ANALYSIS OF THE PHYSICO-CHEMICAL PROPERTIES OF THE HYDRAULIC FLUIDS IN ORDER TO MODIFY CHANGE INTERVALS

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1 ANALYSIS OF THE PHYSICO-CHEMICAL PROPERTIES OF THE HYDRAULIC FLUIDS IN ORDER TO MODIFY CHANGE INTERVALS MICHAELA JANOSOVA 1, ANA PETROVIC 2, VLASTA VOZAROVA 2, LUBOMIR HUJO 1, JAN CSILLAG 2, MARTIN MALINEK 2 1 Department of Transport and Handling 2 Department of Physics Slovak University of Agriculture in Nitra Trieda Andreja Hlinku 2, Nitra SLOVAKIA xpetrovica@uniag.sk Abstract: The present paper deals with laboratory studies of contamination of hydraulic oils with analysis of the physico-chemical properties, in order to determine and lengthen the change interval of hydraulic oils used in stationary pressing devices. The aim was to determine the degree of contamination of samples of hydraulic fluids, to prolong change intervals, to ensure the proper operation of hydraulic presses. Result of the analysis of hydraulic fluids was, that the physico-chemical properties of the used hydraulic fluids, after the two-year period of usage, preserve the properties, which determine the correct operation of the production of pressing equipment. Key Words: hydraulic oil, hydraulic press, physico-chemical properties, contamination INTRODUCTION Today time offers us various kinds of industrial fluids. Hydraulics, which is used in transport and handling equipment, for its operation need the working medium - liquid in its hydrostatic systems (Kosiba 2013). Each liquid has its own characteristics that have different impact on the various elements of the hydraulic system of working equipment. Hydraulic fluid must meet all the conditions, which can occur during the operation of hydraulic systems. Production of hydraulic oil in the required quality, with minimal environmental pressures and acceptable cost will become more complex, and thus creating a space for the use of specific hydraulic oils according to strict performance requirements. Industrial oils are most often characterized and described by the device according to ISO and DIN standards. An important part, in some cases, is also the classification or possible approval by the standards of major equipment manufacturers. Oil analysis can reveal the amount of wear metals, oil pollution, and the amount of additives and physico-chemical parameters of oil. Several authors, e.g. Vasishth et al. (2014), Wan Nik et al. (2005), Kumbár et al. (2012), deal with the similar issues. To determine the technical parameters of oil filling is necessary to use appropriate diagnostic methods. MATERIAL AND METHODS Hydraulic fluids in the hydraulic system have multiple functions. Besides energy transfer, universal oil must lubricate, dissipate the heat and be compatible with seal materials and metal materials of the components of the system (Majdan et al. 2014). The basic prerequisite for the proper functioning and effective care of hydraulic fluids is well chosen methodology of monitoring impurities in liquid and continuous comparison of the level of contamination with the behaviour of the machine (Orlík and Tkáč 2011). Contamination of the liquid can be divided into two categories, namely contamination by particles and contamination by fluids. Contamination by particles includes organic, inorganic and metal particles. Air, water and other foreign fluids are a group contamination of the fluids by other fluids (Tkáč et al. 2010). 858 P age

2 The aim of the paper is analyses of the physico-chemical properties of hydraulic fluids. In case of the new hydraulic oil, as indicators were selected the basic parameters specified by the manufacturer, and subsequently evaluated changes in the physico-chemical properties of hydraulic fluids. Hydraulic oils sampled from running tests were subjected to the following laboratory analysis: 1) Ferrographic analysis - using mentioned analysis with magnetic separation of particles, which are separated during wear of friction pairs in the lubrication system, we investigated the size and the morphology of the particulates of wear. 2) Temperature dependence of viscosity - viscosity as one of the most important rheological parameters is defined as the resistance of a fluid to flow. Viscosity of most of the liquids decreases with increasing temperature according to Arrhenius equation (Figura and Teixeira 2007): ηη = ηη 0 ee EE AA RRTT, (1) where η is, dynamic viscosity (Pa/s), ηη 0 is reference value of dynamic viscosity (Pa/s), E A is activation energy (J/mol), R is gas constant (J/K/mol) and T is absolute temperature (K). Present data have been obtained from measurements performed on laboratory viscometer DV2T fy Brookfield. The experiments have been performed with use of ULA (0) spindle. 3) Measurement of acid value - the total acid number (TAN) is an important indicator of the quality of the used oil, and indicates the quantity of such acid in the oil, to determine the degree of degradation of the oil. 4) Measurement of the content of water - the water in oil is undesirable factor which arises during operation of the machine and causes unfavourable degradation processes which can result in various degrees of failure of the device. For this measurement, we used devices from HYDAC. 5) Monitoring of pour point by differential scanning calorimetry (DSC) - differential scanning calorimetry or DSC is a thermo-analytical technique which monitors heat effects associated with phase transitions and chemical reactions as a function of temperature, at predefined speed of heating (cooling), with assuming that both materials sample and reference are under the same conditions (Haines 1995). Description of the production plant DS Smith Worldwide Dispenser is a part of the division DS Smith Plastics a world leader in the production of plastic dispenser. DS Smith Plastics Division Worldwide Dispensers operates a manufacturing facility in Nitra since 2008, focusing in the production of packaging materials, food industry, which are produced by compressing hydraulic and electric presses. Description of handling equipment In the manufacturing plant is located 53 press lines ARBURG, NETSAL, DEMAG, KRAUSS MAFFEI, which are working on the hydraulic principle and two press lines are electric. Facility requirements were to find out how much is contaminated oil, by physico-chemical analysis, at press lines ARBURG number 40, 41 and 42, and to propose suitable oil change interval. In view of the utilization of hydraulic fluid in a machine, it is the most important to know the running properties of the fluid, i.e. to know the influence of the fluid on the technical state of the hydraulic system parts (Jablonický et al. 2007, Kosiba et al. 2013, Tkáč et al. 2008, Žikla and Jablonický 2006). The parameters of the individual lines are described in the Table P age

