Case Study
Low Pressure Static Seal Design
Challenge
- Seal design with orthogonal requirements
- Passes leak specification while allowing relative motion between two plastic parts
Seal design space is constrained by previous decision to incorporate O-Ring seal
The client’s design requires an airtight seal interface which is also subjected to axial and rotational relative motion. This results in orthogonal requirements with constraints on both the maximum torque required for relative motion, and the minimum sealing force developed at the seal. A numerical model of the O-Ring under compression was developed and incorporated into a pseudo-static kinetic model of the moving components. A Monte-Carlo analysis was used to analyze the performance of the reference design on a statistical basis, and to predict the performance of the system after changing key parameters like lubrication, part dimensions, and O-Ring materials.
Approach
- FBD and simple static force model constructed
- Simple test to extract one key performance related characteristic that could not be analytically determined
Results
- Alternate seal geometries (lip seal) create lower friction forces at a given interference – more robust design w.r.t. specification
Permitted efficient exploration of design space, sensitivity to manufacturing variability
Resulted in the insight that under the initial constraints that there was no solution
Key Takeaways
- Results of simulation show that without lubrication we cannot simultaneously satisfy both leak and torque requirements above 3σ threshold
- It was very unlikely that a test-to-success approach would lead to a solution
- Results of simulation clearly show the viable operating regime and identify critical-to-function tolerances and characteristics
