the problem of length which always arose was added that of the opposite effects which each of them can develop within the same volume. bath and which results in an overall decrease in efficiency.
This handicap, which already appears in pockets of relatively large volume, has been overcome by the use of intermediate partitions.
Such a type of bag is described in USP 3870511. But such a solution cannot be envisaged in an oven because it would lead to enormous difficulties in construction, operation and maintenance.
C'est pourquoi la demanderesse consciente de l'efficacité accrue que présentaient les systèmes où injection et brassage se font simultanément, a cherché malgré tous ces obstacles à trouver une solution au problème de l'installation de ces injecteurs rotatifs dans un four sans avoir recours à aucune modification importante.This is why the Applicant, aware of the increased efficiency presented by the systems where injection and mixing are carried out simultaneously, has sought, despite all these obstacles, to find a solution to the problem of installing these rotary injectors in an oven without having recourse to no significant changes.
Elle y est parvenue en concevant un dispositif de traitement au moyen de gaz d'un bain (2) d'aluminium liquide au repos dans un four (28) où il occupe une surface au moins égale à 10 m² comportant un portique (21) amovible placé au-dessus du four et auquel est suspendu un ensemble (1) d'injection de gaz et de brassage du bain qui plonge en partie dans le bain par l'intermédiaire d'une ouverture (3) qui est pratiquée dans la voûte (4) du four, ledit ensemble comprenant un arbre (5) rotatif percé suivant son axe par une cavité (6) fermée vers le bas et débouchant au-dessus du four en (7), ledit arbre étant équipé à sa partie supérieure d'un moteur (17) et à sa partie inférieure d'un rotor (9) muni de pales (10) percées de canaux (11) reliés à la cavité, caractérisé en ce qu'au portique sont suspendus au moins trois ensembles de longueur supérieure à 2 mètres, d'axe de symétrie vertical qui pris deux à deux sont situés dans des plans différents, dont les parties immergées sont séparées les unes des autres uniquement par le bain et que chacun des arbres est entouré par un stator (13) s'allongeant vers le bas à proximité de la face supérieure du rotor et vers le haut au-dessus de la voûte.It achieved this by designing a treatment device using gas from a bath (2) of liquid aluminum at rest in an oven (28) where it occupies an area at least equal to 10 m² including a gantry (21) removable placed above the oven and to which is suspended a set (1) of gas injection and bath stirring which partially plunges into the bath via an opening (3) which is formed in the vault (4) of the oven, said assembly comprising a rotary shaft (5) pierced along its axis by a cavity (6) closed downwards and opening above the oven in (7), said shaft being equipped at its upper part with '' a motor (17) and at its lower part of a rotor (9) provided with blades (10) pierced with channels (11) connected to the cavity, characterized in that at the gantry are suspended at least three sets of length greater than 2 meters, of vertical axis of symmetry which taken two by two are located in different planes, the submerged parts of which are separated from each other only by the bath and that each of the trees is surrounded by a stator (13) extending downwards near the upper face of the rotor and upwards t above the arch.
Ainsi, le dispositif selon l'invention s'applique non pas à des poches de surface restreinte où le plus souvent le métal circule, mais à des fours où le bain est stationnaire et occupe une surface au moins égale à 10 m².Thus, the device according to the invention applies not to pockets of restricted surface where most often the metal circulates, but to ovens where the bath is stationary and occupies an area at least equal to 10 m².
