Search Results (21)

The selection of mining cutting tools used on the cutting heads of roadheaders and shearers in hard coal mines is primarily based on the uniaxial compressive strength (UCS) of the rock. However, selecting cutting tools solely on the basis of a single parameter characterizing the rock has proven to be insufficient. Therefore, the aim of the presented study was to develop guidelines for the selection of cutting tools with appropriate protective coatings on the working parts, based not only on the mechanical strength properties of rocks, but also on their abrasivity. For the study, twelve rock samples were collected from five different Polish hard coal mines. For each rock type, the UCS (uniaxial compressive strength), BTS (Brazilian tensile strength), and chemical composition (determined using wavelength-dispersive X-ray fluorescence, WD-XRF) were measured, along with the rock abrasivity index Wz, determined using a proprietary method developed at the AGH University of Krakow. The test results were compared with the calculated specific pick wear, defined as the number of picks consumed (replaced) per 1000 m³ of excavated material. As a result, a classification of rocks based on their UCS and abrasivity was developed, along with recommendations for selecting conical picks with suitable protective coatings on the working parts. Full article

In this study, a series of unrelieved cutting tests was conducted to analyze the effect of joints on rock cutting using a conical pick. The tests were performed on jointed rock mass specimens with joint spacings (J_s) of 30, 60, and 90 mm and at cutting depths of 3, 6, 9, and 12 mm. For each case, the distance between the cutting path and the joint plane (d) was varied from 0.1J_s to 0.5J_s. The cutting force decreased as the distance from the joint plane increased but reached the level observed in intact rock at the midpoint between adjacent joint planes (d = 0.5J_s). Regardless of joint spacing, the cutting force reached its minimum when d was between 0.2J_s and 0.3J_s. The rock fragmentation zone extended beyond the joint plane when d was 0.1J_s but became confined within the joint plane from around 0.2J_s to 0.3J_s. These results indicate that the influence of the joint is most pronounced within this range. Three types of crack propagation patterns were observed near the joint plane: (1) cracks that terminate at the joint along the shortest path, (2) cracks that pass through the joint and reach the opposite free surface, and (3) cracks that end at a free surface located just inside the joint plane. These observations suggest that the reduction in cutting force can be attributed to shorter crack propagation paths due to the presence of the joint. This study contributes to a better understanding of the cutting behavior of jointed rock masses when using a conical pick. Full article

In this study, a series of rock cutting tests was conducted using a conical pick to investigate the effect of joints on roadheader performance. Tests were performed on intact rock and jointed rock mass specimens with three different joint spacings. The results indicate that cuttability is enhanced in jointed rock mass compared to intact rock due to the influence of joints on fracture mechanics. When cutting perpendicular to the joint plane, joints shorten the fracture path for rock chip formation, reducing the cutting force (FC). In parallel cutting, the joint plane acts as a barrier to side-crack propagation, leading to a further reduction in FC. The FC and specific energy (SE) were generally lower in parallel cutting than in perpendicular cutting. However, when the cutting depth exceeded 0.2 times the joint spacing and the line spacing surpassed 0.4 times the joint spacing, this trend reversed. This occurred because joints hindered the interaction between adjacent cuts, causing a transition to an unrelieved cutting mode. Additionally, FC and SE increased with joint spacing. When joint spacing reached ten times the cutting depth, their values approached those of intact rock. This suggests that the joint effect becomes negligible. These findings provide a better understanding of the effect of joints on roadheader performance. Full article

This study investigates the correlations between the wear conditions of conical pick cutters and key variables such as the physical properties (shape, aspect ratio, roughness), explosive potential, health and safety implications, and particle size distribution of coal dust and larger fragments using the linear cutting machine (LCM). This research was conducted within the framework of recent regulatory developments, notably implementing the new silica rule in the mining and construction sectors and climate change consideration. This study reveals critical insights into optimizing operational processes while adhering to stringent health and safety regulations. The findings indicate that as cutting tools wear, there is a significant increase in generated fine particles, including respirable crystalline silica (RCS), which elevates the risk of respiratory diseases and, in the case of coal dust, a higher potential for explosions. The results show that the silica content in respirable dust is a function of rock mineralogy; however, the results showed that the absolute amount of silica-containing dust increased with bit wear in rocks containing pertinent minerals. For the larger fragments, the new bit produced a 1699 fragment count, while the completely worn-out bit produced a 5608 count. The results of the dust concentration show that the new bit produces 89.2 mg/m³ (17.84%); the moderate bit produces 165.1 mg/m³ (33.03%), and the worn-out bit produces 245.6 mg/m³ (49.13%). Moreover, this study highlights the impact of bit wear on the production of larger fragments, which decreases with tool degradation, further contributing to dust generation. These results suggest the necessity for proactive equipment maintenance, enhanced dust control measures, and continuous monitoring of cutting tool wear to ensure compliance with regulatory standards and to protect workers’ health and safety. Full article

