一段炉转化炉管的组织性能分析与评估

采用化学成分分析、着色渗透探伤分析、电子探针分析、显微组织分析、力学性能及高温持久性能分析等方法,对大型合成氨一段炉竖琴管排运行1.0×105h的转化管进行综合分析和评估。结果表明：转化管化学成分符合技术要求,宏观组织正常,显微组织形态良好,内外表面轻微腐蚀;经高温持久性能在L-M曲线中拟合外推,该管的剩余寿命远大于2.2×104h;炉管虽使用1.0×105h满足了工艺要求,但壁厚太大,影响热效率,同时内径小,限制了触媒和流量;因此,为提高效率,建议在今后的设计中采用性能较好的材料ZG50Ni35Cr25NbM。     

超临界循环流化床锅炉高温过热器管开裂原因分析

某超临界循环流化床锅炉TP347H钢膜式壁高温过热器管频繁发生开裂,通过宏观检查、光谱分析、力学性能试验、显微组织分析以及运行情况分析等对其失效原因进行了研究。结果表明,取样管化学成分、力学性能均满足标准要求,显微组织未见异常;裂纹起源于管子与鳍片焊趾处,并从外壁向内壁扩展;管子开裂原因为:高温过热器管为大屏膜式壁结构,加之锅炉启动过程中,相邻管壁温度差较大且不断变化,造成管子在轴向方向的膨胀差较大并形成交变热应力,从而在焊趾应力集中部位产生热疲劳裂纹,同时管子与鳍片焊缝处的残余应力以及管子外表面存在的直道沟槽促进了裂纹的形成和扩展。     

制备非晶薄带冷却辊流动换热特性及协同优化

为改善平面流铸冷却辊的换热特性,提高Fe-Si-B非晶薄带的横向厚度均匀性,建立了冷却辊轴向换热通道数值计算模型。在分析现有通道流动换热特性基础上,提出一种球面形换热通道设计方法。基于场协同理论,综合换热与流阻,对所提球面形通道进行优化,并进行实验验证。结果表明:通道内冷却水换热效率沿水流方向逐渐下降,与冷却辊换热主要发生在靠近冷却辊内壁位置,现有冷却辊宽度中部温度远大于两端,轴向温差明显;球面形通道可以加强冷却辊中部换热,降低外壁温度、热变形和轴向变形差,进而改善非晶薄带横向厚度均匀性;随着球面半径的减小,通道中部换热明显增强,但流阻随之急剧增大;综合流阻与换热特性,存在最优通道优化半径。     

滚滑轴承的摩擦热仿真分析

轴承温度升高产生的热膨胀会破坏轴承零件间的配合关系,影响轴承运动的灵敏性,降低轴承的使用寿命.为了解滚滑轴承承载运动时摩擦热引起的温度变化,辅助该新型轴承的结构设计,建立滚滑轴承承载运动的摩擦动力学模型;利用ABAQUS软件对滚滑轴承进行摩擦热仿真分析.结果表明:滚滑轴承从启动到稳定运转过程中,摩擦力矩由小到大,再变小...     

High temperature corrosion of cracking tubes

Coils for pyrolysis cracking of hydrocarbons are made of centrifugically cast FeNiCr‐alloys and exposed to very severe conditions, high temperatures > 1050°C, oxidizing flue gases at the outside and carburizing atmosphere at the inside. Two tube sections have been investigated after some years operation. In the first case the tube wall was thoroughly carburized, the big size of the internal carbides indicated service at too high temperatures > 1100°C. At such temperatures the protective chromia scale fails by conversion to carbides, allowing ingress of carbon. At the outer wall surface obviously Cr was lost by evaporation as CrO₂(OH)₂ and CrO₃ which is significant at high pO₂ and high temperature. In the second case the tube had been operated at more moderate temperature, but showed creep cavities indicating loss of creep strength. This is due to repeated oxidation and loss of the scale by thermal cycling, this process has caused formation of a carbide denuded zone of considerable width at the outer side somewhat less wide at the inner wall. Besides oxide spallation, at the outer wall also evaporation will have played a role.     

