Patent Application
20080224414
The present invention relates to an improved brush seal, including a brush seal which includes a thermally-activated material for controlling a gap associated with the seal.
Brush seals provide a technology for sealing high pressure areas from low pressure areas, for example, areas associated with gas turbine engines. Typically, brush seals inhibit the flow of a gas or liquid in a stream along a shaft.
Some brush seal applications involve very high temperatures, which can produce non-uniform thermal growth among associated components. For instance, many engine parts experience significantly higher temperatures during take-off, only to later be reduced during normal operation or equilibrium. Thermal gradient and thermal expansion differences can cause non-uniform thermal growth among various engine parts. Under such conditions, some brush seals have to work with a reduced gap or with an interference fit with respect to a rotating shaft. Another potential drawback associated with prior art brush seals is their tendency to enter into a vicious cycle once the bristles experience heavy contact with the rotating shaft. With conventional brush seals, one end of the bristle is typically attached (either by welding or mechanical clamping) to the seal housing and the seal housing is pressed into seal carrier of the surrounding structural components. The heat generated by the rubbing between the bristles and shaft commonly leads them to grow more and more into each other, which in turn results in more interference and heavier rubbing until heavy wear of bristles reduces the associated interference. Those conditions can increase or accelerate the wear on the brush seal and degradation of the surface of an associated shaft. Consequently, a brush seal that, among other things, helps to address the conditions associated with temperature gradient and thermal expansion differences is desirable.
According to an aspect of the invention, a brush seal for use with a housing and sealing a high pressure area from a low pressure area is provided. The brush seal includes a retainer and a plurality of bristles. The retainer is comprised of a thermally-sensitive material having a thermal expansion rate. The bristles are connected to and extend from the retainer. In an embodiment, the retainer is not fixedly connected to the housing, and the thermal expansion rate of the retainer is greater than the thermal expansion rate of a portion of the housing adjacent the retainer. In other embodiments, the housing is physically restrained from growth based upon its fit (e.g., press-fit) with respect to surrounding structural components.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:
Reference will now be made in detail to embodiments of the present invention, examples of which are described herein and illustrated in the accompanying drawings. While the invention will be described in conjunction with embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims.
An embodiment of the invention envisions, among other things, the provision of a brush seal that includes a retainer comprised of a thermally-sensitive material that, at least in part, helps to functionally account for differences in thermal gradients and thermal expansion rates among associated components.
The illustrated assembly 10 includes a housing 20 and a brush seal element 30. The brush seal element 30 includes a retainer 40 and a plurality of bristles 50 that are connected to and extend downwardly from retainer 40 toward a shaft 60. By way of example, and without limitation, retainer 40 may be comprised of a stainless steel (e.g., 304L stainless steel) and housing 20 may be comprised of a nimonic 75 high nickel alloy. The bristles 50 may be comprised of various known bristles and generally include a multiplicity of single bristles each bristle having a fixed end and a free sealing end. In an embodiment of the invention, the fixed ends are individually attached in a continuous arrangement at the same angle to retainer 40, the bristles 50 having a substantially uniform pack density throughout the extent of the bristles 50 from the fixed end to the sealing end.
Housing 20 may further include a back plate 70 that is provided on the low pressure side of the brush seal assembly. Back plate 70 may be a separate component, may be comprised of multiple separate components, or may be formed as a single integral portion of housing 20. As generally illustrated, a portion of back plate 70 may abut a portion of bristles 50. In the illustrated embodiment, back plate 70 generally extends downwardly in a direction substantially parallel with the bristles 50 and substantially perpendicular to the housing 20 and/or the shaft 60.
For some applications, the brush seal and/or associated assembly may also include a front plate 80, which may be a separate component or may be formed integrally with the housing 20. Front plate 80 may be provided on the high pressure side of the brush seal assembly and, depending upon the configuration, a portion of the front plate 80 may abut a portion of bristles 50. For some applications, such as that illustrated in
In an embodiment of the invention, a headspace or gap (generally identified as G) is provided above the retainer between the retainer 40 and a surface 90 of housing 20. While retainer 40 is constrained, or at least partially enveloped or surrounded, by a portion of housing 20, the retainer 40 is not fixedly connected to the housing 20. That is, the retainer 40 is free to expand or move (relative to a portion of the housing 20) some distance (D) in a radial direction. For example, the retainer 40 may be permitted to expand or move radially closer to and farther from an associated external shaft 60. The amount of radial movement may, at least in part, be defined or controlled by the configuration of physical components associated with the assembly 10. A benefit of allowing retainer 40 to grow some degree radially is the configuration's ability to help prevent the seal from getting into a vicious cycle of perpetuating interference—i.e., more heat generation and increasing interference until heavy wear of the bristles eventually leads to a reduction in interference. By way of example, and without limitation, the retainer 40 shown in
In an embodiment of the invention, a gap G is provided between the retainer 40 and a surface 90 of housing 20 and the thermal expansion rate (i.e., coefficient of thermal expansion) of retainer 40 is greater than the thermal expansion rate of a portion of the housing 20 adjacent to the retainer 40 due to a smaller coefficient of thermal expansion and/or because the housing is physically restrained from growth based upon its fit (e.g., press-fit) with respect to surrounding structural components. That is, as the temperature associated with the assembly 10 increases, the retainer 40 is permitted to expand or grow into the gap G. For many typical brush seal applications, a small annular gap G2, or “tip region” (which may be about 0.0002 to about 0.005 inches) is provided between the tips of the bristles 50 and a shaft surface. The permitted “growth” of the retainer 40 in the radially outwardly direction can serve to help prevent an undesirable reduction in the tip region associated with the forcing of the tips of the bristles 50 closer to, or in interfering contact with, a surface of shaft 60. Such a condition could occur, for instance, if retainer 40 expands but is constricted from further radially outward movement (e.g., when no gap for growth is provided between the upper portion of the retainer and the adjacent surface of the housing, and/or the retainer 40 is otherwise rigidly connected to a portion of the housing 20 and/or the back plate 70.
A brush seal element 30 according to an embodiment of the invention is generally illustrated in
Another embodiment of a brush seal element 30 is shown in
Embodiments of the present invention provide a mechanism for users to provide an improved control-gap brush seal assembly that is very flexible and is capable of being used both with specially-designed and various conventional housings. Commonly, designers of brush seal assemblies have a thorough understanding of the critical phases associated with a given application. The present invention permits a designer to select materials and provide gaps that provide the most desirable operational or functional sealing characteristics.
For example, an assembly can be configured so that a given starting clearance or tip region is provided. By selecting the materials associated with the brush seal and housing, as well as configuring an associated headspace or gap, a more desirable clearance or tip region may be provided at increased temperatures. Further, depending on the parameters associated with the housing, a designer may utilize a band or other spacing mechanism to further control the gap and the related expansion/movement of the brush seal.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and various modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and its practical application, to thereby enable others skilled in the art to utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.
