METHOD AND ASSEMBLY FOR INFILTRATION AND RAPID PHASE DEPOSITION OF POROUS COMPONENTS

Abstract

A chemical vapor infiltration (CVI) method for densifying at least one porous component includes placing the at least one porous component inside a crucible, bringing temperature inside the crucible to a value adapted to densify the porous component to transform it into a densified component, bringing pressure inside the crucible between 0.1 KPa and 25 KPa, once operational temperature and pressure are reached, flowing gas inside the crucible, gas being suitable for densifying the porous component to transform it into a densified component, and keeping an oxidizing environment outside the crucible, the external environment lapping against the crucible. The crucible is provided of at least one material having thermal conductivity greater than 30 W/mK from room temperature to at least 1000° C. selected from: sintered silicon carbide (SiC), silicon-infiltrated silicon carbide (Si—SiC), sintered boron carbide (B4C), silicon-infiltrated boron carbide (Si—B4C), sintered zirconium carbide (ZrC), silicon-infiltrated zirconium carbide (Si—ZrC), a combination of silicon carbide (SiC), boron carbide (B4C) and sintered and/or silicon-infiltrated zirconium carbide (ZrC).

Claims

1-78. (canceled)

79. A chemical vapor infiltration (CVI) method for densifying at least one porous component, the CVI method comprising: placing the at least one porous component inside a crucible; bringing temperature and pressure inside the crucible to a value adapted to densify the at least one porous component to transform it into a densified or partially densified component; once operational temperature and pressure are reached, flowing gas adapted to densify the at least one porous component to transform it into a densified component inside the crucible; wherein the CIV method further comprises: keeping an oxidizing environment outside the crucible, wherein external environment laps against said crucible; and wherein said crucible is made in at least one of the following materials having thermal conductivity greater than 30 W/mK from room temperature to at least 1000° C.: sintered silicon carbide (SiC), silicon-infiltrated silicon carbide (Si—SiC), sintered boron carbide (B4C), silicon-infiltrated boron carbide (Si—B4C), sintered zirconium carbide (ZrC), silicon-infiltrated zirconium carbide (Si—ZrC), a combination of silicon carbide (SiC), boron carbide (B4C) and sintered and/or silicon-infiltrated zirconium carbide (ZrC).

80. The CVI method of claim 79, further comprising: at operational temperature, pressure and fluxing of the gas, obtaining a non-oxidizing or reducing environment inside the crucible.

81. The CVI method of claim 79, further comprising: keeping temperature and pressure inside the crucible to a value adapted to densify the at least one porous component to transform it into a densified or partially densified component; or bringing temperature inside the crucible between 900° C. and 1300° C.; or bringing pressure inside the crucible between 0.1 KPa and 25 KPa; or adjusting flow of gas at an inlet of the crucible at a value between 0.1 1/min/dm3 and 10 1/min/dm3, where dm3 is meant as the volume of the crucible chamber.

82. The CVI method of claim 79, further comprising: once temperature suitable for densification is reached, obtaining a non-oxidizing or reducing environment inside the crucible, wherein, throughout process, the oxidizing environment is kept outside the crucible, in which said external environment laps against said crucible.

83. The CVI method of claim 79, further comprising: keeping pressure outside the crucible equal to room pressure, that is about 90 KPa, and in any case in over-pressure with respect to the pressure inside of the crucible.

84. The CVI method of claim 79, further comprising: providing said crucible of a material having thermal conductivity between 120 and 80 W/mK at 400° C.

85. The CVI method of claim 79, further comprising: providing a component with a matrix comprising fibers as a porous component; or providing a component with a matrix comprising carbon fibers as a porous component; or providing a component with a matrix comprising silicon carbide (SiC) fibers as a porous component.

86. The CVI method of claim 79, further comprising: coating said crucible with oxidation resistant coating; or providing said coating of a material comprising metals, including refractory steels.

87. The CVI method of claim 79, further comprising: during start-up of the process, as long as temperature inside crucible has not reached a value close to the value adapted to densify the at least one porous component to transform it into a densified component, washing the crucible with nitrogen (N2).

88. The CVI method of claim 79, further comprising: bringing pressure inside the crucible between 1 KPa and 20 KPa; or keeping pressure outside the crucible equal to room pressure.

89. The CVI method of claim 79, further comprising: adjusting gas flow at the inlet to the crucible between 10 l/min and 60 l/min.

90. The CVI method of claim 79, further comprising: separating, at an outlet of the crucible, tar and/or cycloaromatic hydrocarbons from fumes exiting the crucible.

91. The CVI method of claim 79, further comprising: feeding at least one of methane, butane, ethane, propane, or a combination thereof, and/or methane with 96% purity as a gas suitable for densification to the crucible.

92. The method of claim 79, further comprising: storing exhaust gas at room pressure in a storage reservoir; and using the exhaust gas exiting the crucible and brought to room pressure as a fuel to feed at least one burner to bring and/or keep a desired temperature inside of the crucible; or during initial steps of heating the crucible, using methane to feed at least one burner to obtain the desired temperature inside the crucible; then, when fully operational using the exhaust gas exiting the crucible and brought to room pressure as a fuel to feed at least one burner and keep the desired temperature inside the crucible.

93. The CVI method of claim 79, further comprising: integrating fuel gas and combustion air in the exhaust gas exiting the crucible.

94. The CVI method of claim 79, further comprising: arranging the crucible in an oxide oven; and/or keeping an inner oven chamber in an oxidizing environment; or keeping the inner oven chamber at a pressure capable of reaching room pressure; or bringing pressure of the inner oven chamber to a pressure between 15 KPa and 90 KPa; or keeping room temperature outside said oxide oven.

