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1
Content available Influence of pick layouts on the performance of bolter miner cutting head
Qiao S., Wang A. L., Xia Y. M., Liu Z. Z., Liu J. S., Yang M.
Mining Science
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2018
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Vol. 25
147--160
EN
A bolter miner is a new type of mining machinery with cutting and anchoring functions. In order to study the best pick layout of bolter miner cutting head. Based on the constitutive relation of Holmquist-Johnson-Cook (HJC), three simulation models of different cutting heads were established, and the whole crushing process of coal-rock was simulated by finite element method (FEM). The influence of the cutting head on the cutting performance under the condition of different rotational speeds and pick layouts was intensively studied. The results show that the relationship of load fluctuation coefficient among the three pick layouts is as follows: sequential type > hybrid type I > checkerboard type. The circumferential pick layouts can reduce the load fluctuation coefficient of cutting head. The rotational speed from 20 to 40 r/min, the torque linearly decreases with the increase of rotational speed. The rota-tional speed increases from 40 to 50 r/min, the cutting torque is relatively stable. The specific energy of chessboard type is relatively higher than the other three cutting heads. The difference of specific energy between sequential type and hybrid type I is not more than 5.5%, and the reality of the simulation is verified by cutting experiments. The results were successfully applied to the first shield type bolter miner in China.
2
Content available Finite element analysis of load characteristic of shield bolter miner cutting head under complex coal seam condition
Qiao S., Xia Y. M., Liu Z. Z., Liu J. S., Ning B., Wang A. L.
Mining Science
|
2017
|
Vol. 24
85--97
EN
Aiming at the complex conditions of the first shielded bolter miner in the actual work, the mechanical model of bolter miner cutting head was established. Based on cutting mechanism of the conical pick and the cutting head, the cutting head load and torque analysis model under complex coal seam were established. The dynamic characteristics of load and torque in the process of cutting head are analyzed under three different working conditions of cutting roof-coal layers, coal-floor layers and coal seam by finite element method. The results show that when the damage variable D=1, the coal-rock completely lacks the bearing capacity, and it forms arc-shaped crushing groove on the coal-rock. The large difference of torque between roof-coal layers and the roof-coal layers in the conical pick is 112 Nm, which indicates that the cutting head has the best performance with cutting the coal seam first and then cutting the rock. In the process of excavation, the load fluctuation coefficient of cutting the coal-floor layers and roof-coal layers is about 1.2 times of that of the coal seam. The results can provide a reference for the efficient cutting and performance evaluation of the bolter miner.
3
Content available remote First principles study on the improved dehydrogenating properties of MgH2 systems with metal fluorides
Zhou D. W., Liu J. S., Xu S. H., Chen G. Y.
Materials Science Poland
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2010
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Vol. 28, No. 1
229--243
EN
Energies and electronic structures of MgH2 systems were determined from the first principles calculations to explain the improving of their dehydrogenating properties by addition of metal fluorides as catalysts. These calculations show that a Mg vacancy can improve the thermodynamics of MgH2 systems and Mg atom replaced for Fe, Ti, Zr, V, Ni, Nb, Cr, Cu is energetically more favourable than formation of Mg vacancies at lower temperatures. Calculations of density of states (DOS) provide a particularly good explanation for a close agreement between the experimental results and theoretical predictions for improvements to the dehydrogenation kinetics of MgH2 systems for NiF2, NbF5, ZrF4 used as the catalysts.
4
Content available remote Electronic mechanism of dehydrogenation of the Mg-Ge mixture during milling under hydrogen
Zhou D. W., Liu J. S., Zhang J., Huang Z. G., Peng P.
Materials Science Poland
|
2010
|
Vol. 28, No. 1
43--54
EN
The energy and electronic structure of the hydride phase are calculated by using the first-principles plane-wave pseudopotential method to explain experimental results of milling of a Mg-Ge mixture under hydrogen. The electronic mechanism of dehydrogenation of the Ge alloying system is also considered. By calculating heats of formation of MgH2 and (MgGe)H2 solid solutions, it is found that the structural stability of the alloying system is reduced when a little Ge dissolves in MgH2. As the Ge content increases, Mg2Ge may be formed by the reaction: 2MgH2 + Ge - Mg2Ge + 2H2, at the same time, the dehydrogenating properties of the system are improved compared with that of MgH2, but are reduced by contrast with that of (MgGe)H2 solid solutions. Based on the analysis of the densities of states (DOS) of MgH2 before and after Ge alloying, it is found that the improvement of the dehydrogenating properties of MgH2 dissolved into a little Ge is attributed to the weakened bonding between magnesium and hydrogen caused by the interactions between Ge and Mg.
