GB2502309A

GB2502309A - A honeycomb seal a method of manufacturing a honeycomb seal

Info

Publication number: GB2502309A
Application number: GB201209057A
Authority: GB
Inventors: Timothy Hal Summers
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2012-05-23
Filing date: 2012-05-23
Publication date: 2013-11-27
Also published as: GB201209057D0

Abstract

A honeycomb seal and a method of its manufacture, especially for use in sealing between rotating and non-rotating components of turbomachinery. The honeycomb seal has a plurality of open cells and is manufactured from a single strip of material. The strip is repeatedly folded back onto itself so as to form layers wherein each layer abuts at least one neighbouring layer of the strip of material. Each of the layers of the strip has at least one trough corrugation and at least one peak corrugation which define opposing sides of the open cells. Each trough corrugation of each layer abuts a peak corrugation of a neighbouring layer so that the opposing sides define the complete the open cells which may be hexagonal, rectangular or sinusoidal edged shape.

Description

A HON[YCOMB SEAL A M[THOD OF MANUFACTURING A HON[YCOMB SEAL The present invention relates to a honeycomb seal and a method of manufacturing a honeycomb seal. In particular, the present invention relates to a honeycomb seal for use in turbomachinery, for example, a gas turbine engine.

Seals are provided between rotating and non-rotating components in turbomachinery. In steam and gas turbine engines it is preferable to provide a seal between the rotating components and the static components, typically casings, which surround the rotating components. The rotating components are typically compressor, or turbine rotors, having rotor blades. Seals are desirable as they reduce the losses associated with fluid flows bypassing the aerofoil section of the rotor blades and therefore increase the turbo-machines efficiency. Additionally the seals allow for movements caused by general vibrations, out of balance forces and adjustments for shock events such as an aircraft landing.

Typically, the tips of the rotor blades mounted on rotors rotate past a seal disposed against the casing. It is also common for the radially outer blade extremity to have a shroud in which the tip of the aerofoil section terminates. The shroud has circumferential ribs, or fins, which, when combined with the ribs or fins of the remaining blade shrouds, form an annular fin on the rotor engaging against the seal on the casing.

An initial clearance between the cooperating seal and fins is provided when the turbornachine is in a cold state. Thermal expansion takes place in components as the turbomachine runs up to a stable operational temperature.

The clearance between the cooperating seal and blade tips, or seal and fins, through which the fluid may pass is known as windage. By extension, any efficiency losses due to fluid bypassing through the sealed sections are referred to as windage losses. For this reason the clearance between the seal and fins, or seal and blade tips, is intended to be as minimal as possible and generally involves the seal components rubbing or grazing together. This rubbing creates a tight seal which can absorb the movements described above with no damage to the seal or the casings. Because of this attribute of wearing in use, the seals are often termed abradable seals' or abradable liners'.

In a gas turbine engine it is also common to provide seals between rotating and non-rotating components to control auxiliary airfiows in the engine. This need arises due to air, bled from the main flow entering the engine core, being ducted around the engine for cooling purposes. These seals ensure the cooling air is directed to an S appropriate part of a component in need of cooling. In a manner similar to the shrouds described above, ribs or fins are provided circumferentially on the rotating component engaging with, and rubbing against, a seal mounted to the stationary component.

It is recognised in the art that a seal constructed from a honeycomb structure fulfils some of the operational demands placed on the seal. A honeycomb structure typically consists of open cells usually shaped in a hexagonal manner. The cells must be relatively small to ensure the structure acts as a seal. Sealing is achieved by the fins cutting into the structure to form grooves during initial operating of the engine. This process creates the minimum possible sealing gap.

The use of a honeycomb seal has been found to be beneficial in reducing the amount of friction generated heat and associated damage caused by the necessary rubbing required to achieve the seal. This is because a honeycomb structure is less dense than a similarly sized solid seal and results in a minimised contact area with the fins. Notwithstanding this reduced rubbing surface, the open cells must be stiff enough to retain the structure of the honeycomb seal as the rotating component passes. In some cases the cells are filled with a heat-resistant material, thus allowing larger and cheaper cells, which then reduces windage losses; however, this has manufacturing issues and retention of the filler material can be difficult.

The use of honeycomb seals, while beneficial, is not without issues. The construction methods employed to manufacture the honeycomb structure have a tendency to damage the sealing fins. Typically the honeycomb structure is made from a number of separate metal or alloy (for example, nickel alloy) sheets which are corrugated in a specific pattern to form webs, such as semi-hexagons. The separate sheets are then bonded together at the appropriate position to form a honeycomb structure. This results in webs of double thickness where webs of adjacent sheets are bonded together by a brazing alloy. The brazing alloy usually bonds the honeycomb structure to a substrate simultaneously with the bonding of the webs of adjacent sheets.

A spot weld may be used to hold the webs of the adjacent sheets, and thus the honeycomb structure, in position prior to the brazing alloy being applied. Additionally, creating the honeycomb structure in this manner by cutting, corrugating and assembling a number of separate sheets is time-consuming.

By a process known as braze wicking the brazing alloy tends to show as spots on the sealing or rubbing surface of the honeycomb structure and at the juncture of the double thickness webs. This is due to the manufacturing process employed. The brazing alloy, which may contain boron, is very hard and therefore abrasive, especially at higher temperatures. The brazing alloy potentially erodes the fins as they rotate, producing local damage to the fins.

The separate sheets in the honeycomb structure may be oriented in either a circuniferential (the plane of sealing fin rotation), or an axial, direction relative to the axis of the rotor. The benefit of utilising circumferential sheets of alloy (see FIG. 3) is that only a relatively few long separate sheets are required to complete the honeycomb structure. However, orienting the separate sheets in this direction is known to cause substantial damage to the sealing fins if they run through the full length of every juncture, or node, of double thickness webs and wicked brazing alloy in completing each single rotation. The main alternative, which is to rotate the sheets by 90 degrees so that the sheets run in an axial direction (see FIG. 4), is known to be less likely to cause damage to the rotating fins. Unfortunately, this means shorter, but many more, sheets are required to complete the honeycomb structure further increasing complexity and manufacturing cost.

