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of the oil. The starting temperature was 25 °C, but it was increasing as pre ssure generators were heated up within the time. Usually it takes 1 hour to get max. pressure. 30 °C is an average temperature at the end. Figure 6: An estimation of solidification point of low viscosity paraffinic oil As the conductivity of polyglycol and ester oils seems to be too high, low viscosity PAO was the target to check its qualification for very high pressure test machine in Geology Institute. PAO shows more favourable viscosity pressure relationship than mineral oil. Figure 7 shows curves of PAO with KV40 °C = 100 mm 2 /s (gear oil), which reached viscosity 200 000 mPa.s at 520 MPa and 24.7 °C, 760 MPa at 47.2 °C and only 25 000 mPa.s at 76 °C. The estimation of dynamic viscosity and oil formulation for the curve at 30°C was done on this chart by green colour – it results in low viscosity PAO (< 15 mm 2 /s at 40 °C) and the oil should be improved by polymeric viscosity index improvers. Then it is expected the oil can stay liquid in the pressure up to 700 MPa and for the temperature 30 °C and higher. Figure 7: Dynamic viscosity of gear oil 971. PAO.100 (polyalphaolefin) at 24.7, 47.2, and 76.0 ˚C as a function of pressure. Comparison of experimental data and fit by the modulus equation Viscosity – Temperature Relationship Molecules shape influences viscosity – temperature (VT) relationship. Molecules with ball like shape has steep VT curve. Aromatic and naphtenic molecules are an example of it. On the other hand, isoalkanes and n-paraffines especially, which have long hydrocarbon chain inside, create long molecules. Such shape of molecules has higher resistance against flow, especially at higher temperatures. That is why; the change of oil viscosity with temperature is flatter than for ball like molecules. High viscosity index, (flat VT relationship) have synthetic oils based on polymers. Polymers create small clusters at low temperatures, which flow easily, but clusters are spread into fibre like structures at higher temperatures. It results in high resistance against flow; it means in high viscosity at high temperature. That is why polymer based hydraulic oils have higher viscosity index than mineral base stock. Similarly the higher is viscosity index, the lower is viscosity –pressure coefficient α, because of relationship between the coefficient of thermal expansion (free space in fluids) and α. Viscosity index increases in raw: naphtenic, paraffinic, PAO, esters, polyglycol, silicone oils. Oil Lifetime and Pressure Temperature and pressure accelerate oil oxidation and ageing. Usually 10% of oil volume is dissolved air in mineral oil at 20 °C. The air is compressible and dissolves in the oil if the pressure increases. That is why unstable low boiling oils are avoided to use. The oil should be rid of the oxygen, like purging by inert gas. Oil Compatibility with Sealing As NBR sealing were used there, highly polar, low viscosity ester oils are avoided to use. The second solution is to change sealing to fluorinated ones, which are more resistant to different types of oils. Lubricating Properties The pressure intensifier has not special requirements for high pressure medium – any hydraulic oil was originally recommended. As transformer oil lubricate properly, maybe oil with even lower viscosity could be used there. The Final Choice of Oil 1. Transformer oil changed his state from liquid to solid at pressure above 420 Mpa and at 30 °C. It was confirmed by comparison with other experimental data found in literature. 2. Viscosity-pressure relationship depends on temperature of measurements, on oil viscosity and on chemical formulation of oil. 3. As lower is temperature as higher is pressure influence and easier is oil solidification. 4. As lower is oil viscosity as lower is pressure influence. 8 Fuels&Lubricants No. 3 OCTOBER 2018
5. Polyglycole oils, ester oils and PAO show less viscosity increase with pressure than paraffinic and naphtenic mineral oil. Silicone oil is the worst. Considering all details to choose the best oil, which is able to work up to 700 Mpa (7000 bars) at normal and elevating temperatures, it is possible to recommend any aircraft hydraulic oil, based on narrow cut of isoparaffines and polymer viscosity index improver, like AMG 10. Other oils formulated on PAO dimer could suit as well. The knowledge of solidification point gained experimentally in this equipment can be valuable for studies of EP and antiseize properties of oils. Literature [1] Lokajíček, T., and Svitek, T. (2015), Laboratory measurement of elastic anisotropy on spherical rock samples by longitudinal and transverse sounding under confining pressure, Ultrasonics, 56, 294-302. [2] Štěpina, V. and Veselý, V.: Lubricants and Special Fluids, Vol. 23, Elsevier 1992. ISBN 0-444-98674- X [3] Spikes, H.: Basics of EHL for practical application, Lubrication Science, Vol. 27, Issue 1,p. 45-67. Jan. 2015 [4] Gold, P.W., Schmidt, A., Dicke, H., Loos, J., Assman, C.,: Viscosity -Pressure-Temperature Behaviour of Mineral and Synthetic Oils. J. Synthetic Lubrication 18-1, p. 51- 79, April 2001. Fuels&Lubricants No. 3 OCTOBER 2018 9
Page 1: 2018 Fuels &Lubricants JOURNAL FOR
Page 4 and 5: CONTENTS 4 High Pressure Influence
Page 6 and 7: High Pressure Influence on Oil Soli
Page 8 and 9: Table 2: Pressure limit for some oi
Page 12 and 13: REGULATION CORNER New European Fuel
Page 14 and 15: LUBE CORNER The Impact of Safety an
Page 16 and 17: INTERVIEW Using Simulator Training
Page 18: INTERVIEW What type of knowledge op
Page 21 and 22: LEGISLATION CORNER Following the ob
Page 23 and 24: LEGISLATION CORNER Energy Efficienc
Page 25 and 26: Fuels&Lubricants No. 3 OCTOBER 2018
Page 27 and 28: GREEN CORNER Introduction During th
Page 29 and 30: GREEN CORNER CATALYSTS AND REACTION
Page 31 and 32: Fuels&Lubricants No. 3 OCTOBER 2018
Page 33 and 34: FUELS CORNER By 2040, the world pop
Page 35 and 36: NEWS CORNER MOL Group Enters into a
Page 37 and 38: Research Laboratory for Corrosion E
Page 39 and 40: This work is sequential in the sens
Page 41 and 42: Modeling at Operating Stage At this

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