Drilling Tests Research Articles

Development of a roof bolter drilling control process to reduce the generation of respirable dust

The drilling operation in the roof bolting process, especially in hard rock, generates excessive respirable coal and quartz dusts, which could expose the roof bolting operator to continued health risks. Previous research has shown that the amount of respirable dust produced is dependent on the main drilling parameters, specifically the drilling rotational and penetration rate. In this paper, a roof bolter drilling control process was proposed to reduce the generation of respirable dust. Based on the analysis of laboratory drilling test results, a rational drilling control process (adjusting rotational and penetration rates) to achieve the optimal drilling parameter for different rock types was proposed. In this process, the ratio between specific energy and rock uniaxial compressive strength was used as the index to determine the optimal operation point. The recommended drilling operation range for the rock type used in the experiment was provided, and the reduction in respirable dust generation was demonstrated. By following this control process, the drilling efficiency can be monitored in real time, so the system can stay in a relatively high-energy efficiency with less respirable dust production from the drilling source. This algorithm is targeted to be incorporated into the current roof bolter drilling control system for drilling automation so that a safe and productive drilling operation can be conducted in a healthy working environment.

A comparative study of cemented carbide parts produced by solvent on granules 3D-printing (SG-3DP) versus press and sinter

Cemented carbide parts have been manufactured from WC-12Co granules by “Solvent on Granules 3D-Printing” and compared with reference parts produced by conventional press and sintering. SG-3DP consists in growing a green part layer-by-layer by selective solvent jetting on powder-polymer granule beds. Both 3D printed green parts and uniaxially pressed compacts have been consolidated by thermal debinding and liquid phase sintering. Further densification has been achieved by hot isostatic pressing.3D-printed parts subjected to hot isostatic pressing exhibit 99.9% of theoretical density, 1308 ± 10 HV30 hardness and 12.1 ± 0.3 MPa∙m½ indentation toughness, which are comparable to properties of a commercial fine grained WC-12Co. Percussion drilling tests with fully dense SG-3DP drill plates have also been carried out successfully on concrete.

The effects of through tool cryogenic machining on the hole quality in GLARE® fibre metal laminates

GLARE® is a composite-metal laminate currently used in the Airbus A380 fuselage due to its excellent impact and fatigue performance. GLARE® undergo extensive drilling for riveting purposes making it prone to thermal effects and increased tool wear. Therefore, using coolants becomes necessary, however, conventional coolants can lead to moisture absorption. An alternative is to use cryogenic coolants due to their positive impact on machining aerospace materials in the past. In this study, through tool cryogenic machining technology is used for machining GLARE® laminates by delivering liquid nitrogen at −196 °C through the spindle allowing the coolant to be in direct and continuous contact with the cutting zone. The aim is to investigate the impact of drilling parameters and cryogenic cooling on surface roughness, hole size, circularity and hardness at hole entry and exit sides. In addition, microstructural evaluation using scanning electron microscopy. The results indicate that the cryogenic cooling improved hole surface finish and gave better hole size at the top, while it had no impact on hole circularity. The hardness was increased at the entry and exit sides of the hole compared to that observed in dry drilling tests while scanning electron microscopy revealed that burr formation was minimised.

Investigation of the Cross-Cutting Polycrystalline Diamond Compact Bit Drilling Efficiency

