O-rings are circular sealing devices with a round cross-sectional profile, usually made from rubber compounds (or elastomers). They are simple, easily replaceable, and can be highly economical, which has helped them remain in use for hundreds of years and spread to every industry. When buying o-rings, the 3 most basic characteristics needed are material, hardness, and size. When all of these are defined by a customer, quoting and ordering are as simple as they can be. When any or all of these are not specified, Sealing Devices can make recommendations based on a handful of end-use details, captured by the acronym STAAMPS:
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1. Size
As o-rings grew in popularity after their invention, the need to standardize sizing became apparent, leading to the creation of several international standards. The most common standard used in the United States is SAE AS568, which defines over 400 sizes across a range of 5 cross sections. In order to meet demand in an ever-growing number of applications, manufacturers keep molds of many of these sizes readily available to produce thousands of o-rings each day. While the SAE AS568 is the most common, Sealing Devices can supply O-Rings to most international standard sizes. Custom size molded O-Rings can be offered with a one-time tooling charge as well.
Another option, for applications that require non-standard sizes, custom molds may be cut to provide continuous rings in medium and high purchase volumes. Non-standard o-rings can also be fabricated by extruding rubber into a cord and splicing the ends together to meet the required diameter; this option is better for low volumes and can save on tooling costs, especially when the rings can be several feet in diameter. Both cross section and diameter have direct effects on an o-ring&#;s performance in the conditions below.
2. Temperature
A good seal should both conform to the surfaces which it is sealing against and rebound after being squeezed, and rubber&#;s elasticity and relative softness have contributed to its status as a leading sealing material. However, when rubber is heated above or cooled below its recommended temperature range it starts to lose its ability to rebound; we call this taking compression set. Most common elastomers are only useful between -40°F and 250°F. However, some silicone compounds are resilient below -100°F, and some FFKM compounds can be used at over 600°F. For even more extreme temperatures, there are metal o-rings that seal up to °F.
In this section, we&#;ll look a little more closely at what o-rings do, and some of the applications that they&#;re very often used for.
High-temperature sealing o-rings are, as the name implies, designed to withstand extreme heat while continuing to provide a reliable seal between two surfaces or components.
This makes them ideal for demanding industries and environments such as oil and gas refineries, chemical processing, or any other scenario where a high-temperature seal is required, such as performance transport applications like turbo engines and aerospace engineering.
There are a number of popular high-temperature o-ring material choices, including nitrile, hydrogenated nitrile, silicone rubber, polyacrylate and more. Securing the best choice in any given scenario will generally be a balancing act between the specific operating temperature needed, and the most economical material option at that performance point.
For more detail on all types of O-ring materials and designated temperature ranges, feel free to contact our expert support team any time - they&#;ll be glad to offer further advice and assistance on specific high-temperature seals, materials and applications.
Again, all industrial o-ring purchases should be carefully planned with direct reference to the specific role and environment the seal is required to perform in. However, as a rough guide to o-ring temperature rating and use limits, some of the more popular materials on sale generally operate within the following sorts of temperature ranges:
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High-pressure resistance is a common requirement of industrial o-rings, along with reliable performance in high temperature and dynamic environments. For a high-pressure seal to work to optimal levels, o-ring design and manufacture again depends on choosing specific materials for better performance under specific conditions.
O-rings function on the principle that even pressure placed on the (more or less incompressible) o-ring material creates predictable deformation patterns around the perimeter of the gasket in its groove. This means there&#;s a fairly uniform mechanical stress placed on all contacting surfaces of an o-ring.
Provided the internal pressure from fluids being contained stays below a given O-ring's contact stress rating, it&#;s largely impossible for leaks to occur, even under high pressure. However, mechanical failure under high pressure can easily cause extrusion or destruction of the o-ring, which is why it&#;s important to choose the right material for the precise environment you&#;re looking to use it in.
An engine o-ring, especially one used in high performance or turbo engines, is a good example of a product that has to be rugged enough in design and material construction to handle various challenging requirements of temperature, pressure and chemical compatibility.
Many basic rubbers and polymers aren&#;t suitable for use with oils, fuels or solvent-based compounds. For use in an engine, an oil o-ring has to be created specifically from compatible hybrid materials that allow it to maintain crucial o-ring properties (flexibility, incompressibility) while offering more robust resistance to heat, pressure, o-ring leaking and chemical attack than a standard elastomer typically could.
For more advice and information on suitable products to use as engine o-rings, feel free to contact our customer service team through the support pages on our site.
Plumbing o-ring choices are widespread, given the range of materials, sizes and gauges available for use in ducting and pipework applications, as well as to form tight waterproof seals around taps and other fittings. Choosing the best product for the job depends on finding the correct size and shape for the specific role you have in mind.
Food-grade o-rings have been manufactured to more exacting standards of material composition, such that they&#;ve been officially declared &#;food safe&#; for use in the production and preparation of meals, beverages and dining products.
An approved food-grade o-ring must only consist of the material(s) declared and approved as food safety compliant in the country of manufacture/sale. In the UK, this applies to natural and synthetic rubbers, elastomers and polymers.
To achieve food grade approval, an o-ring manufacturer must also take into account extractable ingredients/compounds if the seal is to be used in direct contact with aqueous, acidic or fatty foods and drinks. Some common food-safe o-ring materials include EPDM, fluorocarbon, nitrile, neoprene and silicone.
Carbon dioxide often presents an issue for many types of o-rings, as softer materials have a tendency to absorb the gas over time and swell up. This can lead to an unreliable seal in the short term, and over time the CO2 will actually cause the o-ring to start to break down from within.
Some popular choices for use in applications where the o-ring will have extended CO2 contact include polyurethane, PTFE, nitrile, and fluoroelastomers. However, the best choice will always depend on the consideration of other environmental or application factors.
Aircraft o-rings and aerospace o-rings generally need to be highly chemically resistant, and able to operate within a wide range of temperatures and pressures in order to keep an aerospace craft&#;s powertrain running cleanly, efficiently and smoothly. Typical applications include fuel cap gaskets, fuel system o-rings, and valve cover seals.
Common elastomers for use in aerospace-type applications include nitriles, ethylene-propylene, fluorosilicones and more. Because there are so many different sizes and gauges of o-ring distributed throughout most aircraft engines and systems, most sales for aerospace and aeronautics are through bulk orders of multi-size o-ring kits.
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