Category: MTM

Study of Correlation Between Grease Film Formations and Mechanical Losses on Various Surfaces

In this dissertation thesis, radial ball bearing torque tendency was evaluated with Li type greases, considering base oil and thickener dependence. Analyses of the reason why each grease formulation provides the different bearing torque were conducted considering comprehensive grease properties, such as rheological parameter and thickener structure and friction and film thickness behaviors of EHL films. Observation of EHL film thickness measured by colorimetric interferometry has enabled detailed insight into the behavior of grease within smooth and dented surfaces. Investigating grease film thickness behaviors on non-smooth surfaces and discussing the influence on the bearing torque were novel approaches in this field. It was found that the film thickness behaviors seem to have a relationship with bearing torque at low rotation speeds and the yield stress and traction behaviors correlated with the bearing torque values at high rotation speed conditions. It was observed that the grease thickener entrainments to the contact areas influence on the film thickness at low speed and track pattern formations at the downstream of the contact areas, and starvation behaviors. The reason of the thickener entrainments exists on the chemical structure of thickeners. The high polarity of the hydroxyl group of the thickener promotes the entrainments to the contact surfaces. On the dented surfaces, the grease with the highest polarity showed the frequent entrainments to the dent areas. The obtained findings could be significant knowledge for the development of advanced greases featuring energy-saving performance of machine parts.