真空凝壳炉的真空系统设计

本文主要总结 100公斤真空凝壳炉真空系统的设计经验。 100公斤真空凝壳炉(又叫真空自耗电极电弧凝壳炉)已生产使用十多年,工作已达1000多炉次。实践证明,运行稳定可靠,是目前国内较大的钛铸炉,为我国钛铸业作出了贡献。于1978年底荣获辽宁省科学大会奖和冶金部科技奖。 一、真空系统的选择 真空凝壳炉的真空系统同真空自耗炉(又叫真空自耗电极电弧炉)的真空系统基本相同,计算方法也相似。所不同之处是:真空凝壳炉有较大的熔池,能直接浇注形状比较复杂的铸件,在开始熔炼阶段放气量较大,在浇注的瞬时放气量达最大值,真空自耗炉只能在水冷坩埚…     

真空自耗电弧炉用Φ720mm坩埚的优化和改进

真空自耗电弧炉是生产钛及钛合金铸锭的主要设备.坩埚是真空自耗电弧炉必不可少的部件,是真空自耗电弧炉重要的组成部分.坩埚筒体材料的性能和坩埚结构不仅影响到坩埚的寿命,亦对生产效率和生产成本产生巨大影响.本文就8t真空自耗电弧炉用Φ720 mm×3000 mm坩埚的失效原因做了分析,提出了优化方案及改进方法.     

真空自耗电极电弧炉自动控制系统

本文简述了真空自耗电极电弧炉的构成，详细介绍了真空自耗电极电弧炉自动控制系统的结构，功能及其控制过程，实现了真空自耗电极弧炉生产过程的自动控制。     

全自动称重真空自耗电弧炉研制

简述了国内外真空自耗电弧炉的现状以及最新技术,详细介绍了最新研制的真空自耗电弧炉的结构和特点,特别对电极称重、恒熔速、X-Y调节及全过程计算机控制系统作了重点介绍.     

真空自耗电弧炉熔速控制模型的实验研究

首先对真空自耗电弧炉称重模块采集的数据进行了处理,然后通过设计的试验建立了电极熔化速度与电弧电流之间的关系模型,最后提出了熔速控制的真空自耗电弧炉的系统设计方案.该系统设计已在现场投入使用.     

硫化物形态对超高强度钢冲击韧性的影响

本文对比分析了"真空感应+真空自耗重熔"和"电弧炉+VOD+真空自耗重熔"两种工艺冶炼的超高强度G50钢力学性能.利用扫描电镜和能谱分析等检测手段研究了不同冶炼工艺生产的G50钢中夹杂物类型和尺寸分布.研究结果表明:电弧炉+VOD+真空自耗重熔工艺冶炼的G50钢横向和纵向冲击韧性分别相对"VIM+VAR"工艺得到很大的改善,各向均匀性得到改善.电弧炉+VOD+真空自耗重熔工艺冶炼的G50钢中夹杂物颗粒状和椭圆形弥散均匀分布,阻碍空洞合并,导致冲击性能尤其是横向冲击性能得到极大的改善.     

真空自耗电弧炉真空系统的检漏

主要论述了用于生产钛及钛合金铸锭的真空自耗电弧炉真空系统的组成与特点,针对钛、钛合金的冶金特点及生产实际,阐述真空系统漏率对于生产钛、钛合金的意义;应用最新技术的莱宝300型检漏仪,对真空系统进行了测漏,总结了检漏方法,此法对真空白耗电弧炉真空系统或类似的真空设备测点的设计、检漏具有指导意义.     

钛及钛合金熔炼技术发展现状

目前生产钛及钛合金铸锭最主要的方法是真空自耗电弧熔炼以及冷床炉熔炼方法。详细介绍了真空自耗电弧熔炼、电子束冷床炉熔炼以及等离子束冷床炉熔炼技术的原理、特点和发展现状。     

真空电弧炉动密封的设计及计算

介绍了宝鸡有色金属加工厂设计研制所自行研制的650 kg真空电弧炉和1 t真空电弧炉真空系统与炉室连接处的动密封结构、原理及其计算方法,在类似设备中可作参考.     

