Antun Stoić

DEFINING THE CRITERIA TO SELECT THE WAVELET TYPE FOR THE ASSESSMENT OF SURFACE QUALITY

The paper deals with one of the most important problems in the wavelet analysis – the methodology for mother wavelet selection. In this study, the surface texture of machine parts was assessed applying a wavelet transform. The calculations involved in roughness profile evaluation were based on three selection criteria: an autocorrelation test, a cross-correlation function and an entropy-based test. All the calculations and diagrams were produced using the Wavelet toolbox of the MATLAB package.

EFFECT OF ANTI-WEAR ADDITIVE ON CUTTING TOOL AND SURFACE LAYER OF WORKPIECE STATE UNDER MQCL CONDITIONS

The work presents the results of investigation of the influence of anti-wear additive Crodafos EHA-LQ-(MH) added to the emulsion mist on the condition of machined surface of 1.4310 stainless steel after turning. The investigation included the comparison of the following cutting conditions: dry machining, cooling by the MQCL method and cooling by the MQCL method with Crodafos EHA-LQ-(MH). In the paper, the influence of the Anti-Wear (AW) additive on the roughness parameter Ra of the machined surface for various cutting speeds, vc, and mass flow of the emulsion E has been shown. It was found that the MQCL+AW method decreases the Ra parameter values by 14 % to 35 % in comparison with dry cutting and by 17 % in comparison with MQCL method.The machined material and the rake face of the cutting wedge have been subjected to micro X-ray spectroanalysis. Chemical analysis of the cutting wedge and the surface layer of the machined material has been performed. The results show that water dropletts in MQCL method are very good transport facility for active compounds of AW additive that consequently form the dry-film lubricant on the machined surface.

Measurement of thermal emission during cutting of materials using abrasive water jet

This article deals with measurement of the thermal gradient on material during abrasive water jet cutting. The temperature was measured by thermo camera before the technological process started, during the AWJ cutting process technology, and just after the cutting process. We performed measurements on several types of materials. We calculated the approximate amount of energy during the AWJ cutting process technology that changes into thermo energy, which is the current water pressure drained in a catcher tank.

CUTTING DISTURBANCES INFLUENCED BY VARIATIONS IN CONTACT SURFACE GEOMETRY

The significant cutting disturbances appearing in hard turning processes cause shifting of the process dynamics. Therefore, in this paper the turning process is evaluated by radial force variation analysis, as a function of depth of cut, tool nose radius and effective lead edge angle, through static and dynamic indicators. The tool/workpiece contact zone is, in the case of hard turning, mostly limited within the tool nose radius region. Therefore in this paper, geometry of the tool/workpiece contact line is analyzed. The depth of cut is calculated as a geometric difference of prior and instantaneous tool pass profiles. The calculated values of the depth of cut are time dependant, and can vary by 60%. Various process monitoring techniques have been used to identify and confirm these variations, as well as quantify the level of process stability. The results obtained confirm the assumption that effective lead edge angle and radial force are influenced by depth of cut, feed rate and tool nose radius. Additionally, it is shown that low values of depth of cut and geometry of prior pass-machined surface valleys shift the hard turning process to a dynamically more sensitive level as compared the case of soft machining.

Different Approach to the Aluminium Oxide Topography Characterisation

Different surface topographic techniques are being widely used for quantitative measurements of typical industrial aluminium oxide surfaces. In this research, specific surface of aluminium oxide layer on the offset printing plate has been investigated by using measuring methods which have previously not been used for characterisation of such surfaces. By using two contact instruments and non‐contact laser profilometer (LPM) 2D and 3D roughness parameters have been defined. SEM micrographs of the samples were made. Results have shown that aluminium oxide surfaces with the same average roughness value (Ra) and mean roughness depth (Rz) typically used in the printing plate surface characterisation, have dramatically different surface topographies. According to the type of instrument specific roughness parameters should be used for defining the printing plate surfaces. New surface roughness parameters were defined in order to insure detailed characterisation of the printing plates in graphic reproduction process.

