NBR and FKM are two commonly used materials for rotary shaft oil seals. Both can provide reliable sealing performance, but they differ in temperature capability, chemical resistance, cost and suitability for particular operating environments.
Selecting the correct material is just as important as choosing the correct inner diameter, outer diameter, width and seal profile. An oil seal with the correct dimensions may still fail prematurely if its material is unsuitable for the fluid or operating conditions.
What Is an NBR Oil Seal?
NBR, also known as nitrile rubber or Nitrile Butadiene Rubber, is widely used for general-purpose rotary shaft oil seals.
It generally provides good resistance to many mineral oils, greases and common lubricants, together with useful wear resistance and good value for routine mechanical and industrial applications.
NBR oil seals are commonly considered for equipment such as:
- Electric motors
- Pumps
- Gearboxes
- Agricultural machinery
- Automotive and mechanical assemblies
- General industrial equipment
However, NBR is not suitable for every chemical or high-temperature application. Its performance can also be affected by prolonged exposure to ozone, weathering and incompatible fluids.
MAV Bearings Ltd currently holds more than 90 sizes of TC double-lip NBR oil seals in UK stock for fast dispatch.
What Is an FKM Oil Seal?
FKM is a fluorocarbon elastomer often selected for applications involving higher temperatures or more demanding chemical exposure.
Compared with standard NBR, FKM generally offers improved resistance to heat, fuels, ozone and a wider range of oils and chemicals. It is often considered for demanding automotive, processing and industrial environments where a suitable NBR compound may not provide the required service life.
FKM is normally more expensive than NBR and is not automatically the best material for every application. Its compatibility must still be checked against the specific fluid, operating temperature, shaft speed, pressure and equipment requirements.
NBR vs FKM Oil Seals
| Factor | NBR | FKM |
|---|---|---|
| Typical use | General-purpose oil and grease applications | Higher-temperature or more chemically demanding applications |
| Oil and fuel resistance | Good with many compatible mineral oils and greases | Generally broader resistance to oils, fuels and chemicals |
| Heat resistance | Suitable for many standard operating environments | Generally better suited to higher temperatures |
| Ozone and weathering | More limited resistance | Generally improved resistance |
| Cost | Usually more economical | Usually more expensive |
| Availability | Widely used and commonly available | May require sourcing or production in some sizes |
Temperature Ranges
As a manufacturer-specific reference, the CFKS technical catalogue lists the following temperature ranges for its sealing materials:
- NBR: −40°C to +120°C
- FKM: −20°C to +200°C
- PTFE: −60°C to +250°C
These figures help illustrate why FKM or PTFE may be considered for applications involving temperatures beyond the stated range of NBR. PTFE is not an elastomer like NBR or FKM and may require a different seal design, so it should not be treated as a direct material substitution.
The ranges above are taken from the CFKS catalogue and should not be treated as universal specifications for every oil seal or compound. Actual performance depends on the precise material formulation, seal construction, fluid, pressure, shaft speed, installation, duration of exposure and operating environment.
Why Chemical Compatibility Matters
Temperature capability alone should not determine the choice of material. A material that performs well with one lubricant may swell, harden, soften or deteriorate when exposed to another fluid.
Before selecting an oil seal material, identify:
- The exact fluid or lubricant
- Normal and maximum operating temperature
- Shaft speed
- Operating pressure
- Whether exposure is continuous or occasional
- Exposure to dust, water, mud, ozone or chemicals
When Should You Choose NBR?
NBR is often the practical choice when:
- The application uses a compatible mineral oil or grease
- The operating temperature is within the recommended range of the selected compound
- The environment is not unusually chemically aggressive
- A cost-effective general-purpose oil seal is required
- The original equipment specification requires NBR or nitrile rubber
When Should You Choose FKM?
FKM may be considered when:
- The operating temperature exceeds the recommended range of the available NBR compound
- The seal is exposed to compatible fuels or more demanding chemicals
- Improved resistance to heat, ozone or weathering is required
- The original equipment specification requires FKM or fluorocarbon
- Previous NBR seals failed and material incompatibility has been correctly identified as the cause
Changing from NBR to FKM should not be based only on the assumption that FKM is a superior material. The original equipment requirements and complete operating conditions must still be checked.
Dimensions and Seal Profile Still Matter
Material is only one part of selecting an oil seal. You must also confirm:
- Inner diameter or shaft diameter
- Outer diameter or housing bore
- Seal width
- Lip arrangement
- Spring configuration
- Direction of rotation, where relevant
- Shaft condition and surface finish
- Pressure capability
Use our oil seal size chart to browse TC oil seals available from UK stock by inner diameter, outer diameter and width.
If you are replacing an unidentified seal, read our guide on how to measure an oil seal correctly before ordering.
Need Help Selecting NBR or FKM?
If your required oil seal size or material is not currently listed, MAV Bearings Ltd can check availability or arrange production through its manufacturing partner network.
Please send us the required dimensions, material, quantity, application, fluid and operating conditions through our Request an Oil Seal Quote page.
Always verify the original equipment specification, material compatibility, seal profile and operating conditions before ordering, changing material or installing a replacement oil seal.