EP0635325A1 - Process for making a workpiece in titanium by sintering and a decorative article made by such a process - Google Patents

Process for making a workpiece in titanium by sintering and a decorative article made by such a process Download PDF

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Publication number
EP0635325A1
EP0635325A1 EP94111197A EP94111197A EP0635325A1 EP 0635325 A1 EP0635325 A1 EP 0635325A1 EP 94111197 A EP94111197 A EP 94111197A EP 94111197 A EP94111197 A EP 94111197A EP 0635325 A1 EP0635325 A1 EP 0635325A1
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EP
European Patent Office
Prior art keywords
titanium
binder
atmosphere
sintering
temperature
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EP94111197A
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German (de)
French (fr)
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EP0635325B1 (en
Inventor
Thomas Gladden
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Asulab AG
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Asulab AG
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Priority claimed from CH2246/93A external-priority patent/CH684978B5/en
Priority claimed from FR9309530A external-priority patent/FR2708496B1/en
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Classifications

    • 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
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/22—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip
    • B22F3/225—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces for producing castings from a slip by injection molding
    • 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
    • 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
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/001—Starting from powder comprising reducible metal compounds
    • 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
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/1017—Multiple heating or additional steps
    • B22F3/1021—Removal of binder or filler
    • B22F3/1025—Removal of binder or filler not by heating only
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B19/00—Indicating the time by visual means
    • G04B19/06—Dials
    • G04B19/12—Selection of materials for dials or graduations markings
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B37/00—Cases
    • G04B37/22—Materials or processes of manufacturing pocket watch or wrist watch cases
    • 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
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy

