Fettspalt

Behavior of lubricating greases in the narrow sealing gap of contacting sealing systems - Example: Radial shaft seal
FKM 2015
Booklet number 323
Project no. 300
110 pages

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Abstract:
Lubricating greases are exposed to high shear rates in the narrow sealing gap of contacting sealing systems. It is not known whether existing flow models are valid at such low gap heights and high shear rates. For this reason, a micro-gap rheometer was set up as part of the research project. This was used to investigate the flow behavior of lubricating greases at low gap heights and shear rates. The known flow models were verified in the area relevant to sealing technology.
In addition to the rheological tests, tribological tests were carried out on a rotary tribometer and on radial shaft seals. This makes it possible to check whether the friction behavior can be explained by viscous grease friction.
In addition, extensive analyses of the greases were carried out in order to be able to draw conclusions between the flow behavior in narrow gaps and the behavior in tribological contact.
In addition to the base oil, thickener particles are also present in the sealing gap of grease-sealing radial shaft seals. These have a significant influence on the operating behavior. The level of the coefficient of friction essentially depends on the type of thickener and the base oil viscosity. The thickener content of the lubricating grease plays a subordinate role in the case of full lubrication.
The viscosity of lubricating greases is significantly higher than the base oil viscosity, even at high shear rates. No correlation of the coefficient of friction with the grease viscosity at high shear rates could be determined. The idea of purely viscous friction in the sealing gap of grease-sealing sealing systems therefore falls short of the mark.