Hong Sun

Characteristics Analysis of TBM Disc Cutter Ring

Disc cutter is the key part in Tunnel Boring Machine (TBM). Wear and tear of disc cutter is the main reason of low efficiency and high cost of this machine. Forces and deformations of disc cutter ring are foundation for its design and assembly. In this paper, the analysis of stress and deformation are carried to study their distribution; Wear mechanism of disc cutter ring is presented; modal analysis is carried to study the vibration of disc cutter ring. The results show the yield strength and rigidity of disc cutter ring is very high; disc cutter ring can avoid resonance and meet the engineering requirement. The results are very helpful for digital design of disc cutter ring used in different geology conditions.

Oxygen Reduction Reaction on Pt Surface in PEM Fuel Cell Cathode Based on the First-Principles Molecular Dynamics

In proton exchange membrane (PEM) fuel cell cathode, oxygen reduction reaction (ORR) behavior have important effects on fuel cell performance. In this paper, the dynamic oxygen adsorption model and then the redox reaction model for hydrogen and oxygen system were established on the surface of the electricity catalyst Pt. The reaction process of hydrogen and oxygen on the surface of Pt was simulated by first-principles molecular dynamics method, and the influence of temperature on oxygen reduction reaction characteristics was analyzed. The simulation results show that the oxygen atom adsorption on the Pt (111) surface and reaction with the first hydrogen atom are the control step of the oxygen reduction reaction; and the oxygen reduction reaction accelerates with increasing temperature, but the temperature does not affect the geometric structure of the products in the oxygen reduction reaction steps. The results of the simulation agree well with our previous first-principles calclation, and this will be helpful for understanding the mechanism of oxygen reduction reaction in PEM fuel cell cathode.

Research on the Optimal Disc Cutter Spacing for Rock-Breaking Based on ANSYS

Objective: To study the influence of disc cutter spacing on rock fragmentation efficiency and optimize cutter layout and improve the efficiency of disc cutter. Method: ANSYS, a finite element software was used to simulate double disc cutter cutting process. Result: Find a good corresponding relationship between penetration and cutter spacing. At the process of sandstone, if disc cutter spacing as 54 ~ 55 mm, rock crushing as the largest and rock fragmentation efficiency is the highest; with the penetration of 10 mm. If disc cutter spacing as 66~68.5mm, rock crushing as the largest and rock fragmentation efficiency is the highest with the penetration of 15 mm. Changing the cutter spacing and penetration, rock stress and broken degree will also change. Conclusion: Double disc cutters change within the range of best cutter spacing, cutter spacing is proportional to the rock crushing. If the cutter distance is greater than the best cutter spacing, the ledge will be appeared. For one type of rocks, the penetration would have some effects on the optimal cutter spacing. If the penetration increases, the optimal cutter spacing increases gradually, at the time of other construction parameters unchanged.

Design and Simulation of the Hydraulic System for the Disc Cutter of the Rock Hob Test-Bed

Rock tunnel boring machine is one of the main machineries and equipments for underground engineering, and the failure of its disc cutter is the main failure form of this machinery. The experiment on the failure and wear of the disc cutter is difficult. In this paper, a rock hob test-bed is designed, and the hydraulic-driven system of its disc cutter of rock hob test-bed is simulated; the effect of load and flow rate of hydraulic oil in this hydraulic system on characteristics of this disc cutter system is analyzed. The results show that the vertical movement speed of disc cutter is directly proportional to the flow rate; the effect of the load on this speed and the vertical pressure can be ignored; the delay time of the movement of the disc cutter to the flow rate of hydraulic oil is proportional to the load. These results are very helpful to the structure optimization of disc cutter system of rock tunnel boring machine and the improvement of working efficiency.

Design and Simulation of the Hydraulic System for the Rock Hob Test-Bed

Rock tunnel boring machine is one of the main machineries and equipments for underground engineering ,and the failure of tool systems is the main failure form of this machinery. Rock hob test-bed is the only testing equipment for tool failure and wear. In this paper, the hydraulic-driven system of the rock hob test bench is designed and simulated, and the effect of load and flow rate of hydraulic oil in this hydraulic system on characteristics of this test-bad is analyzed. The results show that the horizontal movement speed of test bench is directly proportional to the flow rate, but the effect of the load on this speed can be ignored; the delay of the movement of the test bench are proportional to the load. These results are very helpful to the structure optimization of tool system and the improvement of working efficiency.

Oxygen Reduction Reaction of PEMFC Cathode by Molecular Simulations

Cathode catalyst layer plays an important role in PEMFC. Electrochemical reaction in cathode catalyst layer is a control process for the performance in PEMFC. In this paper, oxygen reduction reaction (ORR) is studied by molecular simulations based on a series pathway which consist of four steps. We calculated the free energy of four steps respectively by molecular simulations. Comparing free energy of our steps, we found that the fourth step can release more energy than the other steps. At the same time, we found that the energy released in ORR is decreased with the increase of temperature. The process of the first step in the series pathway release less energy than that of other steps. The results are very helpful for optimization of construction in the cathode and improving performance of PEM fuel cell.

Proton Transport in Nafion117 Membranes by Molecular Dynamics

A molecular dynamics model was performed to study the proton transport of Nafion series membrane which is often used in low temperature fuel cells. The simulations intents to investigate the microstructure and the phenomenon of the proton transport processing. The model includes all-atom of main and side chains. The force field includes intermolecular Coulomb and Lennard-Jones terms and intra-molecular terms for harmonic bond stretch potentials, harmonic angle bend potentials and cosine terms for the torsions. The simulations were carried out in two cube systems at different temperature where water content differed from 5 and 10 water molecules per acid group in the polymer, respectively. The results showed that proton transport affected with water content by analyses of snap- shots of the MD simulation, the radial distribution functions between the sulfur atoms of SO3− groups, between the oxygen atoms of H3O+ ions, between oxygen atoms of water molecules and Nafion atoms at various stages.

Study on Precise Rubbing Technology of HIPSN Ceramic Balls

One of the most applications of HIPSN(Hot-Isocratic Pressed Silicon Nitride) ceramic ball bearings is applied to the high-speed spindle of numerical control machine tools and high-speed precise mechanics. However, it is very difficult to process the HIPSN ceramic ball bearing. In this paper, a new grinding process method, taper rubbing method, is applied to process the HIPSN ceramic ball. Mechanical analysis of taper rubbing method is given, and the influence of grinding parameters on the ceramic material excision rate, surface quality of ceramic ball and wear and tear ratio of diamond wheel is studied by taper rubbing method. The experimental results show that the HISPN ceramic balls of G3 and G5 are obtained with taper rubbing method by properly controlling the motion of HIPSN ceramic balls and selecting reasonable processing technological parameters.