The method of estimating the activation energy of the thermo-mechanical degradation of lubricants with friction

 

(57) Abstract:

The invention relates to physico-chemical mechanics of friction and can be used to assess and predict the tribological properties of lubricants at the stage of laboratory tests. The method allows to evaluate the ability of a lubricant to retain its operating characteristics at the specified level. Assessment of the strength of lubricants produced by the amount of energy of chemical bonds principal valences in its molecule, which is equal to the activation energy of the degradation of lubricants and is defined as the difference of the activation energy for the destruction of the pure and modified with the friction surface of the metal sample. To determine the activation energy of the fracture surface method is used, microcanopen carried out at the Vickers microhardness tester PMT-3. The results of the application of this method allows to estimate the energy value of thermomechanical degradation of the lubricant by friction in the area of operating conditions and to characterize the carrying capacity of the lubricating layer. table 1.

The invention relates to physico-chemical mechanics of friction and can be used for the activate your product, processes of destruction of lubricants in the interaction with the contacting surfaces of the parts of the friction units use thermal-kinetic test methods.

Known way to "hot wire" (Matveevskaya R. M. and other Lubricants Handbook. M., 1989, S. 35-36) used to estimate the activation energy of the process of chemical modification of the surface of the metal sample during thermal destruction of lubricants consisting in that the lubricant is placed a thin wire through which intermittently (pulsed) electric current is passed. When this wire is heated (up to 600oC) and formed on its surface a non-conductive layer of corrosion products. The thickness of the modified layer h is determined by the change in the electrical resistance wire according to formue

(1)

where r0is the radius of the wire;

R is the resistance change of the wire;

R0- the initial resistance of the wire.

The activation energy of the process static corrosion is defined as the product of the tangent of an angle of slope of a line approximating the dependence of the h/t 1/T, the gas constant R and equate it to the activation energy Esthe process of destruction of the lubricant.

This method is analogous to the claimed invention.

The shortcoming of the above method of estimating energy Activati what is the low accuracy of the obtained values of the activation energy of the process static corrosion, because change is not considered under the influence of the operating temperature condition of the wire.

There is also known a method (GOST 23.221-84) the estimation of the conditional activation energy of the chemical modification during thermal destruction of lubricants, which produce their tests on the four-ball friction machines (for example, MAST-1) continuous temperature rise test Cup before the onset temperature of thermal destruction of the oil, which then estimate the activation energy of the test lubricant. The activation energy of chemical modification are calculated according to the formula

< / BR>
where C1C2- concentrations of these additives in liquid paraffin;

TGM, TGM- temperature chemical modification at concentrations C1and C2;

R is the universal gas constant.

This method is the prototype of the claimed invention.

The disadvantage of this method is uncharacteristic for friction units of machines mode testing of lubricants: "point" contact three fixed balls with a rotating fourth, push power and thermal load, which makes it difficult chemical modify the activity of the obtained evaluation values of activation energy of thermo-mechanical degradation of lubricants and does not allow to identify non-linear deviations of the activation parameters in the temperature-kinetic dependencies.

The invention consists in the fact that in the proposed method of evaluation of activation energy of thermo-mechanical degradation of lubricants for friction estimation of the activation energy for breaking the surface of the metal sample, the method microcanopen before and after chemical modification, resulting from running the sample surface in the environment of the test lubricant; the difference of the obtained values is equal to the desired value of the activation energy of thermo-mechanical degradation of lubricants. This estimate can be used in tribology to determine the strength of the material of the lubricating layer. This is because in the process of friction, under the action of high temperatures and pressures in the area of the actual touch spot occurs destruction of the molecules of the lubricant with the formation of active centers (free radicals) and their chemical interaction with the metal. At the same time changes the chemical composition and properties of the lubricant due to interaction with oxygen and other components of the environment and the material of the surface of a solid phone as there is no way of directly determining the fracture energy of the molecules of the liquid lubricating the spine of the activation energies of destruction pure and chemically modified surfaces of metals, interacting with the test grease. When thermo-mechanical degradation of the molecules investigated the lubricant deposited on the surface of the metal sample and the chemical interaction of free radicals and metal atoms with lubrication formed new relationships between dissimilar atoms, which leads to higher energy of the metal lattice. However, due to the smallness of the temperature of thermal decomposition of lubricants in relation to the temperature of phase transformations in metal, in the modification process preserves the original crystal structure in the surface layer of the sample, but is changing its chemical composition.

