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Brush seals and methods of fabricating them
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Brush seals and methods of fabricating them Assignee: General Electric Co, USA This patent discusses brush seals and provides details of methods for fabricating them. In particular it relates to bidirectional brush seals and production methods in which accurate control of the bristle cant angle is maintained during manufacture and seal operation, reliability and improved sealing performance are achieved. Various types of brush seals have been proposed and used for sealing purposes in turbomachinery such as generators and turbines, and particularly at the stator-to-rotor interface. Conventional brush seal designs often comprise a bristle pack and a carrier structure for supporting this pack. The latter is an array, preferably in the form of a ring, of densely packed metal bristles or non-metallic (for example, Kevlar) fibres that project from the carrier to engage with an opposing sealing surface. To facilitate bristle flexibility (for example, for varying stator-to-rotor clearances and to avoid excessive metal or fibre stress during rotor excursions) the bristles are arranged at
an angle to both the radial and circumferential directions. The angle defined by a radial vector and the bristles is known as the cant angle. When brush seals are made it is difficult to control this angle accurately while securing the bristles to the carrier. The bristles normally have a tiny diameter. Currently, there are few techniques for handling them effectively during the fabrication of a brush seal. Therefore, there is a need for an improved method of making brush seals while maintaining accurate control over the bristle cant angle. In accordance with a preferred embodiment of this invention, a brush seal is provided that comprises a single carrier for the bristles, in which a single array of bristles is applied to one surface of the carrier for projecting beyond an edge to engage with an opposing sealing surface. Referring to Figure 1, a carrier (10) forms part of a brush seal between a stationary component (12) (mounting the carrier) and a rotating component (14), for example a rotating shaft. The bristles (16) of the seal extend at a cant angle θ which is defined by radii from
Figure 1. This is a schematic illustration of a prior art brush seal that extends from a stationary component and engages with a rotating component.
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Figure 2. A cross-sectional view of a brush seal constructed in accordance with prior art, shown in Figure 1.
the centre (18) of rotation and the longitudinal axis of the bristle. Figure 2 shows a conventional single-row brush seal construction. A large number of bristles (26) is located between a front plate (20) and a back plate (22). That is, the bristles are sandwiched between the plates and have tips (28) which project from common edges of the plates to engage with a sealing surface, for example, the shaft (14). The forward (upstream) plate (20) is inset or recessed at (24) to form a gap between itself and the bristles. A preferred embodiment of this invention is illustrated in Figure 3. Here, a single carrier (42) and bristles (45) extend along opposite surfaces (44) and (46). The tips (48) extend beyond the edge (50) of the carrier (42). A number of grooves (52) and (54)
Figure 3. A cross-sectional view illustrating a brush seal constructed in accordance with a preferred embodiment of patent US 6505835.
Sealing Technology April 2003
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Figure 6. A similar view to Figure 5 illustrating the tips of the ribs that define grooves which are deformed to retain the bristles (this occurs before the step that is illustrated in Figure 4c).
4a
4b
4c
Figure 4. Schematic perspective views illustrating various steps for fabricating the brush seal.
Figure 5. An enlarged fragmentary cross-sectional view of the grooves containing the bristles before they are secured into the grooves.
Sealing Technology April 2003
are formed along respective opposite surfaces of the carrier. The discrete bristles are wrapped about the carrier, and extend along opposite sides in the grooves and project beyond the edge of the carrier adjacent to a sealing surface (for example, the shaft), so that the tips make contact with the sealing surface. The bristles may extend only along one side of the carrier and need not necessarily extend along opposite sides. However, by extending the bristles along opposite sides of the carrier (42), the brush seal is bidirectional – that is, capable of sealing either a positive or negative leakage flow. The way in which the brush seal is fabricated is illustrated in Figures 4–7. In Figure 4a the carrier (42) is in the form of an arcuate segment. A pair of knurling wheels (60) and (62), with oblique cutting ribs (64) and (66), are pressed into contact with the opposite surfaces (44) and (46) of the carrier to form tiny grooves (52) and (54). The width dimension of each groove is less than a millimetre. Where the brush seal is in an arcuate configuration about an axis, the angle formed between the groove and a radius relative to the axis, is the desired cant angle θ. It will also be appreciated that the oblique cutting ribs form grooves at corresponding cant angles on opposite sides of the carrier. The discrete bristles are wrapped about the carrier and laid into the grooves. Various types of machines are available for wrapping or bending the bristles about the carrier and locating the bristles in the grooves. In Figure 5 the grooves (52) contain multiple bristles (45). The grooves are defined in part by ribs (70) that terminate in tips (72), which project beyond the bristles contained in the grooves. Means are provided for joining together (securing) the bristles and the carrier. For example, the tips of the ribs may be bent over to substantially close
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the grooves, locking the bristles from movement within the grooves. To accomplish
this, a pair of smooth rollers (74) and (76) (Figure 4c) are applied to the tips to deform
Figure 7. A similar view to Figure 4a illustrating the fabrication of a brush seal that has a ‘pinchpoint’ inset from the edge of the carrier.
