| name | lip-seal |
| description | Lip seal (radial shaft seal) design — RWSSD selection, shaft speed limits, lip contact pressure, housing/shaft tolerances, materials (NBR/FKM/PTFE), failure modes. |
| metadata | {"priority":7,"promptSignals":{"phrases":["lip seal","radial shaft seal","rotary shaft seal","oil seal","shaft seal"],"minScore":3}} |
Lip Seal (Radial Shaft Seal) — Complete Skill
Types
- Standard (RWSSD / 12-type): single lip, spring-loaded, excludes air side
- Double lip: secondary lip excludes contamination from outside
- With dust lip: primary seal + axial wiper lip
- PTFE lip: contact-free or light contact; highest speed capability
- V-ring (axial lip): slips onto shaft; no housing bore required
- Labyrinth seal: non-contacting; for high speed / low pressure
Shaft Speed Limits
Surface speed v = π d n / 60,000 [m/s; d in mm, n in rpm]
| Lip material | Max v [m/s] | Temp range | Notes |
|---|
| NBR (nitrile) | 4–6 | −40 to +100°C | Most common; mineral oils |
| FKM (Viton) | 6–10 | −20 to +180°C | Petroleum, solvents |
| ACM | 4–8 | −25 to +150°C | High-temp oil |
| PTFE (lip) | 8–18 | −200 to +200°C | Wide range; low friction |
| HNBR | 6–10 | −40 to +150°C | Zinc, refrigerants |
Typical surface speed limit (NBR, standard): 4–5 m/s
Above limit: seal overheats → lip hardens → leakage increases
Shaft Tolerances
Shaft surface finish critical for seal life:
Ra = 0.2–0.8 μm (lead-free ground finish; no spiral marks)
Hardness: HRC ≥ 45 (carburized/induction hardened) for abrasive conditions
Shaft tolerance: h11 or h8 (ISO) — check seal manufacturer spec
Shaft eccentricity and runout:
TIR (Total Indicated Runout) ≤ 0.05 mm for v < 4 m/s
TIR ≤ 0.025 mm for v > 4 m/s
Eccentricity causes dynamic loading on lip → accelerated wear
Housing Bore Tolerances
Housing bore: H8 tolerance standard
Interference of OD: 0.2–0.5 mm (press-in fit)
Surface finish of bore: Ra ≤ 3.2 μm
Housing material: steel or cast iron (stiffer retention); aluminum requires care (thermal expansion)
Lip Contact Pressure
Spring-loaded lip maintains radial contact force:
Radial lip load: F_rad = π × d × k × δ_spring [N]
k = garter spring rate (from manufacturer)
Typical contact pressure: 0.05–0.15 N/mm (linear)
High contact pressure → high friction → overheating
Low contact pressure → leakage, poor sealing
Lubrication of Lip
Oil side: wetted lip = self-lubricated; fill with grease before assembly if dry
Dry side: pre-fill lip cavity with grease (e.g., NLGI 2) at installation
Air-side lip: dry running; limit to low-duty applications
Pressure Rating
Standard lip seal: rated for 0.5 bar (50 kPa) pressure differential maximum
Above 0.5 bar: use PTFE lip design, mechanical seal, or labyrinth
Higher pressure requires back-up ring or pressure-rated design
Installation
- Check shaft for burrs, chamfer 15° at installation lead
- Apply oil or grease to lip before assembly
- Press housing OD squarely (avoid cocking); use installation tool matching OD
- Never drive lip seal with hammer directly on seal face
Common Failure Modes
| Failure | Appearance | Cause |
|---|
| Lip hardening | Cracked/brittle lip | Heat, wrong material, ozone |
| Lip wear | Groove on shaft | Abrasion, contamination |
| Lip eversion | Lip turned wrong way | Installation error, pressure |
| Spring loss | No contact, leaks | Corrosion, over-speed, vibration |
| Housing leak | Oil at OD | Insufficient press fit, bore oversize |
Selection Procedure
- Determine shaft diameter d [mm], speed n [rpm] → v_surface [m/s]
- Identify fluid sealed (oil, water, solvent), temperature range
- Select lip material from table
- Check v_surface vs. material limit; add dust lip if contamination present
- Specify shaft tolerance (h11 recommended) and surface roughness (Ra 0.2–0.8 μm)
- Specify housing bore (H8), check retention
- Pre-fill with grease if dry-side is air
Output
Provide: seal designation (e.g., 35×62×10 NBR), lip material, max surface speed [m/s] vs. actual, shaft tolerance, housing bore tolerance, pressure rating, installation instructions.
