In order to clarify the sealing mechanism of an oil seal, it is necessary to know its fundamental properties and movement now in action. There are two subjects in this study. One is to reveal the temperature dependence of fundamental properties, mainly wringing force, average wringing pressure and lip contact width, and the other is to know the lip temperature now in action and to know how the lubrication is carried out at the lip portion. The
measurements were carried out with our devised instruments for the former subject and with a thermocouple for the latter. A simple analysis of the lip temperature obtained was made in order to know a mechanism of the lubrication.
The results indicate that with the rise of temperature of oil seal, the wringing force and the average wringing pressure decrease because of the reduction of rubber elastic modulus and of thermal expansion of spring, and the lip contact width hardly varies, and also indicate that under a constant temperature of lubricating oil, the lip temperature never rises so high as in the case of free rising of oil temperature, and that the fluid lubrication is carried out at the lip.