EP0633083A1 - Metallic powder for making parts by compression and sintering and process for obtaining the powder - Google Patents
Metallic powder for making parts by compression and sintering and process for obtaining the powder Download PDFInfo
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- EP0633083A1 EP0633083A1 EP94420188A EP94420188A EP0633083A1 EP 0633083 A1 EP0633083 A1 EP 0633083A1 EP 94420188 A EP94420188 A EP 94420188A EP 94420188 A EP94420188 A EP 94420188A EP 0633083 A1 EP0633083 A1 EP 0633083A1
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- granules
- powder
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- gelatin
- metal
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/14—Treatment of metallic powder
- B22F1/148—Agglomerating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F2301/00—Metallic composition of the powder or its coating
- B22F2301/35—Iron
Definitions
- the metal powder which is the subject of the invention relates to the production of parts by compression and sintering from stainless steels, other stainless or refractory metals or alloys and alloy steels, intended for the production of quality.
- powders with angular particles obtained by spraying liquid metal by jet of water under pressure are most commonly used according to various methods known to those skilled in the art.
- metal powders by spraying a metal or liquid alloy by means of a gas jet which may be, for example, a neutral gas such as argon or nitrogen or any suitable gas. Powders are thus obtained having a much lower oxide content than the powders obtained by spraying with water and which thus have substantially the same purity as the starting metal.
- a gas jet which may be, for example, a neutral gas such as argon or nitrogen or any suitable gas. Powders are thus obtained having a much lower oxide content than the powders obtained by spraying with water and which thus have substantially the same purity as the starting metal.
- the elementary particles of these powders have a substantially spherical shape but in the state are not easily shaped.
- these powders make it possible, after compression and sintering, to obtain by compression parts having an apparent density at least equal to that which allow the usual angular powders to be obtained.
- the green part obtained from spherical particles has a mechanical strength often insufficient to allow its manipulation and in particular its ejection from the mold, then the transfer towards the sintering furnace, without chipping or cracking.
- Patent application GB 2 228 744 describes a similar method for joining elements of alloys such as graphite, phosphorus or the like with a base metal. According to this method, a mixture of an acrylic acid ester with a methacrylic acid ester and an unsaturated polymerizable acid is used as binder.
- the aim is to avoid the segregation of finer or lighter particles such as graphite or others compared to a base metal, such as iron, by binding these particles together.
- these binders after implementation, must be removed before or during sintering and contamination of the metal powders is often observed with certain components of the binders.
- the metal powder based on spherical particles, suitable for cold forming by compression followed by sintering, which is the subject of the invention as well as the process for the preparation of this powder which is also the subject of the invention allow to solve all the problems thus posed.
- the metal powder according to the invention consists of a set of granules each comprising a group of elementary metal particles of spherical shape agglomerated by gelatin at a content of at least 0.5% of the weight of the metal powder.
- the spherical particles are advantageously obtained by a spraying process, by means of a gas which can be air or a neutral or reducing gas such as N2, H2, NH3, Ar, or other, of a metal or liquid alloy .
- a gas which can be air or a neutral or reducing gas such as N2, H2, NH3, Ar, or other, of a metal or liquid alloy .
- the main metals or alloys which can be used are, for example, stainless steels, stainless or refractory metals or alloys or even alloy steels with high mechanical characteristics.
- the dimensions of these elementary particles and those of the granules are chosen mainly as a function of the dimensions and, in particular, density characteristics of the molded parts which it is a question of producing.
- each granule in order to obtain, by cold pressure forming, a part having sufficient mechanical strength when raw, it is preferable for each granule to contain a sufficient number of spherical particles agglomerated by the gelatin. It is also necessary that these granules are capable of correctly filling the mold in every corner. However, a certain number of granules can be formed of isolated elementary particles coated with gelatin without affecting the quality of the final product obtained.
- a maximum diameter "d1”, elementary spherical particles and a maximum width "d2" of the granules obtained are determined. It is found that the powder according to the invention must preferably have a ratio of d2 / d1 ⁇ 3 so that the cold-pressure molded parts reach sufficient mechanical strength.
- this d2 / d1 ratio can reach at least 4 or more.
- a maximum width "d2" of the granules of 300 microns constitutes a lower limit.
- the gelatin content must be determined according to the average size of the elementary spherical particles which are agglomerated by the gelatin. This content also depends on the jelly strength of the gelatin. This strength in jelly is expressed in Bloom (standardized unit) and can vary between 50 and 250 blooms depending on the gelatin used.
- gelatin with a stronger Bloom can make it possible to reduce the percentage of gelatin in the granules and therefore bring to a minimum value the duration of elimination of the gelatin before reaching the sintering phase proper at high temperature.
- the granules the elementary spherical particles of which are agglomerated by means of gelatin, do not stick to the walls of the molds, even when the latter heat up to temperatures reaching 100 ° C. or more, lubrication by a small amount of Zn stearate or another suitable lubricant can be used.
- the invention also relates to the process for the preparation of a metal powder based on elementary spherical particles suitable for cold forming by compression and then for sintering.
- an agglomeration is carried out in granules of the elementary spherical particles.
- gelatin is added to the elementary spherical starting particles in the form of an aqueous solution, the amount of water used being of the order of two to five times the amount of gelatin and the temperature of the water being 40 to 80 ° C.
- the amount of gelatin to be used depends on the size of the elementary spherical particles and also on the gel strength of the gelatin.
- the mixture of elementary particles and gelatin solution is triturated for the time necessary to obtain the wetting of the metal particles and during cooling the gradual formation of a gel.
- partial drying is carried out, for example, by blowing a gas stream which makes it possible to give the mixture a pasty consistency, then a fragmentation of this paste is carried out, for example by pressing it on a sieve whose width mesh size is determined by taking into account the diameter of the elementary spherical particles.
- Granules are thus formed, the drying of which is continued until elimination, preferably as complete as possible, of the water.
- the amount of gelatin contained in the granules is at least 0.5% of the weight of the metal powder obtained.
