Creep transport is defined as the velocity of a mass of grease when it is subjected to vibrational and gravitational forces. The method developed to assess this, measured the time taken for the grease submitted to low frequency vibrations to creep, under the influence of gravity, a specified distance down a cylindrical tube. The vibrations were characteristic in frequency and amplitude to those commonly experienced by commercial rotating machinery. Vibrational excitation was found to have a widely varying effect on creep transport of grease, suggesting that this parameter may be important in the selection of greases for specific applications where vibration is present; in contrast, the NLGI number gave almost no indication as to the effect of vibration on a particular grease. A vibration number related to the creep rate is suggested for grease selection. The vibration number correlates to the yield stress of the grease, with higher yield stress correlating to higher creep rate. However, no correlations between creep rate and base oil viscosity or bleed rate were found.
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