The parallel track scraping principle of conventional PDC bits largely limits the cutting efficiency and working life in deep formations. Cross-cutting polycrystalline diamond compact (PDC) bit may be an efficient drilling tool that increases the rock-breaking efficiency through both cross-cutting and alternate-cutting modes of the PDC cutter. The motion track equation of the cross-cutting PDC bit was derived by using the compound coordinate system, and the motion track was analyzed. Meanwhile, through the unit experiment and discrete element simulation, the cutting force, volume-specific load, and crack propagation were analyzed under different cutting modes. Through establishing a nonlinear dynamic model of the bit-rock system, the speed-up mechanism of the novel bit was analyzed based on rock damage, rock stress state, and motion characteristic of the bit during the rock-breaking process. Compared with unidirectional cutting, cross-cutting produces less cutting force, more brittle fracture, and a greater decrease of formation strength. The novel PDC bit can put more rock elements into a tensile stress condition than a conventional PDC bit, and the plastic energy dissipation ratio of the cross-cutting PDC bit is lower while the damage energy consumption ratio is higher than they are for conventional bits, which is beneficial to increasing the ratio of fracture failure and improving rock-breaking efficiency. Laboratory drilling tests show that the cross-cutting PDC bit can create mesh-like bottom-hole features. Drilling contrast experiments show that a mesh-like bottom-hole pattern can be obtained by using the cross-cutting PDC bit, of which the ROP is obviously higher than that of the conventional bit when drilling in sandstone or limestone formation. Meanwhile, the influence of deviation angle, weight on bit, and rock properties on cutting efficiency of the cross-cutting PDC bit are studied.

Real-time rock strength determination based on rock drillability index and drilling specific energy: an experimental study

The geological condition of surrounding rock is essential for supporting design and disaster prevention of roadways in the underground coal mines. The main point of this research is to compare two methods, namely rock drillability index and drilling specific energy, of assessing the geological conditions of surrounding rocks through theoretical analysis and drilling tests. Firstly, this study suggested from a theoretical point of view that the use of drilling specific energy to assess rock strength at low penetration velocity has limitations and pointed out the superiority of rock drillability index. Subsequently, the Measurement While drilling Test System (MWDTS) is introduced and used to perform a series of drilling tests. Then, based on the monitored drilling parameters, the rock drillability index and drilling specific energy are calculated respectively, and feasibility of these two methods is compared. The experiment results indicate that although the drilling parameters vary greatly during the different drilling tests, the rock drillability index can reflect the rock strength well. However, the fluctuation and error of drilling specific energy at the low penetration velocities are considerable and cannot be used to assess rock strength. Besides, it was found that the error of using the rock drillability index to assess rock strength is smaller than that of drilling specific energy. The above results show that the application scope and the stability of the rock drillability index are better than the drilling specific energy in real-time assessment of rock strength.

Assessment of the need and potential for groundwater artificial recharge based on the water supply, water demand, and aquifer properties in a water shortage region of South Korea

Artificial recharge is increasingly necessary to ensure sustainable groundwater supplies and meet the needs of a growing population and crop cultivation in the age of climate change. In this study, artificial groundwater recharging using surplus water resources within the local area is considered for a water shortage area during a drought season, Shingok village, Hongsung-gun, South Korea, that lacks water sources. Based on an analysis of the monthly supply and demand with the water budget method, the current water supply is determined to be entirely dependent on groundwater wells, and water shortages occur in May (approximately 6446 m3) when rice planting begins. The surplus groundwater, which is the amount of natural recharge minus the present usage, and stream discharge are sufficient from December to June, so they are considered source waters for artificial recharge. A depth of 6 ~ 19 m is suggested as the main target region for recharge based on the composition of strata and the vertical distribution of the hydraulic conductivity, which was investigated with electric resistivity survey, drilling, and pumping test methods. Considering the permeability of layers, a vertical well, by which water can infiltrate directly into the target strata, is proposed as the main injection structure, and a ditch is also suggested as an auxiliary system to improve the effect of injection over a broad area. In the future, a detailed design for the injection scenario, injection facility, well and ditch arrangements, and pumping facility will be established through numerical modeling, field injection tests, etc. If it is impossible to obtain water from a long distance, an artificial recharge system based on local water sources may be an appropriate method of securing water considering the storage capacity of permeable strata.