- the fines can be separated by a suitable opening sieve. It is noted that if the maximum diameter "d1" of the elementary spherical particles and the width "d2" of the granules obtained after drying are in a ratio d2 / d1 at least equal to 3 and, preferably, equal or greater than 4, it is possible to obtain by cold compression in a mold parts whose raw mechanical strength is much higher than in the case of the same powder with spherical particles not agglomerated into granules.
- this lubricant and the gelatin are removed by preheating the compressed green part at a temperature generally between 300 and 500 ° C.
- Preheating can be carried out in air or in the presence of a neutral or reducing gas such as Ar, H2, NH3 or other.
- a neutral or reducing gas such as Ar, H2, NH3 or other.
- the examples below describe, without limitation, the characteristics of the metal powder agglomerated into granules based on elementary spherical particles suitable for forming by cold compression and then for sintering according to the invention.
- the examples also describe, without limitation also, an embodiment of such an agglomerated powder and an embodiment of this powder for the production of parts by compression in a mold then sintering.
- This example relates to the process according to the invention for preparing a metallic powder agglomerated in granules from elementary spherical particles which has the properties according to the invention of aptitude for cold compression forming and sintering.
- Spherical particles obtained in known manner are used by spraying with a neutral gas a bath of stainless steel, the composition of which corresponds to grade 316 defined by the ASTM standard.
- a batch of these particles is prepared by sieving, the particle diameter of which is not more than 106 microns.
- An aqueous solution based on deionized water is prepared containing by weight 30% of a gelatin whose jelly strength is 50 blooms. The solution is heated to 50 to 70 ° C to completely dissolve the gelatin.
- a mixture is produced containing 95% of 316 steel particles of not more than 106 microns in diameter and 5% of aqueous solution, ie 1.5% by weight of gelatin.
- An intimate mixture must be produced in order to wet the entire surface of the elementary particles with the solution.
- Granules are thus obtained.
- the drying of these by cold or hot air is continued then a second sieving is carried out in order to separate the granules from each other and to calibrate them by passage through a sieve with a mesh of 500 microns.
- Granules are thus obtained whose dimensional ratio is at least 4.7 compared to the maximum diameter of the metal particles.
- These dried granules are made up of agglomerated spherical metallic particles, firmly bound to one another by gelatin films, certain granules however being able to be constituted by isolated elementary particles coated with gelatin.
- the powder thus agglomerated into granules is capable of forming, by cold compression in a mold, parts having a raw mechanical strength much greater than that obtained with the starting metal particles.
- Adding a small amount of a lubricant such as zinc stearate to the agglomerated granular powder further facilitates forming. Demolding is also facilitated by the fact that the solidified gelatin does not stick to the walls of the molds when they are heated.
- a series of tensile test pieces by cold compression in a mold according to ASTM B312 standard is thus produced by means of the agglomerated powder in granules according to the invention, added with approximately 0.75% by weight of zinc stearate.
- two different compression ratios of 314 and 422 MPa are also produced.
- test pieces compressed under a load of 422 MPa, are preheated in air to around 500 ° C to remove the gelatin and zinc stearate and then sintered by heating to about 1280 ° C.
- Tensile tests carried out on the specimens thus sintered give the following average results: Elastic limit 137.9 MPa (20 ksi) Breaking load 344.7 MPa (50 ksi) Elongation at break 25%.
- a comparative test is made on the same grade of stainless steel 316 using spherical particles having a maximum diameter not greater than 150 microns.
- Agglomeration with gelatin is carried out with the same gelatin concentrations and the same sieving conditions as above, the diameter of the granules obtained being not greater than 500 microns.
- the dimensional ratio between granules and spherical particles is therefore reduced to 3.3.
- the dimensional ratio of 3 between granules and spherical elementary particles is in the immediate vicinity of the acceptable limit and that in practice it is advantageous to choose a dimensional ratio at least equal to 4.
- a metallic powder agglomerated in granules is produced by the method described in Example 1 from a stainless steel type 904 L which contains in% by weight: Cr 20; Ni 25; Mo 4.5; Cu 2: remains Fe.
- the starting material contains spherical particles with a diameter of not more than 106 microns.
- the agglomeration is carried out in the same way as in the case of the steel 316 described in example 1, the final calibration of the granules being made by passing through a mesh screen with a mesh of 500 microns per side, the dimensional ratio between granules and spherical particles therefore being 4.7.
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- Powder Metallurgy (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
Abstract
Description
La poudre métallique qui fait l'objet de l'invention concerne la réalisation de pièces par compression et frittage à partir d'aciers inoxydables, d'autres métaux ou alliages inoxydables ou réfractaires et d'aciers alliés, destinés à la réalisation de pièces de qualité.The metal powder which is the subject of the invention relates to the production of parts by compression and sintering from stainless steels, other stainless or refractory metals or alloys and alloy steels, intended for the production of quality.
Pour la réalisation de ces pièces par compression et frittage, on utilise de façon la plus courante des poudres à particules anguleuses obtenues par pulvérisation de métal liquide par jet d'eau sous pression selon diverses méthodes connues de l'homme de métier.For the production of these parts by compression and sintering, powders with angular particles obtained by spraying liquid metal by jet of water under pressure are most commonly used according to various methods known to those skilled in the art.
Bien que les méthodes de pulvérisation de métal liquide par jet d'eau sous pression soient de très loin les plus utilisées pour la fabrication de poudres métalliques elles ont le grave inconvénient de conduire à des poudres métalliques ayant une forte teneur en oxygène.Although the methods of spraying liquid metal by pressurized water jet are by far the most used for the manufacture of metallic powders, they have the serious disadvantage of leading to metallic powders having a high oxygen content.
On sait aussi préparer des poudres métalliques par pulvérisation d'un métal ou alliage liquide au moyen d'un jet gazeux qui peut être, par exemple, un gaz neutre tel que l'argon ou de l'azote ou tout gaz approprié. On obtient ainsi des poudres ayant une teneur en oxydes beaucoup plus faible que les poudres obtenues par pulvérisation à l'eau et qui présentent ainsi sensiblement la même pureté que le métal de départ.It is also known to prepare metal powders by spraying a metal or liquid alloy by means of a gas jet which may be, for example, a neutral gas such as argon or nitrogen or any suitable gas. Powders are thus obtained having a much lower oxide content than the powders obtained by spraying with water and which thus have substantially the same purity as the starting metal.
