Introducing a new rock abrasivity index using a scaled down disc cutter

Rock abrasivity influences wear of cutting tools and consequently,performance of mechanized tunneling ma-chines.Several methods have been proposed to evaluate rock abrasivity in recent decades,each one has its own advantages.In this paper,a new method is introduced to estimate wear of disc cutters based on rock cutting tests using scaled down discs(i.e.54 and 72 mm diameter).The discs are made of H13 steel,which is a common steel type in producing real-scale discs,with hardness of 32 and 54 HRC.The small-scale linear rock cutting machine and a new abrasion test apparatus,namely University of Tehran abrasivity test machine,are utilized to perform the tests.Tip width of the worn discs is monitored and presented as the function of the accumulated test run to classify the rock abrasion.Abrasivity tests show that by increasing the uniaxial compressive strength(UCS)of the rock samples,wear rate is doubled gradually that reveals the sensitivity of the test procedure to the main pa-rameters affecting the abrasivity of hard rocks.For the rocks with the highest UCS,the normal wear stops after performing 5 to 10 rounds of the tests,and then,deformation of the disc tip is detectable.Two abrasivity indices are defined based on the abrasivity tests results and their correlations with Cerchar Abrasivity Index(CAI)and UCS are established.Comparison of the established correlations in this study with previous investigations dem-onstrates the sensitivity of the indices to the parameters affecting wear of the disc cutters and repeatability of the outputs obtained from abrasivity tests using scaled down discs.Findings of this study can be used to enhance the accuracy of rock abrasivity classifications.

Effect of low-speed waterjet pressure on the rock-breaking performance of unsubmerged cavitating abrasive waterjet

Unsubmerged cavitating abrasive waterjet(UCAWJ)has been shown to artificially create a submerged environment that produces shear cavitation,which effectively enhances rock-breaking performance.The shear cavitation generation and collapse intensity depend on the pressure difference between the intermediate high-speed abrasive waterjet and the coaxial low-speed waterjet.However,the effect of the pressure of the coaxial low-speed waterjet is pending.For this purpose,the effect of low-speed waterjet pressure on rock-breaking performance at different standoff distances was experimentally investigated,and the effects of erosion time and ruby nozzle diameter on erosion performance were discussed.Finally,the micromorphology of the sandstone was observed at different locations.The results show that increased erosion time and ruby nozzle diameter can significantly improve the rock-breaking performance.At different standoff distances,the mass loss increases first and then decreases with the increase of low-speed waterjet pressure,the maximum mass loss is 10.4 g at a low-speed waterjet pressure of0.09 MPa.The surface morphology of cavitation erosion was measured using a 3D profiler,the increase in both erosion depth and surface roughness indicated a significant increase in the intensity of the shear cavitation collapse.At a low-speed waterjet pressure of 0.18 MPa,the cavitation erosion surface depth can reach 600μm with a roughness of 127μm.

A novel approach of jet polishing for interior surface of small-grooved components using three developed setups

It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanwhile keeping the structure intact.To overcome this challenge,small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer.A novel approach to multi-phase jet(MPJ)polishing is proposed,utilizing a self-developed polisher that incorporates solid,liquid,and gas phases.In contrast,abrasive air jet(AAJ)polishing is recommended,employing a customized polisher that combines solid and gas phases.After jet polishing,surface roughness(Sa)on the interior surface of grooves decreases from pristine 8.596μm to 0.701μm and 0.336μm via AAJ polishing and MPJ polishing,respectively,and Sa reduces 92%and 96%,correspondingly.Furthermore,a formula defining the relationship between linear energy density and unit defect volume has been developed.The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm^(-1)to 0.22 J mm^(-1).The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones.Computational fluid dynamics simulation results reveal that material is removed by shear stress,and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove,resulting in uniform material removal.This is in good agreement with the experimental results.The novel proposed setups,approach,and findings provide new insights into manufacturing complex-structured components,polishing the small-grooved structure,and keeping it unbroken.

Optimizing the Diameter of Plugging Balls in Deep Shale Gas Wells

Deep shale gas reserves that have been fractured typically have many relatively close perforation holes. Due to theproximity of each fracture during the formation of the fracture network, there is significant stress interference,which results in uneven fracture propagation. It is common practice to use “balls” to temporarily plug fractureopenings in order to lessen liquid intake and achieve uniform propagation in each cluster. In this study, a diameteroptimization model is introduced for these plugging balls based on a multi-cluster fracture propagationmodel and a perforation dynamic abrasion model. This approach relies on proper consideration of the multiphasenature of the considered problem and the interaction force between the involved fluid and solid phases. Accordingly,it can take into account the behavior of the gradually changing hole diameter due to proppant continuousperforation erosion. Moreover, it can provide useful information about the fluid-dynamic behavior of the consideredsystem before and after plugging. It is shown that when the diameter of the temporary plugging ball is1.2 times that of the perforation hole, the perforation holes of each cluster can be effectively blocked.