One way of increasing engine efficiency is to increase the temperature of the working fluid. This means components within the engine must withstand higher temperatures and therefore require more cooling. Windage heating occurs when the fluid increases in temperature as it passes through a seal because of friction induced work. Cooling air suffering windage heating, when bypassing seals in the auxiliary airflow passages, has a reduced capacity for cooling engine components and thereby impacts the maximum operating temperature and overall efficiency of the engine.

The use of a honeycomb structure for the seal tends to create drag which increases windage heating. The end faces of the honeycomb structure may also increase windage heating as the end faces do not present a suitably favourable aerodynamic surface to the airflow. This is because of the shape of the semi-hexagonal walls which form the end faces of the seal.

US Pat. No. 5,096,376 describes flat strips that are attached to the honeycomb structure end faces to reduce the friction effects on the airflow. An alternative is also disclosed wherein the strips have a semi-hexagonal corrugated strip attached to the honeycomb structure end faces. Both of these proposals require that the alloy sheets S making up the honeycomb structure are oriented in the circumferential direction as described above. This is due to the fact that separate sheets oriented in the axial direction do not provide a suitable surface for bonding the strips to the end faces of the honeycomb seal (see FIG. 4). Thus although windage heating can be reduced utilising the arrangement of FIG. 3, the sealing fins will, as described above, run through the full length of every juncture of double thickness webs.

According to a first aspect of the invention there is provided a honeycomb seal having a plurality of open cells, the honeycomb seal comprising a strip of material; the strip repeatedly folded back onto itself so as to form layers wherein each layer abuts at least one neighbouring layer; each layer having at least one trough corrugation and at least one peak corrugation defining opposing sides of the open cells; and each trough corrugation of each layer abutting a peak corrugation of a neighbouring layer so that the opposing sides define the open cells.

The at least one trough corrugation of each layer may be bonded to the at least one peak corrugation of a neighbouring layer. Each layer of the honeycomb seal may be bonded to a substrate. The bond may comprise a spot weld and/or a brazed join.

This arrangement of honeycomb seal allows manufacture from a single strip of material.

The layers are also oriented in the axial direction of the rotor which is helpful in reducing wear as the seal fins do not run through the full length of every abutting peak and trough of neighbouring layers.

The honeycomb seal may comprise the strip being repeatedly folded back onto itself by alternate turns of positive and negative 180 degrees in the strip. The alternate turns may further comprise two substantially right angle bends spaced apart by a strip portion.

The strip portion may be approximately twice that of the distance between the peak of the peak corrugation and the trough of the trough corrugation of the layer. The strip portion may be approximately the distance between the peak of the peak corrugation of the layer and the trough of the trough corrugation of the neighbouring layer.

The strip portion between the two substantially right angle bends may form a substantially planar surface. The strip portion of the positive 180 degree turn may be aligned with the strip portion of the positive 180 degree turn of the neighbouring layer to form a substantially planar first face of the honeycomb seal. The strip portion of the negative 180 degree turn may be aligned with the strip portion of the negative 180 degree turn of the neighbouring layer to form a substantially planar second face of the honeycomb seal. The provision of planar faces on the strip portions and therefore alternate turns is advantageous as there is no need to provide a face strip to reduce the windage losses from the honeycomb seal.

The alternate turns may comprise radial bends. The radial bend may comprise a radius approximately equal to the distance between the peak of the peak corrugation and the trough of the trough corrugation of the layer.

The honeycomb seal may further comprise alignment of the positive 180 degree turns to form the first face of the honeycomb seal. The honeycomb seal may further comprise alignment of the negative 180 degree turns to form the second face of the honeycomb seal. This creates faces which remove the need for an additional and separate face strip for the honeycomb seal.

The alternate turns may form the last trough corrugation in the preceding neighbouring layer and the first peak corrugation of the layer. The alternate turns may form part of the open cell adjacent to the first or second face of the honeycomb seal.

There may be an equal number of trough corrugations and peak corrugations on each individual layer. There may be an equal number of trough corrugations and peak corrugations on the layer as there are trough corrugations and peak corrugations on the neighbouring layer.

Alternatively, the number of trough corrugations may not be equal to the number of peak corrugations on each individual layer. The neighbouring layers may alternate between having one more peak corrugation than trough corrugation and one more trough corrugation than peak corrugation.

The neighbouring trough and peak corrugations of the layer may comprise an approximate sinusoidal waveform. Alternatively, the neighbouring trough and peak corrugations of the layer may comprise an approximate rectangular waveform.

The honeycomb seal may comprise peak and trough corrugations having a semi-hexagon shape so as to define hexagonally shaped open cells.

The honeycomb seal may comprise each layer following a positive 180 degree turn having at least one sequence of positive, negative, negative, positive, positive, negative 60 degree bends in the strip wherein the 60 degree bends are measured relative to the strip prior to the bend.

The honeycomb seal may further comprise the open cells filled with a heat-resistant material.

According to a further aspect of the invention there is provided a method of manufacturing a honeycomb seal from a strip of formable material comprising the steps of: forming a series of trough and peak corrugations in a first portion of the strip of formable material; forming a series of trough and peak corrugations in a second portion of the strip of formable material; folding the second portion of the strip back onto the first portion to form a first layer and a second layer in the strip of formable material; arranging the trough corrugations on the second layer to abut the peak corrugations on the first layer so as form a plurality of open cells; and repeating the second to fourth steps to form a plurality of layers defining a plurality of open cells.

The fourth step may include the step of bonding at least one of the trough corrugations on the second layer to at least one of the peak corrugations on the first layer. The step of bonding at least one of the trough corrugations on the second layer to at least one of the peak corrugations on the first layer may include spot welding and/or brazing.

The fourth step may include the step of bonding the second layer and/or the first layer to a substrate at least one trough corrugation. The step of bonding the second layer and/or the first layer to a substrate at least one trough corrugation may comprise brazing.

The method may comprise the third step taking place prior to the second step.

The folding of the third step may comprise alternate between positive and negative 180 degrees.

The folding of the third step may comprise forming two substantially right angle bends.

The right angle bends may be spaced apart by a strip portion. The strip potion may form a substantially planar surface.

The method may comprise the trough and peak corrugations having a semi-hexagonal shape so as to define hexagonally shaped open cells.

