In rotary applications, a turning shaft protrudes through the I.D. of the o-ring, continuously exposing the inside surface of the o-ring to friction-generated heat from the rotating shaft.
Elastomers are poor thermal conductors: if heat is generated faster than it can be dissipated, o-ring failure may result.
To help minimize o-ring heat buildup, especially in applications with shaft rotating speeds in excess of 180 surface feet per minute, the following mechanical design safeguards should be considered where applicable:
- Reduce squeeze to as little as .002″ to minimize friction.
- Provide ample diametrical clearance to increase fluid flow and dissipate heat.
- Select an o-ring made of a hard, self-lubricating compound.
- Maintain a system pressure not greater than 250 psi.
- Avoid applications requiring lower than -40°F, or higher than +250°F operating temperatures.
- Locate the gland as close as possible to the lubricating fluid and as far away as possible from the shaft support bearings.
- Assure that relative motion occurs only between the o-ring I.D. and the rotating shaft… not between the o-ring outside diameter and the gland. This can be accomplished by minimizing eccentric shaft rotation (machining shafts concentric to within 0.0005" TIR), finishing shaft surfaces to 16 RMS for smooth, non-abrasive running; and machining gland surfaces to rougher than 32 RMS to discourage o-ring movement within the gland.
In rotary applications, polymer selection is based upon abrasion resistance, heat resistance, and the other environmental considerations mentioned above. For related polymer performance properties, refer to the Material Selection Guide.