Radica Prokic-Cvetkovic

Surface Welding as a Way of Railway Maintenance

Since its early days the development of railway systems has been an important driving force for technological progress. From the 1840s onward a dense railroad network was spread all over the world. Within a few decades railway became the predominant traffic system carrying a steadily increasing volume of goods and number of passengers. This rapid development was accompanied by substantial developments in many areas such as steel production, engine construction, civil engineering, communication, etc (Zerbst et al., 2005). The railway industry worldwide is introducing heavier axle loads, higher vehicle speeds, and larger traffic volumes for economic transportation of goods and passengers. Increasing demands for high-speed services and higher axle loads at the turn of the 21st century account for quite new challenges with respect of material and technology as well as safety issues. The main factors controlling rail degradation are wear and fatigue, which cause rails to become unfit for service due to unacceptable rail profiles, cracking, spalling and rail breaks. Degradation of rail is microstructure and macrostructure sensitive and there is a complicated interaction between wear mechanisms, wear rates, fatigue crack initiation and growth rates, which affect rail life (Eden et al.,2005; Kapoor et al.,2002). Defects such as squats and wheelburns occur even in the most modern and well maintained railway networks and, as a broad general rule, every network develops one such defect each year, every two kilometers. At least one European railway network suffers almost 4000 rail fractures every year. Although such fractures are rarely dangerous when actively managed, they entail a high replacement cost and can be disruptive to the network (Bhadeshia,2002). The replacement of such defects with a short rail section is expensive and not always desirable as it introduces two new discontinuities in the track in the form of two aluminothermic weld that destroy the advantages obtained with long hot-rolled rail.

Application of the High Strength Steel HARDOX 450 for Manufacturing of Assemblies in the Military Industry

The problems related to welding of the high strength steel, aimed for manufacturing of welded structures operating in the prominent wear conditions, is considered in this paper. The paper presents an analysis of possibilities and prescribing the technology for welding the high strength steel HARDOX 450. The methodology for estimate the weldability of this steel was established in the theoretical part of the paper, as well as calculations of the welding parameters, while the hardness was investigated in details and the macro and micro structures of the individual welded joint zones were estimated in the experimental part. Obtained experimental results could be usefully applied for selecting and establishing the optimal welding technology for structures made of this steel. The technology thus established and the GMAW welding regime can enable successful execution of the welded joints and reduce the possibility for appearance of flaws and cracks to a minimum.

Increase energy efficiency of thermal power plant Kostolac B by revitalization ventilation mills

ABSTRACT Ventilation mill for grinding coal is one of the main steam power plants in the system that makes a significant effect on the level of energy efficiency with its work. The aim of this paper is to increase the energy efficiency of thermo power plant Kostolac B by reducing the problem of wear in ventilation mill for coal grinding. The idea of this research is to investigate the optimum hardfacing technologies to increase wear resistance of impact plates in ventilation mill. Before applying hardfacing on impact plates in the exploitation conditions, it is necessary to model test hardfaced samples for determination of the optimal technology and filler material for revitalization. The relative weight loss of the impact plates after 1440 h period of exploitation in real conditions is very small, 5–8%. The application of this approach can reduce the number of possible repairs and extends the period between them, resulting in significant economic effects. Before and after revitalization of ventilation mill is conducted analyzing of failure during the working period. In this paper, we present time of repair of ventilation mills number 22, 23, 24 and 25, the number of repairs before and after revitalization and cost of repairs.

Methods for calculating the preheat temperature welding the high strength steels

With preheating of steel the cooling speed of a heat affected zone decreases, which prevents appearance of structure prone to cold cracks. On the other hand, too small cooling speed, in this area, results with growth the metal grains which, also, leads as to the higher prone to cracks. Common used method for calculation of preheating temperature for high strength steels ar Itto - Bessyo method, and method by standard SRPS EN 1011-2. This paper presents the methods for calculating the preheating temperature of micro aloyed steel P460 NL1. Analysis of the results obtained from both methods shows significant differences in the amounts calculated preheat temperature. It was concluded that both methods have limitations that must be taken into account in their application in practice.

Massive Open Online Courses (MOOC) and Its Possibilities as Instrument of Formal, Nonformal, Informal and Lifelong Learning

In this chapter, we present the definition, development, and providers of massive open online courses (MOOC). We also explain the advantages and disadvantages of MOOC. We also present the structure of participants of MOOC, and also the motivation of participants is analyzed. Some basic statistics of realization and success of participants are also displayed. In one part of this chapter, the authors present case study of MOOC implementation in formal education in Belgrade Polytechnic (BP) College. For informal learning, a MOOC for welding is presented. This MOOC is planned to be organized on faculty of mechanical engineering at Belgrade University. During MOOC, participants also expanded their knowledge base and in that way they created possibilities for rerun of MOOC on a higher level. In that way, a participant can attend the same course after a couple of years and then will upgrade his knowledge. This attribute makes MOOC an instrument for lifelong learning.