FIELD OF INVENTION
The present invention relates to a non-metallic brush seals to restrict oil vapor leakage from lubrication oil chambers of Hydro-generators.
BACKGROUND OF THE INVENTION
Leakage of oil vapor from lubrication oil chambers of Hydro-generator is being arrested using conventional nitrile rubber seals. These type of seals require rotor stator seal gap causing oil vapor leakage. Moreover, rotor and seal rub leads to high vibration and sometimes requiring unit shut down for seal adjustment. In the present invention, non-metallic brush seal for Hydro-generators is proposed to replace nitrile rubber seal in Hydro generators. It shall address the problems associated with present seals.
A brush seal consists of closely packed flexible bristles held inside suitably designed holder. The holder is anchored against stator and the free end of the bristles rub against rotor, thus providing sealing effect. Moreover, as the bristles are flexible in nature, it provides compliance during rotor transients thus eliminating high vibration issues associated with existing seal.

Metallic brush seals are used in high speed machines like gas turbine, steam turbine, compressors etc. to stop leakage of high temperature and high pressure process gas. In these seals special type of temperature resistant alloy wire is used to withstand such extreme operating condition.
In case of low speed and near ambient temperature and pressure conditions, as in Hydro-generator, non-metallic brush seals are preferred over metallic brush seals. Different varieties of polymer like Nylon, PPS, PEEK or aramid bristle materials may be used to make non-metallic brush seals. Selection of bristle material depends mainly upon operating temperature and rotor surface velocity. Presently non-metallic brush seals are used commonly for 250°C continuous operating temperature and rotor surface velocity upto 40 m/s. In most of the Hydro-generator applications the operating conditions are well below the above limits.
The working principle of both metallic and non-metallic brush seals are similar. In both the cases bristle are layed at 40°-45° orientation angle to achieve compact design. However, the method of making such seals are many and each are patented. Since the thin bristles need to be arranged in desired angle with maximum compactness, the method of such laying is unique and also critical part for seal performance. Generally, in case of metallic brush seals, bristles are layed on fixtures using special tools and then

holding plates along with bristles are welded at one end and other end is precision cut to provide desired brush seal profile. Non-metallic brush seals are not made using similar technique, because welding and precision cut like WEDM methods require electric conductive bristle materials.
US Patent 5358312 describes a bristle strip made in channel form to receive bristle pack in U-form having a retaining wire running through the closed end of the U-shape. This bristle pack is retained in the carrying channel by crimping of the sides or flanges of the channel. Automatic crimping machine is used for this purpose. Whenever, there is change in brush design parameters like bristle length, width or length the crimping machine requires considerable changes in both hardware and program set ups. Major disadvantage of the methodology is that bristle lay angle 40°- 45°cannot be achieved.
US Patent 0256807 teaches use of non-metallic brush seals in combination with mechanical seal is proposed for arresting the oil vapor from bearing housing of one rotating machine such that oil vapor does not leak to the adjacent another rotating machine. At least one tooth of existing mechanical seal in stator component is machined and provision is made for retrofit assembly of non-metallic brush seal. The bristle materials proposed in the patents are polymer, ceramic, carbon, graphite or Kevlar suitable for temperature range 40°C- 250 °C. Methodology of making non-metallic brush

seals is not disclosed in this patent. Moreover, the approach requires series of activities like dismantling the rotating components from the stationary components, disassembly of bearing housing, machining the tooth of mechanical seals and making provision for non-metallic brush seals, installing the non-metallic brush seal and final assembly. All these activities are to be performed carefully such that no damage is made in the rotating component and after final assembly machine alignment condition is restored. One more drawback of the approach is that sufficient axial distance between edge of non-metallic brush seal and adjacent tooth of the mechanical seal is to be maintained such that during operation bristles are not stuck in the clearance space which is not always possible. Overall, the installation of non-metallic brush seal along with mechanical seal require substantial machine downtime.
US Patent discloses a 0187900A1 methodology of manufacturing non-metallic brush seals using braided ceramic or polymer bristles supported around a thin rod or core. The bristles are folded around the core. U-channel is used to further secure the bristles to the core wire by crimping the channel over the wound bristles. Automatic brush strip manufacturing machines are used for making such seals. In this process, the bristles are oriented at 90° to the strip axis, whereas present practice is to lay the bristles at 40° - 45° inclination angle in the direction of shaft rotation. When the bristles are normal to the rotor surface the bristles buckle rather than bend during operation thereby

