Everything You Need To Know About Custom O-Rings & Seals

O-rings were introduced at the start of the Twentieth Century and, more than 120 years later, are still going strong. Not only that, they look pretty much the same as they did when they were first introduced and have the same sort of functionality. They have not been replaced by a different solution because they remain simple, practical and reliable: they continue to do what they have always been intended to do.

Although the principle behind o-rings has not altered, they are now used in a much wider range of industries and applications. They are also subjected to many more challenges, being used in much harsher environments. As a result, the materials used to make o-rings and the methods of manufacture have developed over the years.

What is an O-ring?

An o-ring is a type of seal or gasket in the shape of a doughnut or torus. It is used where two components are joined to prevent liquids or gases leaking. Unlike many gaskets that are made of cork or rubber, o-rings are used in high pressure environments that would cause normal gaskets to fail.

The o-ring is positioned in a groove or channel between the two components. When the components are pushed or screwed together, the pressure this creates causes the o-ring to distort within the groove so that an effective seal is formed. However, if the pressure goes beyond the limit for which the o-ring is designed, it will fail so it is important that the working environment is taken into account when choosing an o-ring.

Standard o-rings come in a range of sizes and materials and are suitable for general applications where there are no extreme factors that need to be withstood. In particularly harsh environments, however, where there are extremes of temperature, very high pressure or other factors such as the presence of chemicals or UV rays that can cause degradation, custom o-rings that are designed specifically for the operating environment need to be used. This will ensure higher performance, a longer life and the avoidance of failure.

An important feature of an o-ring is that, once pressure is released as components are disconnected, it will return to its original shape. However, constant use may result in the seal losing its shape and so replacement will be necessary. A careful choice of materials can delay this happening and so reduce maintenance costs.

O-rings can be either static or dynamic. For the former, the components will stay connected and so the seal will remain compressed. A dynamic o-ring will provide a seal between two parts that move relative to each other and so it will need to be made of more durable materials to prevent premature wear. All types of o-ring benefit from some type of lubrication for optimum performance, although this is more important for dynamic versions due to the varying movement they can experience.

How O-rings are Used

The versatility of o-rings means they are used in a wide variety of industries and applications. These include standard versions to provide watertight seals for plumbing and for general domestic purposes but also custom o-rings for specialised applications:

• In the automotive industry, robust seals are needed to resist grease, heat and other hazards in engines, with turbo and high performance engines being particularly challenging. Compound materials are specifically created to provide the required flexibility and durability.
• Aircraft require seals that are completely dependable even when there are extremes of temperature and high pressure. Safety is paramount so all seals are custom-made from suitable material for absolute reliability.
• Food grade materials are necessary for o-rings used in the catering industry where hygiene is of prime importance. This is especially true when the seals come into direct contact with food ingredients that may be acidic or have other challenging properties.
• O-rings used in industry may have to contend with dust, fumes, extreme heat and the presence of chemicals while still providing a reliable seal.

Materials and Manufacturing Methods

Other than choosing an o-ring that will fit, it is also essential to ensure it is made from materials that are suitable for the working environment.

• Natural rubber seals are common but the material is not suitable for more demanding applications.
• Silicone is suitable for outdoor applications since it resists weathering, heat, water and ozone. Tensile strength is low for standard silicone and operating temperatures are -50°C to +200°C.
• Nitrile is a general purpose compound that is tough and resistant to some hydraulic fluids, petrol, propane and water. It is not suitable for high pressure applications or for extreme temperatures, typical ranges being -50°C to +120°C.
• Viton can withstand higher temperatures, up to 205°C, and has good resistance to various chemicals.
• Fluorosilicone works well in the widest temperature ranges, from -60°C to +205°C and is almost matched by butyl.

O-rings are generally made by moulding, the most common types being injection, compression and transfer moulding. The actual method chosen will depend on a number of factors: production quantity, materials and cost-effectiveness.

Factors to Consider when Choosing O-rings

Consideration of the operating environment and processing requirements is essential since this will determine the best material to be used.

• Assess the chemicals, fluids and temperature range that apply and ensure the materials can withstand them.
• If pressure is likely to be particularly high, use harder materials to avoid excessive deformation of the seal.
• For dynamic sealing, ensure the material is sufficiently elastic to maintain its shape.
• Particularly for challenging environments, choose a material that will provide the necessary reliability, durability and longevity.
• To ensure proper installation, the surface of the o-ring needs to be smooth and compatible with the adjoining components. Lubrication is also necessary to reduce friction.

Although o-rings are seemingly simple items that have a straightforward purpose, designing and manufacturing a custom version that does the required job can be complex. Choosing or formulating the most suitable material is a challenge and one we can help you through.

At Gulf Rubber, we have wide experience of all types of seals and know the best types to use in particular situations. We can assess your needs, create a solution that works effectively and provide all the help you need to achieve your aims. Get in touch and we will provide the o-rings you need.