The method may further comprise a further step of filling the open cells with a heat-resistant material.

The method of manufacturing the honeycomb seal in this manner allows the duel benefits of no face strip being required to be added to the faces of the honeycomb seal whilst at the same time manufacturing a honeycomb seal which has corrugated layers oriented in the axial direction of the rotor disc.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. 1 is an axial longitudinal section through a high-bypass gas turbine engine incorporating an embodiment of the present invention; FIG. 2 is a partial perspective view of a section through a turbine stage of a gas turbine engine incorporating an embodiment of the present invention; FIG. 3 is an illustrative view cia related art honeycomb seal; FIG. 4 is an illustrative view of an alternative related art honeycomb seal; FIG. 5 is an illustrative view of an embodiment a honeycomb seal according to the present invention; FIG. 6 is an illustrative view of a method of manufacturing an embodiment of the present invention; FIG. 7 is an illustrative view of an alternative method of manufacturing an embodiment of the present invention; FIG. 8 is an illustrative view of a second embodiment of a honeycomb seal of the present invention; FIG. 9 is an illustrative view of a third embodiment of a honeycomb seal of the present invention; FIG. 10 is an illustrative view of a fourth embodiment of a honeycomb seal of the present invention; and FIG. 11 is an illustrative view of a fifth embodiment of a honeycomb seal of the present invention.

With reference to FIG. 1 a high-bypass gas turbine engine is indicated at 10. The engine 10 comprises, in axial flow, series an air intake duct 11, an intake fan 12, a bypass duct 13, an intermediate pressure compressor 14, a high pressure compressor 16, a combustor 18, a high pressure turbine 20, an intermediate pressure turbine 22, a low pressure turbine 24 and an exhaust nozzle 25.

Air is drawn through the air intake duct 11 by the intake fan 12 where it is accelerated. A significant portion of the airflow is discharged through the bypass duct 13 generating a corresponding portion of the engine 10 thrust. The remainder is drawn through the intermediate pressure compressor 14 into what is termed the core of the engine 10 where the air is compressed. A further stage of compression takes place in the high pressure compressor 16 before the air is mixed with fuel and burned in the combustor 18. The resulting hot working fluid is discharged through the high pressure turbine 20, the intermediate pressure turbine 22 and the low pressure turbine 24 in series where work is extracted from the working fluid. The work extracted drives the intake fan 12, the intermediate pressure compressor 14 and the high pressure compressor 16 via shafts 26, 28, 30. The working fluid, which has reduced in pressure and temperature, is then expelled through the exhaust nozzle 25 generating the remainder of the engine 10 thrust.

Referring now to FIG. 2, which is a view of a turbine stage 40. The turbine stage may be from any of the high pressure turbine 20, intermediate pressure turbine 22 or low pressure turbine 24. In this example the diagram most closely resembles a stage normally found in the high pressure turbine 20. The turbine stage 40 has nozzle guide vanes 42, and turbine blades 44 which are mounted on a rotor disc 46. The nozzle guide vanes 42 are stationary and mounted on a casing 41. The nozzle guide vanes 42 turn the working fluid to ensure the flow strikes the turbine blades 44 at the correct angle. The working fluid increases in velocity and drops in pressure when transiting through the nozzle guide vanes 42. The forces acting on the turbine blades 44 by the working fluid passing over the aerofoil surfaces of the turbine blades 44 cause the rotor disc 46 to rotate. The rotor disc 46 transmits power via the shafts 26, 28, 30 to the appropriate compressor 14, 16, 18.

The turbine blades 44 have a blade shroud 47, the purpose of which is to reduce losses where the working fluid may bypass the aerofoil surfaces of the turbine blades 44.

The shroud 47 has blade seal fins 48 which rub against a blade seal 49 disposed within and against the casing 41. The blade seal 49 thereby contributes to reducing the losses.

The blade seal 49 comprises a honeycomb seal of the type that is described below.

The rotor disc 46 has a number of seal fins 51 which rub against passage seals 53.

The seal fins 51 and passage seals 53 cooperate to form part of cooling airflow passages delivering cooling air to the rotor disc 46 and turbine blades 44. The passage seals 53 ensure the cooling air is maintained at the appropriate pressure. The arrangement of the seal fins 51 and the passage seals 53 also may be used between turbine stages 40 in what is termed an interstage seal'. These interstage seals' are more likely to be found in the intermediate pressure and low pressure turbines 22, 24 where it is more common to utilise multiple turbine stages 40. The passage seals 53 are constructed in segments of different heights to accommodate the corresponding varying heights of the seal fins 51.

This multiple contacting approach provides a torturous path for any cooling air escaping through the passage seal 53 thereby increasing the effectiveness of the passage seal 53.

This type of arrangement is commonly termed a labyrinth seal'. It should be appreciated that these seal arrangements may also be used within the compressor stages 12, 14, 16 of a gas turbine engine 10.

As has been explained above, it is common to utilise a honeycomb structure to form the passage seal 53 or the blade seal 49. FIG. 3 is an illustrative view of a known honeycomb seal 60 viewed in a radial direction of the rotor disc 46 of FIG. 2. An arrow A shows the direction of rotation of the rotor disc 46, relative to the honeycomb seal 60, and therefore indicates the circumferential direction of the rotor disc 46. The honeycomb seal 60 is constructed from a plurality of individual sheets 62 of a nickel alloy and comprises an array of open cells 61 of hexagonal shape. The individual sheets 62 are corrugated and have troughs 64 and peaks 66. The individual sheets 62 are arranged side-by-side so that the troughs 64 of one individual sheet 62 abut the peaks 66 of the neighbouring individual sheet 62. In this manner, the troughs 64 and peaks 66 define opposing sides 68 of the open cells 61. The opposing sides 68 are therefore in the shape of semi-hexagons in order that the open cells 61 are of hexagonal shape. The troughs 64 and peaks 66 of adjacent (neighbouring) individual sheets 62 are bonded 70 together S with welds to permanently assemble each individual sheet 62 to the neighbouring individual sheet 62.