错位环轧工艺

错位环轧工艺是在环件外周的适当位置安置两个辗压轮,同时在环件内孔的两辗压轮与环件接触处之间的近中部位置错位安置一个芯辊,外周的大辗压轮由电动机拖动旋转,它带动环件、芯辊和小辗压轮旋转,构成环轧,外周的两个辗压轮和内孔中的芯辊,在径向发生相向连续的进给运动的过程中,保持内外三个轧辊的错位状态,在此状态下,它们的径向压力难以穿透环件的壁厚,环件壁厚处于未锻透的状态,在轧制过程中,环件的断面面积变化不大,在咬入条件满足时,环件外周及内孔表面的局部连续受压,迫使环件外周表层金属发生轴向流动变形,去充填模具型腔,形成与模具型腔相对应的较复杂的断面形状。     

Oxidation Behaviors of Different Grades of Ferritic Heat Resistant Steels in High-Temperature Steam and Flue Gas Environments

For steam tubes used in thermal power plant, the inner and outer walls were operated in high-temperature steam and flue gas environments respectively. In this study, structure, microstructure and chemical composition of oxide films on inner and outer walls of ex-service low Cr ferritic steel G102 tube and ex-service high Cr ferritic steel T91 tube were analyzed. The oxide film was composed of outer oxide layer, inner oxide layer and internal oxidation zone. The outer oxide layer on the original surface of tube had a porous structure containing Fe oxides formed by diffusion and oxidation of Fe. More specially, the outer oxide layer formed in flue gas environment would mix with coal combustion products during the growth process. The inner oxide layer below the original surface of tube was made of Fe-Cr spinel. The internal oxidation zone was believed to be the precursor stage of inner oxide layer. The formation of internal oxidation zone was due to O diffusing along grain boundaries to form oxide. There were Fe-Cr-Si oxides discontinuously distributed along grain boundaries in the internal oxidation zone of G102, while there were Fe-Cr oxides continuously distributed along grain boundaries in that of T91.     

双层不锈钢管三辊斜轧数值模拟与参数优化

设计了一种核电站一回路主管道用双层不锈钢管的复合成形工艺,解决了传统锻造或铸造工艺成品长度受限的问题,同时满足了复杂工作环境对管道性能的特殊要求。采用Deform-3D有限元模拟软件对外层21-2N奥氏体耐热不锈钢与内层12Cr-12Ni马氏体耐热不锈钢的双层套管三辊斜轧成形过程进行了模拟研究与参数优化,分析了双层不锈钢管的内外层变形情况、应力应变场及温度场的分布规律,并通过设计正交试验获得了最优变形的参数组合。模拟结果表明,三辊斜轧过程中,等效应力、等效应变与温度的最大值均集中在外层管与轧辊的接触区,且外层管整体性能参数要大于内层管。通过正交设计试验的极差分析与方差分析,最终获得最优变形参数为粗轧温度1 100°C,送进角8°,轧辊转速200r/min。     

管内空气流动对大口径厚壁P92管道局部焊后热处理温度场的影响

使用Ansys CFX软件建立了P92管道与管内空气的共轭传热模型，并进行了试验验证.使用该模型计算了不同管内空气流速时，局部焊后热处理的温度场分布.结果表明，管内空气流动对恒温后管道外壁温度影响较小，但会显著降低内壁温度，并增加内、外壁的轴向温度梯度.随着管内空气流速的增加，焊缝中心内外壁温差和轴向温度梯度近似线性增加，空气流速每增加1 m/s，内外壁温差将增大约5.0℃，内、外壁轴向温度梯度分别增加约0.03和0.02.对热处理温度要求很高的P92管道，局部焊后热处理时应限制管道内空气流动，或在选取热处理参数时考虑空气流速的影响.     

数值计算模拟工艺参数对管道环焊缝残余应力的影响

以热——弹塑性理论为基础,建立了厚壁管环焊缝残余应力的二维轴对称有限元模型,利用ANSYS有限元程序分析了三种焊接工艺参数对管道环焊缝残余应力的影响,计算中考虑了材料热物理性能参数和力学性能参数的温度相关性.结果表明,管道内表面焊缝和近缝区的轴向和环向残余应力均为拉应力,而管道外表面焊缝和近缝区的轴向残余应力和环向残余应力均为压应力;接头内表面应力水平高于外表面;残余应力的最大值均位于距管道外表面一定距离处,其数值接近于材料的屈服应力;随着焊接热输入的增加,残余应力峰值变化不大,塑性变形区宽度增加.     