Definitions

  • the invention relates to a method for manufacturing a titanium part by powder technologies and in particular such a method for manufacturing titanium parts by sintering titanium hydride powder (TiH2), parts whose porosity is lower. at around 2%.
  • TiH2 titanium hydride powder
  • the invention also relates to a decorative article produced by such a method.
  • the process of the invention is more particularly suited to the manufacture of semi-finished titanium products which are intended to produce decorative articles such as watch cases, bracelet links, watch dials or the like, which once polished have an intense shiny surface.
  • the TiH2 powder is firstly mixed with a binder formed from a mixture of polymer, plasticizer and wax.
  • the mixture thus obtained is then injected into a mold to obtain a part having the desired shape.
  • the shaped part is then, firstly, freed of its binder by air heating and, secondly, it is introduced into an oven containing an atmosphere of argon, nitrogen or the vacuum in which it is gradually heated to about 1,100 ° C for sintering.
  • micropores appear on the surface of the parts after they have been polished, these micropores producing scattering of the incident light which thus prevents perfect specular reflection of the light reaching the part. This then results in an unattractive matte or milky surface.
  • polishing of titanium parts obtained by this process therefore does not make it possible to obtain sufficiently smooth and shiny surfaces allowing their use as decorative parts, so that these parts are limited to technical uses in which the aesthetic appearance does not has no importance.
  • the main object of the invention is therefore to remedy the drawbacks of the above-mentioned prior art by providing a method of manufacturing by sintering a titanium part which has a very low porosity and which, once polished, has an aesthetic appearance. fulfilling the requirements required for the production of decorative pieces.
  • the invention relates to a decorative article made of titanium sintered from a powder of titanium hydride and having a polished surface obtained by the process described above.
  • Such an article thus has, after polishing, a more intense gloss than the sintered and polished titanium parts obtained according to the methods of the prior art and is particularly well suited to the production of decorative articles such as watch cases, links bracelets or the like.
  • Titanium hydride powder (TiH2), having a high degree of purity (99.5%) and an average particle size of the order of a few microns, typically 10 microns, is mixed, in a conventional manner, with a binder temporary in the form of granules until a homogeneous mixture is obtained.
  • the binder is formed from a thermal polymer or copolymer but can also be formed from wax.
  • This mixing is carried out at a temperature between 120 ° and 180 ° C depending on the nature of the binder used.
  • the temperature of the mixture is of the order of 170 ° C.
  • the binder contained in the shaped part is removed. Disposal is done in accordance with the nature of the binder. Often this removal of the binder is carried out thermally. To do this, the shaped part is then introduced into an oven in which it is gradually brought to a temperature between 200 ° and 300 ° C. During this heating, the binder is gradually removed by evaporation and, in order not to deteriorate the shape of the part, this heating takes place in a time between 6 and 9 hours and preferably in 8 hours. It is also important that the removal of the binder is complete to avoid any pollution of the part by the carbon and / or oxygen of the binder, which can lead to a deterioration of the mechanical properties and the corrosion resistance of the part to to manufacture.
  • the removal of the binder is carried out under vacuum or in a hydrogen atmosphere in order, on the one hand, to avoid any oxidation of the binder during its removal, and on the other hand, to increase the speed of the process of removing the binder from the part without deteriorating the shape of the part.
  • the binder is a thermal polymer
  • the latter can also be eliminated chemically, by decomposition using an appropriate acid vapor.
  • the atmosphere of the furnace is replaced by a hydrogen atmosphere (if the removal of the binder has not already been carried out in a hydrogen atmosphere) and, preferably, this hydrogen atmosphere is produced in the form of a flow circulating continuously in the furnace.
  • the temperature of the part is gradually increased until the desired sintering temperature is reached.
  • the sintering temperature is between 1,000 and 1,400 ° C and preferably substantially equal to 1,200 ° C to avoid getting too close to a temperature where the part would begin to deform.
  • This heating lasts approximately 5 to 7 hours.
  • the titanium hydride gradually releases its hydrogen.
  • the heating is not too rapid so as not to cause a rapid release of the hydrogen which could cause the formation of pores within the room and thereby alter the gloss of the surface once polished.
  • the heating rate is between 150 ° C and 250 ° C per hour.
  • the process according to the invention advantageously eliminates the risk of reaction of titanium with compounds other than hydrogen which could affect the purity of the part obtained.
  • the atmosphere of the furnace that is to say the hydrogen
  • a non-reactive atmosphere such as argon, or helium or vacuum. Argon will be preferred.
  • the replacement of hydrogen by the non-reactive atmosphere is done while maintaining the part at its sintering temperature.
  • the duration of this stage is between 5 and 80 minutes and is preferably approximately 20 minutes.
  • the part is then cooled to ambient temperature in said non-reactive atmosphere at a cooling rate of the order of 300 ° C per hour. During this cooling, the part slowly releases the rest of its hydrogen which is eliminated gradually.
  • the sintered titanium part obtained by the process which has just been described has a remarkably low porosity, less than 2%.
  • this piece can be subjected to a specular polishing of its surface in order to obtain a decorative article such as a watch case, a bracelet link, a dial or the like, having a surface of a polish and a intense shine.
  • a binder formed from a copolymer comprising 32% by volume of polyethylene oxide (246 g) and 4% by volume of polypropylene (26 g) is prepared in a container. This binder is heated to a temperature of about 170 ° C to obtain a homogeneous mass. 64% by volume of TiH2 (1920 g) having a degree are then added in addition. 99.5% purity which is mixed with the binder until a homogeneous paste is obtained.
  • the cooled mixture is then granulated.
  • the granules obtained are then introduced into an injection press and injected into a mold, for example having the shape of a watch case, at a temperature of approximately 140 ° C.
  • the shaped part is then introduced into an oven in which a vacuum of about 10 ⁇ 2 millibar is created.
  • the part is then brought to a temperature of approximately 300 ° C. by linear heating in 8 hours.
  • the part is then sintered.
  • the vacuum of the oven is replaced by a hydrogen atmosphere in the form of a flow having a flow rate of 150 ml / min and the part is brought from 300 ° C to 1,200 ° C linearly in 4 hours.
  • the hydrogen atmosphere is replaced by an argon atmosphere in the form of a flow having a flow rate of 150 ml / min, and the temperature of 1200 is maintained. ° C for about 20 minutes.
  • the part is then cooled linearly under the same argon atmosphere to room temperature.
  • the cooling rate is 300 ° C per hour and a sintered titanium part is obtained, the porosity of which is 1.5%.
  • the sintered element is finally subjected to electropolishing to obtain a watch case having an intense shiny appearance.
  • polyacetal is used as binder and the latter is removed by decomposition in a vapor of nitric acid at 120 ° C.
  • the result obtained with this variant is identical to that obtained with the previous example.

Abstract

The invention relates to a process for making a workpiece in titanium by sintering, characterised in that it consists in: - (a) mixing a titanium hydride powder with a temporary binder, - (b) injecting the mixture obtained into a mould in order to obtain a workpiece of the desired shape, - (c) removing the binder, - (d) heating the workpiece in a hydrogen atmosphere up to the desired sintering temperature, - (e) replacing the hydrogen atmosphere by a vacuum or a non-reactive atmosphere once the sintering temperature has been attained, and - (f) cooling the workpiece in the atmosphere of the non-reactive gas.

