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Determining casting defects in near-net shape casting aluminum parts by computed tomography

Jiehua LI, Bernd OBERDORFER, Daniel HABE, Peter SCHUMACHER

《机械工程前沿（英文）》 2018年第13卷第1期页码 48-52 doi: 10.1007/s11465-018-0493-y

摘要：

Three types of near-net shape casting aluminum parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting (Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy), die casting (A356, Al-7Si-0.3Mg), and semi-solid casting (A356, Al-7Si-0.3Mg), respectively. Unlike die casting (second part), low-pressure die casting (first part) significantly reduced the formation of casting defects (i.e., porosity) due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi-solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.

关键词： near-net shape casting aluminum parts casting defects low pressure die casting die casting semi-solid casting computed tomography

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Semi-solid materials for controlled release drug formulation: current status and future prospects

Michelle TRAN,Chun WANG

《化学科学与工程前沿（英文）》 2014年第8卷第2期页码 225-232 doi: 10.1007/s11705-014-1429-7

摘要： Semi-solid materials represent an important category of inactive ingredients (excipients) of pharmaceutical products. Here we review several common semi-solid polymers currently used in the controlled release formulations of many drugs. These polymers are selected based on their importance and broad scope of application in FDA-approved drug products and include several polysaccharides (cellulose, starch, chitosan, alginate) and carbomers, a group of mucoadhesive synthetic polymers. Glyceride-based polymers used in self-emulsifying drug delivery systems (SEDDS) will also be discussed for its importance in formulating poorly water-soluble drugs. Unique features and advantages of each type of semi-solid materials are discussed and examples of their use in oral delivery of drugs are provided. Finally, future prospects of developing new and better semi-solid excipients are discussed with the objective of facilitating clinical translation.

关键词： controlled release drug delivery semi-solids polymer excipient

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连续铸钢前沿技术的工程化

干勇

《中国工程科学》 2002年第4卷第9期页码 12-18

摘要：

论述了具有我国自主知识产权的高效连铸和薄板坯连铸工程化关键技术的特点；介绍了连续铸钢领域轻压下、液压非正弦振动、电磁连铸等前沿技术的开发现状；阐述了传统连铸技术超高效率、高品质化及近终形连铸、电磁连铸开发的研发方向。

关键词：连续铸钢高效连铸薄板坯连铸轻压下电磁连铸

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Utilization of waste vanadium-bearing resources in the preparation of rare-earth vanadate catalysts for semi-hydrogenation

《化学科学与工程前沿（英文）》 2022年第16卷第12期页码 1793-1806 doi: 10.1007/s11705-022-2191-x

摘要： Recycling industrial solid waste not only saves resources but also eliminates environmental concerns of toxic threats. Herein, we proposed a new strategy for the utilization of petrochemical-derived carbon black waste, a waste vanadium-bearing resource (V > 30000 ppm (10 ⁻⁶)). Chemical leaching was employed to extract metallic vanadium from the waste and the leachate containing V was used as an alternative raw material for the fabrication of vanadate nanomaterials. Through the screening of various metal cations, it was found that the contaminated Na⁺ during the leaching process showed strong competitive coordination with the vanadium ions. However, by adding foreign Ce³⁺ and Y³⁺ cations, two rare-earth vanadates, viz., flower-like CeVO₄ and spherical YVO₄ nanomaterials, were successfully synthesized. Characterization techniques such as scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infrared, and N₂ physisorption were applied to analyze the physicochemical properties of the waste-derived nanomaterials. Importantly, we found that rare-earth vanadate catalysts exhibited good activities toward the semi-hydrogenation of α,β-unsaturated aldehydes. The conversion of cinnamaldehyde and cinnamic alcohol selectivity were even higher than those of the common CeVO₄ prepared using pure chemicals (67.2% vs. 27.7% and 88.4% vs. 53.5%). Our work provides a valuable new reference for preparing vanadate catalysts by the use of abundant vanadium-bearing waste resources.

