Method of manufacturing a part in a degradable mold comprising lanthanum oxide

Abstract

A method of manufacturing a part, the method comprising the following successive steps: a) shaping the part by: - ​​solidifying a liquid bath contained in a sintered mold comprising lanthanum oxide, or - sintering a charge to be sintered contained in a mold comprising lanthanum hydroxide or in a sintered mold comprising lanthanum oxide, b) cooling the part in the mold, and c) maintaining the assembly formed by the part and the mold in a gaseous medium containing water vapor for a holding time suitable for degrading the mold under the effect of the hydrolysis of the lanthanum oxide by the water contained in the gaseous medium. No abstract figure

Description

Title of the invention: Method for manufacturing a part in a degradable mold comprising lanthanum oxide Technical field

[0001] The present invention relates to the shaping of foundry parts or sintered parts. It relates more particularly to the implementation of a mold suitable for this shaping. Prior art

[0002] Uniaxial sintering makes it possible to obtain parts of complex shape. A part of complex shape has at least one of the following characteristics: hole in the compression axis, portions of the part extending at different heights measured along the compression axis, inclined faces not parallel and not perpendicular to the compression axis, absence of an axis of revolution, non-planar faces.

[0003] The shaping of parts of complex shape requires the use of suitable molds in order to obtain a homogeneous densification of the sintered part, easy demoulding, and which furthermore prevent contamination by carbon of at least the portion of the part in contact with the tooling which is generally made of graphite providing carbon.

[0004] Furthermore, in the field of foundry, removing a part from the foundry mold can be complex and lead to breakage of the part.

[0005] There is a continuing need to facilitate the shaping of complex shaped parts and the detachment of these parts from the mold. Statement of the invention

[0006] The invention provides a method for manufacturing a part, the method comprising the following successive steps: a) shaping the part by: - solidification of a liquid bath contained in a sintered mold comprising lanthanum oxide, or - sintering a charge to be sintered contained in a mold comprising lanthanum hydroxide or in a sintered mold comprising lanthanum oxide, b) cooling the part in the mold, and c) maintaining the assembly formed by the part and the mold in a gaseous medium containing water vapor for a holding time suitable for degrading the mold under the effect of the hydrolysis of the lanthanum oxide by the water contained in the gaseous medium.

[0007] The invention substantially eliminates the detachment step, the degraded mold no longer having its own integrity due to the hydrolysis of the lanthanum oxide. The hydrolysis of the lanthanum oxide into lanthanum hydroxide induces a variation in volume generating a progressive pulverization of the mold into a powder of lanthanum hydroxide particles during the holding time. The molded part can thus be recovered directly. Detailed description

[0008] The mold comprises lanthanum oxide or lanthanum hydroxide.

[0009] The mold may further comprise a refractory compound chosen from BN, Si3N4, Al2O3, ZrO2, HfO2, SiC and mixtures thereof. The refractory compound provides thermal stability suitable for shaping, in particular by melting and solidification, of the part. It can thus be adapted to the specific properties of the material constituting the part, and in particular is preferably chemically inert with respect to the material constituting the part. Furthermore, advantageously, the refractory compound is inert with respect to lanthanum oxide, and therefore does not hinder the degradation of the lanthanum oxide in step c). In addition, the refractory compound makes it possible to increase the temperature range of use of the mold for manufacturing the part.

[0010] According to a first embodiment, the mold is sintered.

[0011] The mold may consist of lanthanum oxide, the refractory compound and less than 1% of other constituents. Preferably, it consists of lanthanum oxide and the refractory compound.

[0012] Throughout the present description, by "other constituents" is meant all constituents other than La2O3, La(OH)3, BN, Si3N4, Al2O3, ZrO2, HfO2 and SiC. For example, the other constituents are impurities, that is to say they are introduced unintentionally and necessarily with the raw materials. The impurities are not necessary constituents, but only tolerated.

[0013] Furthermore, the mold preferably comprises more than 10%, preferably more than 25%, of lanthanum oxide. An increase in the lanthanum oxide content makes it possible to accelerate the degradation of the mold after the part has cooled.

[0014] According to a second method of forming, the mold comprises lanthanum hydroxide and the part is shaped by sintering.