Cependant les particules élémentaires de ces poudres ont une forme sensiblement sphérique mais en l'état ne se mettent pas facilement en forme.However, the elementary particles of these powders have a substantially spherical shape but in the state are not easily shaped.
En effet ces poudres permettent, après compression et frittage, d'obtenir par compression des pièces ayant une densité apparente au moins égale à celle que permettent d'obtenir les poudres anguleuses habituelles. Mais, au stade initial de la mise en forme par compression à froid de la poudre dans un moule, la pièce crue obtenue à partir de particules sphériques a une résistance mécanique souvent insuffisante pour permettre sa manipulation et notamment son éjection du moule, puis le transfert en direction du four de frittage, sans écaillage ou fissuration.Indeed, these powders make it possible, after compression and sintering, to obtain by compression parts having an apparent density at least equal to that which allow the usual angular powders to be obtained. But, at the initial stage of shaping by cold compression of the powder in a mold, the green part obtained from spherical particles has a mechanical strength often insufficient to allow its manipulation and in particular its ejection from the mold, then the transfer towards the sintering furnace, without chipping or cracking.
Pour certaines applications qui ne concernent pas les poudres à particules sphériques, on a proposé d'ajouter aux poudres utilisées pour l'obtention de pièces par compression et frittage, différents liants à base de composés organiques. Ainsi, le brevet US 4 456 484 décrit l'addition d'un liant organique à un mélange d'une poudre d'un carbure métallique réfractaire avec une autre poudre métallique, jouant elle-même le rôle de liant métallique. On emploie comme liant une amide qui est une cire. On effectue un broyage du mélange de ces 3 composants en présence d'un liquide tel que de l'eau dans lequel la cire est insoluble et, après séchage, la cire assurant une liaison entre les particules de carbure et celles du liant métallique, on effectue la compression puis le frittage.For certain applications which do not relate to powders with spherical particles, it has been proposed to add to the powders used for obtaining parts by compression and sintering, different binders based on organic compounds. Thus, US Pat. No. 4,456,484 describes the addition of an organic binder to a mixture of a powder of a refractory metal carbide with another metal powder, itself playing the role of metal binder. An amide which is a wax is used as a binder. The mixture of these 3 components is crushed in the presence of a liquid such as water in which the wax is insoluble and, after drying, the wax ensuring a bond between the carbide particles and those of the metal binder, performs compression and then sintering.
La demande de brevet GB 2 228 744 décrit une méthode analogue pour solidariser des éléments d'alliages tels que le graphite, le phosphore ou autres avec un métal de base. Selon cette méthode, on utilise comme liant un mélange d'un ester d'acide acrylique avec un ester d'acide méthacrylique et un acide polymérisable non saturé.Patent application GB 2 228 744 describes a similar method for joining elements of alloys such as graphite, phosphorus or the like with a base metal. According to this method, a mixture of an acrylic acid ester with a methacrylic acid ester and an unsaturated polymerizable acid is used as binder.
Ces composants sont mis en solution dans du toluène.These components are dissolved in toluene.
Le but visé est d'éviter la ségrégation de particules plus fines ou plus légères telles que le graphite ou d'autres par rapport à un métal de base, tel que le fer, en liant ces particules entre elles.The aim is to avoid the segregation of finer or lighter particles such as graphite or others compared to a base metal, such as iron, by binding these particles together.
Il n'est, nulle part, envisagé dans ces documents d'utiliser de tels liants organiques pour améliorer la résistance mécanique crue de pièces moulées.Nowhere in these documents is it envisaged to use such organic binders to improve the raw mechanical strength of molded parts.
Par ailleurs, ces liants après mise en oeuvre, doivent être éliminées avant ou au cours du frittage et on constate souvent une contamination des poudres métalliques par certains composants des liants.Furthermore, these binders after implementation, must be removed before or during sintering and contamination of the metal powders is often observed with certain components of the binders.
Enfin, on se rend compte qu'il ne suffit pas d'améliorer la liaison entre une petite quantité d'une poudre fine telle que le graphite et les particules de poudre par exemple de fer plus grossières pour améliorer la résistance mécanique d'une pièce moulée.Finally, we realize that it is not enough to improve the bond between a small quantity of a fine powder such as graphite and the coarser powder particles, for example of iron, to improve the mechanical resistance of a part. molded.
On a recherché la possibilité de modifier les caractéristiques d'aptitude au formage d'une poudre métallique constituée de particules sphériques, en vue d'obtenir, après formage, des pièces présentant une résistance mécanique à cru bien supérieure à celle résultant de la compaction de ladite poudre utilisée telle quelle.The possibility of modifying the aptitude for forming of a metal powder made up of spherical particles has been sought, in order to obtain, after forming, parts having a raw mechanical strength much greater than that resulting from the compaction of said powder used as it is.
On a recherché aussi la possibilité de conférer à cette poudre métallique de telles caractéristiques de façon durable, cette poudre formable et frittable étant apte au transport sur de longues distances et au stockage sans perte de ses caractéristiques d'aptitude au formage puis au frittage.We have also sought the possibility of giving this metallic powder such characteristics in a lasting manner, this formable and sinterable powder being suitable for transport over long distances and for storage without loss of its characteristics of ability to form then to sinter.
On a recherché enfin la possibilité d'une mise en oeuvre facile d'une telle poudre, les additifs éventuels ne nécessitant pas de traitements particuliers avant frittage pour leur élimination en dehors éventuellement d'un traitement de courte durée, vers 300 à 500°C, d'élimination des lubrifiants tels que le stéarate de zinc, traitement habituel dans le procédé de compression-frittage de poudres métalliques.Finally, we looked for the possibility of easy implementation of such a powder, any additives not requiring any special treatment before sintering for their elimination, possibly outside a short-term treatment, around 300 to 500 ° C. , elimination of lubricants such as zinc stearate, usual treatment in the compression-sintering process of metallic powders.
