Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Chart 3 plots the relationship between the VI of the base oil and thickener content. Again, there are correlations (R-squared 0.57 to 0.90) between the VI of the base oil and the thickener content for all but the Ca sulfonate grease (R-squared = 0.06). The higher the VI of the base oil, the higher the required thickener content, since the VI of petroleum hydrocarbons is strongly inversely correlated with solvency.
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Experimental results illustrated a significant relationship between base oil solvency and thickener yield; this relationship has real economic value for grease manufacturers.
Physical properties including mechanical stability, roll stability, dropping point, oil separation, and mobility exhibited favorable results for all base oils in the study. These observations remind us that base oil selection and preference should differ according to the requirements of the application. Paraffinic chemistries maintain a leading role in engine oil applications; however, it is evident throughout our study that a specialized application, such as grease, can benefit from high solvency and low PAH content as found in modern naphthenic base oils.
Chart 4. Viscosity-Gravity Constant vs Thickener Content
Chart 4 plots the relationship between the VGC and thickener content. For this parameter, there were stronger correlations and the R-squared values ranged from 0.43 to 0.91 for most greases compared to Ca sulfonate (R-squared = 0.22). Li 12-HSA had the highest R-squared at 0.91. The higher the VGC, the higher the solvency and the lower the thickener content.
Conclusions
These data have demonstrated that the solvency of the base oil is critical to the processing of the grease. The NLGI grade is defined by the penetration values which are affected by the efficiency of the thickener system, the base oil, and the thickener. By decreasing the amount of thickener to produce a particular grade of grease, the overall costs of the formulation can be reduced.
References 1. ASTM D611-12 (2016), “Standard Test Methods for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents“, Annual Book of ASTM Standards, Vol. 5.01.
2. ASTM D2270-10 (2016), “Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40°C and 100°C”, Annual Book of ASTM Standards, Vol. 5.01.
3. ASTM D2501-14 “Standard Test Method for Calculation of Viscosity-Gravity Constant (VGC) of Petroleum Oils“, Annual Book of ASTM Standards, Vol. 5.01.
LINK
www.ergon.com
LUBE MAGAZINE NO.144 APRIL 2018
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