FIG. 3 has each of the individual sheets 62 aligned with the circumferential direction of the rotor disc 46. That is the rotor disc 46 rotates in the direction of the arrow A in a generally parallel orientation with the individual sheets 62. Orientation of the individual sheets 62 in this manner allows the cutting length of the individual sheets 62 to be as long as practicable for manufacturing purposes. This orientation allows a face strip 72 to be bonded by welds 73 to the honeycomb seal 60. The face strip 72 presents a planar surface to the airflow, which may be cooling air, passing over the boundary of the honeycomb seal 60.

FIG. 4 is an illustrative view of another known honeycomb seal 60 looking in a radial direction of the rotor disc 46 constructed in an alternative orientation to that described with respect to FIG. 3. Arrow A indicates the rotation direction of the rotor disc 46. As with the honeycomb seal 60 in FIG. 3, open cells 61 are defined by opposing sides 68 formed from troughs 64 and peaks 66. The troughs 64 and peaks 66 are created by forming corrugations in the individual sheets 62. Again, the individual sheets 62 are arranged side-by-side, troughs 64 abutting peaks 66 of the neighbouring individual sheet 62. As with the arrangement of FIG. 3 the troughs 64 and peaks 66 are bonded together with welds 70.

The arrangement of FIG. 4 differs from that of FIG. 3 in that the individual sheets 62 are oriented in the axial direction of the rotor disc 46. The individual sheets 62 are generally perpendicular to the direction of arrow A. This provides some benefit in terms of wear, which is described above, but requires the assembly of many more relatively shorter individual sheets 62. Additionally, a face strip 72 of the kind described with respect to FIG. 3 may be difficult to assemble to the body of the honeycomb seal 60 as depicted in FIG. 4. A face strip 72 is therefore not shown in FIG. 4.

Referring now to FIG. 5, which is an illustrative view of an embodiment of a honeycomb seal 160 of the present invention. The view is in a radial direction of the rotor disc 46. An arrow A indicates the direction of rotation, and circumferential direction, of the rotor disc 46. The honeycomb seal 160 comprises an array of open cells 161. The honeycomb seal 160 is constructed from a single strip 162 of a malleable formable material. The formable material may be a metal or alloy, for example, a S suitable nickel alloy, but other suitable materials may be used for the single strip 162.

The honeycomb seal 160 arrangement comprises the single strip 162 repeatedly folded, or formed, back onto itself to form a plurality of layers 163. The folds therefore define a series of layers 163 in the single strip 162. Each layer 163 of the plurality of layers 163 abuts the preceding layer 163 so as to form the honeycomb seal 160. It follows then, that each layer 163 will also abut the following layer 163 formed in the single strip 162.

Each layer 163 is corrugated and has a series of troughs 164 and peaks 166 which have been formed into the single strip 162. The troughs 164 and peaks 166 are formed by corrugating of the single strip 162. The troughs 164 and peaks 166 may be thought of as a series of convolutions in the single strip 162. The troughs 164 and peaks 166 of the corrugations of each layer 163 define opposing sides 168 of the open cells 161. Pairs of the opposing sides 168 form and complete the open cells 161. The troughs 164 of each layer 163 abut the peaks 166 of the neighbouring layer 163. The arrangement may be described, from the perspective clone orientation, as the troughs 164 of each layer 163 abutting the peaks 166 of the immediately preceding neighbouring layer 163.

Extrapolating this description, it follows that the peaks 166 of the layer 163 will therefore abut the troughs 164 of the following neighbouring layer 163. This arrangement aligns the opposing sides 168 so as to define the open cells 161.

At the junctures, or nodes, where the troughs 164 of each layer 163 abut the peaks 166 of the preceding layer 163, the layers 163 of the single strip 162 are bonded together to consolidate the honeycomb seal 160 and provide structural stability.

The single strip may additionally be bonded to a backing substrate on one interfacing edge of the single strip 162 (not shown in FIG. 5). The interfacing edge may be in the radially inner or radially outer direction of the rotor disc when assembled in the gas turbine engine 10, i.e. a radially outer edge or radially inner edge of the single strip 162.

Whether a radially inner or outer edge is bonded to an optional substrate will depend on the application, and therefore the orientation, of the honeycomb seal 160 in the gas turbine engine 10. The use of a substrate may be beneficial in providing additional structural stability. The substrate may also be used to help locate the honeycomb seal in its correct position within the engine. Where a substrate is provided, the bond may perform the function of bonding the single strip to the substrate, or alternatively, a separate additional bond may be provided. The separate additional S bonds may be provided at the interfacing edge of the single strip at the juncture where the troughs 164 of each layer 163 abut the peaks 166 of the preceding layer 163.

Alternatively, the additional bonds may be provided elsewhere along the interfacing edge of the single strip 162.

The bond 170 may be a braze and/or a weld. In particular, where a brazed join is used and the single strip 162 comprises a nickel alloy, the bond 170 may be formed from a brazing alloy. The brazing alloy may be applied by the way of an adhesive powder or adhesive tape. A spot weld may be applied initially to hold the toughs 164 and abutting peaks 166 of the preceding layer 163 in position prior to the application of a brazing alloy to complete, and importantly strengthen, the bond 170. It is conceivable that some applications of the honeycomb seal 160 will only require a spot, or similar weld, to hold the layers 163, and therefore honeycomb seal 160, together. Thus in such applications any joining by way of brazing is absent altogether. Alternatively, the bond 170 may solely consist of a brazed join.

Where a substrate is attached, by the use of the separate additional bonds described above, the additional bonds may be a brazed join. Alternatively, where the backing substrate is provided, the bonds 170 may simultaneously bond the single strip 162 to the substrate at the same time as bonding the troughs 164 and peaks 166 of the layers 163 together. The bonds 170 may, or may not be, partially formed by way of the spot welds, as described above, prior to the simultaneous bonding of the layers 163 together and the single strip 162 to the backing substrate at the same time. Irrespective of whether spot welds are initially used to hold the troughs 164 and peaks 166 in the correct position, it is preferable to utilise a brazing alloy to complete the bond 170 in this arrangement, although an alternative bonding method may be considered.