Ces fours sont généralement fermés sur le dessus et leur voûte est percée d'ouvertures convenables par lesquelles on introduit les ensembles. Ceux-ci sont suspendus à un portique amovible : espèce de charpente métallique qui permet, par différents moyens mécaniques (poulies, roues, vérins, etc) de les déplacer horizontalement d'une position d'attente jusqu'au-dessus des ouvertures, de les faire descendre simultanément dans le bain et de les retirer après traitement du métal. Chacun des ensembles est relié à un moteur destiné à assurer la rotation de l'injecteur et communique par des tubes souples aux arrivées de gaz. Les mouvements du portique, la vitesse de rotation des moteurs et le réglage des débits de gaz sont commandés à partir d'un poste de pilotage qui gère simultanément toute la chaîne de fonctionnement du four.These ovens are generally closed on the top and their vault is pierced with suitable openings through which the sets are introduced. These are suspended from a removable gantry: a kind of metal frame which allows, by different mechanical means (pulleys, wheels, jacks, etc.) to move them horizontally from a waiting position to above the openings, simultaneously bring them down into the bath and remove them after treatment of the metal. Each of the assemblies is connected to a motor intended to ensure the rotation of the injector and communicates by flexible tubes to the gas inlets. The movements of the gantry, the rotation speed of the motors and the adjustment of the gas flow rates are controlled from a cockpit which simultaneously manages the entire operating chain of the oven.
Ces ensembles plongent en partie dans le bain et les parties immergées sont séparées les unes des autres uniquement par le bain, c'est-à-dire sans qu'aucune cloison solide ne fasse écran entre eux.These assemblies are partially immersed in the bath and the submerged parts are separated from each other only by the bath, that is to say without any solid partition shielding them.
Dans ces conditions, et pour éviter toute interférence entre les actions de chacun d'eux, il a fallu également conférer aux ensembles des caractéristiques particulières à la fois en ce qui concerne leur position réciproque et la structure de chacun d'eux.In these conditions, and to avoid any interference between the actions of each of them, it was also necessary to confer on the sets particular characteristics both as regards their reciprocal position and the structure of each of them.
Du point de vue position, les ensembles ont leurs axes situés deux à deux dans des plans différents de manière à obtenir un décalage et à éviter tout alignement de plus de deux ensembles. Les résultats d'essais faits avec et sans décalage montrent que l'échange liquide-gaz est meilleur en position décalée.From the position point of view, the assemblies have their axes located two by two in different planes so as to obtain an offset and to avoid any alignment of more than two assemblies. The results of tests carried out with and without offset show that the liquid-gas exchange is better in the offset position.
Du point de vue structure, on a constaté que l'efficacité du traitement était également accrue en l'absence de vortex, phénomène qui se traduit par un entraînement et un abaissement du niveau du bain au contact de chaque ensemble et qui est généralement atténué par l'introduction de baffles dans le bain. Comme cette solution était impossible dans un four, la demanderesse a cherché et trouvé qu'en entourant le rotor par un stator, on parvenait au même résultat.From a structural point of view, it was found that the effectiveness of the treatment was also increased in the absence of a vortex, a phenomenon which results in a entrainment and a lowering of the level of the bath in contact with each assembly and which is generally attenuated by the introduction of baffles in the bath. As this solution was impossible in an oven, the applicant sought and found that by surrounding the rotor with a stator, the same result was achieved.
Ainsi, les injecteurs de gaz sont-ils constitués par un arbre rotatif relié à son extrémité supérieure à un moteur d'entraînement et à son extrémité inférieure à un rotor, sorte de disque muni sur sa paroi latérale de pales. L'arbre est percé suivant son axe par une cavité qui s'ouvre sur sa paroi au-dessus du four et qui est fermée vers le bas et reliée à des canaux qui traversent les pales pour déboucher dans le bain par la face non adjacente au rotor. Cette cavité et ces canaux servent à la distribution du gaz dans le bain.Thus, the gas injectors are constituted by a rotary shaft connected at its upper end to a drive motor and at its lower end to a rotor, a kind of disc provided on its side wall with blades. The shaft is pierced along its axis by a cavity which opens on its wall above the furnace and which is closed down and connected to channels which pass through the blades to open into the bath through the face not adjacent to the rotor. This cavity and these channels serve for the distribution of the gas in the bath.
