Simulating aging and chemical effects can help determine how long seals will last.
Numerical simulation of O-ring aging
A manufacturer of stationary gas engines needed O-ring seals in the cylinder liners that would stand up to typical engine fluids, heat, and pressure. And they had to last a long time, as premature leakage results in expensive downtime and high labor costs for the repairs.
One sealing material Parker technicians modeled is HNBR rubber. The fluid is a water-glycol mixture, temperature constant at 95°C, and fluid pressure is 2 bar.
FEA predicts not only changes in sealing force over time but also the resulting compression set. Each image represents stress distribution in the O-ring cross section at various stages in its life. They show, clearly, a decay in stress over time. After 20,000 hr, the test ends and conditions approach initial values: 0-bar pressure and ambient temperature. Any remaining strain energy stored in the O-ring is too small to compensate for thermal shrinkage. A gap on the outer sealing surface leads to leakage. This example of computer simulation using aging data shows the advantages of computer-simulation versus traditional compression-set testing.
For this application, Parker developed a peroxidically cross-linked fluoroelastomer (FKM). It resists oils containing aggressive additive packages, water-glycol, as well as acids and lye. Using the same finiteelement modeling, technicians simulated behavior of the new compound. Results indicated good sealing performance at 95°C and 2 bar, even after 20,000 hr of service. Field tests performed by the customer confirmed the predictions.