RU2371706C1 - Method of determining thermal oxidative stability of lubricants - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method involves testing a sample of the lubricant at optimum temperature, photometering a sample of oxidised lubricant, weighing the lubricant sample after equal time intervals, determination of the mass of evaporated lubricant and determination of thermal oxidative stability from the coefficient of oxidation resistance.

EFFECT: more reliable determination of thermal oxidative stability of lubricants due to determination of the coefficient of oxidation resistance, which takes into account rate of conversion of heat energy into oxidation and evaporation products.

2 dwg, 1 tbl

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. 22199530, IPC G01N 25/00, publ. 2003), which includes heating the lubricant in the presence of air, mixing, photometry and determination of parameters for evaluating the oxidation process. A sample of constant volume lubricant is tested at the optimum temperature selected depending on the base base of the lubricant, photometric absorption coefficient is determined by oxidized lubricant, a graphical dependence of the change in the ratio of light absorption coefficient on the test time is built, the dependence line is extended, after the inflection point of the dependence determine the time of the beginning of coagulation of insoluble impurities, and by the limiting value of the coefficient of absorption light flow sensations determine the service life of the lubricant.

The closest in technical essence and the achieved result is a method for determining the thermo-oxidative stability of lubricants (RF patent No. 2247971, IPC G01N 25/00, published March 10, 2005), which consists in testing a lubricant in the presence of air with constant volume mixing at the 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 degree of oxidation, and at regular intervals webbings sampled oxidized lubricant define photometric absorption coefficient of the light flux oxidized lubricant viscosity and coefficient of thermal oxidative stability K _mod from the ratio K _mod = R _n μ ₀ / μ _ref, K _n - light flux absorption coefficient of oxidized lubricant μ ₀ and the viscosity μ _ref respectively oxidized and the source of lubricant build a graph of coefficient of thermal oxidative stability of the absorption coefficient of the light stream and the oxidized lubricant and the tangent of the angle of inclination of this dependence to the abscissa axis to the inflection point determine the rate of formation of intermediate oxidation products, the tangent of the angle of inclination of the dependence to the abscissa axis after the inflection point determines the rate of formation of the final oxidation products and their effect on the increase in viscosity of the test material, and the coordinates of the inflection point determine the beginning of the formation of the final oxidation products.

A disadvantage of the known methods is the low information content in the identification and classification of lubricants by groups of operational properties.

The objective of the invention is to increase the information content in the identification and classification of lubricants by groups of operational properties.

The problem is solved in that in a method for determining the thermo-oxidative stability of lubricants, in which a test of a lubricant in the presence of air with stirring is tested, 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 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 sample of the studied lubricant is additionally weighed at regular intervals, the mass of the evaporated lubricant is determined, the evaporation coefficient K _{G is} determined from the ratio

K _G = m / M ₀ ,

where m is the mass of the evaporated lubricant during oxidation;

M ₀ is the mass of the remaining sample after oxidation of the lubricant,

and the conversion energy coefficient E _p from the following relationship

E _p = K _p + K _G ,

where K _p - the absorption coefficient of the light flux;

K _G - evaporation coefficient,

then, a graphical dependence of the conversion energy coefficient E _p on the light flux absorption coefficient K _{p is built} , the dependence line is extended to the intersection with the ordinate axis, and the coefficient A characterizing the onset of thermal energy conversion is determined from the ordinate of this point, and thermal oxidative stability is determined by the oxidation resistance coefficient K _co from the relation

K _s.o = (E _p -A) / K _p ,

where A is a coefficient characterizing the beginning of the conversion of thermal energy.

The physical meaning of the conversion energy coefficient E _p lies in the fact that the lubricant cannot indefinitely absorb the supplied heat energy; therefore, its excess provides the conversion of a part of the lubricant into the products of oxidation and evaporation of a part of the lubricant; therefore, using this coefficient increases the reliability of determining the oxidative stability.

Determination of the oxidation resistance coefficient makes it possible to establish the conformity of the tested lubricants to the classification according to the groups of operational properties.

Figure 1 shows the dependence of the conversion energy coefficient on the absorption coefficient of the light flux for motor oils: 1-Elf competition STI 10W-40 SJ / CF; 2-Neste turbo 15W-40 CH-4 / SJ; 3-Mobil 0W-40 SJ / CF; figure 2 - dependence of the conversion energy coefficient on the absorption coefficient of the light flux for transmission oils: 1-Teboil HYPOID 80W-90 GL-5; 2-Spectrol Synax 75W-90 GL-5.

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

A sample of the studied constant-mass lubricant (100 ± 0.1 g) is heated to a certain temperature depending on the base base of the lubricant and the group of operational properties and mixed with air using a mechanical device. The temperature during the test is kept constant.

During the test, at equal intervals of time, the sample of the oxidized lubricant is weighed, the mass of the evaporated lubricant is determined, part of the sample is taken for photometry and determination of the absorption coefficient of the light flux K _p . The tests are terminated when the coefficient K _p reaches values of approximately 0.5-0.6.

According to the data obtained, the evaporation coefficient K _G = m / M ₀ is determined, where m is the mass of the evaporated lubricant during oxidation, M ₀ is the mass of the remaining sample after oxidation of the lubricant, and the conversion energy coefficient is E _p from the following ratio E _p = K _p + K _G , where K _p is the absorption coefficient of the light flux; K _G is the evaporation coefficient.

Then build a graphical dependence of the conversion energy coefficient E _p from the absorption coefficient of the light flux K _p (Fig.1-2), extend the dependence line to the intersection with the ordinate axis, and the coefficient A characterizing the beginning of the conversion of thermal energy is determined by the ordinate of this point.