The influence of the drilling rate of the raise boring machine on the stability of the surrounding rock of a inclined shaft with large dip angle

The drilling method of counter-well drilling rig has become an important construction method for the construction of large inclination Angle pressure pipeline in pumped storage power station. In order to study the effect of the drilling rate on the stability of the surrounding rock of the inclined well. The method of numerical analysis is used to simulate the drilling rate of backwell drilling machine by changing the drilling depth of certain calculation step, and the drilling depth is along the inclined shaft line. The selection of drilling parameters is optimized and the drilling rate of the reverse well rig is determined. The results show that the tunneling rate has a significant influence on the deformation rate of surrounding rock and the change rate of stress gradient in the process of drilling with reverse-well drill. With the increase of drilling rate, the deformation rate and the change rate of stress gradient increase. The variation amplitude of the surrounding rock deformation and stress value at the monitoring point increases first and then decreases, and finally tends to be stable. Under this formation condition and drilling scheme, the deformation of surrounding rocks in wellbore after drilling at the same depth is small, and the effect of stress disturbance is not significant. The maximum deformation of surrounding rocks in inclined Wells is only 0.27mm, and the strong disturbance zone is about 2.0m. Combined with field drilling test results, the optimal drilling rate of reverse well reaming is determined to be 1.2m/h.

Computer modeling of electromagnetic data for mineral exploration: Application to uranium exploration in the Athabasca Basin

Electromagnetic (EM) methods are important geophysical tools for mineral exploration. Forward and inverse computer modeling are commonly used to interpret EM data. Real-life geology can be complex, and our computer modeling tools need to faithfully represent subsurface features to achieve accurate data interpretation. Traditional rectilinear meshes are less flexible and have difficulty conforming to the complex geometries of realistic geologic models, resulting in large numbers of mesh cells. In contrast, unstructured grids can represent complex geologic structures efficiently and accurately. However, building realistic geologic models and discretizing these models with unstructured grids suitable for EM modeling can be difficult and requires significant effort and specialized computer software tools. Therefore, it is important to develop workflows that can be used to facilitate model building and mesh generation. We have developed a procedure that can be used to build arbitrarily complex geologic models with topography using unstructured grids and a finite-volume time-domain code to calculate EM responses. We present an example of a trial-and-error modeling approach applied to a real data set collected at a uranium exploration project in the Athabasca Basin in Canada. The uranium mineralization is closely related to graphitic fault conductors in the basement. The deep burial depth and small thickness of the graphitic fault conductors demand accurate data interpretation results to guide subsequent drill testing. Our trial-and-error modeling approach builds initial realistic geologic models based on known geology and downhole data and creates initial geoelectrical models based on physical property measurements. Then, the initial model is iteratively refined based on the match between modeled and real data. We show that the modeling method can obtain 3D geoelectrical models that conform to known geology while achieving a good match between modeled and real data. The method can also provide guidance of where future drill holes should be directed.

Delamination-free drilling of carbon fiber reinforced plastic with variable feed rate

A large number of drilling have been performed to assemble aircraft parts of carbon fiber reinforced plastic (CFRP). Although high quality is required in machining the holes with high productivity in terms of reliability of parts, delamination often occurs around the holes in drilling. This paper presents a novel drilling method with variable feed rate to machine the delamination-free holes at a high machining rate. In the drilling, the holes are machined at the standard feed rates when the chisel moves in material; and are finished with the negative thrust at higher feed rates after the chisel exits from the workpiece. Orthogonal cutting tests were conducted to measure the cutting forces and the friction angles for the uncut chip thicknesses and the rake angles. The negative thrusts were measured in large uncut chip thicknesses at large rake angles of the lips. Then, the drilling tests were conducted to verify the change in the cutting force in the variable feed rate drilling up to 100 holes. Negative thrust component appears consistently to raise the workpiece up in the exit process even though the tool wear progresses with repeating drillings. As a result, the variable feed rate drilling remarkably controls delamination compared to the constant feed rate drilling in the 100th drilling. The cutting process in the variable feed rate drilling is compared with the constant feed rate drilling in a cutting force model based on the minimum cutting energy. The negative thrust is verified when the friction angle becomes smaller than the effective rake angle with increasing the feed rate.