Description

L'invention concerne un procédé de fabrication d'une pièce en titane par les technologies des poudres et notamment un tel procédé permettant de fabriquer des pièces en titane par frittage de poudre d'hydrure de titane (TiH₂), pièces dont la porosité est inférieure à environ 2%. L'invention concerne également un article décoratif réalisé par un tel procédé.The invention relates to a method for manufacturing a titanium part by powder technologies and in particular such a method for manufacturing titanium parts by sintering titanium hydride powder (TiH₂), parts whose porosity is lower. at around 2%. The invention also relates to a decorative article produced by such a method.

Le procédé de l'invention s adapte plus particulièrement à la fabrication de produits semi-finis en titane qui sont destinés à réaliser des articles décoratifs tels que des boîtes de montre, maillons de bracelet, cadrans de montre ou analogues, qui une fois polis présentent une surface d'un brillant intense.The process of the invention is more particularly suited to the manufacture of semi-finished titanium products which are intended to produce decorative articles such as watch cases, bracelet links, watch dials or the like, which once polished have an intense shiny surface.

Au cours des dernières années, les technologies de la métallurgie des poudres, et notamment le moulage par injection de poudre de métal, ont permis de réaliser des pièces en titane de formes complexes qui ne pouvaient être obtenues auparavant qu'au prix d'un usinage long et coûteux d'un bloc de titane.In recent years, powder metallurgy technologies, and in particular metal powder injection molding, have made it possible to produce titanium parts of complex shapes which could only previously be obtained at the cost of machining. long and expensive of a block of titanium.

Compte tenu des caractéristiques pyrophoriques de la poudre de titane et des conditions délicates de sa manipulation et de sa mise en oeuvre qui en découlent, l'utilisation de poudre de TiH₂, qui ne présente aucun risque d'inflammation spontanée au simple contact de l'air, a été développé pour la réalisation par frittage de pièces en titane.Taking into account the pyrophoric characteristics of the titanium powder and the delicate conditions of its handling and its implementation which result therefrom, the use of TiH₂ powder, which presents no risk of spontaneous ignition upon simple contact with the air, was developed for the production by sintering of titanium parts.

Un tel procédé est décrit dans la publication de Kei Ameyama et al., intitulée "INJECTION MOLDING OF TITANIUM POWDERS" et publiée par la "Metal Powder Industries Federation" 105 College Rd., east, Princeton, New Jersey 08540, USA, 1989, pages 121 à 126.Such a process is described in the publication by Kei Ameyama et al., Entitled "INJECTION MOLDING OF TITANIUM POWDERS" and published by the "Metal Powder Industries Federation" 105 College Rd., East, Princeton, New Jersey 08540, USA, 1989, pages 121 to 126.

Selon ce procédé, la poudre de TiH₂ est tout d'abord mélangée à un liant formé d'un mélange de polymère, d'un plastifiant et de cire. Le mélange ainsi obtenu est alors injecté dans un moule pour obtenir une pièce ayant la forme désirée. La pièce conformée est ensuite, dans un premier temps, débarrassée de son liant par chauffage à l'air et, dans un deuxième temps, elle est introduite dans un four contenant une atmosphère d'argon, d'azote ou du vide dans lequel elle est chauffée progressivement jusqu'à environ 1'100°C en vue de son frittage.According to this process, the TiH₂ powder is firstly mixed with a binder formed from a mixture of polymer, plasticizer and wax. The mixture thus obtained is then injected into a mold to obtain a part having the desired shape. The shaped part is then, firstly, freed of its binder by air heating and, secondly, it is introduced into an oven containing an atmosphere of argon, nitrogen or the vacuum in which it is gradually heated to about 1,100 ° C for sintering.

Après analyse de la porosité des pièces obtenues selon ce procédé, on a constaté que les plus faibles porosités des pièces ont été obtenues avec un frittage dans le vide ou dans l'atmosphère d'argon, et que les porosités atteintes étaient de l'ordre de 3%. Ceci est dû à la libération violente de l'hydrogène à partir de l'hydrure de titane au moment du chauffage qui crée un nombre important de bulles ou pores.After analyzing the porosity of the parts obtained according to this process, it was found that the lowest porosities of the parts were obtained with sintering in a vacuum or in the atmosphere of argon, and that the porosities reached were of the order 3%. This is due to the violent release of hydrogen from titanium hydride upon heating which creates a large number of bubbles or pores.

