•New method for evaluation the absorption coefficient of the crystal melt.•An abrupt variation of emissivity profile across the crystallization front.•Local temperature maximum in the area of phase ...transition zone.•Spectral pyrometry application.
We present a new method for evaluation the absorption coefficient of the crystal melt around the phase transition zone for the spectral range of semitransparency. The emissivity distribution across the crystallization front of the sapphire crystal fiber was measured at the quasi-stationary laser heated pedestal growth (LHPG) process (Fejer et al., 1984; Feigelson, 1986) and the data for solid state, melt and phase transition zone (melt-solid interface) were obtained. The sapphire melt absorption coefficient was estimated to be 14 ± 2 cm−1 in the spectral range 1–1.4 μm around the melt point. It is consistent with data, obtained by different other methods. This method can be applied to determine the absorption coefficient for other materials.
Modeling is one of the most important parts of applied research, the processes for which carrying out full-scale experiments is either expensive or highly labor-intensive. The article deals with the ...problem of modeling the energy distribution at the stage of electron beam input during welding. The solution to this problem will allow not only to reduce the cost of testing the technological parameters of electron beam welding of products with new geometry or from new materials, but also to support the decision-making of the technologist when optimizing the manufacturing process of existing products. Based on the theory of thermal processes, mathematical models have been developed that consider the characteristics of the materials to be welded and the technological parameters of the electron-beam welding process. In the course of experimental studies, the energy distribution was simulated when the electron beam was introduced for structures made of two different materials with different geometries. The obtained models for calculating the temperature at the input section not only supplement the complex of existing mathematical models of the electron beam welding process, but also allow expanding their application for calculating and optimizing the welding process, taking into account the excess temperature at the electron beam input section. In the future, this will allow considering the temperature spread at the input stage and obtaining a more stable quality of the welded seam with fewer root defects.
The article presents the results of mathematical modeling of the thermal process when the AMG-6 alloy is heated to energy sources equivalent to an electron beam in electron beam welding. The analysis ...of the results was carried out using the functional proposed by the authors. We develop the algorithm for searching for the optimal technological regime of electron beam welding, which can be recommended for testing the EBW technology of new construction materials or improving the existing old technological processes and the results of calculations, is proposed. As an example, the results of modeling the parameters of the technological process for welding a plate with a thickness of 2.4 cm from the AMG-6 material are given, which were compared with experiments conducted in laboratory conditions.
In this paper, we researched the influence of the electron beam defocus on the quality of the weld. The carried-out research was based on the theory of the thermal field using mathematical models ...developed by the authors. As a criterion of optimality, the previously developed thermal functional was used. We obtained criteria that can be used to simulate processes in electron beam welding, and to obtain more accurate modes, which is necessary to bind to power equipment. The obtained results of the criteria can be used for electron beam welding of various materials and different thicknesses.
The article describes the development of the software system for selecting the main modes of the diffusion welding technological process, with the implementation of the antifriction coatings based on ...fluoroplastics. The description of the algorithms for determining the main technological regimes from the entered necessary values of the tensile strength and wear rate, working conditions, operating temperature range, and the required composition of the material is given. The choice of the main parameters values of the technological process is made according to the maximum value of the tensile strength and the calculated value of the wear rate. According to the developed algorithm, the current values of the main parameters of the technological process are calculated. In case of insufficient strength of the joint or exceeding the value of the wear rate, the technological parameters are adjusted within the established limits or the coating material is replaced. For the decision support system in the design of technological processes, information bases were developed on the existing modes of polymeric materials diffusion welding to substrates of various types, and a database of tribotechnical information. The information database is implemented in a three-purpose software shell: 1) for entering and searching information in the database by fields, 2) for the work of an expert technologist, for linking information fields on topics, technologies, materials, 3) for work in the information mode, and in the mode of issuing an information array for process control. The constructed models and databases made it possible to create an algorithm for automating the diffusion welding process with the definition of the main modes. An algorithm for automating the selection of the diffusion welding main modes has also been developed. For the implementation of the "query generation" unit of the enlarged search algorithm, a production model of knowledge representation was used. As a result of the algorithm, an array of information is transmitted to the following modules of the algorithm. Databases were filled and logical connections of knowledge representation were established.
The article presents an automated installation for pipelines brazing in protective environments using the induction heating method. The types of pipe connections are considered, and the use of boxes ...to ensure the formation of a protective environment in the process of induction soldering is proposed. A diagram of a projected automated installation for induction brazing of pipelines in protective media, as well as its main technical characteristics are given. Using the proposed installation, soldering of welding of prototypes was carried out, the results of which are presented in the article.
The article considers the problem of mathematical modeling of the electron beam welding process at the stages of input and output of an electron beam. A conceptual model is proposed, developed using ...the mathematical apparatus of the thermal process theory. The models allow the calculation of the individual stages of the process that affect the formation of a welded joint in the vicinity of the "zero point". The proposed models will be used in the future and will be subjected to verification processes by comparison with the results of field experiments.
The article presents the results of a study of the current radiation situation at the uranium legacy site located in the territory of the Bambakai Valley (Transbaikal Territory), formed in the period ...from 1973 to 1989 due to the discharge of mine water. During the radiation survey, the method of pedestrian gamma survey was used to measure the ambient dose equivalent rate. Soil sampling was carried out to study the radionuclide specific activities in the soil. The activity of gamma-emitting radionuclides in the samples was measured with a stationary gamma spectrometer. The activities of
210
Po and
210
Pb were measured after their radiochemical extraction from samples. It was found that the values of ambient dose equivalent rate in the territory of the valley varied over the wide range from 0.1 to 1.4 µSv/h in the areas under manmade contamination. The estimated average value of the gamma background for this place is 0.14±0.02 µSv/h. The specific activities of
238
U,
226
Ra,
235
U,
210
Pb and
210
Po in the surface 10-cm soil layer at the site are from 10-40 times higher than the background values. The most part of radionuclides in the soil is in the acid-soluble form. Effective doses of the workers involved in hay harvesting in the area of the fallow land do not exceed 1.5 µSv/year. Doses of terrestrial environmental media (grass, earthworms) are 100 and more times lower than the safe level of exposure to biota.
The paper presents the results of mathematical modelling of temperature fields when the AMG-6 alloy is heated with energy sources equivalent to an electron beam in electron-beam welding. The ...evaluation of the results was performed using the criterion of optimality proposed by the authors. Used as a functional for calculations was the normalized standard deviation of the temperature from heating by a complex heat source consisting of mobile instantaneous point and linear energy sources. Proposed in this work are both an algorithm for finding solutions using an optimality criterion and the results of calculations for plates with thicknesses of 0.12cm and 1.2cm from the AMG-6 material, which were compared with experiments carried out under laboratory conditions.
Temperature distribution along a single crystal fiber molten zone in the laser heated pedestal growth (LHPG) process of pure sapphire (Al2O3) and yttrium–aluminum garnet (Y3Al5O12) fiber was measured ...for the first time. The temperature was determined from thermal radiation spectra measurements in the visible spectral range. Our measurements indicate the existence of local temperature minimum in the region of source rod melting.
•Experimental measurements of the temperature in molten zone.•Spectral pyrometry application.•Local temperature minimum in the area of source rod melting.•Wavy shape of temperature profile along the molten zone.
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