Understanding Compression Deflection and Compression Set for Gasketing
Pressure-sensitive adhesive (PSA) tapes, when combined with reliable gasketing materials, provide reliable seals under many environmental conditions. When combined with their ability to adhere to different types of substrates, these adhesive tapes make reliable gaskets and seals. Two important properties of PSA single-sided foam tapes that significantly impact their performance as gaskets are compression deflection and compression set. Understanding these properties can help you select the right PSA foam tape for your specific application, ensuring they continue to provide the best performance and longevity.
What is Compression Deflection?
Compression deflection, also referred to as compression force deflection, refers to the ability of a gasket material to resist deformation under a compressive load. It measures the force required to compress the material by a specific amount. It is one of the best indicators of the foam feel from soft to firm.
Compression deflection is an important property in gasketing applications because it determines the ability of the gasket to maintain contact with the mating surfaces and ensure a proper seal. This is crucial in applications where the gasket must accommodate varying loads and pressures, especially those that are applied to the gasket over and over. It also provides the force necessary in application to ensure a positive seal. A gasket with appropriate compression deflection ensures that it remains in contact with the surfaces, maintaining the integrity of the seal even under fluctuating conditions.
The Importance of Compression Deflection in Gasketing
Gasket firmness: depending on the application requirements, a soft, medium, or extremely firm foam gasket may be required. A foam’s compression deflection number provides a clear guide to how firm the material will feel.
Creating a Positive Seal: understanding the correct compression force required, the space available, and matching this with the right material thickness is critical in achieving a positive seal.
Ensuring a Proper Seal Under Varying Loads: compression deflection is vital for gaskets that experience fluctuating pressures and loads, as it ensures the gasket can adapt to changes without compromising the seal.
Gasket Durability and Performance: gaskets with appropriate compression deflection are more durable, as they can withstand repeated compressive forces without losing their sealing capability.
Fluctuating Pressure Environments: gaskets with high compression deflection provide reliable sealing performance in environments with fluctuating pressure, such as HVAC systems or automotive engines.
The Factors that Affect Compression Deflection
Compression deflection is typically measured using a compression test, where a known force is applied to the foam PSA material, and the resulting deformation is recorded. ASTM D1056 is a standardized test method for measuring the compression deflection of cellular elastomeric materials. This test provides valuable data on the material's resistance to compressive forces and helps in selecting the right gasket material for specific applications.
The key factors that impact compression deflection include:
Material: different materials have varying stiffness, elasticity, hardness and resistance to compression. For example, rubber tends to have higher compression deflection compared to the softer foam gasket materials.
Thickness: thicker materials generally require more force to compress, resulting in higher compression deflection values.
Temperature: elevated temperatures can soften materials and reduce their compression deflection, affecting their ability to maintain a tight seal.
What is Compression Set?
Compression set refers to the permanent deformation of a gasket material after being compressed and then released. It’s a measure of the material's ability to return to its original thickness after being subjected to a compressive load. Compression set is critical to understand to ensure gasket performance over time, as it affects the gasket's ability to continue providing an effective seal after being heavily compressed for long periods of time.
The Importance of Compression Set in Gasketing
Long-Term Performance: a low compression set means that a foam will snap back closer to its original form. The higher the compression set, the higher the deformation level of the foam after compression. For applications where continuous access is required over the life of an application, a gasket with lower compression set is optimal so the foam will better recover its original shape and continue providing an effective barrier. In applications where an access door will be opened and closed frequently, a lower compression set foam is optimal. In applications where access is less critical, foams with higher compression set values may be used.
Gasket Reliability and Maintenance: gaskets with low compression set values require less maintenance and are less likely to fail, reducing downtime and repair costs.
Static Sealing Applications: in applications like refrigerator or medical device seals, you can rely on gaskets with a higher compression set to maintain a consistent seal over time since the gasket will not be disturbed by opening and closing.
The Factors that Affect Compression Set
Compression set is measured by compressing a foam PSA gasket material to a specific thickness, maintaining the compression for a defined period, and then releasing the load to measure the material's recovery. ASTM D1056 is the standardized test method for determining the compression set of cellular materials. This test measures the material's ability to recover after being compressed and is crucial for assessing long-term gasket performance.
The factors affecting compression set include:
Open Cell vs Closed Cell Foam: in general, the recovery of open cell foams outperforms that of closed cell foams. That is because what makes closed cell foams able to seal against moisture and air intrusion—air bubbles trapped within the cellular structure of the foam—also lessens their resilience. Under compression, some of those air bubbles will be crushed or distorted, thereby reducing recovery. At the same time, open cell foams are not designed to effectively seal against water and air intrusion.
Material Properties: material type, density, manufacturing technique, and quality can affect compression set values.
Temperature: temperature extremes can also impact compression set, as high temperatures can soften materials, and extremely low temperatures can make them firmer and more brittle.
The Practical Difference Between Compression Deflection and Compression Set
While compression deflection and compression set both relate to a material's response to compressive forces, they describe different aspects of performance. Compression deflection focuses on the material's resistance to deformation under load, whereas compression set addresses the material's ability to recover its original shape after the load is removed. In a dynamic sealing application, such as an engine gasket, a high compression deflection ensures that the gasket maintains contact with moving surfaces, preventing leaks.
Essentially, compression set determines how resilient a material is after sustained compression. A low compression set indicates that the material can recover to near its original shape after compression, ensuring a continuous seal in applications where periodic, repeat compressive stress occurs. High compression set values mean the material is more likely to remain deformed by the stated percentage, leading to potential leaks and seal failure if used in repeat stress applications. Conversely, when load is constant, compression set becomes less important a factor, since gasket recovery is unnecessary.
Compression deflection, on the other hand, measures how well the material can resist the force of a static load, which impacts the performance of your gasket creating a positive seal. In static sealing applications, such as electronic enclosures, a low compression set is crucial to maintain a long-term seal without deformation.
Materials with High Compression Deflection and Compression Set
When choosing a material for gasketing applications, consider the specific application requirements, including material thickness, temperature, compression deflection requirements, compression deflection requirements, and environmental conditions.
Common foam gasket materials will provide differing compression deflection and compression set values.
For low compression set values, open cell foams are an excellent choice. Low density urethane, high density polyurethanes, like 3M’s Isoloss and Poron, and silicone foam, like Bisco, provide some of the lowest compression set values available.
Closed cell foam gaskets come in myriad material types, giving them a wide range of compression deflection and compression set ranges, and a variety of resistances and uses. Open cell foams like polyurethane provide cushioning while offering additional protection from noise and vibration. Closed cell foams like polyethylene, polyvinyl chloride (PVC), neoprene, EPDM, vinyl nitrile foam and silicone sponge are more flexible materials that are impervious to water, vapor, and air.