La poudre métallique à base de particules sphériques, apte au formage à froid par compression suivi d'un frittage, qui fait l'objet de l'invention ainsi que le procédé de préparation de cette poudre qui fait aussi l'objet de l'invention permettent de résoudre l'ensemble des problèmes ainsi posés.The metal powder based on spherical particles, suitable for cold forming by compression followed by sintering, which is the subject of the invention as well as the process for the preparation of this powder which is also the subject of the invention allow to solve all the problems thus posed.
La poudre métallique suivant l'invention est constituée par un ensemble de granules comprenant chacun un groupe de particules métalliques élémentaires de forme sphérique agglomérées par de la gélatine à une teneur d'au moins 0,5 % du poids de la poudre métallique.The metal powder according to the invention consists of a set of granules each comprising a group of elementary metal particles of spherical shape agglomerated by gelatin at a content of at least 0.5% of the weight of the metal powder.
Les particules sphériques sont avantageusement obtenues par un procédé de pulvérisation, au moyen d'un gaz qui peut être l'air ou un gaz neutre ou réducteur tel que N₂, H₂, NH₃, Ar, ou autre, d'un métal ou alliage liquide.The spherical particles are advantageously obtained by a spraying process, by means of a gas which can be air or a neutral or reducing gas such as N₂, H₂, NH₃, Ar, or other, of a metal or liquid alloy .
Les principaux métaux ou alliages qui peuvent être utilisés sont, par exemple, des aciers inoxydables, des métaux ou alliages inoxydables ou réfractaires ou encore des aciers alliés à hautes caractéristiques mécaniques. Les dimensions de ces particules élémentaires et celles des granules sont choisies principalement en fonction des dimensions et caractéristiques notamment de densité des pièces moulées qu'il s'agit de réaliser.The main metals or alloys which can be used are, for example, stainless steels, stainless or refractory metals or alloys or even alloy steels with high mechanical characteristics. The dimensions of these elementary particles and those of the granules are chosen mainly as a function of the dimensions and, in particular, density characteristics of the molded parts which it is a question of producing.
On constate que pour obtenir, par formage sous pression à froid, une pièce présentant une résistance mécanique suffisante à cru, il est préférable que chaque granule comporte un nombre suffisant de particules sphériques agglomérées par la gélatine. Il faut aussi que ces granules soient aptes à remplir correctement le moule dans ses moindres recoins. Cependant un certain nombre de granules peuvent être constitués de particules élémentaires isolées enrobées de gélatine sans que cela nuise à la qualité du produit final obtenu.It is found that in order to obtain, by cold pressure forming, a part having sufficient mechanical strength when raw, it is preferable for each granule to contain a sufficient number of spherical particles agglomerated by the gelatin. It is also necessary that these granules are capable of correctly filling the mold in every corner. However, a certain number of granules can be formed of isolated elementary particles coated with gelatin without affecting the quality of the final product obtained.
Dans la pratique, on détermine un diamètre maximal "d₁", des particules sphériques élémentaires et une largeur maximale "d₂" des granules obtenus. On constate que la poudre suivant l'invention doit avoir, de préférence, un rapport de d₂/d₁ ≧3 pour que les pièces moulées sous pression à froid atteignent une résistance mécanique suffisante.In practice, a maximum diameter "d₁", elementary spherical particles and a maximum width "d₂" of the granules obtained are determined. It is found that the powder according to the invention must preferably have a ratio of d₂ / d₁ ≧ 3 so that the cold-pressure molded parts reach sufficient mechanical strength.
De façon particulièrement avantageuse ce rapport d₂/d₁ peut atteindre au moins 4 ou davantage. Dans le cas, par exemple, d'une poudre dont les particules sphériques ont un diamètre maximal "d₁" de 100 microns, une largeur maximale "d₂" des granules de 300 microns constitue une limite inférieure.In a particularly advantageous manner, this d₂ / d₁ ratio can reach at least 4 or more. In the case, for example, of a powder whose spherical particles have a maximum diameter "d₁" of 100 microns, a maximum width "d₂" of the granules of 300 microns constitutes a lower limit.
Pour obtenir des résultats encore meilleurs, il faut donner aux granules une largeur maximale "d₂" de, par exemple, 500 microns correspondant donc à un rapport d₂/d₁ = 5.To obtain even better results, the granules must be given a maximum width "d₂" of, for example, 500 microns therefore corresponding to a ratio d₂ / d₁ = 5.
La teneur en gélatine doit être déterminée en fonction de la grosseur moyenne des particules sphériques élémentaires qui sont agglomérées par la gélatine. Cette teneur dépend aussi de la force en gelée de la gélatine. Cette force en gelée s'exprime en Bloom (unité standardisée) et peut varier entre 50 et 250 blooms en fonction de la gélatine utilisée.The gelatin content must be determined according to the average size of the elementary spherical particles which are agglomerated by the gelatin. This content also depends on the jelly strength of the gelatin. This strength in jelly is expressed in Bloom (standardized unit) and can vary between 50 and 250 blooms depending on the gelatin used.
L'utilisation de gélatines à plus fort Bloom peut permettre de réduire le pourcentage en gélatine des granules et donc porter à une valeur minimum la durée d'élimination de la gélatine avant d'atteindre la phase de frittage proprement dite à haute température.The use of gelatin with a stronger Bloom can make it possible to reduce the percentage of gelatin in the granules and therefore bring to a minimum value the duration of elimination of the gelatin before reaching the sintering phase proper at high temperature.
Bien que les granules, dont les particules sphériques élémentaires sont agglomérées au moyen de gélatine, ne collent pas aux parois des moules, même lorsque celles-ci s'échauffent à des températures atteignant 100°C ou davantage, une lubrification par une faible quantité de stéarate de Zn ou d'un autre lubrifiant adapté peut être utilisée.Although the granules, the elementary spherical particles of which are agglomerated by means of gelatin, do not stick to the walls of the molds, even when the latter heat up to temperatures reaching 100 ° C. or more, lubrication by a small amount of Zn stearate or another suitable lubricant can be used.
L'invention concerne aussi le procédé de préparation d'une poudre métallique à base de particules sphériques élémentaires aptes au formage à froid par compression puis au frittage.The invention also relates to the process for the preparation of a metal powder based on elementary spherical particles suitable for cold forming by compression and then for sintering.