[0015] The mold may be made of lanthanum hydroxide and less than 1% of other constituents. It may consist of lanthanum hydroxide.

[0016] Alternatively, the mold is comprised of lanthanum hydroxide, the refractory compound, and less than 1% of other constituents. Preferably, it consists of lanthanum hydroxide and the refractory compound.

[0017] Preferably, the mold is preformed and comprises agglomerated particles, optionally by means of a binder. Agglomerated particles are bonded together by contact with each other. They are not bonded together by a common material bridge, as is the case in a sintered part. A preformed mold has a low breaking strength but preferably sufficient to be manipulable. Preferably, the preformed mold is obtained by compression of a starting charge comprising particles made of the material constituting the mold. The mold is preferably manufactured by the production method according to the invention described below.

[0018] Preferably, the mold is sintered during sintering of the part, at a temperature higher than the reaction temperature of lanthanum hydroxide to lanthanum oxide, preferably at 900°C or higher.

[0019] Furthermore, the mold has a cavity for receiving the liquid bath or the charge to be sintered.

[0020] According to a variant, the method comprises shaping by solidification of the liquid bath. The method comprises filling the mold by pouring the liquid bath into the cavity.

[0021] According to another variant, the method comprises shaping by sintering the charge to be sintered. The charge to be sintered is in the form of particles after filling the mold. During sintering, the particles are bonded together under the action of heat to form the part. Preferably, the sintering comprises the application of uniaxial compression in order to densify the part, by reducing the porosity between the particles.

[0022] The part may be made of a ceramic or metallic material. Preferably, the part is made of a metallic material. For example, the metallic material is chosen from steels, aluminum alloys, copper alloys and titanium alloys.

[0023] In step b), the part and the mold are preferably cooled to a temperature below 100°C, preferably below 50°C, in particular between 20°C and 30°C.

[0024] In step c), the gaseous medium is preferably air, the humidity level of which is preferably greater than 40%. Such a humidity level allows handling of the assembly formed by the part and the mold, for example between the device for shaping the part and a storage location, without degradation of the mold, while allowing degradation of the mold during maintenance.

[0025] Furthermore, the gaseous medium may be at atmospheric pressure.

[0026] The holding time may in particular depend on the mass content of oxide of lanthanum in the mold. Preferably, it is less than 15 days, or even less than 5 days.

[0027] At the end of the holding time, the mold is sufficiently degraded so that the part can be detached from the mold. Preferably, at the end of the holding time, the mold is disintegrated and is in the form of a powder.

[0028] Subsequent to step c), the method may include a step of cleaning the part. For example, the part may be brushed to recover the portions of the degraded mold and / or the sodium hydroxide dust in contact with the part.

[0029] The contents of the mold constituents are expressed as percentages by mass based on the mass of the mold.

[0030] Furthermore, the method may comprise, prior to step a) and / or after step c), a step of implementing the method of producing the mold according to the invention which will be described below.

[0031] The invention also relates to a method for producing a mold, in particular for implementing the manufacturing method according to the invention, the method comprising the steps of: - preparation of a starting charge consisting of lanthanum hydroxide particles, optionally of particles made of a refractory compound chosen from BN, Si3N4, A12O3, ZrO2, HfO2, SiC and their mixtures, and of less than 1% of other constituents, preferably free of other constituents, - payment of the initial charge into a counterform, - shaping the starting charge against the counterform, so as to preform a mold, - optionally, sintering of the preformed mold.

[0032] The lanthanum hydroxide particles may originate from the degradation of the sintered mold in step c) of the manufacturing process according to the invention. It is thus possible to recycle an old mold to manufacture a new one by taking advantage of the reversible nature of the lanthanum oxide hydrolysis reaction.

[0033] Preferably, the starting charge consists of lanthanum hydroxide particles and particles made of a refractory compound chosen from BN, Si3N4, Al2O3, ZrO2, HfO2, SiC and mixtures thereof.

[0034] Preferably, the starting charge comprises by volume, at least 10%, or even at least 20%, or even at least 30%, or even at least 40%, or even at least 50% of lanthanum hydroxide.

[0035] The refractory compound is preferably as described above.

