Effect of niobium on thermal stability and impact toughness of Nd-Fe-B magnets with ultra-high intrinsic coercivity

The effects of Nb on the thermal stability and impact toughness of ultra-high intrinsic coercivity of Nd-Fe-B magnets were investigated.The results showed that the addition of Nb could improve the thermal stability,and obviously increased the impact toughness of sintered Nd-Fe-B magnets.The optimum thermal stability of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.0 at.%.The maximum impact toughness of sintered Nd-Fe-B magnets was obtained when the content of Nb was 1.5 at.%,but the magnetic properties of sintered Nd-Fe-B magnets drastically deteriorated when the content of Nb increased from 1.0 at.% to 1.5 at.%.The microstructure showed that overfull Nb addition made many ultra-fine grains get together,which led to the density of sintered Nd-Fe-B magnets decline and drastically deteriorated the magnetic properties of sintered Nd-Fe-B magnets.     

煤泥干燥中变频器的干扰问题

干扰主要是由于变频器要进行大功率电力电子元件的整流、逆变,在输入输出回路产生大量高次谐波,干扰供电系统、负载及其它邻近电气设备。介绍了煤泥干燥系统中变频器干扰产生的原因及传播途径,提出了抗干扰的解决方法,阐述了在煤泥干燥系统中变频器的应用和安装中抑制干扰的具体措施。     

低合金高强钢对接环焊缝焊接工艺研究与应用

特高压工程钢管与带颈法兰采用的材料是低合金高强度结构钢,对焊缝质量要求高。比较3种焊接方式优缺点,法兰与钢管对接环焊缝主要采用GMAW-Ar和SAW-S 2种焊接方式;从工艺顺序、加工效率及产生缺陷比较2种焊接工艺的优缺点,进一步分析工程焊接质量与焊接工艺参数的关系。建议在选择低合金高强度钢焊接方法时,优先采用GMAW-Ar气保焊打底,然后清根,再进行气保焊罩面焊接工艺,在保证焊接质量的情况下也可以采用SAW-S埋弧焊。     

复合地基基础空间变刚度调平设计方法的数值模拟

基于地基基础支承刚度与上部荷载分布特征相对应的原则,考虑地基中的应力场、应变场的分布,对地基基础的空间变刚度设计方法进行了数值分析.建立复合地基基础的三维有限元模型,以地基变形模量的变化来反应地基的支承刚度的空间变化,讨论地基支承刚度空间变化时,基础沉降等值线的分布规律,验证了地基基础空间变刚度对减少基础沉降差,改善建筑结构的受力模式,减小筏板内力和厚度、降低上部结构次应力具有显著效应.     

城市燃气管道入综合管廊的应用分析及技术探讨

近年来综合管廊的建设快速发展,如何提高燃气管道入综合管廊的技术水平是目前推动综合管廊长远发展的关键点。本文首先分析了燃气管道入廊的优缺点、国内外现状及相关设计经验,从如何有效防止泄露、发生泄露时如何有效防止爆炸两方面对燃气管道入廊的技术要点进行探讨,并提出了相应技术方法。     

霄云矿井工程区水土流失防治措施及生态环境恢复对策

针对拟建霄云矿井工程的水土流失特点,以科技为指导,资金投入作保障,采取整体包围分层治理,建立人工防、排水系统,坡面综合治理等措施,因地制宜进行植被恢复等水土流失防治及生态环境恢复对策。     

高强与活性粉末混凝土尺寸效应的分析

活性粉末混凝土(Reactive Powder Concrete,简称RPC)是一种新型超高强、高性能水泥基复合材料.本文分析了高强混凝土以及活性粉末混凝土尺寸效应的研究成果和进展,在此基础上,初步探讨了RPC尺寸效应,分析了其中的难点问题.     

邢钢5号高炉工艺装备分析

介绍了邢钢新建的420m^3高炉所采用的一系列先进成熟的新工艺、新技术。     

Model of temperature field for the preparation process of melt-spun NdFeB powders

Melt-spun ribbons which are the important raw material for hot-deformed magnets can be prepared by single-roller melt-spinning. In order to prepare well-structured ribbons, the model of temperature field for single-roller melt-spinning process was constructed in this work. The heat conduction in this process was simplified as one dimensional heat conduction problem. It was shown by modeling that, the temperature field in the melt-spinning before solidification in this model could be described as this equation T(x,t)=Tmoexp[–k(x–x0)–k2αt]+T0. The temperature T(x,t) of the alloy melts decreased with increased position x and cooling time t exponentially from the wheel-free surface to the wheel-side surface. The constant k determined the decrease speed of alloy temperature T(x,t), which was proportional to the interfacial heat transfer coefficient h and the interfacial area of heat conduction A0, but inversely proportional to the thermal conductivity K. x0 was the thickness of the alloy melt. With increased x0, the temperature difference between wheel-free surface and the wheel-side surface became larger, which would lead to larger difference in grain size. In experiments, the influence of melt-spinning process parameters on the temperature field model was discussed, such as cooling roller materials, wheel speed, and so on. Melt-spun ribbons prepared by single-roller melt spinning at different wheel speed were investigated and magnetic properties of die-upset magnets from melt-spun ribbons on different cooling roller were analyzed. The variation of grain size in the depth direction consisted with temperature field model. This model provided directions for the preparation of melt-spun ribbons with uniformly distributed fine grains, which were very necessary for producing hot-deformed magnets with high magnetic performance.