Seal for a joint or juncture – Seal between relatively movable parts – Brush seal
Reexamination Certificate
2000-12-26
2003-01-07
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Brush seal
C277S556000, C277S653000
Reexamination Certificate
active
06502825
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to seals for static or dynamic rotating applications. More particularly, the present invention relates to pressure activated cloth seals for static and dynamic applications.
BACKGROUND OF THE INVENTION
Seals can be used to minimize leakage of fluids including gas in applications where two relative movable mechanical members are in close proximity. The members may have substantial relative motion between one another, such as a turbine shaft against lubricating oil reservoir, or a rotatable turbine stage relative to a fixed support structure having to withstand a pressure differential across the stage. Also, the movement between members may be caused by vibration or thermal growth.
Leakage of gas and air can negatively impact performance of components in many systems including a gas turbine combustion system. Mating components may be formed of different materials and can be subjected to different temperatures during operation. Consequently, the components commonly experience varying degrees of thermal growth. For example, a fuel nozzle burner tube and a combustion liner cap assembly support structure in a gas turbine move radially, axially, and circumferentially relative to one another based on thermal growth. Similar relative movement may also occur due to dynamic pulsing of the combustion process. To prevent leakage and compensate for the relative movement of the fuel nozzle burner tube, a split ring metal seal has been placed around the outer diameter of the fuel nozzle burner tube providing an interface between the burner tube and a portion the cap assembly support structure.
Rather than an airtight seal, a certain amount of leakage between the fuel nozzle burner tube and the cap assembly support structure is desired. In this regard, hot gases from the combustion reaction zone tend to “backflow” into a tubular cavity between the fuel nozzle burner tube and the cap assembly support structure components. When the hot gases flow into the tubular cavity, they can damage the hardware, which significantly shortens the usable life of the components. To prevent backflow, a certain amount of air leakage needs to be permitted to flow through the seal. In an attempt to address this concern, the conventional split ring metal seal has slots cut through the seal to allow some leakage of air.
Several problems exist with the split ring metal seal. Since the seal is metal and the interfacing components are metal, the components and seal tend to rub, vibrate or otherwise move against one another causing excessive wear of the seal and the components. Further, the burner tube and cap assembly support structure components and the seal generally do not perfectly fit together due to slight physical discrepancies resulting from manufacture. Stated differently, each component is manufactured to a particular tolerance, and is not perfectly shaped due to real world limitations. In addition, over time the components and seal will tend to change shape due to thermal distortion and physical wear. As a result, the amount of leakage of air around the burner tube cannot be effectively controlled and tends to be non-uniform, varying from one location to another.
In the past, a substantial number of seals have been employed in turbine systems. Labyrinth seals have been employed between rotating mating surfaces or vibrating mating surfaces. However, labyrinth seals do not easily conform to vibratory movement or rotating surfaces, particularly when the surfaces have imperfections. Consequently, labyrinth seals have not proven particularly effective.
Brush seals have been used in many environments including in gas and steam turbines. Brush seals generally conform better to rotating and/or vibrating mating surfaces than labyrinth seals including surfaces having imperfections. While brush seals have proven more effective than labyrinth seals, they are exceedingly expensive to manufacture and difficult to handle. For example, the very fine bristle wires of a brush seal are not bound together prior to assembly. As a result, it is an arduous process to lay out a predetermined layer of bristles to the required thickness to form a bristle pack suitable to form the resulting seal. Consequently, there is a need to provide a less expensive mechanism for providing a low leakage seal which is sufficiently resilient to accommodate the dimensional changes in the radial, axial, and circumferential directions resulting from wear and thermal growth. Also, there is a need for a seal that can regulate the amount of leakage there through.
BRIEF SUMMARY OF THE INVENTION
The present invention overcomes many of the shortcomings of prior art seals. According to an illustrative implementation of the present invention, a cloth seal interfaces two mating bodies, taking into account the pressure through the interface. In one aspect of the invention, a low leakage cloth seal is provided where, based on the pressures through the interface, the cloth seal may be designed to include an area where fluids including gas can flow through at least portion of the cloth assemblage of the cloth seal. In another aspect of the invention, gas flowing through the seal can be used to purge a cavity of unwanted gases and/or cool the cavity or surfaces of the mating bodies providing the cavity boundaries.
In yet another aspect of the invention, knowing the pressure differential through the interface, the density of the cloth seal including thickness and number of cloth layers may be designed to allow for a desired leakage amount or flow rate. In another aspect of the invention, an effective seal between mating surfaces can be realized by using a cloth seal, which is flexible and sufficiently resilient to accommodate the dimensional changes in the radial, axial, and circumferential directions resulting from wear, vibration, thermal distortion and other types of movement. In still another aspect of the invention, the density of the cloth seal can be selected based on the pressure drop across the seal in order to minimize the needed contact load to maintain sealing contact, thereby reducing wear of the mating body and the seal.
In another aspect of the invention, a high temperature, woven cloth seal can be provided in a tubular cavity between a burner tube of a fuel nozzle and a cap assembly to act as an interface. In another aspect of the invention, leakage through the woven cloth seal can be controlled to purge a tubular cavity separating the burner tube and cap assembly of unwanted hot gases.
According to another aspect of the invention, a cloth seal design can be implemented with a shim assemblage in contact with a high pressure region and a portion of the shim assemblage making seal contact with a mating member to effectively block leakage while improving wear resistance. In another aspect of the invention, a pressure activated high temperature woven cloth seal can be used as a dynamic seal around rotating components.
In yet another aspect of the invention, shim stiffness can be adjusted to reduce contact forces on a mating body due to pressure loading. Knowing the pressure differential across the cloth seal, the seal design may be tuned or calibrated to have a stiffness which assures seal contact up to a preset pressure level.
In still another aspect of the invention, a seal assembly can include a cloth seal having a cloth assemblage and a shim assemblage, the cloth seal adapted to seal a tubular cavity between a mating body and a tubular member. The cloth seal can be physically attached to the mating body and extend through the tubular cavity to make sealing contact with the tubular member. Also, the cloth seal can divide the tubular cavity into a high pressure region and a low pressure region. In an aspect of the invention, the cloth assemblage is wrapped around the shim assemblage.
One of the advantages of the cloth seals according to embodiments of the present invention is that their relative cost is significantly reduced from the cost of other seals used in circular sealing applications.
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Aksit Mahmut Faruk
Benoit Jeffrey Arthur
Mohammed-Fakir Abdul-Azeez
Banner & Witcoff , Ltd.
General Electric Company
Knight Anthony
Pickard Alison K.
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