Selon ce procédé, on effectue une agglomération en granules des particules sphériques élémentaires. Pour cela on ajoute aux particules sphériques élémentaires de départ de la gélatine sous forme d'une solution aqueuse, la quantité d'eau utilisée étant de l'ordre de deux à cinq fois la quantité de gélatine et la température de l'eau étant de 40 à 80°C. Comme indiqué plus haut, la quantité de gélatine à mettre en oeuvre dépend de la grosseur des particules sphériques élémentaires et aussi de la force en gelée de la gélatine. On triture le mélange de particules élémentaires et de solution de gelatine le temps nécessaire pour obtenir le mouillage des particules métalliques et au cours du refroidissement la formation progressive d'un gel. On effectue, de préférence, un séchage partiel, par exemple, par soufflage d'un courant gazeux qui permet de donner au mélange une consistance pâteuse, puis on effectue une fragmentation de cette pâte, par exemple en la pressant sur un tamis dont la largeur de maille est déterminée en tenant compte du diamètre des particules sphériques élémentaires.According to this method, an agglomeration is carried out in granules of the elementary spherical particles. For this, gelatin is added to the elementary spherical starting particles in the form of an aqueous solution, the amount of water used being of the order of two to five times the amount of gelatin and the temperature of the water being 40 to 80 ° C. As indicated above, the amount of gelatin to be used depends on the size of the elementary spherical particles and also on the gel strength of the gelatin. The mixture of elementary particles and gelatin solution is triturated for the time necessary to obtain the wetting of the metal particles and during cooling the gradual formation of a gel. Preferably, partial drying is carried out, for example, by blowing a gas stream which makes it possible to give the mixture a pasty consistency, then a fragmentation of this paste is carried out, for example by pressing it on a sieve whose width mesh size is determined by taking into account the diameter of the elementary spherical particles.
On forme ainsi des granules dont on poursuit le séchage jusqu'à élimination, de préférence aussi complète que possible, de l'eau. On termine l'opération, de préférence, par un calibrage final qui permet de bien individualiser les granules en les séparant les uns des autres et aussi de leur donner des dimensions relativement régulières. La quantité de gélatine contenue dans les granules est d'au moins 0,5 % du poids de la poudre métallique obtenue.Granules are thus formed, the drying of which is continued until elimination, preferably as complete as possible, of the water. We end the operation, preferably, by a final calibration which allows to individualize the granules by separating them from each other and also to give them relatively regular dimensions. The amount of gelatin contained in the granules is at least 0.5% of the weight of the metal powder obtained.
On peut séparer les fines par un tamis d'ouverture convenable. On constate que si le diamètre maximal "d₁" des particules sphériques élémentaires et la largeur "d₂" des granules obtenus après séchage sont dans un rapport d₂/d₁ au moins égal à 3 et, de préférence, égal ou supérieur à 4, on peut obtenir par compression à froid dans un moule des pièces dont la résistance mécanique à cru est beaucoup plus élevée que dans le cas de la même poudre à particules sphériques non agglomérées en granules.The fines can be separated by a suitable opening sieve. It is noted that if the maximum diameter "d₁" of the elementary spherical particles and the width "d₂" of the granules obtained after drying are in a ratio d₂ / d₁ at least equal to 3 and, preferably, equal or greater than 4, it is possible to obtain by cold compression in a mold parts whose raw mechanical strength is much higher than in the case of the same powder with spherical particles not agglomerated into granules.
On peut, avantageusement, avant formage, incorporer à la poudre ainsi constituée de granules, un lubrifiant tel que le stéarate de zinc.One can advantageously, before forming, incorporate into the powder thus constituted of granules, a lubricant such as zinc stearate.
Après compression, on élimine ce lubrifiant et la gélatine par préchauffage de la pièce crue comprimée à une température généralement comprise entre 300 et 500°C.After compression, this lubricant and the gelatin are removed by preheating the compressed green part at a temperature generally between 300 and 500 ° C.
Le préchauffage peut être effectué à l'air ou en présence d'un gaz neutre ou réducteur tel que Ar, H₂, NH₃ ou autre. Après élimination complète de la gélatine et du lubrifiant, s'il y en a, on effectue le frittage à température appropriée au matériau pour obtenir la densification désirée.Preheating can be carried out in air or in the presence of a neutral or reducing gas such as Ar, H₂, NH₃ or other. After the gelatin and the lubricant, if any, have been completely removed, sintering is carried out at a temperature appropriate to the material in order to obtain the desired densification.
Après refroidissement, on constate, tous les paramètres étant inchangés par ailleurs, que les pièces ainsi obtenues, telles que par exemple des pièces en aciers inoxydables, ont une densité apparente en général supérieure à celle de pièces préparées à partir de poudres anguleuses de même composition et aussi des caractéristiques mécaniques supérieures en ce qui concerne la ductilité.After cooling, it is found, all the parameters being unchanged elsewhere, that the parts thus obtained, such as for example parts made of stainless steels, have an apparent density generally greater than that of parts prepared from angular powders of the same composition. and also superior mechanical characteristics with regard to ductility.
Il apparaît que pratiquement tous les métaux ou alliages inoxydables ou réfractaires susceptibles d'être pulvérisés sous forme de particules sphériques peuvent subir une transformation par métallurgie des poudres grâce au procédé d'agglomération en granules des particules sphériques suivant l'invention.It appears that practically all stainless or refractory metals or alloys capable of being sprayed in the form of spherical particles can undergo transformation by powder metallurgy by means of the agglomeration process into granules of the spherical particles according to the invention.
Les exemples ci-après décrivent, de façon non limitative, les caractéristiques de la poudre métallique agglomérée en granules à base de particules sphériques élémentaires apte au formage par compression à froid puis au frittage suivant l'invention. Les exemples décrivent aussi, de façon non limitative également, un mode de réalisation d'une telle poudre agglomérée et un mode de mise en oeuvre de cette poudre pour la réalisation de pièces par compression dans un moule puis frittage.The examples below describe, without limitation, the characteristics of the metal powder agglomerated into granules based on elementary spherical particles suitable for forming by cold compression and then for sintering according to the invention. The examples also describe, without limitation also, an embodiment of such an agglomerated powder and an embodiment of this powder for the production of parts by compression in a mold then sintering.
