Whether it be designing a new product, or improving an existing piece of equipment, the choice of material is extremely important to ensure a low cost and smooth operation.
Silicone and Hydrogenated Nitrile (HNBR) have distinct physical and chemical properties, which determines what application each material is best suited for. Silicone and HNBR are both commonly used materials for o-rings, gaskets, seals, tubing and membranes. While both elastomers may be used to create similar products, the specific application and environment will ultimately determine whether HNBR or silicone will be the better choice for you. The table below summarises some of the key differences between the two materials.
|-30°C to 150°C||-50°C to 230°C|
|Good compression set||Excellent compression set|
|Good weather resistance||Excellent weather resistance|
|Approx. tensile strength 20 MPa||Approx. tensile strength 5 MPa|
|Great abrasion resistance||Poor abrasion resistance|
|Not compatible with: esters, ethers, halogenated solvents, brake fluids, ketones||Not compatible with: hydrocarbon fuels, alkalis and acids, steam over 121°C, trichloroethylene, aromatic hydrocarbons.|
|Compatible with: most oils and fuels, alkalis and acids, hot and cold water, alcohols.||Compatible with: oils, brake fluids, hot and cold water, saltwater, high molecular weight chlorinated hydrocarbons, fire-resistant hydraulic fluid, ozone.|
Both HNBR and silicone can operate at extremely low temperatures, although silicone is the far better option in high-temperature environments. Silicone can resist intermittent temperatures of up to 230°C, or up to 280°C if a heat stabiliser is added into the raw material.
HNBR has excellent tensile strength and good abrasion resistance, whereas silicone has good tensile strength, but poor abrasion resistance. For dynamic applications with friction, HNBR would most likely be a better option. Granting this, silicone can be formulated to have improved tear strength, making it an ideal choice for applications such as vacuum sheeting and peristaltic pumps. Silicone also has the superior compression set, which makes it a better choice for applications requiring a long-lasting, reusable seal, especially in high-temperature environments.
While silicone has excellent resistance to ozone and UV, HNBR does not have the best resistance to ozone and UV, making silicone the more viable for most outdoor applications. However, HNBR is resistant to most forms of fuels and oils, whereas silicone is not compatible with a lot of hydrocarbon fuels. With this in mind, HNBR would be the superior choice for the automotive industry, although fluorosilicone compounds can be a good fuel-resistant alternative if a silicone-based material is required.
It is clear to see that there is merit in using either HNBR and silicone, depending on what physical properties you require and the operational environment. For help selecting a material for your application, consult our applications page and contact us with any questions.