Ces arbres sont entourés à faible distance par le stator qui s'allonge vers le haut au-dessus du four où il est fixé et vers le bas à proximité de la face supérieure du rotor où il forme un espace relativement étroit de quelques millimètres de sorte que la couche de métal qui s'y trouve joue le rôle de palier hydrodynamique pour le rotor et facilite la rotation de ce dernier.These shafts are surrounded at a short distance by the stator which extends upwards above the furnace where it is fixed and downwards near the upper face of the rotor where it forms a relatively narrow space of a few millimeters so that the layer of metal therein acts as a hydrodynamic bearing for the rotor and facilitates the rotation of the latter.
De plus, l'espace latéral qui sépare le stator du rotor est rempli de métal durant le traitement et joue un rôle amortisseur de sorte que tout effet de "fouet" de l'axe du rotor et tout risque de rupture sont écartés. La mesure de cet espace est de préférence comprise entre 10 et 30 mm.In addition, the lateral space which separates the stator from the rotor is filled with metal during the treatment and plays a damping role so that any "whip" effect on the rotor axis and any risk of breakage are eliminated. The measurement of this space is preferably between 10 and 30 mm.
Sans que cela soit obligatoire pour mettre en oeuvre l'invention, mais afin d'en affiner les possibilités, il est préférable que les injecteurs tournent tous dans le même sens pour éviter les remous susceptibles de gêner la remontée des impuretés en surface.Without this being compulsory for implementing the invention, but in order to refine the possibilities, it is preferable that the injectors all rotate in the same direction to avoid eddies liable to hinder the rise of impurities on the surface.
A rotors identiques, ce qui est le cas le plus général, il est préférable de placer les axes à des distances égales entre elles. Ces distances peuvent varier entre 2 et 6 fois la valeur du diamètre des rotors, qui est généralement comprise entre 100 et 500 mm afin de se tenir dans une fourchette assurant à la fois une dimension convenable pour ne pas multiplier exagérément le nombre d'injecteurs et compatible avec la tenue mécanique des arbres.With identical rotors, which is the most general case, it is preferable to place the axes at equal distances between them. These distances can vary between 2 and 6 times the value of the diameter of the rotors, which is generally between 100 and 500 mm in order to be within a range ensuring at the same time a suitable dimension so as not to excessively multiply the number of injectors and compatible with the mechanical strength of trees.
Par ailleurs, la gamme de vitesses de rotation permettant d'obtenir une bonne dispersion sans recourir à des couples de rotation trop importants se situe entre 150 et 600 tours/minute.Furthermore, the range of rotational speeds enabling good dispersion to be obtained without resorting to excessive torques is between 150 and 600 revolutions / minute.
Quant au débit de gaz, il se situe de préférence entre 6 et 12 m³/h par injecteur, un débit plus faible allongeant inutilement lac durée du traitement et un débit plus fort se traduisant par la formation de bulles trop grosses qui débouchent en surface du bain sans avoir réagi. Ce gaz est distribué de préférence par quatre pales situées dans des plans formant un angle compris entre 3 et 10 degrés par rapport à la verticale, distribuées symétriquement autour du rotor et percées horizontalement dans toute leur largeur par un canal de diamètre de 1 à 3 mm environ qui est relié d'un côté à la cavité de l'arbre et qui débouche de l'autre côté au bout de la pale.As for the gas flow rate, it is preferably between 6 and 12 m³ / h per injector, a lower flow unnecessarily lengthening the duration of the treatment and a higher flow resulting in the formation of too large bubbles which open on the surface of the bath without reacting. This gas is preferably distributed by four blades located in planes forming an angle between 3 and 10 degrees relative to the vertical, symmetrically distributed around the rotor and drilled horizontally throughout their width by a channel of diameter from 1 to 3 mm approximately which is connected on one side to the shaft cavity and which opens on the other side at the end of the blade.
Pour que la hauteur du bain traversée par les bulles de gaz soit suffisante à l'obtention d'une efficacité convenable, on place le rotor de préférence à une distance du fond du four comprise entre le 1/4 et la 1/2 de la hauteur du bain.So that the height of the bath traversed by the gas bubbles is sufficient to obtain a suitable efficiency, the rotor is preferably placed at a distance from the bottom of the oven between 1/4 and the 1/2 the height of the bath.
