Patent ID: 12258866

DETAILED DESCRIPTION

FIG.1illustrates a gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan12through which ambient air is propelled, a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases around the engine axis11, and a turbine section18for extracting energy from the combustion gases.

The compressor14, fan12and turbine18have rotating components which can be mounted on one or more shafts. Bearings20are used to provide smooth relative rotation between a shaft and casing (non-rotating component), and/or between two shafts which rotate at different speeds. An oil lubrication system22including an oil pump24, sometimes referred to as a main pump, and a network of conduits and nozzles26, is provided to feed the bearings20with oil. Seals28are used to contain the oil. A scavenge system30having cavities32, conduits34, and one or more scavenge pumps36, is used to recover the oil, which can be in the form of an oil foam at that stage, from the bearings20. The oil pump24typically draws the oil from an oil reservoir38, and it is relatively common to use some form of air/oil separating device in the return line. Seals may also be used for various uses and in other types of gas turbine engines, such as on a propeller shaft or a power shaft of a propeller airplane or helicopter to name some potential examples.

FIG.2presents an example of a seal assembly28. In this example, the seal assembly28is a brush seal. The seal assembly28generally has an annular geometry defined around an axis which will be referred to as the seal axis40. The seal axis40can coincide with a main axis11of a gas turbine engine10for instance. The seal28has a support ring42which extends annularly around the seal axis40. The seal28has a plurality of bristles of a metal material. The bristles each have two opposite ends which will be referred to as the first ends and the second ends. The first ends are secured to the support ring42, whereas the second ends are free. A circular opening44concentric to the seal axis40is delimited by the second ends of the bristles. The bristles extend radially inwardly from the first ends, and support ring42, to the second ends. In this embodiment, the bristles extend obliquely, i.e. not only radially but also tangentially, and the second ends can thus be circumferentially offset from corresponding ones of the first ends. Alternately, the bristles may extend purely radially, in which case the second ends will not be offset from the first ends. The first ends can be held by the support ring42in any suitable way. A typical way of holding the first ends at the support ring is by welding the first ends between two annular rails, which can leave a radially-external welding seam50, with bristles trapped between a front wall46axially opposite a rear wall48, as best seen inFIG.3.

FIG.3shows a portion of a cross-sectional view, enlarged, showing a relationship between the seal assembly28and a rotor52during use. The rotor52can be engaged in the circular opening44. The seal assembly28can be assembled to a stator or another rotor via the support ring42, and the bristles can extend towards, and engage an external surface of, the rotor52. The second ends of the bristles may remain in contact with the external surface of the rotor52during use, when there is relative rotary movement, around the seal axis40, between the rotor52and the support ring42. The tangential portion of the oblique orientation of the bristles can be selected in a manner to be in the same direction as the direction of rotation of the rotor, in a manner that the second ends of the bristles may trail along the external surface of the rotor52, with the rotor gently pulling the bristles along their length, rather than engage the rotor52in a way which would tend to compress or bend the bristles. In other words, the relative direction of rotation of the rotor52may be as shown with the arrow inFIG.2, when the seal assembly does not rotate.

A first example process of manufacturing such a seal assembly28will now be described. The first example process can include, in sequence, the following steps. To begin, an elongated strand of wire is produced. This elongated strand is cut into a plurality of shorter strands all having a characteristic length. The characteristic length can depend on the diameter of the seal for instance (which can depend on a diameter of the rotor52), or on other parameters associated to the seal's design. The shorter strands are assembled into groups of parallel strands referred to herein as tufts. The tufts can then be stabilized by gluing or welding at one end, corresponding to a first end of the strands composing it, and the other end can remain free. The tufts may then be laid into a fixture and arranged in a desired configuration. At this point, the first ends of the tufts may be cut in order to more closely match the desired configuration. The tufts may then be secured to a support ring, which may be performed by gluing or welding for instance. At this point, the tufts may occupy their definite position in the assembly. The free ends, opposite the frame, may then be cut into the final shape.

While the first example process may be satisfactory in some embodiments, it may be deemed to bear inconveniences in other embodiments. In particular, such a first example process may have several sources of costs. First, the bristles may be made of a metal material which can be relative expensive. For instance, the bristles may be made of an alloy containing nickel, such as cobalt/nickel alloys such as Haynes 25, or nickel chromium alloys such as Hastelloy X, Hastelloy C-276 or Inconel 600, or perhaps stainless steel, which may be relatively expensive materials. In this context, the cutting of material at one or both ends may represent a source of waste associated to the cost that went into manufacturing the raw materials which are lost/not ultimately used in the seal assembly. Moreover, assembling the tufts, or arranging the tufts into the desired configuration, may be time consuming and a source of manufacturing variations which may represent another source of costs and be associated to a loss of or variability in quality. In some cases, there can be low raw material utilization, such as less than 30% of the wire length being present in the final part. The manual operations may require highly qualified work force and extended manual operations with a relatively low yield rate due to the manual operations inconsistencies.