For engine oils Elf competition STI 10W-40 SJ / CF coefficient A = 0.015 (Fig. 1, curve 1); Neste turbo 15W-40 CH-4 / SJ A = 0.014 (Fig. 1, curve 2) and Mobil 0W-40 SJ / CF A = 0.017 (Fig. 1, curve 3).

For Teboil HYPOID 80W-90 GL-5 and Spectral Synax 75W-90 GL-5 gear oils, coefficient A is 0.04 (Fig. 2, curves 1, 2 coincide).

The data on the coefficients K _p , K _G , E _p , A are tabulated and the oxidation resistance coefficient K _{s.o is determined} from the ratio

K _s.o = (E _p -A) / K _p ,

where E _p - conversion energy coefficient;

To _p - the absorption coefficient of the light flux;

A - coefficient characterizing the beginning of the conversion of thermal energy.

The oxidation resistance coefficient K _s.o. for Elf competition STI 10W-40 SJ / CF engine oils is 1.27 (Fig. 1, curve 1); Neste turbo 15W-40 CH-4 / SJ K _s.o. = 1.17 (Fig. 1, curve 2), Mobil 0W-40 SJ / CF K _co = l, 3 (Fig. 1, curve 3).

It is known that the higher the coefficient K _s.o. , the better thermo-oxidative stability is characterized by a lubricant. Based on the values of the oxidation resistance coefficient K _{s.o, the} best thermal oxidative stability is characterized by the synthetic oil Mobil 0W-40 SJ / CF. Since this engine oil has an SJ / CF classification according to the performance group, the Elf competition STI 10W-40 SJ / CF and Neste turbo 15W-40 CH-4 / SJ engine oils are not classified according to the performance group.

The oxidation resistance coefficient K _s.o. for Teboil HYPOID 80W-90 GL-5 and Spectral Synax 75W-90 GL-5 gear oils is K _s.o. = 1.08 (Fig. 2, curves 1, 2). These oils belong to one operational group GL-5.

The proposed method can be carried out on a reduced test technology. For this, it is enough to conduct 3-4 experiments, according to the results of which the values of the coefficients A and K _s.o. , and the thermo-oxidative stability of the tested lubricant are determined.

The proposed technical solution allows to increase the reliability of determining the thermo-oxidative stability of lubricants by determining the coefficient of resistance to oxidation, taking into account the rate of conversion of thermal energy into products of oxidation and evaporation.

Table Thermal oxidative stability test results for engine and gear oils Brand of oil Indicators Coefficient Values Motor oils Elf Competition STI 10W-40 SJ / CF K _p 0,03 0,07 0.13 0.22 0.28 0.33 0.44 0.54 0.6 K _G 0,023 0,034 0.05 0,074 0,091 0.104 0.134 0.161 0.18 E _p 0,053 0.104 0.18 0.294 0.371 0.434 0.574 0.701 0.78 BUT 0.015 To _s.o. 1.27 Neste turbo 15W-40 CH 4 / SJ K _p 0.04 0.09 0.14 0.21 0.3 0.41 0.56 K _G 0,021 0,029 0,038 0.05 0,065 0,094 0.109 E _p 0,061 0.129 0.178 0.26 0.375 0.494 0.669 A 0.014 K _co 1.17 Mobil 0W-40 SJ / CF K _p 0 0.01 0.02 0,03 0.11 0.19 0.26 0.33 0.43 0.46 0.5 K _g 0.17 0.02 0.41 0,026 0.05 0,074 0,095 0.116 0.146 0.155 0.167 E _p 0.17 0,03 0.43 0.056 0.16 0.264 0.355 0.446 0.576 0.615 0.667 A 0.017 K _co 1.3 Transmission oils Teboil HYPOID 80W-90GL5 K _p 0.01 0,03 0.1 0.1 0.14 0.18 0.22 0.31 0.31 0.33 0.34 0.39 0.51 K _g 0.5 0,042 0,048 0,048 0.051 0,054 0.058 0,065 0,065 0,066 0,067 0,071 0,081 E _p 0.51 0,072 0.148 0.148 0.191 0.234 0.278 0.375 0.375 0.396 0.407 0.461 0.591 A 0.04 K _co 1,08 Spectrol Synax 75W-90 GL5 K _p 0.04 0.09 0.12 0.12 0.15 0.19 0.3 0.34 0.39 0.47 0.57 0.6 K _g 0,043 0,047 0.05 0.05 0,052 0,055 0,064 0,067 0,071 0,078 0,086 0,088 E _p 0,083 0.137 0.17 0.17 0.202 0.245 0.364 0.407 0.461 0.548 0.656 0.688 A 0.04 K _co 1,08

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 constant volume stirring at the 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 the sample of the test lubricant at regular intervals, weighed, determine the mass of the evaporated lubricant is determined coefficient of evaporation K _G from the ratio K _G = m / M _0, where m - mass of vaporized lubricant material during oxidation; M ₀ is the mass of the remaining sample after oxidation of the lubricant, and the conversion energy coefficient is E _p from the following ratio: E _p = K _p + K _G , where K _p is the absorption coefficient of the light flux; K _G is the evaporation coefficient, then a graphical dependence of the conversion energy coefficient E _p on the absorption coefficient of the light flux K _{p is built} , the dependence line is extended to the intersection with the ordinate axis, and the coefficient A characterizing the beginning of the conversion of thermal energy is determined from the ordinate of this point, and the thermal oxidative stability is determined according to the oxidation resistance coefficient K _co from the relation K _c.o = (E _p -A) / K _p , where A is the coefficient characterizing the beginning of the conversion of thermal energy.

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