Narrow gap space contributes to chemical metallurgy of self-shielded arc welding

The slag-free self-shielded flux-cored wire was fabricated to apply for the narrow gap welding.The results showed that narrow gap welding shows lower welding spatter compared with hardfacing except under voltage of 30 V and current of 260 A.The deposition efficiency keeps over 90%for both 12 mm and 8 mm narrow gap welding.For 12 mm narrow gap welding,when the voltage is 28 V and the current is 264 A(or 286 A),no pores are found in the narrow gap weld.In the continuous welding process,manganese vapor,aluminum vapor and CO continuously generate to form gasbag and occupy the narrow gap space,thus protecting the droplet and molten pool from the invasion of air.

Formation Mechanism of Inclusion in Self-Shielded Flux Cored Arc Welds

The formation mechanism of inclusion in welds with different aluminum contents was determined based on thermodynamic equilibrium in self-shielded flux cored arc welds.Inclusions in welds were systematically studied by optical microscopy,scanning microscopy and image analyzer.The results show that the average size and the contamination rate of inclusions in low-aluminum weld are lower than those in high-aluminum weld.Highly faceted AlN inclusions with big size in the high-aluminum weld are more than those in low-aluminum weld.As a result,the low temperature impact toughness of low-aluminum weld is higher than that of high-aluminum weld.Finally,the thermodynamic analysis indicates that thermodynamic result agrees with the experimental data.

EFFECT OF Fe_2O_3 ON WELDING TECHNOLOGY AND MECHANICAL PROPERTIES OF WELD METAL DEPOSITED BY SELF-SHIELDED FLUX CORED WIRE

Five experimental self-shielded flux cored wires are fabricated withdifferent amount of Fe_2O_3 in the flux. The effect of Fe_2O_3 on welding technology and mechanicalproperties of weld metals deposited by these wires are studied. The results show that with theincrease of Fe_2O_3 in the mix, the melting point of the pretreated mix is increased. LiBaF_3 andBaFe_(12)O_(19), which are very low in inherent moisture, are formed after the pretreatment. Themechanical properties are evaluated to the weld metals. The low temperature notch toughness of theweld metals is increased linearly with the Fe_2O_3 content in the flux due to the balance betweenFe_2O_3 and residual Al in the weld metal. The optimum Fe_2O_3 content in flux is 2.5 percent approx3.5 percent.

Effect of oxygen-containing additives on weld penetration in self-shielded flux cored arc welding

The effect of Fe203 and Liz CO3 additives in flux core on the weld metal oxygen content and weld penetration in self-shielded flux cored arc welding were studied schematically. The result shows that the oxygen content in the weld metal and weld penetration both increased with the Fe203 addition increased in the range of 5 wt. % to 20 wt. %. The oxygen content in the weld metal was increased with the Li2CO3 addition increased in the range of 1 wt. % to 8 wt. %. However, the weld penetration decreased when Li2CO3 addition exceeding 4 wt. %. High-speed photographic images show that when Fe2O3 addition influx core exceeding 15 wt. %, droplet became excessively large, so that spatters were frequently generated in large numbers. In this study, Fe203 and Li2 CO3 in the amount of 11 wt. % and 4 wt. %, respectively, jointly added in the flux core can achieve a deeper weld penetration with sound usability characteristics.

Effects of CeF_3 on properties of self-shielded flux cored wire

Effects of CeF3 on properties of self-shielded flux cored wire including welding process, inclusions in weld metal and mechanical properties are systematically studied. Welding smoke and spatter are reduced with the addition of CeF3. The main non-metallic inclusions in weld metal are AlN and Al2O3. CeF3 can refine non-metallic inclusions and reduce the amount of large size inclusions, which is attributed to the inclusion floating behavior during the solidification of weld metal. The low temperature impact toughness is improved by adding suitable amount of CeF3 in the flux.

