Chemical resistance for Teflon encapsulated O-rings is evaluated through standardized testing methods and material compatibility charts, typically rated on a scale from 1 (poor) to 10 (excellent). These seal teflon o ring combine an elastomer core with a Teflon (FEP or PFA) sheath, offering exceptional resistance to most aggressive chemicals except specific exceptions like hydrofluoric acid or molten alkali metals. Performance is influenced by temperature thresholds (200°C for FEP, 260°C for PFA) and mechanical stress factors.
Key Points Explained:
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Rating Scale for Chemical Resistance
- Measured on a 1–10 scale, where 10 indicates no degradation or swelling after prolonged exposure.
- Ratings are derived from ASTM or ISO standardized immersion tests, where samples are exposed to chemicals under controlled conditions (time, temperature, concentration).
- Example: A rating of 8–10 for sulfuric acid indicates minimal impact, while a rating of 1–3 for hydrofluoric acid signals incompatibility.
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Materials Used in Encapsulation
- FEP (Fluorinated Ethylene Propylene): Resistant up to 200°C; ideal for acids, bases, and solvents.
- PFA (Perfluoroalkoxy): Higher thermal stability (260°C) and better stress crack resistance.
- Both materials provide non-reactivity but differ in temperature thresholds and cost (PFA is more expensive).
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Chemical Compatibility Testing Methods
- Immersion Testing: O-rings are submerged in chemicals for 24–1,000 hours, then evaluated for weight change, swelling, or hardness loss.
- Permeation Testing: Measures chemical diffusion through the Teflon layer using mass spectrometry or gas chromatography.
- Mechanical Stress Tests: Assess performance under compression or dynamic movement post-exposure.
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Common Chemical Exceptions
- Hydrofluoric Acid (HF): Attacks the silicon dioxide layer in Teflon, causing rapid degradation.
- Molten Alkali Metals (e.g., Sodium): React violently with fluoropolymers.
- Strong Fluorinating Agents (e.g., Elemental Fluorine): Break C-F bonds at high pressures/temperatures.
- Ketones/Amines: Acetone or dimethylamine may cause swelling or reduced elasticity.
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Environmental and Operational Limits
- Temperature: FEP fails above 200°C; PFA withstands up to 260°C.
- Mechanical Stress: Abrasion or compression in corrosive environments accelerates wear.
- UV Exposure: Prolonged sunlight can degrade some Teflon formulations.
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Design Advantages
- Combines elastomer elasticity (e.g., silicone core) with Teflon’s chemical inertness.
- Ideal for pharmaceutical, semiconductor, or chemical processing equipment where purity and resistance are critical.
By understanding these factors, purchasers can select O-rings tailored to specific chemical exposures, ensuring longevity and safety in harsh environments.
Summary Table:
| Factor | Details |
|---|---|
| Rating Scale | 1 (poor) to 10 (excellent); based on ASTM/ISO immersion tests. |
| Materials | FEP (200°C) or PFA (260°C); PFA offers higher thermal stability. |
| Testing Methods | Immersion, permeation, and mechanical stress tests. |
| Common Exceptions | Hydrofluoric acid, molten alkali metals, strong fluorinating agents. |
| Operational Limits | Temperature thresholds, mechanical stress, UV exposure. |
| Design Advantages | Combines elastomer elasticity with Teflon’s chemical inertness. |
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