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Coal augers is a new type of mining equipment used in thin coal seam, and directional drilling performance of its drilling tools becomes the key issue in the equipment service life and drilling efficiency. The drilling test bench of a three-bit coal auger is constructed to study vibration and deflection performance of its drilling tools in this paper. Based on some reasonable simplifications and hypotheses of drilling tools, simulation model of a three-bit coal auger is established to analyze its vibration and deflection performance with different drilling depths. Then a novel drill rod stabilizer is designed and the simulation model of a three-bit coal auger with this stabilizer is constructed compared with a normal coal auger to study vibration and deflection performance of drilling tools, which provides scientific basis for stabilizers’ arrangement form. Research shows that: the simulation results accords with test results, which verifies correctness and rationality of simulation; vibration and deflection of drilling tools become greater with drilling depth increasing; drill rod stabilizers can effectively reduce drilling tools’ vibration and deflection, and are arranged every 5 drill rods and air pipes which is optimal decision.

To investigate the rock fragmentation mechanism and its influence factors under discontinuous water-jet impact, the fluid-structure coupled smoothed particle hydrodynamics (SPH) and finite element analysis (FEA) was used to simulate the rock fragmentation process. A rate-dependent constitutive model was adopted to describe the mechanical behavior of rock, and the shock equation of state was used to simulate the water-jet. The rock fragmentation statuses under continuous and discontinuous water-jet impact were simulated and compared under the same initial impact energy, and the rock failure mechanisms, such as the crushing zone and crack formation, were investigated through the elements of pressure and stresses as a function of time. The effects of water-liquids distance and length on rock fragmentation by the discontinuous water-jet were also analyzed. With the same energy, the rock fragmentation performance of the discontinuous water-jet was better than that of the continuous water-jet. The failure of the rock crushing zone was mainly caused by plastic behavior; however, the crack propagation presented brittle failure. The “water cushioning effect” would appear when the water-liquids distance was too small, which restricted the impact effect on rock fragmentation. Discontinuous water-jet with a shorter water-liquid length would result in a deeper crushing zone and volume fragmentation of rock.

The effects of rare earth element on the microstructures, tensile properties and electrical properties of aluminum alloys have brought about widespread interesting in the last few decades. However, contradictory results are usually reported, and there is little research concerning the effect law of trace lanthanum (the addition is below 0.1 wt%) on the as-cast microstructures, electrical conductivity and the tensile properties of 8176 aluminum alloy which is one of the most widely used aluminum conductor alloy. In this work, solidification experiments were performed with 8176 aluminum alloy and the effects of lanthanum addition was investigated. The results demonstrated that the lanthanum addition can promote the refinement of the alpha Al grains, the modification of Al13Fe4 intermetallic phase. The elongation and electrical conductivity simultaneously enhance with lanthanum addition when the additive amount is less than 0.08%, while the elongation decreases when the additive amount reaches to 0.1% due to the formation of intermetallic phase. The enhancement of the elongation is mainly ascribed to the modification of Al13Fe4 intermetallic phase, the enhancement of the electrical conductivity is attributed to the reduction of solid solubility of Si and Fe elements in Al matrix. These results indicate that the addition of micro-alloying element lanthanum is a prospective method for simultaneously elevating the electrical conductivity and tensile properties of the 8176 aluminum alloy.

Dust suppression is an urgent issue for coal mines because the problem of dust has not been solved effectively, harms the health of miners and is a potentially serious threat to the mine environment and safety. Therefore, an effective method for dust suppression is highly desired. In this work, the formation and suppression of cutting dust are analyzed, and a method for suppressing the cutting dust during the formation process in the crushing zone is discussed. Internal and external water jets are used for dust suppression based on the cutting dust formation mechanism and are examined in rock cutting experiments using a newly developed test-bed. The use of internal water jets reduces the cutting dust concentration by over 90% on average, with no obvious relationship between the dust concentration and the water pressure. The use of external water jets reduces the cutting dust by over 65% on average, with an increasing reduction in dust concentration with increasing water pressure from 5 MPa to 20 MPa. Refereed/Peer-reviewed

To investigate the rock fragmentation and its influence factors under the impact load of water jet, a numerical method which coupled finite element method (FEM) with smoothed particle hydrodynamics (SPH) was adopted to simulate the rock fragmentation process by water jet. Linear and shock equations of state were applied to describe the dynamic characteristics of rock and water, respectively, while the maximum principal stress criterion was used for the rock failure detection. The dynamic stresses at the selected element containing points in rock are computed as a function of time under the impact load of water jet. The influences of the factors of boundary condition, impact velocity, confining pressure, and structure plane on rock dynamic fragmentation are discussed.