铸渗合金层的温度场测试与分析

通过对合金粉膏块内外界面上温度变化曲线的测试,计算出了膏块在合金化形成过程中的热扩散率。并对铸渗合钓饵支外表面上的温度曲线做了分析。     

三相电压型PWM整流器微分平坦控制研究

三相电压型PWM整流器(VSR)通常采用电压外环、电流内环的串级PI控制策略，但电流内环不能精确解耦，致使直流侧电压快速性、鲁棒性不佳。本文采用一种新型非线性控制方法——微分平坦控制(FBC)，用以提升电流内环的控制性能，与PI控制相比，能够实现电流前馈动态精确解耦，对参数变化和外来扰动具有鲁棒性和适应性，明显提高了系统动态响应速度。通过理论分析和仿真实验，验证了FBC控制策略的正确性和优越性。     

空心圆柱体GCr15钢淬火过程的计算机模拟

用有限元法研究了GCr1 5钢圆柱体在油淬过程中的温度、组织及应力变化。在实测了淬火油换热系数的基础上 ,对轴对称空心圆柱体淬火时的温度场和组织场进行了模拟。同时运用热弹塑性理论 ,对圆柱体内外表面点及中心点应力的演化过程进行了模拟。模拟结果表明 :圆柱体内表面的冷速小于外表面。在淬火初期 ,由于热应力的作用使工件表面受拉而心部受压 ,在发生应力反向前 ,发生了组织转变 ,并使表面应力迅速转向 ,在应力达到最低点后又逐渐回升 ,最后表面形成了拉应力。心部的应力变化正好相反 ,最终形成了组织应力型的内应力分布。     

V形面喷涂成膜数值模拟

目的 建立V形面喷涂成膜仿真模型,深入研究V形面喷涂成膜特性,为优化喷涂喷枪轨迹及获取理想涂膜提供理论支撑。方法 采用欧拉–欧拉方法建立包含喷雾流场模型和喷雾沉积模型的V形面喷涂成膜模型,结合动态自适应加密技术和SIMPLE算法,求解分析喷雾流场规律和涂膜厚度分布特性及形成机理,开展喷涂实验验证所建模型及成膜特性的正确性。结果 随着Z轴距离的增大,喷雾流场横向雾形由椭圆形变为长条状,纵向雾形在长轴方向上近壁面时与平面喷涂差别较大。相较平面喷涂,外壁喷涂喷雾覆盖范围广,内壁喷涂结果相反,且喷雾横向扩展程度与Z轴坐标值均呈线性关系。V形面内外壁喷涂涂膜均呈椭圆形,且膜厚均沿径向递减。外壁喷涂涂膜光环宽度最大,涂膜厚度值普遍低于平面喷涂;内壁喷涂涂膜光环宽度最窄,短轴方向涂膜厚度值普遍高于平面喷涂。随着V形面角度变大,涂膜中心厚度不断增加。涂膜厚度值在短轴方向均呈单峰分布,而在长轴方向上,外壁喷涂涂膜厚度均呈双峰分布,内壁喷涂涂膜厚度分布随角度变化有差异。结论 建立的喷涂成膜模型用于V形面喷涂成膜过程仿真是有效的,V形面较大地改变了喷涂过程中的喷雾流场特性和涂膜厚度分布特性。     

9%Cr钢厚壁管道局部焊后热处理温度场的数值模拟

基于热源追踪法开发了一个能够根据控温点温度自动调整热输入的有限元程序. 使用该程序模拟了9%Cr钢管道的局部焊后热处理温度场分布,并进行了试验验证. 结果表明,模拟结果与试验结果吻合良好. 热处理温度场沿管道轴向呈近似抛物线状分布,沿径向呈近似线性分布. 距焊缝中心两倍壁厚范围内,管道内外壁温差均约为17~18 ℃. 按照目前国内焊后热处理规程推荐的参数进行热处理,均温区宽度能够满足要求,可以保证整个接头的热处理效果. 根据温度场分布,还确定了与管道内壁焊缝中心温度相同的外壁等效点位置,以监测热处理过程中管道内壁温度的变化.     

