Film thickness in a ball-on-disc contact lubricated with greases, bleed oils and base oils

• Published in: Tribology international 2012-09, Vol.53, p.53-60
• Main Authors: Cousseau, T., Björling, M., Graça, B., Campos, A., Seabra, J., Larsson, R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Base oil; Bleed oil; Bleeding; Contact; EHD optical interferometry; Exact sciences and technology; Film thickness; Friction, wear, lubrication; Grease; Greases; Lubrication; Machine components; Machine Elements; Maskinelement; Mathematical analysis; Mechanical engineering. Machine design; Oil films; Tribology
• ISSN: 0301-679X; 1879-2464; 1879-2464
• DOI: 10.1016/j.triboint.2012.04.018

Three different lubricating greases and their bleed and base oils were compared in terms of film thickness in a ball-on-disc test rig through optical interferometry. The theoretical values calculated according to Hamrock's equation are in close agreement with the base oil film thickness measurements, which validates the selected experimental methodology. The grease and bleed oil film thickness under fully flooded lubrication conditions presented quite similar behaviour and levels. Therefore, the grease film thickness under full film conditions might be predicted using their bleed oil properties, namely the viscosity and pressure-viscosity coefficient. The base and bleed oil lubricant parameter LP are proportional to the measured film thickness. A relationship between grease and the corresponding bleed oil film thickness was evidenced. ► Base and bleed oil have different film thickness values and rheological properties. ► Greases and the corresponding bleed oils have about the same film thickness values. ► Grease and bleed oil have higher film thickness than base oil at same conditions. ► Such differences are assigned to the grease formulation.