In a still further alternative arrangement, where the supporting substrate (not shown) is provided, the bond 170 may bond the interfacing edge of the troughs 164 only to the supporting substrate. In this alternative arrangement, there may be no joining of the troughs 164 to the peaks 166 of the preceding neighbouring layer 163, such that the structural stability of the honeycomb seal 160 is provided by the bonds 170 to the supporting substrate. However, where the bond 170 joins the interfacing edges of the troughs 164 to the supporting substrate there may also be incidental bonding between the troughs 164 and the peaks 166 of the preceding neighbouring layer 163. In this alternative arrangement this incidental bonding may be both beneficial and desirable in S providing structural stability to the honeycomb seal 160.

The folds or forms in the single strip 162 comprise alternating turns 175 of positive and negative 180 degrees so as form or connect each layer 163 in series. The alternating turns 175 form the plurality of layers 163. The alternating turns 175 may be thought of as opposite-handed turns of 180 degrees. The embodiment of the honeycomb seal 160 depicted in FIG. 5 has an arrangement wherein the alternating turns 175 are formed of two substantially right angle bends 177. The right angle bends 177 are spaced apart by a predetermined length of the single strip 162 which may be termed a strip portion 178.

The embodiment illustrated in FIG. 5 shows an arrangement where the distance between the peaks 166 and the troughs 164 of the corrugations is the same for each layer 163 in the plurality of layers 163. In this arrangement, the predetermined length of the strip portion 178 may described as approximately twice that of the distance between the peaks 166 and the troughs 164 of the corrugations on each layer 163.

Alternatively, the predetermined length of the strip portion 178 may described as approximately the distance between the troughs 164 of the corrugations of the immediately preceding layer 163 and the peaks 166 of the corrugations of the layer 163.

This measurement method is relevant for an alternative arrangement wherein the desired distance between the peaks 166 of the corrugations and the trough 164 of the corrugations is not equal for each alternating layer 163 in the series. If the distance alternates with each alternating layer 163 then the predetermined distance of the strip portion 178 must be measured accordingly.

The embodiment shown in FIG. 5 also shows that the strip portion 178 defines a substantially planar surface 179. The figure also illustrates that adjacent strip portions 178 have been aligned so that the planar surface 179 of the strip portions 178 from the neighbouring layers 163 are aligned. In this manner, the plurality of planar surfaces 179 align to form a substantially planar first face 172 along one boundary of the honeycomb seal 160. Similarly, the plurality of planar surfaces 179, formed from the right angle bends 177 of the opposite handed alternate turns 175, align to form a substantially planar second face 173 of the honeycomb seal 160. Using the alternating turns 175 to form these planar faces 172, 173, which are useful in reducing the windage losses as described above, means the face strip 72 of FIG. 3 is not required. This is beneficial as the face strip 72 is an extra component requiring additional undesirable assembly time.

S It is conceivable that the strip portion 178 may be in some other aerodynamically favourable shape than that of the planar surface 179. It may be found that alternative shapes may provide a larger reduction in windage losses. However, the planar surface 179 between the two right angle bends 177 may be the simplest manufacturing solution to offer reduced windage losses.

The arrangement illustrated in FIG. 5 therefore provides a duel benefit over the known arrangements described with respect to FIGS. 3 and 4. Firstly, as described above, the aligned planar faces 172, 173 remove the need to join an additional face strip 72 to the honeycomb seal 160, which is not possible with the arrangement illustrated in FIG. 4. Secondly, as the corrugated layers 163 are oriented in the axial direction of the rotor disc 46 (arrow A indicating the circumferential and rotational direction), the benefit associated with the known arrangement of FIG. 4 is also advantageously provided by the honeycomb seal 160 of FIG. 5. Thus the honeycomb seal 160 illustrated in FIG. 5 alleviates the worst case rubbing, or friction induced, damage to the sealing fins 48, 51 as the nodes are oriented perpendicular (axial) to the direction of rotor disc 46 movement. The nodes being synonymous with the bonded 170 junctures where the troughs 164 of each layer 163 abut the peaks 166 of the preceding layer 163. Therefore, the sealing fins 48, 51 do not run through the full length of every bonded 170 juncture, or node, of double thickness single strip 162 as the rotor disc 46 rotates, as is the case with the known arrangement of the type depicted in FIG. 3. Thus, the duration of contact between the seal fins 48, 51 and the bonded 170 junctures of double thickness strip 162 on each revolution of the engine 10 is reduced in comparison with that of the arrangement of FIG. 3, thereby reducing wear.

Thus the arrangement illustrated in FIG. 5 reduces both the windage losses and rubbing damage to the sealing fins 48, 51. This is achieved with a manufacturing process which is, at least, no more complicated than that required for the example described with reference to FIG. 4 and does not require the additional face strips 72 depicted in FIG. 3.

The open cells 161 illustrated in FIG. 5 are hexagonal in shape. Conventionally, honeycomb shaped structures would bring to mind a structure comprising a plurality hexagonal shaped open walled structures. However, other shapes of open cells are conceivable, some of which are discussed below. The hexagonal shape of the open cells 161 as illustrated in FIG. 5 are completed by pairs of the opposing sides 168 having a semi-hexagonal or trapezoidal shape. The troughs 164 and peaks 166 of the corrugations, which form the opposite sides 168, are mirrored sides, or opposite hands of, the hexagonal shape forming the open cells 161. It should be noted that the corrugations or sequence of troughs 164 and peaks 166 form a semi-hexagonal waveform in the individual layer 163. The troughs 164 and peaks 166 of the corrugations may also be described as a series of 60 degree bends 182 in the single strip 162. Where the alternating turn 175 is of positive 180 degrees, for a least one trough 164 and one peak 166, the sequence of 60 degree bends 182 is: positive, negative, negative, positive, positive, negative. That is for an even number of troughs 164 and peaks 166 on each layer 163 the sequence is repeated the desired number of times. It follows that, for the opposite hand alternate turn 175 of negative 180 degrees, the sequence of 60 degree bends 182 is: negative, positive, positive, negative, negative, positive. Conceivably, it may be desirable to have an unequal number of troughs 164 and peaks 166, particularly if one of the planar faces 172, 173 is absent and the alternate turn 175 consists of a sharp (very small radius) 180 degree bend.