Copyright © 2014 Hongxiang Jiang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., Rock breakage by coupled mechanical and hydraulic action has been developed over the past several decades, but theoretical study on rock fragmentation by mechanical tool with water pressure assistance was still lacking. The theoretical model of rock breakage by mechanical tool was developed based on the rock fracture mechanics and the solution of Boussinesq’s problem, and it could explain the process of rock fragmentation as well as predicating the peak reacting force. The theoretical model of rock breakage by coupled mechanical and hydraulic action was developed according to the superposition principle of intensity factors at the crack tip, and the reacting force of mechanical tool assisted by hydraulic action could be reduced obviously if the crack with a critical length could be produced by mechanical or hydraulic impact. The experimental results indicated that the peak reacting force could be reduced about 15% assisted by medium water pressure, and quick reduction of reacting force after peak value decreased the specific energy consumption of rock fragmentation by mechanical tool. The crack formation by mechanical or hydraulic impact was the prerequisite to improvement of the ability of combined breakage.

U svrhu istraživanja opterećenja reznih glava opremljenih vodenim mlazom razvijena je oprema za ispitivanje fragmentacije stijene pomoću rezne glave. Vodeni mlaz se tu upumpavao u središte konusnog šiljka (pick). Bez vodenog mlaza, karakteristični indeks reznog momenta i vlačne sile eksponencijalno se povećao s tlačnom čvrstoćom stijene. Nije primijećena jasna povezanost između karakterističnih indeksa reznog momenta i tlačne čvrstoće stijene u slučaju s vodenim mlazom, ali je učinak vodenog mlaza na vlačnu silu rezne glave bio relativno postojan. Rezni moment i vlačna sila su se smanjili za 20 % do 40 % kada je tlačna čvrstoća stijene bila niža od tlaka vodenog mlaza. Ipak, vodeni mlaz koji je pomogao u fragmentaciji stijene, bio je manje učinkovit kad je tlak vode bio slabiji od tlačne čvrstoće stijene. Omjer između tlaka vodenog mlaza i tlačne čvrstoće stijene može pomoći kod prepoznavanja učinkovitosti vodenog mlaza kod reznih glava za fragmentaciju stijene., A test bed for rock fragmentation by cutting head was developed to investigate the load of water jet-assisted cutting heads. In this test bed, water jet was pumped into the center of the conical pick. In the case without water jet, the characteristic index of the cutting torque and pulling force increased with the rock compressive strength exponentially. No obvious relationship was observed between the characteristic indexes of the cutting torque and the rock compressive strength for the case with water jet, but the effect of the water jet on the pulling force of the cutting head was relatively stable. The cutting torque and pulling force were decreased by 20 % to 40 % when the rock compressive strength was lower than the water jet pressure. However, the water jet that assisted in rock fragmentation was less effective when the water pressure was lower than the rock compressive strength. The ratio between water jet pressure and rock compressive strength can help recognize the efficiency of water jets for rock fragmentation by cutting head.

Continuous solidification experiments were carried out with Cu-Bi-Sn alloys under the effects of Electric Current Pulses (ECPs). A model describing the microstructure evolution was developed. The formation of the microstructure in the continuously solidified alloys was calculated. The calculations demonstrated that ECPs mainly affect the solidification process through changing the energy barrier for the nucleation of the minority phase droplets (MPDs). When the matrix liquid has a lower electric conductivity compared to the MPD, the ECPs lead to a decrease in the energy barrier for the nucleation of the MPDs which then promote the formation of a finely dispersed microstructure. When the matrix liquid has a higher electric conductivity compared to the MPD, the ECPs cause an increase in the energy barrier for the nucleation and lead to the formation of a phase segregated microstructure.

Gas-solid injectors are widely used feeding equipment in pneumatic conveying systems. The performance of a gas-solid injector has a significant influence on the type of application it can be employed for. To determine the key factors influencing the injection performance and address clogging problems in a gas-solid injector during a pneumatic conveying process, the particle trajectory model has been utilised as a means to perform simulations. In the particle trajectory model, the gas phase is treated as a continuous medium and the particle phase is treated as a dispersed phase. In this work, numerical and experimental studies were conducted for different nozzle positions in a gas-solid injector. A gas-solid injector test-bed was constructed based on the results of the simulations. The results show that the nozzle position is the key factor that affects the injection performance. The number of extrusive particles first increases and then decreases with the change in the nozzle position from left to right. Additionally, there is an optimum nozzle position that maximises the injection mass and minimises the number of particles remaining in the hopper. Based on the results of this work, the injection performance can be significantly increased and the clogging issues are effectively eliminated.

A test-bed was developed to perform the rock cutting experiments under different cutting conditions. The fractal theory was adopted to investigate the fractal characteristic of cutting load time series and fragment size distribution in rock cutting. The box-counting dimension for the cutting load time series was consistent with the fractal dimension of the corresponding fragment size distribution, which indicated that there were inherent relations between the rock fragmentation and the cutting load. Furthermore, the box-counting dimension was used to describe the fractal characteristic of cutting load time series under different conditions. The results show that the rock compressive strength, cutting depth, cutting angle, and assisted water-jet types all have no significant effect on the fractal characteristic of cutting load. The box-counting dimension can be an evaluation index to assess the extent of rock crushing or cutting. Rock fracture mechanism would not be changed due to water-jet in front of or behind the cutter, but it would be changed when the water-jet was in cutter.