95. The CVI method of claim 79, further comprising: providing a crucible comprising an open container forming an inner loading chamber of the at least one porous component to be densified; providing said open container comprising container supporting surfaces, wherein said container supporting surfaces are grinded and lapped; providing a crucible comprising a crucible lid having lid supporting surfaces for supporting the crucible lid to the open container, wherein said lid supporting surfaces are grinded and lapped; and/or directly supporting said lid supporting surfaces to said container supporting surfaces by sealing said crucible; bringing pressure of the closed inner loading chamber to a pressure between 0.1 KPa and 25 KPa; and/or keeping a pressure differential between the inner loading chamber of the crucible and the inner oven chamber of the oxide oven of at least 5 KPa, so that the inner loading chamber is depressurized with respect to an outer chamber or oven chamber; and/or supporting said lid supporting surfaces to said container supporting surfaces by sealing said crucible by interposition of a sealing gasket; bringing pressure of the closed inner loading chamber to a pressure between 0.1 KPa and 25 KPa.

96. A chemical vapor infiltration (CVI) assembly for densifying porous components, the CVI assembly comprising: at least one crucible configured to receive porous components to be densified; said crucible being made of a material adapted to resist densification temperature and pressure and adapted to be internally exposed to a reducing atmosphere, or process temperature and pressure; said crucible comprising a crucible inlet for introducing a gas suitable for densification into the crucible at a predetermined pressure and a predetermined flow rate; said crucible further comprising a crucible outlet for evacuating exhaust gas; said CVI assembly further comprising an oxide oven configured to internally operate at temperatures suitable for a CVI process; said crucible being placed inside said oxide oven, wherein said CVI assembly further comprises a vacuum pump configured to create a process pressure inside said crucible; wherein said crucible is of a material adapted to be externally exposed to an oxidizing atmosphere; and wherein said crucible is made in at least one of the following materials having thermal conductivity greater than 30 W/mK from room temperature to 1000° C.: sintered silicon carbide (SiC), silicon-infiltrated silicon carbide (Si—SiC), —sintered boron carbide (B4C), silicon-infiltrated boron carbide (Si—B4C), sintered zirconium carbide (ZrC), silicon-infiltrated zirconium carbide (Si—ZrC), a combination of silicon carbide (SiC), boron carbide (B4C) and sintered and/or silicon-infiltrated zirconium carbide (ZrC).

97. The CVI assembly of claim 96, wherein said vacuum pump is configured to create a pressure between 0.1 KPa and 25 KPa inside said crucible; said crucible further comprises an open container and a crucible lid configured to seal said open container; and/or said open container defines an inner loading chamber configured to receive at least one porous component, said open container delimits an inner loading chamber configured to receive at least one braking band for a disc of a disc brake to be densified.

98. The CVI assembly of claim 96, wherein said open container comprises container supporting surfaces and wherein said container supporting surfaces are grinded and lapped; and/or said crucible lid comprises lid supporting surfaces for supporting the crucible lid to the open container, and wherein said lid supporting surfaces are grinded and lapped; and/or said lid supporting surfaces, with closed crucible, rest on said container supporting surfaces, sealing said crucible; and said lid supporting surfaces, with closed crucible, rest on said container supporting surfaces by sealing said crucible by interposition of a sealing gasket; and/or said crucible is of a material adapted to have externally an atmospheric pressure of about 90 KPa.

99. The CVI assembly of claim 96, wherein said CVI assembly further comprises an oxide oven configured to internally operate at room pressure and temperatures suitable for the CVI process; and/or said crucible is externally coated with an oxide-resistant coating; and/or said coating is made of a material comprising metals, including refractory steels; and/or an outer chamber or inner oven chamber is an oxidizing environment, in which said chamber or environment laps against said crucible.

100. The CVI assembly of claim 96, wherein said open container is of silicon carbide (SiC); or said crucible lid is of silicon carbide (SiC); and/or said crucible inlet is provided in said open container; and/or said crucible outlet is provided in said crucible lid.

101. The CVI assembly of claim 96, wherein said vacuum pump is a back-flow nitrogen pump configured to keep said exhaust gas dry; or said vacuum pump is configured to bring said exhaust gas to room pressure downstream of said vacuum pump, or a limited overpressure adapted to convey said exhaust gas to at least one burner; and/or a storage reservoir for the exhaust gas is provided downstream of said vacuum pump; and said reservoir comprises a tar and/or cycloaromatic hydrocarbon separation device; said CVI assembly comprises a cooling device for the exhaust gas; and/or said oxide oven comprises resistance heating components; and/or said oxide oven comprises induction heating components; and/or said oxide oven comprises free-flame heating components, including burners configured to operate at room pressure.

102. The CVI assembly of claim 96, wherein said CVI assembly further comprises a recirculation duct fluidically connecting said vacuum pump to said at least one burner; and said recirculation duct comprises a fuel gas inlet for introducing into said recirculation duct a fuel gas to be integrated with exhaust gas for a burner; and/or said oxide oven comprises a combustion fume exhaust duct.

103. The CVI assembly of claim 96, wherein said CVI assembly comprises at least one gas feeding cylinder or bottle suitable for densification, including methane CH4, connected to said crucible inlet; and/or said assembly comprises a tar and/or cycloaromatic hydrocarbon separation device connected downstream of said crucible outlet.

104. The CVI assembly of claim 96, wherein said CVI assembly comprises an exhaust gas discharge duct connected downstream of said vacuum pump; and/or said gas suitable for densification is at least one of methane, butane, ethane, propane or a combination thereof.

