Creating the Perfect Seal: The Story of the Science Behind the O-Ring

Apple has found yet another use for the versatile o-ring, filing for a patent for a cable design that uses the tiny seal to keep iPhone power connectors water-resistant, CNET says. The patent application lays out a design that seals Lightning power connectors and USB-C connectors from moisture by using an o-ring seal. This can make it easier and safer to recharge smartphones in locations such as kitchen and bathroom countertops where there may be water nearby.

O-ring applications such as this rely on seals with highly precise specifications to achieve their intended purpose. Here’s a look at the science behind the o-ring, how manufacturers have developed specialized o-rings to meet different needs and how to go about choosing the perfect seal for your purposes.

The Invention of the O-ring

The prototypes for o-rings were gaskets made of india rubber that 19th-century plumbers used to seal piping counter-bores. This inspired Thomas Edison to incorporate rubber rings into a pair of designs he patented in 1882: one for a water faucet, where the ring was used to seal gas, and another for a light bulb, where he used a ring to seal mercury into the bulb and keep air out.

The first patent for an o-ring was filed in 1896 by J.O. Lundberg, a Swedish inventor; however, it was Danish-American inventor Niels Christensen who designed the direct ancestor of today’s o-rings. While working on airbrake systems for electric streetcars, Christensen realized that he could use a rubber ring to seal a piston cylinder. Christensen patented his invention in 1937, planning to license to an aircraft company to seal airplane hydraulic cylinders.

However, Pearl Harbor and U.S. entry into World War II changed Christensen’s plans. The United States government recognized that his invention had military value, and seized his patent so that the design could be shared by other military contractors. Christensen was initially compensated $75,000, and his heirs later won another $100,000. Through military contracts, his design became known throughout the aircraft industry, where it became a vital part of postwar hydraulic systems for components such as brakes, wing flaps and landing gear.

Developing Specialized O-rings

The postwar popularity of o-rings in the aerospace industry led to the development of specialized rings made of new materials designed to meet the needs of aircraft and other applications. For example, one new synthetic rubber that was developed in the postwar years to withstand the high temperatures and chemical volatility of aircraft engines was Viton, also known by designations such as fluorocarbon, FKM, Fluorel and Technoflon. Invented in 1954 by DuPont research chemist Dean Rexford, Viton can withstand a temperature range from -13 F to 446 F, and can be modified to withstand temperatures as low as -40 F. It is also highly resistant to chemical change. These properties make Viton highly suitable for use in aircraft engines, as well as other applications involving wide temperature and chemical variations, such as automotive engines and hard vacuum service.

Viton is just one example of the many types of o-ring materials that have been developed for specialized applications. Another example is neoprene, developed at DuPont in the 1930s by a team of scientists working with organic chemist Julius Nieuwland. In addition to tolerating a temperature range from -40 F to 250 F, neoprene is resistant to ammonia and Freon, making it popular for use in the refrigeration industry. Other o-rings use Silicone, which can tolerate a wide temperature range and does not carry odors or tastes, making it useful for food and medical applications.

Choosing the Right O-ring

With so many o-ring materials available, how do you choose the right one? First, you need to consider the type of application you have in mind, including factors such as temperature range and chemical environment, as well as other variables. The next step is to research the range of available materials.

The best way to conduct your research is to get input from a knowledgeable professional experienced with your type of application. Major o-ring manufacturers such as Apple Rubber provide online guides to assist with o-ring material selection. Before ordering specialized o-rings in bulk or putting a product with a custom o-ring into large-scale production, you should request a sample for testing with your intended application.

From plumbing and light bulbs to hydraulic brakes and airplanes, o-rings have had a fascinating history of development. Today this versatile invention comes in a wide variety of specialized materials designed to tolerate a range of temperature and chemical changes and to meet the needs of specialized applications such as aerospace, refrigeration and medicine, to name just a few. For best results when ordering customized o-rings, consult an experienced professional to assist you with choosing the type of material right for your needs.

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