PTFE rotary shaft seals come in various grades, each tailored for specific performance requirements. Virgin PTFE is ideal for low-duty applications, while filled PTFE grades (glass, MoS2, carbon, or combinations) enhance strength, wear resistance, and temperature tolerance. These seals excel in extreme conditions, offering chemical inertness, low friction, and durability under high pressures (35+ BAR) and speeds (up to 35 m/s). Configurations include hydrodynamic, plain, and multi-lip designs, with options for machined or pressed shells based on production volume. The choice of grade depends on factors like speed, load, temperature, and chemical exposure, ensuring optimal sealing performance across industries.
Key Points Explained:
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Virgin PTFE
- Application: Slow, low-duty environments where minimal wear and friction are primary concerns.
- Properties: Pure PTFE with no fillers, offering baseline chemical resistance and non-stick qualities.
- Limitations: Lower mechanical strength compared to filled grades, making it unsuitable for high-load or high-speed applications.
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Glass-Filled PTFE
- Purpose: Enhanced strength and wear resistance for moderate-duty applications.
- Advantages: Glass fibers improve dimensional stability and reduce cold flow, ideal for rotary seals in abrasive environments.
- Trade-off: Slightly higher friction than virgin PTFE, but still lower than many elastomers.
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Glass + MoS2-Filled PTFE
- Unique Benefit: Combines glass reinforcement with molybdenum disulfide (MoS2) for wear resistance without abrasiveness to mating surfaces.
- Use Case: Suitable for dry-running or poorly lubricated conditions where traditional fillers might cause shaft wear.
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MoS2-Filled PTFE
- Performance: Excels in higher-duty applications due to MoS2’s self-lubricating properties.
- Temperature Range: Maintains performance at elevated temperatures (up to 260°C/500°F), making it ideal for industrial machinery.
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Carbon-Filled PTFE
- Key Feature: Provides wear resistance without increasing friction, critical for high-speed rotary seals.
- Chemical Compatibility: Resists most chemicals, though not recommended for strong oxidizers.
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Carbon + MoS2-Filled PTFE
- Hybrid Advantage: Balances wear resistance, high-temperature performance, and dry-running capabilities.
- Applications: Aerospace, automotive, and heavy machinery where seals face extreme conditions.
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Design Flexibility
- Configurations: Hydrodynamic seals for high speeds (via fluid film generation), plain seals for static/low-speed use, and multi-lip designs for redundant sealing.
- Customization: Custom PTFE parts can be machined for low volumes or pressed for cost-effective mass production.
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Operational Limits
- Pressure/Temperature: Withstands >35 BAR and -200°C to +260°C (-328°F to +500°F), outperforming many elastomeric seals.
- Speed: Up to 35 m/s, with optional hydrodynamic features to prevent lip overheating.
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Selection Criteria
- Environment: Match filler type to chemical exposure (e.g., carbon for acids, glass for alkalis).
- Load/Speed: Higher loads demand filled grades; speeds >10 m/s may require hydrodynamic designs.
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Economic Considerations
- Production Volume: Machined seals avoid tooling costs for prototypes/small batches; pressed shells reduce per-unit costs for large orders.
By understanding these grades and their trade-offs, purchasers can specify seals that optimize performance, longevity, and cost for their specific application.
Summary Table:
| PTFE Grade | Key Properties | Best Applications |
|---|---|---|
| Virgin PTFE | Pure, chemical-resistant, low friction | Low-duty, slow-speed environments |
| Glass-Filled PTFE | Enhanced strength, wear resistance | Moderate-duty, abrasive environments |
| Glass + MoS2-Filled | Wear resistance, non-abrasive to shafts | Dry-running or poorly lubricated conditions |
| MoS2-Filled PTFE | Self-lubricating, high-temperature tolerance | Industrial machinery, high-duty applications |
| Carbon-Filled PTFE | Wear resistance, low friction | High-speed rotary seals |
| Carbon + MoS2-Filled | Balanced wear, temperature, dry-running | Aerospace, automotive, heavy machinery |
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