CC BY
1404.00.16 - КОНЧИЛИК МАШИНАЛАРИ
d https://dx.doi.org/10.36522/2181-9637-2023-l-2 UDC: 622.271/.3(045)(575.1)
ENERGY PARAMETERS OF ROCK FRACTURE WITH A WEDGE-SHAPED TOOL
Makhmudov Azamat Makhmudovich,
Candidate of Technical Sciences, Associate Professor, Head of Department "Mining electromechanics", ORCID: 0000-0002-1260-9433, e-mail: [email protected]
Navoi State Mining and Technological University
Abstract. This paper reviews energy parameters of rock fractures made using a wedge-shaped tool. The paper provides diagrams of distribution of forces and stresses under the impact of a wedge-shaped tool and stress components from two sources in the form of a wedge, localized in one row. There is a theory of energy intensity of rock fracture and energy of a single blow with a wedge-shaped tool which explains the energy parameters of rock fracture with a wedge-shaped tool. The new machine is based on static-dynamic methods of applying stresses to rock masses, which justify the development of machines and mechanisms whose operating principle is based on static-dynamic methods of applying of loads to rock masses.
Keywords: block, rock, energy, fracture energy, force, impact, wedge, tool, mechanism, deformation, statics, dynamics.
TOG' JINSLARINI QOZIQSIMON INSTRUMENT BILAN BUZISHNING ENERGETIK O'LCHAMLARI
Maxmudov Azamat Maxmudovich,
texnika fanlari nomzodi, dotsent,
"Konchilik elektr mexanikasi" kafedrasi mudiri
Navoiy davlat konchilik va texnologiyalar universiteti
Annotatsiya. Maqolada qoziqsimon instrument yordamida tog' jinsini buzishda energetik o'lchamlar tadqiq qilingan. Qoziqsimon instru-mentning tog' jinsiga ta'siri natijasida kuchlanish hamda kuchlanganlik va bir qatorda joylashgan qoziq ko'rinishidagi ikkita manbaning kuchlanish komponentlari sxemalari keltirilgan. Qoziqsimon instrumentning tog' jinsini buzishdagi energetik o'lchamlarini asoslash uchun qoziqsimon instrumentning bir martalik zarb energiyasi va tog' jinsini buzish energiya hajmiyligi nazariyasi o'rganilgan. Ushbu ish tog' jinsini statik va dinamik usullar bilan yuklama berish orqali buzuvchi mashina va mexanizmlarni yaratish uchun asos bo'ladi.
Introduction
Fracture of various materials occurs mainly through shear deformation or rupture. Brittle materials generally have a lower fracture resistance than shear fracture, therefore these materials tend to fail under regular stresses [1, 2, 3].
It is obvious that reducing the energy intensity of a fracture during mining operations at block stone deposits will improve preservation of the near-contour massif and blocks. The lowest energy intensity of fracture is achieved in tensile fracture, as the modulus of deformation (Young's modulus) E, Poisson's coefficient and tensile strength of rocks are much lower than the ones derived as a result of compression or bending. It has been experimentally proven that Young modulus in tension is 1.1-1.3 times less than in bending and Young modulus in bending is 0.25-0.35 of Young modulus in compression [4-6].
Materials and methodology
When solving a technological problem of separating blocks of stone from massif, the control of destructive forces is carried out by a uniform distribution of loads and stresses in a massif owing to a special design of wedge-shaped tool, its shape and dimension parameters, as well as frequency and speed of a load application (fig. 1).
The effectiveness of stone block separation depends on the location of the sources in the massif, their configuration and a type of a load on the borehole contour. These factors
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ИЛМ-ФАН ВА ИННОВАЦИОН РИВОЖЛАНИШ НАУКА И ИННОВАЦИОННОЕ РАЗВИТИЕ SCIENCE AND INNOVATIVE DEVELOPMENT
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determine parameters of the stress waves and their destructive effect. At fracturing between boreholes, consider the problem of fracture development when striking using wedge-shaped tools pointing in the opposite direction from two sources (fig. 2).
Figure. 1. Diagram of force and stress distribution under the impact of a wedge-shaped tool
1 and 2 - first and second sources respectively; 3 - voltages in rectangular coordinate system. Figure. 2. Components of voltages from two wedge-shaped sources located in one row
Kalit so'zlar: blok, tog1 jinsi, energiya yig'uv-chanlik, yemirilish energiyasi, kuchlanish, zarb, pona, instrument, mexanizm, shakl o'zgarishi, statika, dinamika.
