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Percussion rock drills have been widely used mainly for blast hole drilling in mineral extraction, tunnel excavation, and underground development. To advance the performance and efficiency of rock drills, it is essential to understand the complex mechanisms of percussive rock drilling: hydraulic mechanisms in a drill body, elastic wave propagation and attenuation in rods and rod joints, dynamic bit penetration into rock, and the effects of thrust, rotation, and flushing. This paper focused on and detailed the bit penetration into rock. Some theories concerning the penetration characteristics of rock drill bits were presented such as elastic contact theory, slip line field theory, and fracture theory. Recent authors’ studies on static and dynamic penetration tests with a single button were introduced as an elementary drilling process of a bit in which a number of buttons are embedded. Then, recent authors’ studies on dynamic penetration tests with a button bit were introduced with the calculation method of force and penetration depth at the bit tip and with the results of force-penetration curves. The loading and unloading phases of the curves were modeled by convex functions, and their variation was discussed with the relation between the force-penetration curves of a bit and buttons. Important future research issues on the bit penetration into rock were presented for the further progress of percussive rock drilling.

Percussion rock drills have been widely used mainly for blast hole drilling in mineral extraction, tunnel excavation, and underground development. To advance the performance and efficiency of rock drills, it is essential to understand the complex mechanisms of percussive rock drilling: hydraulic mechanisms in a drill body, elastic wave propagation and attenuation in rods and rod joints, dynamic bit penetration into rock, and the effects of thrust, rotation, and flushing. This paper focused on and detailed the bit penetration into rock. Some theories concerning the penetration characteristics of rock drill bits were presented such as elastic contact theory, slip line field theory, and fracture theory. Recent authors' studies on static and dynamic penetration tests with a single button were introduced as an elementary drilling process of a bit in which a number of buttons are embedded. Then, recent authors' studies on dynamic penetration tests with a button bit were introduced with the calculation method of force and penetration depth at the bit tip and with the results of force-penetration curves. The loading and unloading phases of the curves were modeled by convex functions, and their variation was discussed with the relation between the force-penetration curves of a bit and buttons. Important future research issues on the bit penetration into rock were presented for the further progress of percussive rock drilling. [ABSTRACT FROM AUTHOR]

Rotary percussion rock drills have been widely used in mining and civil engineering fields, and their performance needs to be further improved. To deeply understand the mechanisms of the rock drills, this article reviews the previous studies from fundamental theories to state-of-the-art techniques on the rotary percussive rock drilling processes, including stress wave propagation, dynamic bit penetration, and factors affecting drilling efficiency and penetration rates. An enormous variety of research approaches and their findings are provided to related researchers and engineers. In addition, important future issues are presented for discussing the further progress of rotary percussive rock drilling. [ABSTRACT FROM AUTHOR]

Workers in the rock face stabilisation sector are exposed to high levels of vibration from pneumatic rock drills, which can lead to vibration injuries. The work situation is also ergonomically challenging since the work often is performed on steep cliffs with heavy equipment and a substantial degree of dust exposure. To reduce exposure to vibrations, the equipment has been redesigned, including the machine's handle, feeding hoist and the implementation of a reciprocating mass generating a counter force to reduce the vibrations. As a side project, a dust removal device was also developed. It was shown that vibration and dust exposure can be substantially reduced. [ABSTRACT FROM AUTHOR]

Data-driven fault diagnosis is an essential technology for the safety and maintenance of rock drills. However, since the signals acquired from a rock drill have different distributions, which arise due to their variable operating conditions, the classification performance of any data-driven method is diminished; this is called the domain-shift issue. This paper proposes a new domain-adaptation-based fault diagnosis scheme to solve the domain-shift problem. The proposed method introduces a data-cropping technique to mitigate the difference in the length of the data measured from a rock drill for each impact cycle. To extract invariant features for all operating conditions, the proposed method combines two methods: a domain adversarial neural network and minimization of the maximum mean discrepancy (MMD) between the features from different domains. In addition, a soft voting ensemble is used to reduce the model uncertainty. The proposed method shows superior performance when validated with a rock drill dataset; the proposed approach was ranked in 2nd place in the 2022 PHM Conference Data Challenge.