Pour réaliser au mieux la fonction de palier hydrodynamique, on prolonge de préférence le stator jusqu'à une distance de la face supérieure du rotor comprise entre 10 et 50 mm.To best perform the hydrodynamic bearing function, the stator is preferably extended up to a distance from the upper face of the rotor of between 10 and 50 mm.
Dans ces conditions, le dispositif selon l'invention présente les avantages suivants :
- pollution atmosphérique très réduite et donc amélioration des conditions de travail du personnel
- amélioration de la qualité métallurgique du métal due à une plus grande efficacité du traitement
- reduction de la durée du traitement
- réduction de la consommation de gaz
- diminution de la perte en métal
- accroissement de la productivité des fours - bonne tenue mécanique des ensembles.Under these conditions, the device according to the invention has the following advantages:
- very reduced air pollution and therefore improvement of staff working conditions
- improvement in the metallurgical quality of the metal due to greater processing efficiency
- reduction in the duration of treatment
- reduction of gas consumption
- reduction in metal loss
- increased productivity of the ovens - good mechanical strength of the assemblies.
L'invention sera mieux comprise à l'aide des figures jointes qui réprésentent :
- - figure 1, vue en coupe verticale axiale, un ensemble injecteur de gaz en place sur un four
- - figure 2, vu en perspective, un portique amovible auquel sont suspendus quatre ensembles injecteurs de gaz plongeant dans un four vu en coupe verticale.
- - Figure 1, view in axial vertical section, a gas injector assembly in place on an oven
- - Figure 2, seen in perspective, a removable gantry to which are suspended four gas injector assemblies immersed in an oven seen in vertical section.
Plus précisément sur la figure 1, on distingue un ensemble injecteur de gaz 1 qui plonge en partie dans le bain 2 par l'intermédiaire d'une ouverture 3 pratiquée dans la voûte 4 du four. Cet ensemble comprend un arbre 5 rotatif percé suivant son axe par une cavité 6 débouchant au-dessous du four en 7 par où est amené le gaz suivant 8. L'arbre 5 est équipé à sa partie inférieure d'un rotor 9 muni de pales 10 percées chacune à leur extrémité par un canal 11 relié à la cavité 6 et qui injecte le gaz dans le bain suivant 12. L'arbre 5 est entouré par un stator 13 de manière à laisser un espace 14 dans lequel pénètre le bain. Ce stator s'allonge vers le bas jusqu 'à une faible distance de la face supérieure du rotor pour permettre au bain de former une zone annulaire 15 jouant le rôle de palier hydrodynamique; vers le haut le stator passe à travers la voûte du four à laquelle il est suspendu par un collet 16. Le moteur 17 assure la rotation du rotor par l'intermédiaire de l'arbre.More specifically in Figure 1, there is a gas injector assembly 1 which partially plunges into the
Sur la figure 2, on peut voir un portique 21 qui repose sur des rails 22 par l'intermédiaire de quatre roues 23. Ce portique est formé d'un cadre supérieur 24 auquel sont fixés les axes des roues, de quatre montants verticaux 25 et du cadre inférieur 26 amovible le long des montants au moyen d'un vérin 27. A ce cadre inférieur sont suspendus les quatre ensembles injecteurs de gaz 1 qui plongent dans le bain du métal à traiter 2 contenu dans le four 28 suivant des positions décalées les unes par raport aux autres.In FIG. 2, one can see a
En fonctionnement, le portique étant en position d'attente A, et le cadre inférieur en position haute, on l'amène en position B située au-dessus du four, puis on descend le cadre inférieur en position intermédiaire C où les éléments sont préchauffés avant d'atteindre la position D où il y a immersion des éléments dans le bain. A ce moment, les moteurs des injecteurs sont mis en route et le gaz est envoyé vers les pales.In operation, the gantry being in the waiting position A, and the lower frame in the high position, it is brought into position B located above the oven, then the lower frame is lowered to the intermediate position C where the elements are preheated before reaching position D where the elements are immersed in the bath. At this time, the injector engines are started and the gas is sent to the blades.