Malgré cette faible porosité, il apparaît des micropores à la surface des pièces après le polissage de celles-ci, ces micropores produisant une diffusion de la lumière incidente qui empêche ainsi une réflexion spéculaire parfaite de la lumière atteignant la pièce. Il en résulte alors une surface d'apparence mate ou laiteuse peu esthétique.Despite this low porosity, micropores appear on the surface of the parts after they have been polished, these micropores producing scattering of the incident light which thus prevents perfect specular reflection of the light reaching the part. This then results in an unattractive matte or milky surface.

Le polissage de pièces en titane obtenues par ce procédé ne permet par conséquent pas d'obtenir des surfaces suffisamment lisses et brillantes permettant leur utilisation comme pièces décoratives, de sorte que ces pièces sont limitées à des utilisations techniques dans lesquelles l'aspect esthétique n'a aucune importance.The polishing of titanium parts obtained by this process therefore does not make it possible to obtain sufficiently smooth and shiny surfaces allowing their use as decorative parts, so that these parts are limited to technical uses in which the aesthetic appearance does not has no importance.

L'invention a donc pour but principal de remédier aux inconvénients de l'art antérieur susmentionné en fournissant un procédé de fabrication par frittage d'une pièce en titane qui présente une très faible porosité et qui une fois polie présente un aspect esthétique remplissant les exigences requises pour la réalisation de pièces décoratives.The main object of the invention is therefore to remedy the drawbacks of the above-mentioned prior art by providing a method of manufacturing by sintering a titanium part which has a very low porosity and which, once polished, has an aesthetic appearance. fulfilling the requirements required for the production of decorative pieces.

A cet effet l'invention a pour objet un procédé de fabrication par frittage d'une pièce en titane, caractérisé en ce qu'il consiste à :

  • (a) mélanger une poudre d'hydrure de titane à un liant temporaire,
  • (b) injecter le mélange obtenu dans un moule pour obtenir une pièce de forme souhaitée,
  • (c) éliminer le liant,
  • (d) chauffer la pièce sous une atmosphère d'hydrogène jusqu'à la température de frittage désirée,
  • (e) remplacer l'atmosphère d'hydrogène par du vide ou une atmosphère non réactive une fois que la température de frittage a été atteinte, et
  • (f) refroidir la pièce dans l'atmosphère du gaz non réactif.
To this end, the subject of the invention is a method of manufacturing by sintering a titanium part, characterized in that it consists in:
  • (a) mixing a titanium hydride powder with a temporary binder,
  • (b) injecting the mixture obtained into a mold to obtain a part of desired shape,
  • (c) removing the binder,
  • (d) heating the part under a hydrogen atmosphere to the desired sintering temperature,
  • (e) replace the hydrogen atmosphere with a vacuum or a non-reactive atmosphere once the sintering temperature has been reached, and
  • (f) cooling the part in the atmosphere of the non-reactive gas.

Grâce à ce procédé,on obtient des pièces en titane frittées qui présentent une porosité inférieure à 2%.Thanks to this process, sintered titanium parts are obtained which have a porosity of less than 2%.

Selon un autre de ses aspects, l'invention concerne un article décoratif en titane fritté à partir d'une poudre d'hydrure de titane et ayant une surface polie obtenu par le procédé susdécrit.According to another of its aspects, the invention relates to a decorative article made of titanium sintered from a powder of titanium hydride and having a polished surface obtained by the process described above.

Un tel article présente ainsi, après polissage, un brillant plus intense que les pièces en titane frittées et polies obtenues selon les procédés de l'art antérieur et est particulièrement bien adapté à la réalisation d'articles décoratifs tels que des boîtes de montre, maillons de bracelets ou analogues.Such an article thus has, after polishing, a more intense gloss than the sintered and polished titanium parts obtained according to the methods of the prior art and is particularly well suited to the production of decorative articles such as watch cases, links bracelets or the like.

L'invention va maintenant être décrite de façon détaillée.The invention will now be described in detail.

