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  • Author: Alan Vaško x
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Abstract

In recent years, the research of nodular cast iron has been focused on increasing fatigue resistence. In the paper, two types of alloyed nodular cast irons have been investigated – SiMo-nodular cast iron alloyed by 4% of silicon and 1% of molybdenum and SiCu-nodular cast iron alloyed by 4% of silicon and 1.5% of copper. SiMo-nodular cast iron is suitable for high-temperature applications, for example the exhaust manifolds of the combustion engines. SiCu-nodular cast iron is used in various components of tribotechnical units. These components are often loaded by fatigue. The mechanical and fatigue behaviour of both nodular cast iron types has been studied by means of tensile test, impact bending test, hardness test and fatigue tests. Fatigue tests were realised at low frequency cyclic push-pull loading up to 10 million cycles. The relationship between the amplitude of stress and number of cycles to failure was investigated and the fatigue strength was determined. Mechanical and fatigue properties of both nodular cast iron types are correlated with the microstructure of specimens.

Abstract

The paper is focused on determination of the accuracy and reliability of static and dynamic (portable) hardness testers. The paper deals with the measurement of hardness of calibration hardness plates by 4 different methods (Brinell, Vickers, Rockwell and Leeb) with using 5 different hardness testers (3 static and 2 portable). The hardness values measured by the different hardness testers were compared to the reference hardness listed in the calibration hardness plates and consequently, the accuracy of these measurements was evaluated. The aim of the work has been to determine the accuracy and reliability of portable hardness testers in comparison with static hardness testers.

Abstract

The proper organization of work is to set the workflow to the slightest effort of man and machine operation to obtain maximum results. The article presents the problem of the allocation of personnel that occurs in a real company. The mathematical model for this issue was formulated. An algorithm solving the problem of personnel allocation is presented. The proposed analysis is a starting point for determining the production capacity and load of each workstation, which is particularly important when using multi-station work and balancing the production line.

Abstract

Aluminium, titanium, and nickel base alloys are mostly and widely used for aircraft jet engine construction. A proper evaluation of its microstructure is important from working safety point of view. To receive a well prepared sample of microstructure, some important steps have to be undertaken. Except for proper grinding and polishing of a sample, structure developing is a significant step, too. In order to develop microstructure various chemical reagents were used to achieve the best results for microstructure evaluation. The chemical reagents were used according to the previous knowledge and some new ones were also tested. Aluminium AK4-1č, titanium VT – 8, and nickel VŽL – 14 and ŽS6 – U alloys were used as an experimental materials. Alloy AK4-1č is used for fan blade production with working temperatures up to 300°C. It is a forged piece of metal machined down into final shape by five-axe milling machine. Alloy VT – 8 is used for high pressure compressor rotor blade production with working temperatures up to 500°C. Blades are forged as well and finally grinded. Finally nickel base alloys VŽL – 14 and ŽS6 – U are used for turbine blade production with working temperatures up 950°C. Blades for turbine are casted into mould with reducible models.

Abstract

Nodular cast irons are used in a wide range of industrial applications, especially in the automotive industry. SiMo-type of nodular cast iron is suitable for high-temperature applications, for example the exhaust manifolds of the combustion engines; SiCu-type of nodular cast iron is used in various components of tribotechnical units. These automotive components often work in a corrosive environment. Therefore, the aim of this paper is to compare the corrosion resistance of two types of the nodular cast irons (SiMo-type and SiCu-type). Corrosion resistance was determined by the exposure immersion test at ambient temperature. Specimens of both types of nodular cast iron were immersed in 3.5 % NaCl solution (to simulate sea water) and gradually removed from the solution after 1, 2, 4 and 8 weeks. Subsequently, the weight loss (g) and the average corrosion rate (g m−2 day−1) were calculated. Experimental results show that nodular cast iron alloyed by Si and Mo has higher corrosion resistance than the nodular cast iron alloyed with Si and Cu. Moreover, the mechanical properties (evaluated by tensile test, impact bending test and hardness test) and fatigue properties of both types of nodular cast iron has been compared in the paper.

Abstract

The paper presents the results of low and high frequency fatigue tests carried out on nodular cast iron. The specimens of synthetic nodular cast irons from three different melts were studied in the high cycle fatigue region (from 105 to 108 cycles) using fatigue experimental equipments for low and high frequency cyclic loading. Low frequency fatigue tests were carried out at frequency f ≈ 120 Hz using the fatigue experimental machine Zwick/Roell Amsler 150HFP 5100; high frequency fatigue tests were carried out at frequency f ≈ 20 kHz using the ultrasonic fatigue testing device KAUP-ZU. Both fatigue tests were realised at sinusoidal cyclic push-pull loading (stress ratio R = −1) at ambient temperature (T = 20 ± 5 °C).

Abstract

The article analyzes of the load capacity of the rotation mechanism of the boom arm sub-assembly for a self-propelled crane. The uneven flexibility of systems supporting structures of the machine was taken into account in the identification of the load. The consideration are illustrated by the example slewing bearing from self-propelled crane. FEM method was used for calculations. The basic problems of construction of numerical model were discussed. Sample calculations of bearing carrying capacity has been done taking into account flexibility of bearings supporting structures, which also allowed to define the internal load distribution in the bearing. On example of the supporting structure of the mobile crane DST 5050 the internal load distribution in the crane bearing at different positions of the crane machine body were defined. During the rotation of the crane body priority angels were indicated. It has been shown that the deformations of the supporting frames are so large that they significantly change the distribution of forces transmitted by the individual bearing rollers.

Abstract

Colour Metallography is a set of light metallographic microscopy methodologies that utilize phase colour contrast as a source of new structure information compared to conventional techniques. In many cases, colour contrast can be induced where no identifiable phase contrast is obtained by conventional techniques. With the help of colour contrast, we gain new information on the structure of Al-Si alloys, especially intermetallic phases, in which the benefits of its use in casting quality control are of benefit.

Blue-yellow contrast is definitely more pronounced than dark grey or light grey contrast. There is no substantial reproducible colour reproduction, since it is irrelevant whether the two phases are distinguished by blue-yellow or green-ocher contrast. When using the colour contrast, the structural components differ not only according to their microscopic appearance, but also based on the knowledge of the chemical composition of alloys, interactions between structural components, knowledge of the possible influence of Al-alloys structure (e.g. refining, modifications, heat treatment).

Colour contrast in quality control of Al-Si alloys was applied to AlSiMg cast alloy (AlSi7Mg0.3; AlSi7MgTi; AlSi10MgMn; etc.)