FIELD OF INVENTION
The present invention relates to a method of manufacturing Non-Metallic brush seals for Hydro-generators using laser fusion technique and the Non-metallic brush seal. More particularly, the invention relates to use of non-metallic brush seals to stop the oil vapor leakage from lubrication oil chambers of hydro-generators.
BACKGROUND OF 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 and maximum sealing effect. 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 seal density, 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 circular profile. Non-metallic brush seals are not made using similar technique, because welding and precision cut like WEDM methods require electric conductive bristle materials.
In this invention a method is disclosed to achieve desired bristle lay angle, bristle holding technique with improved seal density.
Few of the earlier patented methodology and its disadvantages are discussed below.
In the US Patent 5358312 bristle strip is made in channel form and receives 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.
In the US Patent 0256807 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 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 radial 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.
In the US Patent 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 radially 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 radially 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. Radial orientation of seal requires additional arrangement in housing design.
In the US Patent 0210513 A1 use of 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 seals are not described in the patent.
In the US Patent 4204629 & 4732339 different bristle winding methods for manufacturing metallic seals are disclosed. All these methods require special tools for winding 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.
In the earlier applied patent “201731001146” on “A non-metallic brush seal to restrict oil vapor leakage from lubrication oil chambers of Hydro-generators” by the present authors, a methodology was disclosed for making of non-metallic brush seals. In the proposed method circular brush holders are made with having tiny holes at 40°- 45° angle at inner surface and then bristles of required length are inserted inside those holes. Bristles are folded against tiny metal staple and inserted inside the holes using automatic bristle insertion machine to achieve brush seal. However, as gaps are to be maintained between the holes in both horizontal and vertical directions to secure metal staple inside the holes, maximum seal density in the bristle lay cannot be achieved. Therefore, the non-metallic brush seals manufactured using this methodology cannot be used in high pressure applications. In order to achieve further seal density and continuity in bristle lay, use of laser fusion for bonding the bristles in the base holder is disclosed in the present invention.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a method of manufacturing Non-Metallic brush seals for Hydro-generators using laser fusion technique and the Non-metallic brush seal of any shape and size required for Hydrogenerators.
SUMMARY OF THE INVENTION
In this invention, brush seal is made using multiple base holders (9) machined to a circular sector (25) and radial slots (31) when the edges of the base sector (9) are made at an angle (15 & 33) of 45o to the tangent of radius at the point. The base holders are designed with two or multiple layer configuration of equal included angles (26) such that after assembly of brush seal, overlap design feature (32) is achieved. The base holder (9) is inserted inside holding box(6) having inner profile (8) to facilitate bristle (11) insertion.
The base holder (9), metal box (6) and connecting links (2) are assembled using fixing holes (5, 7) to form a circular fixture to facilitate bristle insertion and laser fusion in circular manner. Plurality of bristles (11) are inserted inside the slot (31) of base holder (9) and then oriented against the inclined inner

edge of slot (29) using bristle guide plate (34). The holding box inner design feature (8) prevents bristle to fall through the slots (31) of base holder (9) and then oriented against the inclined inner edge of slot (29) using bristle guide plate (34). The holding box inner design feature (8) prevents bristle to fall through the slots (31) of base holder (9). The guiding plate (34) is made with a particular angle (39) to facilitate 450 angular orientation of bristles inside the slot (31) of base holder (9). Laser fusion among inserted bristles (11) and base holder (9) at outer periphery (13) of base holder is taken up under controlled environment through traverse of laser head (40) in circumferential (41) and radial (42) directions at optimum speed and power rating. This is repeated for each layer separately. After laser fusion, the base holder (9) along with fused bristles (11) are removed from box holder (6). Circular Internal diameter (ID) trimming operation is then taken up using cutter (45) at free edge (44) of fused bristles to obtain brush seal of required size. After ID trimming operation, individual brush holder (9) fused with finish cut bristles (10) are assembled and covered using fixing plates (47) through slots (16) and ribs (54) and thus an entire brush seal assembly is obtained.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig.1: Shows flowchart of brush seal manufacturing process.