It should be noted that how the orientation of the initial measurement of the angles or alternate turns 175 is not important, as long as the following measurements are consistent in their definition of orientation. Thus it is not relevant as to whether one turn 175 is deemed to be positive, as long as the opposite-handed turn 175 is designated a negative bend. That said, it is generally accepted that a clockwise angular measurement will be a negative angle. The same principle applies as to whether corrugations are deemed to be troughs 164 or peaks 166, whose terminology may be reversed as long as consistency is maintained from one layer 163 to the next.

It should also be noted that the alternate turns 175 coincide with and form the first peak 166 of each of the layers 163. The second sequential right angle bend 177 essentially forms the first peak 166 of the new layer 163. Accordingly, the first peak 166 abuts, and may be bonded 170 to (as described above), the last trough 164 of the following neighbouring layer 163. This is a part of the sequence of aligning the opposing sides 168 of the open cells 161 by abutting the troughs 164 of the following neighbouring layer 163 to the peaks 166 of the layer 163.

The open cells 161 of the honeycomb seal 160 may be filled with a heat-resistant material. The filler material may further reduce the windage losses suffered by the honeycomb seal 160 when installed on the engine 10. A further benefit of the filler material within the open cells 161 may be to reduce friction damage and wear to the fins 48.

FIG. 6 illustrates one possible method of manufacturing the honeycomb seal 160.

Starting with the single strip 162 of formable! malleable material, which may be a nickel alloy, the single strip 162 is folded back onto itself to form the plurality of layers 163.

The folding or forming is achieved by creating alternating turns 175 of positive and negative 180 degrees. The alternating turns 175 may comprise pairs of substantially right angle, or 90 degree, bends 177 separated by a predetermined length of the single strip 162, the strip portion 178 referred to above, with reference to FIG. 5.

The series of troughs 164 and peaks 166 of the corrugations are then formed in the single strip 162 of formable material on each layer 163 in turn. The troughs 164 and peaks 166 of the corrugations may take the form of a semi-hexagonal or trapezium shape. Where the corrugations are of a semi-hexagonal shape, the forming (bends) in the layer 163 can be achieved with an appropriately repeating series of positive and negative 60 degree bends 182, described above, with respect to FIG. 5. The orientation of the 60 degree bends 182 is determined by whether the alternating turn 175 forming the layer 163 is a positive or negative 180 degree fold.

Following the step of corrugating the layer 163, the troughs 164 of the corrugations in the layer 163 are aligned to abut the peaks 166 of the corrugations already present in the preceding layer 163 to define a plurality of the open cells 161. The troughs 164 in the layer 163 may be then bonded to the peaks 166 in the preceding neighbouring layer 163. The bond 170 may be achieved by a welding or brazing utilising a brazing alloy, as described above with reference to FIG. 5. Additionally, the step may involve the layers 163 making up the honeycomb seal 160 being bonded to a supporting substrate, where provided, by additional separate bonds. Alternatively, the bonds 170 may simultaneously bond the troughs 164 and peaks 166 together and bond the single strip 162 to the supporting substrate as described above with respect to FIG 5.

Another alternative option is to follow the step of aligning and abutting the troughs 164 of layer 163 with the peaks 166 of the preceding neighbouring layer 163 with the step of bonding 170 the interfacing edge of the troughs 164 to the supporting substrate. There may be associated incidental bonding of the troughs 164 to the S abutting preceding neighbouring layer 163 peaks 166 when the bond 170 is formed.

Alternatively, there may be no direct join between the troughs 164 of the layer 163 and the peaks 166 of the preceding neighbouring layer 163 following the bonding 170 step of this alternative option.

As described above with respect to FIG. 5, the step of bonding the troughs 164 in the layer 163 to the peaks 166 in the preceding layer 163 may include the use of a spot weld (as a part of the bond 170) to hold the honeycomb seal 160 in its structural position prior to the completion of the bonds 170 by brazing with a brazing alloy. The spot welds may be used irrespective of whether the single strip 162 is also bonded to a substrate.

The manufacturing method described above with respect to FIG. 6 generally illustrates a sequential process. It should be appreciated that the steps above may be carried out in a non-sequential process. For example, it may be preferable to produce a batch, or all, of the alternate turns 175 (folds), and thus the plurality of layers 163, at one time. The series of troughs 164 and peaks 166 of the corrugations may then be formed on each layer 163 before the bonding step takes place. It is also possible to perform the corrugation step prior to the folding step and this procedure is described below.

FIG. 7 shows an alternative method of manufacturing the honeycomb seal 160.

This method may allow more semi-automation of the process wherein, for example, the troughs 164 and peaks 166 of the corrugations are formed in a continuous crimping (bending) process between a set of appropriately shaped formers.

As illustrated in FIG. 7 the single strip 162 is fed continuously in a direction of arrow B wherein the troughs 164 and peaks 166 of the corrugations are continuously formed. The troughs 164 and peaks 166 of the corrugations are formed at the appropriate positions, or portions, of the single strip 162 to correspond with the layer 163 on which they will be required. This corrugating of the single strip 162 in this manner also accounts for the orientation of the alternate turn 175 required when the layer 163 is formed.

The process may be described as starting with forming a series of troughs 164 and peaks 166 of the corrugations in a first portion 184 of the single strip 162. An opposite handed series of the troughs 164 and peaks 166 of the corrugations is then formed in a second portion 185 of the single strip 162. The second portion 185 is now folded back onto the first portion 184 to create a first layer 186 and a second layer 187 in the single strip 162 of formable material. The folding is in a direction of arrow C, which in the instance of FIG. 7, is a negative fold of 90 degrees (right angle bend 177) required in order to complete the negative 180 degree alternate turn 175. It follows that the next fold in the sequence the alternate turn 175 will be a positive 180 degree turn, thus making the direction of arrow C anti-clockwise. The folding process is followed by a step of aligning the troughs 164 of the corrugations of the second layer 187 to the peaks 166 of the corrugations of the first layer 186 and so forming the plurality of open cells 161 in the honeycomb seal 160. The troughs 164 of the corrugations of the second layer 187 are then bonded to the peaks 166 of the corrugations of the first layer 186. The bond may be a weld, spot weld or a brazed joint as described with respect to FIG. S and in a similar manner to the method described above with respect to FIG. 6. The bond 170 may be to a substrate, which is not shown. The bond 170 may also involve only bonding the troughs 164 to the substrate.

