RU2247971C1 - Method for determining thermal oxidative stability of lubricants - Google Patents

Abstract

FIELD: measurement technology; material quality control.

SUBSTANCE: method involves testing lubricant material sample in presence of air with stirring constant volume under optimum temperature selected with its dependence on lubricant base and a group of operational properties during a time interval characterizing equal oxidation degree taken into account. Acting in equal time intervals, absorption coefficient is measured for luminous flow absorbed by oxidized lubricant material by applying photometry methods. Viscosity and thermal oxidative stability coefficient K_tos are calculated by using relationship like K_tos = K_a μ₀/μ_in, where K_a is the luminous flow absorption coefficient of oxidized lubricant material; μ₀ and μ_in are the viscosities of oxidized and initial state lubricant, respectively. Graphic dependence of thermal oxidative stability coefficient against luminous flow absorption coefficient of oxidized lubricant material is plotted. Rate of oxidation end products release and their influence upon tested lubricant viscosity growth is determined from plot slope angle tangent with respect to abscissa axis after inflection point. The inflection point coordinates are used for determining the starting point the oxidation end products release begins.

EFFECT: high reliability of estimation method.

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Description

The invention relates to a technology for evaluating the quality of liquid lubricants.

A known method for determining the thermo-oxidative stability of lubricants (RF patent No. 2057326, G 01 N 25/02, 1996), which includes heating the lubricant in the presence of air, mixing and determining the parameters.

The disadvantage of this method is the low information about the thermo-oxidative stability of lubricants, because it determines the temperature of the onset of oxidation, the rate of formation of soluble and insoluble oxidation products and does not take into account the effect of oxidation products on oxidative processes.

The closest in technical essence and the achieved result is a method for determining the thermo-oxidative stability of lubricants (RF patent No. 22199530, G 01 N 25/00, 2003), including heating the lubricant in the presence of air, mixing, photometry and determination of parameters for evaluating the oxidation process. A constant volume lubricant sample is tested at an optimum temperature selected depending on the base base of the lubricant and the group of operational properties over a period of time characterizing the same oxidation state, and at regular intervals, an oxidized lubricant sample is taken, the absorption coefficient of the light flux by an oxidized lubricant is determined by photometry material, build a graphical dependence of the change in the ratio of the absorption coefficient of the light flux from the test time, the dependence line is extended after the inflection point to the intersection with the abscissa axis and the abscissa of this point is determined from the abscissa of this point, the start time of the formation of insoluble impurities is determined, the start time of the coagulation of insoluble impurities is determined from the inflection point, and the service life of the lubricant is determined from the limit value of the light flux absorption coefficient material.

The known method has insufficient information about the quality of commercial lubricants, because it only determines the time of formation of insoluble impurities, the time of their coagulation and the service life of the lubricant from the limit value of the absorption coefficient of the light flux by the oxidized lubricant and does not take into account the effect of oxidation products on oxidative processes.

The objective of the invention is to increase the reliability of assessing the quality of lubricants by taking into account the effect of oxidation products on oxidative processes.

The problem is solved in that in a method for determining the thermo-oxidative stability of lubricants, in which a lubricant sample is tested in the presence of air with stirring, a constant volume at an optimal temperature selected depending on the base base of the lubricant and the group of operational properties over a period of time characterizing the same the degree of oxidation, and at regular intervals, a sample of the oxidized lubricant is taken, determined by photometry to the coefficient of absorption of the light flux by the oxidized lubricant and the oxidation process is evaluated, according to the invention, the viscosity of the sample of the lubricant, the coefficient of thermal oxidative stability K _{tos are also determined} from the ratio

K _tos = K _n μ _о / μ _ref ,

where K _n is the absorption coefficient of the light flux of the oxidized lubricant;

μ _about and μ _ref - respectively the viscosity of the oxidized and initial lubricant,

a graphical dependence of the coefficient of thermal oxidative stability on the absorption coefficient of the light flux of the oxidized lubricant is built, and the rate of formation of intermediate oxidation products is determined from the slope of this dependence to the abscissa axis to the inflection point, and the speed of the dependence of the angle of inclination to the abscissa axis after the inflection point is determined formation of the final oxidation products and their influence on the increase in viscosity of the test lubricant, and according to the coordinates of the point n Dependency dependencies determine the beginning of the formation of the final oxidation products.

A comparative analysis of the prototype and the proposed method showed that the latter has the following distinctive features.

Measurement of the absorption coefficient of the light flux and the viscosity of the oxidizable lubricant allows us to determine the coefficient of thermo-oxidative stability of the studied lubricant, taking into account the influence of oxidation processes on the rate of formation of oxidation products and their effect on the viscosity of the lubricant.

