When selecting the best o-ring material for a specific application, it’s essential to consider various factors, with temperature being a critical one. Temperature fluctuations can significantly impact the effectiveness of a seal. For instance, prolonged exposure to heat can lead to the physical and chemical degradation of o-ring materials, causing them to harden and become inflexible. On the other hand, cold temperatures may cause shrinkage, resulting in leaks.
Low temperatures are often overlooked when evaluating rubber seals. In these conditions, elastomeric materials can shrink, increasing the risk of leaks. Seal failure due to low temperatures typically occurs in two ways: either the seal hardens, resisting deformation and creating leak paths, or it undergoes compression set, leading to leaks when heated above its usual low temperature.
For extreme low temperatures, Vinyl Silicone (VMQ) and Phenyl Silicone (PVMQ) are viable options, with brittle points reaching as low as -85°F and -155°F, respectively. However, these materials may experience excessive swelling in certain environments. Fluorosilicone (FVMQ) is another option, offering resistance down to -75°F in oil and fuel applications, making it suitable for aerospace use where exposure to low temperatures and harsh fluids is common.
General polymers like EP and Nitrile can also be used in low temperature applications, with varying temperature ranges and swell resistance. Fluorocarbons are usable in temperatures ranging from -13°F to -40°F, but for their lower limit, more expensive low temperature polymers are required.
Conversely, high temperatures can cause physical and chemical deterioration of o-ring elastomers, leading to hardening and swelling within the gland. This can result in increased friction, especially in dynamic applications, and is exacerbated in high pressure scenarios where room temperature tests may not accurately predict performance. Special compounds like Fluoroelastomers (FKM), Silicone, and Fluorosilicone are designed to withstand temperatures up to 400°F, with some capable of short-term exposure up to 600°F. Additionally, materials like ethylene propylene offer resistance to specific fluids like steam.
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