105. The CVI assembly of claim 96, wherein said CVI assembly comprises a carousel device comprising a closed-path continuous movement device supporting at least two crucibles, wherein the closed-path continuous movement device comprises a loading section suitable for loading at least one porous component into said crucible when open; the closed-path continuous movement device comprises a discharging section suitable for discharging at least one densified component from said crucible, when open the closed-path continuous movement device comprises a treatment section associated with a continuous oven of the continuous oxide type; and said continuous oven allows introduction of the at least two crucibles and exiting thereof; and/or said carousel device comprises a movable feeding device removably connected to at least one of the at least two crucibles for feeding said densifying gas; said carousel device comprises a movable evacuation device for evacuating the exhaust gas from at least one crucible and putting the crucible under vacuum bringing crucible pressure between 0.1 KPa and 25 KPa.

106. The CVI assembly of claim 96, wherein said crucible inlet comprises a fast-coupling crucible inlet valve for selectively connecting and disconnecting said movable feeding device for feeding the densifying gas; said crucible outlet comprises a fast-coupling crucible outlet valve for selectively connecting and disconnecting said movable evacuation device for evacuating said exhaust gas and generating vacuum in the crucible; and/or said closed-path continuous movement device comprises a porous component loading station for loading at least one porous component into said crucible; and/or said closed-path continuous movement device comprises a densified component discharging station for discharging at least one densified component from said crucible.

Description

FIGURES

[0045] Further features and the advantages of the invention will be made readily apparent from the following description of preferred embodiment examples thereof, provided purely by way of a non-limiting example, with reference to the accompanying figures, in which:

[0046] FIG. 1 shows a diagram of a CVI plant according to the prior art;

[0047] FIG. 2 shows a diagram of a rapid vapor phase infiltration and deposition plant according to a first embodiment, in which the oven uses burner devices;

[0048] FIG. 3 shows a second diagram of a rapid vapor phase infiltration and deposition plant according to a second embodiment, in which the oven uses electrical resistance or induction devices;

[0049] FIG. 4 shows a third diagram of a rapid vapor phase infiltration and deposition plant according to a third embodiment, in which the oven is of the tunnel type and a circuit or carousel is provided for moving a plurality of crucibles passing through in different stations for loading, processing in the oven and unloading the components;

[0050] FIG. 5 shows a fourth diagram of a rapid vapor phase infiltration and deposition plant according to a fourth embodiment, in which a container external to the sealed crucible is provided to bring the pressure into an external chamber and adjacent to the crucible below the room pressure;

[0051] FIG. 6 graphically shows the pattern of the thermal conductivity at the temperature change for different materials compared with SiC.

DESCRIPTION OF SOME PREFERRED EMBODIMENT EXAMPLES

[0052] The term “reducing atmosphere” or “reducing” means, for example, a reducing atmosphere for hydrogen produced by the methane decomposition reaction in the formation of pyrolytic carbon which is deposited on the component to be densified.

[0053] According to a general embodiment, a CVI or chemical vapor infiltration method for densifying at least one porous component 1, comprising at least the steps of: [0054] placing the at least one porous component 1 inside a crucible 3; [0055] bringing the temperature and the pressure Ti, Pi inside the crucible 3 to a value adapted to densify the porous component 1 to transform it into a densified component 2; [0056] once the operational temperature and pressure are reached, flowing a reaction gas 4 inside the crucible; [0057] said reaction gas, or gas 4, is fed into the crucible 3, said gas 4 being suitable for densifying the porous component 1 to transform it into a densified component 2;

[0058] wherein the following further steps are provided [0059] keeping an oxidizing environment outside the crucible 3, wherein said external environment laps against said crucible 3;

[0060] and wherein [0061] said crucible 3 is provided of a material which allows a thermal conductivity greater than 30 W/mK from room temperature to 1000° C.

[0062] This material can be selected from at least one of the following materials: [0063] sintered silicon carbide (SiC);

[0064] or [0065] silicon-infiltrated silicon carbide (Si—SiC);

[0066] or [0067] sintered boron carbide (B4C);

[0068] or [0069] silicon-infiltrated boron carbide (Si—B4C);

[0070] or [0071] sintered zirconium carbide (ZrC);

[0072] or [0073] silicon-infiltrated zirconium carbide (Si—ZrC);

[0074] or [0075] a combination of silicon carbide (SiC), boron carbide (B4C) and sintered and/or silicon-infiltrated zirconium carbide (ZrC).

[0076] By virtue of this solution, the crucible chamber is effectively and quickly heated.

[0077] According to a further embodiment of the method, there is provided the further step of bringing the pressure Pi inside the crucible 2 between 0.1 KPa and 25 KPa.

[0078] According to a further general embodiment independent of the preceding one, a CVI or chemical vapor infiltration method for densifying at least one porous component 1, comprising at least the steps of: [0079] providing a graphite crucible 3; [0080] placing the at least one porous component 1 inside said crucible 3; [0081] bringing the temperature and the pressure Ti, Pi inside the crucible 3 to a value adapted to densify the porous component 1 to transform it into a densified component 2; [0082] feeding gas 4 into the crucible 3, said gas 4 being suitable for densifying the porous component 1 to transform it into a densified component 2;

[0083] wherein the following further steps are provided [0084] at operational temperature and pressure, flowing a reaction gas 4 inside the crucible 3;

[0085] and wherein [0086] the pressure Pe outside the crucible 3 is kept equal to room pressure.

[0087] According to a further embodiment of the method, there is provided the further step of coating and/or covering said graphite crucible with an oxidation-resistant material.

[0088] According to a further embodiment of the method, there is provided the further step of bringing the pressure Pi inside the crucible 2 between 0.1 KPa and 25 KPa.

