#1 What is meant by permanent deformation?
An O-ring is said to be permanently deformed if the former round cross-section of the O-ring has become deformed and no longer returns to its original shape despite the absence of load.
The ability to return to its original shape after pressing is indicated on the material data sheets by the compression set. The compression set is therefore one of the most important quality characteristics of an O-ring material.
#2 How does permanent deformation occur in O-rings?
1. Excessive temperatures cause post-crosslinking, which makes the O-ring stiff. The material should therefore be designed with some certainty with regard to temperature.
2. A common mistake is that the design department has designed the groove space too small. The optimum is 15% to 30% free groove space after pressing the O-ring.
3. If the O-ring is older than specified in DIN 7716 (bearing for elastomers), it is possible that, among other things, the plasticizers will dissolve from the O-ring and the O-ring will lose its elasticity accordingly. Make sure that you order from a supplier who stocks in accordance with DIN 7716.