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them in the same direction, as illustrated in Figure 6. By flattening the tips of the ribs (to at least in part overlie the grooves), the bristles are clamped into the grooves. As shown in Figure 3, an epoxy (78) may be applied over the deformed teeth and bristles in the groove to facilitate retention of the bristles in the grooves. Alternatively, the epoxy may be applied over the entire surface of the carrier, filling in the grooves to retain the bristles, without deforming the rib tips. Referring to Figure 7, the bristle-free radial height of the brush seal can be adjusted by machining a length of flat steps or recessing surfaces of the carrier (42) adjacent to the edge (50) as desired. The carrier (80) includes a pair of inset or recessed face portions or surfaces (82) along opposite sides and adjacent to the edge (50) which will lie opposite the sealing surface. In this way, the bristles are constrained or pinched within the carrier grooves and extend freely from the ‘pinchpoint’ (84) to the tips of the bristles. This bristle-free radial height affects the bristle stiffness and seal flexibility and can be adjusted by machining the surfaces of the carrier, back from the edge (50), to a greater or lesser extent. Patent number: US 6505835 Inventors: W. Tong and Z.-Q. Zhuo Publication date: 14 January 2003
Sealing Technology April 2003
04/04/2003
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PATENTS
Brush seals and methods of fabricating them Assignee: General Electric Co, USA This patent discusses brush seals and provides details of methods for fabricating them. In particular it relates to bidirectional brush seals and production methods in which accurate control of the bristle cant angle is maintained during manufacture and seal operation, reliability and improved sealing performance are achieved. Various types of brush seals have been proposed and used for sealing purposes in turbomachinery such as generators and turbines, and particularly at the stator-to-rotor interface. Conventional brush seal designs often comprise a bristle pack and a carrier structure for supporting this pack. The latter is an array, preferably in the form of a ring, of densely packed metal bristles or non-metallic (for example, Kevlar) fibres that project from the carrier to engage with an opposing sealing surface. To facilitate bristle flexibility (for example, for varying stator-to-rotor clearances and to avoid excessive metal or fibre stress during rotor excursions) the bristles are arranged at
an angle to both the radial and circumferential directions. The angle defined by a radial vector and the bristles is known as the cant angle. When brush seals are made it is difficult to control this angle accurately while securing the bristles to the carrier. The bristles normally have a tiny diameter. Currently, there are few techniques for handling them effectively during the fabrication of a brush seal. Therefore, there is a need for an improved method of making brush seals while maintaining accurate control over the bristle cant angle. In accordance with a preferred embodiment of this invention, a brush seal is provided that comprises a single carrier for the bristles, in which a single array of bristles is applied to one surface of the carrier for projecting beyond an edge to engage with an opposing sealing surface. Referring to Figure 1, a carrier (10) forms part of a brush seal between a stationary component (12) (mounting the carrier) and a rotating component (14), for example a rotating shaft. The bristles (16) of the seal extend at a cant angle θ which is defined by radii from
Figure 1. This is a schematic illustration of a prior art brush seal that extends from a stationary component and engages with a rotating component.
