How to Improve Your Product Performance With Slippery Rubber Seals

O-rings and other types of gaskets are most commonly used in static sealing applications, where the seal is securely fixed in a gland and remains stationary.

In such applications, the seal is not subjected to damage caused by friction or abrasion. However, if relative motion occurs between the gland surface and the seal, it is classified as a dynamic sealing application, which may necessitate the use of a lubricant to enhance performance. Dynamic applications introduce two additional considerations: break-out friction and running friction. Break-out friction refers to the initial force required to start the movement of the seal, whereas running friction is the force needed to maintain that motion. Notably, break-out friction can be as much as three times higher than running friction.

Choosing the Right Rubber Compound

Some compounds are more suitable for dynamic applications than others. For instance, while nitrile and EPDM are appropriate for dynamic use, they tend to exhibit higher-than-average break-out or running friction when employed without lubrication.

Silicone and fluorosilicone exhibit poor tensile strength, making them prone to rupture, and thus unsuitable for high-rate dynamic applications. These materials should be reserved for low-movement dynamic applications involving smooth gland surfaces.

Fluorocarbon is considerably more expensive compared to most other compounds and is incompatible with steam. However, it offers superior performance in terms of temperature and chemical resistance, as well as improved running and break-out friction characteristics relative to most other elastomers.

Main Material sheet

External Lubricants

Hydrocarbon lubricants, as well as silicone and barium-based greases, can be applied to lubricate in-stock components. These lubricants, along with powder-based alternatives such as molybdenum disulfide and graphite, are often the most effective choices for reducing friction during initial operation. They exhibit good compatibility with most elastomers and are capable of withstanding high-temperature conditions. Furthermore, they offer additional protection against oxidative and ozonative degradation.
However, several limitations should also be taken into account. Incompatible chemical interactions between the elastomer and the external lubricant may lead to adhesion between components, thereby hindering assembly processes. Additionally, external lubricants may be compromised through dilution by fluids that come into contact with the seal or through migration away from the sealing interface.

Chlorination
Like external lubricants, chlorination can also be applied to stock O-rings. It is a permanent process which provides a smoother seal surface, reducing running friction. Though it has little effect on break-out friction, it can be used together with an external lubricant to great effect.

Internal Lubricants
Internal lubricants are friction-reducing agents like PTFE, graphite, and molybdenum disulfide, which are mixed into an elastomer. Due to the fact that an internal lubricant is chemically incompatible with the elastomer it is applied to, the elastomer will excrete the lubricant over time. Internal lubricants reduce friction, allow for more consistent performance, and have better assembly productivity in comparison to other lubricants. As with external lubricants, make sure that the internal lubricant is chemically compatible with the fluids it contacts.

Final Tips:

Once your elastomer and lubricant are chosen, run the final tests to ensure optimal performance.