Anaerobic digestion of specific biodegradable waste and final disposal

The present paper investigates the effectiveness of different levels of applied digested residue obtained after anaerobic digestion (AD) of meat-bone meal (MBM) on the morphologic and mineral characteristics of corn. The experiment was conducted in duration of two years and consisted of eight treatments: control (without any fertilizer) ; mineral fertilization only ; treatments with minimum, medium and maximum dosage of digested MBM ; combined fertilization of minimum, medium and maximum dosages of AD residue combined with mineral fertilizer. Combination of treatments with mineral fertilizer and different rate s of AD residue, plants had increased mass yield, they were larger and had more leaves. Contents of mineral substances were within average values, both in plant material and in kernel, and variations in values were conditioned by total mass and ion interactions. MBM after AD treatment is possible to apply as organic fertilizer. It has higher nutritive value and, as such, is suitable for treatment of agricultural plants, especially in crop production.

High-risk bio-waste processing by alkaline hydrolysis and isolation of amino acids

Slaughterhouse waste can be very dangerous and potential risk for animal and human health. Brains and spinal cords are deemed high-risk substances and can be infected with prions ; their treatment is therefore only possible in strictly controlled conditions. One of the methods which can achieve the necessary reduction in health risk is alkaline hydrolysis. Standard alkaline hydrolysis is at 150°C, 3-6 hours, and 4 bars. In this investigations focus was on different alkaline conditions: temperature (135oC, 150oC, 153oC), time (2, 3, 6 hours), and base (NaOH and KOH) due to fact that amino acids are sensitive to variations on temperature, pressure and base media. Analyzed amino acid composition of hydrolyzed material at different testing conditions show successful hydrolysis. Highest value of protein, which is generally relatively low, was achieved with NaOH at a temperature of 135oC and time of 2 hours, whereas in the reaction with KOH the highest obtained value was achieved at 150oC and 3 hours. A dry substance increasing with time, and the highest value was achieved at the temperature of 150oC and time 6 hours for both bases (NaOH, and KOH). Most of the amino acids went full racemization during the process ; especially in D-amino acids like aspartic acid, glutamic acid, tryptophan and isoleucine. Lysine shows higher resistance to alkaline medium than other amino acids. Isolation of certain amino acids, like: asparagine, glutamic acid, glycine, alanine, and leucine, is possible because they show higher concentrations in hydrolysates.

Evaluation of J Integral for Interacting Twin Collinear Through-Wall Cracks in a Plate under Tension

The interaction behavior of twin collinear through-wall cracks in tension loaded plate under elastic-plastic condition is investigated by the finite element method (FEM). The fracture parameter J integral for interacting cracks is calculated and compared to the J integral for a single crack the same size. In this way, the interaction factor of cracks under elastic-plastic condition is defined. This interaction factor is compared to the results of analytical solution of the interaction factor under linear elastic condition. The results show that interaction factor of cracks under elastic-plastic condition is higher than interaction factor of same cracks under linear elastic condition. Also the interaction effect of cracks under elastic-plastic condition is influenced not only by the crack configurations but also by the material properties, especially the strain hardening exponent n.

New Approach of Recycling of Abrasives for Water Jet Cutting

The recycling or reuse of material in production becomes as a saving task for sustainable and environmental competitive production. Sustainability means not only achieving cost efficient process but also eco efficient. The design of the abrasive recycling system is desirable because of the growing growth and development of the abrasive water jet cutting industry. The use of recycled abrasives greatly reduces production costs, and hence the price of products resulting from such processing and increases competitiveness. There is a large space for wide application of cutting technology with abrasive water jet, and thus the application of abrasive recycling. On the environmental side it is very important to have a controlled disposal of the abrasive used.

Machining of Spur Gears Using a Special Milling Cutter

Spur gears have a wide application in the machine-building industry. Machining process primarily selected for these gears is hobbing method with modular hobs, or with Fellows cutters. Other methods which can be applied are profiling using the pull broaches, while the finishing can be done by gear shaving or grinding by the Maag, Niles or Reishauer methods. Moreover, in small (or unit) production, they may be formed using discor finger-type modular cutters. The article presents a method for cutting spur gears using a disc-type mill with a variable cutting plate profile. The influence of the number of blades of the presented milling cutter on the accuracy of the worked tooth profile was investigated.