12
Figure 2. A cross-sectional view of a brush seal constructed in accordance with prior art, shown in Figure 1.
the centre (18) of rotation and the longitudinal axis of the bristle. Figure 2 shows a conventional single-row brush seal construction. A large number of bristles (26) is located between a front plate (20) and a back plate (22). That is, the bristles are sandwiched between the plates and have tips (28) which project from common edges of the plates to engage with a sealing surface, for example, the shaft (14). The forward (upstream) plate (20) is inset or recessed at (24) to form a gap between itself and the bristles. A preferred embodiment of this invention is illustrated in Figure 3. Here, a single carrier (42) and bristles (45) extend along opposite surfaces (44) and (46). The tips (48) extend beyond the edge (50) of the carrier (42). A number of grooves (52) and (54)
Figure 3. A cross-sectional view illustrating a brush seal constructed in accordance with a preferred embodiment of patent US 6505835.
Sealing Technology April 2003
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Figure 6. A similar view to Figure 5 illustrating the tips of the ribs that define grooves which are deformed to retain the bristles (this occurs before the step that is illustrated in Figure 4c).
4a
4b
4c
Figure 4. Schematic perspective views illustrating various steps for fabricating the brush seal.
Figure 5. An enlarged fragmentary cross-sectional view of the grooves containing the bristles before they are secured into the grooves.
Sealing Technology April 2003
are formed along respective opposite surfaces of the carrier. The discrete bristles are wrapped about the carrier, and extend along opposite sides in the grooves and project beyond the edge of the carrier adjacent to a sealing surface (for example, the shaft), so that the tips make contact with the sealing surface. The bristles may extend only along one side of the carrier and need not necessarily extend along opposite sides. However, by extending the bristles along opposite sides of the carrier (42), the brush seal is bidirectional – that is, capable of sealing either a positive or negative leakage flow. The way in which the brush seal is fabricated is illustrated in Figures 4–7. In Figure 4a the carrier (42) is in the form of an arcuate segment. A pair of knurling wheels (60) and (62), with oblique cutting ribs (64) and (66), are pressed into contact with the opposite surfaces (44) and (46) of the carrier to form tiny grooves (52) and (54). The width dimension of each groove is less than a millimetre. Where the brush seal is in an arcuate configuration about an axis, the angle formed between the groove and a radius relative to the axis, is the desired cant angle θ. It will also be appreciated that the oblique cutting ribs form grooves at corresponding cant angles on opposite sides of the carrier. The discrete bristles are wrapped about the carrier and laid into the grooves. Various types of machines are available for wrapping or bending the bristles about the carrier and locating the bristles in the grooves. In Figure 5 the grooves (52) contain multiple bristles (45). The grooves are defined in part by ribs (70) that terminate in tips (72), which project beyond the bristles contained in the grooves. Means are provided for joining together (securing) the bristles and the carrier. For example, the tips of the ribs may be bent over to substantially close
13
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the grooves, locking the bristles from movement within the grooves. To accomplish
this, a pair of smooth rollers (74) and (76) (Figure 4c) are applied to the tips to deform
Figure 7. A similar view to Figure 4a illustrating the fabrication of a brush seal that has a ‘pinchpoint’ inset from the edge of the carrier.
14
them in the same direction, as illustrated in Figure 6. By flattening the tips of the ribs (to at least in part overlie the grooves), the bristles are clamped into the grooves. As shown in Figure 3, an epoxy (78) may be applied over the deformed teeth and bristles in the groove to facilitate retention of the bristles in the grooves. Alternatively, the epoxy may be applied over the entire surface of the carrier, filling in the grooves to retain the bristles, without deforming the rib tips. Referring to Figure 7, the bristle-free radial height of the brush seal can be adjusted by machining a length of flat steps or recessing surfaces of the carrier (42) adjacent to the edge (50) as desired. The carrier (80) includes a pair of inset or recessed face portions or surfaces (82) along opposite sides and adjacent to the edge (50) which will lie opposite the sealing surface. In this way, the bristles are constrained or pinched within the carrier grooves and extend freely from the ‘pinchpoint’ (84) to the tips of the bristles. This bristle-free radial height affects the bristle stiffness and seal flexibility and can be adjusted by machining the surfaces of the carrier, back from the edge (50), to a greater or lesser extent. Patent number: US 6505835 Inventors: W. Tong and Z.-Q. Zhuo Publication date: 14 January 2003
Sealing Technology April 2003