Friction of seals to be overcome at the start of a movement (Figure H 1). It is dependent on both the form of the seal (preload) and the seal material and on the service life of the seal: during longer periods of inactivity, the oil film under the seal is squeezed away allowing dry friction to predominate (Figure H 2).
Stiction of seals is particularly evident during stick-slip movements and during oscillating movements where the stroke remains within the height of the seal. No new lubricating film can develop during this kind of movement, which means the whole process is affected by dry friction.
![3138d2e5c60f13ee86af13e5a458ab8aec77cdfd 0001_haftreibungvondichtungen.gif](/fileadmin/smc/files/3138d2e5c60f13ee86af13e5a458ab8aec77cdfd.gif)
Figure H 1: Stribeck curve
![dd66473f0783e241ef4ebfeec99dd672f803bc71 0002_haftreibungvondichtungen.gif](/fileadmin/smc/files/dd66473f0783e241ef4ebfeec99dd672f803bc71.gif)
Figure H 2: Stiction depending on the period of inactivity a) polyurethane, b) NBR, c) fabric