The problem of generating is analyzed in science and practice in various ways by identifying it once as an element of the machine, and the second time as a part of production, that is, a final product. The nature of the materials of the machine elements, the loads in the contact zone, the relative velocities, the topography of the contact surfaces, and the temperature in the contact zone influence on the tribological characteristics of the elements, and hence on the characteristics of the tribo-mechanical systems. The surfaces of the tribo-mechanical elements of the machines through which mutual contact is realized are essentially thin layers of materials whose composition and properties differ significantly from the properties of the basic mass element material. There are a significant number of tribo-mechanical systems in the energy sector. Gear cutting is the most important operation in the production of gears. The quality of the gear cutting is one of the conditions for achieving the required quality of the work-piece. The gear is an element of a large number of tribo-mechanical systems. The geometrical parameters of the hob milling, the accuracy of the profiling and the accuracy of manufacture significantly affect the productivity and machining costs. In this paper, the topography and roughness parameters of lateral back surfaces of the model hob milling tools are analyzed before and after cylindrical gear cutting.

Abstract. The availability, adaptability, reliability and productivity of modern industrial complexes, maintenance costs, energy costs and industrial production costs depend also on the intensity of wear of the elements of tribo-mechanical systems. Gear cutting operations are usually a bottleneck of production, especially in higher types of production. Therefore, the necessity of researching the process of gear cutting by hob milling is obvious. In the paper a part of the results related to the possibility of direct measurement of the temperature in a very complex process of gear cutting of cylindrical gears by hob milling is given.

Abstract. The improvement of the gear cutting process by hob milling is also significant for the producers of gears as well as for the producers of hob milling tools. Due to the complexity of the process, the high values of the gears, and in particular the hob milling tool, the research of the bases for optimizing the process of gear cutting by hob milling requires significant financial resources and significant efforts of the researchers. In the modern production of gears there is a continuous demand for increasing the economy. In the gear cutting process improvements of the production equipment and materials for the cutting elements of the hob milling tools are necessary. In this paper an analysis of the tool life of coated hob milling tools for gear cutting of cylindrical gears is given. The experimental results have shown that the hob milling tools with inserted combs coated with TiAlN outperform the hob milling tools with inserted combs coated with TiN. They have higher resistance of 60.6 %.

Preliminary communicationThis paper presents a mathematical model for the prediction of the thermal behaviour of a cylindrical roller bearing for axle assembly of the wheel set of the towed railway vehicles. The mathematical model allows for the heat generated due to lubrication, radial and axial loads at different speeds of the train to be calculated. The method of calculating of the heat conducting and converting coefficients in the bearing is also shown. By using the general purpose software system based on the finite elements method, the thermal behaviour of the above mentioned cylindrical roller bearings was analysed. Temperature values of the bearings are determined by the finite elements method values depending on the speed of the train movement on a straight-line section and the curve (v = 20 km/h, v = 40 km/h, v = 60 km/h, v = 80 km/h and v = 100 km/h), the curve radius (R = 500 m), the ambient temperature of 20 °C and the cant height (h = 110 mm, h = 140 mm, h = 180 mm). Keywords: cylindrical roller bearing for towed railway vehicles; finite elements method; mathematical modelling Matematičko modeliranje toplinskog ponašanja valjnog ležaja s valjčićima za vučena željeznička vozilaPrethodno priopćemje U radu je prikazan matematički model za predviđanje toplinskog ponašanja valjnog ležaja s valjčićima za uležištenje vučenih željezničkih vozila. Matematički model omogućava izračunavanje generirane topline uslijed podmazivanja, radijalnog i aksijalnog opterećenja za različite brzine gibanja vlaka. U radu je također prikazan način izračunavanja koeficijenata provođenja i prevođenja topline u ležaju. Uporabom programskog sustava opće namjene na bazi metode konačnih elemenata analizirano je toplinsko ponašanje valjnog ležaja s valjčićima za vučena željeznička vozila. Metodom konačnih elemenata određene su vrijednosti temperature ležaja u ovisnosti o brzini gibanja vlaka (v = 20 km/h, v = 40 km/h, v = 60 km/h, v = 80 km/h i v = 100 km/h), polumjera zakrivljenosti zavoja (R = 500 m), ambijentalne temperature od 20 °C i visine nadvišenja pruge u krivini (h = 110 mm, h = 140 mm, h = 180 mm). Ključne riječi: vmatematičko modeliranje; metoda konačnih elemenata; aljni ležaj s valjčićima za vučena željeznička vozila

An austenitic filler material is traditionally used for welding armor steels, thus avoiding the negative effect of hydrogen content due to slow diffusion towards the sensitive fusion line. For heavy structural engineering such as armored military vehicles, which are frequently affected by impact and dynamic load, it is crucial to know the dynamic properties of the most sensitive area of welded joints, the weld metal zone. Due to a significant interest in quantifying material resistance to crack initiation and propagation, the fatigue crack growth rate was measured in the welded metal zone, while the resistance to crack growth in the weld metal was tested by the amount of austenite transformed into martensite. Accordingly, the threshold stress concentration factor was 10 MPa m1/2. XRD spectral analysis revealed a direct transformation of γ – austenite into α’ – martensite.