3 Table 1 Parameters of production press lines in manufacture DS SMITH ARBURG 470C allrounder Line Date of Date of Volume Pressure Flow Oil No. filling sampling (L) (10 5 Pa) (L/min) OSO S AGIP OSO S AGIP OSO S AGIP Cycle (s) Products/Cycle RESULTS AND DISCUSSION Analysis of physico-chemical properties of hydraulic oils was conducted in the laboratories of the Department of Transport and Handling, and in the laboratories of the Department of Physics at the Slovak University of Agriculture in Nitra. The Department of Transportation and Handling carried out the analysis, which results are shown in Table 2. Table 2 The results of chemical analyses Line No. Ferrographic analysis Acid value (mg KOH/g) Content of water (%) 40 clean clean clean Ferrographic analysis oil in hydraulic presses even after two years of use showed no metal particles. Samples of hydraulic oils were clean. The acid number the oil producers indicates use of oil up to 1.3 mg KOH/g because the hydraulic oil does not exceed this number, it is still suitable for use. The content of water the analysis of the water content of all the three samples was 0%. For monitoring of pour point of oils (phase transition of oil components) by DSC method was used device DSC 1 (METTLER-TOLEDO). Samples of hydraulic oil OSO S 46 Agip with weight (9 13) mg were hermetically sealed in aluminium crucibles and thermally treated at the speed of heating (cooling) 2 K/min in the temperature range from 20 C to the temperature of -45 C. The measurement was carried out in an inert, dynamic atmosphere of N2. As a result we got a DSC thermogram, which was evaluated in STARe software (see Figure 1). Figure 1 DSC measurement of different samples of OSO S 46 Agip hydraulic oil 860 P age

4 In the process of oil freezing and in the case of a new oil sample, we observed exothermal peak at the temperature C. This point is defined as a freezing point and temperature is nearly equal to the melting point (depending on the material purity). In the case of oil from press line No. 40, the temperature of peak was C. In the sample, where was used oil from press line No. 41, the temperature of exothermal peak was almost the same as previous C. The last sample was from press line No. 42 and its pour point was at C. The graph indicates that peaks for used samples are almost identical, so we can assume that the difference between them is not significant in terms of pour point, but the difference between new and used sample is distinct. The experiment shows that the new sample has higher temperature of pour point. Dynamic viscosity, as a function of temperature of four samples of hydraulic oil OSO S 46 Agip 46, has been considered. First sample was new. The others were used oils in three different press lines. The procedure of sample preparation for viscosity measurements corresponded to a typical sampling procedure. The adequate volume (20 ml) of oil was put into the apparatus cuvette. The viscosity data were obtained in temperature range from 25 C to 90 C. All samples were measured in approximately equal conditions. More precisely, at about the same torque (50%) and shear stress (0.36 N/m 2 ). Figure 2 Temperature dependent viscosity of one unused and three samples of used hydraulic oil Dynamic viscosity (mpa.s) 120,00 100,00 80,00 60,00 40,00 20,00 New oil OSO S 46 Agip 40 0, Temperature ( C) As the samples of the oil were taken from the press lines where the operating temperature is 50 C, most attention has been paid what happens with the viscosity at that temperature. It is possible to observe from Figure 2 that dynamic viscosity of hydraulic oils is decreasing exponentially with increasing of temperature, what was expected and corresponds with conclusions reported in literature (Hlaváč and Božiková 2014, Hlaváč et al. 2014, Severa et al. 2012, Trávníček et al. 2013, Valach et al. 2015, Vozárová et al. 2015). Regression equations and determination coefficients for individual samples are in the Table 3. As it can be seen from the results, the determination coefficients for all the samples are very high, which also confirms strong exponentially decreasing dependence. Table 3 Determination coefficients and regression equations Sample Regression equation Determination coefficient R 2 New oil η = 210.6e t OSO S 46 AGIP 40 η = e t OSO S 46 AGIP 41 η = e t OSO S 46 AGIP 42 η = e t CONCLUSION Hydraulic equipment are widely used in executive mechanisms of agricultural and forestry machinery, as well as in many other areas. Development of advanced hydraulic components is aimed at 861 P age

