An o-ring may seem like a simple part, but the materials it is made from can be very complex, and can have a major impact on performance. Some materials are designed for use at very high temperatures for applications such as aircraft engines and automotive fuel handling systems. Others are designed for extremely low temperatures for use in refrigeration. Still others are designed to provide a sterile material for medical applications.
Here’s a closer look at some of the ways that o-ring material selection can affect suitability for different types of applications, how different materials have been developed for specialized applications and why it’s so important to choose the right material when ordering a customized o-ring.
Buna-S: Supporting the Aircraft Industry
The modern o-ring design used in today’s o-rings was originally developed in the 1930s as a solution to the need for seals for hydraulic cylinders in planes. Danish-American inventor Niels Christensen had a background designing airbrake systems for electric streetcars. While experimenting with airbrake designs, Christensen found that he could seal a piston cylinder by using a rubber ring. He realized he could market his idea to the aircraft industry for sealing hydraulic cylinders in airplanes, and applied for a patent in 1937. After World War II started, the U.S. government used Christensen’s invention for military aircraft. Aircraft use hydraulic systems for various parts of the plane, including brakes, wing flaps and landing gear.
At this time, the rubber industry was in the middle of a transition from natural rubber to synthetic rubber. Natural rubber was the most popular form of rubber before the war, but once Japan seized control of rubber plantations in Southeast Asia, the U.S. began producing synthetic rubber. The main type of synthetic rubber the U.S. produced during the war was known as GR-S (Government Rubber S), a version of a synthetic rubber called Buna-S first developed in Germany in the 1930s. Buna-S is made from styrene and butadiene and is more resistant to abrasion than natural rubber. The o-rings U.S. aircraft used during the war and throughout the 1940s and early 1950s relied primarily on either natural rubber or the GR-S version of Buna-S.
Viton: Empowering Aerospace Applications
After World War II, flight technology continued to develop, leading to the emergence of supersonic jet aircraft and spacecraft. This exposed the o-rings in airplanes and spaceships to more extreme temperature and pressure conditions than previous aircraft. Additionally, o-rings were also being used in aircraft engines, exposing them to harsh chemical conditions.
To address this, the aerospace industry turned to o-rings made of a new type of synthetic rubber made of fluorocarbon, known in the industry as FKM and branded as Viton. Viton is made from rubbers based on fluorocarbon, known as fluoroelastomers, which have strong carbon-fluorine bonds. This allows them to resist changes caused by extreme temperature and chemical environments. Viton can withstand a temperature range from -13 degrees F to 446 degrees F, and can be modified to withstand -40 degrees F. These and other properties make Viton fluorocarbon o-rings well-suited to aerospace applications.
Neoprene: Sealing for Refrigeration
Another important application of o-rings is refrigeration. Refrigeration systems need to be kept airtight and leak-proof. They may use refrigerants such as ammonia and Freon, exposing o-rings to extreme chemical as well as temperature conditions.
To address these issues, o-rings intended for refrigeration applications typically use neoprene, a synthetic rubber invented by DuPont in the 1930s. Made from chloroprene, neoprene combines a wide range of temperature resistance, from -40 degrees F to 250 degrees F, with chemical resistance to ammonia and Freon. These properties make neoprene ideal for refrigeration applications.
Silicone: Making Medical Uses Possible
Another important use of o-rings is serving as seals in medical devices. Medical equipment such as insulin pumps, syringes and surgical tools often involve containing, pumping, draining or otherwise using liquids and gases. Leaks can cause contamination as well as loss of necessary fluids and gases, so o-rings used in medical devices must be both leak-resistant and contamination-resistant.
To ensure that medical devices remain both leak-proof and sterile, medical o-rings typically use rubber made from silicone. Synthesized from natural silicon, along with hydrogen, carbon and oxygen, silicone rubber retains its flexibility and shape over an exceptionally wide range of temperature conditions, from -85 degrees F to 400 degrees F. Silicone rubber can also be sterilized through a variety of means. Together these properties make silicone an excellent material for medical o-ring applications.
Over the years, o-ring designers have used specialized materials for a wide variety of uses, from airplanes and aerospace to refrigeration and medical devices. As researchers continue to develop new forms of rubber and other substances, more materials will continue to emerge to meet the enormous range of applications that o-rings support.