Mechanism of hot cracking in the heat affected zone of repair welds. Repair weld cracking of service‐exposed HP‐modified heat‐resisting cast alloys (3rd report)

For several decades it has been possible to observe a tendency to light structures, particularly when they are destined to develop power and movement by consuming energy, especially when this energy derives from conventional fuel (petroleum derivates).

Lighter means of transport permit savings on fuel consumption and contribute to the environmental protection due to the reduction of greenhouse gases. The first approach in this direction had been the utilization of innovative materials able to offer further improved mechanical strength.

Nevertheless, this way presents natural limits depending on the loss of rigidity, hence excessive deformability even in the elastic field. This fact leads to the necessity to add stiffeners and reinforcing elements, but this at the same time means increase again the heaviness. Under these conditions more complex structural solutions step forward as the ‘sandwich’-structures manufacturable in a modular way provided with remarkable versatility in terms of design and choice of material. In the 1990s a European research project named ‘Sandwich’ financed by the European Union had given a significant contribution to the industrialization of structural solutions, which present a high level of innovations using aforementioned structures.

The present work proposes a preliminary study and several results of an investigation, which has as the main subject the production of innovative structural sandwich panels, in other words hybrid-sandwich panels in steel-aluminium assembled using two different joining technologies as laser and FSW, which can successively be connected as well to steel structures as to aluminium ones.     

Self-feed device behaviour evaluation designed for assessment of operability of coated electrodes

The objective of the present work is to evaluate the effectiveness of a self-feed device for coated electrodes. This device is able to eliminate disturbances from manual operation or the use of automatic control systems during the study of coated electrode behaviour. The conjugation of different methods such as short-circuit time statistical analysis and metallographic analysis (penetration, heat-affected zone, shape and mean distance between successive solidification fronts) together with the analysis of the electric arc and electrode melting parameters allows us to obtain relationships between arc behaviour, mass transfer processes and bead appearance. This permits the extraction of criteria to describe process stability and the behaviour of the feed device employed. An appropriate statistical methodology was obtained to process the ‘duration of the short-circuit’ parameter through an appropriate adjustment of empirical distributions to a log-normal model. The self-feed device for coated electrode welding allows the repeatable and reproducible execution of welding beads in the flat position, keeping the arc length based on physical and chemical characteristics of the electrode during welding trials using 125, 140 and 160 A.     

Design and optimization of ceramic membrane structure: From the perspective of flux matching between support and membrane

The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m³m^?2h^?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization.     

定向爆破技术在水泥厂窑尾框架拆除中的应用

广西鱼峰太阳村5 500 t/d熟料生产线项目是在拆除老线的基础上新建,老线总高75 m的窑尾框架需要拆除。拆除场地狭小,且附近有已有建筑需要保护,采用定向爆破技术进行拆除。在实施爆破过程中,选取合理的爆破参数,通过精心组织施工,在爆破过程中成功保护了需要保护的建筑。     

基于LSTM-SVM的风电机组齿轮箱故障诊断

针对风电机组齿轮箱的故障诊断中特征提取过分依赖人为经验和准确率不高的问题,提出一种基于长短时记忆网络(LSTM)与支持向量机(SVM)相结合的方法。对原始时域振动信号作傅里叶变换,利用LSTM神经网络自适应智能提取特征的优势,结合SVM的分类功能,实现对风电机组齿轮箱更加准确的故障诊断。仿真结果显示,该网络模型在经过16轮训练后准确率可以达到100%,使用测试集数据准确率也可以达到99.1%。     

40Cr表面微裂纹研究与应用

通过研究三钢1号小方坯连铸机振动参数,对比各种工艺对铸坯表面质量的影响,改善了铸坯的表面质量。振动参数优化如下：结晶器振动方式由采用正弦振动改为非正弦振动,偏斜率[ɑ]采用0.2,振动频率由152次/min提高至182 次/min,振动幅度由8.2 mm降低至7.2 mm,负滑脱时间由0.168 s降低至0.117s,铸坯表面质量得到有效改善。同时在保证铸坯表面质量的情况下,可以通过适当的提高连铸拉速,减少铸坯振痕深度。     

New method for evaluation of kinetic parameters and mechanism of degradation from pyrolysis–GC studies: Thermal degradation of polydimethylsiloxanes

Thermal degradation of polydimethylsiloxane (PDMS) polymers having hydroxyl (PS) and vinyl (PS‐V) terminals was studied by pyrolysis‐gas chromatography (PGC) in the temperature range from 550 to 950°C. The degradation products were primarily cyclic oligomers ranging from trimer (D₃) to cyclomer D₁₁ and minor amounts of linear products and methane. The product composition varied significantly with pyrolysis temperature and extent of degradation. A new method was developed to derive a mass loss‐temperature curve (pyrothermogram, PTG) and to determine the kinetic parameters of decomposition (k, n, and E_a) from sequential pyrolysis studies. It was shown that isothermal rate constants can be derived from repeated pyrolysis data. Good agreement between the rate constants derived from the two methods validates the methodology adopted. This was further confirmed from thermogravimetric studies. The E_a values for the decomposition of PS and PS‐V derived from sequential pyrolysis were 40 ± 2 and 46 ± 2 kcal mol⁻¹, respectively. Various mechanisms for the degradation of PDMS were reviewed and discussed in relation to the PGC results. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 441–450, 1999     

Electrochemical behaviour of indium ions in molten equimolar CaCl2–NaCl mixture at 550 ∘C

The stability of indium chloride and oxide as well as the electrochemical behaviour of indium ions have been studied in the equimolar CaCl2–NaCl melt at 550 C by X-ray diffraction (XRD) and different electrochemical techniques, using molybdenum and tungsten wires as working electrodes. Voltammetric and chronopotentiometric studies showed signals attributed to the presence of three oxidation states of indium, i.e. 0, i and iii. The standard potential of the redox couples, as well as the solubility products of indium oxides have been determined, showing that In(iii) ions are completely reduced to monovalent indium by the indium metal according to the reaction: In () + 2 In 3 In () and that In₂O is a strong oxide donor according to the reaction: In₂O(s) 2 In() + O^2- These results have allowed the construction of E-pO2– equilibrium diagrams summarising the properties of In–O compounds. The electrodeposition of indium was uncomplicated at Mo and W electrodes. Very good adherence of liquid indium to the electrode materials was observed, with the formation of Na–In alloys at highly reducing potentials, and there was no evidence of indium dissolution into the melt. Moreover, the voltammograms corresponding to the electrochemical In(iii)/In(i) exchange were well defined. The two electrochemical steps were found to be quasi-reversible, and the values of the kinetic parameters, ko and , for both reactions, as well as the diffusion coefficients, DIn(III) and DIn(I) were calculated.     

承上启下 精益求精——龙滩水轮发电机组招标回顾

龙滩水电站水轮发电机组设备招标是三峡之后，最具代表性的一种采购模式。根据龙滩工程的特点，充分考虑国内外市场的现状，围绕机组稳定性的这一主线，合理选择机组参数，按强强组合的原则择优选定制造厂家，确保龙滩水轮发电机组性能优良，满足工程需要，价格适宜。本文介绍了龙滩机组招标的实施情况。