When designing a component that includes a spring-loade […]
When designing a component that includes a spring-loaded China PTFE tubing, it is not sufficient to specify all the sealing parameters; another key part of the design is the surface finish of the mating surface. Surface finish on the seal life, and then recommend the use of spring-type PTFE seal surface finish.
Surface finish is a measure of surface roughness. If you look at the surface in the contour under a microscope, you will see that even a smooth surface is made up of tiny valleys and peaks. The average surface height is the average height of all valleys and peaks for a given surface. The value RA is the average of the peak and valley deviations from the average surface height, and RMS is the root mean of the deviation. The RMS value is more sensitive to the extreme deviation of RA, and some consider it to be a better measure of surface finish.
A smoother surface has a smaller value for RA and RMS, which makes sense because a smoother surface should have smaller peaks and valleys.
If the surface finish is too rough, not only can wear the sealing lip, but also can produce leakage path, thus undermining the purpose of sealing.
However, if the film PTFE transferred to the mating surface, this is a good thing. The film can reduce the friction between the seal and the surface, and increase the sealing life. This means something else, but if the surface is too smooth, then the PTFE film will not form on the mating surface.
For spring-loaded PTFE seals, the recommended surface finish for the mating surface is typically 2 R MS to 16 RMS, depending on your application. For low temperature gases and liquids, you need a smooth finish between 2 and 4. For non-cryogenic gases, the recommended surface finish is between 6 and 12 RMS. For liquids, the surface finish is between 8 and 16.