As detailed in ASTM D 2632, resilience (also known as rebound) refers to a compound’s ability to regain its original size and shape following temporary deformation. Resilience testing typically involves the dropping of a small weight onto a test specimen (such as a compression set button, see Figure 28). The extent to which the weight bounces back is then noted as a percentage of the initial drop height. A highly resilient material (one that can rapidly regain its dimensions) might engender a 70% rebound value, but values in the range of 40 to 50% are more typical for the majority of elastomers tested. Though compounding may improve an elastomer in this area, it can also detract from good resilience, which is largely an inherent property. As a general rule, resilience is most critical in dynamic seals (such as shaft seals) because it allows them to regain their original shape following deformation. This can be seen, for example, when a shaft seal’s elastomeric lip flexes (is distorted) to follow a shaft imperfection, then returns to its original (“resting”) position. Resilience in a shaft seal lip is closely linked to flexibility.

“The extent to which these properties are present in a material has a huge impact on the material’s ability to function effectively as part of a shaft seal.”

Figure 28