FKM is the benchmark elastomer for aggressive service. It resists mineral oils, fuels, hydraulic fluids, acids and aliphatic hydrocarbons at temperatures to 230 °C, and holds compression set better than any other rubber we mould. When a seal has to keep working in hot oil for years without being touched, FKM is the default answer — and the engineering question becomes which cure system and which filler.
Typical values for standard moulding grades. Exact figures depend on the specific compound or grade — confirm against your drawing before quoting.
Key properties
| プロパティ | Typical value |
|---|---|
| Hardness range | 60 – 90 Shore A |
| Service temperature | -20 to +230 °C (+250 °C short term) |
| Tensile strength | 8 – 15 MPa |
| Elongation at break | 150 – 300 % |
| Compression set (22 h / 200 °C) | 10 – 25 % |
| Fluid resistance | Excellent in oils, fuels, hydraulic fluids |
Values are typical for unfilled moulding grades at 23 °C unless stated. Glass-filled and specialty grades differ.
Typical applications
- O-rings and shaft seals in engines and gearboxes
- Hydraulic and pneumatic system seals
- Chemical process valve and pump seals
- Automotive fuel system and injector seals
- Oilfield and downhole sealing elements
Processing notes
- FKM stiffens below about -20 °C. If the seal must work cold, specify a low-temperature grade or move to FVMQ.
- FKM is attacked by ketones, esters, amines and hot anhydrous ammonia. Confirm the media before specifying — this is where FKM failures originate.
- Compression set is FKM's strength. Specify the post-cure schedule; skipping it costs 10 to 15 points of set resistance.
- High-hardness grades above 85 Shore A are difficult to demould and prone to tearing at the parting line.
Frequently asked questions
Is FKM the same as Viton?
Viton is a brand of FKM, not a separate material family. We specify to the ASTM D2000 or ISO 1629 designation (FKM) plus the hardness and any special requirement, so the compound is defined by properties rather than by brand.
Which FKM grade for a steam application?
Standard FKM is poor in steam. For steam service we specify a peroxide-cured or a specialty grade, and above about 150 °C saturated steam we would normally recommend EPDM instead.
Related materials
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