Rock Abrasion Research Articles

COMPARATIVE ANALYSIS OF THE TECHNIQUES FOR DETACHMENT OF NATURAL STONE BLOCKS FROM THE MASSIF WITH FLEXIBLE HIGH-EXPLOSIVE CHARGES AND BULK-EXPANDING CHEMICAL COMPOSITIONS

Studies of foreign experience in the extraction of magmatic rocks for decorative and cladding purposes show a continuing trend for the use of high-speed explosives in the primary separation of the rock block from the massif. The belief that this is the cheapest way for primary extraction against the background of the prices for cutting of hard and highly abrasive rocks with diamond-rope, chain- and disk-stone cutters, makes quarry owners to put up with the losses from unwanted cracking of high-quality material. The authors undertook a series of experiments on samples of magma rock with hardness f = 16 according to Protodyakonov. The advantages and disadvantages of an alternative non-explosive technology for stone splitting with bulk-expanding mixtures were analysed. The results were compared with those using detonating cord charges to detach rock blocks with the same characteristics.

From rock‐boring organisms to tunnel boring machines: A new rock breaking technology by bioinspiration

The purpose of this study is to achieve better understanding of associated mechanisms and to recommend and identify new strategies to develop new rock breaking technology for Tunnel Boring Machines (TBMs). Tunnel Boring Machine tunnelling mainly depends upon the rock breakage caused by cutters moving on a rock surface in a rolling and sliding motion while under the action of thrust force. The rock breaking behaviour is controlled by the mechanical interaction between the cutters and the rock. Due to the high hardness and high abrasiveness of rock, the cutters have to work under very high thrust force and suffer heavy-load-impact and abrasive wear, causing serious wear and low rock breaking efficiency. Rock-boring organisms exist in nature, which achieve drilling and/or tunnelling in rocks through a tribochemical interaction. This phenomenon is called bioerosion and the organisms are natural ‘TBMs’ to some degree. In this study, the interaction between TBM cutters and rock is presented, and current measures to improve cutter wear and rock breaking efficiency and their limitations are reported. Then, the connotation, mechanism and typical cases of bioerosion are presented. Finally, inspired by bioerosion, a new chemically assisted rock breaking technology is proposed for TBMs.

Study on Pipe Wear Based on Large Scale Experiment and Scale Effect for Deep Sea Mining

Abstract For the production of seafloor massive sulfides, the ores are expected to be transported as a slurry up to the sea surface. The pipe wear is caused mainly by the collision of the ores against the pipe wall; thus, the evaluation of pipe wear is required for the operation of the production system. The authors conducted a full-scale experiment for evaluating pipe wear due to slurry flow. As the result, the pipe wear resistance of a SUS304 stainless steel is higher than the ultrahigh molecular weight polyethylene. In addition, the pipe wall thickness was measured before and after the experiment to obtain the distribution of the erosion on the pipe wall. The authors confirmed that the wall thickness reduced uniformly along the circumferential direction for vertical pipe, and the erosion occurred mainly along the bottom surface of the pipe for the horizontal and inclined pipes. Also, the authors investigated the relation between the index of rock abrasivity and erosion and proposed a correlation for pipe wear with the index of rock abrasivity. Finally, the authors predicted the pipe wear on the condition of full-scale experiment based on the data obtained in the reduced-scale experiment conducted previously. Then, the authors compared the predicted pipe wear with that measured in the full-scale experiment.

Conical picks of mining machines with increased utility properties – selected construction and technological aspects

