Chemical resistant elastomer. Fuel compatible. 230 °C service.
Viton (FKM fluoroelastomer) combines rubber flexibility with chemical resistance approaching PTFE. Handles fuels, oils, aggressive chemicals, 230 °C continuous service. Standard seal material for automotive, aerospace, oil and gas, chemical processing.
At a glance
- Density
- 1.85 g/cc
- Tensile strength
- 12 MPa
- Elongation
- 200%
- Hardness
- 75 Shore A
- Temperature range
- -20 to +230 °C
- Compression set
- 15% @ 22h/200°C
- Ozone resistance
- Excellent
- Fuel compatibility
- Excellent
Key data
- Density
- 1.85 g/cc
- Tensile strength
- 12 MPa
- Elongation
- 200%
- Hardness
- 75 Shore A
- Temperature range
- -20 to +230 °C
- Compression set
- 15% @ 22h/200°C
- Ozone resistance
- Excellent
- Fuel compatibility
- Excellent
FKM grades.
FKM Type A
Dipolymer (VDF + HFP). 66% fluorine. Standard Viton A grade — most common. Good chemical and temperature balance.
FKM Type B
VDF + HFP + TFE. 68% fluorine. Better chemical resistance than Type A. For aggressive applications.
FKM Type F
Higher fluorine content (70%+). Best chemical resistance. For very aggressive media.
FKM GLT
Extended low-temperature capability to -40 °C. Slightly reduced chemical resistance.
FFKM
Kalrez, Chemraz family. 73%+ fluorine. Essentially chemical inert — handles anything short of molten alkalis. Premium cost.
FEPM
Fluorocarbon-base resistant grade. Better resistance to amines and caustic environments than standard FKM.
Different fluorine content and crosslinking chemistry produces different property balances. Standard A-type for general, specialty G/GLT for low-temperature, FFKM for extreme chemistry.
Why FKM.
Fuel and oil resistant
Standard for automotive fuel system seals — doesn't swell or degrade in gasoline, diesel, synthetic fuels.
230 °C continuous service
Among the highest-temperature elastomers. Handles under-hood automotive, chemical processing, aerospace hot section seals.
Aggressive chemicals
Resists most acids, alkalis, solvents. Exceptions: amines, some ethers, very polar solvents (choose FEPM for base-heavy).
Long service life
15-20 year service life in typical applications. Oxygen-aging resistance, ozone resistance excellent.
FKM dominates chemical-resistant elastomer applications. Few materials handle the same combination of chemistry, temperature, and flexibility.
FKM applications.
Automotive fuel seals
Fuel injector O-rings, fuel pump seals, fuel rail seals
Engine seals
Crankshaft seals, valve stem seals, cam shaft seals in hot engine environments
Aerospace fluid seals
Aircraft fuel system, hydraulic system, lubrication system seals
Chemical processing
Pump seals, valve seals, processing equipment gaskets for aggressive chemistry
Oil & gas
Wellhead seals, downhole tool seals in sour service (sour-grade FKM)
Semiconductor
Vacuum chamber seals where aggressive etch chemistry is used
Pharmaceutical
Process equipment seals for pharmaceutical manufacturing
Power generation
Gas turbine seals, steam system seals, refinery equipment
Rocket propulsion
Propellant system seals where extreme chemistry + temperature combined
FKM processing.
Compression molded
Primary process for larger parts. Cured rubber pressed in heated mold.
Transfer molded
Mid-volume process — compound transferred into cavity during cure cycle.
Injection molded
High-volume production of small complex parts — fastest cycle time, best precision.
Post-cured
Secondary cure at 200 °C for 24 hours removes volatiles, improves properties.
O-ring standard
Stock standard O-ring sizes per AS568 and BS-2951 available immediately.
Custom geometry
Custom geometry via mold tooling. Tool cost typically $3,000-15,000 for small-medium parts.
Colored
Black is standard. Custom colors (brown, green, violet for FFKM) for specific applications.
Secondary machining
Limited — molded to shape preferred. Machining FKM generates dust, rough edges.
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Chemical resistant elastomer — questions
Viton vs Buna-N (NBR) for fuel seals?
Buna-N (nitrile): cheap, good fuel/oil resistance at moderate temperature, -40 to +120 °C service. Standard for consumer automotive fuel. Viton (FKM): premium cost, better resistance to aggressive fuels (E85 ethanol, biodiesel, ultra-low sulfur diesel), higher temperature (230 °C), better fuel-aging. For modern automotive with biofuels or under-hood elevated temperature: FKM. For basic fuel systems at moderate temperature: NBR. Automotive is transitioning FKM for mandatory standards.
FFKM (Kalrez) vs FKM — when justified?
FFKM (perfluoroelastomer — Kalrez, Chemraz): $200-500 per small O-ring. FKM: $1-10. Justify FFKM when: (1) aggressive chemistry FKM can't handle (amines, specific solvents, concentrated oxidizers), (2) high-purity semiconductor applications, (3) maximum chemical certainty for critical sealing. For most applications, FKM is adequate. FFKM is specialty premium material.
Temperature range for FKM?
Standard FKM: -20 to +230 °C continuous. Short-term to +260 °C. Low-temp grades (GLT, GBL): -40 °C capable but reduced chemical resistance. For service below -40 °C, FKM becomes brittle — use silicone or HNBR. For service above 230 °C, use FFKM (up to 316 °C) or specialty elastomers.
O-ring sizes available?
Stock AS568 and BS-2951 inch and metric O-ring sizes in Viton 75A and 90A durometer, black color. Immediate availability: diameter 1 mm to 500 mm, cross-section 0.5 mm to 20 mm. Custom sizes: 2-4 week lead time depending on volume. For special shapes (T-seals, custom gaskets): mold tooling required.
Tooling cost for custom parts?
Compression mold tool: $3,000-15,000 depending on part size and complexity. Transfer mold: $8,000-25,000. Injection mold: $15,000-50,000 for production volumes. Tool amortizes over production volume — for 10,000+ parts, tool cost is negligible per part. For prototype or low volume, machining from sheet or standard compound slabs may be more economical.
Lead times?
Standard O-rings: in stock. Custom FKM parts: compression molding 3-4 weeks after tool, injection 1-2 weeks after tool. Tool lead time: 3-6 weeks. First production run: 6-10 weeks from design approval. Sample parts for testing: 4-5 weeks typical. For rush, aluminum rapid-prototype tooling can cut 2-3 weeks from timeline at slight cost premium.
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