Low Pressure Sealing Integrity of O-Rings Based on Initial Squeeze and Counterface Finish

Abstract

Sealing integrity of O-rings at low pressures is studied. For a given squeeze, this is found to be independent of hardness (modulus), i.e., squeeze alone determines the degree of infilling and the resulting leakage path geometry for a particular surface finish.

Relationships for footprint width and contact pressure as functions of squeeze, size and modulus are presented and correlated with other published results. Infilling of rubber into typical sawtooth machining finishes is calculated, measured and presented as a function of O-ring squeeze, independent of rubber hardness. Sealing can be improved by increasing the squeeze (greater infilling) or the O-ring cord diameter (greater leakage path length), or by reducing the steepness and roughness height of the finish.

Sealing is limited by an O-ring's upper limit of squeeze, a test methodology to find this is described. Results are presented for a particular fluorocarbon rubber, showing significant permanent damage beginning at about 45 percent squeeze. Various approaches to calculation of leakage are discussed.

For designers, the conclusions for better sealing are to use fat, highly squeezed O-rings, and be aware that steepness (average slope) of the finish perpendicular to potential leakage paths is more important than a simple roughness number for the counterface.

Presented at the 49th Annual Meeting in Pittsburgh, Pennsylvania May 15–1994

KEY WORDS:

• Static Seals

Notes

Presented at the 49th Annual Meeting in Pittsburgh, Pennsylvania May 15–1994