[0036] All of the lanthanum hydroxide particles may have a median size D50 of between 100 nm and 500 pm, for example equal to 300 nm. The size of a particle may be measured by laser granulometry.

[0037] The starting charge may consist of lanthanum hydroxide particles and less than 1% by volume of other constituents. Preferably, the starting charge consists of lanthanum hydroxide particles. Furthermore, the sintering temperature of the preformed mold and / or the sintering temperature of the part in step a) of the manufacturing method according to the invention may be between 900°C and 1300°C.

[0038] The starting charge may consist of lanthanum hydroxide particles, Si3N4 particles and less than 1% by volume of other constituents, the mass content of lanthanum oxide particles preferably being at least 10%. Preferably, the starting charge consists of lanthanum hydroxide particles and Si3N4 particles. Furthermore, the sintering temperature of the preformed mold and / or the sintering temperature of the part in step a) of the manufacturing method according to the invention may be between 1265°C and 1760°C.

[0039] The starting charge may consist of lanthanum hydroxide particles, Al2O3 particles and less than 1% by volume of other constituents, the mass content of lanthanum oxide particles preferably being at least 50%. Preferably, the starting charge consists of lanthanum hydroxide particles and Al2O3 particles. Furthermore, the sintering temperature of the preformed mold and / or the sintering temperature of the part in step a) of the manufacturing method according to the invention may be between 920 °C and 1420 °C.

[0040] The starting charge may consist of lanthanum hydroxide particles, SiC particles and less than 1% by volume of other constituents, the mass content of lanthanum oxide particles preferably being at least 50%. Preferably, the starting charge consists of lanthanum hydroxide particles and SiC particles. Furthermore, the sintering temperature of the preformed mold and / or the sintering temperature of the part in step a) of the manufacturing method according to the invention may be between 1400°C and 1700°C.

[0041] The starting charge may consist of lanthanum hydroxide particles, BN particles and less than 1% by volume of other constituents, the mass content of lanthanum oxide particles preferably being at least 10%. Preferably, the starting charge consists of lanthanum hydroxide particles and BN particles. Furthermore, the sintering temperature of the preformed mold and / or the sintering temperature of the part in step a) of the manufacturing method according to the invention may be between 1300 °C and 1850 °C.

[0042] Furthermore, the shaping of the starting load may include the compression, preferably uniaxial, of the starting load against the counterform.

[0043] The method may include, after preforming the mold and, where appropriate, prior to sintering the preformed mold, an optional step of demolding the preformed mold and / or a step of drying the preformed mold, in particular until the residual humidity is between 0 and 0.5%.

[0044] Compression, in particular uniaxial compression, of the preformed mold may be implemented during sintering of the preformed mold. The compression may be between 35 MPa and 500 MPa. Brief description of the drawings

[0045] The invention may be better understood by reading the examples presented for illustrative and non-limiting purposes, and the attached drawing in which: - [[Fig.l]] is a group of photographs of an example of an assembly formed from a part obtained by the method according to the invention and a mold used in the method, at different stages of maintenance in the gaseous medium, - [[Fig.2]] are diffractograms of samples made of lanthanum oxide, taken from the mold immediately after cooling of the part and the mold, then 48 h after keeping the mold in the open air respectively, according to an example of implementation of the process, and - [[Fig.3]] is a set of photographs of pellets made of BN and La2O3 for, on the abscissa, different mass contents of La2O3 expressed in contents of lanthanum hydroxide La(OH)3 in the starting charge and, in the column, after manufacture, after 3 days of keeping in the open air and after 13 days of keeping in the open air. Example 1

[0046] A starting charge consisting of lanthanum hydroxide particles was provided which was poured into a counterform. The starting charge was compacted to preform a preformed pellet.

[0047] Particles of a tungsten carbide-cobalt (WC / Co) cermet were disposed on the preformed pellet to manufacture a part.

[0048] The assembly was then heated according to a ramp of 100 K / min to a temperature suitable for sintering the pellet 1 as well as a part 2 made of the cermet. A photograph of the sintered assembly, obtained after cooling to room temperature is illustrated in [Fig.l] a).

[0049] The assembly formed by the part and the mold was then kept for several days at room temperature and humidity, in the open air.

