M-Cor Inc: Teflon® Encapsulated O-Rings: Core Material:  Compression Set  Implications

Introduction:

Teflon® Encapsulated O-Rings are components used in various mechanical systems, their effectiveness is dependent on the material properties of the elastomers utilized.. This M-Cor blog focuses on two important  aspects: the compression set of the elastomer, which indicates its ability to maintain a seal over time, and the Shore A hardness, a measure of the elastomer’s resistance to indentation. Understanding these properties is essential for successfull seaing designs.

Measuring Compression Set:

The compression set of an elastomer is measured by compressing a standard test specimen between two parallel plates under specified conditions (temperature and time). After decompression, the specimen is allowed to recover, and the permanent deformation is measured. The compression set is expressed as a percentage of the original thickness. Standardized test methods, such as ASTM D395 and ISO 815, are  used for this purpose. See our Material Info page for elastomer mechanical properties.

Shore A Hardness Scale: Durometer

Shore A hardness is a measure of an elastomer’s resistance to indentation, providing an indication of material stiffness and flexibility. It is measured using a durometer gage, a device that applies a force to an indenter tip pressed against the elastomer. The depth of indentation correlates to the Shore A hardness, with higher values indicating a harder material. This property is critical in applications where the O-ring must resist deformation under load.

Average total shore A hardness.
85-90 shore A for solid silicone core.
90-95 shore A for solid Viton® core.
75-80 shore A for hollow silicone core

** Hollow Core/Tubing reduces Duro by 10%

The Role of Elastomer Fillers:

The elastomer filler content percentage can significantly impact both the compression set and Shore A hardness. While fillers may enhance certain properties, excessive use can increase the compression set, leading to a loss of sealing capability. A high filler content can also affect the Shore A hardness, potentially rendering the O-ring too stiff or too flexible for the intended application.

Balancing Quality and Cost:

Manufacturers may use high filler content in elastomers to reduce costs, as fillers are generally less expensive than the base polymer. However, this can compromise the O-ring’s quality, leading to increased compression set, altered Shore A hardness, and reduced overall performance. Selecting the right elastomer formulation is crucial to the performance of Teflon® Encapsulated O-Rings.

Conclusion: The quality of elastomers, as assessed by compression set and Shore A hardness, is a key determinant of O-ring performance. Understanding and accurately measuring these properties are essential for selecting the right material for specific applications. While managing costs is important, prioritizing elastomer quality is crucial for ensuring the reliability and longevity of O-rings in industrial sealing applications.

References

1. ASTM D395 – Standard Test Methods for Rubber Property—Compression Set.
2. ISO 815 – Rubber, vulcanized or thermoplastic — Determination of compression set.
3. ASTM D2240 – Standard Test Method for Rubber Property—Durometer Hardness.

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