Method for densifying porous annular substrates by chemical vapour infiltration

1. A process for densifying annular porous substrates by chemical vapour infiltration, the process comprising:

providing a plurality of unit modules, each unit module comprising a support plate on which is formed a stack of annular porous substrates, the support plate comprising a central gas inlet opening communicating with an internal volume formed by the central passages of the stacked substrates and gas outlet openings angularly distributed around the central opening, and a thermal mass cylinder wrapping the stack of substrates having a first end integral with the support plate and a second free end so that a closed peripheral duct is formed between the stacked substrates and the cylinder,

forming stacks of unit modules in the chamber of a densification furnace, each stack comprising at least one second unit module stacked on a first unit module, the support plate of the second unit module resting on the second free end of the cylinder of the first unit module, the central gas inlet opening of the second unit module communicating with the internal volume of the stack of substrates of the first unit module, and the peripheral duct of the second unit module communicating with the peripheral duct of the first unit module via the gas outlet openings of the second unit module, and

injecting into the stacks of unit modules a gas phase comprising a gas precursor of a matrix material to be deposited within the porosity of the substrates,

wherein, to form a stack of annular porous substrate on the support plate of a unit module, arms of a loading device are inserted into the unit module through the outlet openings of the support plate, the stack of substrates is formed on the ends of the arms inserted into the unit module, and the arms are removed from the unit module so as to deposit the stack thus formed on the support plate.

2. The process as claimed in claim 1 , wherein each cylinder is made of graphite.

3. The process as claimed in claim 1 , wherein each unit module comprises shims between the porous substrates, each shim providing a leakage passage between the internal volume of the stack of substrates and the external volume to the stack of substrates.

4. The process as claimed in claim 1 , wherein each support plate is circular in shape and has a diameter comprised between 110% and 120% of the outer diameter of an annular porous substrate.

5. The process as claimed in claim 1 , wherein the chamber of the densification furnace is delimited by a susceptor coupled to an inductor.

6. The process as claimed in claim 1 , wherein each annular porous substrate comprises carbon.

7. The process as claimed in claim 1 , wherein each annular porous substrate constitutes a fibrous preform for a brake disc.

8. The process as claimed in claim 1 , wherein the arms are vertical arms and wherein the loading device comprises a disc-shaped lower plate from which the vertical arms extend.

9. The process as claimed in claim 1 , wherein the gas outlet openings of the second unit module communicate directly with the external volume to the stack of substrates of the first unit module.

10. The process as claimed in claim 1 , wherein the external volume to the stack of substrates of the first unit module, the gas outlet openings of the second unit module and an external volume to the stack of substrates of the second unit module collectively form a gas channel.

11. The process as claimed in claim 1 , wherein each of the gas outlet openings extends through an entire thickness of the support plate.