The proposed method for the evaluation of activation energy of thermo-mechanical degradation of lubricants based on assessing the difference in the strain energy surfaces of metallic materials method microcanopen before and after chemical modification in the tested oil at friction.

The proposed method is as follows:

On the surfaces of the samples in the mode of plastic deformation to form a micro abrasions. After assessment of the amount of deformation (amount of inferior material) and tangential stresses by the formula

< / BR>
where A

The work of ADefspent on the plastic deformation, for small speeds and amounts of deformation equal to the friction force (Kuznetsov C. D. Physics of the cutting and friction of metals and crystals. M., 1977, S. 74-79) and evaluate how

ADef=FDefl10-3=mgfl10-3, (4)

where m is the load on the indenter, kg;

g - free fall acceleration, g = 9.8 m/s;

f - ratio plastic friction for metals f 0,2;

l - the way of friction, m

Tested the above method, the samples are subjected to wear in the environment of the test lubricant. Sample material, type of surface, type of test devices and test mode are selected according to the purpose of the study the friction. Trials are ongoing to establish the mode of wear, which gives a complete modification of the surfaces of the elements contained in the lubricant.

On smooth surfaces re-evaluation of the strain energy, but modified layer of material.

The difference in the strain energy of freshly cut and worn samples is interpreted as the activation energy thermomechanical d is:

< / BR>
where Vo- the volume of the grooves formed in one pass of the indenter, μm3;

V- the volume of the grooves formed in N repeated passages of the indenter on the first furrow, μm3;

Vmis molar volume of the metal, mm3/mol;

N is the number of repeated passes of inductor, N = 3...5;

S0- the first furrow width, µm;

SN- the width of the furrow after N passes of the indenter;

l is the length of the scratches, m

Activation energy:

< / BR>
The accuracy of the obtained values of the activation energy of thermo-mechanical degradation of lubricants in friction is provided by the material properties addtive accumulate the internal energy of the lattice in the establishment of new relations of atoms of base metal and free radicals and breaking to release the stored energy, thereby increasing the resistance to mechanical destruction, but also due to the structural similarity transformations scratching freshly cut and modified surfaces.

Implementation method:

to obtain an estimate of previously unknown tribological characteristics of the lubricant - activation energy of thermo-mechanical degradation of the lubricant by friction, ha is Smriti testing due to the lack of the need to control the temperature of the chemical modification.

Emissions were estimated activation energy of thermo-mechanical degradation of lubrication Chevron-SR". This was carried out the following sequence of operations.

A sample of steel 40X processed according to the technology adopted for steel rectilinear guides - cementation (HRC 50) and grinding R = 0.1 ám.

Have assessed the activation energy U01freshly cut surface layer of the sample by applying microcanopen. When you do this:

On the surface of the sample lowered the indenter with the sample of 0.05 kg

Rotation of handwheel transverse offset table produced scratching the surface of the sample by the indenter. The length of the scratch l 0,5 mm

The indenter was raised and set the sample under the microscope with which to measure the width of the resulting furrows.

Repeated scratching with the number of repeated passes of the indenter N = 4.

For each experiment was determined by the activation energy of the material according to the formula (6).

Tested samples on the machine friction in the medium lubrication Chevron-SR" at a temperature of 50oC, normal load of 5 MPa, the number of double strokes per minute n = 200, the stroke length of 20 mm, the test time 2 hours

Have assessed the activation energy USa test results (scattering about 5%) are shown in the table.

Thus, the activation energy thermomechanical degradation of lubrication Chevron-SR" amounted to Ecm= U02- U01= 36 kJ/mol.

The method of estimating the activation energy of thermo-mechanical degradation of lubricants in friction, namely, that produce chemical modification of the surface of the metal sample and estimate the activation energy of a lubricant, characterized in that the activation energy of thermo-mechanical degradation of the lubricant by friction appreciate the value of the stored energy of the crystal lattice of the metal accumulated in the process of chemical modification of the sample surface, occurring when the friction in the environment of the tested lubricant, as the difference of the activation energy for the destruction of the pure and modified surface layers of the metal sample.

 

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