真空自耗电弧炉恒熔速控制系统改造

为真空自耗电弧炉设备由恒电压控制升级改造至恒熔速控制系统。通过对2000kg真空自耗电弧炉熔炼钛合金的生产工艺、过程参数、产品要求进行了详细分析,选取恰当的数据采样算法,为更好的掌握真空弧电压、真空弧电流、钛合金熔炼速度等工艺参数间的耦合关系提供了良好的依据。同时对真空自耗电弧炉的控制系统现状及熔炼技术发展做了综述。在PLC中建立弧电压、弧电流,熔炼速率等的计算公式来实现设定各级控制回路的设定值。     

Issues of contact etching and pre-treatment in Schottky contact

This paper reports on the process dependence of contact resistance of silicide/n+ Si and silicide/p+ Si contact. Three processes such as contact etching, Si treatment and pre-treatment are investigated with contact resistance point of view. Only silicide/p+ Si contact resistance has been changed as etching time of contact increases while silicide/n+ Si contact resistance has been regularly maintained. We have modeled that fluorine used in contact etching can scavenge or deactivate boron in p+ Si, resulting in degradation of silicide/p+ Si contact resistance. In order to confirm the model, two different gases (hydro carbon fluoride/carbon fluoride) during Si treatment right after contact etching were applied. As a result, the silicide/p+ Si contact resistance was increased in carbon fluoride case, which has higher fluorine ratio to carbon than hydro carbon fluoride case. It is also observed that the silicide/p+ Si contact resistance was increased proportionally with time of fluorine-based pre-treatment before silicide formation.     

Ag基触头材料的研究现状与展望

触头材料是开关系统的关键,其性能决定了电器设备运行的可靠性。低压开关中的触头材料以Ag基为主,Ag/CdO综合性能优异,但是Cd的毒性限制了它的应用。近几十年来,Ag/SnO_2、Ag/ZnO、Ag/Ni、Ag/C、Ag/W等触头材料在部分领域替代了Ag/CdO,但是这些替代材料的温升高、接触电阻大、抗材料转移性能差、抗熔焊性能差等问题无法得到有效解决。从触头材料的发展历史出发,围绕应用、制备、性能及研究现状等,介绍了低压开关中常用Ag基触头材料的研究概况,探讨了Ag基触头材料的发展动向,并介绍了MAX作为增强相在Ag基触头材料中应用的前景。     

Selective epitaxial silicon growth in high aspect ratio contact on 70 nm node flash memory

Selective epitaxial growth (SEG) silicon as sacrificial layer is proposed to circumvent junction leakage (I_jun) of bit line contact due to silicon substrate loss by high aspect ratio contact etching and spontaneous salicide formation. The result indicates that the appropriate SEG silicon in contact area significantly reduces I_jun about three orders compared with no SEG silicon. In addition, the SEG method provides acceptable Kelvin contact resistance. Furthermore, during salicide formation, the consumed ratio of titanium to silicon is 0.7. It is confirmed that the feasible approach not only prevents from I_jun deterioration but also adjusts contact resistance as well.     

碳纤维水泥基材料与电极的接触电阻

论述了接触电阻的产生及其表征,并在试验的基础上分析研究了影响碳纤维水泥基材料(Carbon fiber reinforced cement,CFRC)与电极之间接触电阻的各种因素.研究表明:实际接触面积是影响接触电阻的主要因素,增大实际接触面积是减小接触电阻的一种可行方法.     

真空低温下接触表面对接触热阻的影响

通过接触表面的形貌分析，建立了表面形貌和界面接触热阻的理论模型。通过实验得出了有关参数对接触热阻的影响关系。     

Measurement of the Intrinsic Thermal Conductivity of a Multiwalled Carbon Nanotube and Its Contact Thermal Resistance with the Substrate

