Ivan Samardžić

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.

IMPACT OF THE HARD FACING TECHNOLOGY AND THE FILLER METAL ON TRIBOLOGICAL CHARACTERISTICS OF THE HARD FACED FORGING DIES

Subject review The forging dies are parts, which are operating at elevated temperatures, while simultaneously subjected to variable loads that can be compressive even impact and shear. Impact of the hard facing technology is very strong since varying of the hard facing parameters directly affects the output characteristics of the hard faced layers. The criterion for estimating that impact was based on results of performed tribological investigations. The tribological parameters that were monitored were the friction coefficient, the wear scar/trace width and the wear area of the hard faced layers, with the two different types of lubricants. Hard facing technology implied selection of the welding process, filler metals, preheating temperatures and other parameters of the hard facing process. The influence of the proposed hard facing technology was determined by monitoring hardness, microstructure and wear resistance of the executed joints after the hard facing and after tempering. The objective of this work was to establish the correlation between the selected hard facing technology, filler metals and applied heat treatment on mechanical and tribological characteristics of the executed hard faced layers.

Determination of clad plates residual stresses by x-ray diffraction method

The paper elaborates the influence that clad procedure has on the level and nature of residual stresses in clad plates. There are three clad procedures applied, as follows: hot rolling, submerged arc welding (SAW) with strip electrode in two layers and explosion welding. Theoretical basics on residual stresses measured by x-ray diffraction are reviewed in the paper, with special emphasis put on problems of underclad cracking tendency. In all applied cladding procedures, usage of heat treatment by anealing resulted in the decrease of residual stresses values. However, transformation of commpresed stresses into tensile stresses in some cases was very unfavourable, if referring to the tendency of plating corrosion resistant steel to stress corrosion and to underclad cracking.

Calculation of Reaction Forces in the Boiler Supports Using the Method of Equivalent Stiffness of Membrane Wall

The values of reaction forces in the boiler supports are the basis for the dimensioning of bearing steel structure of steam boiler. In this paper, the application of the method of equivalent stiffness of membrane wall is proposed for the calculation of reaction forces. The method of equalizing displacement, as the method of homogenization of membrane wall stiffness, was applied. On the example of “Milano” boiler, using the finite element method, the calculation of reactions in the supports for the real geometry discretized by the shell finite element was made. The second calculation was performed with the assumption of ideal stiffness of membrane walls and the third using the method of equivalent stiffness of membrane wall. In the third case, the membrane walls are approximated by the equivalent orthotropic plate. The approximation of membrane wall stiffness is achieved using the elasticity matrix of equivalent orthotropic plate at the level of finite element. The obtained results were compared, and the advantages of using the method of equivalent stiffness of membrane wall for the calculation of reactions in the boiler supports were emphasized.

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.

Application of semantic technology for calculation of welding time in the development of new products

Determining the time of execution is very important in the early stages of each project (e.g. making offers, design phase etc.), especially in the stage of planning. This paper presents our approach to estimating the welding time for the purposes of planning the manufacturing processes. The approach is based on the knowledge of welding experts from the Nieros metal d.o.o. company and standards of welding (international and internal). An expert system was developed based on semantic web technologies for calculating the welding time in the product design phase and it is strongly integrated with the main ERP system of the Nieros metal d.o.o. company. Test results are presented at the end of this article.

Application of expert systems for selection of installation pipes

The enterprises want to minimise the overall production costs, to maintain the quality and to increase the competitiveness on the market. It is possible to increase the number of customers, efficiency and effectiveness through the product quality. Therefore, every enterprise needs to have a good organisational structure, good experts and the knowledge how to do qualitative work. The paper shows the application of expert system to the problem of selection of installation pipes according to the given attributes. The input attributes are: mechanical load, material, colour, flame resistance, length, packaging, temperature range and outer diameter. The output parameter is the type of installation pipe. The expert system can give a second opinion, explicitly and in detail. They have the intelligent database and the possibility to adopt new knowledge, but also have a disadvantage that they use only the stored data to create solutions. Therefore, it is necessary to change the data according to a situation in the given environment. Despite the disadvantages of expert systems, their application is becoming increasingly important for the progress of enterprises.

Influence of fatigue impact loading on radial carrier and rapping device fillet weld strength

The device used to shake off the ash of the steam boiler harp consists of a drive shaft which has radial carriers welded on. During the operation of the waste incinerator steam boiler in Riverside, a fracture of the radial carrier and drive shaft weld occurred. Such a welded T-joint is made as a double fillet weld. It is loaded with the impact loading which causes the fatigue of material because of its repetition. The analytical calculation, with which the load-bearing capacity of the welded joint is determined, is suggested in this paper. The suggested analytical calculation of the mean impact force is based on the law of momentum conservation during the collision of rapping device and elastically deformable heat exchanger harp. The mean impact force is applied for the weld strength calculation. The results showed that the use of double fillet weld loaded with the fatigue impact loading was a bad choice. The suggested analytical calculation model is applicable for the rapping device design.

Analytical heat conduction models at arc fusion welding

It is of high importance to determine the distribution of thermal fields in arc fusion welding processes due to their influence on mechanical properties and quality of welded joints. This paper presents analytical models for 2D and 3D heat conduction based on solutions of the Fourier’s heat conduction differential equation. Furthermore, authors provide simplified equations for the calculation of cooling time and cooling rate for 2D and 3D heat conduction models.

The mechanics behind formation of secondary ledeburite during tool steel welding

In this article we describe the microstructural changes in the heat affected zone (HAZ) of the tool steel W. Nr. 1.2379, which was surfaced or welded by the submerged arc welding technique (SAW) with different welding parameters. Microstructure of the welds and of the surfacing welds was analysed by optical and scanning electron microscope. In this research, we particularly studied microstructural changes in the area of primary chromium carbides in the HAZ and their effect on the weld crystalization. We came to the conclusion that the temperature in the HAZ is high enough during the welding process that it caused primary carbides to dissolve and concentration of the carbide-forming elements and carbon increased in the surrounding austenite matrix area to eutectic composition, which remelts and solidified as secondary eutectic (ledeburite).