Patent Application
20130043658
The subject matter disclosed herein relates to a brush seal assembly, and more specifically to a brush seal assembly having a backing plate including at least one backing tooth for selectively contacting a sealing surface.
Brush seals are commonly found in a variety of applications such as gas and steam turbines, and are typically employed to seal a gap located between a rotary shaft and a stationary member. Brush seals have a plurality of bristles that are sandwiched between a forward plate and a backing plate. The bristles extend towards a sealing surface and provide a seal between the rotary shaft and the stationary member.
The backing plate of the brush seal provides axial support to the bristles and also partially obstructs the gap located between the rotary shaft and the stationary member. A clearance is located between the backing plate and the rotary shaft in an effort to substantially prevent the backing plate from contacting the rotary shaft during operation. This clearance is sometimes referred to as the fence height of the backing plate. The fence height of the backing plate is typically more than the conventional metal-to-metal clearance. In an effort to improve brush seal pressure capability and reduce bristle wear, the fence height is reduced such that the bristles have increased support and are subjected to less bending stress from pressure loading. However, reducing fence height may increase the risk of rubbing against the rotary shaft during transient conditions, such as when the system is passing resonant speeds or in the event thermal equilibrium between components is reached. If the fence height is not adequate, the surface of the backing plate that opposes the rotary shaft may mushroom or smear when rubbed by the rotating surface of the rotary shaft during transient conditions.
In the event a backing plate tip is rubbed, the edges of the backing plate may become irregular and intermittent. This may create a difficult situation, as the bristles may not slide easily along on the backing plate. If the bristles are stuck on an irregular edge of the backing plate, the bristles may become permanently bent and worn where there are rotary shaft excursions. Thus, the backing plate should provide axial support to the bristles while still substantially avoiding contact with the rotary shaft.
Several approaches currently exist for reducing or preventing the surface of the backing plate from contacting the rotary member while still maintaining axial support of the bristles. For example, in one approach, the surface of the backing plate is coated with a tribologically compatible coating or backing layer to be more tolerant to rubbing. In another approach, a material that facilitates rubbing between the backing plate and the rotary surface could be employed as well to substantially avoid mushrooming of the backing plate tip. However, these approaches may introduce added cost and complexity to the brush seal. In another approach, the forward plate is set to a relatively tight clearance to serve as a bump element to protect the backing plate, but it is typically not a viable option, because this approach will create a jet flow that may destabilize the brush seal bristles, causing fluttering and relatively quick wear. Therefore, it would be desirable to provide a cost effective system for reducing contact between the backing plate of a brush seal and a rotary shaft.
According to one aspect of the invention, a brush seal assembly is provided, including a sealing surface, a side plate, a backing plate, a plurality of bristles, and a biasing member. The backing plate is selectively located in a stationary position and has at least one backing tooth and a backing tip. The backing tooth has a tooth surface and the backing tip has a tip surface. A tooth clearance is measured between the tooth surface and the sealing surface. A tip clearance is measured between the tip surface and the sealing surface. The tooth clearance is less than the tip clearance. The bristles are located between the side plate and the backing plate. The bristles include an end portion for sealing to the sealing surface. The biasing member exerts a biasing force upon the backing plate in a direction towards the sealing surface. The backing tooth is configured for selectively contacting the sealing surface. Contact between the backing tooth and the sealing surface urges the backing plate out of the stationary position and towards the biasing member. The biasing force re-positions the backing plate back to the stationary position.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
The seal bristles 30 have a first end portion 40 and a second end portion 42. The first end portion 40 is received between two siderails 44, 46, where a first siderail 44 is attached to the side plate 26 and the second siderail 46 is attached to the backing plate 28. The siderails 44, 46 exert a compressive force to secure and position the seal bristles 30 in place. In one embodiment the siderails 44, 46 are attached to the seal bristles 30 by welding. The second end portion 42 of the seal bristles 30 are configured to provide sealing to a sealing surface 48 of the rotary member 20. In one embodiment, the second end portion 42 of the seal bristles 30 may contact the sealing surface 48 as the rotary member 20 operates. The sealing bristles 30 may be angled in the direction of rotation. Specifically, referring to
Continuing to refer to
Referring back to
The backing tooth 52 is configured to selectively contact the sealing surface 48 of the rotary member 20. That is, the backing tooth 52 is positioned such that in the event the backing plate 28 comes within proximity of the sealing surface 48 of the rotary member 20, only the backing tooth 52 is configured to contact the sealing surface 48. Thus, contact between backing tip 60 and the sealing surface 48 is generally avoided. The backing tooth 52 of the backing plate 28 typically contacts the sealing surface 48 during a rotary member excursion, which may occur due to thermal transient conditions, or rotor vibration when passing a resonant speed. The functions of the backing tooth 52 are typically two fold. First, the backing tooth 52 generally provides protection to the backing plate tip 68 in the event of rotor excursion or thermal pinching. The second function of the backing tooth 52 is to act as a backup seal.
In the embodiment as shown in
The biasing member 32 exerts a biasing force F upon the backing plate 28. The biasing force F is oriented in a direction towards the sealing surface 48 of the rotary member 20. If the backing tooth 52 contacts the sealing surface 48 of the rotary member 20, the respective segmented portion 50 of the brush seal assembly 10 is urged radially outwardly, and towards the biasing member 32. The biasing member 32 exerts the biasing force F towards the sealing surface 48 of the rotary member 20, which re-positions the segment 50 back into the stationary position S.
The backing tooth 52 is employed to reduce or substantially avoid contact between the backing tip 60 and the rotor 20, while also reducing the tip clearance C2 between the backing tip 60 and the sealing surface 48. Specifically, the tip clearance C2 of a backing plate 28 employing the backing tooth 28 is generally less than the tip clearance C2 of a backing plate 28 that does not include the backing tooth 28. The tip clearance C2 should be reduced to the smallest dimension possible to provide axial support to the seal bristles, while still substantially avoiding contact with the rotary shaft 20 through sacrificing the backing tooth 52 in a rub situation. Meanwhile the backing tooth 52 may also work as a backup seal as well
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
