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What Are Seals?
Oct 18, 2018

Imagine rolling up your car window, revving up the engine, and backing up out of your driveway. In three seconds, you have employed over three types of seals. From the rubber seal strips along your car window frame to the sealing surrounding the coolant in your engine to the ball bearing seals in the wheels of your car, there are hundreds of these parts in your car alone. These parts are an integral part of everyday life that ensure that mechanical objects continue working without leaks and reduced friction. A flexible seal is used for multiple applications: barriers between two objects, “preventing leakage, containing pressure, or excluding contamination” (en.wikipedia.org/wiki/seal_(mechanical)). Here are the four most common types of seals are listed below:

  • Hydraulic Seals – These non-metallic types can stand a wide temperature range with little maintenance. Hydraulic seals are most often used as a barrier between fluids in a reciprocating motion application, such as a piston in a car. These parts can be static or dynamic. A static seal does not move but is located in a groove, or confined space. A dynamic seal, on the other hand, is exposed to movement and moves itself (en.wikipedia.org/wiki/hydraulic_seal).

  • O-Rings – Designed in 1937 by Niels Christensen, the O-ring, while one of the simplest seals developed, is one of the most useful and precise variations of sealing devices used today. This is an elastomer seal that acts as a gasket in the shape of a torus. A torus is a loop of plastic with a disc shaped cross-section that is set into a groove and compressed between two or more parts. The O-ring prevents leaking as long as the contact stress of materials deforming the ring is within the range of the O-ring. The O-ring cannot withstand extreme temperatures. Due to the nature of an elastomer seal, if an O-ring gets too cold, it becomes brittle and crystalline. If they are too hot they contract, rendering them useless. To avoid contraction from the heat, they can be placed peripherally out of the main section of heat.

  • Bearings and Seals – Bearings are generally used to help constrain motion between two or more parts to only the desired movement, i.e. around an axle or a linear motion. Coming from the verb “to bear,” bearings allow objects to continue working while withstanding each other. Composed of many parts, bearings are a very flexible seal that need to be packed in grease or oil as lubrication. Often used in between metal surfaces, bearings create a fluid barrier so that the metal can keep revolving without rubbing one another and creating friction. Bearings require maintenance periodically as they need to be lubricated to enhance bearing life and prevent premature failure.

  • Rubber Seals – These are used for a large variety of applications due to the different compounds and properties of rubber. The most common use of rubber seals is to create air tight spaces, such as the cap of a jar of jam or your car door. These vacuums help to keep food fresh or to keep people safe. If airplanes did not use rubber seal strips on their doors, airplanes would not be able to reach such high altitudes without collapsing the cabin. Although some rubber compounds are not chemical resistant, nitrile rubber is resistant to oil and fuel. This makes nitrile rubber well suited for the automotive and aeronautical applications such as oil handling hoses in the engine. Nitrile can also withstand a large range of temperatures so airplanes can use nitrile strips without worrying about the rubber strips failing Silicone rubber is an extremely stable compound of rubber that can withstand extreme temperatures while still remaining functional. Silicone rubber is generally used for home repair and hardware as well as food storage products. Silicone can be used as freezer sealants because it does not become brittle in the cold temperatures and does not contain a carbon molecule, which makes silicone safer around food. Silicone is also used to wrap airplane wiring because it is a non-flammable material. Natural rubber is also used for sealants due to its elastic nature and high resistance to tear.

Just because you may not notice seals in your everyday routine, you may wonder exactly what are seals good for. These are almost universally present in all mechanical products we own or are exposed to. They protect our food, our cars, and, most importantly, ourselves. They are used to prevent dangerous leaks, to keep two materials joined, to create a barrier between two harmful objects, and in the case of a rubber seal strip to make sure our glass windows are closed tight. While some may only keep cereal crunchy, others allow space shuttles to rocket off into the stars.