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Workers in the rock face stabilisation sector are exposed to high levels of vibration from pneumatic rock drills, which can lead to vibration injuries. The work situation is also ergonomically challenging since the work often is performed on steep cliffs with heavy equipment and a substantial degree of dust exposure. To reduce exposure to vibrations, the equipment has been redesigned, including the machine’s handle, feeding hoist and the implementation of a reciprocating mass generating a counter force to reduce the vibrations. As a side project, a dust removal device was also developed. It was shown that vibration and dust exposure can be substantially reduced.

Anti-jamming system has been widely used in rock drill rigs, in order to avoid uncontrolled jamming of the bit. An anti-jamming valve is the core component of the anti-jamming system. The backpropagation neural network (BPNN) was used in this study to construct an estimating model for the prediction of feed pressure, so as to find the key factors of jamming problems. Because the parameters of BPNN have a significant influence on results, and genetic algorithm (GA) is capable of quickly finding optimal solutions. We integrated GA and BPNN so that the convergence rate was improved and precision was relatively enhanced. The results showed that, BPNN realised a reasonable prediction for the feed pressure of anti-jamming valve. Moreover, when the parameters for GA are set between reasonable ranges, GA optimisation for such neural network is feasible, and the obtained results are satisfying, which has relatively higher accuracy of prediction, non-linear mapping and better network performance. [ABSTRACT FROM AUTHOR]

Rock drills were developed about two hundred years ago, and hydraulic percussion rock drills are about half-century old. Performance and efficiency of rock drills have been increased by a number of researchers and engineers. Percussion energy was dramatically increased with changing the power source from pneumatic to hydraulic pressures; rods and rod joints were improved to endure the high percussion energy; carbide button bits were developed for hard rock drilling. This paper reviewed the previous studies and future issues on the drilling processes with hydraulic percussion rock drills. Studies on the stress wave propagation in rods and rod joints were based on theoretical and graphical methods and recently on numerical simulation. Studies on the interaction between a button bit and rock included crack propagation in rock, force-penetration relationship during drilling, and bit wear. Studies on the factors affecting drilling efficiency and drilling rate made a transition from simple to precise numerical simulations. Finally, important future issues were presented for the further progress of hydraulic percussion rock drills.

Computer simulation of percussive rock drilling requires appropriate numerical models for the interactions among the drill body, rod, rod joint, bit, and rock. In this study, the impact penetration of a bit into rock was investigated for the modeling of the bit-rock interaction. Impact penetration tests on Inada granite were carried out with six rod-bit configurations which were composed of four kinds of button bits and two kinds of rods. In the calculation of force-penetration curves from the measured rod strains, the bit model constructed from the acoustic impedance was simplified, and the empirical data correction method proposed by the authors was applied to all the rod-bit configurations. The force-penetration curves for the six rod-bit configurations showed that the bit force in loading phase was approximately proportional to the square of the penetration. The curves in unloading phase had a linear relation between the bit force and the penetration. The final penetration of each blow had a linear relation with the maximum penetration, and the measured borehole depth was proportional to the maximum penetration. The effect of rod diameter on the force-penetration curves was not obviously observed. On the other hand, the bit force corresponding to the same penetration increased and the specific energy decreased with an increase in bit diameter or in the number of button tips on the bit. These findings will contribute to the improvement of the accuracy in the simulation of percussive rock drilling.

Taking a piston of air-leg rock drill as the research object， a finite element analysis model of the impact system including the piston and drill rod was set up based on the actual conditions. Its nonlinear dynamic characteristics were analyzed using the ANSYS/LS-DYNA software. Therefore， the stresses and strains of the impact system at different time were obtained. The results showed that there are minor deviations between the calculated and experimental results. The maximum stress， which is greater than the fatigue limit and less than the yield limit， appears at the impacting face. The spline root of the piston with strong stress is also a weak link. The failure form of the piston is the contact fatigue of the end face or fatigue fractures of the spline root， which coincides well with the actual situation and provides a scientific basis for reliability design of the piston. [ABSTRACT FROM AUTHOR]