Après traitement, le cadre inférieur est relevé progressivement de manière à faire s'écouler le bain contenu dans l'espace rotor-stator. Ce cadre étant en position haute B est ensuite ramené à la position A.After treatment, the lower frame is gradually raised so as to drain the bath contained in the rotor-stator space. This frame being in high position B is then brought back to position A.
L'invention peut être illustrée à l'aide de l'exemple d'application suivant :The invention can be illustrated using the following example of application:
Dans un four de maintien contenant 35 tonnes d'Al 5182 suivant les normes de l'Aluminium Association qui formait un bain de surface 30 m de profondeur 0,60 m et dont la surface libre était située à 1,60 m de la voûte, on a plongé quatre éléments disperseurs de gaz disposés suivant un carré de 3 m de côté.
Ces éléments avaient pour caractéristiques :
- longueur de l'arbre : 2,625 m
- diamètre du rotor : 0,25 m
- inclinaison des pales : 4 degrés
- diamètre des canaux : 0,0025 m
- espace latéral rotor-stator : 0,016 m
- espace vertical rotor-stator : 0,050 m.In a holding furnace containing 35 tonnes of Al 5182 according to the standards of the Aluminum Association which formed a surface bath 30 m deep 0.60 m and whose free surface was located 1.60 m from the roof, four gas dispersing elements were placed in a 3 m square.
These elements had the following characteristics:
- tree length: 2.625 m
- rotor diameter: 0.25 m
- blade tilt: 4 degrees
- channel diameter: 0.0025 m
- lateral rotor-stator space: 0.016 m
- vertical rotor-stator space: 0.050 m.
Les conditions de fonctionnement étaient les suivantes :
- distance du bas des rotors au fond du four : 0,20 m
- vitesse de rotation 260 t/min
- gaz mis en oeuvre : 95 % en volume d'argon et 5 % de chlore
- débit de gaz : 10 m³/h par injecteur
- quantité de chlore introduite : 0,06 kg/tonne
- durée : 20 min.The operating conditions were as follows:
- distance from the bottom of the rotors to the bottom of the oven: 0.20 m
- rotation speed 260 rpm
- gas used: 95% by volume of argon and 5% of chlorine
- gas flow: 10 m³ / h per injector
- quantity of chlorine introduced: 0.06 kg / tonne
- duration: 20 min.
Un échantillon de métal ainsi traité a été soumis à la méthode d'analyse télégaz pour déterminer la teneur en hydrogène. La quantité trouvée était égale à 0,10 µg/g de métal.A sample of metal thus treated was subjected to the telegas analysis method to determine the hydrogen content. The amount found was 0.10 µg / g of metal.
Pour comparaison, un bain identique au précédent traité avec une quantité d'hexachloroéthane correspondant à 2 kg Cl₂ pendant 120 minutes a conduit à une teneur en hydrogène de 0,35 µg /g alors qu'en utilisant des cannes d'injection il a fallu 60 minutes et 1,5 kg Cl₂ pour obtenir une teneur en hydrogène égale à 0,2 µg/g.For comparison, a bath identical to the previous one treated with an amount of hexachloroethane corresponding to 2 kg Cl₂ for 120 minutes led to a hydrogen content of 0.35 µg / g while using injection pipes it was necessary 60 minutes and 1.5 kg Cl₂ to obtain a hydrogen content equal to 0.2 µg / g.
On peut constater le progrès important réalisé avec l'invention à la fois en ce qui concerne la durée du traitement, la quantité de chlore mise en oeuvre et la qualité du métal obtenu.One can note the significant progress made with the invention both with regard to the duration of the treatment, the amount of chlorine used and the quality of the metal obtained.