Fig.2: Shows front and side view of base holder.
Fig.3: Shows front and sectional view of holding box.
Fig.4: Shows side and front view of fixture for laser fusion.
Fig.5: Shows front and top view of bristle guide plate.
Fig.6: Shows laser fusion process and sectional view of bristle joining.
Fig.7: Shows zoomed in cross sectional view of bristle joining with brush
holder.
Fig.8: Shows ID trimming operation of fused bristles.
Fig.9: Shows brush seal assembly.
Fig.10: Shows brush seal fixing metal plate.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
Overall flowchart of non-metallic brush seal manufacturing process using laser fusion technique is shown in Fig.1. The non-metallic brush seal in accordance with this invention comprises of plurality of base holders (9) in which non-metallic bristles (11) are inserted in slots that are made at an angle (33). The slots are oriented at 40° to 45° angle to the tangent to the radius at that point. The bristles are oriented inside the slots using guide plate (34) and then laser fusion is taken up between bristles (11) and base holder (9). The laser fusion is carried out under a controlled environment.
Herein, the manufacturing process starts with the design of holder (9) as per the rotor diameter of the Hydro-generator. Base holders (9) could be made using plastic molding or machining process. In the present invention, the base holders are machined from Nylon 6 material as a circular sector (23).
As shown in Fig.2, each base holder (9) has inner diameter (12) of 770 mm and outer diameter (13) of 820 mm and may vary as per Hydro-generator rotor diameter producing a particular holder radial thickness (17) and circular profile (23). The base holder has particular included angle (25) of 45o with two

layers (31) and overlap design feature (32) which produce slot edges (29 & 30). The slot edges (29 & 30) of each layer is made at a particular angle (15 & 33). Individual layers are made at equal included angles (26) of 40o producing slot length (27) and slot width (28).
The fixing of the base holders (9) during assembly is achieved by suitable slots (16) with the mating plate ribs (54). As shown in Fig.3 holding box (6) with holes (7) are made with particular outer diameter (21) and inner diameter (22). The holding box (6) is made at particular angle (55) with an inner profile (8) and inner angle (56) to facilitate base holder (9) insertion inside it. The box holder inner profile (8) is machined with interference as compared to outer profile of base holder (9) to achieve press fit insertion. The cross section of the box holder (6) shows the base holder (9) is accommodated within radial thickness (20) while radial height (19) aligned with the base holder slots (31) facilitate bristle insertion. Similarly, base holder width (14) is accommodated inside the box width (17) producing the space for bristle effective height (18) aligned with the slots (31).
As shown in Fig.4 holding box (6) is attached to base ring (1) using fixing holes (7, 5) and connecting links (2). The circular base ring is designed with particular OD (3) and ID (4). Entire assembly is held to chuck of laser bed using

base ring (1). Bristles are cut to length from a hunk using special cutter and then the bristle bunch is inserted into the base holder slots (31). The bristle orientation angle is achieved by using bristle guide plate (34). At its initial position, guide plate (34) is held against the slot edge (29) and then moved along the arrow direction shown in Fig.4. Manual or semi-automatic mechanism can be adopted for movement of the bristle guide plate inside the slot (31). Holding box (6) is designed with particular inner sector angle (56) and outer sector angle (55) as shown in Fig.3 to facilitate insertion of base holder (9) and laser fusion at its circumference.
Refer Fig.5 for the details of bristle guide plate (34). The bottom surface of the head (35) is machined to a particular radius (36) such that it matches with the outer surface of base holder (9). The guide plate is inclined at 45° angle (39) for orientation of bristles. The bottom edge of guide plate (34) is also machined at particular radius (37). The plate width (38) is made to facilitate entry of guide plate (34) inside the base holder slot (31).
The laser fusion process is shown in Fig.6 wherein laser head (40) traverse in both circumferential (41) and radial (42) directions at an optimized speed in circumferential direction (41) as 2.4 mm/sec and in radial direction (42)