The construction of graphical dependences of the change in the coefficient of thermo-oxidative stability on the absorption coefficient of the light flux by the oxidized lubricant makes it possible to visualize the relationship between these quality indicators of the lubricant, and from the tangent of the angle of inclination of this dependence to the abscissa in the area to the inflection point, determine the rate of formation of intermediate oxidation products, from the tangent the angle of inclination of the dependence on the abscissa in the area after the inflection point to determine the rate of formation of of the final oxidation products and their influence on the viscosity of the test lubricant, and by the coordinates of the inflection point of the dependence to determine the beginning of the formation of the final oxidation products. All these indicators are aimed at solving the problem - increasing the reliability of the quality assessment of lubricants.

Figure 1 shows the dependence of the coefficient of thermal oxidative stability on the absorption coefficient of the light flux of motor oils on a mineral and semi-synthetic basis: 1 - Sibi Motor Suite 15W-40 SG / CD; 2 - Sibi Motor M-10-G2k; 3 - Neste turbo LXE 15W-40 CH-4 / SJ; 4 - elf Competition STI 10W-40 SJ / CF; 5 - Zic 5000 10W-40 CC-4 / SH; 6 - ZICA 10W-40 SL; figure 2 - dependence of thermal oxidative stability on the absorption coefficient of the light flux of industrial oils: 7 - I-12-A; 8 - I-40-A; figure 3 - dependence of the coefficient of oxidative stability on the absorption coefficient of the light flux of synthetic synthetic motor oils: 9 - Mobil 5W-50 SJ / CF; 10 - Mobil OW-40 SJ / CF; figure 4 - dependence of the coefficient of thermo-oxidative stability on the absorption coefficient of the light flux of gear oil 11 - Consol trans. 85W-90-GL-5.

The method for determining the thermal oxidative stability of lubricants is as follows.

A test sample of a constant-volume lubricating oil is heated to a temperature depending on the base base (mineral, semi-synthetic or synthetic) and mixed with air using a mechanical device. The temperature of the test oil during the test should be kept constant (± 1 ° C).

During the test, at equal intervals of time, for example 2 hours, a lubricant sample is taken for photometry and determination of the light flux absorption coefficient K _{n with} oxidized oil and viscosity (μ). Tests are terminated when the coefficient K _n reaches values approximately equal to 0.75-0.8.

According to the results of the analysis, the coefficient of thermal oxidative stability K _{tos of the} tested lubricant is determined from the ratio

K _tos = K _n μ _о / μ _ref ,

where K _n is the absorption coefficient of the light flux of the oxidized lubricant;

μ _o and μ _ref are the viscosity of the oxidized and initial lubricant, respectively.

Build a graphical dependence of the coefficient of thermo-oxidative stability K _tos on the absorption coefficient of the light flux K _n (Fig.1-4), which shows that it has two linear sections with an inflection point A ₁ -A ₁₁ . In the dependence 0-A ₁ -A _11, at small values of the coefficients of thermo-oxidative stability and absorption of the light flux, oxidative processes occur with the formation of intermediate products (hydrocarbon peroxide). The second section of the dependence K _to = f (K _n ) after the inflection point is characterized by a more intensive increase in the coefficient K _to due to the formation of the final oxidation products (hydroperoxide) and a more intensive increase in the viscosity of the test lubricant. In this regard, three indicators are proposed to evaluate the thermo-oxidative stability of lubricants.

The tangent of the slope of the dependence K _to = f (K _n ) to the abscissa axis in the section OA ₁ -A ₁₁ to the inflection point determines the rate of formation of intermediate oxidation products.

The slope of the dependence K _to = f (K _n ) to the abscissa in the area after the inflection point determines the rate of formation of the final oxidation products and their influence on the increase in viscosity of the test lubricant.

The coordinates of the inflection point (A ₁ ... A ₁₁ ) of the dependence K _to = f (K _n ) determine the beginning of the formation of the final oxidation products.

The results of the analysis of mineral, semi-synthetic and synthetic oils are summarized in the table.