Shearers and roadheaders are commonly used to extract useful mineral deposits, especially hard coal, and for drilling roadways in underground mines, tunnels and other underground buildings in civil engineering. As the primary working process of this type of machines, mechanical mining of rocks is carried out by cutting. These machines' working units are equipped for this purpose with picks, usually conical (point-attack). They have the form of an axially symmetrical body consisting of a steel shaft and a tip usually made of tungsten carbide, connected by a hard brass solder. Due to the possibility of spontaneous rotation in the pick holders and even wear and tear of their tip around the entire perimeter, conical picks have a much longer service life compared to radial picks. Their life, especially when cutting hard and sharp abrasive rocks, is, however, still unsatisfactory. Rapid wear of the picks leads to a decrease in mining efficiency, an increase in this process's energy consumption, and an increase in dynamic surplus to which the cutting machine is subject. Among many forms of wear and tear of the conical picks, attention was paid to the problem of asymmetrical abrasive wear of the tips, pulling out the connection of the soldered pick tip and fatigue breaking of the pick shafts in the transition zone of the shank into the shoulder. The article presents original propositions of modification of the construction of the roadheaders/shearers conical pick shafts and the method of fixing the tip in the pick shaft in order to increase their operational durability significantly. The technologies and devices necessary to manufacture conical picks of the proposed structure were described. The developed modifications significantly contribute to the improvement of functional properties, including the reliability of conical picks, used in particular for hard rock mining.

Development of a new test method for evaluating the abrasivity of granite building stones during polishing process based on weight loss of abrasive tool

Abrasivity of building stones is one of critical parameters during polishing stage in stone processing plants, which can significantly affect the abrasive tool consumption and the processing costs. Hence, the main purpose of this paper is to evaluate the building stone abrasivity based on the weight loss of abrasive tool during polishing process. For this purpose, a new laboratory test rig was developed, which can simulate the polishing process in laboratory scale as far as possible. Using this laboratory rig, a new test method was proposed, which gives an index herein called building stone abrasivity index (BSAI). This index was defined as the weight loss of abrasive tool during polishing process in order to estimate the building stone abrasivity. The proposed test method was carried out on 15 different types of Iranian granite building stones and the correlation of obtained BSAI with the physico-mechanical and petrographic properties of stone was investigated. Meaningful and reasonable relationships were observed. To evaluate the accuracy of proposed method, the correlation of BSAI with two most common abrasivity indices i.e. Schimazek abrasivity factor (F) and rock abrasivity index (RAI) was also discussed. The results indicated that there is a strong relationship between these indices, which verifies the accuracy of proposed method. Furthermore, the laboratory results were compared with data obtained from stone processing plants in order to validate the proposed test method. It was shown that the obtained BSAI has a good agreement with abrasivity of building stones in real conditions of stone processing plants. Therefore, the proposed test can be adopted as an accurate and rapid tool for evaluating the abrasivity of building stones in polishing process. Finally, relationship between BSAI and the abrasive tool lifespan (ATL) was examined and a model was suggested to predict ATL with acceptable accuracy.

Wear mechanisms of LCPC rock abrasivity test impellers of materials equivalent to TBM cutter head face tools

This study aims at performing the LCPC (Laboratoire Central des Ponts et Chaussées) rock abrasivity test to explore the wear characteristics of LCPC test impellers of different material hardness (i.e., 70–75 HRB; 46–48 HRC; 54–56 HRC; 60–61 HRC and 78–82 HRC). The LCPC tests were carried out on two hard and abrasive minerals quartz and garnet. In terms of weight loss, the test results showed an inverse relationship between the material hardness and corresponding ABR (g/t) values. Microscopic examination was conducted to study the wear mechanisms of selected impellers tested on both quartz and garnet samples. The micrographs of LCPC steel impellers showed furrow deformation accompanied by micro cutting and brittle fracture in the case of soft standard test impellers (70–75 HRB). When the material hardness of impellers was increased from (46–48 HRC) to (78–82 HRC) the wear mechanism began to show micro cutting and brittle fracture. For both minerals in general with increase in hardness of impellers there was a decrease in material deformation along with gradual increase in brittle fracture. In the case of the quartz mineral, higher amounts of weight loss of impeller materials and hence higher ABR (g/t) values were observed due to angular morphology of quartz compared to the rounded grains of garnet. When comparing ABR (g/t) of quartz against garnet, it was found to be increased by 48%, 57%, 59% and 147% when testing using impellers of 46–48 HRC, 54–56 HRC, 60–61 HRC and 78–82 HRC respectively.

