SEALS Control fluid (and/or dust) interchange between two regions with a common boundary Fluid

Transcription

1 SEALS Housing (Stationary) Fluid 1(p 1 ) Fluid 2 (p 2 ) Shaft (rotation or translation or stationary) Control fluid (and/or dust) interchange between two regions with a common boundary Liquid Fluid Gas Static GASKET RELATIVE MOTION CONTACT Dynamic Rotation Translation WITH WITHOUT (Fluid film) Seal Material Metallic Nonmetallic Seal Parameters Speed Pressure (A) Gaskets - Metallic or Nonmetallic seals Key design elements STATIC SEALS Material selection Compression (B) O-rings - Nonmetallic seals IC Engine Gasket (C) Sealants Chemical sealants, Coatings, Mastic DYNAMIC SEALS - Principles Housing p 1 p 2 Shaft With contact Lip seal Contactless Labyrinth Wear ~ p contact velocity Leakage ~ (clearance) 3

2 Low HYDRAULIC SEALS (PISTON SEALS) (RECIPROCATING SHAFTS) Lip Seal High FEATURES Nonmetallic seals Reciprocating seals Contacting seals PROBLEMS Wear Resistance to hydraulic fluids HYDRAULIC SEALS (RECIPROCATING SHAFTS) Pneumatic Rod Seals High Low SCRAPER HYDRAULIC SEALS (RECIPROCATING & ROTATING SHAFTS) O-Ring Seal FEATURES Nonmetallic seals Contacting seals PROBLEMS Wear Resistance to hydraulic fluids Groove dimensions - important

3 Triangular groove Crush static seal HYDRAULIC SEALS STATIC O-Ring Seals Taper Piston type seal (Shaft groove) Radial deformation Face (Flange) static seal Axial deformation Piston type seal (Bore groove) Radial deformation Radial /Rotary Lip Seals ROTATING SHAFT SEALS FEATURES Nonmetallic seals Contacting seals Max. speed 40 m/s Secondary (dust) lip Low High Metallic insert Toroidal spring Sealing lip ROTATING SHAFT SEALS Lip Seals

4 ROTATING SHAFT SEALS RECOMMENDATIONS Lip Seal Instalation Tolerances Surface treatment (Hard chroming) Surface roughness R a <0.8 Engagement taper ROTARY SHAFT SEALS MODERN DYNAMIC SEALS Clearance Seals - Labyrinth Seals (1900) Mechanical Face Seal ( 50) Brush Seal (1988) Axial Finger Seal (1996) High resistance materials Compliant Contacting/ noncontacting Static sealing Radial Finger Seal (1999)

5 CLEARANCE SEALS Single Labyrinth Seal Annular Grooved and Spigotted Labyrinth Thrower and Labyrinth Seal for Vertical Shaft MECHANICAL FACE SEAL spring PUMP rotor Secondary seal(o-ring) stator FACE MECHANICAL FACE SEAL PUMP Multiple helical springs rotor stator Bellow springs

6 MECHANICAL FACE SEAL stator spring Secondary seal(o-ring) rotor FACE Floating rotor Secondary seal (O-ring) Spring Housing po pi Shaft Stator pi F ri po Rotor ri MECHANICAL FACE SEAL Ff ro Fh rh Fe rh ω po ro Floating stator Spring po Stator pi Housing Rotor Shaft Secondary seal (O-ring) F - opening force F h - closing force (hydraulic) F e - elastic closing force ω The pumping screw expels the slurry fluids away from the sealing face.

7 GENESIS Lip seal Brush seal BRUSH SEAL Labyrinth High speed seals Contacting seals ω BRUSH SEAL With contact High compliance allows shaft excursions Static seal Low durability LABYRINTH Non contact Rigid damaged by the contact Important leakage 3 Q h BRUSH SEAL vs. LABYRINTHE? PRO s CON s Low leakage (2-5 times) Static seal High compliance (accept important shaft excursions/eccentricities) Small axial dimension Improved dynamic characteristics Power loss is similar One-directional Low durability High technology More expensive Heavier Few manufacturers No reliable design method PRICE 6$/mm. dia Boeing-Φ1215mm US $ APPLICATIONS Gas turbines Turbo-chargers Turbo-pumps Parameter Now (2000) Future (2010) Velocity 360 m/s 450 m/s Temperature 650 C 820 C Pressure (one stage) 7 bar 10 bar BRUSH SEAL Design parameters 3 5 mm l, d Weld soudure anneau Front anneau Backing aval ring Bristle amont ring Q Backing - jeu anneau gap aval mm 5 15 mm ω fibres Clearance or α Interference ω mm High compliance bristles/mm. of circumference l/d = (7 12 rows of bristles) d= mm bristles

8 RADIAL FINGER SEAL Improvement of brush seal technology AXIAL FINGER SEAL Up stream Down stream h>>hi hi λi he shaft λe Up stream Compensating orifice Compensating chamber Housing Upper finger Lower finger shaft Fig. 2. Cross-section Down stream Seal clearance SEALS - Conclusions Selection from catalogues (no calculation methodology available for end-users) Environmental hazard important selection factor Type of fluid factor for material selection Wear main mode of failure High speed (> 20m/s) CONTACTLESS SEALS Dynamic seals behavior in static conditions Design data Relative speed Pressure differential Type of motion Type of sealed fluid