Choosing the proper material is as crucial to the success of an O-Ring as the design. Key questions must be asked — what type of environment will the application face? What outside factors affect the material? A complete understanding of conditions and context will result in the choice of the proper sealing material.
NBR seals are considered standard and commonly used. NBR is ideal for engine applications, but not for applications where weathering is a concern. NBR contains weak bonds that will crack in the presence of even small levels of ozone.
There is a better way: hydrogenation. HNBR is similar to NBR, but adds the hydrogen component. Hydrogenation of the double bond in the polymer chain adds an element of resistance and limits ozone attack on the material. Using HNBR will greatly prolong the life of the seal when it comes to this type of application.
Aside from external factors like ozone, it is important to know the temperature range of a compound chosen for an O-Ring. Where will the application be used? What types of temperatures will the material be exposed to? Will temperatures vary over the course of its lifetime?
Some NBR compounds with very low fuel swell may only function to -25°C. Most NBR compounds can reach temperatures as low as -40°C or, in some cases, even -65°C. Clearly, within a given polymer, there may be different low temperature service ranges. Be sure to speak with the experts to make sure your compound meets the appropriate temperature range.
There are multiple levels of fuel swell. The amount of swell is dependent on the chemistry of the oil and the temperature at which exposure occurs. Manufacturers have spent time and money developing elastomers that swell very little when exposed to oil or water. Swelling will continue until the internal stresses inside the elastomer reach equilibrium. Too much swell can cause cracking, deterioration or premature failure.
There are many other compounds suitable for different seal environments such as the most common, FKM, EPR, Silicone, and many more in standard and metric sizes. Contact Rocket Seals to find out the compound that is best suited to your needs.