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Sagin Sergii Victorovych, Candidate of Technical Sciences, associate professor of National University "Odessa Maritime Academy", E-mail: [email protected]
IMPROVING THE PERFORMANCE PARAMETERS OF SYSTEMS FLUIDS
Abstract: Complex tribotechnical and optical research of systems fluids (fluids that are used for lubrication and cooling of metal surfaces) have been performed. The relations between the properties of the boundary lubricating layer of systems fluids (thickness and degree of ordering of molecules) and the tribological characteristics of the contacting surfaces (resistance to normal load and Friction torque) were established. Tests have shown that the thickness of the boundary layer of lubricating coolant liquids can reach 13.5.. .15.8 mkm, which contributes to an increase in the elastic-damping properties of lubricating coolant liquids and provides a reduction in the frictional torque of tribocoupling.
Keywords: lubricating coolant liquids, frictional boundary layer, boundary layer thickness, Friction torque.
Introduction
Sea endurance of a ship and need to ensure the operation of all structural elements of the ship power plant (main and auxiliary engines, steam and oil boilers, auxiliary machinery) makes it necessary to carry large volumes of working substances on board the ship. Along with fuel, oil, fresh and drinking water this includes lubricating coolant liquids (LCL). They are used to compensate for temperature and mechanical stresses during machining of high-strength parts (primarily cylinder bushings, pistons and connecting rods of engines, as well as main and intermediate shafts of auxiliary mechanisms). Repair and restoration work with the use of LCL, can take a long time, while the LCL usage can be measured in tens and hundreds of liters per workpiece. LCL amount during repairs in the sea is limited by the volumes of the corresponding technical tanks and by the lack of the ability to replenish it. LCL that can be synthesized on the ship, as well as those that have high lubricating power, have the clear advantage.
Relevance of research
When compared to the standard lubricants, one of the disadvantages of LCL is their low lubric-
ity, which makes it necessary to supply LCL to the contact zone with increased pressure and in a large volume. The first requires more power of auxiliary equipment and the second increases its deterioration. Both limit the use of LCL in ship power plants, as it requires not only their increased reserves, but also increases the necessary productivity of the purification mechanisms that perform their regeneration [1]. Therefore, the actual objective of this research is to increase the performing parameters of the LCL (most importantly their antifriction parameter), which can be achieved by activating the intermolecular interactions of LCL and increasing the elastic-damping properties of the lubricating layer separating the contact surfaces.
Research objective
The composition of modern LCL includes special chemical compounds that fulfill the functions of surface-active agents. These compounds and elements, due to polymolecular forces, adsorb the boundary level of the liquid on the metal surface, which is characterized by the orientational order of the molecules. The research objective was to determine the influence of the thickness of the
orientational boundary layer of the liquid on the antifriction properties of the metal surface-LCL-metal surface complex, and to develop an experimental express method allowing LCL grading according to their performance parameters.
Research results
The most common research techniques that determine the properties of a lubricant in the boundary friction mode are techniques performed using rheometers and friction machines [2].
Tribotechnical researches were performed on a friction machine. The main check parameter was the friction torque [3]. Also, the setting pressure and the time of stable operation of the steel-steel
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For most of the tested materials, the setting pressure was 3.0...5.0 kN, and the operating time before setting begins was 75.95 s. The maximum compressive force produced by the friction machine was 7.0 kN. When working with LCL Greterol (in a wide spectrum of it concentration changes in water), this amount of compressive force was not enough to destroy the boundary lubricating layer, so the setting moment of it was not recorded (Fig. 1, d). The sinusoidal section on the oscillogram corresponds
friction pair (as the most common for the marine diesel engine components) were evaluated during functioning under normal load when various LCL were fed to the tribocoupler. The results of the tests are shown in figures 1, 2 and in table 1. The setting moment corresponds to a sharp change in the character of the corresponding graphical dependence (line 2 in Fig. 1, a, b, c). LCL of various brands and manufacturers (which are referred to as «1», «2», «3» for commercial reasons) were subjected to the tests, as well as LCL Greterol (granted by Vladimir Vasilyevich Teregerya, candidate of sciences (engineering), professor of Vladimir State University).