Claims (10)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT90420406T ATE103992T1 (en) | 1989-09-20 | 1990-09-17 | GAS FILLING DEVICE FOR A STATIONARY ALUMINUM MELTING BATH WITH A LARGE SURFACE SURFACE. |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8912540 | 1989-09-20 | ||
| FR8912540A FR2652018B1 (en) | 1989-09-20 | 1989-09-20 | DEVICE FOR TREATING WITH GAS FROM A LARGE SURFACE ALUMINUM LIQUID BATH MAINTAINED IN A STATIONARY STATE IN AN OVEN. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0419378A1 true EP0419378A1 (en) | 1991-03-27 |
| EP0419378B1 EP0419378B1 (en) | 1994-04-06 |
Family
ID=9385802
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90420406A Expired - Lifetime EP0419378B1 (en) | 1989-09-20 | 1990-09-17 | Apparatus for treating a static aluminium bath of large surface area using gases |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US5028035A (en) |
| EP (1) | EP0419378B1 (en) |
| AT (1) | ATE103992T1 (en) |
| AU (1) | AU621531B2 (en) |
| CA (1) | CA2023753C (en) |
| DE (1) | DE69007921T2 (en) |
| ES (1) | ES2050989T3 (en) |
| FR (1) | FR2652018B1 (en) |
| NO (1) | NO176925C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2261033A (en) * | 1991-09-26 | 1993-05-05 | Charles Edward Eckert | Impeller for treating molten metals. |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2645456B1 (en) * | 1989-04-11 | 1994-02-11 | Air Liquide | METHOD AND PLANT FOR TREATING A LIQUID WITH A GAS |
| US6056803A (en) * | 1997-12-24 | 2000-05-02 | Alcan International Limited | Injector for gas treatment of molten metals |
| US9127332B2 (en) * | 2008-03-11 | 2015-09-08 | Pyrotek, Inc. | Molten aluminum refining and gas dispersion system |
| CN110607461B (en) * | 2018-11-16 | 2023-05-09 | 柳州职业技术学院 | Long-acting composite graphite stirring device for aluminum alloy refining and preparation method |
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| US1635037A (en) * | 1925-09-28 | 1927-07-05 | Edwards John | Means for agitating and stirring molten metal in open-hearth and like furnaces |
| US3227547A (en) * | 1961-11-24 | 1966-01-04 | Union Carbide Corp | Degassing molten metals |
| US3743263A (en) * | 1971-12-27 | 1973-07-03 | Union Carbide Corp | Apparatus for refining molten aluminum |
| US3870511A (en) * | 1971-12-27 | 1975-03-11 | Union Carbide Corp | Process for refining molten aluminum |
| AT330470B (en) * | 1974-07-17 | 1976-07-12 | Vmw Ranshofen Berndorf Ag | GASING DEVICE FOR METALLURGICAL VESSELS, IN PARTICULAR MELTING FURNACES |
| AT336900B (en) * | 1974-04-04 | 1977-05-25 | Vmw Ranshofen Berndorf Ag | DEVICE FOR INTRODUCING GASES IN LIQUIDS, IN PARTICULAR MELTS |
| US4327901A (en) * | 1980-03-10 | 1982-05-04 | Kaiser George S | Melt and hold furnace for non-ferrous metals |
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| EP0245601A2 (en) * | 1986-03-05 | 1987-11-19 | Showa Aluminum Corporation | Apparatus for treating molten metal |
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| US3703340A (en) * | 1970-10-09 | 1972-11-21 | Us Reduction Co | Mechanical puddler |
| US4203581A (en) * | 1979-03-30 | 1980-05-20 | Union Carbide Corporation | Apparatus for refining molten aluminum |
| FR2568267B1 (en) * | 1984-07-27 | 1987-01-23 | Pechiney Aluminium | ALUMINUM ALLOY CHLORINATION POCKET FOR ELIMINATING MAGNESIUM |
