Dissolution behavior of different additives and lubricating oil blends in liquid and supercritical CO2

Cryogenic Minimum Quantity Lubrication (cMQL) with oil and liquid or supercritical CO 2 provides efficient cooling and lubrication for machining difficult-to-cut materials. For drilling, oil and CO 2 should be in a single-phase state to avoid separation in the fast-rotating drill spindle before expanding at the drill tip. This article presents the phase behavior, dissolution kinetics and expansion behavior of three sulfur-based additives and three additive-oil blends with CO 2 . Phase behavior is analyzed at 25 °C, 40 °C, and 60 °C between 60 bar and 250 bar. Dissolution kinetics are observed in a transparent flow cell and correlated with phase behavior. Trisulfide and polysulfide additives show high solubility and rapid homogenization, while a sulfurized methyl ester exhibits insufficient dissolution behavior. Oil blends reflect the behavior of their components. Expansion of the oil-CO 2 mixtures at the drill tip was investigated using a high-speed camera. A fine, homogeneous spray was observed under all conditions. • Investigation of additives and oil blends for cryogenic Minimum Quantity Lubrication. • Mutual solubility of lubricants and CO 2 was measured up to 250 bar. • Observation of dissolution kinetics in a transparent high-pressure cell. • Expansion behavior of oil and CO 2 was investigated with a high-speed camera. • Evaluation of flow behavior and solubility with respect to drilling application.