ЭНЕРГЕТИЧЕСКИЕ ПАРАМЕТРЫ
РАЗРУШЕНИЯ ГОРНЫХ ПОРОД
КЛИНОВИДНЫМ ИНСТРУМЕНТОМ
Махмудов Азамат Махмудович,
кандидат технических наук, доцент, заведующий кафедрой «Горная электромеханика» Навоийского государственного горного и технологического университета
Аннотация. В данной работе произведено теоретическое и практическое исследование энергетических параметров разрушения горных пород клиновидным инструментом. Приведены схемы распределения усилий и напряжений под воздействием клиновидного инструмента и компонентов напряжений от двух источников, находящихся в одном ряду в виде клина. Для обоснования энергетических параметров разрушения горных пород клиновидным инструментом приведена теория энергоемкости разрушения горных пород и энергии единичного удара ударным клиновидным инструментом, что также демонстрирует направление создания машин и механизмов, принцип действия которых основывается на статико-динамических методах приложения нагрузок на массивы горных пород.
Ключевые слова: блок, горная порода, энергоемкость, энергия разрушения, усилие, удар, клин, инструмент, механизм, деформация, статика, динамика.
The energy intensity E, (specific or surface energy), which is the amount of energy (work) required to separate a unit volume of rock from the massif, can be considered as a determining factor of the efficiency of the fracturing process. Indeed, the lower the energy intensity, the more perfect the fracturing process is [6-15].
Most of the research has focused on the influence of individual factors and parameters on the efficiency of the fracturing process. From the analysis of the works performed, it can be concluded that the main research tasks in the design of rock fracturing machines are:
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a) quantitative assessment of the effect of properties of the medium to be destroyed on the impact energy transfer process, selection of optimal parameters of impact machines, as well as the choice of their field of rational application;
b) evaluation of the effects of time and repeatability of dynamic impact on the efficiency of impact fracture;
c) optimization of individual parameters of the fracturing process and machines based on the theory of the impact fracturing process and physical substantiation of experimental data.
The energy intensity of fracturing rocks with a wedge-shaped impact tool can be fairly fully represented in the following structural form:
E = f
(1)
[AJ [nz] Dg [b] [a])
where K - a factor that considers technology of the machine;
£ - factor taking into account the type of a rock;
AeD - unit impact work; m - moisture content of rocks;
- total efficiency of the given type of working equipment;
vpu - pre-impact velocity of the striker; a, b - angle and width of working tool sharpening.
The structural formula (1) can be used to determine the effect of the following parameters on the fracture energy intensity (in addition to those directly included in the formula):
C - number of dynamic shocks; Wn - number of plasticity; h, hy - values of unit and total depth of working body immersion;
o, o, or - strength limits of rocks for compression, tearing and indentation respectively;
v - impact frequency; t - impact time; - distance from the wedge to the edge of the face;
/3 - angle of axis inclination of working body to horizon;
Tc - working cycle time;
A - extent of face preparation;
l - the distance between neighbouring work equipment installations, etc.
The energy intensity of rock failure depends on the physical condition of the rock, geometry and size of the tool, technological parameters of a development, method of bottom hole preparation, impact efficiency and others. Let's consider the system "tool-rock" in the system of the impact working tool whose collision occurs at a certain boundary velocity. From comparison of static and dynamic indentation of conical tools into rock it follows that work of dynamic indentation is 2-2.5 times more than static one [8, 12, 14, 15].
Dynamic penetration is assessed by loading rate (sink rate). Static loading is characterized by loading rates of approximately 70-2700 kN/(m2 . s) and dynamic loading reaches loading rates of (2*2,7) 104 kN/(m2 . s). Static and dynamic load data are given for the initial and complete penetration of the wedge tool into the rock mass. In this range a and a t
° c cm
(t ) vary in accordance with patterns close to logarithmic. Moreover, in the region of small load durations the curvature tends to increase. The issue is complicated by the fact that the value of the immersion work can change significantly with the change in the work of a single impact. This dependence has been observed by many researchers and concluded that it represents a hyperbola E = /(A). The increase in fracture energy at impact energies lower than the optimum explains the fact that the stresses developed in the impact do not reach critical values and most of the energy is spent on elastic deformations, i.e. the fracture is mainly of a fatigue nature.
If the value of A is excessive for rock breakage by impact, the excess work is absorbed by the massif or goes to regrind. An
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important component of any hammer design is the working tool, its shape and dimensions.
To solve the problem of effective rock destruction it is necessary to control the energy input, change the parameters of a single impact and the geometric shape of the tool (indenter). It is most expedient to use a wedge-shaped cutting tool with sharp edges for rock excavation. The wedge can be one-or two-sided, symmetrical or asymmetrical, with different angles of sharpening and width of the blade.
Earlier researches have established that it takes 2,5-3 times more work to plunge a biaxial symmetrical wedge with angle y = 300 than to plunge a wedge with angle y = 70 under the same conditions.