Development and application of coupling model of aluminum thin-gauge high-speed casting

Based on the analyses of aluminum melt flow, solidification, heat transfer during the process of twin-roll casting, a coupling mathematical model of aluminum thin-gauge high-speed casting was developed, which included the casting roller shell. At the same time, Galerkin method was adopted to solve the coupling model. The fluid field and temperature field of aluminum melt in casting zone, the temperature field and thermal stress field of roller shells were simulated by the coupling model. When the casting velocity is 7 m/min, and the thickness of strip is 2 mm, the circumfluent area comes into being in the casting zone, and the mushy zone dominates the casting zone, while the temperature of melt decreases rapidly as it approaches the rollers. The temperature of the roller shell varies periodically with the rotation of roller, and reaches the highest temperature in the casting zone, while the temperature of roller shell decreases gradually as it leaves the casting zone. The difference of thermal stress between the inner surface and outer surface of the roller shell is very large, and the outer surface suffers tensile-compressive stress.     

Fabrication of a probe needle using a tubular cathode by electrochemical etching

To fabricate a probe needle, a tubular cathode was applied by electrochemical etching. A tungsten wire was used as an anode, and a stainless steel tube was used as a cathode, respectively. The stainless steel tube was partially immersed into a sodium hydroxide solution. After the tungsten wire was aligned at the center of the stainless steel tube, electricity was supplied from an external power source. During the experiment, the level of solution that was inside the stainless steel tube rose higher than that of the outer solution of the stainless steel tube, due to bubbles generated on the inner surface of the stainless steel tube, and the inner solution increased in volume. Using this process, the length of the probe needle tapering could be controlled without using a vertical loading system or controller.     

高速空心滚珠丝杠螺母副热特性的影响因素分析

滚珠丝杠作为机床伺服进给系统的重要元件,其热变形会降低伺服进给系统的定位精度,在机床高速化发展的过程中,滚珠丝杠热变形成为其发展的瓶颈,采用通有冷却介质的空心滚珠丝杠为解决这一问题提供了方法。空心滚珠丝杠定位精度受到以下因素影响:滚珠丝杠轴向载荷、转速、通入空心滚珠丝杠的冷却介质的种类、冷却介质流速以及空心滚珠丝杠内孔的大小,这些因素不仅影响空心滚珠丝杠的冷却效果,而且对空心滚珠丝杠的变形也有很大的影响。研究结果表明:轴向载荷和转速对温度影响较小;专业冷却油更适合用于滚珠丝杠的冷却,合理控制其温升和热变形;热变形和热-结构耦合的分析,给出了最佳内孔直径。为空心滚珠丝杠的设计及研究提供理论依据。     

热式MEMS流量传感器的设计及测试

根据已有的热式MEMS气体微流量传感器芯片的各部分热敏电阻热串扰现象严重,造成很大的测量误差,改进设计了一种MEMS热式流量传感器,将加热电阻和上下游测温电阻采用悬臂梁隔离结构,并相互隔离,有效的避免了热膜流量传感器各部分热敏电阻间相互热串扰现象。基于改进的MEMS热式流量传感器,设计了流量传感器的测试系统,包括恒温差电路、桥式测量电路及放大、滤波电路,所采集的流量信号经过滤波放大后输入AD模块进行模数转换,最后经过单片机处理,利用单片机与计算机串口通信功能,在不同流速下打印出不同的电压值;通过Matlab对所测出的数据进行拟合,完成对传感器性能的检测。测量结果表明:在一定的流量范围内,该流量传感器具有测量精度高、响应速率快、输出信号平滑等特点,能够广泛应用于工业、医疗领域的流量测量。     

Thermal-mechanical model of the tube elongation process in Diescher''s mill

The steady-state finite element approach is used to model the tube elongation process in Diescher's mill. The material is deformed between two rotating cone shaped rolls and a plug. The material is dragged by the rolls, moves forward and rotates. The analysis of the process is performed in the cylindrical coordinates. Tube ovalness is neglected. The material flowing in the circumferential direction is accounted for. The velocity field components in r,θ,z directions are discretized using parabolic shape functions. An iterative algorithm is employed for correction of the outer and inner free surfaces that determine the control volume. The material flow and torsion, distribution of the effective strain and temperature are computed and analysed for the tube elongation process in Diescher's mill using a parabolic plug.