关键词： petrochemical solid wastes vanadium recovery resource utilization nanomaterials semi-hydrogenation

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Determination of selected semi-volatile organic compounds in water using automated online solid-phase

Yongtao LI, Christina L. MCCARTY, Ed J. GEORGE

《环境科学与工程前沿（英文）》 2011年第5卷第3期页码 417-425 doi: 10.1007/s11783-011-0310-x

摘要： A rapid, sensitive, and cost-effective analytical method was developed for the analysis of selected semi-volatile organic compounds in water. The method used an automated online solid-phase extraction technique coupled with programmed-temperature vaporization large-volume injection gas chromatography/mass spectrometry. The water samples were extracted by using a fully automated mobile rack system based on x-y-z robotic techniques using syringes and disposable 96-well extraction plates. The method was validated for the analysis of 30 semi-volatile analytes in drinking water, groundwater, and surface water. For a sample volume of 10 mL, the linear calibrations ranged from 0.01 or 0.05 to 2.5μg·L , and the method detection limits were less than 0.1μg·L . For the reagent water samples fortified at 1.0μg·L and 2.0?μg·L , the obtained mean absolute recoveries were 70%–130% with relative standard deviations of less than 20% for most analytes. For the drinking water, groundwater, and surface water samples fortified at 1.0μg·L , the obtained mean absolute recoveries were 50%–130% with relative standard deviations of less than 20% for most analytes. The new method demonstrated three advantages: 1) no manipulation except the fortification of surrogate standards prior to extraction; 2) significant cost reduction associated with sample collection, shipping, storage, and preparation; and 3) reduced exposure to hazardous solvents and other chemicals. As a result, this new automated method can be used as an effective approach for screening and/or compliance monitoring of selected semi-volatile organic compounds in water.

关键词： automated solid-phase extraction programmed-temperature vaporization large-volume injection gas chromatography/mass spectrometry semi-volatile organic compounds water analysis

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Novel casting processes for single-crystal turbine blades of superalloys

Dexin MA

《机械工程前沿（英文）》 2018年第13卷第1期页码 3-16 doi: 10.1007/s11465-018-0475-0

摘要：

This paper presents a brief review of the current casting techniques for single-crystal (SC) blades, as well as an analysis of the solidification process in complex turbine blades. A series of novel casting methods based on the Bridgman process were presented to illustrate the development in the production of SC blades from superalloys. The grain continuator and the heat conductor techniques were developed to remove geometry-related grain defects. In these techniques, the heat barrier that hinders lateral SC growth from the blade airfoil into the extremities of the platform is minimized. The parallel heating and cooling system was developed to achieve symmetric thermal conditions for SC solidification in blade clusters, thus considerably decreasing the negative shadow effect and its related defects in the current Bridgman process. The dipping and heaving technique, in which thin-shell molds are utilized, was developed to enable the establishment of a high temperature gradient for SC growth and the freckle-free solidification of superalloy castings. Moreover, by applying the targeted cooling and heating technique, a novel concept for the three-dimensional and precise control of SC growth, a proper thermal arrangement may be dynamically established for the microscopic control of SC growth in the critical areas of large industrial gas turbine blades.

关键词： superalloy investment casting Bridgman process directional solidification single crystal turbine blade

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Novel technologies for the lost foam casting process

Wenming JIANG, Zitian FAN

《机械工程前沿（英文）》 2018年第13卷第1期页码 37-47 doi: 10.1007/s11465-018-0473-2

摘要：

Lost foam casting (LFC) is a green precision casting process categorized as a near net forming technology. Yet, despite its popularity, it still suffers from some technological problems, such as poor filling ability of the castings, coarse and non-dense microstructure, low mechanical properties for the Al and Mg LFC processes, and defective carburization for the low carbon steel LFC process. These drawbacks restrict the development and widespread application of the LFC process. To solve these problems, the present study developed several novel LFC technologies, namely, LFC technologies under vacuum and low pressure, vibration solidification, and pressure solidification conditions; expendable shell casting techno- logy; and preparation technology of bimetallic castings based on the LFC process. The results showed that the LFC under vacuum and low pressure evidently improved the filling ability and solved the oxidization problem of the alloys, which is suitable for producing complex and thin-wall castings. The vibration and pressure solidifications increased the compactness of the castings and refined the microstructure, significantly improving the mechanical properties of the castings. The expendable shell casting technology could solve the pore, carburization, and inclusion defects of the traditional LFC method, obtaining castings with acceptable surface quality. Moreover, the Al/Mg and Al/Al bimetallic castings with acceptable metallurgical bonding were successfully fabricated using the LFC process. These proposed novel LFC technologies can solve the current technological issues and promote the technological progress of the LFC process.