Modeling of Coal Deposition Using the Resistivity Method with Wenner Configuration in the Bentarsari Basin Area, District of Salem, Brebes Regency, Central Java

Research to model coal deposits in the Bentarsari Basin area of Salem District in Brebes Regency has been done using the geoelectric-resistivity method with Wenner configuration. Resistivity data acquisition is carried out on five tracks, with each track has a length of 200 m. The least squares inversion method is applied to obtain a 2D-resistivity section model. Furthermore, the 2D-resistivity section model data for each line is combined into a 3D model to determine the coal deposit model in the area. The results of the interpretation indicate that the subsurface structure of the area consists of clay, sandy clay, coal, and sandstone; where the type of coal is lignite. This coal deposit has resistivity values with interval of 86.1 – 219.0 Ωm, which is distributed evenly with depth of 0.0 – 26.5 m, where the southern part of the all track has a higher potential. This research can be followed up with log drill testing to determine the actual subsurface layer, so that it can be utilized as a very economical alternative energy.

Synthesis and evaluation of high-performance diamond films with multilayer structure on printed circuit board drills

Printed Circuit Board (PCB) filled with a large amount of Alumina ceramics has broad application prospects in the fifth-generation industry but is hard to drill. This work focuses on high-performance diamond films to improve the working life of drilling tools and holes quality of products. By utilizing hot filament chemical vapor deposition (HFCVD) methods, the monolayer microcrystalline diamond (MCD), bilayer micro-nanocrystalline diamond (MNCD), and four-layer diamond (MNMNCD) are coated on commercial PCB drills (WC-6% Co). Solid particle erosion tests are conducted to study erosive wear mechanism of diamond films impacted by ceramic powders/particles. Besides, cutting performances of diamond coated drilling tools are evaluated by performing high-speed drilling tests with PCB as workpieces. In Erosion tests, the monolayer MCD film presents intergranular fracture and shows the lowest erosive resistance. The MNCD and MNMNCD films have similar fracture forms, where curved boundaries and steps between layers indicate their discontinuous fracture, and minor deep cone holes on the surfaces demonstrate their high resistance to crack growth. Moreover, only one minor deep cone hole is observed on the four-layer film which indicates it has the best resistance to particle impinging. In drilling tests, the number of holes drilled by the diamond coated tools before failure is regarded as criteria of working life. Then surface and sectional morphologies of holes are also observed to evaluate the quality of products. The results indicate the number of holes machined by the four-layer MNMNCD coated drills reaches 10,000, while that of the monolayer and the bilayer MNCD ones are 3000– 4000 and 6000 respectively. More importantly, different from the other two types of diamond coated tools, almost no burrs with a height of over 20 μm are observed on the hole entrance using the four-layer diamond coated tools. Therefore, considering both the working life and holes quality, the MNMNCD films excel in the cutting performance of the new type of PCB drilling.

Effect of cutting parameters on thrust force, torque, hole quality and dust generation during drilling of GLARE 2B laminates

The present study investigates the effects of machining parameters and the tool coating during drilling of a GLARE® hybrid aerospace material on the cutting forces, hole quality and the generation of harmful dust particles. The drilling tests were conducted using twist drills with diamond-like carbon (DLC), Cristall coating and without coating. Obtained results indicate that feed, in contrast to spindle speed, has an important effect on thrust force and torque. In addition, when DLC coated tools are used less surface deviation was detected in comparison with uncoated and Cristall coated drills. Moreover, dust measurement in terms of total number of particles, harmful particles and mass particles generated during drilling of GLARE® laminates was investigated. The results reveal that, the number of harmful particles in the air was found to be dependent on machining parameters. In fact, a lower spindle speed promotes the reduction of the number of harmful particles in the air by 50% compared to that observed at higher spindle speed.

