Molecular tribology of lubricants and additives (original) (raw)
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Tribology Enhancement of Lubricant Quality and Safety
2014
A question of huge importance of applying tribology is the development and creation of higher quality of lubricants and additives to them, which influence equipment reliability and life, energy and raw material savings, as well as provide safety solutions to many environmental tasks. The paper stresses on the repair-regeneration oil additives. Added to oils or greases they form a thin protective layer, diminishing friction and wear, and assuring partial regeneration of worn surfaces under special friction conditions. Most interesting are the organic oil-soluble additives. An illustration with one of the newest additives, the oil-soluble metal-plating composite additive called "Valena", manufactured in Kazakhstan, is presented in the paper. The influence of this additive on the enhancement of the tribological parameters of contact pairs lubricated by oils and greases was studied as per the tasks of the International Faculty Agreement between the Faculty of Mechanical Engine...
Determination of Critical Temperatures for Lubricants by Molecular Tribology
Tribology - Solving Wear and Friction Problems, International Colloquium, 1996
A calculation method for estimating boundary lubricant critical temperatures, as a criterion for rating oil antiwear performance, is introduced. This method is applied to lubricants that are considered as a binary mixture of a (pure or additivated) base oil plus an antiwear additive (the representative chemical species pair). The temperature determination is made by solving a characteristic transcendental equation for the binary lubricant. An analogous equation is deduced for the antiwear additive alone. All the parameters needed for the proposed equations can be obtained from friction coefficient laboratory measurements. According to the results, antiwear additives can raise base oil critical temperature. A discussion about the influence of the macroscopic contact geometry on the friction coefficient, is also presented.
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Surface-active agents play an important role in lubrication technology and are often used as additives in liquid lubricants films to reduce the friction and wear. Under high loads, in asperity contacts or when there is no relative motion between two surfaces, fluid lubrication breaks down and boundary lubricants are essential to prevent wear and seizure. In other applications where the use of ‘thick’ films of liquid lubricants is not possible or desirable (i.e. micromotors, hard disk drives), lubrication between contacting surfaces is exclusively in the boundary regime. Despite the use of boundary lubricants in engineering applications for centuries, our understanding of how boundary lubricants work at the molecular level remains unclear. My thesis describes the use of total internal reflection (TIR) Raman scattering to characterise model boundary lubricants both ex situ and in situ, under realistic conditions of pressure and shear. The model systems comprise either Langmuir-Blodget...
A MOLECULAR MODEL FOR BOUNDARY LUBRICATION: ON THE BASICS OF MOLECULAR TRIBOLOGY
8th International Colloquium, Esslingen "Tribology 2000", 1992
A boundary lubrication regime model in which almost all the friction and wear are due to physical interaction processes in the interface between tribological surfaces is introduced. In this model the operation conditions for the tribological system are related with its solid elements properties and the physical-chemical characteristics of the lubricant. This generic lubricant has been considered as formed by a modified base stock and an anti-wear/extreme pressure a.w./e.p. additive. In this picture, molecular sizes and adsorption energies play an important role in the interface where the macroscopic contact geometry is taken into account based in the Hertz's theory for the calculation of the surface-surface direct real contact area under applied load. The block on ring FALEX-TIMKEN tester was used for measurements of friction force at different temperatures as function of the sliding velocity and applied mechanical load. These tests were carried out using three different formulated lubricant oils. Also, measurements of wear as function of the applied load were done. Once the generic additive adsorption energy and the effective base stock molecular size were estimated, they were introduced in the calculation for simulation. The model reproduces the experimental wear trends at low temperatures and explanations of data features can be drawn. Chemical wear may be involved as shown by the estimated values for the energies of adsorption. However, the model under estimates the measure of wear at high temperatures owing to the explicit neglection of chemical wear processes.
Lubricants
Based on the analysis of standards for the testing of lubricants, both liquid and plastic, on a four-ball tribometer, and the analysis of the parameters by which lubricants are evaluated, this paper proposes a methodology and an integral parameter for the estimation of tribological properties. The methodological approach proposed in this paper allows for the integration of a variety of parameters provided in the standards for the testing of lubricants into one indicator. Herein, we show that the developed technique is based on the energy approach and takes into account the specific wear work of the test material (steel balls) in the lubricating medium to be investigated. The results of laboratory tests of a wide range of lubricants are presented: hydraulic fluids, motor and transmission oils of various purposes and classifications. It is shown that the magnitude of the integral parameter can be used to assess the effectiveness of anti-wear and anti-scuff additives in base lubricants...