HARDENING & EMBRITTLEMENT
Occurring in both static and dynamic seals, piece hardening is chiefly caused by exposure to high temperatures. Hardening results when exposure extends for a period sufficient to:
1) cause additional cross-linking among the material’s macromolecular chains
2) evaporate plasticizers in the compound
Hardening of an item in service dramatically reduces its resilience, and, as a result, severely limits its ability to act as an effective seal.
Unwanted cross-linking of the rubber can also be caused by chemical attack.
Progressive hardening of the seal has two phases: surface cracking and/or pitting, followed by hardening of the entire cross-section. Compressed seals will also undergo high degrees of compression set as they harden.