Tribology in Industry

9-16

Authors: D. Stamenković, M. Nikolić, M. Milošević, M. Banić, A. Miltenović, M. Mijajlović

In most of the cases, the friction is considered as a negative side-effect concerning energy loss following every process of the power transmission. However, the friction has significant positive side effects, because it is an indispensable prerequisite for the movement of people, machines, transportation means and others. Efficiency of these movements mostly depends on the friction between rubber and different materials such as metals, concrete, earth, wood, plastic, etc. Certain standards relating to measurement and determination of the friction characteristics of rubber were established. However considering that tribology of the rubber is very complex problem, numerous studies around the world are conducted. This paper gives an overview of some of the existing standards and conducted researches in this area. The paper also provides an overview of theoretical and experimental studies of friction the rubber and the other materials, which are done at Faculty of Mechanical Engineering in Niš.

22-32

Authors: K. Sathyan, H.Y. Hsu, S.H. Lee, K. Gopinath

Momentum/reaction wheels are used in a spacecraft for the attitude control. They are used for the real time control of spacecraft attitude towards the desired direction as required by the mission. These are one of the few systems of a spacecraft which need to work continuously from the beginning to end of the mission. Thus the life of a space mission depends largely on the performance of the attitude control wheels. The common mode of failure in momentum/reaction wheel is mechanical and mostly related to the bearing and lubrication. This paper presents the design and development of a bearing cartridge assembly including the lubrication system for long-term performance of spacecraft attitude control wheels. The results of both theoretical and experimental analysis are presented. The experimental study of the assembly shows that it can perform continuously for a period of 30 years with reduced frictional losses.

40-48

Authors: B.M. Viswanatha, M.P. Kumar, S. Basavarajappa, T.S. Kiran

The present investigation shows the wear behaviour of as-cast and heat treated, A356 aluminium alloy reinforced with SiC and Graphite particles subjected to different ageing durations. The liquid metallurgy technique was used to fabricate the composites. The reinforcement content was varied from 0 to 9 % by weight in steps of 3 % of SiCp and fixed quantity of 3 % by weight of graphite particles. The castings were machined to ASTM standard and T6 heat treatment was carried out at 540 0C ± 5 for 12 hrs and quenched at 60 0C in water. All the specimens were artificially aged at different durations of 3, 6, 9 and 12 hrs at a temperature of 155 0C ± 5. The wear tests were performed for alloy and composites by varying load, speed and sliding distance for both aged and as-cast conditions by using a pin on disc wear testing machine. The results reveal that the wear rate of composites was less than that of non-reinforced alloy. It was found that the wear resistances of A356-9 SiCp-3 Gr composites aged at 9 hrs showed better wear resistance compared with other samples. However in both aged and as-cast materials, the wear rate was increased with the increase in load, speed and sliding distance. The tested samples were examined and analyzed using Scanning Electron Microscope (SEM) and X-ray energy-dispersive spectrometry (EDX).

67-73

Authors: F. Živić, N. Grujović, G. Manivasagam, C. Richard, J. Landoulsi, V. Petrović

The potential of magnesium alloys as bioabsorbable / biodegradable implants for biomedical applications has been extensively studied as emerging direction. This paper gives a review of current topics in this field. Research activities related to biomedical magnesium alloys have been pursued in two main directions, orthopedic and cardiovascular implants, by investigating different aspects of alloying system design, novel structures, degradation rate control, and surface modification methods. Magnesium alloys are currently considered for applications as load-bearing implant devices such as plates, screws and pins for repairing bone fracture. Highly important direction of research is degradable coronary stents. Degradable vessel stents promote stable vessel regeneration, unlike permanent stents. Different combinations of alloying elements have been investigated in order to decrease corrosion rate.Tribological issues are also important for understanding of different phenomenon related to prolongation of Mg alloys corrosion degradation time/rate, such as tribocorrosion, corrosion fatigue, and fatigue crack growth behavior.

79-89

Authors: R.M. Castro, L.C.C. Cavaler, F.M. Marques, V.M. Bristot, A.S. Rocha

Due to the necessity of obtaining a surface that is resistant to wear and oxidation, hydraulic cylinders are typically coated with hard chrome through the process of electroplating process. However, this type of coating shows an increase of the area to support sealing elements, which interferes directly in the lubrication of the rod, causing damage to the seal components and bringing oil leakage. Another disadvantage in using the electroplated hard chromium process is the presence of high level hexavalent chromium Cr+6 which is not only carcinogenic, but also extremely contaminating to the environment. Currently, the alternative process of high-speed thermal spraying (HVOF - High Velocity Oxy-Fuel), uses composite materials (metal-ceramic) possessing low wear rates. Research has shown that some mechanical properties are changed positively with the thermal spray process in industrial applications. It is evident that a coating based on WC has upper characteristics as: wear resistance, low friction coefficient, with respect to hard chrome coatings. These characteristics were analyzed by optical microscopy, roughness measurements and wear test.

97-106

Authors: M.S. Priyan, P. Hariharan

The objective of this study was to develop a theoretical model and associated wear mode map to identify the regimes in which two body abrasion (grooving abrasion) and three body abrasion (rolling abrasion) dominate in the micro-abrasive wear test (also known as the ball cratering wear test). This test is generally considered to be a three body wear test. The wear mechanisms and wear rates were investigated using diamond abrasive over a range of loads (0.05, 0.1 and 0.2 N), and slurry concentrations (0.05, 0.1, and 0.2 volume fraction abrasive). It was found that during abrasion wear, a transition from grooving to rolling wear could be identified for a load with respect to time. The critical condition for the transition between two-body and three-body abrasion was determined from a continuum mechanics model for the penetration of the abrasive particles into the surfaces of the ball and the specimen, coupled with considerations of equilibrium. Two wear modes are usually observed in this type of test: ‘rolling abrasion’ results when the abrasive particles roll on the surface of the tested specimen, while ‘grooving abrasion’ is observed when the abrasive particles slide; the type of wear mode has a significant effect on the overall behaviour of a tribological system. Wear rates of metallic samples were determined and the worn surfaces were examined by optical microscopy, SEM and Talysurf profilometry.