Another embodiment of a seal assembly128will be presented in relation withFIG.4. More specifically,FIG.4presents a cross-sectional view taken in a radial plane relative the seal axis140, where the seal assembly128may otherwise have an annular geometry similar to the embodiment shown inFIG.2. More specifically, the seal assembly128has a support ring142extending annularly around the seal axis140, and a seal154extending annularly around the seal axis142, the seal154assembled to the support ring142. In this embodiment, however, rather than having a seal consisting of a plurality of distinct bristles assembled to the support ring, the seal154has a succession of lobes159circumferentially distributed around the seal axis.

The succession of lobes are made of one or more strips161of a flat metal material. The succession of lobes can have a plurality of segments156extending between a number of alternating folds158,160, and is overall arranged in an annular configuration. The one or more strips161of the flat metal material can be elongated and flat. The one or more strips161can have two opposite faces, each facing a corresponding side of the strip. The one or more strips161can be folded regularly but alternatingly onto the first face, forming the first folds, or external folds158, then onto the second face, forming the second folds, or internal folds160, back onto the first face, then onto the second face, and so forth. A length of the one or more strips161can extend from one segment156to an adjacent segment156across a fold160,158. The external folds158can have an external fold bending radius defined around an external fold bending axis163which extends parallel to the seal axis140. The internal folds160can have an internal fold bending radius defined around an internal fold bending axis165which also extends parallel to the seal axis140. In one embodiment, a single strip161may be folded on alternating sides and extend around the entire circumference of the seal154and have a single discontinuity where two opposite ends of the single strip161meet. In another embodiment, a plurality of strips161may be joined in an end to end configuration (length wisely) and the succession of lobes159may have a corresponding plurality of discontinuities where longitudinal ends of adjacent ones of the plurality of strips161meet. During operation, rotation of a rotor engaging the internal folds during use may break the internal folds and form a plurality of discontinuities at the radially inner ends of the segments156where the internal folds formerly were. In one embodiment, the latter process may separate a formerly single strip into a plurality of strips where each one of the strips is associated to a corresponding lobe.

The succession of lobes159can be arranged generally in an annular shape as shown, with a width of the one or more strips161extending parallel to the seal axis140. The external folds158may be circumferentially adjacent one another in the annular shape, and the internal folds160may also be circumferentially adjacent one another in the annular shape. The first folds may be at a radially-external region of the annular shape and the second folds may be at a radially-internal region of the annular shape. Straight segments156of the seal154can connect respective ones of the first folds to respective ones of the second folds. In the illustrated embodiments, the segments156can be straight and extend obliquely, both radially and tangentially, relative the axis of the annular shape (e.g. at an angle α relative to the radial orientation). A support ring142may receive the external folds158and extend concentrically around the seal154. In one embodiment, the seal154is continuous around the entirety of the circumference of the annular shape, and two free ends of the strip161may meet adjacent one another at the support ring142. In another embodiment, it may alternately be preferred to include more than one strip161to form the entire circumference.

As can be seen in the example presented inFIG.4, the segments156of each pair of segments extending from a same external fold158are non-parallel, and slightly inclined towards one another, with a spacing distance between the segments156of each pair of segments reducing along a length of the segments156, in a direction radially inward from the external fold158. Indeed, the bending radius of the internal folds160is significantly smaller than the bending radius of the external folds158. The internal folds160connect adjacent ones of the straight segments156.

An embodiment of a seal assembly128such as shown inFIG.4may be produced with a process which will be explained in relation with the examples shown inFIGS.5,6A and6B. Generally, the process may involve the following steps. First, a strip of flat metal material is formed in a width spanning the expected seal thickness. Then, the strip is folded and packed into an annular configuration, such as in a pack ready to weld. The pack may then be installed between a back plate and a front plate, centered, and assembled by welding. After welding, the seal assembly may go through a series of mechanical and thermal treatment operations, while being closer to a functional inner diameter than in the first example presented above. Accordingly, in one embodiment, trimming of the bristles may be avoided.

