The existing experience of noise and vibration specialists has shown that the problem of noise reduction is very relevant, especially for the mining industry. Traditional methods of dealing with industrial noise are not effective enough. In solving this issue, it is advisable to reduce the noise level at the source of its occurrence through the use of metal alloys with enhanced dissipative properties. The article presents the results of experimental studies of developing steels with increased damping properties for manufacturing perforator parts: bit bodies and drill rods. In this article, the sound pressure level of alloys dependence on the type of heat treatment has been studied, and the optimal content of alloying elements has been established to ensure the development of the ferrite-pearlite structure. This structure is characterized by an increased dislocation density and is the reason for reducing the noise of the drill rod and the body of the perforator bit by 10–12 dB A. In addition, the article establishes the pattern of noise intensity at different frequency intervals for standard and developed alloys.

This article reveals the nature, causes, and main stages of occurrence and development of endogenous fires in coal mines. It is emphasized that one of the key tasks of fire protection specialists is the most accurate determination of the stage of oxidation and self-heating of coal. A review of existing gas analysis methods for identifying the initial and subsequent stages of endogenous fire development is conducted. Particular attention is focused on the importance of obtaining prompt reliable information on the self-heating temperature of coal and the dynamics of its change in the early stages of the process. Since self-heating zones are usually inaccessible for direct instrumental control, the main source of information is the gas analysis of air samples. The authors present the results of research on the dependence of the indicator gas content on the coal self-heating temperature. Based on the Graham criterion, the stages of thermal development of the process are predicted. Correlation dependencies between temperature and integral parameters of indicator gas concentrations are developed, allowing for a sufficient degree of reliability in determining the stages of coal self-heating and spontaneous combustion. Based on the results of the work, methodological recommendations for the prevention and warning of endogenous fires in coal mines and opencasts are proposed. They are based on the most informative and accessible signs suitable for quantitative assessment. The implementation of these recommendations will improve the level of industrial safety and reduce the risks of fires and explosions during mining operations.

Purpose. To investigate the stress-strain state of the coal-rock mass surrounding a gob-side development roadway and to justify its support parameters under the mining conditions of the Karaganda Coal Basin. Methods. The study was based on geomechanical modeling of the coal-rock mass surrounding a roadway driven adjacent to the goaf of a previously extracted longwall panel and separated from it by a limited-width coal pillar. The simulations were performed in ANSYS using the finite element method in 2D. The computational model incorporated the goaf, protective coal pillar, stratified structure of the surrounding rocks, mining depth, physical and mechanical rock properties, loading conditions, and roadway support parameters. The stress-strain state and strength factor were additionally assessed in Rocscience RS2 for a ventilation roadway driven along the boundary of the goaf. Findings. The width and strength of the coal pillar were found to affect stress redistribution around the gob-side roadway significantly. A limited-width pillar shifted the peak maximum stress 5-10 m deeper into the intact coal mass and reduced its magnitude by approximately 1.6 times compared with the pillarless configuration. Stresses directly above the roadway decreased by a factor of 1.2-1.3. Increasing the pillar strength or its width to 20 m reduced the maximum stresses in the rock mass by almost twofold. The RS2 simulations showed that increasing the mining depth from 450 to 700 m increased the maximum principal stresses by a factor of 1.7-1.9 and the roadway contour displacements by a factor of 1.2-1.35. Originality. Relationships governing stress redistribution and the formation of reduced-stability zones around gob-side development roadways were established as functions of coal pillar parameters, mining depth, and roadway support conditions. Practical implications. The results provide a geomechanical basis for selecting support schemes for gob-side roadways located within zones of elevated rock pressure.

Purpose. Research aims to study the influence of alloying elements on the properties of steels contributing to the increased sound energy dissipation and reduced acoustic emission in order to develop alloys for the manufacture of mining equipment parts operating in impact mode (drill string and drill bit housing. Methods. Six alloys were developed during the research based on standard steels. Samples were melted in LPZ-1-67 high-frequency induction furnace at a melting temperature of 1700°C. All the samples were made in the form of 50×50×5 mm plates. KazNTU-2017 setup was used to study the impact noise level. The sound signal was calibrated using a ZG-10 generator. The results were corrected for atmospheric pressure using a PF-101 piston telephone. The temperature and humidity in the laboratory were maintained at a constant level. Acoustic measurements were made five times, with subsequent averaging of the results. Findings. The developed alloys No. 4 and No. 6 have increased dissipative characteristics, which allows them to be classified as “quiet” steels. This is due to the increased graphite and ferrite content in their structure, which promotes effective absorption of sound energy. Alloy No. 3 has medium dissipative properties due to the presence of residual cementite in the structure. Originality. Alloys No. 3, 4 and 6 have been found to have a damping logarithmic decrement (δ) of 2 times higher, relative scattering (ψ) of 3 times higher, and internal friction (Q-1) also 3 times higher than that of standard steel grades used in mining machine parts. Practical implications. The developed alloys No.3, No.4 and No.6 are recommended to be used in the manufacture of mining equipment parts. Their increased dissipative properties reduce the noise level of drill string and drill bit housing by 10-12 dBA, help increase the service life of units, as well as improve the working conditions of workers in the mining industry.

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Researches of thermodynamic processes of oxidation, self-heating and self-ignition of coal are necessary for studying of dependence of terminal parameters on a set of the influencing factors. In practice of coal mining by the underground method cases of coal self-ignition in the mined-out spaces of production units (lavas) are frequent. In this case one of the tasks consists in determination of temperature in arbitrary point of the nubbly-porous medium of the mined-out space. Need of the solution of this difficult task is caused by the probability of emergency situations in places with the explosive concentration of methane. It is possible that for each seam and grade of coal it is necessary to develop, substantiate and accept an individual indicator for assessing the state of fire hazard. It is proposed to systematize and methodically process the results of field measurements and observations on the analyzed and investigated cases of endogenous fires in problem areas of mines in order to create basin databases for subse- quent operational decisions in emergency situations.