Analysis of internal crack in a six-ton P91 ingot

P91 is a new kind of heat-resistant and high-tensile steel. It can be extruded after ingot casting and can be widely used for different pipes in power plants. However, due to its mushy freezing characteristics, a lack of feeding in the ingot center often generates many defects, such as porosity and crack. A six-ton P91 ingot was cast and sliced, and a representative part of the longitudinal section was inspected in more detail. The morphology of crack-like defects was examined by X-ray high energy industrial CT and reconstructed by 3D software. There are f ive main portions of defects larger than 200 mm~3, four of which are interconnected. These initiated from continuous liquid f ilm, and then were torn apart by excessive tensile stress within the brittle temperature range(BTR). The 3D FEM analysis of thermo-mechanical simulation was carried out to analyze the formation of porosity and internal crack defects. The results of shrinkage porosity and Niyama values revealed that the center of the ingot suffers from inadequate feeding. Several criteria based on thermal and mechanical models were used to evaluate the susceptibility of hot crack formation. The Clyne and Davies' criterion and Katgerman's criterion successfully predicted the high hot crack susceptibility in the ingot center. Six typical locations in the longitudinal section had been chosen for analysis of the stresses and strains evolution during the BTR. Locations in the defects region showed the highest tensile stresses and relative high strain values, while other locations showed either low tensile stresses or low strain values. In conclusion, hot crack develops only when stress and strain exceed a threshold value at the same time during the BTR.     

NiCr薄膜电阻TCR的影响因素

影响NiCr薄膜电阻TCR的因素很多，我们分别从溅射淀积工艺和热处理工艺来研究和探讨NiCr薄膜电阻TCR与溅射时的真空度、溅射速率、基片温度、薄膜厚度及热处理温度和时间等因素的关系，从而为提高NiCr薄膜电阻的稳定性和降低其TCR值提供有益的条件。     

质检业务集中受理系统模型设计

对综合型实验室来说,质检业务集中受理的难点是因专业技术分工细致复杂所带来的挑战,如何让不具备复合型专业知识背景的人员能够胜任业务受理的工作正是本文试图解决的问题.     

支承刚度对输流管道振动特性的影响分析

为研究实际支承条件下管路系统的振动特性,文中采用一端固支一端具有弹性约束梁的前两阶振型来近似相同边界条件下输流管道的前两阶振型．通过拉格朗日方程推导出了带有弹性约束管道系统的控制方程,利用模态法对其进行求解,分析了支承刚度对梁前两阶振动特征值的影响,并分析了支承刚度对管道固有频率、跨中最大振动位移和动静失稳临界流速的的影响．研究结果表明：支承刚度在0～1000N／m范围内对固有频率影响不大,当支承刚度大于1000N／m对固有频率有明显影响;随着支承刚度的增大,管道系统的首次失稳形式由动态失稳变为静态失稳．     

卧式连铸铜锭坯连接式分体炉

国内外卧式连铸铜锭坯，绝大多数生产厂家均采用熔化炉与保温炉分开的，在铜液体从熔化炉往保温炉倾注时，会从空气中吸收大量的氧。在连接式分体炉中，熔化炉与保温炉是连通整体式的，熔融铜液体与空气隔离，含氧量很少，可达无氧铜级。     

IC电路封装内部水汽含量的分析与控制研究

为了使IC电路封装能广泛满足航空、航天及航海等特殊领域对内部水汽含量的要求(≤5000ppm),提出了降低金属或陶瓷结构封装的IC电路封装内部水汽含量的控制方法和工艺条件要求。     

20％呋虫胺SG防治棉盲蝽象田间药效试验

[目的]为明确20％呋虫胺SG对棉盲蝽象的防治效果,开展了该药的田间药效试验.[结果]20％呋虫胺SG450、300、225、150 g a.i./hm2和50％马拉硫磷EC 750 mL a.i./hm2对棉盲蝽象的防效,药后ld依次为100％、80％、81.82％、75％和50％,药后3d的防效依次为100％、100％、94.29％、80.25％和46.45％;药后7d的防效依次为100％、95.15％、95％、80.11％和41.86％.[结论]20％呋虫胺SG防治棉盲蝽象具有速效、持效且对棉花安全的特点,是防治棉盲蝽象理想药剂.在中等偏轻发生年份用量为150～225 g a.i./hm2,在中等以上发生程度年份用量为225～300 g a.i./hm2.     

实验室器具样品流转及过程控制自动化

实验室器具样品的流转与检测环节及过程紧密相关,器具样品的流转及过程控制自动化可以充分利用有限资源,提高工作效率,缩短服务周期,为流程优化及过程跟踪提供实时分析数据.     

银川市水资源管理存在问题及其对策分析

随着银川市城市建设规模迅速扩大、工业化进程加快,对水资源的需求不断增加,水资源供需矛盾日渐突出。为此,2002年银川市政府施行了机构改革,建立了相关水资源管理法规,推进了水资源有偿使用制度,制定了较合理的用水价格和阶梯水价。然而,在水资源统一管理中仍然存在法律依据不足、执法力度不够、水资源管理体制和运行机制不合理、基础工作薄弱、公众意识不强等问题,未来还需要在法制法规建设、水管体制改革、合理水价机制、水资源优化配置、管理队伍建设、公众参与等方面加强工作。     

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