[0089] According to a further embodiment of the method, there is provided the further step of coating said crucible 3 with an oxidation-resistant coating.

[0090] According to a further embodiment of the method, there is provided the further step in which said coating is made of a material comprising engobbio®, or engobe (see for example www.stradaceramica.it/glossario2/ or en.wikipedia.org/wiki/Slipware).

[0091] According to a further embodiment of the method, there is provided the further step in which said coating is made of a material comprising metals, for example refractory steels.

[0092] According to a further embodiment of the method, there is provided the further step of obtaining a reducing environment inside the crucible (3), at operational temperature, pressure and fluxing of the gas.

[0093] According to a further embodiment of the method, there is provided the further step of providing as a porous component 1 a component with a matrix comprising fibers.

[0094] According to a further embodiment of the method, there is provided the further step of providing as a porous component 1 a component with a matrix comprising carbon fibers.

[0095] According to a further embodiment of the method, there is provided the further step of providing as a porous component 1 a component with a matrix comprising carbon fibers and pyrolytic carbon.

[0096] According to a further embodiment of the method, there is provided the further step of providing as a porous component (1) a component with a matrix comprising silicon carbide (SiC) fibers.

[0097] According to a further embodiment of the method, there is provided the further step of providing as a porous component (1) a component with a matrix comprising silicon carbide (SiC) and pyrolytic carbon fibers.

[0098] According to a further embodiment of the method, there is provided the further step of providing as a porous component (1) a component with a matrix comprising silicon carbide (SiC) and silicon carbide fibers.

[0099] According to a further embodiment of the method, there is provided the further step of bringing the temperature Ti inside the crucible 3 between 900° C. and 1300° C., preferably from 1050 to 1200° C.

[0100] According to a further embodiment of the method, there is provided the further step of: once an operational temperature suitable for densification is reached, obtaining a non-oxidizing environment inside the crucible (3); and wherein, throughout the process, an oxidizing environment is kept outside the crucible (3), in which said external environment laps against said crucible (3).

[0101] According to a further embodiment of the method, there is provided the further step, once an operational temperature suitable for densification is reached, of obtaining a reducing environment inside the crucible 3; and wherein, throughout the process, an oxidizing environment is kept outside the crucible 3, in which said external environment laps against said crucible 3.

[0102] According to a further embodiment of the method, there is provided the further step of providing said crucible 3 of a material which allows a thermal conductivity between 120 and 80 W/mK at 400° C.

[0103] According to a further embodiment of the method, there is provided the further step of keeping the pressure Pe outside the crucible 3 equal to room pressure about 90 KPa.

[0104] According to a further embodiment of the method, there is provided the further step, once an operational temperature and pressure suitable for densification are reached, of obtaining a reducing environment inside the crucible 3; and keeping an oxidizing environment outside the crucible 3, in which said external environment laps against said crucible 3.

[0105] According to a further embodiment of the method, there is provided the further step of adjusting the flow of gas (4) at the inlet (5) to the crucible (3) to a value of between 0.1 l/min/dm3 and 10 l/min/dm3.

[0106] According to a further embodiment of the method, there is provided the further step of adjusting the flow of gas 4 at the inlet 5 of the crucible 3 to a value of between 1 l/min/dm3 and 5 l/min/dm3.

[0107] The flow of gas 4 may be slower to have a greater deposition of pyrolytic carbon which can be restructured in graphite with post-treatment, allowing a higher conductivity of the material.

[0108] Going towards a greater gas flow speed, a carbon deposit is obtained which is more difficult to restructure, but production times are reduced.

[0109] According to a further embodiment of the method, there is provided the further step, during the start-up of the process, as long as the temperature of the crucible has not reached a value close to the value adapted to densify the porous component 1 to transform it into a densified component 2, of washing the crucible with nitrogen N2.

[0110] According to a further embodiment of the method, there is provided the further step of bringing the pressure (Pi) inside the crucible (2) between 1 KPa and 20 KPa.

[0111] According to a further embodiment of the method, there is provided the further step of bringing the pressure Pi inside the crucible 3 between 10 KPa and 15 KPa.

[0112] According to a further embodiment of the method, there is provided the further step in which said crucible 3 avoids a thermal barrier between the environment outside the crucible itself and the environment inside the crucible itself from being defined.

[0113] According to a further embodiment of the method, there is provided the further step of providing said crucible 3 so that its thermal conductivity is higher than 30 W/mK at 1000° C.

[0114] According to a further embodiment of the method, there is provided the further step of keeping the pressure Pe outside the crucible 3 equal to room pressure.

[0115] According to a further embodiment of the method, there is provided the further step of adjusting the flow of gas 4 at the inlet 5 of the crucible 3 between 10 l/min and 60 l/min.

[0116] According to a further embodiment of the method, there is provided the further step of bringing the pressure Pe outside the crucible 3 not less than 15 KPa.

[0117] According to a further embodiment of the method, there is provided the further step of keeping a pressure difference between the environment inside the crucible 3 and outside the crucible 3, in which the external environment has an over-pressure with respect to the internal environment of above 5 Kpa.

[0118] According to a further embodiment of the method, there is provided the further step of keeping a pressure difference between the environment inside the crucible 3 and outside the crucible 3, in which the external environment has an over-pressure with respect to the internal environment of above 5 Kpa.

[0119] According to a further embodiment of the method, there is provided the further step, at the outlet 6 of the crucible 3, of separating the tar and/or cycloaromatic hydrocarbons 9 from the fumes 7 exiting the crucible.

