O-rings are essential for preventing leaks. Also known as toric joints, they are commonly found around mating surfaces. O-rings seal mating surfaces so that pressurized water, fluid or gas can travel through the parts without leaks. When shopping for O-rings, however, you should consider their Shore Hardness.
The Basics of Shore Hardness
Shore Hardness is a measurement of how resistant a material is to indentation. It ranges from 00 to 100. The higher the Shore Hardness rating, the harder the material.
How Shore Hardness Is Calculated
To calculate the Shore Hardness of a material, a device known as a durometer is used. Durometers feature a needle. With the durometer turned on, press the needle against the material while attempting to penetrate it. The durometer will then measure the depth of the needle’s indentation. Using this information, the durometer will calculate a Shore Hardness rating of 00 to 100, which represents the O-ring’s hardness.
How Shore Hardness Affects O-Rings
O-rings are available in different materials, some of which have a higher Shore Hardness rating than others. O-rings with a high Shore Hardness rating are harder than those with a low rating. Therefore, you can refer to an O-ring’s Shore Hardness rating to determine whether it’s soft, hard or somewhere in between.
O-rings with a Shore Hardness rating of 40 to 60 — typically the lowest in which O-rings are available — are soft. They compress and conform easily, making them an excellent choice for low-pressure applications. Silicone and flexible rubber often have a Shore Hardness rating within this range.
There are also O-rings with a Shore Hardness rating of 40 to 50. They are harder than those with a 40 to 60 rating, but they are still relatively soft. Silicone and neoprene are common materials used for these O-rings.
Hard O-rings are typically classified as those with a Shore Hardness rating of 60 or higher. They provide superior resistance to extrusion but may not seal as effectively under low pressures. Nitrile, Buna-N and hard rubber may exhibit a Shore Hardness rating of 60 or higher.
The Shore Hardness of an O-ring will affect its sealing performance, durability and compatibility with other materials. Hard O-rings offer superior protection against wear and tear, but they require more force for compression. Softer O-rings, on the other hand, are better suited for irregular surfaces, but they may deform under high pressure.