increasing the mechanical contact pressure leading to higher bristle wear and lower seal life. To avoid this problem, bristle strip is inclined axially in the direction of fluid flow to facilitate the bristle bending. Flexible front and back plates are incorporated in the design to provide support to bristles against pressure and centrifugal forces. The drawback of the proposed design is bristles are oriented at 90° to the mating surface and then tilted axially towards low pressure zone to provide flexibility to the bristles. This feature makes the design less effective for high pressure application as due to the pressure difference the bristles may blow down towards low pressure side. Flexible front and back plates hold only enclosed portion of bristles but tips are free and may disarray. A separate brush seal housing having rigid front and back plates are required for its fixing purpose. Axial orientation of seal requires additional arrangement in housing design.
US Patent 0210513 A1 teaches non-metallic seals to prevent mixing of bearing oil and process gas/ liquid is proposed in rotary machines like subsea pumps. These pumps are used to handle heavy crude oil, gas or sometimes corrosion prone medium. This embodiment proposes to attach non-metallic brush seal in the stator component such that its free end is allowed to rub against the rotor. The brush seal attachment is such that it becomes a barrier between leaking bearing lubrication oil and process fluid. The bristle materials proposed for making the seals are aramid, carbon fiber, PEEK, or

polymer compatible to the bearing and process fluid. Manufacturing of non-metallic brush seal are not described in the patent.
US Patents 4204629 & 4732339 disclose different bristle winding methods for manufacturing metallic seals are disclosed. All these methods require high end winding mechanism to achieve continuously varying bristle lay angle and compact bristle packing. After winding, all these techniques require bristle joining using welding. Whereas, non-metallic bristles cannot be joined using conventional welding. Therefore, the disclosed methodology cannot be used for manufacturing of non-metallic brush seals and hence not discussed in detail.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a non-metallic brush seals to restrict oil vapor leakage from lubrication oil chambers of Hydro-generators. A further object of invention is to propose a non-metallic brush seals to restrict oil vapor leakage from lubrication oil chambers of Hydro-generators which is adaptable to any shape and size of circular rotors of Hydrogenartors in a cost effective manner.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1: Shows a flowchart of brush seal manufacturing process according to the invention.

Fig.2: Shows a side and top view of a base holder according to the invention.
Fig.3: Shows drilled holes at base holder ID of Fig.2
Fig.4: Shows automatic bristle insertion in base holder according to method of Fig-1.
Fig.5: Shows bristle ID trimming operation according to method of Fig-1.
Fig.6: Shows top view of brush seal assembly according to the invention.
Fig.7: Shows side and top view of brush seal fixing plate according to method of Fig-1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Overall flow chart of the inventive methodology for manufacturing a nonmetallic brush seal is shown in Fig.1. Description of each step is further explained below.
As shown in Fig.2, the non-metallic brush seal assembly in accordance with this invention comprise of plurality of circular base holders (1) in which non-metallic bristles (2) are inserted in holes (12) that are made at angle (11). The holes are oriented at 40 ͦ to 45 ͦ to the tangent to radius at that point and due to this, bristles (2) also get oriented at same angle (11).

Herein the manufacturing process starts with design of base holder (1) as per rotor diameter of Hydro-generator. Base holders (1) could be made using plastic molding or machining process. In this case, base holders (1) are machined from Nylon6 polymer as sector of included angle (9). Base holder (1) design is shown in Fig.3.
As shown in Fig.3, each base holder (1) has inner radius (4) and outer radius (5) producing a particular holder radial thickness. Through holes (3) are made on each base holder (1) at particular PCD (24) for fixing seal in place of existing circular nitrile rubber seal. Base holders (1) are assembled in overlap design (10) one by one through the fixing holes (3) to make an entire seal. This overlap design feature (10) incorporated to avoid discontinuity in bristle laying at joining face of base holders (23). Due to this overlap design feature (10), two different layers of bristle packs of equal thickness is produced. One individual brush seal holder (2) has total included angle (8) and each layer has equal angle (9) on that sector.
After manufacturing of base holders (1) cores for bristle insertion are made through drilling holes (12) at inner face (4) of each base holder (1) and has a uniform depth of core diameter (14). Drilled holes (12) are shown in Fig. 4. These tiny holes (12) are drilled using automatic marking and drilling machine. Direction of rotor rotation (7) is shown in Fig.2 and the holes (12) are drilled such that after bristle insertion the free end

