The O-ring is a seal that is ring shaped with a round cross-section, such as a donut. O-rings are among the most commonly used seals used in machines and equipment because they are cheap, easy to produce, reliable and easy to assemble. The material from which this seal is made is mainly an elastomer (rubber). But the O-ring is also manufactured, for example, in PTFE, other thermoplastic materials and in metal, both solid and hollow. In this article you will read everything you need to know about the O-ring.
The history of the O-ring
People have been working with rubber for centuries, but it was only in 1936 that Niels Christensen invented the O-ring. Christensen, originally from Denmark, came to the United States when he was 26 years old and became a leading draughtsman at Fraser and Chalmers, a manufacturer of mining machines, boilers and pumps in Chicago. From there he worked for the Colombian Exhibition of Chicago and for the E.P. Allis Company of Milwaukee (a manufacturer of agricultural machinery, construction machinery and power transmission).
In 1936, Christensen discovered that a ring shaped piece of rubber in a groove, one and a half times as long as the small radius of the ring, was a reliable, tight seal for a piston/cylinder application. In 1937 he applied for a patent, which was granted in 1939.
However, the O-ring was not widely accepted until the increase in demand for aircraft during the Second World War. Christensen sold his O-rings to the military after demonstrating their effectiveness on a Northrop aircraft. Within a few years the O-ring became the standard seal for air force hydraulic systems. The United States bought out major military patents and gave them away to manufacturers.
Operation of the O-ring
The O-ring is used as a seal in a groove that is milled or rotated in the structure. Pressing the O-ring deforms it. This is how the O-ring seals the two parts of the sub-area. In most cases the connection is static, but it can also be dynamic. Because the O-ring is flexible, it adapts easily to the tolerances in the construction to be sealed.
In construction, O-rings are one of the most important elements. Usually invisibly, they have to complete their task. They are available in various metric and inch sizes, with inch sizes being the most used and also widely used in Europe.
O-rings are produced in the following materials:
- Nitrile (NBR or Buna-N)
- Siliconen (VMQ)
- FKM (Viton ®)
- FFKM (Kalrez®)
- Fluorsilicone (FVMQ)
- Polyurethaan (AU, EU)
Depending on the application, the right material can be chosen. On our website you will find a chemical resistance list that you can consult. The specialists at NDS-Seals will be happy to advise you.
It is not always possible to use standard O-rings. When in existing situations a seal is needed that has specific requirements, a standard O-ring can no longer satisfy. Think of bridging large tolerances, easier assembly, lower friction or of course a non-round shape of the construction.
In this case we can do an inventory for you and if necessary design a special custom-made seal for your application. We prefer to be involved at the beginning of the development of a new device so that we can use our experience to come to the best solution.
Other properties of the O-ring
- Static axial (flange seal)
- Static radial (shaft seal)
- Linear (piston/rod seal)
- Rotating (shaft seal)
- Oscillating (shaft seal)
- Static up to 50 bar, above with Back-Up rings
- Dynamic up to 50 bar
- -60°C to 320°C
- Depending on the choice of material, O-Rings can be used in all chemical applications
All the benefits of O-ring seals at a glance
- Sealing with a wide range of pressures, temperatures and tolerances
- Easy to use
- Standard dimensions and groove dimensions
- Compact and lightweight
- Long life
- Distortion possible over a wide range and compensates for tolerances
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