Investigation on mechanism of fixing nitrogen in self-shielded flux cored arc welding

Prevention of nitrogen porosity in weld metal deposited with self-shielded flux cored wire with CaF2-TiO2-MgO slag system can be accomplished by using a 'killing agent' such as titanium to react with nitrogen dissolved in the weld metal. The amount of titanium needed to prevent porosity is calculated thermodynamically for various dissolved nitrogen levels. Experimental flux cored wires are used to verify the thermodynamic model. It is concluded that approximately 0.11 wt% titanium in the weld deposit is need to prevent nitrogen porosity when welding without externally applied shielding.

Assessment of Resonance Self-shielding Models during Burn-Up Calculations

Various approaches and models are used in deterministic codes to treat the resonance self-shielding behavior of cross-sections.The accuracy of the models used has a significant effect on the precision of calculations;hence it is essential to select the best self-shielding method that yields accurate results within a reasonable computational time.In the present paper,the performance of the statistical subgroup method and the subgroup projection method associated with the DRAGON5 code is assessed during the burnup of a fuel pin.Two types of fuel are investigated:UO2,and PuO2-UO2.The accuracy of the methods is determined by calculating the variation of the infinite multiplication factor and the reaction rates during burnup,and then the results are compared to the stochastic MCNP6 code.It is indicated that the performance of both methods in treating the resonance self-shielding effect is satisfactory and that the subgroup projection method has a better performance during burnup calculations.

STUDY ON METAL TRANSFER MODES OF SELF-SHIELDED FLUX-CORED WELDING WIRE

Metal transfer behavior of six kinds of self shielded flux cored wire(SSFCW) is studied using the apparatus of SSFCW high speed photography self made. Six kinds of metal transfer modes of SSFCW were obtained through observation for high speed photograph film and analysis. It is believed that the research is of magnificent for improving operative performance and mechanical properties of SSFCW and dynamics characteristic of welding power.

自密实高抗裂混凝土在盾构隧道工作井侧墙中的应用

采用明挖顺作法施工的盾构隧道工作井侧墙位于由维护结构、环框梁、底板及模板组成的密封空间内,其受到的约束作用强,施工难度大,容易因混凝土收缩开裂及浇筑不密实导致渗漏。依托在建的江阴靖江长江隧道工程,在室内研究的基础上,通过现场系列模型试验,比较了采用不同混凝土材料及施工工艺时混凝土结构的密实性。模型试验及工程应用结果表明,采用自密实高抗裂混凝土,结合布料工艺、浇筑速率、分层浇筑静置时间的控制,并辅以必要的振捣,可保证混凝土浇筑密实,进一步结合抗裂温控措施,可消除混凝土收缩裂缝,避免工作井侧墙出现渗漏。

兼具紫外屏蔽功能的自修复聚氨酯涂层的制备与性能研究

在聚氨酯主链中引入芳香族二硫键,制备了一种兼具高自修复率和高紫外吸收的自修复聚氨酯涂层。红外光谱、核磁共振氢谱、动态力学分析、力学测试及修复测试结果表明,R值为4时聚氨酯拥有优异的自修复效果,样条在120℃下加热15 min后断裂伸长率的修复率可达98.8%,涂层在120℃下加热5 min划痕完全修复。同时该聚氨酯涂层(膜厚100μm)对穿透力较强的UVA波段(320~400 nm)有着很强的屏蔽性能,透过率仅为0.07%。