The influence of extremely abrasive rock on the drilling velocity and tool wear in bored piles

The significance of the excavatability for the successful completion of constructional projects has been recognized in recent years, but little attention has been paid specifically to rotary pile boring. Given the quantity of geological parameters alone which need to be taken into account, it is apparent that the estimation of the drilling rate is difficult. Based on a case study in extremely abrasive tertiary silcretes (quartzite), the engineering geological influences on the drillability are examined. A minutely detailed documentation of the drilling process was produced, and laboratory testing was conducted to gain a better understanding of the correlation between significant rock properties and wear on drilling tools. The examined silcretes (quartzite) show CERCHAR abrasivity indices (CAI) up to a value of more than 6. It comes as no surprise that this highly abrasive rock causes extensive wear on piling equipment and an extremely high consumption of wear parts. In combination with the drilling velocity of both the drill tools and the casing shoe remaining well below 10 cm/min, it is obvious that the drilling performance is significantly impacted in more than one way. A correlation between the lifespan of the wear parts and the net drilling velocity is developed, allowing for a more reliable performance prediction for bored piles.

Comparative Wear Resistance of Existing and Prospective Materials of Fast-Wearing Elements of Mining Equipment

The results of tests for resistance to abrasive wear on highly abrasive hard rock white electrocorundum are presented. The main material of fast-wearing elements of mining and processing equipment-110G13L steel (Gadfield steel) in comparison with other 9 grades of steel and cast iron, including specially developed wear-resistant foreign steels such as Hardox and Miiluks, is analyzed. The studies were carried out using an experimental stand for studying the material wearing process. On the stand the sample was fixed in a holding device and, after being brought into contact with the abrasive, it was rotated under a constant load. As a result of the experiments, it was confirmed that the order of placement of the tested materials in terms of increasing wear resistance coincides with their placement in terms of increasing hardness. At the same time, the wear resistance of the most resistant material – U8A steel after quenching – is about 4 times higher than this indicator for the least resistant components – low-carbon steel 25L, including gray and high-strength cast iron SCH21, VCH35. The wear resistance of 110G13L steel, as well as 65G, U8 steels in the hardened state, is from 1.5 to 2 times higher than that of foreign steels M400, H450, M500, H500. The results of the conducted studies allow us to evaluate the analyzed materials on the basis of their wear resistance and hardness indicators on the feasibility of using them in the manufacture of fast-wearing parts of mining equipment. Based on the research data, it seems promising to develop new ways to increase the wear resistance of domestic steel, including 110G13L steel traditionally used in mining.

Evaluating the Efficiency of a\xa0New Cutterhead Design to Counteract the Drawbacks of Excavation through Very Hard Rocks

The application of appropriate excavation equipment in difficult grounds is of crucial importance and consequently improves the performance of hard rock Tunnel Boring Machines (TBMs). The cutterhead is one of the main components of TBMs which is directly involved in the excavation process, and its design can highly affect the cutting efficiency, the overall balance of the head, the performance of main bearing in long term, and the wear of the whole cutting face and muck buckets. This paper mainly focuses on the significant role of a proper design on the cutting efficiency with reference to a TBM tunneling project. Due to existence of very hard and abrasive rocks on the path of Kerman water conveyance tunnel, a new cutterhead was designed to be applied on a second hand TBM. The new cutterhead contains larger 19-inch disc cutters with a new disc cutter layout. Since the new cutterhead was launched following the excavation of the old one in a specific chainage of the tunnel, the performance of the two cutterheads in pyroclastic rocks could be compared with respect to the cutting efficiency, and lower specific energy values were observed for the new cutterhead which is the indicator of a better cutting efficiency in this geological condition.