Cet exemple concerne le procédé suivant l'invention de préparation d'une poudre métallique agglomérée en granules à partir de particules sphériques élémentaires qui présente les propriétés suivant l'invention d'aptitude au formage par compression à froid et au frittage.This example relates to the process according to the invention for preparing a metallic powder agglomerated in granules from elementary spherical particles which has the properties according to the invention of aptitude for cold compression forming and sintering.
On met en oeuvre des particules sphériques obtenues de façon connue par pulvérisation par un gaz neutre d'un bain d'acier inoxydable dont la composition correspond au grade 316 défini par la norme ASTM. On prépare par tamisage un lot de ces particules dont le diamètre des particules n'est pas supérieur à 106 microns. On prépare une solution aqueuse à base d'eau désionisée contenant en poids 30 % d'une gélatine dont la force en gelée est de 50 blooms. On chauffe la solution entre 50 et 70°C pour mettre en solution la gélatine de façon complète.Spherical particles obtained in known manner are used by spraying with a neutral gas a bath of stainless steel, the composition of which corresponds to grade 316 defined by the ASTM standard. A batch of these particles is prepared by sieving, the particle diameter of which is not more than 106 microns. An aqueous solution based on deionized water is prepared containing by weight 30% of a gelatin whose jelly strength is 50 blooms. The solution is heated to 50 to 70 ° C to completely dissolve the gelatin.
On réalise un mélange contenant 95 % de particules d'acier 316 de pas plus de 106 microns de diamètre et 5 % de solution aqueuse, soit 1,5 % en poids de gélatine. On doit réaliser un mélange intime afin de mouiller par la solution toute la surface des particules élémentaires.A mixture is produced containing 95% of 316 steel particles of not more than 106 microns in diameter and 5% of aqueous solution, ie 1.5% by weight of gelatin. An intimate mixture must be produced in order to wet the entire surface of the elementary particles with the solution.
Le refroidissement progressif de la solution entraîne la formation du gel. On fait évaporer une partie de l'eau par soufflage d'air et on fait passer le mélange qui a une consistance pâteuse, à travers un tamis ayant des mailles d'environ 630 microns.The gradual cooling of the solution results in the formation of the gel. Part of the water is evaporated by air blowing and the mixture, which has a pasty consistency, is passed through a sieve having meshes of approximately 630 microns.
On obtient ainsi des granules. Le séchage de ceux-ci par air froid ou chaud est poursuivi puis un deuxième tamisage est effectué afin de séparer les granules les uns des autres et de les calibrer par passage à travers un tamis à mailles de 500 microns.Granules are thus obtained. The drying of these by cold or hot air is continued then a second sieving is carried out in order to separate the granules from each other and to calibrate them by passage through a sieve with a mesh of 500 microns.
On obtient ainsi des granules dont le rapport dimensionnel est d'au moins 4,7 comparé au diamètre maximal des particules métalliques. Ces granules séchés sont constitués de particules métalliques sphériques agglomérées, solidement liées entre elles par des films de gélatine, certains granules pouvant cependant être constitués par des particules élémentaires isolées enrobées de gélatine.Granules are thus obtained whose dimensional ratio is at least 4.7 compared to the maximum diameter of the metal particles. These dried granules are made up of agglomerated spherical metallic particles, firmly bound to one another by gelatin films, certain granules however being able to be constituted by isolated elementary particles coated with gelatin.
On constate que la poudre ainsi agglomérée en granules est apte à former par compression à froid dans un moule des pièces ayant une résistance mécanique à cru très supérieure à celle qu'on obtient avec les particules métalliques de départ. L'addition, à la poudre agglomérée en granules, d'une faible quantité d'un lubrifiant tel que le stéarate de zinc facilite encore le formage. Le démoulage est également facilité par le fait que la gélatine solidifiée ne colle pas aux parois des moules lorsque ceux-ci sont échauffés.It is found that the powder thus agglomerated into granules is capable of forming, by cold compression in a mold, parts having a raw mechanical strength much greater than that obtained with the starting metal particles. Adding a small amount of a lubricant such as zinc stearate to the agglomerated granular powder further facilitates forming. Demolding is also facilitated by the fact that the solidified gelatin does not stick to the walls of the molds when they are heated.
On réalise ainsi au moyen de la poudre agglomérée en granules suivant l'invention, additionnée d'environ 0,75 % en poids de stéarate de zinc une série d'éprouvettes de traction par compression à froid dans un moule selon la norme ASTM B312 sous deux taux de compression différents de 314 et 422 MPa.A series of tensile test pieces by cold compression in a mold according to ASTM B312 standard is thus produced by means of the agglomerated powder in granules according to the invention, added with approximately 0.75% by weight of zinc stearate. two different compression ratios of 314 and 422 MPa.
Les mesures de résistance mécanique à la traction effectuées à cru sur une partie de ces éprouvettes donnent des résultats de charge de rupture de respectivement 6,55 et 9,65 MPa (950 et 1400 psi). Ces valeurs sont tout à fait satisfaisantes car bien supérieures au minimum considéré comme acceptable de 3,44 MPa (500 psi).Measurements of mechanical tensile strength carried out bare on a part of these specimens give results of breaking load of 6.55 and 9.65 MPa (950 and 1400 psi) respectively. These values are entirely satisfactory since they are much higher than the minimum considered acceptable of 3.44 MPa (500 psi).
Les éprouvettes restantes, comprimées sous une charge de 422 MPa, sont préchauffées à l'air jusque vers 500°C pour éliminer la gélatine et le stéarate de zinc puis frittées par chauffage jusqu'à environ 1280°C. Des essais de traction effectués sur les éprouvettes ainsi frittées donnent les résultats moyens suivants :
Limite élastique 137,9 MPa (20 ksi)
Charge de rupture 344,7 MPa (50 ksi)
Allongement de rupture 25 %.The remaining test pieces, compressed under a load of 422 MPa, are preheated in air to around 500 ° C to remove the gelatin and zinc stearate and then sintered by heating to about 1280 ° C. Tensile tests carried out on the specimens thus sintered give the following average results:
Elastic limit 137.9 MPa (20 ksi)
Breaking load 344.7 MPa (50 ksi)
Elongation at break 25%.
