Gaskets and o-rings are those familiar mechanical seals placed between separate substrates in order to prevent leakage when the substrates are connected. High-temperature seals may be more well-known than low-temperature ones, but in either instance, the sealant must meet material requirements to withstand extreme temperatures, immense pressure, and constant wear. Therefore, it’s important to know how temperature affects gaskets, o-rings, and other kinds of seals to ensure that their application is robust enough to function as intended in a variety of environments.
Applications and Materials for High-Temperature Sealants
Certainly, the mechanical properties of gaskets and o-rings are defined by their application. Their use is more often associated with engines for such industries as the automotive, aerospace, marine, and agricultural, but sealants are also in machinery used in factories, plants, and manufacturing centers. In all likelihood, anywhere that an engine or machine is in operation it is sealed with a low or high-temperature sealant that must have the mechanical properties necessary to perform effectively in extreme environments.
Materials for seals are derived from rubber, or more precisely, elastomers, a synthetic elastic polymer. A polymer can be cured to enhance mechanical properties specific to its performance. Mechanical properties may include a need for flexibility, absorption, tensile strength, and resistance to tears, corrosive environments, or the ability to withstand extreme heat or cold. For example, elastomeric material for a high-temperature o-ring might be designed to function in an application subjected to corrosion and extreme heat, or designed for a low temperature, tear-resistant application. In each case, the engineers must know how the mechanical properties of the seal will respond to a reaction force, i.e., the temperature and how it will affect the seal in order to ensure the integrity of the component.
How High and Low Temperatures Affect Seals?
Every material has a high or low-temperature limit that, once it is reached, the material will fail. Governed by the coefficient of thermal expansion (CTE), contraction or expansion of material occurs as the material cools or warms. Stresses that occur at low temperatures may not happen at higher temperatures and vice versa. To prevent failure, gaskets, o-rings and other elastomeric sealing material must have specific compounds added to make sure its mechanical properties can withstand the necessary temperature. It’s important to know a seal’s temperature limit before application to avoid component failure.
Low-temperature applications for seals are critical to a number of industries. Pharmaceutical, medical, aerospace, petrochemical, oil, and gas, food and dairy all rely on sealants that must perform in low-temperature environments. When a seal reaches its low-temperature limit it will harden, become stiffer, begins to lose its elastic properties and flexibility, and crack. As the temperature lowers, at some point it will undergo a glass transition phase and become glassy and brittle. If a state of glass transition occurs, though some elasticity may be present, the seal will no longer function. Once a leak path has formed in a seal, even after temperatures return to “normal,” the leak path will remain.
High-temperature applications for seals, such as in engines, also require the right material to prevent leakage and failure. Environmental conditions or excessive and extreme heat will gradually degrade elastomeric materials and the performance level will deteriorate. The fact is an elastomer ability to resist thermal degradation plays a significant role in its ability to function effectively as a seal over time. To ensure thermal stability, the material selected for a high-temperature sealant application should be tested through heat aging.
Obviously, design engineers are well aware that temperature fluctuations can alter the mechanical properties of elastomers. In today’s market, elastomers are tested to meet temperature performance requirements. Gaskets, o-rings, and other seals are designed for specific work environments. However, it is the consumer’s responsibility to know or be aware that not just “any” elastomeric material will suffice as a sealant. To avoid complications and leakage in sealing applications, and that your rubber seal will perform at its fullest potential, consult with your vendor and let them guide you through the process.