De la poudre d'hydrure de titane (TiH₂), présentant un grand degré de pureté (99,5%) et une granulométrie moyenne de l'ordre de quelques microns, typiquement de 10 microns, est mélangée, de façon classique, à un liant temporaire sous forme de granules jusqu'à obtenir un mélange homogène.Titanium hydride powder (TiH₂), having a high degree of purity (99.5%) and an average particle size of the order of a few microns, typically 10 microns, is mixed, in a conventional manner, with a binder temporary in the form of granules until a homogeneous mixture is obtained.

De préférence, le liant est formé d'un polymère ou d'un copolymère thermique mais peut être également formé de cire. Ce mélange est réalisé à une température comprise entre 120° et 180°C selon la nature du liant utilisé. Typiquement, avec un copolymère thermique, la température du mélange est de l'ordre de 170°C.Preferably, the binder is formed from a thermal polymer or copolymer but can also be formed from wax. This mixing is carried out at a temperature between 120 ° and 180 ° C depending on the nature of the binder used. Typically, with a thermal copolymer, the temperature of the mixture is of the order of 170 ° C.

Le mélange sous forme de pâte qui est obtenu est ensuite injecté de façon classique dans un moule ayant la forme de la pièce que l'on désire obtenir, par exemple une boîte de montre, avec des dimensions qui tiennent compte du rétrécissement de la pièce au cours des étapes ultérieures du procédé, rétrécissement qui est typiquement de l'ordre de 15%. L'injection est réalisée de préférence à une température d'environ 140°C.The mixture in the form of a paste which is obtained is then injected in a conventional manner into a mold having the shape of the part which it is desired to obtain, for example a watch case, with dimensions which take account of the narrowing of the part at during the subsequent stages of the process, shrinkage which is typically of the order of 15%. The injection is preferably carried out at a temperature of approximately 140 ° C.

On procède ensuite à l'élimination du liant contenue dans la pièce conformée. L'élimination se fait en accord avec la nature du liant. Souvent cette élimination du liant est réalisée thermiquement. Pour ce faire, la pièce conformée est alors introduite dans un four dans lequel elle est amenée progressivement à une température comprise entre 200° et 300°C. Au cours de ce chauffage, le liant est progressivement éliminé par évaporation et, pour ne pas détériorer la forme de la pièce, ce chauffage s'effectue en un temps compris entre 6 et 9 heures et de préférence en 8 heures. Il est également important que l'élimination du liant soit complète pour éviter toute pollution de la pièce par le carbone et/ou l'oxygène du liant, pouvant conduire à une détérioration des propriétés mécaniques et de la résistance à la corrosion de la pièce à fabriquer.Next, the binder contained in the shaped part is removed. Disposal is done in accordance with the nature of the binder. Often this removal of the binder is carried out thermally. To do this, the shaped part is then introduced into an oven in which it is gradually brought to a temperature between 200 ° and 300 ° C. During this heating, the binder is gradually removed by evaporation and, in order not to deteriorate the shape of the part, this heating takes place in a time between 6 and 9 hours and preferably in 8 hours. It is also important that the removal of the binder is complete to avoid any pollution of the part by the carbon and / or oxygen of the binder, which can lead to a deterioration of the mechanical properties and the corrosion resistance of the part to to manufacture.

De préférence, l'élimination du liant est réalisée sous vide ou dans une atmosphère d'hydrogène afin, d'une part, d'éviter toute oxydation du liant lors de son élimination, et d'autre part, d'augmenter la vitesse du processus d'élimination du liant de la pièce sans détériorer la forme de la pièce.Preferably, the removal of the binder is carried out under vacuum or in a hydrogen atmosphere in order, on the one hand, to avoid any oxidation of the binder during its removal, and on the other hand, to increase the speed of the process of removing the binder from the part without deteriorating the shape of the part.

Selon une variante du procédé et notamment dans le cas où le liant est un polymère thermique, ce dernier peut être également éliminé de façon chimique, par décomposition à l'aide d'une vapeur d'acide appropriée.According to a variant of the process and in particular in the case where the binder is a thermal polymer, the latter can also be eliminated chemically, by decomposition using an appropriate acid vapor.

