The paper presents a static lateral stability of a sub-compact tractor MT8-070 Mini in relation to a safe tractor operation. Axle weight distribution of the tractor was measured to calculate the vertical and longitudinal coordinates of a centre of gravity (COG). Experiments were aimed at the tractor equipped with no and four levels of rear wheel ballast weights (30.5, 61, 91.5 and 122 kg) at standard and extended overall width on tyres. A static overturning angle was calculated and experimentally measured when the tractor with right wheels touching the ground was in a state of unstable equilibrium. Comparing the experimental data with ISO 16231-2 (2015), the differences were 2.57%, 2.80%, 3.04%, 3.42% and 3.88% in the case of the standard overall width on tyres and 2.40%, 2.61%, 3.11%, 3.67% and 3.99% in the case of the extended overall width on tyres at 0, 30.5, 91.5 and 122 kg of the rear wheel ballast weight. Considering the vertical tyre deformation and the lateral shift of the tyre, the differences decreased to 0.95%, 1.11%, 1.29%, 1.85% and 1.42% (standard overall width on tyres) and 0.91%, 1.18%, 1.69%, 2.27% and 2.57% (extended overall width on tyres). The length of a rubber lug of a tyre contact patch did not change when the tractor was inclined at various ballast weights and did not affect the static overturning angle calculation according to ISO 16231-2 (2015). Results showed higher static overturning angle experimentally measured in comparison with calculated according to ISO 16231-2 (2015) due to the tyre deformation. Limiting the tractor operation on the basis of the static overturning angle calculated according to ISO 16231-2 (2015) avoids the tractor usage under dangerous operation conditions.
Hard turning is a turning operation performed on hard materials (hardness more than 45 HRC) in order to reach surface roughness close to that obtained in grinding. The development of this technology was accompanied by the development of new cutting materials such as cutting ceramics, cubic boron nitride and polycrystalline diamond. Especially cubic boron nitride has found its use in hard part turning operations because of its characteristics. However, new cutting materials result in new questions, which researchers are trying to solve. The major consideration for a user of this relatively new technology is the quality of parts produced and how the new cutting material will behave during machining. This paper aims to document and describe the process of wear on the cutting edge of a tool made from cubic boron nitride of a different grade and with a different geometry of the cutting edge, and its influence on surface roughness and quality. Wear was documented by a digital microscope with measurement option. Surface roughness was measured by a roughness meter. A notable observation from this research is that the flank wear of the cutting tool has a large impact on the quality of machined parts (especially surface finish and surface integrity) [1].
The paper deals with the hardness, chemical composition (using spectrometer) and microstructure (using light microscopy and scanning electron microscopy with EDX spot analysis) of the weld deposit based on Fe-Cr-Ni used for renovation of the functional surface of wheel for mineral wool spinning and with impacts of operational processes onto these characteristics. Deposit samples were analysed after service wear having an abrasive-erosive-thermal character. Analysis results were compared to a deposit sample with no wear. Based on results of weld deposit microstructure analysis, duplex ferrite-austenitic structure with ferrite matrix and austenite precipitation in various morphologies was found in the all cases. No substantial hardness changes caused by operational processes were found by comparing the analyses results. Increased melt temperature was the most important process parameter affecting the chemical and phase composition of the examined material, inducing the precipitation of new phase with a high Cr content.
The paper deals with the issue of occupational health and safety in a metalworking manufacturing organization. Hazard and threat have been defined when cutting metal materials with a band saw. We assessed the risk by an extended point method, where we determined the risk rate values. In most cases of sawmill work, we found a “moderate” or “negligible” risk. The highest, ‘serious’ risk we found in a possible electric shock. In this case, we have also taken the necessary actions. As a precaution, we have also proposed safety measures for other threats.
Abrahám R., Majdan R., Drlička R. (2015): Possibilities of improving the wheel tractor drive force transmission to soil. Res. Agr. Eng., 61 (Special Issue): S37-S42.The possibility of increasing maximal drawbar pull of tractor working on the soil was evaluated. The increase in drawbar pull occurred due to special wheels mounted on the drive axle. The special wheels were equipped with auto-extensible blades and designed at the Slovak University of Agriculture in Nitra. The main advantage of the special wheels is an automatic extension of steel blades to increase the drawbar pull during a wheel slip and automatic return to the base position to allow the transport of tractor by the route. The testing operation points at the decrease of wheel slip resulted in the increase of drawbar pull. The drawbar pull of tractor equipped with standard tyres and special wheels was compared in different soil moisture conditions. The higher increase in drawbar pull was measured during the tractor operation on the soil with higher moisture in comparison to the soil with lower moisture level.
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