Polyurethane materials are based on either ether (polyetherurethane) or ester (polyesterurethane) and are very wear resistant, although many varieties exist. It is therefore very important to make sure to choose a seal made of a material with appropriate properties for the demands of the application in question and a material which does not vary from one manufacturing batch to another.
Polyetherurethane has better low temperature properties than polyesterurethane and is more resistant to environmentally adapted hydraulic oils. Other thermal and physical properties of polyetherurethane are now also equivalent to those of polyesterurethane. Most rod seals manufactured of polyurethane, normally with a hardness value of 92 to 95° IRH, are designed as U-ring seals in order to provide optimal sealing properties.
High contact force is concentrated to the sealing edge, which can be made very sharp if manufactured of polyurethane. This results in a high specific surface pressure on a small contact surface, which provides optimal sealing ability at low-pressure conditions through effectively wiping off the lubrication film from the rod surface.
In order to achieve a good static sealing function with rod seals of polyurethane a careful treatment of the seal housing groove surface is needed. In our installation instructions, we normally suggest generally established surface roughness values. These are, however, not good enough in most demanding applications. We then suggest a surface roughness value.
Some Examples :