The friction factor dependence on the load and revolutions in sliding bearings without relubrication

Ovaj članak se bavi eksperimentalnim istraživanjem faktora trenja kod kliznih ležaja bez ponovnog podmazivanja. Istraživanje uključuje određivanje iznosa faktora trenja i usporedbu ovisno o opterećenju i broju okretaja mjerenih na kliznom paru bez ponovnog podmazivanja koji se sastoji od kliznih ležaja i vratila. Rezultat ovog pokusa je pokazatelj izmjerenih vrijednosti kliznog para u radnim uvjetima. Sve slike mjerenja i uvjeta opterećenja za svaki ležaj predstavljene su pomoću dijagrama.This article is focused on experimental research of the friction factor in sliding bearings without relubrication. The research includes study of friction factor values and their comparison depending on load and revolutions measured on sliding pairs, consisting of a sliding bearing and a shaft, without relubrication. The result of this experiment is an evidence of values measured reflecting the sliding pair actions under operation conditions. All the represented measured results and load conditions of each bearing are presented via graphs

The Shapes of Teeth of Circular Saw Blade and Their Influence on its Critical Rotational Speed

The main problems during cutting with circular saw blade are inaccurate cut, low quality of surface, high level of noise. These adverse effects are related to oscillation of circular saw blade. This oscillation cause adverse effects not only on workpiece but also on tool. In some case the circular saw blade reaches the value of critical rotational speed which leads to its instability and cause the oscillation of blade which may leads to destruction of tool. So the reduction of the amplitude of oscillation is essential for removing the adverse effects. This paper deals about influence of shapes of teeth as a type of modification that has positive effect oncritical rotational speed of circular saw blade. The parameters of studied models of circular saw blade were 42 number of teeth and the height of teeth with slice from sintered carbide was 14 mm. The variable parameter was the ratio between surface of teeth and surface of teeth gap. In this study was used computer software Creo Parametric 1.0 for obtaining natural frequencies of studied models. This software uses in analysis finite element method (FEM). There were done some steps to idealize the models. For calculating static and dynamics natural frequencies of modelswere used modal analysis. The critical rotational speed was calculated from obtained results by Creo Parametric 1.0 and compared on 5 models of tool

Accuracy in the geometrical characteristics reduction method of step shaft at deflection computing

Ovaj rad se bavi računalnom metodom određivanja progiba stupnjevane osovine koristeći metodu redukcije promjera.Ova metoda je proučavana analitički na odabranom obliku vratila u različitim varijantama promjera i duljine pojedinih raspona, gdje su vrijednosti progiba uspoređivane s izračunatim vrijednostima bez tog smanjenja. Te vrijednosti su odabrane kao točne i verificirane su numerički proračunom u PTC Creo softveru za simulaciju. Relativni postotci pogreške su interpretirani grafički, a u ovom radu su istraženi i ograničavajući uvjeti za njihovo korištenje. Cilj rada je ukazati na ograničavajuće uvjete korištenja ove metode, koja se ne može uvijek susresti u praksi. Isto tako u radu se ukazuje na moguće propuste koji se mogu učiniti u ovom postupku, i to je prikazano na pogrešnoj dimenziji osovine koja utječe na pouzdanost i sigurnost rada.The paper deals with the computing method of step shaft deflection in an intended place by using the diameter reduction method. This method is analytically studied on the selected shaft shape at different variants of diameters and individual span lengths, where values of deflection are compared with computed values without using this reduction. These values were selected as exact, which was verified by numerical computing in PTC Creo Simulate software. The relative percentage errors are graphically interpreted, and the contribution also deals with the creation of limiting conditions for their use. The aim is to point at limiting conditions of using this method, which may not be always met in practice. It also points to possible failures of this method, which is shown in an incorrect dimension of the shaft, influencing the reliability and safety of operation