主动式多重性方法对黄饼中铀定量的模拟研究

黄饼材料中铀的准确定量是后续处理工艺选择的关键,文中在主动式多重性方法的基础上,提出了一种通过记录分析中子源诱发238U裂变信息,进行铀定量的方法。但由于黄饼材料自身存在中子自屏蔽效应以及含水量的差异,导致定量结果存在偏差。为了进一步提高定量准确性,使用MCNP(Monte Carlo N-Particle Transport)结合MATLAB程序优化选择了241Am-Be源作为激发源;另外,通过对不同质量及含水量系列化样品的模拟发现:铀定量误差主要来自于泄漏增殖因子ML与增殖因子M差距的不匹配。通过MCNP模拟获取M随铀质量变化规律的曲线后,根据样品净含量选择合适的增殖因子M,再根据二重计数率D进行定量计算,获得铀定量的相对误差小于5%;含水量的变化带来的中子自屏蔽效应对多重计数率影响较大,通过S0/Si与D0/Di的关系对二重计数率D进行修正后再进行计算,铀定量的相对误差能够控制在10%左右;该研究对中子多重性方法在黄饼生产与测量中的应用推广具有重要的参考价值。

Design of Miniature and Self-Shielding Electron-Beam Radiation Processing System

This paper describes the structure and work principle of a miniature and self-shielding electron-beam radiation processing system.Centering on the miniaturization and self-shielding,this system has been manufactured. Test results show that the energy of the electron beam is 2.5MeV,the average power of the beam is 1.2kW,the width of scanning is 300ram,and the radiation emission from this equipment to the environment is under 2uSv/h.This system is reliable,safe,easy to operate and suitable for online radiation processing for manufacture or setting on a vehicle.

自修复聚二甲基硅氧烷/单壁碳纳米管电磁屏蔽材料的制备及性能

传统金属屏蔽材料以反射电磁波为主,易产生二次辐射,且存在高密度、高硬度及易腐蚀等问题。因此,开发新型的以吸收电磁波为主的柔性聚合物电磁屏蔽材料成为研究热点。文中利用超声分散辅助液相沉积技术,将单壁碳纳米管包覆在具有动态性的聚二甲基硅氧烷粉末表面,并通过热压工艺制备了复合材料。由扫描电子显微镜分析,表明单壁碳纳米管在聚合物基体中形成了隔离网络结构。通过矢量网络分析仪测试电磁屏蔽性能,单壁碳管质量分数为1%时,在X波段电磁屏蔽性能超过20 dB;当质量分数为5%时,屏蔽效能高达70 d B,而且吸收损耗占比高达93%。此外,复合材料中聚合物基体的动态性与碳管的光电特性相结合,可以实现在热、电、近红外光等多种刺激下的自修复。

疏水性自修复聚氨酯复合弹性体的制备及其电磁屏蔽性能

通过在聚二甲基硅氧烷基聚氨酯主链上引入四重氢键和二硫键,制备疏水性自修复聚氨酯弹性体(ISH-PU-X),研究二硫键和四重氢键对聚氨酯弹性体力学性能和自修复性能的影响。结果表明,ISH-PU-2的拉伸强度为4.49 MPa,断裂伸长率为331%,划痕在80℃条件下完全消失,力学性能可恢复至原始样条的98%。利用动态键合分子链的流动性,实现银纳米线(AgNWs)在聚氨酯表层的均匀嵌入,获得疏水自修复聚氨酯电磁屏蔽复合材料(AgNWs/PU-X),进一步探究AgNWs含量对复合材料的电磁性能、疏水性和自修复性能的影响规律。结果表明,AgNWs/PU-X的电磁屏蔽效能可达60 dB左右,水接触角可达122°左右,在80℃下修复后电导率可恢复至原始样条的85%。AgNWs/PU-X复合材料可拓展电磁屏蔽材料的应用领域,满足复杂多变应用环境下可持续性的需求。

电容变换的自校准浮地电压传感器

在侵入式浮地电压测量中,由于探头与地的耦合电容受探头距地高度、安装位置下方带电导体的影响,导致传感器增益不稳定,无法准确测量待测电压。针对该问题,提出一种基于电容变换的侵入式浮地电压测量校准方法,实现传感器增益的自标定。介绍浮地电压测量的基本原理,并分析导致耦合电容发生变化的因素,进而提出基于电容变换的自校准方法。为了减少空间杂散电场对测量系统的耦合作用,设计具有对后端电路进行等电位屏蔽的传感器探头,并选取合理的电路参数。搭建实验平台进行幅值精度、相位精度、电场屏蔽抗干扰、不同高度适应性测试。实验结果显示:电压幅值最大相对误差为1.99%,相位绝对误差为0.51°;等电位探头对外界噪声具有屏蔽作用;针对传感器不同高度所重构的待测电压最大相对误差为1.66%。