Après l'élimination complète du liant de la pièce et selon un aspect particulièrement important de l'invention, l'atmosphère du four est remplacée par une atmosphère d'hydrogène (si l'élimination du liant n'a pas déjà été réalisée dans une atmosphère d'hydrogène) et, de préférence, cette atmosphère d'hydrogène est réalisée sous la forme d'un flux circulant de façon continue dans le four. Simultanément, la température de la pièce est progressivement augmentée jusqu'à atteindre la température de frittage désirée. La température de frittage est comprise entre 1'000 et 1'400°C et, de préférence, sensiblement égale à 1'200°C pour éviter de se rapprocher trop d'une température où la pièce commencerait à se déformer.After the complete removal of the binder from the part and according to a particularly important aspect of the invention, the atmosphere of the furnace is replaced by a hydrogen atmosphere (if the removal of the binder has not already been carried out in a hydrogen atmosphere) and, preferably, this hydrogen atmosphere is produced in the form of a flow circulating continuously in the furnace. At the same time, the temperature of the part is gradually increased until the desired sintering temperature is reached. The sintering temperature is between 1,000 and 1,400 ° C and preferably substantially equal to 1,200 ° C to avoid getting too close to a temperature where the part would begin to deform.

Ce chauffage dure environ 5 à 7 heures. Au cours du chauffage, l'hydrure de titane libère progressivement son hydrogène. A ce propos il est important selon le procédé de l'invention que le chauffage ne soit pas trop rapide afin de ne pas provoquer une libération rapide de l'hydrogène qui pourrait provoquer la formation de pores au sein de la pièce et par là même altérer le brillant de la surface une fois polie. De préférence la vitesse de chauffage est comprise entre 150°C et 250°C par heure.This heating lasts approximately 5 to 7 hours. During heating, the titanium hydride gradually releases its hydrogen. In this regard it is important according to the method of the invention that the heating is not too rapid so as not to cause a rapid release of the hydrogen which could cause the formation of pores within the room and thereby alter the gloss of the surface once polished. Preferably the heating rate is between 150 ° C and 250 ° C per hour.

Grâce au chauffage de la pièce dans une atmosphère d'hydrogène, l'hydrogène de l'hydrure de titane est libéré progressivement, ce qui diminue ainsi fortement la tendance à la formation de bulles ou pores au sein de la pièce. Par ailleurs, compte tenu de la grande réactivité du titane à température élevée, le procédé selon l'invention élimine, de façon avantageuse, le risque de réaction du titane avec des composés autres que l'hydrogène qui pourraient affecter la pureté de la pièce obtenue.By heating the room in a hydrogen atmosphere, the hydrogen from titanium hydride is gradually released, which greatly reduces the tendency to form bubbles or pores within the room. Furthermore, given the high reactivity of titanium at high temperature, the process according to the invention advantageously eliminates the risk of reaction of titanium with compounds other than hydrogen which could affect the purity of the part obtained.

La température de frittage atteinte et l'hydrogène de la pièce ayant été en majeure partie libéré, on remplace à nouveau l'atmosphère du four, c'est à dire l'hydrogène, par une atmosphère non réactive telle que l'argon, ou l'hélium ou par le vide. L'argon sera préféré. Le remplacement de l'hydrogène par l'atmosphère non réactive est fait tout en maintenant la pièce à sa température de frittage. La durée de ce palier est comprise entre 5 et 80 minutes et est de préférence d'environ 20 minutes.Once the sintering temperature has been reached and the hydrogen in the part has been released for the most part, the atmosphere of the furnace, that is to say the hydrogen, is again replaced by a non-reactive atmosphere such as argon, or helium or vacuum. Argon will be preferred. The replacement of hydrogen by the non-reactive atmosphere is done while maintaining the part at its sintering temperature. The duration of this stage is between 5 and 80 minutes and is preferably approximately 20 minutes.

La pièce est alors refroidie jusqu'à la température ambiante dans ladite atmosphère non réactive à une vitesse de refroidissement de l'ordre de 300°C par heure. Au cours de ce refroidissement, la pièce libère lentement le reste de son hydrogène qui est éliminé au fur et à mesure.The part is then cooled to ambient temperature in said non-reactive atmosphere at a cooling rate of the order of 300 ° C per hour. During this cooling, the part slowly releases the rest of its hydrogen which is eliminated gradually.

La pièce en titane frittée obtenue par le procédé qui vient d'être décrit présente une porosité remarquablement faible, inférieure à 2%.The sintered titanium part obtained by the process which has just been described has a remarkably low porosity, less than 2%.

Ainsi, cette pièce peut être soumise à une polissage spéculaire de sa surface afin d'obtenir un article décoratif tel qu'une boîte de montre, un maillon de bracelet, un cadran ou analogue, présentant une surface d'un poli et d'un brillant intense .Thus, this piece can be subjected to a specular polishing of its surface in order to obtain a decorative article such as a watch case, a bracelet link, a dial or the like, having a surface of a polish and a intense shine.

