PTFE Rotary Seal Shaft Considerations

Today, we'll take a deeper look at PTFE rotary seal shaft concerns.

In rotating applications, adequate surface finishing is critical for achieving good sealing and the longest seal life feasible. Rotating surfaces that are overly rough might cause leaks and be extremely abrasive. Unlike elastomer contact seals, PTFE lips may operate on very smooth surfaces without lubrication.

Because of their hardness and low coefficient of friction, PTFE lip seals, unlike other seals, slide over the mating surface's high points and withstand wear. the appropriate surface finish for PTFE lip seal applications.
 

Dynamic surfaces with relatively rough finishes may wear faster, reducing seal life and perhaps compromising performance. In addition, dynamic surfaces with a smoother than required finish may reduce the seal's efficiency. The optimal surface roughness permits a layer of the sealed fluid to pass between the seal and the mating surface, lubricating and prolonging the seal's life.

PTFE rotary seal applications necessitate a firm running surface on the dynamic section of the hardware. The tougher surface enables for the use of more reinforced seal material, which increases seal and hardware life. Softer running surfaces require less wear-resistant material, which will not harm the hardware and will typically result in a shorter seal life.

To keep the seal as the sacrificial component, a balance between seal material and dynamic surface hardness must be achieved. 

When the dynamic surface hardness is less than 45 Rc, most seal materials polish the running surface of the hardware and seal. This first break-in phase will cause seal wear to taper down, depending on the material, surface polish, and PV of the application.

When hardness exceeds 45 Rc, the initial surface polish becomes more important to seal life. The hardness of the dynamic hardware surface influences the seal's wear rate. In addition, some seal lip materials are abrasive and will wear down weaker metal shafts or dynamic components.
 

In general, a finer surface polish indicates improved overall seal and hardware performance. The optimal hardness of the hardware's dynamic surfaces is 50 to 60 Rockwell C. The exact hardness employed is usually a compromise between the increased expenses involved with polishing tougher materials and the longest possible seal life.