Tribology in Industry

165-182

Authors: L. Lentini, M. Moradi, F. Colombo

Friction and wear are tribological phenomena that have produced significant economic damage and environmental issues throughout our history. Different kinds of lubricants and coatings have been employed in the attempt of reducing friction losses. Because of their remarkable performance, gas lubricated systems are characterized by almost zero friction and wear. For this reason, they can be utilized in applications where rolling and fluid bearings cannot, e.g., metrology, medical equipment and tool machine. This paper reviews the evolution of gas lubrication through history. The topography of the subject is described from its origins to how it was shaped over the centuries, trying to preserve the logical cause and effect relationship of the events. For the sake of consistency, the review considers only the key past contributions which are strictly related to gas lubrication.

195-202

Authors: Ye. Ventsel, O. Orel, O. Shchukin, N. Saienko, A. Kravets'

The degree of dispersion of particles of pollution and their amount in the lubricating medium substantially affects the anti-wear properties of the latter. At the same time, if the particle size of the contaminants is 5 microns or less, the anti-wear properties of such a lubricant medium are improved and, consequently, the wear of the friction surfaces decreases. The equation for the wear rate is obtained taking into account the interaction of charged wear particles with friction surfaces. It is shown that on the basis of the obtained equation, the wear rate can be presented as a decreasing function of the coefficient of the lubricant anti-wear properties, which is the ratio of concentrations of finely dispersed to coarsely dispersed particles.

213-224

Authors: H.U. Jamali, A. Al-Hamood

One of the most problems that affects the performance of the journal bearing is the shaft misalignment. Misalignment may result due to installation error, shaft deformation, manufacturing error, bearing wear, etc. This paper presents a solution for the misaligned journal bearing problem under hydrodynamic regime. The Reynolds equation has been solved numerically for a finite length bearing based on the finite difference method. The solution demonstrates a new model for the representation of the 3D misalignment geometry and also a detailed procedure for the implementation of the boundary condition in the numerical solution is explained. Furthermore, the convergence of the solution to the required load is investigated. The results reveal a severe thinning in the levels of film thickness and significant rising of the maximum pressure value when the misalignment is taken into consideration.

239-246

Authors: S. Aribo, I. Adedapo , C. Nwogwugwu, O. Olaniran, A. Olaseinde, O. Ige, P.A. Olubambi

A slurry pot has been designed, fabricated and evaluated for erosion-corrosion investigations. A variable voltage controller was used to vary the input voltage into the one-horse-power motor that controls the slurry pot. The actual speed of the slurry pot shaft was also calibrated using a non-contact digital tachometer. Voltages of 100 and 200 V resulted in rotational speeds of 1100 and 2100 rpm, respectively employed for the subsequent erosion-corrosion tests. Erosion-corrosion of a dual-phase carbon steel was investigated with the aid of the slurry pot in aerated 3.5 wt.% NaCl environments. The sample was normalised at 850 oC and then cooled in air to room temperature. Prior to the test, the normalised samples were heated to 700, 725, 750, 775, 800 and 825 oC, respectively and quenched in oil. Erosion-corrosion rates of between 0.027 to 1.26 g/cm2.hr at 1100 rpm and 0.57 to 1.9 g/cm2.hr at 2100 rpm were recorded. It was also observed that as hardness increased there was reduction in weight loss of the heat treated alloy.

254-262

Authors: I.O. Oladele, N.I. Agbeboh, S.M. Omokafe, O.I. Ibrahim

Fiber reinforced polyester composites were developed by reinforcing polyester resin with Cow hair fibers obtained from the tail of Zebu breed cattle in Nigeria. Composites were fabricated using hand lay-up techniques in which the 10 mm lengths of the NaOH treated fibers were randomly dispersed in a polyester matrix using open molds and allowed to cure at ambient temperature before testing. The tensile, flexural, abrasion and water absorption properties of the cow hair fiber (CHF) reinforced polyester composites were evaluated. Different Fiber reinforced composites showed the greatest enhancement in mechanical (tensile, flexural), abrasion resistance and water absorption properties compared to the unreinforced polyester material. The different fiber fractions which showed the best blend of properties were noted and plausible justifications for such values in each measured property were deduced. Ultimate tensile strength (UTS), abrasion resistance and hydrophobicity were optimum at 4 wt% CHF content with a value of about 10 MPa (UTS) while Young’s Modulus and flexural modulus were 756 and 5179 MPa at 15 wt%, respectively. Flexural strength at peak was best with a value of 35 MPa at 20 wt% CHF content.

274-282

Authors: Y. Lyu, J. Wahlström, M. Tu, U. Olofsson

The friction, wear and particle emission from an AlSiC MMC brake disc/non-asbestos organic brake pad system is studied using a pin-on-disc tribometer. The results show that this unconventional AlSiC MMC brake disc system presents friction performance as good as a conventional cast iron brake disc system. During braking, brake pad materials are transferred to the brake disc surface to form a protective third body tribo-layer, resulting in a negative specific wear rate of the brake disc. A higher contact load is likely to make it easier to generate the tribo-layer. The tribo-layer also seems to depend on the disc surface grinding features and the contact temperature during braking. By reusing an AlSiC MMC disc where the tribo-layer is already formed, the airborne emission in terms of mass is about 50% lower and in terms of number about the same as the conventional brake contact pair under a similar braking condition. Further full-scale studies are suggested to determine the validity of the findings.

300-310

Authors: A.V. Gritsenko, E.A. Zadorozhnaya, V.D. Shepelev

Failures of friction bearings of the crank mechanism comprise from 5 to 25 % of engine failures. The analysis of the main reasons for failures shows that the dominant reasons are the following: excess of loading conditions; severe operating conditions; non-observance of the periodic maintenance of the lubrication system; violation of the procedure and conditions of maintenance (contamination, oil residues, etc.); use of poor-quality oils and filters, etc. It is possible to prevent the growth of failures of friction bearings by a continuous monitoring of their complex technical state. For that purpose, we have supposed that the technical state of the crankshaft main bearings of the crank mechanism can be determined by measuring the pressures in the central oil line and calculating their difference in the cycles with the maximum load and without it at different engine crankshaft rotation frequency. As a result of the experimental work, we developed a method for in-place diagnostics of the state of friction bearings of the internal combustion engine, as well as an instrument that provides loading conditions for the bearings of the crank mechanism. We obtained an experimental dependence for determining the wear degree of the crankshaft main journal by the difference in the minimum pressure amplitudes of two adjacent cycles during the operation of the diagnosed cylinder in various modes.

326-334

Authors: J. Bautista-Ruiz, J.C. Caicedo, W. Aperador

Studies of materials in biomedical applications have focused on the generation of new biomaterials and the development of surface modifications, mainly of metals. Amorphous silicon containing diamond like carbon DLC-Si coating deposited on titanium substrate with the purpose of studying its biofunctionality. The behavior against the phenomenon of tribocorrosion of coatings DLC-Si deposited on titanium was evaluated, through the plasma-assisted chemical vapor deposition technique. The nanoindentation technique was used to determine the coating mechanical properties. The DLC-Si coatings were structurally analyzed through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, the characteristic binding energy for the signal C1s was obtained from XPS. Via XRD results the amorphous structure of DLC-Si coating was determined. The triboelectrochemical results indicate that the coating shows an adequate wear and to corrosion protection when exposed to the synergic mechanism, thus demonstrating the protective coating effect.