subject: Advancements In Rubber O-ring Technologies [print this page] For typical non-commercial users, the most relatable O-ring application is the use of round rubber seals to seal the mouth of a jar. Apart from this simple application, rubber O-rings have also found use in relatively complex household applications such as pressure cookers. Although these cookers contain O-rings, they are rarely made of pure natural rubber. Usually, natural rubber undergoes vulcanization, a process where the rubber is heated along with sulfur and cured with either bisphenol or peroxide. As natural rubber has a melting point as low as 27C, vulcanization arrests O-ring failure due to heat. The process also provides rubber with better elasticity and mechanical properties. However, in industrial applications, vulcanized rubber has been replaced with elastomers having relatively superior elastic and mechanical properties. Thus started the evolution of rubber O-ring materials.
Impact of advancement in material technology:
Initially, the material of choice for an O-ring was limited to nitrile rubber (Buna N), neoprene, and natural rubber. Among the available raw materials, nitrile rubber exhibited relatively better sealing properties and was used for most O-ring sealing applications. In addition to being susceptible to flame, nitrile rubber was ineffective in handling fireproof hydraulic fluids, ketones, and concentrated acids. Materials like fluoro-silicone were compatible with most chemicals, but they had poor wear resistance and tensile strength handling capability. After the development of Fluoroelastomers such as Viton, O-rings can be used in almost all applications, handling most materials apart from ketones and alkalis. Furthermore, Viton offers an improved thermal performance of about 69C. In the last three decades, perfluoroelastomers such as Kalrez have penetrated high performance sealing applications. This elastomer offers flame resistance, better shore A hardness, temperature resistance of about 327C, and compatibility with most chemicals. However, in comparison with Viton, Kalrez exhibits lower tensile strength and inferior compression set.
Besides the advancements in the core materials of O-rings, the development of chemical agents, such as fillers and accelerators, has also improved the performance characteristics of O-rings. Inert fillers like carbon black and reinforcing agents are used with O-rings to improve the physical performance of the O-rings. Accelerators, curing agents, and retarders are used to manipulate various parameters of the O-rings. Anti-degradants have also been developed and used to avoid chemical reaction during compounding. Some agents, such as plasticizers, are added to the O-ring material to increase softness and improve low-temperature performance. To enhance the thermal capabilities of the O-ring, cooling agents are also introduced inside the hollow O-rings. Glass transition temperature, which has been marring the performance of O-rings under low temperature, has also been lowered in elastomers that are used in cold weather applications.
Transition from material to performance specification:
In the recent past, end users are migrating from material specification analysis to performance specification analysis. The performance specification analysis is a comprehensive and realistic test of sealing abilities. In this analysis, the material undergoes test under simulated application environment to get a better picture of its performance. The simulated application environment can be manipulated to test the materials under extreme process variables for worst-case scenarios in sensitive processes. Such analysis also checks the nature of cross-links under compression to predict the seal failure. New technologies are being developed that analyze the effects of stress-relaxation, mimicking dynamic sealing applications.
Conclusion:
Recent developments in analytics, combined with higher computational capabilities, have made it possible to predict seal failure. The material technology is evolving to weather harsh sealing conditions and a wide range of chemicals that were not catered by traditional rubber O-rings. Additives and auxiliary material have also been developed that can negate the disadvantages of a material.