The relationship between strength and abrasion characterizations in granite building stones

The wear of cutting blades during the preparation of building stones is an inevitable issue that occurs as a result of the contact of the blade with rock components. The present study aims to investigate the feasibility of proposing experimental relations of strength parameters and mineralogical hardness with Cerchar and Laboratoires Central des Ponts et Chaussées France (LCPC) tests. For this purpose, 18 samples of granite building stones were selected and equivalent quartz content (EQC), compressive and Brazilian tensile strength (uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS)), and Cerchar and LCPC abrasivity indices (CAI and LAC) were determined. The results showed the lack of any significant relationship between strength and abrasion properties. However, when evaluating the simultaneous impact of EQC and UCS using the rock abrasion index ( RAI = UCS × EQC ), significant valid empirical RAI–CAI and RAI–LAC relationships were derived. To investigate the simultaneous effect of UCS, BTS and EQC, a dimensionless parameter (i.e. modified rock abrasion index; MRAI = ( UCS / BTS ) × EQC ) was introduced. Moreover, it was found that the empirical MRAI–CAI relationship was more significant and valid than the previous relations. Verification of the proposed relationship with the values of other researchers and six new samples for estimating CAI and LAC based on UCS, BTS and EQC was found to be highly accurate for granite building stones.

Evaluation of Rock Abrasiveness Based on a Digital Drilling Test

Abstract The accurate evaluation of rock abrasiveness is the basis for the cutting tool design of tunnel boring machines and efficient tunneling. However, the conventional test method is complicated and costly, and in situ measurement cannot be obtained easily. A new digital drilling test system was developed to assess rock abrasiveness in which drilling parameters, including the thrust on bit, rotational speed, torque, and drilling displacement, can be simultaneously collected. Based on the force analysis of the drill bit and the energy conservation law, the energy dissipation per unit volume of drilling or modified specific energy was proposed as an evaluation index, and the quantitative relationship between the index and rock abrasiveness was explored and verified. The results showed that the average difference rate between the Cerchar abrasiveness indexes obtained from the digital drilling test and Cerchar test was less than 15 %, thus proving the effectiveness and feasibility of this method for evaluating rock abrasiveness. The method is easy to implement and has few requirements for sample preparation. It can also be used for the in situ testing of rock abrasiveness in engineering sites.

Correlation between Cerchar Abrasivity Index with Rock Properties in Sandstone and Tuff samples

The abrasivity of materials is of vital importance in selecting an affordable excavation method in the early stages of a tunneling project. Vickers hardness number rock (VHNR), rock abrasivity index (RAI), Cerchar abrasivity index (CAI), LCPC abrasivity coefficient, and Norwegian University of Science and Technology (NTNU) abrasion test are among the methods for estimating rock abrasivity. Correlations were proposed in this study for estimating the CAI of sandstone and tuff. To achieve reliable comprehensive results, various kinds of sandstone and tuff with different geological properties were selected. Sandstone and tuff samples were collected from different regions. Various tests were then carried out on prepared rock specimens to determine the uniaxial compressive strength (UCS), tensile strength, velocity of longitudinal waves, Schmidt hammer rebound hardness, and the equivalent quartz content (EQC). Two correlations were presented by analyzing the experimental results with the help of SPSS and Excel. The first correlation estimated the CAI of sandstone based on the UCS and EQC with a coefficient of determination (R2) of 0.81. Moreover, using data analysis in Excel, another correlation was proposed to estimate the CAI of tuff. The second correlation estimated the Schmidt hammer rebound hardness of tuff with an R2 of 0.88.

Investigation on the relationship among the Cerchar abrasivity index, drilling parameters and physical and mechanical properties of the rock

Rock abrasivity is an important factor that affects tool wear and tool parameter design, construction efficiency, and cost budgeting during rock excavation. The Cerchar abrasivity index (CAI) is used as a standard parameter to characterize the abrasiveness of rocks. It can be obtained through the Cerchar abrasivity test in a laboratory. However, conventional laboratory Cerchar abrasivity tests and petrophysical and mechanical tests are associated with certain problems, such as long cycles, high costs, and measurement delays, which cannot serve the determination of rock abrasiveness in field. Digital drilling technology is an efficient in situ test method that can effectively link drilling parameters with rock properties. Based on the test results for the CAI and physical and mechanical properties of 13 groups of rock samples collected from southwestern China, this paper focuses on the correlations of the CAI value with rock strength, petrographic characteristics and drilling parameters. By adopting a flat bottom diamond bit that mainly relies on grinding, according to the principle of mechanical balance and energy conservation during rock drilling, the grinding energy per unit volume of rock (ηe) is defined and derived. The univariate regression analysis results show that the uniaxial compressive strength (UCS) and equivalent quartz content (EQC) are the most important factors for explaining CAI and that the CAI can be well estimated using the ηe. Additionally, two optimal regression models for predicting CAI were established using stepwise multiple regression analysis. UCS and ηe were introduced into the model, and the use of both can predict approximately 96% of the variance in the CAI. In addition, a performance evaluation of the models proposed in this paper and previously published CAI prediction models that the prediction models established in this paper are verify statistically more reasonable and reliable than the previously proposed models. The research methods and results provide a new method for the rapid and accurate determination of rock abrasiveness in engineering field.