The Impact of Heat Treatment and Surface Treatment on Thermal Conductivity of Heat Sinks Made of Aluminium Die Casting Alloys

This research contributes to understand the thermal management capabilities of Plate Fin Heat Sinks(PFHS)fabricated from AlSi10Mg.The uniqueness in this study is that the heat sinks were exposed to abrasive blasting,heat treatment,and graphene coating,and a full evaluation of the influence of the aforementioned treatments on the thermal management capacities of PFHS was found.Untreated PFHS is compared with 1)abrasive blasted and graphene coated heat sink,and 2)heat treated and graphene coated heat sink.To assess the thermal efficiency of the PFHS variants,a dedicated experimental set up was meticulously constructed.It is noteworthy that a junction temperature of 60℃was assumed as the reference point for the analysis.The results revealed that the charging cycle time which denotes the time required attaining the junction temperature,increased 1.3 times for the sample being abrasive-blasted at 0.5 MPa pressure and graphene-coated for 0.5 mm when the maximum heat input of 45 W is evaluated.When low heat input of 15 W is evaluated,the results revealed that there is no significant difference in charging cycle when compared to the untreated heat sink.The charging cycle time increased 2 times for the sample which is heat-treated at 450℃and graphene-coated for 0.5 mm at heat input of 15 W.This finding unequivocally underscores the heightened capacity of the heat treated and graphene coated PFHS made of AlSi10Mg to withstand elevated junction temperatures.

Experimental Abrasion Study of the Evolution of Gold Morphological Criteria in Different Sediments as a Function of Time

The use of gold as a tracer element for understanding the mode of emplacement of these formations requires a good knowledge of its dynamics. To this end, we have carried out experimental studies to investigate the evolution of contour states (regular, irregular), surface states (blunt, rough), shape (elongation) and dimension (size). The study of these criteria is carried out on SEM photos of particles, taken before and after the experiment, using Aphelion image processing software. Five experiments were carried out to study the influence of sediment granulometry and water dilution on particle morphological changes. The results of these experiments show that coarse sediments (>1 mm) are largely responsible for morphological changes in gold. They cause fragmentation and/or folding of the particle edges, depending on the magnitude of the impact forces. Strong impacts due to high water dilution cause staking on the particle surface. Fine sediments (<1 mm) slow down particle evolution as they cushion impacts and particles tend to flatten rather than fragment.

Dry sliding wear behavior of cast Mg-11Y-5Gd-2Zn magnesium alloy

Dry sliding wear tests on as-cast and cast＋T6 Mg-11Y-5Gd-2Zn magnesium alloys were performed using a ball-on-plate configuration. The wear rates were measured within a load range of 3-15 N, sliding speed range of 0.03-0.24 m/s, test temperature range of 25-200 °C and at a constant sliding distance of 400 m. The wear tracks, worn surfaces and wear debris of the alloys were analyzed using scanning electron microscope （SEM）. The results show that the wear rate of the alloys increases almost linearly with increasing applied load and decreases with increasing sliding speed. The wear rate of the as-cast alloy is higher than that of the cast＋T6 alloy. The amount of Mg12Y1Zn1 phase, surface oxidation and retained wear debris affect the wear rate. The dominant wear mechanisms under the test condition are abrasion and plastic deformation.

Study on the new materials for fiberboard refiner plate of defibrator

Defibrator is a very important machine in the wood industry for producing fiberboard. The refiner plates are the key parts of defibrator that directly act with the wood, and broken easily. The working life of the refiner plates is of significance to the wood industry. It may affect refining quality, production efficiency, and power consumption. In this paper, the abrasion resistance of the refiner plate made of different materials, the stainless steels and high chromium cast irons, were tested and compared. The results showed that abrasion resistance of refiner plate made of high chromium cast irons was better than that of the stainless steel materials. Although the two kinds of materials have the same compositions, their abrasion resistances have ap-parent difference. The main reason is that the material microstructures have very important effects on their performance. The refiner plates made of developed high chromium cast irons don抰 demand the complex heat treatment. This can simplify the producing process, save the cost of production, decrease labor strength, and increase the production efficiency.