If y is small, the resistance to wedge penetration is small; but the forces developing on the jaws may also be small enough to create ultimate bursting stresses in the ground.
A large angle y increases the volume of compressible soil, which leads to a significant increase in the energy intensity of fracture. Therefore, the optimal fracture parameters for specific conditions are determined experimentally by the dependence of energy parameters on the angle of tool sharpening E = f(Y).
The width of the tool also has a great influence on the amount of rock volume to be separated from the massif. It is required to maintain the dependence (E = f(b)) between the wedge width b and the distance to the face at which the energy intensity of the fracture process is minimal, by experiments and calculations.
The wedge sinks with a simultaneous raise in immersion volume and contact area. Cheek stresses cause compression of the wedge and make it difficult for it to sink further. Under these conditions, when an initial hole already exists, the wedge sinking process at the same single impact energy slows down, as the elastic and oscillation losses associated with wedge sinking begin to influence.
The research has led to the conclusion that the dynamic loading force Pdin, the single impact energy A and the fracture energy E can be used to analyze the fracturing process.
The main factors relate to the system defining the conditions, the energy transferred from the machine striker to the wedge (A2):
А = An
(2)
where A1 = mb v2u /2 - impact energy.
According to the law of conservation of energy and the principle of superposition of impact energy components, the value of A2 is expended to perform the main work and possible losses:
А2 = А3 + А4 + А5 + А + А7 '
(3)
where A3 - is the energy reflected from the rock into the wedge;
A4 - energy of plastic deformation;
A5 - energy of wave processes in the ground;
A6 - energy going into oscillation of plastic domain;
A7 - thermal losses in the rock.
The A3 energy reflected from the rock into the wedge, according to E.S. Vatolin, is determined by the following relationship:
F К
A„ =
o2
+ pv1
(4)
where Fa - is the cross-sectional (maximum immersion depth) area of the wedge; t1 - time of wedge and rock contact; a - stress in rock at wedge-impactor contact (or wedge-rock for falling wedge); v1 - velocity of particles in reflected wave. Using formula (4) A3 can be calculated for the case of maximum loss at h = var and a = f(h) = const. For wedge with beam width b = 0,02 m and dipping depth up to 0,04 m; ap = 2 . 105 kN/m2; E = 2 . 106 kN/m2; v1 = vu = 10 m/s we get, that energy reflected to wedge is approximately 105 J, i.e. for impact work 1 500 J losses are 7 %, but this is
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for high rigidity of material being destroyed. The stiffness of the rock (acoustic) depends practically only on the speed of the (elastic or plastic) stress waves. The velocity of these waves in rocks varies from 600 to 1600 m/s, depending on the structural structure. At great penetration depths, the proportion of A3 in the total energy balance will be greater than at shallow depths.
When penetrating into the rock, the energy values A5 and A6 vary depending on the penetration depth, impact velocity, contact area of the tool and the strength properties of the rock. For wedge-shaped working body with 0,1 m width and 0,05 m depth of penetration energy loss A6 is 3-5% on impact. Energy loss A5 is relevant to energy loss A3 and depends on rock strength and is up to 7%.
Experimental studies on the energy performance of percussion tools have been carried out in the Nurata marble and Gazgan marble deposits.
Research findings
A necessary condition in the direction of reducing the energy intensity of the massif is the choice of the work front direction, established depending on the direction of the main fracture systems, anisotropy and cleavage of rocks.
The development of the fractures in the bending plane depends on the stressstrain state of the monoblocks, created by the working body. The working body must contribute to the creation of tensile normal stresses in the bending plane and at the whole height of the monoblock.
The nature of load application and its quantitative value should be based on the nature of brittle failure. The disturbance of rocks is evaluated by the degree of impact and the nature of distribution (branching) of the main cracks at static, dynamic, static-dynamic and impulsive application of loads.
The most promising area is making machines and mechanisms whose principle of operation is based on static and dynamic methods of applying loads on the rock mass.
So, the total loss is no more than 19% of the single impact energy, and it increases in this limit from a minimum at h = 0 to a maximum at h = h = 400*500 mm.
max
As a result, it is possible to draw the following main conclusion: even in the presence of an ideal impact system, guaranteeing us a value of n = 1,0, the total efficiency nY will have values much lower, if technical and technological parameters of the working tool are not selected so as to ensure minimization of mechanical losses into the surrounding rock environment.
Conclusions
Efficiency in solving the technological problem of separating blocks of stone from the massif by controlling the action of destructive forces, carried out by the uniform distribution of loads and stresses in the massif by a special design of wedge-shaped tool, its shape and dimensional parameters, as well as the rate of application of the loads. The optimum length of the crack (distance between the boreholes), created under the action of the impact tool from two boreholes, depends on the elastic modulus of the destructible material (E), the Poisson's ratio (v), the borehole radius (R), the value of the sustained cracking stresses developed on the wedge jaws inside the borehole (P), the effective specific surface energy of fracture of the rock (y).
