International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The subject of this study is leaching process of nickel-bearing laterite ore from Ržanovo, R. Macedonia. The influence of sulfuric acid concentration (0.5, 1 and 3 M H2SO4) on the extracted Ni (%, wt.) was studied. The leaching process intensified by magnetic stirring at different temperatures (298, 323, 348 and 363 K) in the time interval of 120 min. was performed. The results were used for kinetic analysis of the leaching process. It was found that for 3 M H2SO4, the best fitting has shown the Jander and Ginstling-Braunshtein models, which point out that limiting step of the process is diffusion. Activation energy was calculated to be 42,67 kJ·mol–1 (Jander model) 40,28 kJ·mol–1 (Ginstling – Brousthein model), which confirm the diffusion controlled process.

In this this research work, the results of investigation corrosion condition of the steel pipe system for the heated water transportation and distribution after long years of exploitation are presented. The analysis was performed on the pipe segments after their removing i.e. cutting. Thirty segments were taken for inspection. The outer and inner surface of the pipes was inspected. Plan for inspection was prepared basing of the literature revue and personal experience. All specimens were visually inspected. For the investigations of pitting corrosion measuring of depth of pits was done. Performed investigations confirmed that general corrosion, uniform and no uniform is represented on the pipe from the outer side. From the inner side are presented different types of pitting: narrow, shallow, and elliptical and corrosion under layer. Performed investigation confirmed that the most dangerous for the piping systems is corrosion on the outer sides of the pipes which their perforation. Measurement of the pits deepness showed that pitting corrosion is not so danger because pits deepness is in the range between 0.18-1.24 mm which is negligible compared with the pipes wall thickness.

This practical research work is devoted to the adaptation of technology for ion plasma nitriding of mechanical parts (pins and gears). Formerly these parts were inductive hardened, and requirement of the purchaser was to replace inductive hardening technology with the chemical-heat treatment i.e. ion plasma nit riding.

Procedure for ion plasma nitriding of pin hammers and gears made of 4M2CrMo4 steel was described. Starting from the heat treatment of the parts, their cleaning and charging of the parts in the chamber. Description of the chamber and complete installation for nitride in is described. Experimental nitriding parameters are given too. Finally, accuracy of obtained results was checked using hardness measured of nitrided parts. Hardness values were in accordance with purchaser requirement.

In this research work, metallographic investigation of two parts which are implemented to railway wagons breaking system was performed. Both parts are produced from EN-GJS-500-7 nodular iron. One of delivered parts leading nut (part 1) was broken during the exploitation and the second part working nut (part 2) was new. Metallographic investigation based on standard EN 945-1was implemented in order to check the quality of the parts. The reason for breaking of part 1 one was analyzed too. After metallographic preparation, the polished specimens they were analyzed under optical microscope in order to determine form, size, density and distribution of graphite per unite area as first graphite nodules were analyzed after that microstructure of nodular iron. Figures from optical microscope were compared with reference images under the same magnification. After etching the specimens their microstructure was analyzed. It was concluded that quality of the part 2 is much better concerning the requirement of the EN 945 -1 standard.

Basic idea in this metallographic investigation is checking the effect of induction (surface) quenching of produced part, two-side lever made of 42CrMo4 steel. This part is build in railway wagon. According its production assignation it has to be surface hardened just in some positions. Formerly surface hardness of this part was realized by chemical-heat treatment i.e. case hardening of 16MnCr5 steel. But because of specific form of the part and increased britlness which appear in the thinnest parts of lever (between the rounded opening and the surface) and idea was obtained to change the case hardening with induction quenching. Efficiency of performed induction quenching i.e. hardness values and depth of quenched layer was controlled by optical microscopy and hardness measurement.