激光强化电刷镀技术试验研究

系统研究了激光强化电刷镀技术的原理、特点、设备、工艺、镀层性能及强化机理.结果表明激光强化电刷镀Ni镀层与普通电刷Ni镀层相比,显微硬度提高了200 HV,耐磨性是普通电刷镀层的1.5倍,表面残余应力降低了 200 MPa,与基体结合强度高且可靠,是装备再制造工程中可广泛推广应用的一种新技术.     

A Photoaddressable Liquid Crystalline Phase Transition in Graphene Oxide Nanocomposites

The multifunctionality of graphene has the potential to unlock important developments in nanocomposite science. However, the manipulation of graphene without interfering with its unique properties and while controlling its spatial organization remains challenging. Here, the formation of a photoaddressable liquid crystalline (LC) solution through the stabilization of graphene oxide (GO) with photocleavable brushes is described. The LC behavior leads to the thermodynamic entrapment of GO into low aspect ratio domains that fail to display the properties typically predicted for graphene nanocomposites. The morphology and structural and electronic performance of these nanocomposites are regenerated through the brush cleavage, which controls the phase transition of the LC phase. These results show that kinetic control of graphene assembly can be an attractive tool toward the dynamic regulation of processable sol states and structured percolated networks for rational composite manufacturing.     

Analysis of abnormal wear on a certain type of CRH380 high-speed railway grounding brush

This paper investigated the causes of premature wear of grounding brushes in high-speed train which was less than 40 % of design service life. The grounding brushes were analyzed from the material composition, microstructure and mechanical property under different wear conditions. The results indicated that their material composition and microstructure were basically identical, and the phase compositions of the four samples were mainly copper (Cu) and carbon (C). There were no obvious defects in the structure. The load differences will give rise to vibration of the friction pairs and lead to electrical erosion on the worn surface. The electrical erosion produced oxides and fused hard particles as well as caused abrasive wear. The test results also indicated that the spring-induced gap across the contact surfaces resulted in electrical erosion.     

The synthesis of poly(3‐hydroxybutyrate)‐g‐poly(methylmethacrylate) brush type graft copolymers by atom transfer radical polymerization method

Brush type of poly (3‐hydroxy butyrate), PHB, copolymer synthesis has been reported. Natural PHB was chlorinated by passing chlorine gas through PHB solution in CHCl₃/CCl₄ mixture (75/25 v/v) to prepare chlorinated PHB, PHB‐Cl, with the chlorine contents varying between 2.18 and 39.8 wt %. Toluene solution of PHB‐Cl was used in the atom transfer radical polymerization (ATRP) of methyl methacrylate, MMA, in the presence of cuprous bromide (CuBr)/2,2′‐bipyridine complex as catalyst, at 90°C. This “grafting from” technique led to obtain poly (3‐hydroxybutyrate)‐g‐poly(methylmethacrylate) (PHB‐g‐PMMA) brush type graft copolymers (cylindrical brush). The polymer brushes were fractionated by fractional precipitation methods and the γ values calculated from the ratio of the volume of nonsolvent to volume of solvent of brushes were ranged between 2.8 and 9.5 depending on the molecular weight, grafting density, and side chain length of the brushes, while the γ values of PHB, PHB‐Cl, and homo‐PMMA were 2.7–3.8, 0.3–2.4, and 3.0–3.9, respectively. The fractionated brushes were characterized by gel permeation chromatography, ¹H‐NMR spectrometry, thermogravimetric analysis (TGA), and differential scanning calorimetry techniques. PHB‐g‐PMMA brush type graft copolymers showed narrower molecular weight distribution (mostly in range between 1.3 and 2.2) than the PHB‐Cl macroinitiator (1.6–3.5). PHB contents in the brushes were calculated from their TGA thermograms and found to be in range between 22 and 42 mol %. The morphologies of PHB‐g‐PMMA brushes were also studied by scanning electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

基于HHT的双馈异步发电机电刷滑环烧伤故障诊断

在实际工程应用中,双馈异步发电机电刷滑环故障发生较为频繁,对电机励磁稳定性影响也较大,严重时还会导致发电机组的解列。因此提出一种基于HHT的双馈异步发电机电刷滑环烧伤故障诊断方法。首先通过PSCAD/EMTDC电力系统仿真软件模拟滑环烧伤故障,得到故障前后流经电刷滑环的励磁电流。然后基于希尔伯特-黄变换理论提取故障特征量,并将仿真结果与实测励磁电流信号所得Hilbert谱图进行对比分析,验证了故障特征量诊断法的可行性。最后提出能量商的诊断特征值概念,计算不同故障等级下特征量的能量商值,并与红外测温探头测量滑环表面的温度值进行对比。分析二者变化趋势,发现高于100 Hz的周期性高频分量不但可以作为故障特征量,而且其能量商在诊断滑环发生轻微烧伤故障时具有更高的精度和灵敏度。该方法为实际工程研究提供了一定的指导意义。     

汽轮机汽封技术的应用

针对汽封对汽轮机经济性的影响,总结了近年来的汽轮机汽封新技术,分别从结构、原理、性能各方面介绍了常用的几种汽封,并对今后汽封技术的发展进行了展望。     

Cellulose Sponge with Superhydrophilicity and High Oleophobicity Both in Air and under Water for Efficient Oil–Water Emulsion Separation

Oil–water emulsions stabilized by surfactants are fine dispersions of oil in water or of water in oil and difficult to separate which will lead to serious water pollution. A more recent development is the ability to fabricate oleophobic–hydrophilic surfaces in air, which are not easy to construct due to the difference surface tension between water and oil. Herein, a cellulose sponge with multipore structure is fabricated to increase the removal efficiency. Amphiphilic molecular brushes of polyethylene glycol with short perfluorinated end caps (F‐PEG) are grafted on cellulose sponges to solve the contradictory relation of hydrophilicity and oleophobicity and improve oil/water selective wettability and fouling resistance. Besides, stable superhydrophilicity and superoleophobicity under water, corrosive liquids, and high oleophobicity in air conditions are exhibited in the F‐PEG grafted porous cellulose sponges with textured surfaces (F‐g‐CS). And the separation efficiency and rate of F‐g‐CS with surface of nanopores are 99.92% and 180 L m⁻² h⁻¹, while that of micropores are 99.83% and 297 L m⁻² h⁻¹ only under gravity. It is demonstrated that the grafting F‐PEG molecules imparted F‐g‐CS of micropores surface with high flux and separation efficiency simultaneously. Furthermore, antifouling property and collection of water in oil–water mixture without fouling are possessed in F‐g‐CS.

     

5200KW同步电机无刷励磁装置

阐述了无刷励磁装置的结构,恒功率因数控制,恒励磁控制,速度反馈控制系统及ＰＬＣ技术在励磁装置中的应用。     

SnCu钎料合金镀层钎焊连接机理及界面反应

通过在LD31铝合金表面电刷镀Ni,Cu后再沉积SnCu钎料合金镀层的钎焊实验,研究了钎料镀层的连接机理及界面反应,改进了可降低Ni层应力的电刷镀镀Ni液的配方,开发出适合镀层钎焊的SnCu钎料合金镀液,钎焊时钎料润湿为附着润湿,研究了在300℃钎焊时焊缝界面金属间化合物的生长规律,结果表明：焊缝中Cu-SnCu界面处生成了球状和棒状的Cu6Sn5金属间化合物;拉伸时焊缝主要沿着SnCu金属间化合物和富Sn相之间的界面断裂。