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to the destruction of the boundary layer LCL and to the direct contact of the surfaces. A step-like increase in temperature corresponds to an increase in the number of direct contact between surfaces and an increase in the intensity of their wear. Note that both the sinusoidal variation of the frictional moment and the abrupt temperature rise in the friction zone were observed only for LCL «1», «2», «3». When researching LCL Greterol, these occurrences were not recorded.
c) d)
Figure 1. Test results of various LCL on the friction machine: a - «1»; b - «2»; c - «3»; d ■ Greterol; 1 - applied force, 2 - friction moment, 3 - temperature in the contact zone
The boundary friction (under which LCL operates) is characterized by the anisotropy of some of its parameters, in particular, optical parameters (that is the intensity of absorption of transmitted light). Observation of the changes of this parameter was carried out using the mechanical device, with it the scheme shown in (figure 2) [4].
The light beam from the light source (2) was focused by the lens (1) and directed by a parallel beam through the polarizer (3) to the researched liquid (5).
Glass was used to perform the scanning procedure for the boundary layer along the thickness, a wedge-shaped cuvette (4) made of polished quartz. The cuvette was filled with the researched LCL. The molecules ofLCL formed a boundary layer with an ordered molecular structure near the quartz surface. During the experiment, the cuvette moved in a direction perpendicular to the direction ofthe light. The intensity oftransmitted light was fixed with a photoelectronic device (6) and transmitted to a personal computer (7) [3].
Figure 2. The scheme of the device that determines the anisotropy of the optical characteristics of the boundary layer LCL: 1 - focusing lens; 2 - light source; 3 - polarizer; 4 - wedge-shaped cuvette; 5 - researched liquid; 6 - photoelectronic device; 7 - personal computer
Scanning was carried out using a mechanical device that allowed the cuvette to move without opening the chamber and record the movement with an accuracy of 0.1 mm, which corresponded to a change in the thickness ofthe gap in the cuvette 1.. .2 nm. The layer thick-
ness was scanned in the range 3.20 mkm, which corresponded to the assumed thickness of the boundary layer LCL. The temperature during the experiments was maintained in the range of(20 ± 2)° C. The results of the research are shown in figure 3 and in (table 1).
Figure 3. Dependences of the optical density of LCL D (relative units) on the thickness of their multimolecular layer d (mkm): 1 - «1»; 2 - «2»; 3 - «3»; 4 - Greterol
Table 1. - LCL Research Results
LCL Type Parameter
Setting load, kN Operating time (before setting), s Thickness of boundary layer, d, mkm
Water + LCL «1» 3.2 77 8.0.8.3
Water + LCL «2» 4.3 84 11.0.11.5
Water + LCL «3» 5.1 94 11.2.13.1
Water + LCL Greterol (density 0.5.4%) exceeds 7.0 exceeds 185 13.5.15.8
The performed research made it possible to experimentally determine the dependences of the optical density of different LCL D (relative units) on the thickness of their multimolecular layer d (mkm) - (figure 3).
These dependences can be characterized by two sections - the first corresponds to the optical density of LCL in the boundary layer, the second - to the bulk phase. The inflection point of the correspondence D = f(d) coheres to the thickness of the boundary layer ds, and the initial section is the ordering degree of the LCL molecules in the boundary layer.
The results show that different LCL have unequal tribotechnical characteristics, most important of which are the load at which surface setting occurs and the operating time before setting. We consider that this is due to the different molecular structure of LCL. Among them exists LCL, which consist of long molecular chains with branched groups that aid the formation of oriented molecular structures in their boundary layers. Ordered boundary layers of LCL (as well as in any lubricant) are characterized by a thickness and a degree of order. The conducted research shows that LCL, which possess a more ordered structure of the multimolecular boundary layer, provide the best tribotechnical characteristics of the contacting surfaces [5].
