Axial turbomachine compressor outer casing

Abstract

The invention relates to a casing, particularly of an axial turbomachine compressor. This casing comprises a support of cylindrical overall shape made of composite material, a metal ring fitted by bonding to the internal surface of the support, and a layer of abradable material fitted by plasma spray onto the internal surface of the metal ring. The metal ring is preferably made of stainless steel and is preferably perforated. The perforation allows better keying of the adhesive and allows the degassing thereof. The external surface of the metal ring is preferably sandblasted prior to bonding. Its internal surface is also preferably sandblasted prior to the plasma spraying of the abradable material.

Claims

1. A method of manufacturing a shell of a compressor of an axial turbomachine, said method comprising the following steps: providing a support of a composite material with an organic matrix having one of a generally ring-shaped and a generally cylindrical shape with a generally circular inner surface, the support being a structural element ensuring rigidity of the turbomachine; fixing a metal ring on the support, the ring being a strip comprising a series of perforations distributed over its surface and having an inner surface and an outer surface opposite to the inner surface wherein the metal ring is fixed on the support by gluing the metal ring on an inner surface of the support; and applying an abradable layer on the inner surface of the ring.

2. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein applying the abradable layer on the inner surface of the ring is performed by plasma spraying, and wherein the abradable material comprises AlSi polyester.

3. The method of manufacturing the shell of an axial turbomachine according to claim 1 further comprising a step of preparing the inner surface of the ring by one of sandblasting and chemical etching prior to applying the abradable layer on the inner surface of the ring.

4. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the perforations have a diameter that is one of less than 1 mm and equal to 1 mm.

5. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the ring comprises a wire mesh.

6. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the metallic material of the ring is comprised of at least one of stainless steel, titanium, nickel-iron alloy and FeNi36.

7. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the ring is made of a porous material.

8. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the ring has a thickness between 0.1 mm and 1 mm.

9. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the ring is made of a plurality of segments.

10. The method of manufacturing the shell of a compressor of an axial turbomachine according to claim 1, wherein the adhesive layer is in direct contact with the inner surface of the support and the outer surface of the ring.

Description

FIGURES

(1) FIG. 1 is a schematic sectional view of a dual rotor axial flow turbofan, the type of aircraft engine whose low-pressure and/or high pressure compressor is likely to be equipped with an external and/or internal shell described in the invention.

(2) FIG. 2 is a partial sectional view of the low-pressure compressor of the engine of FIG. 1, the low-pressure compressor being fitted with the shells described in the invention.

(3) FIG. 3 is a perspective view of a compressor stator stage, comprising a shell according to the invention.

(4) FIG. 4 is a sectional view of the shell of FIG. 3.

(5) FIG. 5 is a greatly enlarged view of the shell in FIG. 4, illustrating the role of one of the perforations in the metal ring.

DETAILED DESCRIPTION

(6) In the following description, the terms “internal” and “external” used to describe the surfaces of the support and the ring relate to the envelope formed by the support and/or the ring; “internal” then means inside that envelope, and “external” means outside that envelope.

(7) Note that the term “external” for the shell refers, in contrast, to the generally annular fluid stream, “outer shell” denotes a shell on the side of the outer edge or outer surface the fluid stream, and “inner shell” designates a shell on the side of the inner edge or inner surface of the fluid stream.

(8) The axial turbomachine 2 shown in FIG. 1 is a double-flow turbofan jet aircraft engine. The turbomachine 2 comprises, from upstream to downstream, a low-pressure compressor 4, a high-pressure compressor 6, a combustion chamber 8 and a turbine 10. The low-pressure and high-pressure compressors are not subject to the high temperatures to which the turbine is subjected. It is therefore possible to use organic matrix composite materials for the production of various components of these compressors, such as the outer shell of the stator.

(9) The low-pressure compressor 4 in FIG. 1 is shown in FIG. 2. As shown in FIG. 2, the low-pressure compressor 4 includes a rotor 20 carrying a plurality of the so-called rotor blade rows 24, a stator formed of a housing 12 and a wall 16 defining the secondary airflow. The housing 12 supports a series of fixed blades 26, so-called stator blade rows. Each circumferential row of stator blades 26 forms a stator stage. Each circumferential row of stator blades 26 together with a circumferential array of rotor blades 24 constitute a compression stage that functions to increase the pressure of the fluid, in this case air, passing through the compression stage. Since the pressure gradient is in a generally axial direction, it is necessary to provide sealing means between the rotating and the stationary parts along the fluid stream. A layer of abradable material 22 is positioned in relation to the tips of each row of rotor blades 24 so as to provide a certain degree of contact in order to ensure a seal.

