RU2567087C1 - Method of defining of oil lubricity - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method of defining of oil lubricity means that friction pair is operated upon lubricant presence, electric current is conducted through it, direct current is measured at fixed friction pair and stable friction mode, oil sample with permanent weight is heated at definite temperature for permanent time period. Then part of oxidized oil is sampled and photometric measured; coefficient of light flux absorption is determined; another part of the oxidized oil sample is tested on friction machine, and lubricity is determined according to current effect coefficient. At that the oxidized oil sample is tested on the friction machine at permanent friction parameters, direct current is conducted through the friction pair from the external stabilized voltage source, diagram of current changes during friction is plotted, it is used to determine start of the stable wear and current value. Then coefficient of electrical conductivity of the barrier layer is determined as ratio of current flowing through the barrier layer to the set current, wear sport diameter and ratio of coefficient of light flux absorption to the wear spot diameter are determined. The voltage drop, U_BL, of the barrier layer separating friction surfaces is determined at stable wear using the empirical formula: $$U_{BL}=\frac{{К}_A}{U}\cdot {К}_{BLE},$$

where K_A is coefficient of light flux absorption; U is wear spot diameter, mm; K_BLE is coefficient of barrier layer electrical conductivity. Diagram of barrier layer voltage drop vs. coefficient of light flux absorption is plotted, based on it the tested oil lubricity is determined. The higher barrier layer voltage drop is the higher lubricity is.

EFFECT: justified selection of oils for the internal combustion engines based on comprehensive estimation of the tested oil lubricity based on its optical properties, wear value and coefficient of electric conductivity of the friction contact representing resistance of the barrier lubricating layer.

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Description

The invention relates to a technology for evaluating the quality of lubricating oils, in particular to determining their lubricity.

A known method for determining the lubricity of oils is that a friction pair is operated in the presence of a lubricant, an electric current is passed through it, and the lubricity is estimated by the ratio of the currents flowing through a stationary friction pair and under steady-state friction (USSR copyright certificate No. 1054732, date priority 08.07.1982, publ. 15.11.1983, authors Kovalsky B.I. et al., RU).

The disadvantage of this method is the lack of a quantitative assessment of the relationship between the concentration of aging products in oil, wear and electrical conductivity of the friction contact, since this relationship determines the properties of the boundary layers separating the friction surfaces.

, где U_Т - параметр износа при пропускании через пару трения постоянного тока от внешнего стабилизированного источника питания, мм; U - параметр износа при отсутствии тока в паре трения, мм, а смазывающую способность испытуемого масла определяют по значениям коэффициента влияния тока, где отрицательное значение коэффициента влияния тока К_ВТ означает повышение смазывающей способности окисленного масла, а положительное значение коэффициента влияния тока К_ВТ показывает понижение смазывающей способности окисленного масла (патент РФ №2408866, дата приоритета 30.11.2009, опубл. 10.01.2011, авторы Ковальский Б.И. и др., RU, прототип).The closest in technical essence and the achieved result is a method for determining the lubricating ability of oils, which consists in using a friction pair in the presence of a lubricant, passing an electric current through it, measuring direct current with a stationary pair of friction and with a steady state friction, a sample of constant weight oil heated with stirring at a certain temperature depending on the purpose of the lubricating oil for a constant time, part of the sample of oxidized oil is taken, photometer The absorption coefficient of the light flux is determined by testing, and the other part of the sample of oxidized oil is tested twice on a friction machine with constant friction parameters when a direct current is passed through a friction pair from an external stabilized power source and without current, wear parameters are measured when current is passed through a friction pair and without current determine the coefficient of influence of current K _VT on the lubricity of oxidized oil by the formula: $${\mathrm{TO}}_{\mathrm{AT}T}=\frac{U_T-U}{U_T}\cdot \mathrm{one\; hundred}\%$$

where U _T is the wear parameter when passing through a friction pair of direct current from an external stabilized power source, mm; U is the wear parameter in the absence of current in the friction pair, mm, and the lubricity of the test oil is determined by the values of the coefficient of influence of the current, where a negative value of the coefficient of influence of the current K _W means an increase in the lubricity of the oxidized oil, and a positive value of the coefficient of influence of the current K _W shows a decrease the lubricity of oxidized oil (RF patent No. 2408866, priority date 11/30/2009, publ. 01/10/2011, authors Kovalsky BI and others, RU, prototype).