Lubricant Test Results

Table Sample Number Brand of tested oil Basic foundation
oils Slope angle tangent
K _tos = f (K _n ) The coordinates of the inflection point of the dependence K _TO = f (K _n ) by: Test temperature, ° С to the inflection point after the inflection point K _tos K _n 1. Motor Sibi Motor Suite 15W-40 SG / CD miner. 1,0 1.33 0.3 0.3 180 2. Motor Sibi Motor M-10-G2k miner. 1,0 1,67 0.23 0.23 180 3. Motor Neste turbo LXE 15W-40 CH-4 / SJ miner. 1,0 1,1 0.33 0.33 180 4. Motor elf Competition STI 10W-40 SJ / CF half sines. 1,0 1.14 0.33 0.33 180 5. Motor Zic 5000 10W-40 CC-4 / SH half sines. 1,0 1.85 0.24 0.23 180 6. Motor ZICA 10W-40 SL half sines. 1,0 2,3 0.35 0.34 180 7. Industrial I-12-A miner. 1,0 1.46 0.22 0.21 150 8. Industrial I-40-A miner. 1,0 1.13 0.35 0.34 150 9. Motor Mobil 5W-50 SJ / CF synthetic 0.75 2,5 0.41 0.56 180 10. Motor Mobil OW-40 SJ / CF synthetic 0.75 1,6 0.37 0.51 180 eleven. Transmission Consol trans. 85W-90-GL-5 miner. 1.17 1.33 0.54 0.46 150

According to the table it can be seen that the tangent of the slope of the dependence K _to = f (K _n ) to the inflection point is equal to unity (i.e. 45 °) for mineral motor (Fig. 1) and industrial oils (Fig. 2), as well as semi-synthetic (figure 1) motor oils (samples No. 1-8). This means that the rate of increase of the coefficients K _tos and K _{n is the} same and the intermediate oxidation products equally affect these coefficients. The viscosity of the oxidized lubricant does not affect the value of the coefficient K _tos .

For synthetic (Fig. 3) motor oils (samples No. 9 and 10), the slope of the dependence K _to = f (K _n ) to the inflection point is 0.75, which indicates that the rate of increase in the coefficient K to _is less than the increase rate coefficient K _n . Intermediate oxidation products more affect the value of the coefficient K _n than the coefficient K _tos . This is due to the fact that the viscosity of these oils during oxidation decreases, and they have high viscosity-temperature properties.

For transmission (4) The oil (sample 11) depending on the slope angle _mod K = f (K _n) is equal to 1.17, which indicates a more intense increase coefficient K _mod due to viscosity increase in the oxidation of oil.

Thus, the smaller the tangent of the slope of the dependence K _to = f (K _n ) to the abscissa to the inflection point, the better viscosity-temperature properties of the lubricant.

The slope of the dependence K _to = f (K _n ) after the inflection point characterizes the rate of formation of the final oxidation products and their influence on the viscosity of the oxidized oil, therefore the smaller this angle, the lower the rate of contamination of the lubricant with the final oxidation products. Such oils include mineral mineral No. 3, semi-synthetic engine No. 4 and industrial No. 8. Synthetic engine oil sample No. 9, semi-synthetic engine oil sample No. 6, semi-synthetic engine oil sample No. 5 are characterized by a high rate of formation of end oxidation products.

The coordinates of inflection points depending K _mod = f (K _n) define the beginning of formation of the final oxidation product (hydroperoxides), however, the larger the value of coefficient K _n and smaller value of the coefficient K _mod, the better thermo-oxidative properties is characterized by the lubricant, and the more resources it health. These properties are possessed by synthetic motor oils of sample No. 9 and No. 10 (figure 3).

The proposed technical solution allows to increase the reliability of evaluating the thermo-oxidative stability of lubricants and is industrially applicable.

Claims (1)

A method for determining the thermo-oxidative stability of lubricants, in which a lubricant sample is tested in the presence of air with stirring, of a constant volume at an optimum temperature selected depending on the base base of the lubricant and the group of operational properties over a period of time characterizing the same oxidation state, and at regular intervals time, a sample of oxidized lubricant is taken, the absorption coefficient of the light flux is determined by photometry acidification lubricant and evaluated the oxidation process, characterized in that it further determine the viscosity of the sample lubricant thermooxidative stability factor K from the ratio _tos K _tos = K _n μ _o / μ _ref , where K _n is the absorption coefficient of the light flux of the oxidized lubricant; μ _about and μ _ref - respectively the viscosity of the oxidized and initial lubricant, a graphical dependence of the coefficient of thermal oxidative stability on the absorption coefficient of the light flux of the oxidized lubricant is built, and the rate of formation of intermediate oxidation products is determined from the slope of this dependence to the abscissa axis at the site to the inflection point, the speed is determined from the slope of the dependence of the dependence on the abscissa axis after the inflection point formation of the final oxidation products and their influence on the increase in viscosity of the test lubricant, and according to the coordinates of the point n Dependency dependencies determine the beginning of the formation of the final oxidation products.

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