Low temperature properties of hydraulic fluids design tools available for the formulator

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1 Low temperature properties of hydraulic fluids design tools available for the formulator Synthetic and Hydraulic Lubricants Prof. Thomas Norrby, Nynas AB, Naphthenics Technical Development and Market Support Nynäshamn, Sweden Introduction Hydraulic fluids are utilized under varying ambient conditions. Globally, there are clear regional demand differences. In the Northern hemisphere, a robust demand for low-temperature adapted lubricants, e.g. in the Arctic regions of Eurasia and America, for outdoor applications during the long winter season [1], [2]. High performance lubricants are required in hydraulic systems; and can deliver reliable service even under harsh conditions. The challenge for the Lubricant Formulator is how to create a lubricant solution with an attractive price/ performance ratio, and with favourable rheological properties. Some important aspects are long-term storage stability, and ease of start-up properties of the hydraulic systems. Design of hydraulic fluids with attractive low temperature properties The low temperature performance of a hydraulic fluid is dominated by the base oil properties, and additional optimization of the performance is achieved though the selection of efficient additives. For hydraulic fluids for outdoor and/or mobile applications in cold climates, special attention must be given to the slow formation of crystalline wax phases, which might form and develop after prolonged (2-7) days of stand-still at low temperatures. Once a solidification or gelling has occurred, the re-melting or thawing of the crystalline phases, is slow and requires significant heating above the gelling point/pour Point, e.g. the system displays a large temperature Hysteresis. Field experience from Scandinavia indicated that, once significant solidification has occurred the fluid system temperature must allowed to reach around + 15 C; as this requires towing or trailing to a heated garage (that might be far away from a logging area), the preservation of fluidity and ease of start-up is a crucial requirement. A hydraulic fluid serves as the medium for power transmission between the pump and the actuators, and lubricates and cools the components. Other core tasks are protection against wear and corrosion Challenges that the hydraulic fluid must help overcome include:

2 Low temperature fluid flow and ease of pumping Ease of product handling when performing system filling and top-ups Hydraulic system pressure control and handling Thus, high-performance hydraulic formulations need to provide Good low-temperature properties: A low base oil viscosity and a high viscosity index (VI) facilitates start-up of hydraulic systems in severe cold and delivers reliable operation at varying temperatures Very good wear protection and excellent protection against corrosion Filterability, low foaming tendency, fast air release and water-separating capacity Oxidation stability Specifically, the initiation of wax crystallization influences the low temperature rheology, and also appears to influence tribology by a combination of effects, e.g. increasing viscosity or hindered flow leading to changing conditions in the tribological contact [3]. A naphthenic-rich blends displays Newtonian rheology behaviour and a smooth viscosity increase as the temperature drops, Figure 1. Figure 1. The effect of blending a Group II base oil and a Naphthenic base oil. As the wax content drops, Non-Newtonian behavior is not observed (as seen in the Gr III sample, red line)

3 Some suggested conclusions are: Important design tools for the Formulator thus include the controlling of the wax (precursor) content of the fluid, which varies with base fluid type, and is related to crude type source, and refining technology. Wax-free synthetic base fluids are one road to excellence The best low temperature performance is found in wax-free base oils such as Naphthenics, PAO or synthetic esters Alternatively, wax crystal formation may be controlled by blending with Naphthenic base fluids, and by the addition of PPDs By careful recommendation and selection of the proper lubricant by the Lubricant company, operational problems can be avoided in the Customer s business ACKNOWLEDGMENTS The Author would like to acknowledge the contributions from the co-authors Fathi-Najafi, M., Hedlund, D., Nyman, P [3], and from Nynas AB for supporting this work REFERENCES [1] Wikström, V. & Höglund, E., (1996) Starting and Steady-State Friction Torque of Grease-Lubricated Rolling Element Bearings at Low Temperatures Part I: A Parameter Study Tribology Transactions. 39(3), pp [2] Kinker, B. G., Souchik, J. M. & Neveu, C. D., (1998), "The Scanning Brookfield Technique: Background and Evaluation of the Low Temperature Performance of Engine Lubricants," SAE Technical Paper Series E, # [3] Fathi-Najafi, M., Hedlund, D., Nyman, P. & Norrby, T. Low temperature tribology - A study of the influence of base oil characteristics on friction behaviour under low temperature conditions Eurogrease, 2012, Issue 4 Keywords Low temperature, Wax-free oils, PPD, Rheology, Tribology

4 Low temperature properties of hydraulic fluids design tools available for the formulator Prof. Thomas Norrby, Senior Technical Coordinator Lubricants Nynas AB Naphthenics TechDMS, Nynäshamn, Sweden

