Tribology in Industry

236-243

Authors: M. Madić, M. Radovanović, M. Manić, M. Trajanović

Selection of optimal cutting parameter settings for obtaining high cut quality in CO2 laser cutting process is of great importance. Among various analytical and experimental optimization methods, the application of Taguchi and response surface methodology is one of most commonly used for laser cutting process optimization. Although the concept of dual response surface methodology for process optimization has been used with success, till date, no experimental study has been reported in the field of laser cutting. In this paper an approach for optimization of CO2 laser cutting process using Taguchi and dual response surface methodology is presented. The goal was to determine the near optimal laser cutting parameter values in order to ensure robust condition for minimization of average surface roughness. To obtain experimental database for development of response surface models, Taguchi’s L25 orthogonal array was implemented for experimental plan. Three cutting parameters, the cutting speed (3, 4, 5, 6, 7 m/min), the laser power (0.7, 0.9, 1.1, 1.3, 1.5 kW), and the assist gas pressure (3, 4, 5, 6, 7 bar), were used in the experiment. To obtain near optimal cutting parameters settings, multi-stage Monte Carlo simulation procedure was performed on the developed response surface models.

259-268

Authors: S.J. Patel, G.M. Deheri, J.R. Patel

An attempt has been made to study and analyze the combined effect of roughness and slip velocity on the performance of a ferrofluid based rough porous hyperbolic slider bearing. Beavers and Joseph’s slip model has been used to evaluate the effect of slip velocity. The stochastic modeling of Christensen and Tonder has been employed to estimate the effect of transverse surface roughness. The associated Reynolds’ type equation is solved with suitable boundary conditions to obtain the pressure distribution leading to the calculation of load carrying capacity. Further, the expressions for friction and position of centre of pressure are obtained. It is observed that the bearing system gets adversely affected by the transverse surface roughness. The slip velocity further enhances this adverse effect. However, the magnetization saves the situation in the case of negatively skewed roughness when variance (-ve) occurs. But for an overall improved performance of the bearing the lower values of slip parameter may be favorable.

281-286

Authors: F. Zivic, M. Babić, S. Mitrović, D. Adamović, S. Pelemis

This paper deals with the friction coefficient behaviour during dry reciprocating sliding of UHMWPE in contact with alumina (Al2O3), within a range of velocities typical for hip implants. Five values of normal force (100 - 1000 mN) and three values of sliding speed (4 - 12 mm/s) have been observed. Real time diagrams of the friction coefficient as a function of the sliding cycles were recorded for each test. Dynamic friction coefficient curves exhibited rather uniform behavior for all test conditions. Somewhat larger values of friction coefficient could be observed during the running-in period in case of low loads (100 - 250 mN) and the lowest velocity (4 mm/s). In case of high loads and speeds, friction coefficient reached steady state values shortly after the beginning of the test.

293-299

Authors: S. Aleksandrović, M. Đorđević, M. Stefanović, V. Lazić, D. Adamović, D. Arsić

The sheet metal stripe ironing laboratory test has been developed to study tribological appearances and performance of lubricants in ironing process. Most common way for friction coefficient determination in the test is use of different equations which gives relation between active forces and reactive friction forces. In application of such equations some difficulties occurs because of improper friction coefficient values, especially at small intensities of tensile or drawing forces. In this paper for literature an approach were analyzed and after that defining of new equation was proposed. New equation was tested numerically and experimentally. Obtained results indicated that the suggested improvement gives much more acceptable values of friction coefficient. That fact is particularly significant in lubricant evaluation process.

308-315

Authors: S. Perić, B. Nedić, A. Grkić

Confirming the basic causes of failures and their elimination, control of certain phenomena, is defining proactive maintenance, as a new method that reduces maintenance costs and prolongs the life of assets. Determination of tribomehanical systems condition has very important role in development of friction theory and practice, wear and lubrication. There are used today different physical and chemical methods and tribology methods for tribomehanical system diagnosis. Experience in technical systems exploitation shoved that the most effective failure prognosis is according to parameters, particles created as result of wear, which are reliable indicators of wear. Analysis of oil samples which contain particles, created as results of wear, enable evaluation of system tribology condition in different phases of system exploitation. The paper presents the physical chemical tests in the analysis of oils that are used for the assessment of his condition. Furthermore the results of experimental research of physical chemical characteristics engines oil was sampled from engines of vehicles, which were in use. The research results are originating from the research of the paper authors.

326-338

Authors: S.C. Nwigbo, S.O. Mbam, C.U. Atuanya

This work has developed new brazing alloys for joining mild steel to mild steel (SAE1018) at a lower temperature. The alloys blends and error analysis were done by experimental design software (Design Expert 8.0.7.1). Design of experiments was done by Scheffe quadratic mixture method. The liquidus temperatures were predicted by calculation of phase diagrams of the alloying metals. The brazing alloys were produced by gravity technique and melted using silicon carbide graphite crucible. The quality of the brazing alloys was analyzed by optical microscopy (OM), atomic absorption spectroscopy (AAS) and fourier transform infrared spectroscopy (FT-IR). Brazed joints were produced by torch method with a commercial flux. Brazing temperatures (liquidus) were tracked by a digital infrared/laser pyrometer. Some mechanical properties studied were tensile strength and hardness. Finally, brazed joints produced from the developed brazing alloys were compared to that produced from muntz brass. Six (6) brazing alloys were successfully developed. Zinc and manganese were the main components, to which were added; 3 to 4 %wt silver and 11 to15 %wt modifying element. The microstructure showed a typical eutectic structure with zinc-rich phase distributed uniformly in the matrix with a combination of different sizes of dendrite, rounded blocks of compounds and hypoeutectic structures. AAS results indicated minimal out-gassing of zinc and FT-IR results indicated very low presence of atmospheric gas. The range of brazing temperature for best results was recorded from 690.90 to 735.10 0C. The joints produced from the developed brazing alloys had acceptable strengths with improved stress-strain behaviour compared to muntz brass.