24th International Colloquium Tribology - January 2024 63 An investigation of Using Ultra-low Viscous Naphthenic Oil in Lubes and Greases Jinxia Li * , Mehdi Fathi-Najafi, Thomas Norrby Nynas AB, Raffinadervagen 21, SE-14982 Nynäshamn, Sweden * Jinxia.li@nynas.com 1. Introduction Ultra-low viscosity naphthenic oil (ULVN) has some well-appreciated properties such as excellent solvency and superb fluidity at low temperature. However, due to a relatively low flash point, it is more recommended to be used for the low temperature applications such as hydraulic fluids that are targeting low to artic conditions, sometimes in combination with other type of oils. The aim of this study was to investigate the performance of the ultra-low viscosity naphthenic oil in three different types of applications namely, I) Metal Working Fluid, MWF, II) Hydraulic Fluids, HF, and III) Lubricating Greases, LG. 2. Experiment part Three commercial ULVNs have been used in this study: Base Oil nr.1 (BO1), Base Oil nr.-2 (BO2), and Base Oil nr.-3 (BO3). Some of the typical characteristics are shown in table 1. Table 1: Basic characteristics of the three ULVNS Specification- BO1 BO2 BO3 Viscosity 40-°C, (mm 2 / s) 2.8 2.9 3.7 Viscosity 100-°C, (mm 2 / s) n/ a 1.2 1.3 Flash Point PM, °C 84 105 104 Aniline Point, °C 66 72 68 Pour Point, °C <-70 <-70 <-70 It is well known that one of the most critical properties of a hydraulic oil is to have good to excellent viscosity index (VI) which cannot be fulfilled by the ULVN’s due to low VI. Hence, the use of viscosity index improver was necessary. In total, three hydraulic fluid models were formulated in which the same VI improver and additive package were used. For Metal Working Fluids, two different types of concentrates for water-based fluids have been prepared based on BO1: Emulsifier package Span80/ Tween80 for Conventional soluble oils concentrate and Semi-synthetic Model A. The emulsions were formulation by 5 (wt%) concentrate and 95 (wt%) distilled water, and the particle sizes have been investigated by Mastersizer 3000E at Day 0, Day 1 and Day 7. In the case of lubricating greases, BO2 has been used to investigate the possibilities of incorporating ULVN in the formulation of lithium greases. Due to the low flash point, BO2 has been used as cooling oil while one heavy naphthenic base oil has been used as cooking oil. In addition to the above experiment, BO2 in the grease formulation was replaced by a low viscous API group II oil. The purpose of this part was a comparative study between the two types of low viscous oils in grease application. 3. Results and discussion 3.1 ULVN in Hydraulic fluid The final compositions and basic properties of the HF Iso VG 15 (HF15) are shown in table 2. Table 2: formulations and some properties of three hydraulic fluids Specification Base oil (wt%) VI I (wt%) Additive package (wt%) Viscosity 40-°C, mm 2 / s) VI BO1_HF15 83.2 15.9 0.85 14.4 406 BO2_HF15 83.1 16.0 0.85 14.8 406 BO3_HF15 86.1 13.0 0.85 15.0 348 For the Iso VG15, the Swedish Standard 15 54 34 [1] has a low temperature limit of 1600 (mm 2 / s) at -30-°C, which means all three ULVN (BO1, BO2 and BO3) could meet this standard requirement, shown in Figure1. However, according to the requirement of the British Defense Standard 91-48 [2], the low temperature kinematic viscosity limits of 500 (mm 2 / s) at -40-°C, and 3000 (mm 2 / s) at -54-°C are indicated in Figure 1 by the red horizontal lines. As shown, only BO1 and BO2 do meet this requirement. The two formulated Hydraulic fluids BO1_HF15 and BO2_ HF15, which meet both Swedish standard and British Defense Standard, have been proceeded with some essential physical chemical properties of hydraulic fluids. The results demonstrate low foam, fast air release and good demulsibility. Figure 1: Kinematic viscosity of Hydraulic fluids at lower temperatures. 64 24th International Colloquium Tribology - January 2024 An investigation of Using Ultra-low Viscous Naphthenic Oil in Lubes and Greases 3.2 ULVN in Emulsions BO1 has been selected to study of the stability of Emulsions. The results are shown in Figure 2. For Span80/ Tween 80 system, the Dx (50) of the emulsion shows ‘U’ shape from HLB 11 to HLB 15, gives the minimum value at HLB 13 and keeps stable from day 1 to day 7. For semi-synthetic model fluid, there was warning about the data quality, which can be explained by the smaller particles less than 10 nano meter in the semi-synthetic emulsion which cannot be detected by Mastersizer with red laser. Figure 2: Median droplet Size (Dx (50)) for Span/ Tween system and Model A 3.3 ULVN in Lubricating Greases The final viscosity of the high viscous naphthenic oil and BO2 (alternatively with the Low viscous API Group II) is determined to be about 107 (mm 2 / s) which is in the same range of a straight naphthenic base oil called T110 (which is recognised by the grease industry an excellent oil for the preparation of e.g., lubricating greases). The results of the grease shown in Table 3. Table 3: some characteristics of the conventional lithium greases based on 107 mm2/ s in base oil viscosity Properties; Method Grease A Grease B Grease C Base oil - type NSP + BO2 NSP + Gr.II T110 Thickener - type Li Li Li Thickener Content; wt% 9.0 8.7 7.6 Dropping Point; °C; IP 396-2 194 199 196 Pen (after 60 str.); mm -1 ; ASTM D217 271 268 269 Pen (after 105 str.); mm -1 ; ASTM D217 309 312 295 Diff after 105 str.; mm -1 +38 +44 -+26 Roll stab.; mm -1 ; ASTM 1831 +16 +18 +14 Oil separation; wt%; IP121 5.3 6.1 4.9 Flow pressure -20-°C; hPa; DIN51805 345 320 220 Flow pressure -25-°C; hPa; DIN51805 495 345 420 Flow pressure -30-°C; hPa; DIN51805 645 570 N/ A Flow pressure -35-°C; hPa; DIN51805 945 820 N/ A From table 3, by using blends of heavy naphthenic base oil and BO2 or API Group II, more thickener is required comparing with grease produced using T110. The shear stability of the greases remains almost the same despite of the differences in the thickener content. The oil separation increases for the greases using BO2 and API Group II, compared with Grease C which is based on T110. 4. Conclusions This multitasks study has demonstrated that - Hydraulic fluids based on ULVN, can meet different standards specially with regards to the low temperature properties; both pour point and viscosities at low temperatures. - MWF, concentrates for water-based fluids formulated with ULVN results to stable emulsion with conventional soluble oils formulation as well as with semi-synthetic formulation. - Lubricating Greases, ULVN can be used in conventional lithium greases as cooling oil. The greases show slightly better properties at temperatures below -20-°C. However, this grease model doesn’t show any significant drawback when compared with the T 110 based grease model. In summary, the outcomes of this study suggest that Ultra Low viscous Naphthenic Oil can also be used successfully in the various types of formulations with added values such as in MWF, Hydraulics Fluids and Lubricating Greases. References [1] Swedish Standard SS 15 54 34: 2015, “Hydraulic Fluids - Technical requirements, environmental properties and test methods”. [2] British Defense Standard 91-48/ 2.