Experimental investigation on rock breaking performance of cutter assisted with hydraulic fracturing

To improve the efficiency of cutting hard rocks in roadway tunneling, a rock breaking method using a cutter assisted with hydraulic fracturing is proposed. In addition, the influence of the circumferential distribution of holes on the crack propagation was studied through a hydraulic fracturing experiment. On this basis, an experiment of rock breaking by a cutter assisted with hydraulic fracturing was conducted, and the effect of the hydraulic fracturing on the cutting performance was analyzed. The results show that the main cracks’ initial direction and propagation path were influenced by the location and number of circumferentially distributed holes, around which the secondary cracks appeared. During the fracturing process, the main cracks expanded to the circumferentially distributed holes and developed into a crack network; the more empty holes there were, the denser the crack network was. Compared with the original rock samples, the cutting torque and propelling force of the non-directionally and directionally perforated fractured rock samples were significantly lower, and the cutting performance of the directionally perforated fractured rock samples was better. The research provides a possibility for the rapid excavation of extremely hard and abrasive rock.

Comparison of Russian Index of Rocks Abrasivity with CAI

Development of technical means of excavation for tunnelling and minerals extraction requires the use of relevant experience and brand-new scientific achievements in the field of rock destruction by mechanical tools. Important problems of the use of rock cutting tools are wearing and tool consumption, which influence technical and economical performance of mining projects. Therefore, the paper provides an overview of existing domestic and abroad methods for determination of abarsivity of rocks, which are testing methods by Baron and Kuznetsov and by CERCHAR. The paper provides with a description of the essence of the method for determining the Russian abrasivity index and CAI, equipment for their implementation, as well as requirements for the styluses and rock samples. It is also given the classification of rock abrasiveness according to both methods. The important conclusion, which can be made based on this study, is that Russian abrasivity index by Baron and Kuznetsov can be correlated with CAI as we have done it in the first approximation.

Prediction of rock abrasivity and hardness from mineral composition

Rock abrasivity and hardness are two of the crucial mechanical properties in geological exploration and petroleum engineering. To figure out how the rock mineral composition determines the rock mechanical properties, ninety-six samples from ten provinces of China were collected to carry out tests including mineral contents, mineral particle size, abrasivity and hardness, and testing results indicated there is strong relationship between them. Through data processing of normalization, correlation analysis, and grouping, the raw testing data were used to establish a prediction function with Back-Propagation Artificial Neural Network (short as BP-ANN). With this prediction function, rock abrasivity and hardness can be accurately calculated from input parameters including rock type, mineral contents, and particle size. Besides, the calculation results from this prediction function also revealed the changing trend of abrasivity and hardness on how to be affected by mineral contents and particle size.

Simple Approach for Evaluation of Abrasive Mixing Efficiency for Abrasive Waterjet Rock Cutting

The abrasive mixing variables, such as the abrasive and water flow rates and the focus geometry parameters, determine the profitability of an abrasive waterjet system. In this study, the mixing efficiency characteristics in abrasive waterjet rock cutting were investigated. To demonstrate comprehensively the efficiency reduction due to collision during abrasive mixing, the chance of collision was expressed as the distance between the abrasive particles in the focus. The mixing efficiency was then assessed by utilizing the empirical relationship between the experimental results and the developed model. Based on the particle density and the velocity, the closer particles showed higher chances of collision, thus yielding a reduced cutting performance. Using the distance between particles model, the optimum abrasive flow rate and the cutting performance of abrasive waterjet systems can be estimated. This developed model can be used for the design selection of abrasive flow rate and systems for the cost-effective use of abrasive waterjets.