This paper is an attempt to investigate the rock indentation behaviors of a conical pick under different loading rates (1, 2, 3, and 4 mm/min), indenter types (sharp and blunt indenters), and types of rock (concrete, limestone, granite). Serial indentation tests by indenters were first performed by an automatic universal testing machine and monitored by an i-SPEED high-speed camera to record the peak pick force, indentation depth, rock fracture area, and rock failure process. Accordingly, the effect of loading rates, rock brittleness, and pick type on rock indentation behaviors was subsequently analyzed for a sound understanding of rock fragmentation mechanisms with indenters. It was found that higher loading rates necessitate a higher pick force and indentation depth to achieve rock fragmentation, resulting in a larger fractured area. Notably, a positive linear relationship exists between loading rates, rock-breaking forces, and fracture areas. A sharp indenter induces multiple cycles of repeated crushing and chipping phases, resulting in an arcuate-shaped fracture pattern with a smaller fractured area. Conversely, the rounded blunt indenter leads to a single stage of compression, with cracks propagating directly through the rock specimen, producing a larger fractured area. In addition, rock brittleness is another key factor to control rock failure efficiency, with tensile strength serving as a significant component. Full article

This study introduces a simplified method for predicting the optimal cutting conditions to maximize excavation efficiency based on tool forces. A laboratory-scale linear rock-cutting test was conducted using a conical pick on Finike limestone. The tool forces and their ratios were analyzed in relation to cutting parameters such as penetration depth and spacing. While the cutting force (FC) and normal force (FN) increased with the penetration depth and spacing, this relationship could not predict the optimal cutting conditions. The ratio of the mean normal force to the mean cutting force (FN_m/FC_m) increased with the penetration depth and the ratio of spacing to penetration depth (s/d). However, even while including this relationship, predicting optimal cutting conditions remained challenging. The ratio of the peak cutting force to the mean cutting force (FC_p/FC_m) reached a maximum value at a specific s/d, which is similar to the relationship between the specific energy (SE) and s/d. The optimal s/d obtained through the SE methodology was found to be between 3 and 5, and FC_p/FC_m reached a maximum at s/d. The error between the optimal s/d and the s/d in which FC_p/FC_m was maximized was less than 5%. Therefore, it was confirmed that the optimal cutting conditions could be predicted through the relationship between FC_p/FC_m and s/d. Additionally, by using the results from previous studies, the optimal cutting conditions obtained from the SE methodology and the proposed methodology were found to agree within a margin of error of 20%. The proposed methodology can be beneficial for the design of cutter heads and the operation of excavation machines. Full article

This study evaluated the ingestion of microplastics (MP) by copepods in Terminos Lagoon (TL), a RAMSAR-listed site in the southern Gulf of Mexico. The evaluation was carried out in two contrasting seasons of 2022, as follows: the dry (April) and the rainy (October). Copepods were collected using a conical plankton net (mesh size of 200 μm). In the laboratory, a pool of all pelagic adult copepod taxa was picked, and the MP inside the organisms were extracted, classified, and photographed using traditional optical and scanning electron microscopy. A total of 268 MP particles were extracted from the interior of copepods; among them, 149 and 119 corresponded to the dry and rainy seasons, respectively. The ingestion rate in the dry season was 0.14, while in the rainy season, it was 0.11. In addition, fibers, plastic fragments, and microspheres with different colors (blue, red, black, green, transparent, and multicolored), sizes, forms (angular, round, triangular, and twisted), and textures were also detected. Fibers were the most abundant MP found in a proportion of more than 85%. In addition, in some sampling sites, microspheres were observed with high relative abundance values (80%). In some sites, fragments reach 20% of the total abundance. Significant differences were observed between the two seasons. The sites closest to the urban area adjacent to TL observed high diversity and abundance of MP. The higher abundance of MP in the dry season is due to lower river discharge, on the other hand. Thus, MP particles accumulate and become available for consumption by copepods. This is the first study that has revealed that the MP was ingested by the copepods in TL. Furthermore, this study provides a baseline information for future research on the abundance of MP in the Gulf of Mexico region. Full article