(10) FIG. 3 illustrates a segment 30 of the stator housing 12 in FIG. 2, segment 30 corresponding to a compression stage. The housing section 30 comprises a generally cylindrical wall 34 carrying a row of stator blades 26 and a layer of abradable material 22 directly downstream of the stator blades 26 positioned facing the tips of the rotor blades 24 directly adjacent downstream.

(11) The structure of the wall 34 forming the support and the layer of abradable material 22 of the wall is shown in FIG. 4. This is a sectional view. Note that this construction is illustrated and described in relation to the wall 34 of the housing forming a so-called outer shell.

(12) The wall 34 forming the shell support is a composite material with an organic matrix, such as carbon fibers coated with an epoxy resin made using resin transfer moulding (RTM)—injecting pressurized resin into a closed mould containing a preformed or compacted reinforcement. When the resin is cured, the mould can be opened and the composite removed.

(13) A metallic strip 36 in the form of a generally cylindrical ring is pressed against the inner surface of the wall 34 by means of an adhesive layer 38. The strip 36 can consist of a single piece forming a complete ring or several segments. The strip 36 is perforated to allow optimum mechanical bonding of the adhesive. The perforations also allow degassing of the adhesive after application, also providing improved malleability when fixing.

(14) This arrangement of the materials also reduces crack propagation.

(15) The adhesive or glue can be epoxy-based, for example. It can be applied as a film, for example on the outer face of the metallic strip.

(16) The abradable layer 22 is attached to the inner surface of the metallic strip 36. An abradable material is one having characteristics of abradability, ensuring that the rotor tips remain undamaged when in contact with the material. More particularly, an abradable material can consist of three main components: a component which ensures structural rigidity of the coating and corrosion resistance, a non-structural component to lubricate the contact portion of the blade tip (this component is sometimes called a solid lubricant), porosities that allow the coating particles to detach easily on contact.

(17) In various embodiments, the abradable material 22 can be comprised essentially of a heterogeneous material with a metallic phase, deposited by thermal spraying, especially by plasma spraying. This material can be of AlSi polyester.

(18) The plasma spraying technique is a metallurgical powder manufacturing technique that is used in the creation of a large number of high abradability materials. The plasma is generated by applying a large potential difference between concentric electrodes at a high DC current. This ionizes an inert gas (nitrogen, argon, helium) making it reach a high pressure and an extremely high temperature (more than 16,000° C. at a current of 1,000 A). A stream of powder stream is then injected into the plasma jet. This technique allows any metal to be fused, even the most refractory, because of the high temperature reached.

(19) In various embodiments, to ensure optimal bonding of the abradable material 22, sandblasting the inner surface of the metallic strip 36 is employed.

(20) The perforations in the strip 36 are ideally distributed over its entire surface so as to ensure homogeneous bonding. The strip 36 is relatively thin, for example between 0.1 mm and 1 mm, preferably about 0.2 mm. The strip 36 can be of stainless steel such as grade 316L. Or, the strip 36 can equally be of titanium or Invar® (an alloy of iron (64%) and nickel (36%) with a low carbon and chromium content, whose main property is having a very low coefficient expansion). Alternatively, the strip 36 can be a wire mesh or foam such as a nickel or nickel-chromium foam.

(21) Preferably, the outer surface of the metallic strip 36, that is to say the surface that will be bonded to the structural composite wall 34 of the shell can be sandblasted prior to application. This sandblasting has the effect of partially closing the perforations, allowing greater mechanical bonding. This effect is illustrated in FIG. 5 which is a greatly enlarged view of a perforation in the ring, i.e., the metal strip 36, the glue and the abradable layer 22. FIG. 5 illustrates well the mushroom shape of the adhesive 38 in one of the perforations of the metallic strip 36. This effect is also true for the other side of the strip 36, i.e. the side that will attach to the abradable layer 22.