Durometer is one of several measures of the hardness of objects like rubber and plastic. There are a few different measurement scales, called Shores, including Shore 00, Shore A, Shore D and others. The Shore A type durometer scale is generally used to measure the hardness (defined as a material's resistance to permanent indentation) of most rubber compounds, including O-rings and seals. Normally, durometer hardness is referred to in increments of five or ten, such as 50 durometer, 70 durometer, 75 durometer, etc.
O-rings are available in many different durometers, with 70 or 90 durometer, the most common in most compounds. Backup rings are typically 90 durometer. A 70 durometer o-ring is about the same hardness as a shoe heel and 90 durometer is halfway between a shoe heel and a shopping cart wheel.
Softer sealing materials, with lower hardness readings, will more easily flow into the microfine grooves and imperfections of the mating parts. Consequently these softer compounds, like 50 durometer compounds, wear and extrude very quickly.
Harder materials, like 70, 75 or 90 durometer compounds offer greater resistance to extrusion. In dynamic applications, the hardness of the o-ring is doubly important because it also affects both breakout and running friction.
For most applications, compounds having a durometer hardness of 70 to 90 are the most suitable compromise.
For over 60 years, Rocket Seals has provided application specific expertise and stocked the full range of standard and metric o-rings and other seals. Call us to confirm your seal durometer will perform to your expectations at 800-445-7803