To complete the honeycomb seal 160 the process involves repeatedly repeating appropriate steps described above. Upon completing the aligning of the second layer 187 to the first layer 186, the second layer 187 may now be considered to be the first portion 184 of the single strip 162 when repeating the appropriate steps of the initial process. Repetition begins with the step of forming an opposite-handed series of the troughs 164 and peaks 166 of the corrugations in the second portion 185 of the single strip 162. The first portion 184, due to being the second layer 187 in the previous cycle, is already furnished with an appropriately oriented series of the troughs 164 and peaks 166 of the corrugations. It follows that the second layer 187 is then considered the first layer 186 upon the folding step being performed. Repeatedly repeating all the steps described above thereby forms the full honeycomb seal 160 structure, the honeycomb seal 160 having the plurality of layers 163 defining a plurality of open cells 161. The first step of forming the corrugations in the first portion 184 is not required to be a part of the repeated sequence of steps.

It should be noted that the first layer 186 may be thought of as synonymous with the preceding neighbouring layer 163 of the plurality of layers 163, referred to in FIG. S S and FIG. 6 above. Similarly, the second layer 187 is synonymous with the layer 163 of the plurality of layers 163. It should also be noted that the methods, described with respect to FIGS. 6 and 7, provide the benefit of forming the planar first 172 and second 173 faces of the honeycomb seal 160 within the same process of producing the plurality of open cells 161.

The method described with respect to FIG. 7 does not preclude the possibility of re-ordering the steps where it is beneficial to do so. In particular, the step of forming the series of troughs 164 and peaks 166 of the corrugations in the second portion 185 may be performed after the step of folding the second portion 185 back onto the first portion 184 (creating the first layer 186 and the second layer 187 in the single strip 162). As with the method described above, the series of troughs 164 and peaks 166 of the corrugations will only need to be formed in the first portion 184, or first layer 186, in the first instance to begin the manufacturing process.

The methods described with respect to FIGS. 6 and 7 may additionally include the step of filling the open cells 161 formed by the respective manufacturing methods. The open cells 161 may be filled with a heat-resistant filler. The heat-resistant filler may additionally have friction reducing properties.

Alternative arrangements of honeycomb seal 160 are conceivable utilising the method described above. FIG. 8 shows one such an arrangement manufactured from the method so described. The honeycomb seal 160 is constructed in a similar manner to that described with respect to FIG. S. The single strip 162 is formed into the plurality of layers 163. The series of 60 degree bends 182 form the troughs 164 and peaks 166 corrugations wherein the troughs 164 of one layer 163 abut the peaks 166 of the preceding neighbouring layer 163 serving to create the open cells 161.

One orientation of repeating alternate turns 175 serves to form the planer first face 172; this is in the same manner as described above with reference to FIG. 5.

However, the opposite handed alternate turns 175 are formed, in part, by the apex 189 of one of the hexagonal shaped open cells 161 as shown in FIG. 8. The remainder of the alternate turn 175 is formed by the 60 degree bends 182. Many other arrangements of angles or shapes are conceivable to form 180 degree bends which make up the alternate turns 175. In this particular case, the alternate turns 175 are formed by the angles S required to bend the hexagonal shape of the open cell 161 at the boundary of the honeycomb seal 160. This has an effect of creating a jagged or serrated face 190 along the boundary of the honeycomb seal 160. This may be beneficial in reducing windage losses as cooling air passes across the boundary of the honeycomb seal 160. Although the serrated face 190 is shown in FIG. 8 as being present on only one boundary, it may be beneficial to provide a similarly shaped serrated face 190 boundary on the other face of the honeycomb seal 160. An additional benefit of a serrated face 190 shaped, as illustrated in FIG. 8, is that one honeycomb seal 160 may interface, or abut, with another across all the alternate turns 175 of the face. This may be required where it is simpler to manufacture honeycomb seals 160 with layers 163 that are of a shorter length across the width of the seal 160. Therefore, abutting two seals 160 of the arrangement in FIG. 8 by mating across the serrated face 190, would create a wider overall sealing surface.

Turning to FIG. 9, which shows another embodiment of the honeycomb seal 160 formed from the single strip 162 of formable material. The plurality of layers 163 are arranged to form the open cells 161 in the same manner as the arrangement described with respect to FIG. 5 and are bonded together by a plurality of bonds 170. The arrow A indicates the direction of rotation of the rotor disc 46. The arrangement has the layers 163 sloped at an angle to the direction of rotation of the rotor disc 46. This contrasts with the arrangement of FIG. 5, where the layers 163 are generally perpendicular to the direction of rotation of the rotor disc 46. The first and second planar faces 172, 173 retain their generally planar direction parallel to the circumferential direction of the rotor disc 46. This arrangement may further reduce the wear on the rotating seal fins 51 as they pass over the sealing surface of the honeycomb seal 160.

FIGS. 10 and 11 show two other arrangements of honeycomb seal 160. FIG. 10 illustrates a honeycomb seal 160 with open cells 161 which are rectangular in shape. The honeycomb seal 160 may also have open cells 161 which are square in shape. The alternate turns 175 are formed in the manner required to shape the planar first and second faces 172, 173 of the honeycomb seal 160. The troughs 164 and peaks 166 of the corrugations are formed by a series of 90 degree bends in the single strip 162. In this example the each of the layers 163 of the single strip 162 forms a rectangular waveform 192.

FIG. 11 illustrates a honeycomb seal 160 with open cells which are formed from a sinusoidally shaped 194 single strip 162. The alternate turns 175 between each layer 163 are formed from radial bends 195. In this example each layer 163 of the single strip 162 forms a sinusoidal waveform 194. The open cells 161 in this arrangement are therefore formed of opposing sides 168 which approximate sine waves. Although this arrangement may not prove as effective as a sealing surface in comparison with those embodiments described above, which have hexagonal shaped open cells 161, the arrangement may be simpler and cheaper to manufacture and remain effective as a sealing surface. These benefits may also apply equally to the rectangular shaped 192 open cells 161 illustrated in FIG. 10.