L'exemple qui suit est un exemple préféré de mise en oeuvre du procédé de fabrication par frittage d'une pièce en titane, objet de l'inventionThe example which follows is a preferred example of implementation of the manufacturing process by sintering of a titanium part, object of the invention

ExempleExample

On prépare dans un récipient un liant formé d'un copolymère comprenant 32% en volume d'oxyde de polyéthylène (246 g) et 4% en volume de polypropylène (26 g). On chauffe ce liant à une température d'environ 170°C pour obtenir une masse homogène. On ajoute alors en complément 64% en volume de TiH₂ (1920 g) ayant un degré de pureté de 99,5% que l'on mélange avec le liant jusqu'à obtenir une pâte homogène.A binder formed from a copolymer comprising 32% by volume of polyethylene oxide (246 g) and 4% by volume of polypropylene (26 g) is prepared in a container. This binder is heated to a temperature of about 170 ° C to obtain a homogeneous mass. 64% by volume of TiH₂ (1920 g) having a degree are then added in addition. 99.5% purity which is mixed with the binder until a homogeneous paste is obtained.

On procède ensuite à une granulation du mélange refroidi. Les granules obtenus sont alors introduits dans une presse à injecter et injectés dans un moule, ayant par exemple la forme d'une boîte de montre, à une température d'environ 140°C.The cooled mixture is then granulated. The granules obtained are then introduced into an injection press and injected into a mold, for example having the shape of a watch case, at a temperature of approximately 140 ° C.

La pièce conformée est alors introduite dans un four dans lequel on fait un vide d'environ 10⁻² millibar. La pièce est ensuite amenée à une température d'environ 300°C par un chauffage linéaire en 8 heures.The shaped part is then introduced into an oven in which a vacuum of about 10⁻² millibar is created. The part is then brought to a temperature of approximately 300 ° C. by linear heating in 8 hours.

On opère ensuite le frittage de la pièce. Pour ce faire, le vide du four est remplacé par une atmosphère d'hydrogène sous forme d'un flux ayant un débit de 150 ml/mn et la pièce est amenée de 300°C à 1'200°C linéairement en 4 heures. Une fois la température de 1'200°C atteinte, on remplace l'atmosphère d'hydrogène par une atmosphère d'argon sous forme d'un flux ayant un débit de 150 ml/mn, et on maintient la température de 1'200°C pendant environ 20 minutes.The part is then sintered. To do this, the vacuum of the oven is replaced by a hydrogen atmosphere in the form of a flow having a flow rate of 150 ml / min and the part is brought from 300 ° C to 1,200 ° C linearly in 4 hours. Once the temperature of 1200 ° C is reached, the hydrogen atmosphere is replaced by an argon atmosphere in the form of a flow having a flow rate of 150 ml / min, and the temperature of 1200 is maintained. ° C for about 20 minutes.

On refroidit ensuite linéairement la pièce sous la même atmosphère d'argon jusqu'à la température ambiante. La vitesse de refroidissement est de 300°C par heure et on obtient ainsi une pièce en titane frittée dont la porosité est de 1,5%.The part is then cooled linearly under the same argon atmosphere to room temperature. The cooling rate is 300 ° C per hour and a sintered titanium part is obtained, the porosity of which is 1.5%.

L'élément fritté est finalement soumis à un électropolissage pour obtenir une boîte de montre ayant un aspect brillant intense.The sintered element is finally subjected to electropolishing to obtain a watch case having an intense shiny appearance.

Dans une variante de l'exemple ci-dessus, on utilise du polyacétal comme liant et ce dernier est éliminé par décomposition dans une vapeur d'acide nitrique à 120°C. Le résultat obtenu avec cette variante est identique à celui obtenu avec l'exemple précédent.In a variant of the above example, polyacetal is used as binder and the latter is removed by decomposition in a vapor of nitric acid at 120 ° C. The result obtained with this variant is identical to that obtained with the previous example.