Selon la norme ASTM B525, les valeurs typiques de caractéristiques mécaniques de cet acier 316 sont :
Charge de rupture 413,7 MPa (60 ksi)
Allongement de rupture 7 %.According to ASTM B525, the typical values of mechanical characteristics of this 316 steel are:
Breaking load 413.7 MPa (60 ksi)
Elongation at break 7%.
Un essai comparatif est fait sur la même nuance d'acier inoxydable 316 en utilisant des particules sphériques ayant un diamètre maximal pas supérieur à 150 microns.A comparative test is made on the same grade of stainless steel 316 using spherical particles having a maximum diameter not greater than 150 microns.
L'agglomération par de la gélatine est effectuée avec les mêmes concentrations en gélatine et les mêmes conditions de tamisage que ci-dessus, le diamètre des granules obtenus n'étant pas supérieur à 500 microns. Le rapport dimensionnel entre granules et particules sphériques est donc réduit à 3,3.Agglomeration with gelatin is carried out with the same gelatin concentrations and the same sieving conditions as above, the diameter of the granules obtained being not greater than 500 microns. The dimensional ratio between granules and spherical particles is therefore reduced to 3.3.
On constate qu'on obtient dans ces conditions une résistance mécanique à cru des éprouvettes moulées sous pression beaucoup plus faible que dans l'exemple précédent et on constate de plus une tendance à la fissuration des éprouvettes de traction au cours du frittage.It is found that under these conditions a raw mechanical strength of the pressure molded test pieces is much lower than in the previous example and there is moreover a tendency to cracking of the tensile test pieces during sintering.
Dans un autre essai comparatif, on utilise à nouveau de l'acier 316 composé de particules de diamètre pas supérieur à 106 microns mais on réduit la dimension des granules par calibrage final à travers des trous de 300 microns de côté. Le rapport dimensionnel est donc réduit à 2,8. On constate qu'en essayant de mouler par compression à froid des éprouvettes de traction on observe des ruptures de celles-ci dès le démoulage.In another comparative test, use is again made of steel 316 composed of particles of diameter not greater than 106 microns but the size of the granules is reduced by final calibration through holes of 300 microns on each side. The dimensional ratio is therefore reduced to 2.8. It is found that when trying to cold compression mold tensile test pieces, they are observed to rupture as soon as they are removed from the mold.
On voit donc que le rapport dimensionnel de 3 entre granules et particules élémentaires sphériques est au voisinage immédiat de la limite acceptable et que dans la pratique il est avantageux de choisir un rapport dimensionnel au moins égal à 4.It can therefore be seen that the dimensional ratio of 3 between granules and spherical elementary particles is in the immediate vicinity of the acceptable limit and that in practice it is advantageous to choose a dimensional ratio at least equal to 4.
On realise, par le procédé décrit dans l'exemple 1, une poudre métallique agglomérée en granules à partir d'un acier inoxydable type 904 L qui contient en % en poids : Cr 20 ; Ni 25 ; Mo 4,5 ; Cu 2 : reste Fe.A metallic powder agglomerated in granules is produced by the method described in Example 1 from a stainless steel type 904 L which contains in% by weight: Cr 20; Ni 25; Mo 4.5; Cu 2: remains Fe.
Le produit de départ comporte des particules sphériques de diamètre pas supérieur à 106 microns. On effectue l'agglomération de la même façon que dans le cas de l'acier 316 décrit dans l'exemple 1, le calibrage final des granules étant fait par passage à travers un tamis à mailles de 500 microns de côté, le rapport dimensionnel entre granules et particules sphériques étant donc de 4,7.The starting material contains spherical particles with a diameter of not more than 106 microns. The agglomeration is carried out in the same way as in the case of the steel 316 described in example 1, the final calibration of the granules being made by passing through a mesh screen with a mesh of 500 microns per side, the dimensional ratio between granules and spherical particles therefore being 4.7.
Après formage d'éprouvettes de traction par compression à froid avec une pression de 422 MPa puis frittage, ces opérations étant effectuées comme dans le cas de l'exemple 1, la mesure des caractéristiques mécaniques en traction donne les résultats suivants :
Charge de rupture en traction 448,2 MPa (65 ksi)
Allongement de rupture : 15 %.
Un essai de corrosion, effectué à température ambiante, en solution sulfurique à 1 % ne fait apparaître aucune attaque après 48 heures.After forming of tensile specimens by cold compression with a pressure of 422 MPa then sintering, these operations being carried out as in the case of Example 1, the measurement of the mechanical characteristics in traction gives the following results:
Tensile breaking load 448.2 MPa (65 ksi)
Elongation at break: 15%.
A corrosion test, carried out at room temperature, in 1% sulfuric solution shows no attack after 48 hours.
Ces résultats, en particulier l'ensemble 2, montrent que la poudre métallique suivant l'invention comportant des granules constitués de particules sphériques élémentaires liées par de la gélatine permet la réalisation par compression et frittage de pièces en acier inoxydable qu'on ne sait pas réaliser par la méthode habituelle qui s'applique aux poudres anguleuses, l'élaboration par pulvérisation dans l'eau de tels aciers fortement alliés étant difficile à envisager du fait de la teneur en oxygène qui en résulterait.These results, in particular assembly 2, show that the metal powder according to the invention comprising granules consisting of elementary spherical particles linked by gelatin allows the production by compression and sintering of stainless steel parts which are not known. achieve by the usual method which applies to angular powders, the development by spraying in water of such highly alloyed steels being difficult to envisage because of the oxygen content which would result therefrom.