[0120] According to an embodiment, the exhaust gas exiting the crucible is used for burners which raise or maintain the temperature of the oven. By virtue of this provision, it is possible to avoid the total separation of the tar and the cycloaromatic hydrocarbons since they are burned by the burners as in a thermo-destruction plant.

[0121] According to a further embodiment, there is provided the further step of feeding methane gas, or butane, or ethane, or propane, or a combination thereof, and/or preferably methane with 96% purity as a gas 4 being suitable for the densification to the crucible 3.

[0122] According to a further embodiment of the method, there is provided the further step of bringing the exhaust gas 9 exiting the crucible 3 to room pressure Pe.

[0123] According to a further embodiment of the method, there is provided the further step of storing the exhaust gas 9 at room pressure in a storage reservoir 50.

[0124] According to a further embodiment of the method, there is provided the further step of using the exhaust gas 9 exiting the crucible 3 and brought to room pressure Pe as a fuel to feed at least one burner 10 to bring and/or keep the desired temperature Ti of the crucible 3.

[0125] According to a further embodiment of the method, there is provided the further step, during the initial heating steps of the crucible 3, of using substantially pure methane to feed at least one burner 10 to bring the desired temperature of the crucible 3.

[0126] According to a further embodiment of the method, there is provided the further step, at operational temperature, of using the exhaust gas 9 exiting the crucible 3 and brought to room pressure Pe as a fuel to feed at least one burner 10 and keep the desired temperature Ti of the crucible 3.

[0127] According to a further embodiment of the method, there is provided the further step of integrating the fuel gas 13 into the exhaust gas 9 exiting the crucible 3.

[0128] According to a further embodiment of the method, there is provided the further step of arranging the crucible 3 in an oxide oven 11.

[0129] For example, said oxide ovens are ovens with oxide refractories such as alumina and/or mullite in which cycles with oxidizing atmospheres are performed. In these ovens the use of Kanthal® or super Kanthal® electric resistances is provided. For example, an oven of this type is the Nabertherm GmbH p muffle oven with a maximum temperature of 1400° C. and a volume of 400 liters.

[0130] According to a further embodiment of the method, there is provided the further step of keeping the inner oven chamber 12 in an oxidizing environment.

[0131] According to a further embodiment of the method, there is provided the further step of keeping the inner oven chamber 12 at the pressure that can reach the room pressure Pe.

[0132] According to a further embodiment of the method, there is provided the further step of bringing the pressure of the inner oven chamber 12 to the pressure of 30-90 KPa.

[0133] According to a further embodiment of the method, there is provided the further step of keeping a room temperature Ta outside said oxide oven 11.

[0134] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of silicon carbide SiC.

[0135] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of silicon-infiltrated silicon carbide (Si—SiC).

[0136] According to a further embodiment of the method, there is provided the further step of providing a crucible (3) of silicon-infiltrated (Si—SiC) sintered silicon carbide (SiC).

[0137] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of boron carbide B4C.

[0138] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of silicon-infiltrated boron carbide (Si—B4C).

[0139] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of zircon carbide ZrC.

[0140] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of silicon-infiltrated zirconium carbide (Si—ZrC).

[0141] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 in a combination of silicon carbide SiC, boron carbide B4C and zirconium carbide BZrC.

[0142] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 of sintered silicon carbide SiC.

[0143] According to an embodiment, the crucible is 100% sintered with silicon-infiltrated SiC or SiC, for example obtained from a SiC powder preform infiltrated with Si. This material allows working up to 1400° C., although it is much easier and faster to produce than traditional crucibles.

[0144] This crucible has the desired conductivity in addition to the desired resistance to the oxidizing environment.

[0145] These crucibles resist oxidation because they passivate upon contact with oxygen, where part of the product is transformed into a micrometric layer of SiO2 or oxide glasses which protects the crucible itself.

[0146] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 comprising an open container 14 forming an inner loading chamber 15 of the porous components 1 to be densified.

[0147] According to a further embodiment of the method, there is provided the further step of providing an open container 14 comprising container supporting surfaces 16 wherein said container supporting surfaces 16 are grinded and lapped.

[0148] According to a further embodiment of the method, there is provided the further step of providing a crucible 3 comprising a crucible lid 17 having lid supporting surfaces 18 for supporting the lid 17 to the open container 14, wherein said lid supporting surfaces 18 are grinded and lapped.

[0149] According to a further embodiment of the method, there is provided the further step of directly supporting said lid supporting surfaces 18 to said container supporting surfaces 16 by sealing said crucible; bringing the pressure of the closed inner loading chamber to a pressure between 0.1 KPa and 25 KPa.

[0150] According to a further embodiment of the method, there is provided the further step of keeping a pressure differential between the inner chamber 15 of the crucible 3 and the chamber 12 of the oven 11 of at least 5 KPa, so that the inner chamber 15 is depressurized with respect to an outer chamber or oven chamber 11.

[0151] According to a further embodiment of the method, there is provided the further step of keeping a pressure differential between the inner chamber 15 of the crucible 3 and the chamber 12 of the oven 11 of at least 10 KPa, so that the inner chamber 15 is depressurized with respect to an outer chamber or oven chamber 11.

[0152] According to a further embodiment of the method, there is provided the further step of supporting said lid supporting surfaces 18 to said container supporting surfaces 16 by sealing said crucible by means of the interposition of a sealing gasket 19; bringing the pressure of the closed inner loading chamber to a pressure between 0.1 KPa and 25 KPa.

[0153] The present invention also relates to an assembly which allows implementing one of the methods described above.