Development and Application of Cutterhead Working Status Monitoring System for Shield TBM Tunnelling

During the shield TBM tunnelling, the working status of the cutterhead is difficult to be determined because the pressured chamber is located behind the cutterhead. In this paper, a cutterhead working status monitoring system for shield TBM tunnelling was developed to monitor the working status of the cutterhead in real time. The system consists of data acquisition subsystem, control and data transmission subsystem, as well as data processing and display subsystem. The cutter wear, cutter rotation speed and cutterhead temperature can be monitored and transmitted to the system software through the central port by cable and wireless. The system software can simultaneously display the TBM operating parameters and cutterhead working status parameters, predict the cutter life and present early warning of abnormal working status. The system has been successfully applied in a shield tunnelling project. Based on the analysis of the monitoring data, it was found that the normal cutter wear mainly depended on the rock abrasiveness and cutter rotation distance. The difference in cutter wear rate in the different ground was more than 3 times. The relative sliding between the cutter and the tunnel face was widespread. The sliding distance in low-abrasive formations exceeded 1/3 of the cutter track length. Under the normal tunneling conditions, the cutterhead temperature was lower than 50°. The successful application shows that this system can work stably in long term under harsh work environment and provide guidance for shield TBM tunnelling.

TBM tunneling in extremely hard and abrasive rocks: Problems, solutions and assisting methods

Extremely hard and abrasive rocks pose great challenges to the past and ongoing TBM projects by increasing cutter wear and reducing penetration rates. A considerable amount of research has been conducted to improve the performance of TBMs in those challenging grounds by either improving the capacity of TBMs or developing assisting rock breakage methods. This paper first highlights the challenges of hard and abrasive rocks on TBM tunneling through case studies. It then presents the development of hard rock TBMs and reviews the technologies that can be used individually or as assistance to mechanical excavators to break hard rocks. Emphases are placed on technologies of high pressure waterjet, laser and microwave. The state of the art of field and laboratory research, problems and research directions of those technologies are discussed. The assisting methods are technically feasible; however, the main challenges of using those methods in the field are that the energy consumption can be over 10 times high and that the existing equipments have robustness problems. More research should be conducted to study the overall energy consumption using TBMs and the assisting methods. Pulsed waterjet, laser and microwave technologies should also be developed to make the assistance economically viable.

Long-term abrasion of rocks assessed by micro-Deval tests and estimation of the abrasion process of rock types based on strength parameters

Abstract Testing long-term properties of aggregates requires time consuming laboratory tests. Alternatively, mathematical models can also be used to describe the abrasion process of aggregates. The paper uses another approach it links long-term abrasion to rock mechanical properties to facilitate a quick assessment of long term behavior of aggregates. It explores the long-term durability of aggregates through the application of long-term micro-Deval tests, extending the validity range of the relevant European standard (EN 1097-1:2012), that only requires 12,000 rotations for quality testing. Seven andesite lithotypes obtained from four Hungarian quarries were analyzed. The long-term micro-Deval coefficients were determined by increasing the number of rotations from the standardized 12,000 until the material loss reached the value of 99 m%. With some andesites, only 240,000 rotations were needed, while other ones required 2,000,000 rotations to a material loss of 80 m%. Regression analyses were used to find suitable models that describe the behaviour of the aggregates subjected to abrasion. The test results and the regression analyses supported previous studies suggesting that exponential functions are suitable to model abrasion. The abrasion model parameters introduced here were compared with the rock mechanical parameters of andesites and other lithotypes. It was found, that the newly introduced abrasion parameter A, which is a material-dependent empirical parameter, correlates with the ratio of the uniaxial compressive strength and water absorption. The introduction of the abrasion parameter provides an easy-to-use tool for the description of the behavior of aggregates exposed to natural or artificial abrasive effects. The knowledge of the abrasion process is essential for the lifetime analyses of crushed stones used as construction material or for the investigation of mass change of the grains in sedimentary systems such as riverbeds or coastal zones.