Relationship between rock uniaxial compressive strength and digital core drilling parameters and its forecast method

The rock uniaxial compressive strength (UCS) is the basic parameter for support designs in underground engineering. In particular, the rock UCS should be obtained rapidly for underground engineering with complex geological conditions, such as soft rock, fracture areas, and high stress, to adjust the excavation and support plan and ensure construction safety. To solve the problem of obtaining real-time rock UCS at engineering sites, a rock UCS forecast idea is proposed using digital core drilling. The digital core drilling tests and uniaxial compression tests are performed based on the developed rock mass digital drilling system. The results indicate that the drilling parameters are highly responsive to the rock UCS. Based on the cutting and fracture characteristics of the rock digital core drilling, the mechanical analysis of rock cutting provides the digital core drilling strength, and a quantitative relationship model (CDP-UCS model) for the digital core drilling parameters and rock UCS is established. Thus, the digital core drilling-based rock UCS forecast method is proposed to provide a theoretical basis for continuous and quick testing of the surrounding rock UCS.

Experimental study of the effect of cooling/lubricating fluids on penetration rate in hard and soft rock drilling process

Rock drilling is the process of penetrating and crushing rocks, which is characterized by the low rate of penetration (ROP) and drilling rate because of the amount of cuttings that remain in the drilling environment and the thermal stresses generated at the bit-rock interface. Any improvement in ROP and drilling rate can be of great technical and economic value for drilling projects. ROP can be improved through the proper use of cooling-lubricating fluids during drilling. ROP is a key indicator of drilling performance and the ability to predict this rate can be very useful for mining projects. ROP prediction can also be used to estimate the total cost of a drilling operation. ROP depends on a variety of parameters, which, when available, can be used to estimate ROP. To reach a better understanding of the parameters affecting ROP and how it can be optimized, in this study, the results of 492 laboratory drilling tests were analyzed by linear and nonlinear multivariate regression in SPSS to build a number of models for ROP prediction. These tests were conducted on seven soft and hard rock samples while using six fluids as the cooling-lubricating agent. The tests were performed with a laboratory-scale drilling rig on cubic specimens at several different rotation speeds and thrust forces. The results showed that the drilling achieved significantly higher ROP in the presence of the cooling-lubricating agent. After reviewing the results, several models that were able to produce ROP predictions with the lowest average estimation error were picked as suitable choices for predicting ROP in the presence of cooling-lubricating fluids. The results of statistical tests of these models showed with over 90% confidence that they can produce highly accurate ROP estimates based on mechanical properties of the rock, physical characteristics of the cooling-lubricating fluid, and operating parameters of the drilling rig.

Segment Matrix Design and Drilling Test of Diamond Bit for Sapphire

This paper introduces the characteristics of sapphire and sapphire digging bits in LED field. The segment matrix design principle of bit and the rule of diamond selection are put forward. In addition, this paper analyzes the function of different metal powders and diamond parameters in the segment matrix. The results show that the finer grained (for example 80/100 mesh) diamond should be used with the concentrations of 30-60%. In the segment matrix, tin element can make the matrix more brittle and then the bit is sharper. Copper, silver and nickel element can enhance the matrix toughness and strength, cobalt and tungsten element can increase abrasive resistance. All of the above designs enable the sapphire bit to high sharpness and long life. A 4-inch sapphire bit was prepared for drilling sapphire crystal, the efficiency is increased by 8% than the Taiwan drill bit with the same specifications, the life is equal to Taiwan's drill bit, and the defect rate of sapphire bar is less than 0.5%, which satisfies the requirement of customers.

Influence of concrete bleeding due to mix proportion on the drilling speed of hardened surface layer

<abstract> The significance of micro-destructive testing, which can estimate the durability of reinforced concrete structures with minimal damage and high accuracy, in the investigation and diagnosis of reinforced concrete structures has been increasing. This study aims to evaluate the quality of the surface layer of concrete structures via a small-diameter drilling test, which is one of the micro-destructive tests developed to estimate the strength of concrete. Hence, it would be possible to evaluate the quality and strength of concrete simultaneously, which is very important. In this study, the influence of the bleeding amount which affects the surface quality of concrete on the drilling speed, was experimentally studied, considering the water-cement ratio and unit water content as experimental factors. The influence of bleeding on the drilling speed of the specimen surface was also investigated through measurements at the top and bottom surfaces. The following points were clarified from the experimental results and their analysis. (1) The drilling speed changes depending on the water-cement ratio and the unit water content. (2) The amount of bleeding affects the drilling speed; however the drilling speed is affected by the volume of the fine aggregate in the specimen. Therefore, (3) there is a possibility that it can be used for surface quality evaluation of concrete by examining in detail the method for calculating and correcting the drilling speed. </abstract>