De nombreuses modifications ou variantes peuvent être apportées aux caractéristiques de la poudre agglomérée en granules qui fait l'objet de l'invention et aussi au mode de préparation suivant l'invention de cette poudre agglomérée en granules à partir des particules métalliques sphériques qui la constituent.Many modifications or variants can be made to the characteristics of the agglomerated powder in granules which is the subject of the invention and also to the method of preparation according to the invention of this agglomerated powder in granules from the spherical metallic particles which constitute it. .
Ces variantes et ces modifications font également partie de l'invention.These variants and modifications also form part of the invention.
Claims (11)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR9308535 | 1993-07-06 | ||
| FR9308535A FR2707191B1 (en) | 1993-07-06 | 1993-07-06 | Metallic powder for making parts by compression and sintering and process for obtaining this powder. |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0633083A1 true EP0633083A1 (en) | 1995-01-11 |
| EP0633083B1 EP0633083B1 (en) | 2001-09-12 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP94420188A Expired - Lifetime EP0633083B1 (en) | 1993-07-06 | 1994-07-04 | Metallic powder for making parts by compression and sintering and process for obtaining the powder |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US5460641A (en) |
| EP (1) | EP0633083B1 (en) |
| JP (1) | JP3325390B2 (en) |
| KR (1) | KR960013531A (en) |
| AT (1) | ATE205430T1 (en) |
| CA (1) | CA2127344A1 (en) |
| DE (1) | DE69428236T2 (en) |
| DK (1) | DK0633083T3 (en) |
| ES (1) | ES2162849T3 (en) |
| FR (1) | FR2707191B1 (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE511834C2 (en) | 1998-01-13 | 1999-12-06 | Valtubes Sa | Fully dense products made by uniaxial high speed metal powder pressing |
| SE518986C2 (en) * | 2000-04-28 | 2002-12-17 | Metals Process Systems | Method of sintering carbon steel using binder as carbon source |
| US6585795B2 (en) * | 2000-08-07 | 2003-07-01 | Ira L. Friedman | Compaction of powder metal |
| US6537489B2 (en) | 2000-11-09 | 2003-03-25 | Höganäs Ab | High density products and method for the preparation thereof |
| SE0102102D0 (en) * | 2001-06-13 | 2001-06-13 | Hoeganaes Ab | High density stainless steel products and method of preparation thereof |
| SE0201825D0 (en) | 2002-06-14 | 2002-06-14 | Hoeganaes Ab | Hot compaction or steel powders |
| US7192464B2 (en) * | 2003-09-03 | 2007-03-20 | Apex Advanced Technologies, Llc | Composition for powder metallurgy |
| US7470307B2 (en) * | 2005-03-29 | 2008-12-30 | Climax Engineered Materials, Llc | Metal powders and methods for producing the same |
| US7604679B2 (en) * | 2005-11-04 | 2009-10-20 | Sumitomo Metal Mining Co., Ltd. | Fine nickel powder and process for producing the same |
| DE102014113425A1 (en) * | 2014-09-17 | 2016-03-17 | Fachhochschule Münster | Method for coating an article |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0029389A1 (en) * | 1979-11-14 | 1981-05-27 | Creusot-Loire | Process for producing shaped articles from spherical metal-particle powders |
| US4787934A (en) * | 1988-01-04 | 1988-11-29 | Gte Products Corporation | Hydrometallurgical process for producing spherical maraging steel powders utilizing spherical powder and elemental oxidizable species |
| DE4027887A1 (en) * | 1990-09-03 | 1992-03-05 | Stoess & Co Gelatine | GRAINY AGGLOMERATE AND METHOD FOR THE PRODUCTION THEREOF |
| US5126104A (en) * | 1991-06-06 | 1992-06-30 | Gte Products Corporation | Method of making powder for thermal spray application |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4006838A (en) * | 1974-11-25 | 1977-02-08 | Western Industries, Inc. | Brazing alloy and brazing paste for gas container joints |
-
1993
- 1993-07-06 FR FR9308535A patent/FR2707191B1/en not_active Expired - Fee Related
-
1994
- 1994-06-29 JP JP17023794A patent/JP3325390B2/en not_active Expired - Fee Related
- 1994-07-04 EP EP94420188A patent/EP0633083B1/en not_active Expired - Lifetime
- 1994-07-04 CA CA002127344A patent/CA2127344A1/en not_active Abandoned
- 1994-07-04 ES ES94420188T patent/ES2162849T3/en not_active Expired - Lifetime
- 1994-07-04 AT AT94420188T patent/ATE205430T1/en not_active IP Right Cessation
- 1994-07-04 DK DK94420188T patent/DK0633083T3/en active
- 1994-07-04 DE DE69428236T patent/DE69428236T2/en not_active Expired - Lifetime
- 1994-07-06 KR KR1019940016267A patent/KR960013531A/en not_active Application Discontinuation
- 1994-07-06 US US08/268,117 patent/US5460641A/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0029389A1 (en) * | 1979-11-14 | 1981-05-27 | Creusot-Loire | Process for producing shaped articles from spherical metal-particle powders |
| US4787934A (en) * | 1988-01-04 | 1988-11-29 | Gte Products Corporation | Hydrometallurgical process for producing spherical maraging steel powders utilizing spherical powder and elemental oxidizable species |
| DE4027887A1 (en) * | 1990-09-03 | 1992-03-05 | Stoess & Co Gelatine | GRAINY AGGLOMERATE AND METHOD FOR THE PRODUCTION THEREOF |
| US5126104A (en) * | 1991-06-06 | 1992-06-30 | Gte Products Corporation | Method of making powder for thermal spray application |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2707191A1 (en) | 1995-01-13 |
| CA2127344A1 (en) | 1995-01-07 |
| US5460641A (en) | 1995-10-24 |
| JPH0754002A (en) | 1995-02-28 |
| EP0633083B1 (en) | 2001-09-12 |
| KR960013531A (en) | 1996-05-22 |
| DE69428236T2 (en) | 2002-06-27 |
| JP3325390B2 (en) | 2002-09-17 |
| ATE205430T1 (en) | 2001-09-15 |
| DE69428236D1 (en) | 2001-10-18 |
| ES2162849T3 (en) | 2002-01-16 |
| DK0633083T3 (en) | 2002-01-14 |
| FR2707191B1 (en) | 1995-09-01 |
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