It is established that according to the law of energy conservation and the principle of superposition of impact energy components, the value transferred to the tool is spent to perform the main work on destruction and on plastic deformation of the rock, as well as on losses in the form of energy reflection from the rock into the tool, on energy of wave processes in the rock, energy of vibration in the plastic region and on thermal losses in the rock.
Quantitative energy indices of percussion tool operation are determined by experimental research for specific field conditions at account physical and mechanical properties of the rock constituents.
Making machines and mechanisms, the dynamic methods of applying loads on rock principle of action of which is based on static- masses, is promising.
REFERENCES
1. Baron L.I., Klyuchnikov A.V. Konturnaya vzryvnaya obrabotka pri prokhodke tunnelya [Contour Blasting during Tunneling]. Leningrad, Nauka Publ., 1968, 204 p.
2. Grigorovich M.B. Otsenka mestorozhdeniy oblitsovochnogo kamnya pri poiske i razvedke [Estimation of facing stone deposits in prospecting and exploration]. Moscow, Nedra Publ., 1976, 151 p.
3. Nikolaevsky V.N. Dinamicheskaya prochnost' i skorost' razrusheniya [Dynamic Strength and Fracture Rate]. Impact, Explosion and Fracture, Ser. of Mechanics. New in Foreign Science. Moscow, Mir Publ., 1981, pp. 81-87.
4. Karkashadze G.G. Mekhanicheskoye razrusheniye gornykh porod [Mechanical destruction of rocks]. Moscow, MSU Press Publ., 2004, 222 p.
5. Drukovany M.F., Komir V.M., Kuznetsov V.M. Deystviye vzryva v gornykh porodakh [Action of explosion in rocks]. Kyiv, Naukov Dumka Publ., 1973, pp. 14-19.
6. Kutuzov B.N., Shifrin E.I. Opredeleniye ratsional'nykh parametrov konturnogo vzryvaniya. Fizicheskiye protsessy gornogo proizvodstva [Determination of Rational Parameters of Contour Blasting. Physical Processes of Mining Production]. Leningrad, 1980, pp. 3-8.
7. Razrusheniye. Razrusheniye nemetallov i kompozitnykh materialov [Destruction. Fracture of non-metals and composite materials]. Ed. G. Liebowitz. Part 1. Inorganic Materials (Glass, Rocks, Composites, Ceramics, Ice). Moscow, Mir Publ., 1976, vol. 7, pp. 60-128.
8. Rakishev B.R. Energoyemkost' mekhanicheskogo razrusheniya gornykh porod [Energy intensity of mechanical destruction of rocks]. Almaty, Baspager, 1998, 210 p.
9. Rodionov V.N. O nekotorykh kachestvennykh sootnosheniyakh parametrov vzryvnogo vozdeystviya v tverdoy srede [About Some Qualitative Relations of Explosion Action Parameters in a Solid Medium]. Explosives. Book 5. Moscow, 1974, vol. 73/30, pp. 66-75.
10. Rakhimov V.R., Makhmudov A.M. Faktory, opredelyayushchiye effektivnost' tekhnologii dobychi kamennykh blokov udarnymi mashinami [Factors determining the effectiveness of technology of stone block extraction by percussion machines]. Mining Bulletin of Uzbekistan, Navoi, 2010, no. 3, pp. 6-8.
11. Tangayev I.A. Energoyemkost' dobychi i pererabotki poleznykh iskopayemykh [Energy intensity of mining and processing of minerals]. Moscow, Nedra Publ., 1986, 231 p.
12. Cherepanov G.P. Mekhanika razrusheniya gornykh porod pri burenii [Mechanics of rock destruction during drilling]. Moscow, Nedra Publ., 1987, 308 p.
13. Khanukaev A.N. Fizicheskiye protsessy pri razrushenii gornykh porod vzryvom [Physical processes at rock breaking by explosion]. Moscow, 1974, 233 p.
14. Makhmudov A.M. Scientific basis for controlling the mechanism of rock fracture along the contour. Mining Bulletin of Uzbekistan, Navoi, 2010, no. 3, pp. 27-29.
15. Makhmudov A.M. Theoretical study of the method of preparation of rocks for excavation on the basis of impact fracture. Mining Bulletin of Uzbekistan, Navoi, 2022, no. 2, pp. 13-15.
Reviewer: Zaripov Sh.U., Candidate of Technical Sciences, Associate Professor, Deputy Head of the Navoi Mining and Metallurgical Plant Design Bureau.
