The material of a skeleton oil seal affects sealing performance because the sealing lip must remain flexible, chemically compatible with the working medium and stable at the operating temperature throughout its service period. A seal with the correct dimensions can still perform poorly if its rubber compound is unsuitable for the lubricant, temperature or mechanical conditions.
The sealing lip is the part of the oil seal that has the most demanding job. It must deform around the shaft during installation, maintain contact while the shaft rotates and tolerate repeated friction at the sealing interface. These requirements make the physical and chemical properties of the elastomer important.
For general oil-sealing applications, NBR is commonly used because of its compatibility with many mineral oils and greases and its useful mechanical properties. This makes NBR suitable for a wide range of conventional machinery when the temperature and fluid conditions are within the compound's working range.
FKM is used when the operating environment places greater demands on heat resistance or chemical resistance. It is often considered for applications involving higher temperatures, certain fuels, oils or more aggressive media. However, selecting FKM simply because it has a higher temperature capability is not enough. The actual fluid, temperature cycle, shaft speed and seal design still need to be considered.
Temperature affects the material in two directions. At high temperature, elastomers can age faster and gradually lose their original properties. At low temperature, some materials can become less flexible. For a rotary oil seal, these changes matter because the lip needs to follow the shaft and maintain a suitable contact condition.
The working fluid is equally important. “Oil resistant” does not mean
resistant to every fluid that happens to be called oil. Different lubricants can
contain different base fluids and additives, and their effects on elastomers can
vary. Material compatibility therefore needs to be checked against the actual
medium used by the machine.
Material also influences wear behavior. The lip is not stationary after installation; it continuously interacts with the shaft. If the compound is poorly matched to the operating temperature, lubricant or shaft speed, the sealing edge may wear faster. Once the lip geometry changes significantly, the original contact condition can also change.
This is why changing an NBR oil seal to FKM is not simply an upgrade in material. The two compounds have different physical characteristics, and the seal design has to work with those characteristics. The correct choice depends on what the seal actually encounters during operation.
There is also a practical point for equipment manufacturers and replacement-seal buyers: material and dimensions should be treated as two separate selection conditions. The dimensions determine whether the seal can be installed correctly. The material determines whether the sealing element can continue working properly in the specified environment.
Therefore, the effect of material on sealing performance is not simply about whether one rubber is “stronger” than another. It is about how well the compound maintains its elasticity, fluid compatibility, temperature resistance and wear behavior under the actual working conditions of the oil seal.
