International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Self-propagating high-temperature synthesis (SHS), refers to a technology for the production of useful materials (mainly composite powders) that uses combustion processes. The solid combustion process results in the release of more heat which is needed to rebond the elements of the system and it is this extra amount of heat that is used to self-sustain the combustion process and its development. This process is known as self-propagating high temperature synthesis.
This paper presents the study of the magnetic properties of the products obtained by this method in comparison with other methods which use nickel-zinc ferrites. The latter are widely used in radio devices, antennas and transformer cores, as well as in high-frequency filters where the current loss is significant.

On the basis of separate fractions of granular foam glass and inorganic binders, various modifications of heat-insulating composite material have been developed. A promising opportunity for potential application of the material is the preparation of composite elements and profiles suitable for installation around doors and windows during the construction or reconstruction of buildings. In connection with the study of the possibilities for optimal distribution of the granules, various options for their arrangement have been analyzed and evaluated. The mathematical tools of stereometry and 3D computer modeling were used. Visualizations of the obtained structures are presented and their compactness is evaluated. Recommendations are made for the ratio between the sizes and quantities of the granules used in order to achieve maximum density.

The development refers to an innovative technology and technological scheme of a workshop for the production of beehives made of amorphous quartz ceramics. The conditions for obtaining stable suspensions from quartz glass are emphasized and investigated. The time for the treatment of the glass in the grinding device, the amount of water, the influence of the modifiers in stabilizing the suspension by adjusting the pH level, as well as the most suitable sedimentary composition of the glass particles are established. The factors determining the speed and degree of sintering of the ceramics are investigated and established. They include the density of the raw products, the dispersion of the quartz glass particles and its purity, as well as the environment in the furnace and the sintering mode.

A general overview of a number of thermal insulation materials and products made on the basis of inorganic binders (mainly Portland cement) is presented. The technological methods of production, the main operational indicators and the application in construction of various heat-insulating and structural-heat-insulating lightweight concretes are examined. The structure of various cellular concretes (foam concretes and aerated concretes), composite materials and lightweight aggregate concrete was analyzed. The role of the origin, technological processing, characteristics and composition of different types of light additive materials for the formation of the final operational properties of the products has been traced.

An innovative collapsible frame hive was developed, consisting of structural elements made of technical ceramics containing thermal insulation air chambers. Experimental prototypes were prepared using the slip casting method and based on modified recipe compositions, prepared casting molding masses, original gypsum matrices and optimal heat treatment mode. A comparison was performed between the main operational characteristics of the experimental samples and the traditional non-separable hives which have existed throughout history and made primarily of various plant materials and natural plastic raw materials (clays).

A financial project was presented for the construction of a technological line for the production of high-quality replicas of the socalled “yellow paving stones” and an additional assortment of products with different characteristics based on raw materials originating in Bulgaria. After many years of investigation in laboratory and semi-industrial conditions, polycomponent formulations and an original hightemperature technological regime for the preparation of functional and long-lasting silicate products have been developed. The planned technological approach is in accordance with the existing machine park and the qualification of the industrial production personnel, characteristic of the silicate industry. The main possibilities for the realization of the production are the full restoration of the street areas of the central historical part of Sofia and the construction of long-lasting and aesthetic pavements with a variety of functional purposes in different areas of the capital and other populated areas. The current applied development is oriented towards possible potential producers and investors and various specialists from the field of public infrastructure and cultural-historical heritage.

A financial project has been prepared for the construction of a plant equipped with a technological line for the production of foam glass products. It is planned to build a warehouse for raw materials, a sector for preparation of materials, various production workshops for the manufacturing of foamed granules and pieces, a continuous tape or block of foam glass, various composite materials (thermal insulation and color decorative panels, various small and large composite elements, etc.), repair section and two warehouses for finished products. Approximate calculations have been made for the necessary raw materials, technical equipment, electricity, personnel and other costs for the realization and operation of the plant.

In summary form, some trends in the production and application of foamed silicate materials obtained from recycled waste materials are presented. The existing possibilities for the use of different fractions of foam glass granules for the preparation of various products (lightweight concrete, colored decorative panels, etc.) are considered. Experimental samples are prepared in which the average value of the thermal conductivity coefficient =0.24±0.13 W/m. K was established. The main technological factors determining the operational characteristics of the material and the existing potential prospects for their optimization are analyzed.

A conceptual design of a technological line for the production on the one hand of a continuous flat strip and block and on the other hand granules and pieces of foam glass, including a ware house for raw materials, a workshop for preparation of materials, workshops for foamed granules and a continuous flat strip of foam glass, workshop for composite elements semi O, P and slabs, repair section and warehouse for finished products is presented The necessary equipment and materials, building the technological line and functioning of the plant as a whole, are presented.

Experimental ceramic samples were obtained in which the presence of CaMgSi2O6 (predominant phase), MgCr2O4, CaAl2Si2O8 and quartz was detected by X-ray diffraction analysis. During the microscopic examination of the prepared sections, two mineral phases were established: main – clinopyroxene and secondary – green spinel. The presence of prismatic-granular and skeletal structure was found. In the formed dominant diopside phase the presence of numerous inclusions of magnesium-chromium spinel with green color (sizes up to 0,05 mm) was observed evenly distributed in the sections determining the characteristic green color of the samples.

Compression was carried out of modified copper powder workpieces at a pre-determined value of the pressure. High temperature sintering of the workpieces in a neutral medium at a temperature of 1,000°C was performed. A high density metal-ceramic composite material was obtained. Its structure and physico-chemical parameters were determined. Lead-free prototypes were created, corresponding to the weight and dimensions of the reference standard lead passive elements for high energy impact.