as 2.4 mm/sec and laser power rating of 500 watt under controlled environment such that proper laser fusion among bristles (11) and base holder (9) takes place, as shown in Fig.8.
Fig.7 shows the closer view of the laser fusion operation between base holder (9) and bristles (11) through generation of melted joining face (43) due to controlled heat input. After laser fusion operation, the sector (9) is taken out from the holding box (6). The uncut free edge (44) of the inserted bristles (11) may have unevenness that may cause oil vapor leakage. To remove this unevenness, bristles (11) are cut at the free edge (44) using circular trimming machine (45) to the desired length (10) as per required brush size. The bristle trimming operation is shown in Fig.8.
Plurality of base holders (9) made as per methodology disclosed above, are secured using slots (16) and ribs (54) of metal fixing plates (34) at the same envelope of nitrile seals as a retrofit replacement. During assembly of brush seal, the bristles (10) are oriented towards direction of rotation of rotor (24).
Fixing plate details shown in Fig.10. It consists of particular OD (51) and ID (52) and fixing holes (49) made at PCD (46) for fixing the plate with the machine enclosure. On the other side, the base holders are held to plates (47)

through slots (16) and mating ribs (54). The outer profile (50) of rib (54) is such that it can be inserted inside the slots (16) of base holder (9) by press fit and does not allow movement of the brush assembly during machine operation. Fixing plate radial width (48) is maintained smaller than the cumulative width (14) of brush holder (9). This ensures, in extreme machine vibration the fixing plates (47) does not come in contact with the rotor component. The fixing plates (47) enclose brush seal assembly and its exposure to the environment is avoided. After assembly of the plates (47) a joining face (53) between two plates is formed. Thus an entire brush seal assembly of circular profile suitable for Hydro-generator rotor is obtained. Refer Fig.9 for entire brush seal assembly along with fixing plates (47).
Advantages
1. Improved seal density
2. Lower oil vapor leakage
3. Lower maintenance
4. Longer seal life
5. Eliminates seal rub related issues
6. In case of any local seal damage, change of damaged sector alone, without removing the entire seal which makes seal repair cost very low

WE CLAIM
1. A method of manufacturing Non-Metallic brush seals for Hydro-generators using laser fusion technique, the said method comprising the steps of;
machining nylon 6 materials to a circular sector (23) of particular angle (25) of 45o to make base holders (9) in plurality as per rotor size;
making through slots (31) on base holder (9) with multiple layer configuration with edges of base holder (9) made at 450 to the tangent of the radius at that point;
making each slot (31) of base holder (9) at equal particular angle (26) of 40o achieve overlap design feature after assembly of brush seal;
making a holding box (6) with holes (7) and particular outer diameter (21) and inner diameter (22) and at particular angle (55) with an inner profile (8) and inner angle (56) to facilitate press fit insertion of base holder (9);
inserting the base holder (9) inside holding box (6);
inserting plurality of bristle (11) inside the slot (31) of base holder (9) orienting against the inclined inner edge of slot (29) using bristle guide plate (34) disposing the bristles to a 450 angular orientation inside the slot (31), the inner design (8) of holding box (6) preventing bristle to fall through the slots (31) of base holder (9); wherein,

after orientation of bristles (11) inside slots (31) of base holder, laser fusion between bristles (11) and base holder (9) at outer periphery (13) of base holder is taken up under controller environment through traverse of laser head (40) in circumferential (41) and radial (42) directions at optimum speed of 2.4 mm/sec and power rating of 500 watt, creating proper fusion among bristle (11) and base holder (9), when after laser fusion, the base holder (9) along with fused bristles (11) are removed from box holder (6), wherein circular internal diameter trimming operation with a cutter (45) is carried out at the free edge (44) of fused bristles to remove unevenness at the free edge obtaining brush seal of required size, wherein individual brush holders (9) containing the bristles cut to length (10) are assembled in machine using fixing plates (47) and slots (16) of base holders and ribs (54) of fixing plates in circular manner to obtain an entire seal.
2. The non-metallic brush seal manufactured by the method claimed in claim 1, comprising;
a plurality of base holders (9) having non-metallic bristles (11) inserted in slots made at an angle (33), the said slots oriented at 400 to 450 angle to the tangent to the radius at that point, the said bristles oriented inside the slots (31) using guide plate (34) inclined at an angle of 45o (39);

Characterized in that,
laser fusion between bristles (11) and base holder (9) under controlled environment resulting fused bristles in the base holder (9) wherein the said bristles being cut to length (10) and assembled in machine using fixing plates (47), using slots of base holder (9) and rib (54) of fixing plates in circular manner to obtain an entire non-metallic brush seal.