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It is difficult to characterize the shaft surface, which is the running surface of the radial lip seal, by only using the average roughness, Ra. Usually, roughness measurement instruments provide a lot of other parameters besides Ra. A discriminant analysis can be applied to these parameters with seal function tests. The discriminant function generated from roughness parameters in addition to Ra and the results from functional tests could be a useful tool to classify the preferred and non-preferred shaft surfaces for seal applications. The logic of the discriminant analysis is presented. The application of the discriminant function in shaft surface classification is discussed. A case study of a real application is given. The benefit and the limitation of the approach are also discussed.

For a long time, seal manufacturers and seal users have used Ra= 10 - 20 μin and machine lead <̱ ±0.05 degree to control shaft surface finish for radial lip seal applications. However, even when a shaft meets these requirements, the shaft finish may still be a cause of seal failure. In this research work, the deficiency of Ra is studied. The test data obtained in the work suggest that Rsk (skewness), Rku (kurtosis) and Rv (the maximum depth of the surface profile below the mean line) have the capability to separate the “good” and “bad” shaft surfaces for seal applications. The preferred value of Rsk, Rku and Rv parameters are recommended based on this preliminary study.

In this work the role of the squeeze motion, which is the relative radial motion between the seal lip and the shaft, as a part of the pumping mechanisms of the elastomeric radial lip seal has been studied. Six operational factors; shaft speed, fluid temperature, dynamic runout, seal wear track width, rubber material and shaft surface roughness have been considered. The results reveal that the shaft runout and the shaft speed are the most important influential factors on the squeeze pump rate. However, the squeeze pump rate is less than 10% of the total pump rate of the seal. Therefore, the squeeze pumping is not a dominant pumping mechanism.

In this experimental investigation of the sealing mechanism, the rate of oil leakage through the gap formed by rigid seals and the shaft was measured as the function of the shaft speed, oil level, oil temperature and the gap geometry. It has been found that the oil can dynamically seal itself within a range of the shaft speed, even when the gap size is relatively large. This sealing phenomenon is due to the rotational oil flow generated by the shaft. The results of the investigation suggested that the radial seals can be functioning under the unfavorable condition of a gap between the shaft and the seal lip, if the operating parameters are carefully chosen.