5 increasing the transmitted power, reducing energy severity, minimize environmental pollution and improve the technical life and reliability of the machine (Tkáč et al. 2007). Hydraulic oil is often faces unforeseen operating conditions that have a significant impact on its life. The reason for the exchange of the hydraulic oil is degradation, loss of additives and impurities in the oil. Kumbár (2014) states that the suitability rises when the samples of used oil are compared with the sample of new (unused) oil with same specification. Our analysis consists of comparison physico-chemical properties of samples of new and used hydraulic oil OSO S 46 Agip. Results of ferrographic analysis show that oil in hydraulic presses even after two years of use showed no metal particles. Samples of hydraulic oils were clean. Values of the acid number of the used hydraulic oils does not exceed number which the oil producers indicates (up to 1.3 mg KOH/g), oils are still suitable for use. The water content of all the three examined samples of used oils was 0%. In the case of pour point of oils the experiment shows that the new sample has higher temperature of pour point. However, it is important to indicate, that pour point specified by hydraulic oil producer is -27 C. This difference in temperature between the information from the producer and the measured values is not so significant in the case of using oil in hydraulic systems, because press lines are located in halls with temperatures above zero. But it is considerable when it comes to the storage of oil, because the warehouse is not heated, practically oils are exposed to the outside temperature. If the winter temperatures are below -10 C, it may change the characteristics of the aforementioned material. It can be concluded that knowledge of viscosity behaviour of a hydraulic oil as a function of temperature is of great importance, especially when considering running efficiency and performance of press line. Thus, its function can be sensitive to the viscosity characteristics of the oil. Viscosity influences the oil s ability to flow through the hydraulic system, therefore affects the pressure required to push the oil sufficiently to develop the necessary flow. The rate of oil flow is important to the life of the hydraulic system. Our measurements of viscosity as a function of temperature did not show significant differences between new and used hydraulic oils. Dynamic viscosity of hydraulic oils is decreasing exponentially with increasing of temperature in accordance with theory (Arrhenius equation) and other authors (Hlaváč and Božiková 2014, Hlaváč et al. 2014, Severa et al. 2012, Valach et al. 2015, Vozárová et al. 2015). That results are also in compliance with results of ferrographic analysis that showed no metal particles. Samples of hydraulic oils were clean, they probably content no particles (neither non-metal), which should change viscosity of used oils. Result of the analysis of hydraulic fluids was, that the physico-chemical properties of the used hydraulic fluids, after the two-year period of usage, preserve the properties, which determine the correct operation of the production of pressing equipment. ACKNOWLEDGEMENTS This work was co-funded by European Community under project no : Building Research Centre AgroBioTech and it was also supported by the project of Scientific Grant Agency of Slovak Republic (VEGA) under No.: 1/0854/14 and 1/0337/15. REFERENCES Figura, L.O., Teixeira, A. A Food physics, Physical properties - measurement and applications. 1 st ed., USA: Springer. Haines, P.J Thermal Methods of Analysis. London: Blackie Academic & Professional. Hlaváč, P., Božiková, M Effect of Temperature on Dynamic Viscosity and Activation Energy of Milk and Acidophilus Milk. Advanced Materials Research, 1059: Hlaváč, P., Božiková, M., Presová, R Temperature relations of selected engine oils dynamic viscosity. Acta technologica agriculturae, 17: Jablonický, J., Abrahám, R., Majdan, R., Cvíčela, P Skúšky traktora s biologicky odbúrateľným olejom (Tests of the tractor with biodegradable oil). In Assurance Quality Responsibility, 3rd International Scientific Conference. Košice: Technical University, P age

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