Nitrile Rubber Seals vs. Fluororubber Seals: Which Is Better for Oil Seal Applications?

NBR vs. FKM: What Is the Difference?

The NBR is the nitrile butadiene rubber, which is a form of rubber that can be used in sealing systems operating under mineral oils, lubricants, greases, and petroleum products. Due to its combination of oil resistance, physical strength, and cost-effectiveness, it is often used in the manufacture of industrial and automotive oil seals.

The fluororubber is the general name for a range of fluoroelastomers, known either as the FKM or FPM depending on the naming convention. It is used in applications where more heat or chemical resistance or certain types of oil or fuels are required.

This is a general comparison of material families, not a guarantee of performance for every oil seal. For final selection, refer to the seal manufacturer's compound data and compatibility guidance.

How NBR and FKM Perform in Oil Seal Applications

Oil and Lubricant Compatibility

NBR is extensively utilized for oil sealing due to the fact that numerous types of NBR have good compatibility with mineral oils, lubricants, and grease. Hence, the material is an ideal starting point for several common industrial applications.

The term "oil" has a wide variety of formulations. Oil base, additives, temperature, and time of exposure may affect swelling, change of hardness, and material properties. The compatibility of NBR with one lubricant does not guarantee compatibility with another lubricant.

Consideration is usually given to FKM if the oil or the conditions become too difficult for the selected NBR rubber to withstand. The material offers good resistance to many kinds of oils and fuel, but compatibility must still be tested with the exact medium. There are some chemicals and fluids that may not be suitable for certain formulations of FKM.

Temperature Resistance and Thermal Aging

Temperature influences the flexibility, compression properties, wear, and aging of elastomers. When temperatures are high, an elastomer with poor formulation could harden, become non-elastic, and deteriorate faster. At low temperatures, the elastomer will be less flexible and have difficulty maintaining the necessary sealing pressure.

Most FKM compounds are selected for use at higher temperatures compared to those that can accommodate general NBR compounds. However, there is no universal temperature range applicable to all grades. The temperature range allowed is dependent on several factors such as fluid type and whether the temperature is constant or fluctuating.

Wear, Friction, and Shaft Conditions

The efficiency of an oil seal does not only rely on the elastomeric component alone, as factors such as lip shape, shaft velocity, shaft hardness, surface finish, runout, misalignment, lubricant, and pressures will affect the friction and wear rates.

Even if a material exhibits excellent chemical stability, it could fail due to the condition of the shaft, poor installation of the seal lip, and speeds and temperatures beyond the recommended levels. Similarly, a well-chosen NBR compound could function effectively if the operational conditions are within its proven capacity.

When troubleshooting the problem of recurring leaks, examine the entire sealing system rather than immediately making changes in the material. The replacement of NBR rubber with FKM rubber will not solve the problem of the shaft being worn out.

When Should You Choose NBR or FKM Oil Seals?

The best way to select would be by comparing the real conditions with tested material properties. These situations may serve as a guideline for the initial selection, but further compatibility testing will be required for individual compounds.

When Neither Material Should Be Selected Automatically

In some instances, either the fluid, temperature, or mechanical requirements could make both the standard NBR compound and the standard FKM compound inappropriate. Instances can range from some chemicals to special fuel, very low temperatures, or high wear requirements.

In such situations, evaluate the particular medium or operating environment against data for that particular compound. In other instances, you might need another family of elastomers or a different seal construction. Do not rely on resistance properties only to make your choice of materials.

How to Select the Right Oil Seal Material

A robust oil seal specification should cover the material, seal design, shaft and housing conditions, and the operating environment. Review the following factors before finalizing a material choice.

Evaluate Total Operating Cost, Not Material Price Alone

Though NBR is normally more economical from a materials standpoint, lowest material cost does not necessarily result in lowest operational cost. In case the chosen material does not match up with the lubricant or temperatures, the failure could lead to leakage, maintenance costs, downtime and replacement costs.

The high cost of FKM might be justified by the use of material in applications where its proven characteristics are needed. However, where the chosen NBR material matches all the requirements of the application, using the FKM would not only be unnecessary but also costly.

To get accurate assessment of the situation, evaluate the service life expectancy, maintenance schedule, consequences of leakage and application experience. Avoid making any assumptions about the service life increase without tests or any proof.

What Should Buyers Confirm Before Ordering Oil Seals?

In the case of OEM manufacture, replacement part supply, and industrial maintenance, technical data serves to help suppliers determine the right material composition for seals. The name of a particular material does not fully describe it.

FOREVER SEALS provides an oil seals product range for buyers evaluating sealing options. Confirm the available material, profile, dimensions, and application requirements with the supplier before approving a specification.

For a previously installed seal that is not working properly, pictures, the part number, operating conditions, and any information on how the seal failed should be provided. This will help determine whether it was a result of incompatibility or some other issue.

Frequently Asked Questions

Conclusion: Match the Material to the Working Conditions

Both NBR and FKM have significant contributions to make in the application of oil seals. The use of NBR is quite practical in oil sealing that uses a suitable compound in meeting the necessary operating conditions. FKM should be considered when the temperature requirement and the fluid compatibility requirement exceed what can be met by the standard NBR compound.

Before making a choice, it will be wise to consider the lubrication, temperature requirements, shaft speed, design of seal, surface state and material requirements. Selection will depend on the full operating environment and not just the material name or cost alone.

The industrial buyer should supply proper drawings and application information in order to help the supplier choose the right material and construction of oil seal.