Claims (12)

Procédé de fabrication par frittage d'une pièce en titane, caractérisé en ce qu'il consiste à: - (a) mélanger une poudre d'hydrure de titane à un liant temporaire, - (b) injecter le mélange obtenu dans un moule pour obtenir une pièce de forme souhaitée, - (c) éliminer le liant, - (d) chauffer la pièce sous une atmosphère d'hydrogène jusqu'à la température de frittage désirée, - (e) remplacer l'atmosphère d'hydrogène par le vide ou une atmosphère non réactive une fois que la température de frittage a été atteinte, et - (f) refroidir la pièce dans l'atmosphère du gaz non réactif. Method for manufacturing a titanium part by sintering, characterized in that it consists of: - (a) mixing a titanium hydride powder with a temporary binder, - (b) inject the mixture obtained into a mold to obtain a part of desired shape, - (c) removing the binder, - (d) heating the part under a hydrogen atmosphere to the desired sintering temperature, - (e) replace the hydrogen atmosphere with a vacuum or a non-reactive atmosphere once the sintering temperature has been reached, and - (f) cooling the part in the atmosphere of the non-reactive gas. Procédé selon la revendication 1, caractérisé en ce que l'étape (d) consiste à chauffer la pièce à une température comprise entre 1'000 et 1'400°C.Method according to claim 1, characterized in that step (d) consists in heating the part to a temperature between 1'000 and 1'400 ° C. Procédé selon la revendication 2, caractérisé en ce que l'étape (d) est réalisée pendant un temps compris entre 4 et 8 heures.Method according to claim 2, characterized in that step (d) is carried out for a time between 4 and 8 hours. Procédé selon l'une des revendications précédentes, caractérisé en ce qu'au cours de l'étape (d), l'hydrogène est fourni sous la forme d'un flux continu.Method according to one of the preceding claims, characterized in that during step (d), the hydrogen is supplied in the form of a continuous flow. Procédé selon l'une des revendications précédentes, caractérisé en ce qu'au cours de l'étape (e), la pièce est maintenue à ladite température de frittage pendant un temps compris entre 5 et 60 minutes.Method according to one of the preceding claims, characterized in that during step (e), the part is maintained at said sintering temperature for a time between 5 and 60 minutes. Procédé selon l'une des revendication précédentes, caractérisé en ce qu'aux étapes (e) et (f) l'atmosphère non réactive comprend, l'argon, ou l'hélium.Method according to one of the preceding claims, characterized in that in stages (e) and (f) the non-reactive atmosphere comprises, argon, or helium. Procédé selon l'une des revendications précédentes, caractérisé en ce que l'étape (c) est réalisée chimiquement et/ou thermiquement.Method according to one of the preceding claims, characterized in that step (c) is carried out chemically and / or thermally. Procédé selon la revendication 7, caractérisé en ce que l'étape (c) est réalisée sous vide à une température inférieure à 300°C.Method according to claim 7, characterized in that step (c) is carried out under vacuum at a temperature below 300 ° C. Procédé selon la revendication 8, caractérisé en ce que l'étape (c) est réalisée pendant une temps compris entre 6 et 9 heures.Method according to claim 8, characterized in that step (c) is carried out for a time between 6 and 9 hours. Procédé selon la revendication 7, caractérisé en ce que le liant est un polymère thermique et en ce que l'étape (c) comprend la décomposition chimique du polymère par une vapeur d'acide.Method according to claim 7, characterized in that the binder is a thermal polymer and in that step (c) comprises the chemical decomposition of the polymer by an acid vapor. Procédé selon l'une quelconque des revendications 1 à 10, caractérisé en ce qu'il comprend une étape supplémentaire (g) au cours de laquelle la pièce est soumise à un polissage spéculaire.Method according to any one of claims 1 to 10, characterized in that it comprises an additional step (g) during which the part is subjected to specular polishing. Article décoratif en titane fritté à partir d'une poudre d'hydrure de titane et ayant une surface polie obtenu selon le procédé défini par la revendication 11.Decorative article made of titanium sintered from a powder of titanium hydride and having a polished surface obtained according to the process defined by claim 11.
EP94111197A 1993-07-23 1994-07-19 Process for making a workpiece in titanium by sintering and a decorative article made by such a process Expired - Lifetime EP0635325B1 (en)

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CH2246/93A CH684978B5 (en) 1993-07-23 1993-07-23 A method of manufacture by sintering of a titanium part and decorative article made by such a method.
CH2246/93 1993-07-23
CH224693 1993-07-23
FR9309530 1993-07-30
FR9309530A FR2708496B1 (en) 1993-07-30 1993-07-30 Method of manufacturing by sintering a titanium part and decorative article produced according to such a method.

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