[0154] According to a general embodiment, an assembly 1 for densifying porous components, according to the method known as Chemical Vapor Infiltration, comprises: [0155] at least one crucible 3 adapted to receive porous components 1 to be densified; [0156] said crucible 3 is made of a material adapted to resist the densification temperature and pressure and adapted to be internally exposed to a reducing atmosphere; [0157] said crucible 3 comprises a crucible inlet 5 for introducing a gas 4, which is suitable for densification, into the crucible 3 at a predetermined pressure Pi and a predetermined flow rate Q;

[0158] said crucible 3 comprises a crucible outlet 7 for evacuating the exhaust gas 10;

[0159] said assembly 1 further comprises an oven 12 adapted to internally operate at temperatures which are suitable for the CVI process.

[0160] According to an embodiment, said crucible 3 is placed inside said oven 12; and wherein said assembly 1 further comprises a vacuum pump 22 adapted to create a pressure between 0.1 KPa and 25 KPa inside said crucible 3.

[0161] According to an embodiment, said crucible 3 is made of a material adapted to be externally exposed to an oxidizing atmosphere; and wherein said crucible 3 is made of a material having a thermal conductivity greater than 30 W/mK from room temperature to 1000° C. This material is selected from at least one of the following: [0162] sintered silicon carbide (SiC);

[0163] or [0164] silicon-infiltrated silicon carbide (Si—SiC);

[0165] or [0166] sintered boron carbide (B4C);

[0167] or [0168] silicon-infiltrated boron carbide (Si—B4C);

[0169] or [0170] sintered zirconium carbide (ZrC);

[0171] or [0172] silicon-infiltrated zirconium carbide (Si—ZrC);

[0173] or [0174] a combination of silicon carbide (SiC), boron carbide (B4C) and sintered and/or silicon-infiltrated zirconium carbide (ZrC).

[0175] According to a different general embodiment completely independent of the previous one, an assembly 1 for densifying porous components, according to the method known as Chemical Vapor Infiltration, comprising: [0176] at least one crucible 3 adapted to receive porous components 1 to be densified; [0177] said crucible 3 is made of graphite adapted to withstand the densification temperature and pressure; [0178] said crucible 3 comprises a crucible inlet 5 for introducing a gas 4, which is suitable for densification, into the crucible 3 at a predetermined pressure Pi and a predetermined flow rate Q;

[0179] said crucible 3 comprises a crucible outlet 7 for evacuating the exhaust gas 10;

[0180] said assembly 1 further comprises an oven 12 adapted to internally operate at temperatures which are suitable for the CVI process.

[0181] Advantageously, said crucible 3 is placed inside said oven 12.

[0182] According to an embodiment, said assembly 1 further comprises a vacuum pump 22 adapted to create a pressure between 0.1 KPa and 25 KPa inside said crucible.

[0183] According to an embodiment, said crucible 3 is made of a material adapted to be externally exposed to an oxidizing atmosphere.

[0184] According to an embodiment, said oven 12 defines an inner oven chamber 12 which laps against said crucible 3 and placed at an atmospheric pressure of about 90 KPa.

[0185] According to an embodiment, said assembly 1 further comprises a vacuum pump 22 adapted to create a pressure ranging from 0.1 KPa to 25 KPa inside said crucible so that, in operational state, inside said crucible 3 a reducing environment is formed.

[0186] According to an embodiment, said crucible 3 is adapted to have externally an atmospheric pressure of about 90 KPa.

[0187] According to an embodiment, said open container 15 delimits an inner loading chamber 16 adapted to receive at least one braking band 1 for a disc of a disc brake to be densified, preferably a plurality of braking bands 1 for a disc of a brake disc to be densified.

[0188] According to an embodiment, said assembly 1 further comprises an oxide oven 12 adapted to operate internally at room pressure and temperatures suitable for the CVI process.

[0189] According to an embodiment, said crucible is made of graphite.

[0190] According to an embodiment, said crucible 3 is externally coated with an oxide-resistant coating.

[0191] According to an embodiment, said coating comprises engobbio® or engobe.

[0192] According to an embodiment, the outer crucible chamber 12 or inner oven chamber 12 is an oxidizing environment, in which said external environment laps against said crucible 3.

[0193] According to an embodiment, said crucible 3 comprises an open container 15 and a lid 17 adapted to seal said open container 15.

[0194] According to an embodiment, said open container 15 defines an inner loading chamber 16 adapted to receive at least one porous component 1, preferably a plurality of porous components 1.

[0195] According to an embodiment, said open container 14 comprises container supporting surfaces 16 and wherein said container supporting surfaces 16 are grinded and lapped.

[0196] According to an embodiment, said crucible lid 17 comprises lid supporting surfaces 18 for supporting the lid 17 to the open container 14, and wherein said lid supporting surfaces 18 are grinded and lapped.

[0197] According to an embodiment, said lid supporting surfaces 18, with closed crucible 3, rest on said container supporting surfaces 16, sealing said crucible 3.

[0198] According to an embodiment, said lid supporting surfaces 18, with closed crucible, rest on said container supporting surfaces 16 by sealing said crucible by means of the interposition of a sealing gasket 19.

[0199] According to an embodiment, said crucible 3 is of a material adapted to have externally an atmospheric pressure of about 90 KPa.

[0200] According to an embodiment, said assembly 1 further comprises an oxide oven 12 adapted to operate internally at room pressure and temperatures suitable for the CVI process.

[0201] According to an embodiment, said crucible 3 is externally coated with an oxide-resistant coating.

[0202] According to an embodiment, said external coating of the crucible 3 comprises engobbio® or engobe.

[0203] According to an embodiment, said coating is made of a material comprising metals, for example refractory steels.