Effect of particulate reinforcement on wear behavior of magnesium matrix composites

The friction and wear behavior of magnesium matrix composites reinforced with particulate Mg2Si was characterized. The influence of Si, applied load and sliding rate on the wear behavior of Mg2Si/AM60 magnesium matrix composites was studied. The results indicate that the particulate Mg2Si can be synthesized by adding Si into magnesium alloy. The wear properties of AM60 magnesium alloy are significantly improved with MgzSi particles. The wear mass losses of AM60 magnesium alloy and MgaSi/AM60 magnesium matrix composites decrease with increase in applied load and sliding rate. The wear feature of the AM60 magnesium alloy is adhesion wear. The wear mechanism of Mg2Si/AM60 magnesium matrix composites transforms from abrasive wear to adhesion wear with the increase of load.

Experimental investigation on the effects of microwave irradiation on kimberlite and granite rocks

This study is a part of an overall research project on the effects of microwave(MW)irradiation on rocks for assisted rock breaking systems as well as mineral processing at McGill University.For the first time,this paper highlights a comprehensive investigation on the effects of microwave irradiation on Canadian kimberlites.Potential contribution to the continuous rock excavation and rock weakening effect prior to implementation of mechanical techniques was explored.Two different kimberlite rocks,i.e.volcaniclastic kimberlite(VK)and hypabyssal kimberlite(HK),and granite samples were studied.Some important physical properties of the rock samples were measured including rock quality designation(RQD),specific gravity,porosity,and specific heat capacity.Rock samples were treated for various exposure times using a multi-mode MWunit at different power levels ranging from 2 kW to 15 kW.The effect of MW irradiation on rock samples was investigated.The results indicate that the mechanical properties including unconfined compressive strength(UCS)and Brazilian tensile strength(BTS)were significantly dropped as a result of MWirradiation.Finally,the effect on rock abrasivity using the Cerchar abrasivity index(CAI)has also been discussed.

Drillability prediction in some metamorphic rocks using composite penetration rate index(CPRI)–An approach

Assessment of drillability of rocks is vital in the selection,operation,and performance evaluation of cutting tools used in various excavation machinery deployed in mining and tunneling.The commonly used rock drillability prediction methods,namely,drilling rate index(DRI)and Cerchar hardness index(CHI)have limitations in predicting the penetration rate due to differential wear of the cutting tool in rocks with varied hardness and abrasivity.Since cutting tools get blunt differently in different rocks,the stress beneath the tip of the bit decreases until it reaches a threshold value beyond which the penetration rate becomes constant.In this research,a new composite penetration rate index(CPRI)is suggested based on the investigations on four metamorphic rocks viz.quartzite,gneiss,schist and phyllite with varied hardness-abrasivity values.The penetration-time behavior was classified into active,moderate,passive,and dormant phases based on the reduction in penetration rate at different stages of drilling.A comparison of predicted penetration rate values using DRI and CPRI with actual penetration rate values clearly establishes the supremacy of CPRI.Micro-structure and hardness-based index was also developed and correlated with CPRI.The new indices can help predict cutting tool penetration and its consumption more accurately.

STUDIES ON MAGNETIC ABRASIVE MACHINING

This paper deals with the machining process using magnetic abrasives. Using an apparatus designed and made, a series of experiments are carried out, where the workpiece is cylindrical and the magnetic abrasives used are mainly Fe and Al 2O 3, for investigating the effects of machining time, working gap, rotating speed of workpieces, magnetic flux density on machining efficiency and surface roughness. At the end of this paper, the machining mechanism is also discussed.

Numerical Simulation and Analysis of Solid-liquid Two-phase Flow in Centrifugal Pump

The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics （CFD） code based on the mixture model of the two-phase flow and the RNG k-~ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.

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.

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics /Finite Element Method

In dealing with abrasive waterjet machining（AWJM） simulation,most literatures apply finite element method（FEM） to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics（SPH） coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.

The Sandfish's Skin:Morphology,Chemistry and Reconstruction

The sandfish is a lizard having the remarkable ability to move in desert sand in a swimming-like fashion. The most outstanding adaptations to this mode of life are the low friction behaviour and the extensive abrasion resistance of the sandfish skin against sand, outperforming even steel. We investigated the topography, the composition and the mechanical properties of sandfish scales. These consist of glycosylated keratins with high amount of sulphur but no hard inorganic material, such as silicates or lime. Remarkably, atomic force microscopy shows an almost complete absence of attractive forces between the scale surface and a silicon tip, suggesting that this is responsible for the unusual tribological properties. The unusual glycosylation of the keratins was found to be absolutely necessary for the described phenomenon. The scales were dissolved and reconstituted on a polymer surface resulting in properties similar to the original scale. Thus, we provide a pathway towards exploitation of the reconstituted scale material for future engineering applications.

