Hung-Gu Han

Wear monitoring based on the analysis of lubricant contamination by optical ferroanalyzer

Abstract Lubricant contamination analysis is one of the common and prospective methods of machine condition monitoring. Wear debris formed in rubbing is a source of valuable information on the wear mechanism and severity, while total oil contamination gives information on oil lubricity. Development of new methods and means of reliable condition monitoring of friction units remains a challenging task for rating the condition of equipment, reducing losses for idle time or failures, and saving lubricants. Despite the fact that direct reading (DR) ferrograph was proposed more than 20 years ago its main principle—accumulation and estimation of deposited particles content—underlies the basis of creation of new effective built-in devices and criteria for condition monitoring. In the presented paper, the principle of operation of the optical ferroanalyzer (OF) jointly developed by V.A. Belyi Metal-Polymer Research Institute of Belarus National Academy of Sciences and Korea Institute of Science and Technology is presented. Optical ferroanalyzer in addition to ferrograph allows us to estimate total contamination of oil, increasing reliability of tribosystem condition monitoring. The results of bench tests of the analyzer are described and example of its application for condition monitoring of engine is shown.

A magnetoelastic viscometer for on-line monitoring of viscosity of lubricating oils

The paper discusses the prospects for developing means for on-line measurement of the viscosity of lubricating oils, including diagnostic instrumentation based on magnetoelastic interaction. The theoretical basis for the development of magnetoelastic sensors and the main concept of measuring the fluid viscosity are presented. Two methods of measuring the viscosity are described. The first method is based on estimating variations in the natural frequency of oscillations of a sensitive element and the second involves analysis of the decay rate of the amplitude of oscillations. The design of the developed magnetoelastic sensor and the experimental results of comparing the two measurement methods are reported. The paper also presents the comparative results of measurement of the oil viscosity by a magnetoelastic sensor, a capillary viscometer, and a solid-state piezoacoustic sensor. It is shown that the reliability of the magnetoelastic sensor is high from the viewpoint of on-line monitoring; owing to its relatively low cost and ease of maintenance, it has wide potential for application in monitoring of lubricating oils in tribosystems.

Friction mechanisms of Silicon wafer and Silicon wafer coated with diamond-like carbon film and two monolayers

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-on-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 mm, 0.5 mm and 1 mm were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer. Interestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains.

Influence of viscosity modifiers on the rheological properties of synthetic oils

The study of the effect that the molecular weight and concentration of the polymer gelling additive PMMA (polymethylmethacrylate) introduced into the synthetic base oil PAO6 has on viscosity. The empirical dependence of the viscosity of the thickened oil on the content of additives has been established and the coefficients of the thickening efficiency of additive have been determined. An experimental study of the viscosity of synthetic oils on the shear rate has been carried out at different contents of viscosity modifier PMMA with different molecular weights in a base of PAO6. The ranges of velocities have been determined at which the oil exhibits properties of non-Newtonian fluid. It has been shown that, with an increase in the molecular weight of PMMA of additive at the same concentration in its base, the non-Newtonian behavior of oil begins to emerge at lower shear rates. It has been found that the use of an acoustic arsenal of the operational control of the viscosity of lubricating oils based both on the piezoelectric and the magnetoelastic interaction is promising for the operational control of the viscosity of lubricating oils.

Experimental Investigation of the Frictional Behaviors at Particle-Surface Interfaces in CMP Application Using an Atomic Force Microscope

In order to obtain a fundamental understanding of the tribological characteristics at chemical-mechanical polishing (CMP) process for wafer planarization, an experimental investigation of the frictional behavior between nano/microscale tips and various surfaces were performed using atomic force microscope (AFM) cantilevers with different stiffnesses and tips. In this paper, frictional behaviors according to load/pressure and materials were obtained by using various semiconductor material surfaces. Contact stiffnesses were observed in various tip-surface contact situations. Based on the experimental results, the relationship between the frictional behaviors observed, contact stiffness, and particle-surface material was carefully investigated.

Fluorescent express-method for monitoring of oil condition in tribosystems

Current interest in evaluating the oil condition in tribosystems is discussed. Fluorescent express-methods for oil condition monitoring are analyzed and their main advantages and disadvantages are noted. The basic concept of the fluorescent method developed for evaluating oil oxidation rate by recording the shift of fluorescence spectrum to the long-wave region is described. The realization of the method is exemplified and the results of the analysis of fresh and worked hydraulic oils with the developed fluorescent sensor are given. The sensor can be used as both built in the oil line and a portable device under manufacture and laboratory conditions.

Friction Characteristics of Self-Assembled Monolayers Coated on Si-Wafer by Chemical Vapor Deposition at Nano/Micro-Scale

Friction characteristics of self-assembled monolayers (SAMs) coated on Si-wafer by chemical vapor deposition technique was studied at nano-scale using AFM, and at micro-scale using micro-tribo tester. Three self-assembled monolayers, such as diphenyldichlorosilane, dimethyldichlorosilane and perfluorodecanoicacid, were tested in this work. Results showed that SAMs exhibited superior frictional property than Si-wafer. Friction in the case of Si-wafer was significantly affected by its inherent adhesion, and in the case of SAMs by their physical/chemical properties. At micro-scale, the effect of ball size on coefficient of friction of the test materials was also investigated.Copyright