[0204] According to an embodiment, the outer crucible chamber 12 or inner oven chamber 12 is an oxidizing environment, in which said chamber 12 or said environment laps against said crucible 3.

[0205] According to an embodiment, said crucible comprises silicon carbide SiC.

[0206] According to an embodiment, said crucible (3) comprises silicon-infiltrated silicon carbide (Si-SiC);

[0207] and/or wherein [0208] said crucible (3) comprises silicon-infiltrated (Si—SiC) sintered silicon carbide (SiC);

[0209] and/or wherein [0210] said crucible 3 comprises boron carbide B4C;

[0211] and/or wherein [0212] said crucible (3) comprises silicon-infiltrated boron carbide (Si—B4C);

[0213] and/or wherein [0214] said crucible 3 comprises zirconium carbide ZrC;

[0215] and/or wherein [0216] said crucible (3) comprises silicon-infiltrated zirconium carbide (Si—ZrC);

[0217] and/or wherein [0218] said crucible 3 comprises a combination of silicon carbide SiC, boron carbide B4C and zirconium carbide ZrC;

[0219] and/or wherein [0220] said crucible 3 comprises sintered silicon carbide SiC.

[0221] According to an embodiment, said open container 14 comprises silicon carbide SiC.

[0222] According to an embodiment, said crucible lid 17 comprises silicon carbide SiC.

[0223] According to an embodiment, said crucible inlet 5 is provided in said open container 14.

[0224] According to an embodiment, said crucible outlet 6 is provided in said crucible lid 17.

[0225] According to an embodiment, said vacuum pump 21 is a back-flow nitrogen pump adapted to keep said exhaust gases 9 dry. For example, said vacuum pump 21 is a screw pump NC 0100 B, NC 0200 B, NC 0300 B from Ateliers Busch SA, or a cryogenic pump, for example a NIKKISO cryogenic pump from Lewa GmbH.

[0226] According to an embodiment, said vacuum pump 21 is adapted to bring said exhaust gases 9 to a room pressure downstream of said vacuum pump 21, or a limited overpressure adapted to convey said exhaust gases 9 to at least one burner 10.

[0227] According to an embodiment, a storage reservoir 50 for the exhaust gas 9 is provided downstream of said vacuum pump 21.

[0228] According to an embodiment, said reservoir comprises a device for separating tar and/or cycloaromatic hydrocarbons 40; and said assembly 1 comprises a cooling device 51 for the exhaust gases 9.

[0229] According to an embodiment, said oxide oven 11 comprises resistance heating components 22, 42.

[0230] According to an embodiment, said oven 11 comprises induction heating components.

[0231] According to an embodiment, said oxide oven 11 comprises free-flame heating components, for example burners 10 adapted to operate at room pressure.

[0232] According to an embodiment, said oxide oven 11 comprises four burners 10.

[0233] According to an embodiment, said assembly 1 comprises a recirculation duct 23 fluidically connecting said vacuum pump 21 to said at least one burner 10.

[0234] According to an embodiment, said recirculation duct 23 comprises a fuel gas inlet 24 for introducing into said duct a fuel gas 13 to be integrated with exhaust gas for a burner.

[0235] According to an embodiment, said oxide oven 11 comprises a combustion fume exhaust duct 38.

[0236] According to an embodiment, said assembly 20 comprises at least one gas feeding cylinder or bottle 39 suitable for densification, for example methane CH4, connected to said crucible inlet 5.

[0237] According to an embodiment, at least technical service gas feeding cylinder or circuit is provided, such as for example nitrogen and/or argon or the like for washing the inner chamber of the crucible during the heating steps until the desired crucible temperature is reached.

[0238] According to an embodiment, said assembly 20 comprises a tar and/or cycloaromatic hydrocarbon separation device 40 connected downstream of said crucible outlet 6.

[0239] According to an embodiment, said assembly 20 comprises an exhaust gas discharge duct 41 connected downstream of said vacuum pump 21.

[0240] According to an embodiment, said gas suitable for densification 4 is methane gas, or butane, or ethane, or propane or combination of at least two of these.

[0241] According to an embodiment, said assembly 1 comprises a carousel device 25 comprising a closed-path, continuous movement device 26 supporting at least two crucibles 3.

[0242] According to an embodiment, a closed-path continuous movement device 26 comprises a loading section 27 suitable for loading at least one porous component 1 into said crucible 3 when open.

[0243] According to an embodiment, a closed-path continuous movement device 26 comprises a discharging section 28 suitable for discharging at least one densified component 2 from said crucible 3, when open.

[0244] According to an embodiment, a closed-path continuous movement device 26 comprises a treatment section 29 associated with a continuous oven 30 of the continuous oxide oven type, for example a tunnel oven from Riedhammer.

[0245] According to an embodiment, said continuous oven 30 allows the introduction of the at least two crucibles 3 and the exiting thereof.

[0246] According to an embodiment, said carousel device 25 comprises a movable feeding device 31 removably connected to at least one of the at least two crucibles 3 for feeding said densifying gas 4; and said carousel device 25 comprises a movable evacuation device 32 for evacuating the exhaust gas 9 from at least one crucible 3 and putting under vacuum the crucible 3 thus bringing the crucible pressure between 1 KPa and 15 KPa.

[0247] According to an embodiment, said crucible inlet 5 comprises a fast-coupling crucible inlet valve 33 for selectively connecting and disconnecting said movable feeding device 31 for feeding the densifying gas 4; and said crucible outlet 6 comprises a fast-coupling crucible outlet valve 34 for selectively connecting and disconnecting said movable evacuation device 32 for evacuating said exhaust gas 9 and generating vacuum in the crucible 3.

