Property | Ceramic | Graphite | NBR Rubber |
Hardness | HV 1500-2000 (Mohs 9) | HB 50-80 (self-lubricating) | Shore A 70-90 |
Max Temp(℃) | 1500 (oxidizing) | 450 (air) / 3000 (vacuum) | -40~120 (peak 150) |
Friction Coeff | 0.1-0.3 (lubricated) | 0.08-0.15 | 0.3-0.6 (dry) |
Chemical Res | All chemicals (except HF) | Strong acids/solvents | Oil/water (fails in ketones) |
Compression Rate | 0% (rigid) | 5-15% | 15-30% |
Applications | High-speed pumps, rockets | High-temp reactors | Automotive pumps, food machinery |
Failure Mode | Brittle fracture | Oxidation (>400℃ air) | Swelling/cracking |
Technical Insights
1. Ceramic Seals (Al₂O₃/SiC)
Pros:
Extreme wear resistance (5x life in sand)
Zero leakage (flatness ≤0.3μm)
Cons:
Thermal shock failure (ΔT>200℃/min)
Demands precision installation
Solutions:
SiC-tungsten composite:Impact resistance ↑300%
Bellows compensation:Absorb misalignment
2. Graphite Seals
Key Features:
Self-healing surface (tolerates Ra≤1.6μm)
Electrical conductivity (5-30μΩ·m)
Enhanced Types:
Resin-impregnated:Phenolic (acid-proof) / Furan (alkali-proof)
Carbon-fiber reinforced:Compressive strength →120MPa
Avoid:
Fuming HNO₃ / liquid oxygen
High-speed rotation (>30m/s)
3. NBR Seals
Advantages:
Elastic sealing (compensates ±0.5mm vibration)
Low cost (1/50 of ceramic)
Chemical Limits:
Max swelling:
Gasoline: ≤15% vol. expansion (>20% fails)
Benzene solvents: Prohibited
Ozone cracking:>0.1ppm in air
Upgrades:
HNBR:Temp→150℃ / ozone resistance ↑10x
PTFE coating:Friction coeff. →0.05