of bristles are oriented towards the direction of rotor rotation (7). Moreover, holes (12) are made as closely as possible such that inter hole distances (15) in both horizontal and vertical directions are as minimum as possible. Additionally, holes are made in Zig-zag fashion (13) such that after bristle (2) insertion compact bristle pack is achieved. Across the total base holder height, holes (12) are made over the length (17) leaving the edges (16) in both sides.
Refer Fig. 5 for the bristle insertion process (20). Bristle insertion in base holder (1) is carried out using available automatic tufting machines. In this process, plurality of bristles (2) are folded around a tiny metal staple (18) and the folded end of the bristles, along with metal staple (18) are inserted inside holes (12) using the bristle insertion process (20). All the holes (12) of base holders (1) are filled in controlled manner, and thus an entire tufted base holder sector is made.
Uncut free edge of inserted bristles (19) have unevenness that may cause oil vapor leakage. To remove this unevenness, bristles (2) are cut at the edge (19) using circular trimming machine (22) to length (21) as per required brush seal size (6). Bristle trimming operation is shown in Fig.6.
Plurality of base holders (1) made as per methodology disclosed above, are secured using fixing holes (3) at the same envelope of nitrile seals, as a retrofit replacement. At the top of the brush holders (1), plurality of fixing plates (25) as shown

in Fig.7 are assembled using through holes (27) located at the PCD (24). However, after assembly, radial width (26) of fixing metal plate (25) is maintained smaller than cumulative width of brush holder including bristle cut length (21). This ensures in extreme machine vibration the fixing plate (25) does not come in touch with rotor component. The fixing plates (25) enclose the brush seal assembly and its exposure to the environment is avoided. Thus, an entire non-metallic brush seal assembly of circular profile, suitable for Hydro-generator rotor is obtained. Refer Fig. 2 for the entire brush seal assembly prior to fixing plate (25) assembly.

WE CLAIM
1. A non-metallic brush seals to restrict oil vapor leakage from lubrication oil
chambers of Hydro-generators comprising:
- A plurality of base holders (1) having each an inner face (4) and
corresponding dimensions of that of the circular rotor, the base holders (1)
disposed on the rotor at an angle (8)
- A plurality of holes(12) drilled on the inner faces (4) of base holders (1)
- A plurality of bristles (2) inserted using automatic tufting process (20) into said drilled holes (12) located at base holder inner face (4),
- A matching number of metal staples (18) provided to secure the bristles (2) inside the drilled holes(12).
- A cutter (22) adapted to conduct a circular ID trimming operation at free edge (19) of the inserted bristles to obtain brush seal of required size (6), wherein:
- the individual base holders (1) containing the bristles cut to a desired length (21) after the ID trimming operation and assembled in machine using fixing holes (3) in circular manner and thus an entire seal is obtained.
2. The nonmetallic brush seal as claimed in claim 1, wherein the base holder (1)
comprises:
- materials selected from Nylon6 or equivalent polymer;
- Shape of base holder is circular having internal diameter (4) and external diameter (5) matching with that of the circular rotor;

- total included angle (8) with two bristle pack layers of equal angle (9);
- closely packed drilled holes (12) at inner face (4) wherein drilling is made in jig-jag (13) orientation;
- holes (12) drilled at 40°-45° inclination angle (11) such that after bristle insertion its free end gets aligned with the direction of rotor rotation; and
- consisting of a plurality of fixing holes (3) for assembly purpose with an overlapping
- joining (10) arrangement to avoid discontinuity in the bristle pack

3. The nonmetallic brush seal as claimed in claim 1, comprising a plurality of fixing plates (25) forming a circular angular sector.
4. A method of manufacturing a non-metallic brush seal to restrict oil vapour leakage from lubrication oil chambers of hydrogenerators as claimed in claim 1 and as herein described.
Dated the 11th day of JANUARY, 2017.

(P.D.GUPTA) OF L.S.DAVAR & CO APPLICANTS’ AGENT