5 Nynas was founded in 1928 Nynas is the largest specialty oil producer in Europe Offices in more than 30 countries around the globe Net Sales: 3 Billion USD Average number of employees: 1000 Refineries in Nynäshamn (SE), Gothenurg (SE), Harburg (DE), Eastham JV (UK), Antwerp JV (BE), Isla JV (Curacao) Base Oils 2

6 Nynas: The Different Oil Company Typical oil company 12% Fuel 18% Specialty oils 96% Fuel 70% Bitumen 4% Bitumen, Specialty oils and Lubes 3

7 Global Oil Consumption Other Lubricants, 97% (39 Mio tons / y) Tyre oils, 3% (1.3 Mio tons / y) Only 0.03% of total global oil demand Lubricants, 1% including motor oils, base oils, process oils, tyre oils 3.9 Billion tons / y 4

8 Chemical composition of mineral base oils Mineral base oils consist mainly of naphthenic, paraffinic and aromatic molecules Paraffinic The relative amount of these molecules in the oil determines whether the oil is considered naphthenic or paraffinic C P (IR) 42-50% Naphthenic C P (IR) 56-67% Paraffinic Aromatic molecules confer high solvency to the oil, but some aromatics are toxic and harmful to the environment so these are removed or converted during the hydrorefining process Naphthenic Aromatic 6

9 Base Oil Carbon Type Chart PAO Group II New fluid Gr. I Paraffinic Multi-Ring Naphth. Aromatic T 22 0% 20% 40% 60% 80% 100% 7

10 Low temperatures prevail on the Northern Hemisphere during winter time Scandinavia Russia - Central & Eastern Europe are regions which all regularly demonstrate temperature challenges 8

11 Important Low Temperature Applications Very important for all types of machinery exposed to the elements: Automotive (engine, transmission, hydraulic) Off-Shore & Marine Aerospace Industrial (hydraulic, gear, compressor) Power industry (Wind, Hydro) 9

12 Challenges facing the Formulator How to create a lubricant solution with an attractive price/ performance ratio, and with favourable rheological properties? Flow and Pumpability Some important aspects are long-term storage stability and ease of start-up properties Special attention to the slow formation of crystalline wax phases might form, from the long chain n-paraffinic fluid content, also after prolonged (2-7) days of stand-still at low temperatures re-melting/thawing of the crystalline phases, once formed, is slow and requires significant heating Any wax crystal formation will greatly affect the Pour Point! 10

13 Properties of Fluids Viscosity is a physical property of the fluid, in turn dependent on the chemical structure and composition of the fluid The temperature-dependence of the fluid is very important for lubricant applications, and the Viscosity Index, VI, (ASTM D 2270, SS-ISO 2909) is a well-known descriptor of this property Lubricant base fluids with a high VI undergo less change of viscosity with a change in temperature, and thus enables the design of multi grade lubricants suitable e.g. for mobile hydraulics applications The Pour Point (PP), ASTM D 97/ ISO 3016 is the lowest temperature at which movement (under gravitational forces) of the test fluid is observed 11

14 Properties of Fluids (II) Low-temperature viscosity and rheological properties are strongly correlated to the fluid s wax content and behaviour Wax content is by design low in PAO Polyglycols (PAGs), and Synthetic esters, both API Gr (V), can readily be manufactured to be wax-free Wax crystal growth can be controlled by Adding Pour Point Depressants (PPDs) Or by blending with wax-free fluids Naphthenic base oils are naturally wax-free as a result of crude oil selection and refining technology 12

15 How does a PPD additive work? A PPD additive prevents the wax crystals from agglomerating as they form when the fluid temperature is lowered The PPD additive consists of a polymer backbone, with paraffinic side chains that match those of the paraffin in the wax The PPD co-crystallises with the wax in small units The polymer backbone keeps the small crystalline units apart, and stays in solution This improved flow and filterability, as larger wax crystals do not form 13

16 A close look at low temperature effects limited number of studies have been done in this field [1] although pioneering studies at Luleå University of Technology were made in the mid 1990 s, and a number of SAE Technical Papers addressed low temperature engine oil gelling in the late1990 s, e.g. Kinker [2] et. al. Some years ago, we performed a study aiming to increase the understanding of low temperature tribology It relates tribological phenomena to test data from rheology measurements and data from calorimetric studies of phase transitions at different temperatures Results indicate that there indeed is a relationship between these three quite different methods of characterizing oils at low temperatures [1] Wikström, V. & Höglund, E., (1996) Tribology Transactions. 39, 3, s [2] Kinker, B. G., Souchik, J. M. & Neveu, C. D., (1998), SAE Technical Paper Series E, #

