Influence of Li grease thickener types on film thicknesses formed between smooth and dented surfaces

The lubricant film thickness behaviors of lithium (Li) thickener type greases and their base oil were investigated for the contact between a glass disk and a smooth/dented steel ball using an optical interferometry. The main focus is to understand grease film behaviors including high speed history and contact surface conditions. A Li stearate thickened grease showed similar behaviors to the base oil itself and the thickener particles were not observed on the contact. Thickener particle entrainments were observed in greases with Li 12-hydroxy stearate and Li complex thickeners. Track patterns formed in the downstream of the contacts correlated with the thickener particle entrainments to the contacts. The Li stearate thickened grease showed quick starvation phenomenon without a scoop which maintains fully flooded conditions. The particle entrainments of Li 12-hydroxy stearate and Li complex thickened greases were less observed after measurements at high speeds. On the dented surfaces, the particle entrainments of the Li 12-hydroxy stearate grease were more frequent than those of Li complex grease. These results suggest that thickener chemical structures have influence on the grease film formation. The thickener with higher polarity could promote the entrainment of greases into contact. © 2018 Japanese Society of Tribologists.