In underground coal mining, machine operators put themselves at risk when getting close to the machine or cutting face to observe the process. To improve the safety and efficiency of machine operators, a cutting force sensor is proposed. A linear cutting machine is used to cut two separate coal samples cast in concrete with conical pick cutters to simulate mining with a continuous miner. Linear and neural network regression models are fit using 100 random 70:30 test/train splits. The normal force exceeds 60 kN during the rock-cutting tests, and it is averaged using a low pass filter with a 10 Hertz cutoff frequency. The sensor uses measurements of the resonant frequency of capacitive cells in a steel case to determine cutting forces. When used in the rock-cutting experiments, the sensor conforms to the tooling and the stiffness and sensitivity are increased compared to the initial configuration. The sensor is able to track the normal force on the conical picks with a mean absolute error less than 6 kN and an $R^2$ score greater than 0.60 using linear regression. A small neural network with a second-order polynomial expansion is able to improve this to a mean absolute error of less than 4 kN and an $R^2$ score of around 0.80. Filtering measurements before regression fitting is explored. This type of sensor could allow operators to assess tool wear and material type using objective force measurements while maintaining a greater distance from the cutting interface. Full article

In this paper, we propose an ultrasonically coupled mechanical rock-breaking technology, creatively design an ultrasonically coupled mechanical rock-breaking drum, concurrently develop an ultrasonic cracking simulation method based on test coordination, and study the cracking mechanism and characteristics of ultrasonically pre-broken rock in order to increase the rock-breaking efficiency of shearer drums and lengthen pickaxe service life. To further understand the theory behind ultrasonic-coupled mechanical rock breaking, the operation of a fusion drum and the implications of ultrasonic field theory in a solid medium are first examined. Second, the impact and mechanism of the ultrasonic pre-crushing of the target red sandstone are investigated in conjunction with conducting a rock uniaxial compression test and RFPA^2D modeling. Furthermore, an ultrasonic pre-crushing fracturing mechanism test of the target red sandstone further reveals the effect and mechanism of ultrasonic fracturing. The efficacy of ultrasonic-coupled mechanical single-cutter cutting is then investigated using the discrete element cutting model (PFC^2D) of red sandstone. The results show that under the action of ultrasonic waves with an excitation frequency of 41 kHz, cracks can effectively be produced inside the rock mass of the target red sandstone, and the cumulative amount of acoustic emission is as high as 513, which reduces the strength of the rock mass and disintegrates its internal structure; the average cut-off force of the purely mechanical rock-breaking mode is 6374 N, and that of ultrasonically coupled rock breaking is 4185 N, which is a reduction of 34.34%, and can be attributed to the fact that ultrasonic waves can loosen the structure of the rock mass. This is explained by the ability of ultrasonic vibrations to weaken the structure of rock. The coupled rock-breaking technology not only simplifies mechanical cutting and rock breaking but the lower force can also reduce a pick-shaped trunnion’s wear failure cycle. This improves the environment for subsequent pick-shaped trunnion cutting and rock breaking and prevents the pick-shaped trunnion from being subjected to high-stress loads for an extended period of time so as to prolong its working life. Full article

The wearing of cutting tools is a bottleneck of many branches in the industry. However, the tools used in the mining sector are extraordinarily prone to rapid deterioration since many rocks exhibit aggressive abrasive properties. A typical example of a fast wearing cutting tool is a conical pick. It is used in the mining industry and other businesses requiring rock cutting, such as in roadworks and tunnelling. Both manufacturers and users attempt to find a way to enhance the lifespan of the working surface of conical picks via different approaches, namely heat treatment, chemical treatment, work hardening, and hardfacing, etc. To correctly estimate the resistance to abrasive wear for a particular conical pick, one must select appropriate procedures and methods. By this time, the most common estimation method is to measure the mass loss before and after cutting, preserving the specified and constant conditions. This method was developed for users (mines) and manufacturers of cutting tools, especially conical picks. Alternative methods of assessing the picks’ wear are also sought. In this paper, the authors perform additional volumetric loss measurements via a photogrammetric approach, which results in a 3D scan of brand-new and exploited conical pick. Three different sets of four picks were measured both in the domain of mass loss and volume loss, and the results were compared. Slight differences in parameters C2 and C3 were found. Additionally, the authors enclose recommendations regarding the proper use of the methods mentioned above, mainly focusing on the ability to perform linear and angular measurements of the tool performed on the 3D scan. Full article

Mechanical mining is a widely used method of separating materials from the face to obtain a useful mineral (e.g., coal, metal ores, salts, and diamonds), to make underground workings (e.g., mine galleries, tunnels, and underground garages), level roads, shape slopes, or to dig ditches. Mechanical mining is applied in the mining branch, tunnelling, road, and construction industries. Depending on the mechanical properties of the rocks, most frequently described by uniaxial compression strength, various machines and tools are used. The methods of mining high-strength abrasive rocks that have been used and developed in recent years are particularly applicable to the mining of copper, gold, tungsten, platinum ores, diamond deposits, and tunnelling. In addition to rock strength, the effectiveness of the mining process is affected by abrasiveness, which influences the rate of abrasive tool wear. Therefore, in various research and development centres, but also in production companies, tools are tested on unique stands. Tests are carried out to determine the cutting resistance and assess the wear rate. This article reviews methods and benches for testing mining tools, conical picks, and discs. Various solutions for testing single tools and cutting heads have been presented. The analysis conducted has revealed that despite the large number and great diversity of different test benches, there are no appropriate methods and stands for testing the wear rate of materials intended for mining tools. Full article

