PTFE O-rings

O-Ring Sizes for Industrial Applications

From machine design to applications in household appliances, the use of the o-ring is practically indispensable. Availability of o-rings comes in the form of metric as well as inch sizes.

Industrial applications of o-rings

A precisely engineered mechanical mounting is essential for the successful use of o-rings in joint design. Such a mounting must take into consideration the deformation of the o-ring. The amount of stress, which is mechanical in nature, should be of a precisely calculated amount at the o-ring contacting surface with the mounting. In principle, the fluid pressure that is been contained must not be greater than the stress that is imposed on the o-ring. As such, leakage in the component will not happen. And because the o-ring material is virtually incompressible, the pressure of the fluid that is being contained is transferred and the pressure at the interface increases as the operating pressure goes up. The specification of o-ring sizes is by means of the inner diameter as well as the thickness, otherwise known as the cross section diameter. As long as the o-ring does not fail in a mechanical way, the sealing of high pressure fluid can be done effectively. The usual mode of sealing failure is at the interface of the adjoining parts.

The design of the seal is such that a contact exist between the sealing surfaces, that is between the o-ring and the mounting surfaces. This method of sealing allows for the containment of high pressure fluids. This can be achieved within the failure stress limits of the o-ring. Imperfections are common in the contact surfaces of the mounting parts, and o-ring material which is highly flexible in nature, effectively fills out and accommodates all uneven surfaces. Nevertheless, an excellent surface finish is imperative for all the parts that comes into contact, meaning that there should be as little imperfections as possible on the surfaces between o-ring as well as the contact surfaces of the mounting. This is especially critical in low temperature applications because the material of the sealing compound is at its glass transition temperature threshold, making it more crystalline in its properties. The same principle would apply to applications of o-ring sealing in dynamic environments. An exceedingly rough finish to the surface of the contact parts will cause abrasion to the surface of the o-ring. On the other hand, the sealing would not be sufficiently lubricated by fluid film in the situation that the surfaces that come into contact are exceedingly smooth.

In conclusion, the correct choice of o-rings in terms of sizes and material would have to take into consideration its nature of application and the environment, including that of physical and chemical resistance. O-rings are available in a number of materials that include Viton, nitrile, FFKM, FKM, silicone, epdm and more.