Bonded O-Rings


Silicone O-ring

Bonded O-rings refer to an O-ring that is converted from an extrusion or cord stock into an O-ring that is either vulcanized or bonded together. Sometimes O-rings that are molded are needed for an application. Sometimes it may be acceptable for the O-ring to be vulcanized or bonded. It may be helpful to differentiate between vulcanize and bond first.

Vulcanized O-rings refer to O-rings that are bonded together under heat and pressure with a bonding agent. This is usually done in combination with a fabricator and a heat press(vulcanizing machine). Typically, NEDC vulcanizes silicone O-rings and fluorosilicone O-rings. These types of bonds typically meet or exceed the strength of the material itself.

Bonded O-rings may also be referred to as “Cold Bonds” which is a tough adhesive that bonds two sides of an cord stock together to form the O-ring. This may be done with EPDM extrusion, Neoprene® extrusion, Butyl Extrusion, and others types of cord stock or extrusions.

The way O-rings must be bonded, depends on how much stress the O-ring will face as well as the environment of the application. It is best to have the bond surface optimize the amount of surface area contact to ensure the bond is as strong as possible. To bond an O-ring there are a few steps that may be advantageous to know(this is not for all bonded O-rings, nor a “guide to bonding;” this is merely an example to show the general process):

Find out the the developed length of the O-ring, this may be done by a simple calculation. First take the I.D(inner diameter) of the O-ring, and add the cross section. This gets you to the middle of the cross section because you have the cross section twice on both sides of the O-ring. You then multiply by pie or 3.14 to get the developed length. You can also find the developed length with the O.D(outer-diameter), this is done by a similar process that you can deduce from the previous method.

You now want to “butter” each end of the developed length with your adhesive or RTV.

You now want to place both buttered ends in a fixture to bond the pieces to form the O-ring, this may be done by cold-bond or vulcanization.

You now have an bonded O-ring!

If you have an O-ring that you would like to be bonded, or questions about a bonded O-ring, please contact