On selected nitrided and CrN coated dies for Al hot extrusion main reasons for their decreased service times were revealed and explained. Main influential parameters in this study refer to contact pressure, die design, length of bearing surface, quality of nitrided layer, surface preparation prior coating and die maintenance. Relationships between service times and influential parameters are very complex was confirmed in this study. Results of laboratory wear tests which were carried out at various contact pressures and quality of nitrided samples were combined with results of wear analysis on industrial dies. Achieving of lower contact pressure on bearing surface by improved dies design can increase their service times was verified also by laboratory testing of wear using “block on cylinder” test configuration. Lower quality of nitrided layer in combination with short bearing surface and occurrence enough high contact pressure close to exit edge of bearing surface can considerably decrease die service time. Furthermore, appropriate shaping of die contours around inlet and outlet edges of bearing surface can decisive influence on die service time. Inappropriate bearing surface preparation and maintenance of dies lead to premature CrN coating removal that is not in accordance to its wear resistance.
B.04 Guest lecture
COBISS.SI-ID: 27320871The behavior of the high squeezing grounds at greater depths during the progress of the excavation and primary support installation in the underground construction requires the appropriate yielding elements adapted to shotcrete or similar support element lining during their load bearing capacity arising. The analysis should take into an account the possibilities that rock pressures exhaust from different ways to reduce the excavation profile of the tunnel. The construction of underground facilities in high squeezing grounds follows to the big radial displacements towards excavation space not only during the time of the construction but later on when the inner lining is installed. In addition to showing some of the methods of excavation and support of such ground circumstances are being given the results of the calculations effect of the support elements influence on preventing shotcrete damage in the time of curing stage. Numerical method is used to calculate the vertical shaft and access tunnels wall displacements. Particularly, the results of loads and displacement calculations of the designed support system are given, which were obtained by 3D geomechanical model.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 1060958A new mathematical expression for describing the soil-water characteristic curve (SWCC) over a range of water contents where fine-grained soils exhibit plastic properties was presented. The finding that the relationship between the soil suction and the water content can be expressed in terms of the specific surface area of soils was based on experimentally determined relationships between the water content and the soil’s specific surface area, as well as between the thickness of the adsorbed water layer on the external surfaces of clay minerals and the quantity of free-pore water.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 16996374The problem of reducing CO2 emissions in the atmosphere is indirectly related to the potential storage options in different environments in the earth’s crust. One of the promising possibilities for reducing emissions of carbon dioxide (CO2) into the atmosphere is the geological storage of CO2 in deep, unminable coal seams. Measurements of the CO2 adsorption of 10 lignite samples from the Velenje Coal Mine and different rocks and soils from surrounding areas were carried out using Langmuir isotherm principles. Adsorption measurements were taken using the gravimetric method, where exposed samples at a selected temperature to different CO2 pressures were done. Also, the measures of mass changes in the measuring and reference cells were the basis of calculations for the mass and volume of the adsorbed CO2. Measurements were taken at a temperature of 23˚C and at CO2 pressures varying from 18 to 38 bars. The results of laboratory investigations of the lignite from the Velenje Coal Mine have shown the capacity adsorption from 9 to 14 m3 CO2/ton (at measuring pressures up to 4 MPa) of coal in the given conditions, which cannot compare with other rocks and soils.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 1260383The presentation considers the approach of active soil pressure determination of confined deep excavations during excavation pit works, locally unprotected excavations constructing retaining structures, canalization tunnels and protecting deep excavations when outer stability of excavations constructing deep RC diaphragms is estimated. The presented procedure gives considering ψ=Φ realistic results what is verified with comparative analyses using FEM. Smaller dilatation coefficients should be used for practical use i.e. ψ=Φ/2 depending on properties of individual soils.
B.04 Guest lecture
COBISS.SI-ID: 16997142