Elastomerics Blog

Gasket failures can have consequences that range from minor leaks to equipment downtime to expensive damage. The causes of seal failure are numerous, but there are some common problems that engineers need to avoid. Stockwell Elastomerics can help you to reduce the risk of these and other gasket failures through expert design assistance and help with material selection.

Compression Set

Compression set occurs when a gasket fails to return to its original thickness after being subjected to prolonged compressive stresses at a given temperature and deflection. The causes include excessive loads or overtightening, but exposure to high heat and chemicals can also contribute to this form of failure.

To prevent compression set, select a gasket material (such as silicone rubber) with good compression set properties. Silicone has a molecular structure that rebounds better than most elastomers, and it maintains its elasticity over time. It’s also important to determine if the gasket design and material are right for the application, and if the installation procedure is correct.

Overfilling the Gland

A gland is a groove or cavity that houses, supports, and compresses a custom gasket. To provide proper sealing, the gasket needs enough space to compress and deform under pressure. If the gland is overfilled, however, the seal will extend beyond the lower pressure side and begin to tear. This can cause one side of the gasket to appear frayed, worn, or “nibbled”.

To avoid overfilling the gland, aim for 80% to 90% gland fill. If redesigning the gland isn’t possible, reducing the gasket’s width is often the simplest adjustment. Many high consistency rubber (HCR) materials are available in a range of standard thicknesses, and liquid silicone rubber (LSR) supports molded gaskets for specific gland dimensions.

Chemical Swell

Chemical swell occurs when a rubber gasket absorbs a fluid to which it’s exposed. This causes the gasket material to expand, soften, or become distorted. Absorption changes the gasket’s physical dimensions, but it also affects mechanical properties such as hardness and tensile strength. That’s why chemical swell is related to compression set and other types of gasket failure.

To prevent chemical swell, select a gasket material that resists the substances to which it will be exposed. For example, fluorosilicones can withstand jet fuel. In addition, consider whether the chemical exposure is continuous or intermittent. A gasket material that can withstand fuel splash may not be able to withstand long-term immersion, especially at high temperatures.

Thermal Degradation

Thermal degradation happens when a gasket is subjected to temperatures beyond its recommended range. Short-term extremes may not cause immediate failure, but prolonged exposure can cause materials to harden, crack, or lose their elasticity. Thermal degradation is associated with excessive heat, but extreme cold can also make some materials brittle and cause performance issues.

To prevent this form of failure, design gaskets for the full range of expected temperatures and not just ambient. Consider worst-case scenarios for both extreme heat and extreme cold. For applications that require resistance to extreme temperatures, use materials that are engineered to withstand them.

Installation Damage

Installation damage is sometimes called “pock marking” because this form of failure results in large notches on the surface of the seal. Often, overstretching the gasket material is to blame. Installation damage can also occur if an enclosure has sharp or rough surfaces that scratch or tear elastomeric components.

Designers can apply chamfers or lead-ins to housings to simply gasket installation, but assemblers need to avoid scraping the seal along an enclosure’s edges. In addition, installers must avoid stretching solid elastomers beyond 50% of their original diameter. This is especially important with door or hatch gaskets because they may not fit if they’re overstretched.

Get Expert Assistance from Stockwell Elastomerics

Contact Stockwell Elastomerics for assistance with troubleshooting a failed gasket or designing a better and more effective seal.