The disadvantage of the prototype is the lack of information of the method due to the lack of a comprehensive assessment of the lubricating properties of oils, taking into account the resistance of the boundary lubricating layer.

The objective of the invention is a comprehensive assessment of the lubricating properties of the test oil by its optical properties, the amount of wear and the coefficient of electrical conductivity of the friction contact, reflecting the resistance of the boundary lubricating layer.

,To solve the problem and obtain a technical result in a method for determining the lubricating ability of oils, which consists in using a friction pair in the presence of a lubricant, passing an electric current through it, measuring direct current with a fixed pair of friction and with a steady state friction, an oil sample of constant mass heated at a certain temperature for a constant time, take part of the sample of oxidized oil, which is photometric, and determine the absorption coefficient of the light flux, and the other part of the sample of oxidized oil is tested on a friction machine, the lubricity is determined by the values of the current influence coefficient, according to the invention, the sample of oxidized oil is tested on a friction machine at constant friction parameters, a direct current is passed through a friction pair from an external stabilized voltage source, a diagram of the current change is recorded in the process of friction, by which the onset of steady-state wear and the current value are determined, the conductivity coefficient of the boundary layer is determined as the ratio of the current flowing through the boundary layer to a given current, determine the diameter of the wear spot and the ratio of the absorption coefficient of the light flux to the diameter of the wear spot, determine the voltage drop U _ГС on the boundary layer separating the friction surfaces during steady-state wear, according to the empirical formula: $$U_{G\mathrm{FROM}}=\frac{{\mathrm{TO}}_P}{U}\cdot {\mathrm{TO}}_{EG\mathrm{FROM}}$$

,

Where

K _P - light absorption coefficient;

U is the diameter of the wear spot, mm;

_EHS - the conductivity coefficient of the boundary layer,

construct a graphical dependence of the voltage drop on the boundary layer on the absorption coefficient of the light flux, which is used to determine the lubricity of the test oil, and the greater the value of the voltage drop on the boundary layer, the higher the lubricity.

In FIG. 1 shows diagrams of recording the current flowing through the frictional contact during tribological testing of oxidized oils Mobil Super Syn 0W-40 SJ / SL / CF (a) and THK Super 10W-40 SL / CF (b), in FIG. Figure 2 shows the dependences of the voltage drop at the boundary layer of oxidized oils on the absorption coefficient of the light flux for mineral oils: Spectrol Super 15W-40 SF / CC (1); Lukoil Standard 10W-40 SF / CC (2); partially synthetic THK Super 10W-40 SL / CF (3) and synthetic Mobil Super Syn 0W-40 SJ / SL / CF New Life (4).

A method for determining the lubricity of oils is as follows.

Commodity lubricating oil of constant weight (for example, 100 ± 0.1 g) is heated in a glass beaker at atmospheric pressure and stirred with a glass stirrer at a constant speed using an electric motor at a constant temperature (for example, 180 ° C). At regular intervals (for example, 8 hours), a portion of the sample of oxidized oil is taken for direct photometry and determination of the absorption coefficient of the light flux K _P. When the values of the coefficient K _P equal to 0.1; 0.2; 0.3 ... 0.8 units, an additional sample of oxidized oil is taken for testing on a friction machine and determining the amount of wear, after which the glass cup is refilled with marketable oil to its original mass and the tests continue until the next value of the coefficient K _P. The friction parameters were chosen constant (for example, a load of 13 N, a sliding speed of 0.68 m / s, a test time of 2 hours, and an oil temperature of 80 ° C). A constant current (for example, not more than 100 μA) from an external source of stabilized voltage (for example, 3 V) is passed through a friction pair. The current value is set at the static position of the samples (for example, 100 μA), and in the process of friction is recorded through a converter on a computer display in the form of a diagram (Fig. 1).

The magnitude of the current flowing through the friction contact depends on its resistance, therefore, with a small resistance of the contact, when plastic deformation of the microroughness of the friction surfaces occurs, the magnitude of the current is maximum and equal to the specified value (100 μA). With a high resistance to frictional contact, and this is possible when modified boundary layers are formed on the friction surfaces, as a result of a chemical reaction of metal surfaces with organic acids, which change the electrical conductivity of these layers (contact) and determine the amount of wear. If we arbitrarily denote the resistance of the boundary layer through the symbol R, the magnitude of the current flowing through it is determined by the formula:

where U _GS is the voltage drop at the boundary layer; I is the magnitude of the current flowing through the boundary layer.