A series of multiphase CFD (computational fluid dynamics) simulation was carried out in order to evaluate the design study of flushing device of rock reaming machine. The Star-CCM+ code was adopted for simulating rock particle discharge flow of flushing air during the rock reaming process. The input parameters for the flow simulation of rock particle were obtained from a previously performed in-situ drilling test results. After three design factors (degree of swash plate, radius of curvature of swash plate, and diameter of flushing channel) were determined, the experimental design method (response surface methodology) was applied to determine optimum value of each factor. [ABSTRACT FROM AUTHOR]

Rock drilling machines are commonly used for surface drilling, soil nailing reinforcement, tunnel excavation, and underground mining. These machines use drill bits that directly impact into the rock and are operated by percussive force and torque. Drill-bit buttons need to be designed to increase drilling efficiency; here, we present the results of a series of single blow tests on granitic rock samples using a piston drop type percussion testing system that enable us to compare the drilling efficiency of a new button arrangement design with conventional arrangements. Drilled rock volumes were measured by laser scanner after testing, and drilling efficiencies were evaluated by calculating percussive energies and drilled volumes. The results indicate that the new button arrangement design can be used to improve the drilling efficiency. [ABSTRACT FROM AUTHOR]

Descriptions of two known hydraulic impact mechanism are realized. One of the impact structures is to be patented. Improvements in the constructive structure and in the operating hydraulic scheme of these impact mechanisms are analyzed. The aim is to simplify the hydraulic scheme and the command and control structure, to minimize the hydraulic parasitic capacities and to attain an adjustable impact frequency. In brief, the goals are to improve the constructive structure of a hydraulic impact device or a hydraulic rotary percussive mechanism controlled by a rotary distributor and the operating principle of the mechanism. [ABSTRACT FROM AUTHOR]

The degree to which a rock abrades another rock is called its 'abrasivity'. Laboratory tests of abrasivity can be broadly divided into four kinds: drilling, rubbing, turning-operation and tumbling tests. The present study was initiated 30 years ago with the objective of investigating and developing methods for measuring rock abrasivity, and making some contribution towards understanding the relationships between the above test methods. Within the range of tests conducted, the turning-operation test turned out to be superior to the drilling test, albeit slightly, in terms of practicality. We have also conducted in situ tests using rock drills for the last 20 years. The results of those tests have been investigated and compared with the results of laboratory tests. There is a large degree of scatter in the data on gauge loss in button bits, which has obscured any correlations with laboratory data. Some correlations were found between height loss in button bits and laboratory findings. [ABSTRACT FROM AUTHOR]

Abstract: Force (penetration resistance)–penetration curves have a very important role for accurately predicting the performance of excavation machinery. The simplest model to represent the bit–rock interaction is a linear spring, in which the spring constant has been determined experimentally, but it is difficult to find a relationship between this and the physical properties of the rock. In the present study, a variable-compliance-type constitutive equation proposed on the basis of experimental data was used to model force–penetration curves instead of the conventional linear springs. Simulations were carried out to estimate penetration-time and force–time curves for four excavation machines, a rock drill, large rock hammer, roadheader, and tunnel boring machine. In all cases, force increases linearly at first and soon reaches a peak value that depends on the parameters in the constitutive equation. Thereafter, the force rapidly decreases. The calculated results are considered to be reasonable and consistent with the measured data, qualitatively. The proposed method can be applied to more realistic and sophisticated simulations combined with the finite element method (FEM) or other appropriate calculation methods. [ABSTRACT FROM AUTHOR]

Abstract: Traditional preparation of metallographic cross sections by cutting, polishing and etching has a long and successful history of revealing grain sizes, phase composition, gradients, etc. However, the technique is limited with respect to precision in the positioning of the cross section, and it also tends to inadvertently remove brittle constituents and conceal cracks and small details close to ductile phases, that may become smeared out by the polishing. The present paper presents an alternative cross sectioning technique for worn surfaces, developed to automatically reveal weak zones in the surface layer of a material, without the need of precise positioning, and also avoiding inadvertent removal of brittle phases. The technique is applicable to materials that exhibit brittle fracture, and is normally used for characterisation of unworn materials. It is primarily intended for studies in the SEM, since the cross sections produced typically exhibit too coarse topography to be sharply pictured in the light optical microscope. The simple and rapid preparation technique is described and examples from worn cemented carbide rock drills and hot rolls are presented to illustrate some of the capabilities of the technique. [Copyright &y& Elsevier]

