铝酸钠溶液中钒酸盐的析出行为研究

以氧化铝生产流程中氢氧化铝的洗涤液为原料,研究了苛性碱浓度、反应温度及反应时间对溶液中钒酸盐析出情况的影响。结果表明,钒酸盐的析出率随苛性碱浓度的升高和反应时间的延长而增大,随反应温度的升高而减小。当铝酸钠溶液的苛性碱浓度为200g/L、反应温度为30℃、反应时间为72h时,溶液中的钒元素可减少60%以上。结晶析出的钒酸盐主要为钒酸钠和偏钒酸钠,其晶体结构为八面体。     

特种冶金生产流程的发展趋势

特种冶金是生产高端特殊钢和特种合金的主要手段,代表了一个国家的工业化发展水平,一直是国内外冶金技术竞争的制高点.本文首先回顾和总结了传统特种冶金技术的种类和主要生产流程;其次,概述了典型特殊钢品种的特种冶金生产流程;再次,对典型特钢企业的特种冶金生产流程进行了介绍;最后,对特种冶金生产流程的未来发展趋势作出预测.新技术将进一步促进特种冶金生产流程的变革与发展.     

Influence of Five-Year Degradation on Mechanical and Tribology Properties of Ultra-High-Molecular-Weight Polyethylene

Ultra-high-molecular-weight polyethylene (UHMWPE) has been the most commonly used bearing material in total joint replacement. The degradation of UHMWPE components has a notable influence on its mechanical properties. UHMWPE samples were immersed in simulated fluid (SBF) up to 5 years and the change in chemical composition and mechanical and wetting properties was investigated. It was found that the oxygen/carbon (O/C) ratio and crystallinity increased from 14.5 and 50.0% before immersion to 52.8 and 60.7% after immersion in SBF for 5 years, respectively. These resulted in a reduction in ball indentation hardness, scratch coefficient, peak load, and contact angle by 35.7, 21.0, 15.8, and 14.0%, respectively, after 5 years of immersion. The steady-state friction coefficient and wear rate increased 83.3 and 43.8%, respectively, after immersion in SBF for 5 years. The preliminary study indicated that the scratch test was an effective method to evaluate the surface performance of UHMWPE after short-term degradation, and small punch test was often used to assess the bulk properties of UHMWPE after long-term degradation.     

Numerical study of geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell

We have numerically studied the geometrical effects on the performance of an H-type cylindrical resonant photoacoustic cell, composed of one resonator and two symmetrical buffer cylinders, by performing simulations on the generation of acoustic waves in the cell. Here, the acoustic response (pressure), resonance frequency and quality factor are calculated for the cell performance, while the lengths and diameters of both resonator and buffer cylinders are considered for the geometrical parameters or dimensions. Our calculation solves linearized forms of the continuity equation, Navier-Stokes equation, energy equation, and equation of state using a finite element method under an assumption that the heat addition due to the laser passage and thus the variations in the velocity, pressure and temperature fields inside the cell are small enough. First, we performed a statistical analysis using a design of experiment method to evaluate the relative impacts of the cell dimensions on the acoustic response. Subsequently, we performed a parametric study to quantify the cell performance with the dimensional variations. Our results, along with the response surface methodology, provide guidance for a systematic design optimization of the cell for the best acoustic response. The approach in this study may be applied to the design of various types of resonant photoacoustic spectroscopy devices.     

Finite element analysis of the impact of liner thickness and hydrodynamic limit on the penetration depth of a shaped charge warhead

In this work, an identification method for the hydrodynamic limit of shaped charge jets (SCJs) is proposed using numerical analysis. To identify the hydrodynamic limit, we consider situations where two targets of the same density but different strengths are penetrated by the same SCJ. As a result, the SCJ corresponding with the hydrodynamic theory is a jet region with a velocity larger than 4 km/s. In addition, an investigation based on the hydrodynamic limit and liner thickness indicates that the penetration capability before and after the hydrodynamic limit improves as apex thickness decreases and base thickness increases, respectively. The simple and clear identification of the hydrodynamic limit is expected to be possible using the proposed method. Accordingly, a selective and organized liner thickness design can be developed.

     

An improved thermal model for characteristics analysis of multi-link ultra-precision press system

Journal of Mechanical Science and Technology - In traditional models, only the effect of temperature change of bearings on the heat generation power and thermal contact resistance is considered....     

Lyapunov exponent of friction-induced vibration under smooth friction curve

This paper studies the nonlinear behavior of the friction-induced vibration by using spring-mass model subject to the smooth frictionvelocity curve. The nonlinearity and instability of the friction may produce the chaotic vibration depending on the friction curve. In order to show this, the Lyapunov exponents are calculated for a variety of the slope and magnitude in the smooth friction curve. In turn, the dependency of the friction curve on the chaotic attractor is illustrated.     

Effects of work hardening models on low-cycle fatigue evaluations of coiled tubing with CT-100 steel

In the present study, low-cycle fatigue life of a coiled tubing (CT) with a CT-100 steel was evaluated by using various work hardening models. Tensile and low-cycle fatigue tests were performed, and experimental results were used to calibrate material model constants. A nonlinear finite element model was constructed in the ABAQUS program by using a CT fatigue test machine. During the test cycles, bending and straightening conditions were repeated and histories of strains were collected. The multiaxial low-cycle fatigue life was calculated by using Manson–Coffin relation and Tresca criterion. The kinematic and combined hardening models can be used to evaluate the fatigue life of CT, and their results are conservative compared with the fatigue test results. Results of the present study can be used as the basic data in establishing CT fatigue analysis.     

Wear resistance characteristics of materials used in oil sands plants

The surge in demand for natural resources has shifted the focus of the international community toward the development of oil sands, shale oil, shale gas and other non-traditional energy sources. In extreme environments, materials used in petroleum gas plant modules are accompanied by various problems caused by low-temperature brittleness such as damage, corrosion and wear. Many researchers have been conducting studies to discover a suitable material whose lifespan could be improved by performing characteristics analyses and performance assessments. In this study, a material characteristics assessment was conducted based on a wear resistance test on materials that are commonly used at oil sands plants. Prior to a wear resistance test, a chemical composition analysis was performed on each of the specimens, and tensile, impact, hardness and corrosion tests were carried out to examine the correlation between their results with the results of the wear resistance test. Each test was performed according to ASTM G 105 standards, and the change in weight according to wear length was analysed for each material to determine the related tendencies. In addition, the results of the wear test were derived by analysing the change in the mass of the specimen before and after the test, and the surface roughness was assessed to analyse the performance related to wear and define the service life. The aim was to use these results to select a material that would be suitable for the abrasive environment of the key equipment and materials of plants.     

Geometric accuracy long-term continuous monitoring using strain gauges for CNC machine tools

The accuracy retentivity has become one of the most important performance index of CNC machine tools, which are affected by many complicated factors, such as stress-induced deformations, bolt preload loss, wear, and the manufacturing process itself. The long-term continuous monitoring can bridge the wide gap between the accuracy retentivity and the manufacturing processing of machine tools. In this research, a geometric accuracy monitoring approach using the discrete strain gauges is proposed. The machine basis is firstly simplified based on the structural characteristics and stress condition. And, the straightness is evaluated through the reconstructed strain field of machine tool basis. Finally, to verify the validity of our method, a vertical machining center has been monitored for 7 months using the established wireless monitoring system.