Claims

CLAIMSI claim: 1. A honeycomb seal having a plurality of open cells, the honeycomb seal comprising a strip of material; the strip repeatedly folded back onto itself so as to form layers wherein each layer abuts at least one neighbouring layer; each layer having at least one trough corrugation and at least one peak corrugation defining opposing sides of the open cells; and each trough corrugation of each layer abutting a peak corrugation of a neighbouring layer so that the opposing sides define the open cells.
2. A honeycomb seal as claimed in claim 1 wherein the at least one trough corrugation of each layer is bonded to the at least one peak corrugation of a neighbouring layer.
3. A honeycomb seal as claimed in claims 1 or 2 wherein each layer is bonded to a substrate.
4. A honeycomb seal as claimed in claims 2 or 3 where the bond is a spot weld and/or a brazed join.
5. A honeycomb seal as claimed in any of claims 1 to 4 wherein the strip is repeatedly folded back onto itself by alternate turns of positive and negative 180 degrees in the strip.
6. A honeycomb seal as claimed in claim 5 wherein the alternate turns comprise two substantially right angle bends spaced apart by a strip portion.
7. A honeycomb seal as claimed in claim 6 wherein the length of the strip portion is approximately twice that of the distance between the peak of the peak corrugation and the trough of the trough corrugation of the layer.
8. A honeycomb seal as claimed in claim 6 wherein the length of the strip portion is approximately the distance between the peak of the peak corrugation of the layer and the trough of the trough corrugation of the neighbouring layer.
9. A honeycomb seal as claimed in any of claims 6 to 8 wherein the strip portion between the two substantially right angle bends forms a substantially planar surface.
10. A honeycomb seal as claimed in any of claims 6 to 9 wherein the strip portion of the positive 180 degree turn is aligned with the strip portion of the positive 180 degree turn of the neighbouring layer to form a substantially planar first face of the honeycomb seal.
11. A honeycomb seal as claimed in any of claims 6 to 9 wherein the strip portion of the negative 180 degree turn is aligned with the strip portion of the negative 180 degree turn of the neighbouring layer to form a substantially planar second face of the honeycomb seal.
12. A honeycomb seal as claimed in claim 5 wherein the alternate turns are radial bends.
13. A honeycomb seal as claimed in claim 12 wherein the radial bend has a radius approximately equal to the distance between the peak of the peak corrugation and the trough of the trough corrugation of the layer.
14. A honeycomb seal as claimed in any of claims 5 to 13 wherein the positive 180 degree turns are aligned to form the first face of the honeycomb seal.
15. A honeycomb seal as claimed in any of claims 5 to 13 wherein the negative 180 degree turns are aligned to form the second face of the honeycomb seal.
16. A honeycomb seal as claimed in any of claims 5 to 13 wherein the alternate turns form the last trough corrugation in the preceding neighbouring layer and the first peak corrugation of the layer.
17. A honeycomb seal as claimed in claim 16 wherein the alternate turns form part of the open cell adjacent to the first or second face of the honeycomb seal.
18. A honeycomb seal as claimed in any preceding claim wherein there are an equal number of trough corrugations and peak corrugations on each individual layer.
19. A honeycomb seal as claimed in any of claims ito 17 wherein there are an equal number of trough corrugations and peak corrugations on the layer as there are trough corrugations and peak corrugations on the neighbouring layer.
20. A honeycomb seal as claimed in any of claims 1 to 17 wherein the number of trough corrugations is not equal to the number of peak corrugations on each individual layer.
21. A honeycomb seal as claimed in claim 20 wherein the neighbouring layers alternate between having one more peak corrugation than trough corrugation and one more trough corrugation than peak corrugation.
22. A honeycomb seal as claimed in any preceding claim wherein neighbouring trough and peak corrugations of the layer comprise an approximate sinusoidal waveform.
23. A honeycomb seal as claimed in any of claims 1 to 21 wherein neighbouring trough and peak corrugations of the layer comprise an approximate rectangular waveform.
24. A honeycomb seal as claimed in any of claims 1 to 21 wherein the peak and trough corrugations have a semi-hexagon shape so as to define hexagonally shaped open cells.
25. A honeycomb seal as claimed in any of claims 1 to 21 wherein each layer following a positive 180 degree turn has at least one sequence of positive, negative, negative, positive, positive, negative 60 degree bends in the strip wherein the 60 degree bends are measured relative to the strip prior to the bend.
26. A honeycomb seal as claimed in any of preceding claim wherein the open cells are filled with a heat-resistant material.
27. A method of manufacturing a honeycomb seal from a strip of formable material comprising the steps of: a) forming a series of trough and peak corrugations in a first portion of the strip of formable material; b) forming a series of trough and peak corrugations in a second portion of the strip of formable material; c) folding the second portion of the strip back onto the first portion to form a first layer and a second layer in the strip of formable material; d) arranging the trough corrugations on the second layer to abut the peak corrugations on the first layer so as form a plurality of open cells; and e) repeating steps b) to d) to form a plurality of layers defining a plurality of open cells.
28. A method according to claim 27 wherein step (d) includes the step of bonding at least one of the trough corrugations on the second layer to at least one of the peak corrugations on the first layer.
29. A method according to claim 28 wherein the step of bonding at least one of the trough corrugations on the second layer to at least one of the peak corrugations on the first layer includes spot welding and/or brazing.
30. A method according to claim 28 or claim 29 wherein step (d) includes the step of bonding the second layer and/or the first layer to a substrate at least one trough corrugation.
31. A method according to claim 30 wherein the step of bonding the second layer and/or the first layer to a substrate at least one trough corrugation comprises brazing.
32. A method according to any of claims 27 to 31 wherein step (c) takes place prior to step (b).
33. A method of any of claims 27 to 32 wherein the folding of step (c) alternates between positive and negative 180 degrees.
34. A method according to claim 33 wherein the folding of step (c) comprises forming two substantially right angle bends.
35. A method according to claim 34 wherein the right angle bends are spaced apart by a strip portion.
36. A method according to claim 35 wherein the strip potion forms a substantially planar surface.
37. A method according of any of claims 27 to 36 wherein the trough and peak corrugations have a semi-hexagonal shape so as to define hexagonally shaped open cells.
38. A method according to any of claims 27 to 37 comprising a further step of filling the open cells with a heat-resistant material.
39. A honeycomb seal substantially as described herein with reference to, and as shown in, FIGS. 5 to 11.