[0248] According to an embodiment, said closed-path, continuous movement device 26 comprises a porous component loading station 35 for loading at least one porous component 1 into said crucible 3.

[0249] According to an embodiment, said closed-path, continuous movement device 26 comprises a densified component discharging station 36 for discharging at least one densified component 2 from said crucible 3.

[0250] According to a further embodiment, a plant, for example a plant useful for experimentation, comprises a crucible or reactor chamber of silicon carbide or SiC. The material used is silicon-infiltrated silicon carbide. The chamber consists of two parts, the main container and the lid. The structure is cylindrical with dimensions of the useful part for loading the preforms of 400 mm of diameter and 335 mm of height. The thickness of the walls is 8 mm. The two parts are in contact by means of a lapped flange on a surface of 700 cm2 which allows obtaining the vacuum seal. The chamber was built based on our project.

[0251] The commercial type oven (for example for oxides) consists of a simple pit oven which can work at a maximum temperature of 1320° C., has Kanthal® resistors and an electrical power of 13.2 kW. The insulation is in alumina-based refractory oxide.

[0252] The cooling line is in stainless steel with an internal diameter of 100 mm, coated and water cooled. It consists of 3 inclined sections for an overall length of about 10 meters. Along the line are two wells for collecting condensed hydrocarbons.

[0253] The pumping group consists of a double screw dry pump with a maximum flow rate of 150 m3/h and a maximum vacuum level of 0.5 mbar.

[0254] The specific construction of the plant used for the experimentation had the main purpose of demonstrating the validity of the innovative concepts introduced and, secondly, of having available the information necessary to design a more efficient and functional plant.

[0255] Summary of experimental tests. The first part of the experimentation concerned the verification of the plant design specifications, in particular: [0256] maximum operating temperature, [0257] heating gradients and thermal dissipation, [0258] minimum vacuum level and leakage, [0259] control of process gas flows, [0260] cooling water flows of the vacuum line.

[0261] Above all, this step allowed optimizing the vacuum sealing systems.

[0262] Subsequently the densification tests were started in order to identify the process parameters that would allow maximizing the carbon deposition efficiency. The relevant parameters are the temperature in the stationing step of the process, the methane flow, the partial pressure level, the duration of the process, the geometry of the load. The ranges of the aforementioned variables that have been explored are the following: [0263] maximum stationing temperature: 1040-1140° C.; [0264] methane flow: 15-60 nl/min; [0265] partial pressure: 75-220 mbar

[0266] The composition of methane that has been kept constant (Siad 98%)

[0267] Initially, carbonized felt was used as a starting material. The felt, in the form of a 300 mm high roll, was wound to form a cylinder with a diameter such as to occupy the entire useful space of the reaction chamber. The gas flow therefore occurred entirely through the mass of the material to be densified. Following 5 test cycles, having identified the best process conditions, a maximum weight gain of 17.5% was achieved in one hour and 34.5% in two hours. The deposit appeared morphologically inhomogeneous and the fibers did not appear homogeneously coated with CVI carbon.

[0268] Later, maintaining the same geometry, it was switched to the use of graphitized felt, with which an important increase in deposition efficiency was generally obtained. By adjusting the process parameters a weight increase of 24.6% was achieved in an hour and 92.6% in 4 hours. With this type of preform, the CVI carbon was homogeneous in thickness from the first deposit layers.

[0269] Therefore for the tests done it seems that it is possible to densify without particular further precautions and with the same efficiency of the traditional CVI ovens: [0270] preforms of different geometry; [0271] different load configurations; [0272] preforms with different densities.

REFERENCE LIST

[0273] 1 porous component [0274] 2 densified component [0275] 3 crucible [0276] 4 gas suitable for densification [0277] 5 crucible inlet [0278] 6 crucible outlet [0279] 7 fumes exiting the crucible [0280] 8 tar and/or cycloaromatic hydrocarbons [0281] 9 exhaust gas exiting the crucible [0282] 10 at least one burner [0283] 11 oxide oven [0284] 12 inner oven chamber [0285] 13 fuel gas to be integrated with exhaust gas for burner [0286] 14 open container [0287] 15 inner loading chamber [0288] 16 container supporting surfaces [0289] 17 crucible lid [0290] 18 lid supporting surfaces [0291] 19 crucible sealing gasket [0292] 20 assembly [0293] 21 vacuum pump [0294] 22 resistance heating components [0295] 23 recirculation duct [0296] 24 fuel gas inlet [0297] 25 carousel device [0298] 26 closed-path continuous movement device [0299] 27 loading section [0300] 28 unloading section [0301] 29 treatment section [0302] 30 continuous oven—Riedhammer SACMI oven for sanitary ware trolley tunnel oven for sanitary ware are mentioned [0303] 31 movable feeding device [0304] 32 movable evacuation device [0305] 33 fast-coupling crucible inlet valve [0306] 34 fast-coupling crucible outlet valve [0307] 35 porous component loading station [0308] 36 densified component unloading station [0309] 37 flowmeter [0310] 38 combustion fume exhaust duct [0311] 39 gas feeding bottle or circuit suitable for densification, for example CH4 [0312] 40 tar and/or cycloaromatic hydrocarbon separation device [0313] 41 exhaust gas discharge duct [0314] 42 resistance heating elements, for example in Kanthal or super-Kanthal [0315] 50 exhaust gas storage reservoir [0316] 51 exhaust gas cooling device [0317] 52 vacuum pump for environment outside the crucible and inside the oven [0318] Pi pressure inside the crucible [0319] Ti temperature inside the crucible [0320] Ta room temperature [0321] Pe pressure outside the crucible [0322] Q predetermined flow rate of densifying gas