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Influence of dynamic eccentricity on the pumping rate of rotary shaft seals at sub-zero temperatures
Elastomeric rotary shaft seals are complex tribological systems. They prevent lubricants from leaking between rotating (e.g. shaft) and stationary (e.g. gear housing) machine parts. Their sealing performance is essentially determined by the back pumping capability of the system. During the dynamic operation, rotary shaft seals can actively pump leaking fluid back to the fluid side. For the assessment of the pumping capability and the leak-tightness of the sealing system, the pumping rate can be used. The pumping rate measures the pumped fluid volume per time or distance.
In several research projects at the University of Stuttgart, analyses for the assessment of the leak-tightness by means of the pumping rate were performed for mineral and synthetic oils. An empirical model for calculating the pumping rate was developed. The calculation model is valid for a wide parameter range of the analysed rotary shaft seals. In further publications, the influence of static and dynamic eccentricities and of low temperatures on the pumping rate of rotary shaft seals was separately presented. However, the pumping rate behaviour was not checked for the combined variation of dynamic eccentricity and low operating temperatures. Elastomer materials lose elasticity at low temperatures. A low elasticity of rotary shaft seals can affect the leak-tightness even for light eccentric sealing systems negatively.
In this paper, the influence of dynamic eccentricity and low operating temperatures on the pumping rate of elastomeric rotary shaft seals is analysed experimentally. For this purpose, the pumping rate was measured at different oil sump temperatures between +40 and –20 °C and different dynamic eccentricities up to 0.3 mm. The experimental analyses were performed with rotary shaft seals made of nitrile rubber (NBR) and fluoro rubber (FKM) in combination with synthetic polyalphaolefin oil FVA PAO1.