Olegas Černašėjus

Investigation of Cathodic Cleaning Processes of Aluminum Alloy

On covering aluminum and its alloys with coatings resistant to high-temperature corrosion and attrition, abundant technological problems arise. The key problem is a removal of the film of aluminum oxide Аl2O3 from the aluminum substrate. This permanent, chemically continuous film of oxide reduces adhesion between the substrate and the coating. For improving cohesion of the coating with the substrate, an appropriate pre-treatment of aluminum is required. In the paper, cleaning of aluminum alloy AW 5754 by electric discharge is investigated. This method is considered one of most environmentally friendly methods of surface cleaning. The impact of the parameters of aluminum alloy cathodic cleaning on the surface cleaning width, its roughness and free energy of the surface were examined. In addition, the topography, microstructure and chemical composition of the surface of cleaned aluminum alloy were estimated.

Preparing Al-Mg Substrate for Thermal Spraying: Evaluation of Surface State After Different Pretreatments

The article deals with the pretreatment technique for preparing the surface of aluminum alloy EN AW 5754 before thermal spray. The surface after different pretreatments, including degreasing with acetone, chemical etching with acidic and alkali solutions, grit-blasting, cathodic cleaning, and some combinations of these techniques, has been studied. The investigation of pre-treated surfaces covered the topographical study (using scanning electron microscopy, atomic force microscopy, and 3D profilometry), the chemical analysis by x-ray photoelectron spectroscopy, the evaluation of surface wettability (sessile drop method), and the assessment of surface free energy. Compared with all the techniques used in present work, the cathodic cleaning and its combination with grit-blasting provide the most preferable chemistry of the surface. Due to the absence of hydroxides at the surface and, possible, due to the diffusion of magnesium to the surface of substrate, the surface wettability and the surface free energy have been significantly improved. No direct correlation between the surface topography and the surface wettability has been established.

Reuse of ultrafine mineral wool production waste in the manufacture of refractory concrete

The paper deals with the mineral wool production waste (cupola dust - CD), presents CD characterization and aims to reuse CD in production of refractory concrete with calcium aluminate cement. The study of CD covers its chemical, phase and thermal analyses along with the morphological study and determination of particles size distribution. Zeta-potential, electrical conductivity and pH values of CD suspension are presented in the paper as well. Commercial microsilica additive in refractory concrete has been replaced with cupola dust. Compositions of refractory concrete have been prepared by incorporating 1%, 2% and 3% of CD. The bulk density, ultrasonic wave velocity, cold crushing strength and thermal shock resistance of the created refractory concrete have been determined. Based on experimental results, it has been found that cupola dust may be used for the production of refractory concrete. The environmental impact related to the CD reuse in refractory concrete production has been evaluated as well.

Research of Properties of Sprayed Coatings on the Aluminium Alloys

In article the cathodic cleaning processes of aluminum alloy AW 5754 and cleaned substrate surface coating by plasma with Ni-Cr-Fe-Si powder were researched. Aluminium substrate roughness after cathodic treatment at different cathodic treatment parameters was established during the experiments. During the investigation a comparison of the calculated medium power 1.6 to 9 kW plasma torch voltage-current characteristics with the experimental results was made. The optimized parameters of aluminium cathode substrate cleaning process were selected; porosity and morphology of plasma sprayed nickel-based coating were determined.

Thermite welding of Cu–Nb microcomposite wires

Abstract Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

Investigation of the Laser Polishing Influence on the Parts Built by SLS

The use of laser systems in the industrial manufacture of complex geometry details is growing. This phenomenon takes place thanks to laser technologies, such as selective laser sintering (SLS), direct laser metal sintering (DLMS) and selective laser melting (SLM) that make possible, in addition to production of details with complex geometric shapes, also the fast, cheap and effective restoration of damaged elements of the details. However, despite the abundant advantages of the above-mentioned technologies, the details produced on the basis of these innovative methods have typical problems (large value of surface roughness, low wear resistance). In the paper, the influence of changes of the principal technological parameters of the laser polishing on the technological characteristics of the external surface of details built by SLS was studied. Changes of the laser’s technological parameters impact the amount of energy supplied onto the area under processing. Thus, the correct selection of the technological parameters of the laser beam positively affect the microstructure and topography of the top surface layer of the manufactured details, its chemical composition and physical properties as well as diffusive processes in the laser beam impact area.

The Investigation on Destruction of the Compressor in Residue Conversion Set

In the paper, the problems of reliability and safe exploitation of the piston compressor in a residue conversion set are discussed upon. After a long exploitation, an emergency shutdown of the above-mentioned compressor occurred. On the primary examination, a fracture of the cylinder and the hub of the compressor were found. The goal of the investigation: to identify the cause of destruction of the compressor of the naphtha residue conversion set.

The Analysis of Laser Modification of the Surface of SLS Specimens

In the Paper, an analysis of laser modification of the surface of specimens produced of powder steel 1.2083 by SLS (selective laser sintering) method is carried out. Three main structures being formed on laser modification of the sintered steels are presented: periodical, interim and degrading. The dependence of the changes of the technological parameters of the laser equipment on the geometrical parameters of the specimen under processing is provided.

The Research of Influence of Vibromechanical Treatment on Ni Coatings PT-19N-01 Adhesion

Thermal spray coating is very widely used in various fields. It is technologically simple, compact, inexpensive, universal and mobile mode, which ensures a high process efficiency and good surface quality. In this paper, the examination of the possibilities to improve nickel base coating properties made by thermal spraying with vibromechanical treatment into the coating process. Studies at 30, 60, 90, 120, 150 Hz frequencies of introducing vibrations, and three different vibration amplitudes (different signal strength), the steel S235JR specimens was coated by thermal spraying. The nickel base powder PT-19N-01 for thermal spraying was used. The analysis of experimental results shows that, irrespective of signal strength and frequency, adhesion is low. Maximum adhesion value was achieved when the working frequency of vibromechanical treatment was 120 Hz, and the signal strength of 10 V. The lowest adhesion value was achieved when vibromechanical treatment frequency was 30 Hz, and the signal strength of 5 V.