| Lubricant migration is a significant factor which can result in the failures of space lubrication. Here, the migration refers to the phenomenon that lubricant freely expands on a contact surface in the absence of external forces. In consideration of lower dosage and long operating life on lubrication of mechanical components in spacecrafts, lubricant migration is the main way of oil loss in space environment. Therefore, it is essential to study the characteristics of lubricant migration and its effects on the mechanism of the lubrication failures.The characteristics of lubricant migration and the corresponding lubrication properties were discussed. Firstly, the influences of oil content, lubricant viscosity, and temperature gradient on lubricant migration were studied. Based on the migration results, the lubrication characteristics affected by oil content, lubricant viscosity, temperature gradient and initial migration time were discussed. Secondly, we analyzed the characteristics of the migration by using magnetic fluid(MF) under temperature gradient and magnetic field. The results of research as follows:(1) The lubricant under temperature gradient moves from the high temperature region to the low temperature region. It also shows that the increment of temperature gradient, oil content and viscosity can all enhance the average velocity of drop migration.(2) Lubricant migration has a great effect on the lubrication properties. Undergoing a period of stable friction test, a significant increase of the friction appears. The stage of stable and low friction will shorten with the decreasing of oil content, decreasing of oil viscosity, increasing of temperature gradient and the initial migration time. Meanwhile, the lifetime of lubrication will decrease.(3) The MF also migrates under temperature gradient field, and its migrating speed on initial position increases with increasing of temperature gradient. Otherwise, magnetic field shows obstacle effect on the MF migration. With the increasing of magnetic field, the migrating speed decreases obviously. When the surface magnetic flux density reaches to 500 Gs, the MF can be adsorbed permanently on the initial position and no migration was observed.(4) The MF migration under magnetic field also shows great effect on surface lubrication. The time of stable friction will be extended with the increasing of magnetic field. According to the results, the friction coefficient can remain around 0.075 for a long time when the magnetic flux density in the friction region is 500 Gs. |
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