To ensure lubrication functions, LCL include surface-active agents. Moreover, in the "metal-lubricant liquid-metal" triad additional wedging forces arise due to the orientational ordering of molecules in the boundary layers of the liquid. Such forces in-
crease the carrying capacity of the multilayer LCL layer and prevent contact of surfaces. At the same time, these layers have clear "Non-Newtonian" properties and, under certain conditions, acquire the properties of liquid crystals. It is primarily due to an increase in the orderliness of molecules in the boundary layers of the LCL - a property that is completely absent in the bulk phase and is ineffective under hydrodynamic lubrication [6].
Greterol is a type of LCL and its surface active agent is potassium oleate, which is a typical lyotropic liquid crystal, and upon adsorption of its micelles, a 13.0.16.5 ^m thick boundary layer is formed on the metal surface that blocks the metal surface and protects it from direct contact with another surface. In addition, we note that the thickness of the boundary layer of LCL Greterol is higher than that of other similar researched LCL. That is why this LCL provides the best tribotechnical characteristics of friction units, primarily the temperature resistance of the lubricating-cooling layer.
Sizes of the boundary layer of researched LCL differ from each other (Table 1). Water-and-Greterol LCL has the greatest thickness of the layer. Moreover, an increase in the concentration of the latter from 0.5 to 4% increases only the thickness of the layer, while the tribological parameters of the friction node remain practically unchanged with such a change in the concentration (in all cases the setting moment was not recorded).
Lower concentration of LCL Greterol relative to water should be noted as well (the recommended
concentration of LCL Greterol is 0.5.4%, and for the other researched LCL it is 10.25%), which, among other parameters, makes it possible to use Greterol more economically. The rational use of LCL contributes both to increased reliability in the machining of parts, and to increase the economical operation of the ship power plant, similar to when motor oils and fuels are used.
Conclusion
The main points of conclusion are:
1. Some chemicals (metal salts of fatty acids) added to LCL as surface-active agents contribute to the formation molecules order in thin lubricant films of these substances. Depending on the type of surfactants used, the thickness of the LCL boundary layer (for the samples studied) is in the range 8.0.15.8 mkm.
2. A direct dependence of the thickness of the boundary layer LCL (which is formed at the metal surface) on the tribological characteristics of the fric-
tion of triad of metal-LCL-metal exists. With increasing thickness of the boundary layer of LCL, its ability to withstand normal loads, and also 2.5.3 times the time of stable operation of the friction unit, increases more than 2 times. Therefore, the thickness of the boundary layer of LCL contributes to the increase in the elastic-damping properties of LCL, which provides a reduction in friction torque in tribocoupling.
3. Given the relationship between the thickness of the boundary layer of LCL and the elastic-damping properties of LCL, an optical method for determining the dichroism of light absorption in the boundary layer can be used as an express method for estimating the tribological characteristics of LCL. This method is characterized by the relative simplicity of the hardware design and carrying out the experiment, and by the thickness of the defined boundary layer, LCL allows them to be ranked according to tribotechnical characteristics (without corresponding long and energy-intensive studies).
References:
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2. Kiriyan S. V., Altois B. A. Rheology of motor oils with quasi-liquid crystalline layers in friction triad // Friction and Wear.2010.- Vol. 31.- Iss. 3.- P. 312-318.
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4. Поповский А. Ю., Сагин С. В. Оценка эксплуатационных свойств смазочно-охлаждающих жидкостей судовых технических средств // Автоматизация судовых технических средств: наук.-техн. сборник.2016.- Вып. 22.- С. 66-74.
5. Zablotsky Yu. V., Sagin S. V. Maintaining Boundary and Hydrodynamic Lubrication Modes in Operating High-pressure Fuel Injection Pumps of Marine Diesel Engines // Indian Journal of Science and Technology.- May 2016.- Vol. 9(20).- P. 208-216. DOI: 10.17485/ijst/2016/v9i20/94490
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