DESCRIPTION OF THE DRAWINGS
In order that the invention may be readily understood, one embodiment of the invention is illustrated by way of example in the accompanying drawings.
FIG. 1 is an axial cross-sectional view through a prior art gas turbine engine, showing the various components that are assembled to produce an engine, and an example of a prior art fan case with an encapsulated layer of abradable material.
FIG. 2 is a detailed axial cross-sectional view through another example of a prior art fan case with an encapsulated layer of abradable material having metal to metal contact in an upstream portion with abradable material recess downstream.
FIG. 4 is a detailed sectional view of the embodiment shown in FIG. 3.
FIG. 5 is an exploded isometric view of the metal fan case shell bounded by front and rear flanges, and showing abradable material tiles removed from the recess in which they are bonded.
FIG. 6 is a like isometric view of the metal fan case shell showing abradable material tiles installed in the recess.
Further details of the invention and its advantages will be apparent from the detailed description included below.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows an axial cross-section through a turbo-fan gas turbine engine. It will be understood however that the invention is equally applicable to any type of engine with a combustor and turbine section such as a turbo-shaft, a turbo-prop, or auxiliary power units. Air intake into the engine passes over fan blades 1 in a fan case 2 and is then split into an outer annular flow through the bypass duct 3 and an inner flow through the low-pressure axial compressor 4 and high-pressure centrifugal compressor 5. Compressed air exits the compressor 5 through a diffuser 6 and is contained within a plenum 7 that surrounds the combustor 8. Fuel is supplied to the combustor 8 through fuel tubes 9 which is mixed with air from the plenum 7 when sprayed through nozzles into the combustor 8 as a fuel air mixture that is ignited. A portion of the compressed air within the plenum 7 is admitted into the combustor 8 through orifices in the side walls to create a cooling air curtain along the combustor walls or is used for cooling to eventually mix with the hot gases from the combustor and pass over the nozzle guide vane 10 and turbines 11 before exiting the tail of the engine as exhaust.
The prior art fan case 2 shown in FIG. 1 has a recessed portion adjacent the tips of the fan blades 1 that includes an encapsulated layer of abradable material 12 and some designs include other impact absorbent materials such as ballistic fabric or mesh and metal honeycomb structures. The recess to house the abradable material in the prior art is radially outward of the front flange 13 and the fan case 2 is bolted to the engine with the rear flange 14. Due to the geometry of the recess, the fan case 2 is generally fabricated by machining the recess from an oversized casting and abradable material 12 is plasma spray coated into the recess.
FIG. 2 shows another example of a prior art fan case 2 with an enclosed layer of abradable material 12. The upstream tip of the blade 1 is in metal to metal contact with a circumferentially grooved portion of the fan case shell 15 and the blade tips contact the abradable material 12 housed in the recess downstream. Metal of the fan case shell 15 axially bounds or encapsulates the relatively softer abradable material 12 upstream and downstream in this prior art example as well.
FIG. 3 shows an axial cross-section through the fan case 2 according to the invention with the fan case 2 being fabricated with a hollow tubular metal shell 15 having a central axis 16 of symmetry; an inlet surrounded by the front flange 13; an outlet surrounded by the rear flange 14; and peripheral metal wall 17 about the axis 16 to encompass the tips of the rotary fan blades 1.
As better seen in the detail of FIG. 4, the shell wall 17 includes an upstream portion defining an annular abradable material recess 18. The recess 18 fully extends axially from it's upstream end at the shell inlet 19 surrounded by the front flange 13 to the downstream end 21 located upstream from the shell outlet 20 surrounded by the rear flange 14.
The shell inlet 19 has an inlet diameter and the recess has a recess diameter that is no greater than the inlet diameter. Compared to the prior art examples shown in FIGS. 1-2, the prior art examples show recess diameters greater than the inlet diameters and hence the abradable material is axially bounded by the metal of the fan case shell 15 in the prior art.
The recess diameter shown in the embodiment of FIGS. 3-4 is tapered in a downstream direction having a maximum recess diameter at the upstream end of the recess 18 that is equal to the shell inlet diameter and a minimum recess diameter at the downstream end 21 of the recess 18. The abradable material 12 partially or fully fills the recess and an upstream edge 22 of unsupported abradable material 12 radially inward of the shell inlet 19.
The shell 15 includes a front flange 13 at the inlet 19 to which an inlet cowl is bolted and a rear flange 14 at the outlet 20 to bolt the fan case 2 to the engine. Of advantage in manufacturing, the front flange 13 has an external diameter greater than an external diameter of the rear flange 14 as illustrated with a dashed line parallel to the axis 16. This feature enables access to use simple metal forming techniques and reduces the need to use relatively expensive metal forging and machining methods of the prior art. Fabricating the hollow tubular metal shell 15 can be accomplished with less expensive metal fabrication procedures such as: press forming sheet metal; welding; rolling sheet metal; and spin forming and need not follow the prior art methods of forging the metal shell 15 as a single oversized forging and then machining to remove excess metal material.
As best seen in FIGS. 5-6 the metal fan case shell 15 may be fabricated with the forwardly open recess 18 and prefabricated molded abradable tiles 23 can slide into the recess 18 to be bonded to the metal shell 15 thereby filling the recess 18. In the embodiment illustrated there are four tiles 23 each covering one quarter of the circumference of the recess 18, however various other tile patterns can be used. The axial seam between the tiles 23 may be filled and bonded together to fill the entire recess 18. The molded abradable tiles 23 also have a molded upstream edge 22 of unsupported abradable material 12 that is disposed radially inward of the shell inlet on installation.
As a result of using prefabricated molded tiles 23 costs may be reduced and a greater variety of materials can be used for the abradable layer 12. Molding of the tiles 23 frees the choice of abradable materials from materials that can be powdered and plasma spray coated to materials that can be molded and then bonded to metal.
Although the use of a particular abradable tile is described and preferred, any suitable abradable provided in any suitable format may be used with the present method and/or apparatus.
Recapping the process of manufacturing a fan case 2 in accordance with the invention, the following steps are involved. A hollow tubular metal shell 15 is fabricated having: a central axis of symmetry 16; an inlet 19; an outlet 20; and peripheral wall 17 about the axis 16 to encompass the tips of a plurality of rotary fan blades 1. The metal shell wall 17 includes an upstream portion defining an annular abradable material recess 18 that extends axially from the upstream end at the shell inlet 19 to the downstream end 21 located upstream from the shell outlet 20. The recess 18 is filled with abradable material 12 leaving an upstream edge 22 of unsupported abradable material 12 radially inward of the metal shell inlet 19.
Since the abradable material 12 can slide into the recess 18 as shown in FIGS. 5-6, the step of filling the recess 18 can include molding prefabricated abradable material tiles 23 apart from the metal shell 15 and then bonding the tiles 23 into the recess 18 formed in the shell 15.
Although the above description relates to a specific preferred embodiment as presently contemplated by the inventors, it will be understood that the invention in its broad aspect includes mechanical and functional equivalents of the elements described herein.
Patent Application
20080063508