The intrinsic thermal conductivity of an individual carbon nanotube and its contact thermal resistance with the heat source/sink can be extracted simultaneously through multiple measurements with different lengths of the tube between the heat source and the heat sink. Experimental results on a 66‐nm‐diameter multiwalled carbon nanotube show that above 100 K, contact thermal resistance can contribute up to 50% of the total measured thermal resistance; therefore, the intrinsic thermal conductivity of the nanotube can be significantly higher than the effective thermal conductivity derived from a single measurement without eliminating the contact thermal resistance. At 300 K, the contact thermal resistance between the tube and the substrate for a unit area is 2.2 × 10^?8 m² K W^?1, which is on the lower end among several published data. Results also indicate that for nanotubes of relatively high thermal conductance, electron‐beam‐induced gold deposition at the tube–substrate contacts may not reduce the contact thermal resistance to a negligible level. These results provide insights into the long‐lasting issue of the contact thermal resistance in nanotube/nanowire thermal conductity measurements and have important implications for further understanding thermal transport through carbon nanotubes and using carbon nanotube arrays as thermal interface materials.     

一种接触热阻的预测方法

采用当量热流量通道的概念对接触热阻的预测进行简化分析，即对表面情况建立相应的表面模型后，确定出当量热流量通道上的各个参数，整个接触面上的接触热阻即可视为有多个当量热流量通道形成的接触热阻并联而成，从而可以预测出两上物体间的接触热阻。     

Polygon‐based contact resolution for superquadrics

The representation of discrete objects in the discrete element modelling is a fundamental issue, which has a direct impact on the efficiency of discrete element implementation and the dynamic behaviour of particulate systems. Disks and spheres are the most commonly used geometric shapes due to their geometric simplicity and computational efficiency, but they are unable to provide resistance to rolling motion. For this reason, some non‐circular/spherical objects, such as polygons/polyhedrons, superquadrics, or the clustering of disks/spheres to form irregular shapes, are introduced. When superquadrics are used as discrete elements, the bottleneck of contact resolution is associated with the searching for intersections of two non‐linear functions, which is a very expensive operation and may sometimes fail in finding the solution. In this work, an efficient and robust algorithm is proposed for contact resolution of 2D superquadrics, in which any superquadric is approximated with a convex polygon through adaptive sampling; then by clipping two polygons, an efficient linear algorithm is performed to search for intersections and overlap area of the polygons; the contact forces and directions are determined by employing a newly established corner/corner contact model. It is important to highlight that the proposed methodology can also be extended to general non‐circular discrete object cases. The performance of the algorithm is demonstrated via numerical examples. Copyright © 2005 John Wiley & Sons, Ltd.     

A formulation for electrostatic‐mechanical contact and its numerical solution

The progress in advanced technology fields requires more and more sophisticated formulations to consider contact problems properly. This paper is devoted to the development of a new constitutive model for electrostatic‐mechanical contacts, based on a micro–macro approach to describe the contact behaviour. The electric‐mechanical contact constitutive law is obtained considering the real microscopic shape of the contacting surfaces, the microscopic behaviour of force transmission and current flow. Some thermo‐mechanical macroscopic models based on microscopic characterizations have already been developed to compute the normal and tangential contact stiffness and the thermal contact resistance. On the basis of such macroscopic models, a similar model, suitable for the electric‐mechanical field, is developed. With reference to the thermal constriction resistance the electric contact resistance is studied, assuming a flux tube around each contacting asperity, and choosing a suitable geometry for its narrowing at the contact zone. The contact element geometry is based on well known theoretical and experimental micro‐mechanical laws, suitably adapted for the FEM formulation. The macroscopic stiffness matrix is calculated on the basis of the microscopic laws and it is continuously updated as a function of the changes in the mechanical and electric significant parameters. A consistent linearization of the set of equations is developed to improve the computational speed, within the framework of implicit methods. Copyright © 2005 John Wiley & Sons, Ltd.     

Analysis of high contact resistance in silver impregnated graphite (SIG) contacts

Silver impregnated graphite (SIG) contacts are used in high safety applications of railway signaling, traffic signaling, and numerous other applications due to high silver content that eliminates the risk of welding in the presence of graphite. High contact resistance (>200 mΩ) was observed in SIG contacts in a railway signaling operation after a few thousand operations of the relay. The high contact resistance was discovered to be a result of loose dust/foreign particles residing between the two contacts. Silver had been preferentially removed from the contacting surfaces during switching operations by an abrading effect of the dust/foreign particles, leaving only graphite on the contact area. Wear was accentuated by the presence of porosity and low hardness of the contacts, leading to improper interaction between the mating surfaces.