New Iron-based SiC Spherical Composite Magnetic Abrasive for Magnetic Abrasive Finishing

SiC magnetic abrasive is used to polish surfaces of precise, complex parts which are hard, brittle and highly corrosion-resistant in magnetic abrasive finishing（MAF）. Various techniques are employed to produce this magnetic abrasive, but few can meet production demands because they are usually time-consuming, complex with high cost, and the magnetic abrasives made by these techniques have irregular shape and low bonding strength that result in low processing efficiency and shorter service life. Therefore, an attempt is made by combining gas atomization and rapid solidification to fabricate a new iron-based SiC spherical composite magnetic abrasive. The experimental system to prepare this new magnetic abrasive is constructed according to the characteristics of gas atomization and rapid solidification process and the performance requirements of magnetic abrasive. The new iron-based SiC spherical composite magnetic abrasive is prepared successfully when the machining parameters and the composition proportion of the raw materials are controlled properly. Its morphology, microstructure, phase composition are characterized by scanning electron microscope（SEM） and X-ray diffraction（XRD） analysis. The MAF tests on plate of mold steel S136 are carried out without grinding lubricant to assess the finishing performance and service life of this new SiC magnetic abrasive. The surface roughness（Ra） of the plate worked is rapidly reduced to 0.051 μm from an initial value of 0.372 μm within 5 min. The MAF test is carried on to find that the service life of this new SiC magnetic abrasive reaches to 155 min. The results indicate that this process presented is feasible to prepare the new SiC magnetic abrasive; and compared with previous magnetic abrasives, the new SiC spherical composite magnetic abrasive has excellent finishing performance, high processing efficiency and longer service life. The presented method to fabricate magnetic abrasive through gas atomization and rapid solidification presented can significantly improve the finishing performance and service life of magnetic abrasive, and provide a more practical approach for large-scale industrial production of magnetic abrasive.

Influence of abrasive hardness on erosion wear of abrasive air jets

To make clear the influence of abrasive hardness on the erosion effect,the erosion experiments of abrasive air jet with the same impact energy were carried out.The influence of abrasive hardness on the erosion effect is clarified by comparing the different erosion depths.The main conclusions are as follows.Under the same mass flow rate and mesh number,the abrasive with a higher density needs greater pressure irrespective of hardness.After erosion damage,the abrasive size exhibits a Weibull distribution.The shape parameterβand Weibull distribution function of four types of abrasives are derived by the least squares method;moreover,βis found to have a quadratic relation with abrasive hardness.The results of the erosion experiments show that abrasive hardness and erosion depth are quadratically related.By calculating the increase in surface energy after abrasive erosion crushing,it is found that abrasive hardness has a quadratic relation with surface energy and that the increases in erosion depth and surface energy consumption are basically identical.In conclusion,the effect is a soft abrasive impact when the ratio of abrasive hardness(Ha)to the material hardness(Hm)is<2.6,and it is a hard abrasive impact when Ha/Hm>3.

Research and application of water jet technology in well completion and stimulation in China

In recent years, rapid progress in the use of high pressure water jets （HPWJ） has been made in oil and gas well drilling, completion, and stimulation; and good results have been achieved in field applications. Advances in technologies and developments of well completion and stimulation with hydrajet are reviewed in this paper. Experiments were conducted to study the characteristics of abrasive water jetting and to optimize jet parameters, which can provide methods for the well completion and hydrajet fracturing. Deep-penetrating hydrajet perforating can create a 2-3 m clean hole with a diameter of 20-35 mm. Multilayer hydrajet fracturing is a process whereby multiple layers are stimulated in a single run without using mechanical packers, thereby reducing operation procedure and risk. Multilateral radial wells can be drilled using hydraulic jetting up to 100 m in length. The technique to remove sand particles and plugs with rotating self-resonating cavitating water jets in horizontal wellbores has been developed and oilfield-tested, which shows promising, cost effective prospects.

Two-Body Abrasive Wear of the Surfaces of Pangolin Scales

The Pangolin, a soil-burrowing animal, is covered with scales. These scales are often abraded by soil and rock and their surface is corrugated. The abrasive wear of the surface of the scales was examined. The scales were taken from a pangolin that had died of natural causes. The tests were run on a rotary disc abrasive wear tester. The abrasive material was quartz sand （96.5 wt.%） and bentonite （3.5 wt.%）. The morphology of the abraded surfaces and the abrasion were examined by stereoscopic microscopy and scanning electron microscopy. The concepts are proposed of ＂Guiding-Effect＂ and ＂Rolling-Effect＂ on the textured surfaces under free abrasive wear conditions and the critical dimensions of the ＂Rolling-Effect＂ are discussed.