The effects of liquid-CO2 cooling, MQL and cutting parameters on drilling performance

An investigation is made into the effects of liquid carbon dioxide (LCO2) cooling, minimum-quantity lubrication (MQL) and cutting speed in drilling. Experimental measurements of torque, thrust force and temperature are made over a wide range of process and operating conditions. The resulting empirical models are used to quantify the individual contributions of the controlled parameters on drilling performance, and to facilitate temperature-based process optimization. Of particular interest is the need to carefully adjust the LCO2 flow rate for any combination of MQL flow rate and cutting speed. The optimization is validated both in simulation and actual drilling tests.

A phenomenological transient model of bit foundering

In this paper we developed a phenomenological transient model of bit foundering which accounts for cuttings transport around the bit through time-dependent erosion and deposition terms. By bit foundering we mean the observed effect where Rate of Penetration no longer increases (and potentially decreases) with Weight on Bit. The model is compared against several experimental data sets and a data set from a full-scale drilling test, and is shown to qualitatively replicate the foundering behavior observed in the data. The simple formulation of the bit foundering model makes it attractive for drilling optimization and control applications.

In-situ test and bolt-grouting design evaluation method of underground engineering based on digital drilling

The reasonable design and in-time optimisation of the supporting scheme is very important for ensuring the safe control of the surrounding rock. The key steps are to conduct in-situ real-time tests and quantitative evaluation of the surrounding rock before and after being supported. In order to solve the difficult problem of in-situ testing the surrounding rock, the surrounding rock digital drilling test system (SDT system) of underground engineering is developed, and the in-situ test and bolt-grouting design evaluation method of surrounding rock in underground engineering based on digital drilling is proposed. The systematic test studies including digital drilling test, borehole inspection and coring test are conducted on typical surrounding rock of chamber in the high stress mine of China. The effectiveness of SDT system and the prediction model of rock equivalent strength based on drilling applied to on-site engineering are validated. The zoning of surrounding rock of deep chamber based on equivalent strength is obtained, which are the strength deterioration zone, strength recovery zone and original rock strength zone, respectively. Based on the results of the in-situ digital drilling test of surrounding rock, the bolt-grouting support scheme to reinforce the surrounding rock is designed and evaluated. The average equivalent strength increase rate of the fractured regions of chamber surrounding rock reinforced by bolt-grouting is 61.6%. The bolt-grouting support can effectively enhance the strength of the fractured surrounding rock and reinforce the fractured rock mass. This study provides an effective means for classifying surrounding rock based on their strengths and design optimisation of the support system.

Semi-Destructive and Non-Destructive Tests of Timber Structure of Various Moisture Contents.

The condition of heritage and historic timber constructions depends on how they are exploited. Numerous environmental factors degrade the physical and mechanical properties of timber and hence, affect the load-bearing capacity of constructions. As a result, frequent evaluations of their technical condition become necessary. Currently, modern technologies allow for extensive diagnostics of timber constructions using non-destructive and semi-destructive methods; yet, in contrast to classical laboratory tests, there is insufficient knowledge of the impact of individual factors on the results of such studies. This article presents an assessment of the influence of the moisture content of timber elements on the results of ultrasonic stress wave, sclerometric, and resistance drilling tests. Additionally, computed tomography scans were performed on selected samples to demonstrate the destruction mechanism occurring during the semi-destructive tests. The research involved three types of wood: pine, spruce, and fir of different moisture contents. The results reveal a strong relation between the moisture of timber and all the tests conducted in terms of both hygroscopic and capillary moisture.