Using formula 1, the frictional contact resistance R is defined as:

For the convenience of applying formula (2), it is proposed to replace the current value with the coefficient of electrical conductivity of the boundary layer K of the _EHS , defined by

where I is the magnitude of the current flowing through the boundary layer, µA; I _З - the set current value at the static position of the friction pair, (100 μA).

Then formula (2) can be written as:

The electrical conductivity of the boundary layer depends on the properties of the lubricating oil, which are determined by the concentrations of oxidation products, thermal and mechanical degradation, and its acidity, then the total concentration can be determined by the photometric method from the light flux absorption coefficient K _P.

The influence of the oxidation products formed in the lubricating oil is determined by their concentration in the boundary layer separating the friction surfaces, and their electrical conductivity, which is proposed to evaluate the voltage drop across the boundary layer, according to the empirical formula:

) и их электропроводность К_ЭГС, определяющим свойства граничного слоя и величину износа.The voltage drop U _ГС is a complex indicator characterizing the conditional concentration of the oxidation products of lubricating oil at the nominal area of friction contact ( $$\frac{{\mathrm{TO}}_P}{U}$$

) and their electrical conductivity K _EHS , which determines the properties of the boundary layer and the amount of wear.

Therefore, according to the current recording diagrams, the start time of the steady-state wear (the period of stabilization of the current during friction) is determined. According to the formula (3), the conductivity coefficient of the boundary layer K _EHS is determined, U _GS is determined by the formula (5), a graphical dependence of the voltage drop U _GS on the absorption coefficient of the light flux is constructed (Fig. 2), which determines the change in the lubricity of the tested oil from the total concentration of oxidation products.

According to the presented data (Fig. 2) it was found that when the values of the absorption coefficient of the light flux K _P <0.3 units the voltage drop coefficient U _ГС acquires values less than unity for all the oils studied, which is explained by the poor lubricity of the oils at the beginning of the oxidation process. With an increase in the coefficient K _{P, the} lubricity of oxidized oils increases, and the greater the voltage drop U _GS , the higher their lubricity due to the formation of resinous products of oxidation and increase the acidity of oils, which contributes to the formation of chemisorption boundary layers on the friction surfaces as a chemical compound of metal surfaces with organic acids.

Higher lubricating properties are characterized by mineral oil Lukoil Standard 10W-40 SF / CC (curve 2) and synthetic Mobil Super Syn OW-40 SJ / SL / CF New Life (curve 4).

The application of the proposed method allows a reasonable choice of oils for internal combustion engines.

Claims (1)

The method for determining the lubricating ability of oils, which consists in the fact that a friction pair is operated in the presence of a lubricant, an electric current is passed through it, a direct current is measured with a fixed friction pair, and with a steady friction mode, a constant mass oil sample is heated at a certain temperature for a constant time, part of the sample of oxidized oil is taken, which is photometric, and the absorption coefficient of the light flux is determined, and the other part of the sample of oxidized oil is tested on a friction machine, divide the lubricating ability by the values of the coefficient of influence of the current, characterized in that the sample of oxidized oil is tested on a friction machine with constant friction parameters, a constant current is passed through a friction pair from an external stabilized voltage source, a diagram of the current change during friction is recorded, by which the beginning of the steady state is determined wear and current value, determine the conductivity coefficient of the boundary layer as the ratio of the current flowing through the boundary layer to a given current, determine the diameter of the wear spot and the ratio of the absorption coefficient of the light flux to the diameter of the wear spot, determine the voltage drop U _ГС on the boundary layer dividing the friction surfaces with steady wear, according to the empirical formula: $$U_{G\mathrm{FROM}}=\frac{{\mathrm{TO}}_P}{U}\cdot {\mathrm{TO}}_{EG\mathrm{FROM}}$$

,
Where
K _P - light absorption coefficient;
U is the diameter of the wear spot, mm;
_EHS - the conductivity coefficient of the boundary layer,
construct a graphical dependence of the voltage drop on the boundary layer on the absorption coefficient of the light flux, which is used to determine the lubricity of the test oil, and the greater the value of the voltage drop on the boundary layer, the higher the lubricity.

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