关键词： LFC under vacuum and low pressure vibration solidification pressure solidification expendable shell casting bimetallic castings

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Hybrid forming mechanism of patternless casting and laser cladding

Zhongde SHAN, Fuzhen SUN, Yang LIU

《机械工程前沿（英文）》 2019年第14卷第4期页码 393-401 doi: 10.1007/s11465-019-0550-1

摘要： In accordance with the requirement of manufacturing dies quickly and economically, a hybrid forming method of stamping dies for automobile panels is proposed. The method combines digital patternless casting and high-power laser cladding. An experimental study is conducted on the hybrid forming process and its trial production and application in the manufacturing of stamping dies for typical panels. Results prove that the laser cladding layer exceeds HRC60 (Rockwell hardness) and thus meets the production efficiency requirement of automobile dies. The rate of defects is well controlled. Compared with traditional technology, this technology has remarkable advantages and advancement.

关键词： patternless casting laser cladding hybrid forming rapid tooling

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Micromixing performance of the teethed high shear mixer under semi-batch operation

《化学科学与工程前沿（英文）》 2022年第16卷第4期页码 546-559 doi: 10.1007/s11705-021-2069-3

摘要： Semi-batch operated reaction processes are necessary for some competitive reaction systems to achieve a desirable process selectivity and productivity of fine chemical products. Herein the structural and operating parameters of the teethed high shear mixers were adjusted to study the micromixing performance in the semi-batch operated system, using the Villermaux/Dushman reaction system. The results indicate that the rising of the rotor speed and the number of rotor teeth, the decrease of the width of the shear gap and the radial distance between the feed position and the inner wall of stator can enhance the micromixing level and lead to the decrease of the segregation index. Additionally, computational fluid dynamics calculations were carried out to disclose the evolution of the flow pattern and turbulent energy dissipation rate of the semi-batch operated high shear mixer. Furthermore, the correlation was established with a mean relative error of 8.05% and R² of 0.955 to fit the segregation index and the parameters studied in this work, which can provide valuable guidance on the design and optimization of the semi-batch operated high shear mixers in practical applications.

关键词： high shear mixer semi-batch operation micromixing performance Villermaux/Dushman system segregation index

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Numerical investigation of the influence of casting techniques on fiber orientation distribution in ECC

Chung Nguyen VAN; Hai TRAN THANH; Thuc Nhu NGUYEN; Jianchun LI

《结构与土木工程前沿（英文）》 2022年第16卷第11期页码 1424-1435 doi: 10.1007/s11709-022-0870-9

摘要： Engineered cementitious composites (ECC), also known as bendable concrete, were developed based on engineering the interactions between fibers and cementitious matrix. The orientation of fibers, in this regard, is one of the major factors influencing the ductile behavior of this material. In this study, fiber orientation distributions in ECC beams influenced by different casting techniques are evaluated via numerical modeling of the casting process. Two casting directions and two casting positions of the funnel outlet with beam specimens are modeled using a particle-based smoothed particle hydrodynamics (SPH) method. In this SPH approach, fresh mortar and fiber are discretized by separated mortar and fiber particles, which smoothly interact in the computational domain of SPH. The movement of fiber particles is monitored during the casting simulation. Then, the fiber orientations at different sections of specimens are determined after the fresh ECC stops flowing in the formwork. The simulation results show a significant impact of the casting direction on fiber orientation distributions along the longitudinal wall of beams, which eventually influence the flexural strength of beams. In addition, casting positions show negligible influences on the orientation distribution of fibers in the short ECC beam, except under the pouring position.