17 Experimental Study in a Ball-on-Plate Tribometer [3] Tribo-cell The tribometer consists basically of a steel ball that is rotating, and presses against three plates (these can be made of different materials) Ball-on-Flat contact, 3 wear scars Rotational speed of the shaft results in a sliding speed of the ball with respect to the contact point on the plates Stribeck Curves can be measured with controlled rotational speed from 10-6 to 3000 rpm [3] Fathi-Najafi, M., Hedlund, D., Nyman, P. & Norrby, T. Eurogrease, 2012, Issue 4 15

18 Tribology measurements Tribo-cell - conditions Sliding speed (V s ): 1x10-2 to 1.4 m/s Operating temperatures (T): - Steel ball: AISI Steel ball radius (R): 6.35 mm Normal force (F N ): 10 N Material of plates: Bronze Contact pressure: 322 MPa Composition Cu Sn Al Fe Mn Ni P Pb S Sb Si Zn [%] ~86 ~12 <0,01 <0,25 <0,2 <2 0,4 <1 <0,05 <0,2 <0,01 <0,5 The composition of the Bronze material

19 Apparatus & Condition Rheometer- Conditions Geometry Plate on plate (PP25) Gap: 0.20 mm Measurements: Temperature sweep 2 C/min Constant shear stress DSC - Conditions Operating Temperature: C Cooling medium: Liquid Nitrogen Size of the sample: 3-5 mg May

20 Characteristics of the base fluids in the study Characteristics Unit Test method ASTM S1 S2 S3 S4 S5 S6 Fluid type Naphthenic S1+S5 Naphthenic API Gr II API Gr III PAO Density at 15 C kg/dm3 D Viscosity at 40 C mm 2 /s D Viscosity at 100 C mm 2 /s D Viscosity index - D Flash point C D 93A Pour point C D Aniline point C D Sulfur content ppm D Hydrocarbon Type Analysis IR C A (aromatic) % C N (naphthenic) % C P (paraffinic) % T grade NS Grade 18

21 Fluid Characteristics (II) Characteristics Unit Test method ASTM S1 S2 S3 S4 S5 S6 Fluid type Naphthenic S1+S5 Naphthenic API Gr II API Gr III PAO Density at 15 C kg/dm3 D Viscosity at 40 C mm 2 /s D Viscosity at 100 C mm 2 /s D Viscosity index - D Flash point C D 93A Pour point C D Aniline point C D Sulfur content ppm D Hydrocarbon Type Analysis IR C A (aromatic) % D C N (naphthenic) % D C P (paraffinic) % D T grade NS Grade 19

22 Viscosity & Phase angle vs. Applied temperature Viscosity Phase Angle 10 5 Pa s ' S6(PAO) S7(Friction modifier) PP = - S6(PAO) PP= - Perfectly viscous Perfectly elastic C 50 T

23 Pure base fluids temperature-viscosity properties 10 2 Pa s S5 Gr III S4 Gr II Viscosity vs. Applied temperature 10 1 PP = - PP = - 18 Deviations start ca. 15 C above the Pour Point in a wax-containing fluid S3 Naphthenic ' 10 0 PP = - 45 S1 Naphthenic PP = C 50 T 21

24 Base fluid blend temperature-viscosity properties 10 2 Pa s Gr III PP = - Viscosity vs. Applied temperature 10 1 PP = - 45 S1 Naphthenic Deviations start ca 15 C above the Pour Point ' 10 0 S2 Gr II & Naphthenic blend PP = C 50 T 22

25 X (Tg) S6 (PAO) S1 (Naphthenic) S2 (S1+S5) S5 (Gr III) May

26 A comparison of base fluid blend friction Frictional behaviour of a Gr III fluid, compared to a blend with a naphthenic oil at - Naphthenic and Gr III blend Pure Gr III mm/s 10 4 Sliding Speed v s 24

27 What is happening in the base oil market? The base oil market is rapidly changing! The needs of the automotive industry, driven by fuel economy legislation, is driving the major shift away from traditional Group I base oils towards Gr. II and Gr III. The needs of the industrial lubricant market is inconsequential to this development Collateral damage is caused to industrial lubricants blenders (and users), if they cannot resolve their supply issue Currently, 70% of Group I go into industrial lubricants 30% into automotive engine oils and transmission fluids Global Usage of Group I Oils 2013 (total market approx. 17 million tons) Source: Kline Consulting 25