Conical picks are applied to rock breaking, and the cutting parameters greatly influence cutting performance and rock damage. A conical pick rock-cutting numerical simulation model and software to provide a quantitative analysis of rock damage are established to research the influence of cutting parameters on cutting force and rock damage. The research results indicated that the average peak cutting force decreases with an increased cutting angle, and the average peak cutting force increases with a decreased cutting speed. The average peak cutting force of the second conical pick increases as the distance between double conical picks increases in the process of rock-cutting with double conical picks. There is a positive correlation between the volume of rock damage, the volume of rock breaking, and the cutting force of the conical pick. The research results provide a reference for optimizing the cutting parameters of conical picks. Full article

The cutting heads currently used in longwall shearers, roadheaders, road milling machines and excavators are equipped with cutting tools called picks. The most commonly applied are conical picks, less frequently—radial picks or tangent picks. The picks are detachably mounted in holders installed on the body of the cutting head, to which they are usually welded (shearers) or, less frequently, form-connected (road milling machines). The arrangement of picks and holders (positioning) on the body of the cutting head, according to a previously designed diagram (pick arrangement), enables extraction of the mineral with a specific width (web) and diameter (height). Ideally, the pick arrangement should generate the lowest cutting resistance, which loads the cutting machine. The pick arrangement is characterized by design parameters (number of holders, pitch in the line and between the cutting lines) and kinematic parameters (rotational speed and advance speed). The values of these parameters result mainly from the properties of the mineral and the type of mining machine. Therefore, the correct positioning of the holders on the cutting head and their setting (cutting angles) are vitally important. This applies to both the design and implementation stages. For this purpose, the authors first developed models of pick arrangements and, next, the algorithm and software enabling the determination of cutting resistance, both in terms of the average value and its variation. Then, based on the performed calculations and the obtained results, it can be assessed whether the cutting head and the pick arrangement are properly designed. As a result of the performed calculations and analysis of the test results, the average values of the cutting resistance moment and the cutting machine advance forces were determined. It was found that the proposed pick arrangements are characterized by similar values of moments and forces. The greatest differences were found in the variability of these parameters, which translates into the dynamics of the cutting machine operation. Full article

Prediction of rock fracturing capacity demands particular requirements for the exploitation of mineral resources, especially for the parameter design of conical pick performance for hard rock fragmentation, which must take into account differences in rock mechanical properties. Among these parameters, the peak cutting force (PCF) is important in designing, selecting, and optimizing the cutting head of mining equipment and a cutability index of rocks. Taking high lithological tolerance as demand traction, this study proposes a theoretical model for estimating the peak cutting force of conical picks based on the improved projection profile method for which the influence of alloy head, pick body structure, and installation parameters are taken into consideration. Besides, experimental results corresponding to different numbers of rock samples are used to verify the accuracy and stability of the theoretical model. Meanwhile, the comparison of performance in cutting force estimation between this model and four other existing theoretical models is conducted. The results found that the new method has the highest correlation coefficient with the experimental results and the lowest root mean square error comparing with other models, i.e., the estimation performance of this method has high lithological tolerance when the rock type increases and the lithology changes. Consequently, the proposed peak cutting force estimation of improved projection profile method will provide a more valid and accurate prediction for rock fracturing capacity with large differences in rock mechanical properties. Full article

The rapid wear of conical picks used in rock cutting heads in the mining industry has a significant economic impact in cost effectiveness for a given mineral extraction business. Any mining facility could benefit from decreasing the cost along with a substantial durability increase of a conical pick; thus, the hardfacing method of production and regeneration should be taken into account. In order to automatize the regeneration, the wear rate assessment is necessary. This paper presents a methodology used to create a 3D photogrammetric model of most of the commercially available tangential-rotary cutters in their before and after abrasive exploitation state. An experiment of three factors on two levels is carried out to indicate the proper setup of the scanning rig to obtain plausible results. Those factors are: light level, presence of polarizing filter and the distance from the scanned object. The 3D scan of the worn out specimen is compared to the master model via algorithm developed by the authors. This approach provides more detailed information about the wear mechanism and can help either in roadheader cutting head diagnostics or to develop a strategy and optimize the toolpath for the numerically controlled hardfacing machine. Full article