[0050] Photographs b) to e) of [Fig.l] illustrate the progressive degradation of the mold in contact with the humidity in the air. At the end of holding, the WC / Co cermet part can be recovered directly without detachment, the mold being completely pulverized ([Fig.l] e)). Only a few traces of lanthanum oxide remain on the surface of the part.

[0051] The degradation of the mold by transformation of lanthanum oxide into lanthanum hydroxide was confirmed by means of the diffractograms illustrated in [Fig.2] in which the square and round markers correspond to the theoretical positions of the peaks of lanthanum oxide and lanthanum hydroxide respectively. After sintering and then cooling of the part and the mold, the diffractogram (represented at the top of [Fig.2]) corresponds to the diffractogram of lanthanum oxide, while after 48 hours, a mixture of the peaks of lanthanum oxide and lanthanum hydroxide is observed (diffractogram represented at the base of [Fig.2]). Example 2

[0052] A powder of lanthanum hydroxide particles as in Example 1 and a powder of boron nitride particles of the Carbotherm reference marketed by the company Saint Gobain were available. Different starting charges were prepared by varying the respective mass proportions of said powders.

[0053] Preformed pellets were then obtained by compacting the starting charges and were then sintered according to the temperatures and proportions indicated in Table 1 below. The sintering temperature was reached according to a ramp of 100 K / min. Once the sintering temperature was reached, the pellet was removed from the furnace.

[0054] [Tables 1] Sample L a(OH)3 content (% by volume) Sintering temperature (°C) Appearance after 3 days in the open air Appearance after 13 days in the open air 1 1 1890 not degraded not degraded 2 2 1800 not degraded not degraded 3 5 1800 not degraded slightly degraded 4 10 1470 slightly degraded pulverized 5 25 1400 Strongly degraded pulverized 6 40 1350 Strongly degraded pulverized 7 50 1300 Strongly degraded pulverized 8 60 1300 Strongly degraded pulverized 9 99 1850 pulverized pulverized

[0055] Sintered pellets were thus obtained, which were then kept in the open air for a period of 13 days. The visual state of each pellet was qualified after sintering, then at 3 days and 13 days of keeping in the open air. Photographs of the different samples are shown in [Fig.3].

[0056] The following criteria listed in Table 2 were used to qualify the condition of a pellet:

[0057] [Tables2] Criterion Definition Not degraded No visible cracks and handling without risk of the pellet breaking Slightly degraded Visible cracks and / or crumbling of the pellet during handling Heavily degraded Pellet broken into several pieces or pellet breaking during handling Pulverized Pellet reduced to a powder state

[0058] A faster degradation is observed with an increase in the mass content of La(OH)3 in the starting charge, and therefore in the content of lanthanum oxide La2O3 in the sintered pellet. Example 3

[0059] A powder of lanthanum hydroxide particles as in Example 1 and powders of silicon carbide particles marketed by the company Kyocera of grade UF 05, UF 10, UF 15 and UF 25 were available, having respectively a median size D50 of 2.2 pm, 0.9 pm, 0.75 pm and 0.65 pm. Different starting charges were formed by varying the respective mass proportions of said powders.

[0060] Preformed pellets were then obtained by compacting the starting charges and were then sintered according to the temperatures and proportions indicated in Table 3 below.

[0061] The visual state was then determined after 1 day of keeping in the open air.

[0062] [Tables3 Sample La(OH)3 content (% by volume) Sintering temperature (°C) Appearance after 1 day in the open air 10 90 1750 Pulverized 11 50 1470 Pulverized Example 4

[0063] A powder of lanthanum hydroxide particles was available as in Example 1 and a powder of alumina particles marketed by the company Baikowski under the reference BMA 15 and having a median size D50 of 0.17 pm. Different starting charges were formed by varying the respective mass proportions of said powders.

[0064] Preformed pellets were then obtained by compacting the starting charges and were then sintered according to the temperatures and proportions indicated in Table 4 below.

[0065] The visual state was then determined after 1 day of keeping in the open air.