28 The base oil pool evolution watch Group I! Group II; bpd; 19% Group III; bpd; 3% Naphthenics; bpd; 9% Group III; 9% Group I; bpd; bpd; 11% 47% Naphthenics; bpd; Group I; bpd; 69% Group II; bpd; 33% Source: Lubes-n-Greases 26

29 Blends of naphthenics and Group II/III are the alternative to Group I most closely machting key features like viscosity and solvency 500 cst (Bright stock) High 100 cst (SN 500) 50 cst (SN 250) Viscosity Group II Blends Group of I oils Group II/III and Naphthenics Naphthenic oils Group III 10 cst (SN 60) Low Low Solvency High 27

30 Base Oil Carbon Type Chart PAO Group II New fluid Gr. I Paraffinic Multi-Ring Naphth. Aromatic T 22 0% 20% 40% 60% 80% 100% 28

31 The New Speciality base oil range vs. SN reference base oils Nybase 70 SN 70 Nybase 100 SN 100 Nybase 150 SN 150 Nybase 300 SN 300 Nybase 500 SN 500 Nybase 600 SN 600 Density (kg/dm 3 ) 0,873 0,849 0,867 0,859 0,871 0,868 0,886 0,876 0,889 0,879 0,876 0,880 Flash point COC ( C) Pour point ( C) C (cst) ,1 2,9 4,2 3,7 5,0 5,2 7,3 7,8 10,2 10,7 12,6 12,2 VI Aniline Point ( C) Sulfur wt-% 0,02 0,20 0,01 0,20 0,04 0,20 0,02 0,20 0,03 0,30 0,02 0,30 C A (%) C N (%) C P (%) Refractive index 1,477 1,468 1,475 1,472 1,479 1,477 1,485 1,481 1,487 1,483 1,481 1,483 29

32 The effect of added Pour Point Depressant (0,25 m-% PPD) 0 NB 70 NB 100 NB 150 NB 300 NB 500 NB 600 SN 150 Neat Pour Point (ºC) PPD@ 0.25%

33 Blends for ISO VG 46 Hydraulic Fluids 0 Blend VG 46 I Blend VG 46 II Blend VG 46 III SN 150 (VG 32) Pour Point (ºC) Neat PPD 0.25% PPD 0.50% 31

34 PPD in Blends for ISO VG 46 HF:s, Method Study Treat rate 0.50 % PPD, screening method MPP ASTM D 7346 vs. CPP 5Gs ASTM D 97 0 Blend VG 46 I Blend VG 46 II Blend VG 46 III SN 150 (VG 32) Pour Point (ºC) Neat MPP D

35 HM 46 (Nybase) vs. M 46 (Commercial) HM 46 M ºC 46,8 45,8 100 ºC 6,6 6,6 VI Density 15 ºC) 0,877 0,879 Flash point (COC, ºC) Pour Point (ºC) Nz (mg KOH/g) 0,2 0,4 Water (ppm) 20 11

36 Physical Properties HM 46 (Nybase) vs ISO Test Unit HM 46 ISO , HM Method Filterability I/II* 97/94 80/60 ISO Foam 24 ºC ml/ml 10/0 150/0 ISO 6247:1998 Foam 93 ºC ml/ml 30/0 80/0 ISO 6247:1998 Foam 24 ºC ml/ml 10/0 150/0 ISO 6247:1998 Air Release min 2,0 10 ISO 9120 Demulsibility min ISO 6614 Oil/water/emuls. ml 40/40/0 40/37/3 ISO 6614 TOST (1000 h) mg KOH/g - a ISO RPVOT min a ASTM D method A *= Dry (no added water), Applied Pressure 100 kpa a = SS :2015, Swedish Standard for Hydraulic Fluids, Level A, equal to 1000 h TOST 35

37 Design tools and solutions for Hydraulic fluids Important design tools for the Formulator thus include controlling of the wax (precursor) content of the fluid, which varies with base fluid type, source, and refining technology By utilizing wax-free base fluids, extended low temperature performance can be created Creative solutions could well include blends with wax-free fluids, which has been shown to work very well Finding a matching Pour Point Depressant (PPD) chemistry is another solution for wax-containing fluids 38

38 Conclusions By design, wax content and behaviour can be controlled and manipulated Specifically, the initiation of wax crystallization appears to influence rheology and tribology by a combination of effects, e.g. increasing viscosity or hindered flow leading to changing conditions in the contact Wax-free base fluids are one road to excellence Alternatively, wax crystal formation may be controlled by PPDs By careful recommendation and selection of the proper lubricant by the Lubricant supplier, operational problems can be avoided in the Customer s business 39

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