5
Content available remote Density functional study of Mg2FeH6 complex hydride
Zhang J., Huang Y. N., Long G. G., Zhou D. W., Liu J. S.
Materials Science Poland
|
2010
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Vol. 28, No. 1
357--366
EN
Mg2FeH6, which has the highest volumetric hydrogen density, is considered a promising hydrogen storage material. Within the framework of the density functional theory, the crystal structure, physical properties, electronic structure and formation capacity of Mg2FeH6 complex hydride have been investigated. The optimized structural parameters correspond closely with the experimental data from X-ray and neutron powder diffraction measurements. A detailed study of the electronic structures, including the energy band, density of states (DOS) and charge density distribution, reveals the orbital hybridization and bonding characteristics within this hydride. It was shown that Mg2FeH6 is a semiconductor with the energy gap of ca. 2.3347 eV, and that a mixed ionic-covalent bond between Fe and H in FeH6 complexes is embedded in the matrix of Mg2+ cations. The calculated formation enthalpies of Mg2FeH6 , based on the possible synthesis routes, indicate that optimum conditions are achieved if this hydride is fabricated from pure elements, and that the preparation of other compounds would lead to inferior synthesis.
6
Content available remote First-principles plane-wave pseudopotential method calculations for Cu alloying Mg2 Ni hydride
Zhang J., Zhou D. W., Peng P., Liu J. S.
Materials Science Poland
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2008
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Vol. 26, No. 3
681--691
EN
Energetics and electronic structures have been calculated based on the first-principles plane-wave pseudopotential method for Cu alloying Mg2Ni phases and the corresponding hydrides. These calculations show that the Mg2Ni(II)1-xCux (x = 1/3) phase has the highest structural stability and Cu alloying Mg2Ni hydride benefits the improvement of the dehydrogenating properties of the system, which is also well explained through the density of states (DOS) and the charge distributions of Mg2Ni phases and Mg2Ni hydrides with and without Cu alloying.
7
Content available remote Energetics, electronic structure, and structure stability of the calcium alloying Mg17Al12 phase from first principles calculations
Zhou D. W., Peng P., Liu J. S.
Materials Science Poland
|
2007
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Vol. 25, No. 1
145--153
EN
The energetics and electronic structure of the Ca alloying Mg 17Al12 phase have been calculated using a first principles pseudopotential plane-wave method based on the density functional theory. According to the calculation results, the negative heat of formation and the cohesive energy of (Mg17-xCax)Al12 (x = 0. 1, 4, 12) gradually increase when the Mg atoms at the I, II, III positions of the Mg17Al12 phase are substituted with Ca, which indicates that the alloying ability of (Mg17-xCax)A,)Al12 with the replacement of Ca for Mg(III) atoms is the strongest among the three substitutions and (Mg5Ca12)Al12 formed in this manner has the highest structural stability. After comparing the densities of states (DOS) for (Mg17-xCax)Al12 (x = 0. 1, 4, 12), it is found that the increase in the structural stability of Mg 17Al12 alloyed by Ca attributes to an increase in the bonding electron numbers at energy levels below the Fermi level, which mainly originates from the contribution of the valence electron numbers of Al (p) and Ca (s) orbitals.
8
Content available remote Alloying effects on the energy and electronic structures of vanadium hydrides
Zhou D. W., Zhang J., Peng P., Liu J. S.
Materials Science Poland
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2007
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Vol. 25, No. 4
947--956
EN
A first-principles plane-wave pseudopotential method based on the density functional theory is used to investigate the energy, electronic structure and stability of VH and VH2 alloyed by a 3d transition metal. It is found that the stability of VH and VH2 decreases after alloying, which originates from a small number of bonding electrons at the Fermi level. In the case of VH2, the ionic interaction is dominant between alloying atoms and H atoms, while the ionic bond interaction between the later 3d alloying atoms and H atoms is important in VH.
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