[0066] [Tables4] Sample La(OH)3 content (% by volume) Sintering temperature (°C) Appearance after 1 day in the open air 12 90 1350 Not degraded 13 50 1420 Pulverized Example 5

[0067] A powder of lanthanum hydroxide particles as in Example 1 and a powder of grade 7 silicon nitride particles, marketed by the company HC Starck, were available. Different starting charges were formed by varying the respective mass proportions of said powders.

[0068] Preformed pellets were then obtained by compacting the starting charges and were then sintered according to the temperatures and proportions indicated in Table 5 below.

[0069] The visual state was then determined after 1 day of keeping in the open air.

[0070] [Tables5] Sample La(OH)3 content (% by volume) Sintering temperature (°C) Appearance after 1 day in open air 14 90 1760 Pulverized 15 50 1710 Pulverized

Claims

Claims

1. A method of manufacturing a part, the method comprising the following successive steps: a) shaping the part by: - ​​solidifying a liquid bath contained in a sintered mold comprising lanthanum oxide, or - sintering a charge to be sintered contained in a mold comprising lanthanum hydroxide or in a sintered mold comprising lanthanum oxide, b) cooling the part in the mold, and c) maintaining the assembly formed by the part and the mold in a gaseous medium containing water vapor for a holding time suitable for degrading the mold under the effect of the hydrolysis of the lanthanum oxide by the water contained in the gaseous medium.

2. A method according to claim 1, the mold further comprising a refractory compound selected from BN, Si3N4, Al2O3, ZrO2, HfO2, SiC and mixtures thereof.

3. A method according to any one of claims 1 and 2, the mold being sintered and consisting of lanthanum oxide and the refractory compound.

4. A method according to any one of claims 1 and 2, the part being shaped by sintering and the mold being constituted by lanthanum hydroxide and the refractory compound.

5. Method according to any one of the preceding claims, the gaseous medium being air, the humidity level of which is preferably greater than 40%.

6. Method according to any one of the preceding claims, the holding time being less than 15 days, or even less than 5 days.

7. A method according to any preceding claim, the part being metallic.

8. Method for producing a mold, in particular for implementing the method according to any one of the preceding claims, the method comprising the steps of: - preparing a starting charge consisting of lanthanum hydroxide particles, optionally particles made of a refractory compound chosen from BN, Si3N4, A12O3, ZrO2, HfO2, SiC and mixtures thereof, and less than 1% of other constituents, preferably free of other constituents, and - pouring the starting charge into a counterform, - shaping the starting charge against the counterform, so as to preform a mold, and - optionally, sintering the preformed mold.

9. Method according to the preceding claim, the lanthanum hydroxide particles originating from the degradation of the sintered mold in step c) of the method according to any one of claims 1 to 7

10. / . Method according to any one of claims 8 and 9, the starting charge comprising by volume, at least 10%, or even at least 20%, or even at least 30%, or even at least 40%, or even at least 50% of lanthanum hydroxide.

11. A method according to any one of claims 8 to 10, the starting charge consisting of lanthanum hydroxide particles and less than 1% by volume of other constituents and the sintering temperature of the preformed mold preferably being between 900°C and 1300°C.

12. A method according to any one of claims 8 to 10, the starting charge consisting of lanthanum hydroxide particles, Si3N4 particles and less than 1% by volume of other constituents, the mass content of lanthanum hydroxide particles preferably being at least 10% and the sintering temperature of the preformed mold preferably being between 1265°C and 1760°C.

13. A method according to any one of claims 8 to 10, the starting charge consisting of lanthanum hydroxide particles, Al2O3 particles and less than 1% by volume of other constituents, the mass content of lanthanum hydroxide particles preferably being at least 50% and the sintering temperature of the preformed mold preferably being between 920°C and 1420°C.

14. A method according to any one of claims 8 to 10, the starting charge consisting of lanthanum hydroxide particles, SiC particles and less than 1% by volume of other constituents, the mass content of lanthanum hydroxide particles preferably being at least 50% and the sintering temperature of the preformed mold preferably being between 1400°C and 1700°C.

15. A method according to any one of claims 8 to 10, the starting charge consisting of lanthanum hydroxide particles, BN particles and less than 1% of other constituents, the mass content of lanthanum hydroxide particles preferably being at least 10% and the sintering temperature of the preformed mold preferably being between 1300°C and 1850°C.

Images