In the example embodiment presented inFIG.5, the strip161is formed by arranging a plurality of wires162side by side in a single layer, over a given strip width. A holding media such as wax may be injected onto the wires to maintain the wires in the strip configuration. In the illustrated embodiment, the wires162are individually unwound from corresponding spools164, and the spools164are arranged in alternating orientations, above and below the strip mid line, such that the remanent wire deformation of each wire cancels. The wires162can be arranged side-by-side to cover the specified width of the strip161. The number of wires162in the width can be of between 8 and 20, such as between 12 and 14 for example. The wires162are pressed by opposed straightening rollers166(or more if desired) upstream of the wax injection nozzle168. A composite strip of wires170distributed in the wax can be extruded from the hot wax injection nozzle168. The resulting strip161may be referred to as being of a flat metal material independently of the presence of the wax or other holding media. The strip161can then be pressed by opposed laminating rollers172to set the dimension. In an alternate embodiment, the strip161may consist of a single flat, continuous strip of metal, e.g. a metal band, rather than of an assembly of wires162.

Referring now toFIGS.6A and6B, the strip161can be engaged into an automated folder or packaging machine. In this example, two rollers172,174drive the strip161. The strip161can be bias-bent to one side of the folder and follow one of the rollers172. In this example, the strip161goes first to the left, until it meets the corresponding “hammer”176(or mould) which can be triggered by the mechanical action of the strip161and apply a rapid impact on the strip161thus both forming a precise bending radius and pushing the fold on the stack, thus liberating the hammer for the next cycle. The impact on the strip161may generate a wave in the strip161which may propagate and be fed by the incoming strip161to form the next fold on the right hand side. The right side hammer178may operate in a similar manner to left one. In the illustrated embodiment, the right side hammer178has a larger bending radius, and two “catching” grooves which are staggered by a depth y which plays a role in arranging the strip into an annular configuration such as an annular configuration where the straight segments156extend obliquely as exemplified above. The process may continue to alternate between the left side hammer176and the right side hammer178which may move laterally to accommodate the functionality. In the illustrated embodiment, the folded strip is received by a curved magazine180provided with a receiver plate182which can be spring loaded or motioned by an actuator for instance.

Once the folded strip package reaches the desired dimensions, it can be transferred from the magazine180to a holding device, where it can be welded to a holding element forming the support ring142. Referring back toFIG.3, the holding element can include two annular rails to which the folded strip package, and more specifically the folds, can be welded, which can leave a radially-external welding seam50, as best seen inFIG.3, and the folds trapped between a front wall46and a rear wall48. In an embodiment where the strip161is formed of a plurality of wires held by a holding media such as wax, the holding media may be selected in a manner to melt away during welding, or a holding media removal operation may be used (e.g. solvent, oven heating, etc). In one example embodiment of forming a brush seal having an inner diameter of 7″, 3300 double folds may be integrated to the manufacturing process, and a packaging machine may form10to20folds per seconds, producing one pack every 5 minutes or so.

Referring back toFIG.4, the resulting bristle pack can have a particular geometry. The folding radius of the inner folds160may be close to zero, with the strip being bent far into the plastic domain. The folding radius of the outer folds158may be sufficiently large to account for the increased circumference, such as of the order of ⅓ of the wire diameter. The staggering between two consecutive large radius folding can be in the order of the wire diameter, and can be used to accommodate a desired angle α. The finished seal assembly128may expose internal folds160on the inner functional diameter. In a context where the stiffness may be pronounced due to the presence of the two adjacent straight segments156, the internal folds, forming internal tips, may wear fast at a first contact with the rotor, and free two loose ends to operate as a typical brush seal or, if the strip is made of a single band of metal rather than a plurality of wires, as a leaf seal. The pattern can be made very regular, which may combine better sealing performance with reduced wear. The repeatability of the bristle pack geometry may improve performance of a double brush seal by allowing uniform pressure load distribution between the two bristle packs.

Overall, depending on the details of implementation, the proposed method may offer repeatability, elimination of manual operation requiring qualified work, more raw material utilization, and uniform micro and macro geometry around the seal circumference.

In summary, as presented inFIG.7, a process200of making a seal assembly can include folding210a strip of metal material into an alternating sequence of internal folds and external folds, and securing220the strip of metal material to a support ring having an annular shape defined around a seal axis, including securing the external folds to the support ring in a manner for the strip to be arranged circumferentially relative the axis with the internal folds located radially inwardly relative corresponding ones of the external folds.

The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. For example, a method similar to the one described in detail above may be used for “leaf” seals. The “leaf” seals are similar to brush seal except that instead of adjacent bristle across the thickness they use rectangular “leaves”-like thin metal sheet strips spanning the seal thickness, laid at an angle corresponding to the rotor direction of rotation and stacked around the circumference. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.