Abstract: In percussive and rotary percussive rock drilling, the rock is crushed into small fragments by the repeated hard impact of the drill bit, and subsequently removed by flushing water or air. To avoid excessive wear, the steel drill bit is equipped with a set of cemented carbide buttons that protrude from the bit to take the actual impact. The severe contact against the rock results in some wear of the button, but also in formation of surface layers of rock material and penetration and impregnation of rock material into the cemented carbide structure. This situation, with serious implications for the wear and fracture of the buttons, have previously not been reported. The present findings represent a significantly new understanding of the wear of the rock button material. The deterioration mechanisms are described in detail, using examples from a range of real drilling applications in different rock types. During operation, material in the surface layer of the drill button shifts from that of the original cemented carbide into an uncontrolled composite. This composite is formed by the WC carbide hard phase and a binder consisting of a mixture of cobalt and rock. This new material should be expected to exhibit properties significantly different from the original cemented carbide. [Copyright &y& Elsevier]

Abstract: WC/Co cemented carbide is a material developed for highly demanding applications. The unique combination of hardness and toughness makes it especially suitable for wear resistant parts of tools for rock drilling. The wear of cemented carbide rock drill buttons has been the focus of numerous studies, and a large amount of wear data has been published. However, the broad range of possible wear mechanisms, the large number of rock types of very different character, and finally the large local property variations even within a single drill hole, has made it difficult to sort out a good general understanding. One conclusion stands out very clear: the wear data for one rock drill in one rock type is unique to that particular situation and should not be expected to apply to other rock drills in other rock types. Even so, some general wear mechanisms can be observed. Against this backdrop, this paper seeks to present a new, more comprehensive, view on the deterioration and wear mechanisms of cemented carbide rock drill buttons. The new view combines some of most important aspects, including two life limiting factors, five classes of mechanisms of deterioration and five classes of material removal mechanisms. The view is based on careful high resolution investigations of worn rock drill buttons selected from drilling of different rock types. The deterioration includes a fundamental change of material and properties due to intermixing of rock material and cemented carbide in the surface layer of the button. It further includes corrosive decay and oxidation of WC and formation of large-scale cracks in a reptile skin pattern. [Copyright &y& Elsevier]

Abstract: In this study, the fracture of piston for rock drill produced from case hardening steel is investigated. In order to study the causes of the fracture, specimens prepared from the damaged pistons were subjected to experiments such as hardness, chemical analysis and metallurgical tests. The effect of microstructure on the fracture was also considered. The detailed metallurgical analysis was conducted on the fractured pistons and compared with the unfailed pistons in service. Results showed that the obtained pistons hardness values were lower than the values stated in the literature. Geometrical analysis of the pistons revealed that early failure of the structure started from a notch by which stress concentrations are created at the end of the threaded region. [Copyright &y& Elsevier]

Drilling, transportation and handling of rock always result in wear of the equipment that comes into contact with the rock and rock fragments. Rock is normally considered rather hard, and the contact leads to abrasion, erosion and point fatigue. However, the wear mechanisms of the tools are often complex and vary in character depending on the rock type.To understand the wear mechanisms of the cemented carbide used in rock drill bits, it is central to understand how different rock types respond to severe scratching from hard tips. A cemented carbide tip with radius 10 μm was used in a scratch tester at progressive loads of 0 to 20 N and at constant loads of 10 N. The tested rock types were calcite, two types of magnetite, hematite, leptite, mica schist, granite, sandstone and quartz spanning average hardness values from 190 up to 1220 HV. The scratches were investigated in SEM and the friction coefficient between rock and the tip was measured. In addition, the wear volume of the cemented carbide tip is measured.The rock types differed significantly with respect to damage mechanism and critical load for transition from a mild to a more severe damage. The friction behaviour correspondingly shifted from rather smooth to very fluctuant. The wear of the tip was found to be correlated to the hardness of the rocks, but was also influenced by the grain size, the quartz content and isotropy. The implications from the present results on full-scale rock drill wear are discussed. [Copyright &y& Elsevier]