关键词： ECC fiber orientation distribution casting direction casting position

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An energy consumption prediction approach of die casting machines driven by product parameters

《机械工程前沿（英文）》 2021年第16卷第4期页码 868-886 doi: 10.1007/s11465-021-0656-0

摘要： Die casting machines, which are the core equipment of the machinery manufacturing industry, consume great amounts of energy. The energy consumption prediction of die casting machines can support energy consumption quota, process parameter energy-saving optimization, energy-saving design, and energy efficiency evaluation; thus, it is of great significance for Industry 4.0 and green manufacturing. Nevertheless, due to the uncertainty and complexity of the energy consumption in die casting machines, there is still a lack of an approach for energy consumption prediction that can provide support for process parameter optimization and product design taking energy efficiency into consideration. To fill this gap, this paper proposes an energy consumption prediction approach for die casting machines driven by product parameters. Firstly, the system boundary of energy consumption prediction is defined, and subsequently, based on the energy consumption characteristics analysis, a theoretical energy consumption model is established. Consequently, a systematic energy consumption prediction approach for die casting machines, involving product, die, equipment, and process parameters, is proposed. Finally, the feasibility and reliability of the proposed energy consumption prediction approach are verified with the help of three die casting machines and six types of products. The results show that the prediction accuracy of production time and energy consumption reached 91.64% and 85.55%, respectively. Overall, the proposed approach can be used for the energy consumption prediction of different die casting machines with different products.

关键词： die casting machine energy consumption prediction product parameters

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Thermal deflection analysis of the solidified shell in continuous casting of slab

LIU Hongzhao, WANG Zhongmin

《机械工程前沿（英文）》 2007年第2卷第2期页码 175-179 doi: 10.1007/s11465-007-0029-3

摘要： The thermal deformation problem in the continuous casting of a slab subjected to thermal loading because of the temperature gradient along the solidified shell thickness is investigated. On the basis of the reciprocal theorem of work or Betti-Maxwell s reciprocal theorem and the superposition principle, the deflection expressions for a rectangular plate with the two opposite edges simply supported, and the other two opposite edges clamped under the action of the uniformly distributed load and nonuniform temperature field are derived respectively. The meaning of each term in the deflection expression obtained by the reciprocal theorem of work is explained. Then the practical example is given to calculate the thermal deformation and the bulging deformation of the solidified shell under three tension speeds. This research is useful for analyzing the bulging deformation in the continuous casting of a slab under the static pressure of the molten steel and the thermal loading because of the temperature gradient along the solidified shell thickness.

关键词： s reciprocal loading deflection expression reciprocal opposite

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Ultrasonic measurement of tie-bar stress for die-casting machine

《机械工程前沿（英文）》 doi: 10.1007/s11465-021-0663-1

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铸件凝固过程的宏观及微观模拟仿真研究进展

柳百成

《中国工程科学》 2000年第2卷第9期页码 29-37

摘要：

面向市场经济，迎接全球化竞争的挑战，为国民经济的发展作贡献，就要十分重视制造业特别是铸造行业的发展。但是，我国铸造行业与国外相比有很大差距，它制约着国民经济的发展。世界各国在铸造成形加工技术的发展趋势方面，认识是一致的，即：一是大型工程中特大型铸件的关键铸造技术；二是向精确成形技术方向发展；三是用计算机模拟仿真逐步代替传统的经验性研究方法。铸造过程计算机模拟仿真是改造传统铸造产业的必由之路，是当今世界各国专家学者关注的热点。铸造充型凝固过程的数值模拟可以帮助工程技术.人员优化工艺设计，缩短试制周期、降低生产成本、确保铸件质量，已成为铸造领域最热门的研究课题之一。目前，凝固过程的流场、温度场数值模拟及缩孔缩松预测已应用于实际生产，应力分析、微观组织模拟等方面的基础研究及实用化进程都取得了很大进展。

关键词：铸造凝固过程模拟仿真净形铸造

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Bending and rotational behaviour of semi-continuous composite beams

WANG Jingfeng, LI Guoqiang

《结构与土木工程前沿（英文）》 2008年第2卷第2期页码 116-122 doi: 10.1007/s11709-008-0015-9

摘要： Stresses and deflections were measured in various semi-continuous composite beams. The bending and rotational capacities of the composite connections were measured in terms of beam curvatures and deflections by using two full-scale semi-rigid composite frames with monotonic loadings. The effect of semi-rigid connections on the performance of composite beams with various loadings was compared with predictions and codes. The tests show that the semi-continuous composite beams are more economic and effective than the simple or continuous composite beams. The semi-rigid connections affect the bending capacities and beam deflections, so the connection behavior should be considered in the design of composite beams. Yielding analysis of the steel beam bottom flange has some influence on the deflection calculation of composite beams.

关键词： rotational effective deflection calculation semi-continuous composite full-scale semi-rigid