| JP2505525B2 (en) * | 1988-04-08 | 1996-06-12 | 三菱重工業株式会社 | Gas-liquid contact treatment device for slurry |
| US4884786A (en) * | 1988-08-23 | 1989-12-05 | Gillespie & Powers, Inc. | Apparatus for generating a vortex in a melt |
| IL93349A0 (en) * | 1989-02-17 | 1990-11-29 | Carborundum Co | Method and apparatus for injecting gas into molten metal |
-
1989
- 1989-09-20 FR FR8912540A patent/FR2652018B1/en not_active Expired - Fee Related
-
1990
- 1990-07-13 US US07/551,905 patent/US5028035A/en not_active Expired - Lifetime
- 1990-08-07 NO NO903464A patent/NO176925C/en unknown
- 1990-08-23 CA CA002023753A patent/CA2023753C/en not_active Expired - Fee Related
- 1990-09-07 AU AU62303/90A patent/AU621531B2/en not_active Ceased
- 1990-09-17 DE DE69007921T patent/DE69007921T2/en not_active Expired - Fee Related
- 1990-09-17 AT AT90420406T patent/ATE103992T1/en active
- 1990-09-17 EP EP90420406A patent/EP0419378B1/en not_active Expired - Lifetime
- 1990-09-17 ES ES90420406T patent/ES2050989T3/en not_active Expired - Lifetime
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1635037A (en) * | 1925-09-28 | 1927-07-05 | Edwards John | Means for agitating and stirring molten metal in open-hearth and like furnaces |
| US3227547A (en) * | 1961-11-24 | 1966-01-04 | Union Carbide Corp | Degassing molten metals |
| US3743263A (en) * | 1971-12-27 | 1973-07-03 | Union Carbide Corp | Apparatus for refining molten aluminum |
| US3870511A (en) * | 1971-12-27 | 1975-03-11 | Union Carbide Corp | Process for refining molten aluminum |
| AT336900B (en) * | 1974-04-04 | 1977-05-25 | Vmw Ranshofen Berndorf Ag | DEVICE FOR INTRODUCING GASES IN LIQUIDS, IN PARTICULAR MELTS |
| AT330470B (en) * | 1974-07-17 | 1976-07-12 | Vmw Ranshofen Berndorf Ag | GASING DEVICE FOR METALLURGICAL VESSELS, IN PARTICULAR MELTING FURNACES |
| US4327901A (en) * | 1980-03-10 | 1982-05-04 | Kaiser George S | Melt and hold furnace for non-ferrous metals |
| EP0077282A1 (en) * | 1981-10-14 | 1983-04-20 | Aluminium Pechiney | Installation for the continuous treatment of liquid metals or liquid metal alloys in the form of magnesium or aluminium |
| EP0245601A2 (en) * | 1986-03-05 | 1987-11-19 | Showa Aluminum Corporation | Apparatus for treating molten metal |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2261033A (en) * | 1991-09-26 | 1993-05-05 | Charles Edward Eckert | Impeller for treating molten metals. |
| US5314525A (en) * | 1991-09-26 | 1994-05-24 | Eckert Charles E | Method for treating a liquid with a gas using an impeller |
| GB2261033B (en) * | 1991-09-26 | 1996-05-15 | Charles Edward Eckert | Impeller for treating molten metals |
Also Published As
| Publication number | Publication date |
|---|---|
| NO176925C (en) | 1995-06-21 |
| US5028035A (en) | 1991-07-02 |
| FR2652018B1 (en) | 1994-03-25 |
| DE69007921T2 (en) | 1994-10-06 |
| DE69007921D1 (en) | 1994-05-11 |
| CA2023753C (en) | 1997-10-07 |
| NO176925B (en) | 1995-03-13 |
| AU621531B2 (en) | 1992-03-12 |
| NO903464D0 (en) | 1990-08-07 |
| AU6230390A (en) | 1991-03-28 |
| NO903464L (en) | 1991-03-21 |
| EP0419378B1 (en) | 1994-04-06 |
| ATE103992T1 (en) | 1994-04-15 |
| FR2652018A1 (en) | 1991-03-22 |
| ES2050989T3 (en) | 1994-06-01 |
| CA2023753A1 (en) | 1991-03-21 |
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