Dimensionally confined nanosheets self-assembled through self-shielding multiple hydrogen bonding interactions in aqueous media

Herein,we adopt a simple supramolecular strategy to effectively control the tautomerism of ureidopyrimidinone(UPy)moiety and ultimately realize the complete arrangement of enol configuration.The obtained UPy derivatives containing self-complementary quadruple hydrogen bonding interactions can spontaneously self-assemble towards the formation of well-controlled,self-organized supramolecular nanostructure morphologies in both chloroform and water.The resulting aggregates had been fully characterized by various spectroscopy(absorption,emission)and microscopy(TEM,SEM and AFM)studies.It is anticipated that this study can provide an exact and excellent monomeric unit for controllable and precise supramolecular polymerization.The results achieved here also demonstrate the utility and feasibility of multiple hydrogen bonds to direct the self-assembly of small-molecule building blocks in aqueous media,which provides a strategy for the construction of well-defined and stable supramolecular architectures with chemical functionalities and physical properties as advanced materials for biological applications.

自保护药芯焊丝管道全位置自动焊接工艺研究

针对目前城市管道建设中广泛存在的传统手工焊和半自动焊接工艺所导致的焊接质量不稳定等问题,设计了一种自保护药芯焊丝管道全位置自动焊接工艺。采用氩弧自动焊根焊+自保护药芯焊丝自动焊填充及盖面焊的焊接方法,选用22°U形坡口及Φ1.6 mm JC-29Ni1焊丝。结果表明,焊接接头力学性能能够达到标准要求。该工艺能够为城市管道全位置自动焊提供参考。

Confidence estimation in the prediction of epithermal neutron resonance self-shielding factors in irradiation samples using an ensemble neural network

Large neutron absorption resonances in the nuclides present in irradiation samples reduce the irradiating neutron flux at energies close to a resonance.In neutron activation analysis of optically thick samples with resonant isotopes,this self-shielding effect can be significant,and must be accounted for to ensure accurate measurements.Here we show that an ensemble artificial neural network can be used to accurately predict the epithermal selfshielding factors in wires composed of up to 57 nuclides.Importantly,the neural network can account for resonance interference that affects the self-shielding in samples containing nuclides with large overlapping resonances.We use Monte Carlo simulations of sample wires irradiated in a thermal neutron spectrum to create the data for training the neural network and validate its predictions.A Gaussian negative log likelihood loss function is combined with the ensemble to estimate the confidence in the predicted self-shielding factors when ground-truth data are unavailable.

考虑电缆铜编织带穿错零序TA的配网故障跳闸案例分析

针对一起10 kV配网接地短路故障,加之电缆铜编织带穿接零序TA错误而引起自愈系统误判,出现越级跳闸事件的典型案例。首先,对故障进行深入研究分析和开展检修工作,完成了铜编织带穿接TA的接线整改和验收。然后,为消除地网接地不良的影响,对相关配电房的地网实施了接地电阻的验收和检测。最后,为避免不必要的停电检修,开展了基于电缆内窥镜的铜编织带TA接线带电检测研究,实验结果验证了所提方法的有效性,保障了配网设备安稳可靠运行。

盾构泥砂在吹填施工中的研究

研究对盾构泥砂渣样进行了成分分析,为满足吹填技术指标,采用自航耙吸船改进施工技术,直接将盾构泥砂吹填至现场,对整个吹填过程中的管线布置、流失量控制等技术进行了改进。同时对采用盾构泥砂吹填的具体工程进行了造价对比分析,以期为类似工程提供借鉴。