Browsing by Author "Gavrilova R."

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    Plasma-arc reactor for production possibility of powdered nano-size materials
    (2011-01-01) Hadzhiyski V.; Mihovsky M.; Gavrilova R.
    Nano-size materials of various chemical compositions find increasing application in life nowadays due to some of their unique properties. Plasma technologies are widely used in the production of a range of powdered nano-size materials (metals, alloys, oxides, nitrides, carbides, borides, carbonitrides, etc.), that have relatively high melting temperatures. Until recently, the so-called RF-plasma generated in induction plasma torches was most frequently applied [1-3]. The subject of this paper is the developments of a new type of plasma-arc reactor, operated with transferred arc system for production of disperse nano-size materials. The new characteristics of the PLASMALAB reactor are the method of feeding the charge, plasma arc control and anode design. The disperse charge is fed by a charge feeding system operating on gravity principle through a hollow cathode of an arc plasma torch situated along the axis of a water-cooled wall vertical tubular reactor. The powdered material is brought into the zone of a plasma space generated by the DC rotating transferred plasma arc. The arc is subjected to Auto-Electro-Magnetic Rotation (AEMR) by an inductor serially connected to the anode circuit. The anode is in the form of a water-cooled copper ring. It is mounted concentrically within the cylindrical reactor, with its lower part electrically insulated from it. The electric parameters of the arc in the reactor and the quantity of processed charge are maintained at a level permitting generation of a volumetric plasma discharge. This mode enables one to attain high mean mass temperature while the processed disperse material flows along the reactor axis through the plasma zone where the main physico-chemical processes take place. The product obtained leaves the reactor through the annular anode, from where it enters a cooling chamber for fixing the produced nano-structure. Experiments for AlN synthesis from aluminium power and nitrogen were carried out using the plasma reactor described here above.
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    Production of Barium Sulfate with Considerably Improved Whiteness Through Calcination of Barite Recovered from Waste Material
    (2025-01-01) Mitov I.; Stoilova A.; Gavrilova R.; Yordanov B.
    The study presents calcination of barite recovered from gangue stored in а tailings dam located in Bulgaria with the aim to product BaSO4with improved whiteness. The calcination was carried out in a rotary kiln at 1150oC under air. Samples from three batches of barite with different particle size, namely 40 µm, 20 µm and 6 µm, were processed and the colour and brightness value of the product was measured. The residence time of the material in the kiln, respectively in the heated zone, was also determined. The results show that the brightness of the barite recovered from the gangue could be improved by 4 - 20 units through calcination.
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    Prognostication of main parameters during casting under pressure and crystallization of metal alloys - An assessment of technological improvements and benefits
    (2017-01-01) Gavrilova R.
    Possibilities for mathematical modelling of heat transfer processes during crystallization of model metal alloys with different chemical composition, manufactured in a laboratory furnace injection moulding to 5.0 MPa, are discussed in this work. A method for experimental measurement of the temperature in the volume of the metal during crystallization and its dependence on the registered time to complete hardening of the metal is applied. The adequacy of the mathematical model is tested. The proposed approach allows for prognostication of the main features of the processes and assessment of technological improvements that directly increase the yield of the production with around 68 %.
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    STUDY OF STEELS FOR THE PURPOSE OF COMPARISON IN TERMS OF QUALITY INDICATORS AND ENERGY EFFECT OF THEIR PRODUCTION
    (2024-01-01) Gavrilova R.
    The main purpose of this work is to examine ingots of steel grades 35HGSL, GS-34CrMo4 and GS-42CrMo4 and to obtain data on the microstructure and mechanical properties in the cast state and after heat treatment. Based on the results, it is necessary to evaluate the effectiveness of the heat treatment used and possibly prove its justification, since this type of additional treatment is usually recommended to improve the quality of materials, but it is not mandatory, as in the present case. The economic costs of the manufacturer for conducting heat treatment can be a good solution only in the case of achieved better performance indicators of the materials, and the energy efficiency of the applied processes is essential. For all these reasons, as a result of researches will be created databases, which will give the opportunity to definite opinion on the problem.