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.

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.

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.

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.

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%。

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.

全谱系中子学计算程序FSAR的研发进展及其共振方法初步验证

为满足覆盖广域中子能量范围的先进反应堆研发需求,中国核动力研究设计院开发了先进反应堆全谱系中子学计算程序FSAR。FSAR程序是基于确定论两步法计算策略、由二维截面生成计算程序和三维堆芯计算程序组成的中子学计算程序。二维截面生成程序采用超细群条件下的子群方法进行共振自屏效应处理,在共振计算中嵌入特征线方法求解慢化方程以获得精确的共振自屏截面。在截面生成计算中采用特征线方法求解二维组件的中子通量密度,从而获得少群均匀化截面。全谱系先进反应堆中子能量跨度大,不同的中子平均自由程导致了全堆芯局部非均匀性和全局空间耦合效应强烈。为更好地处理上述效应,截面生成计算中采用了超均匀化方法和泄漏修正模型进行均匀化截面修正。堆芯计算程序采用离散纵标法进行三维中子输运计算,采用微观燃耗计算方法模拟堆内全寿期内各核素的消耗和累积。本文采用快谱、中间能谱及热谱条件下的计算问题对FSAR程序共振计算方法进行了初步验证。计算结果表明,对于不同能谱条件下的测试问题,FSAR程序均能够获得与参考解符合较好的有效共振截面,具备良好的全中子能谱共振效应处理能力。

DRAGON程序在压水堆燃料栅元计算中的研究

在压水堆核设计中,不同的输运计算方法、共振自屏计算方法和多群截面库会对最终的反应性精度造成较大的影响,所以需要针对不同的组合方式进行研究,从而得到精度最高的组合。因此,本文以压水堆常见的燃料栅元为研究对象,利用DRAGON程序中自带的不同输运计算方法(界面流/碰撞概率方法)、共振自屏计算方法(等价理论/子群方法)和多群截面库(DRAG-281/WIMS-D 281)进行计算,并将结果与蒙卡程序进行对比。通过一系列压水堆算例进行测试,结果发现碰撞概率方法、子群方法和DRAG-281库在压水堆燃料栅元计算中精度较高,而界面流方法、等价理论与WIMS-D 281库匹配性较好,整体精度较高。

基于中子自屏蔽校正的氯氢比确定含油饱和度的改进方法

提出用铁的俘获伽马射线标记中子自屏蔽校正因子并组合氯氢比确定含油饱和度的方法。利用蒙特卡罗方法建立井筒-地层模型,模拟不同孔隙度和地层水矿化度条件下的俘获伽马能谱,研究中子自屏蔽因子及含油饱和度测井响应,并通过模拟实例来验证该方法。结果表明:铁标记中子自屏蔽校正后的氯氢比随孔隙度增加而增大,孔隙度相同时与含水饱和度呈线性变化关系,相对灵敏度可提高到1倍以上,能够解决常规氯氢比确定含油饱和度灵敏度下降的问题;计算含油饱和度误差降低,为高矿化度水地层脉冲中子俘获测井定量评价含油饱和度提供一种新方法。

TOPAZ-Ⅱ反应堆慢化剂正温度效应研究

TOPAZ-Ⅱ空间核反应堆电源采用热离子静态热电转换方式,系统输出电功率为5 kW,寿命可达3 a,是当前可迅速工程化的最先进的空间核电源系统之一。然而TOPAZ-Ⅱ反应堆的慢化剂温度系数是一个较大的正值,并导致了全堆的温度系数也是正值,这对反应性控制系统的可靠性提出了很高要求,因而有必要对其产生的机理进行详细的研究。采用MCNP程序构建了TOPAZ-Ⅱ反应堆堆芯三维精确几何模型,从中子能谱的变化、中子平衡关系的变化以及中子循环因子的变化3个方面详细分析了TOPAZ-Ⅱ反应堆慢化剂正温度效应产生的原因。通过设计验证算例验证了分析的正确性,并找到了可减小慢化剂正温度效应的方法,为未来热离子反应堆的优化设计提供了一个指导方向。

TiO_(2)对自保护药芯焊丝熔敷金属组织与性能的影响

针对自保护药芯焊丝焊接熔渣中TiO_(2)和Al、Mg的冶金反应引起熔敷金属成分变化的问题,本文以CaF_(2)-Al-Mg为基础渣系,制备了不含TiO_(2)和在药粉中分别添加5%、10%和20%TiO_(2)的4种自保护药芯焊丝,并以熔化极自保护焊接方式堆焊了相应的熔敷金属,通过落锤冲击试验、直读光谱仪、光学显微镜、SEM、拉伸试验和冲击试验,研究了TiO_(2)对脱渣率以及熔敷金属成分、组织、夹杂物和力学性能的影响规律.试验结果表明,TiO_(2)能有效改善脱渣性,并会与Al、Mg发生冶金反应:2Al+Mg+2TiO_(2)→2Ti+MgAl_(2)O_(4),还原出来的Ti经过渣-金属界面进入熔敷金属,导致熔敷金属中的Ti含量明显升高,C、Si、N含量降低;无TiO_(2)焊丝的熔敷金属组织主要为针状铁素体,夹杂物主要为直径<1μm的圆形MgO·Al_(2)O_(3),此时的屈服强度为411MPa,0℃冲击功为86 J,冲击断口放射区的微观形貌由韧窝和河流花样构成,属于混合断裂;添加5%的TiO_(2)后,熔敷金属中形成大量细小准多边形铁素体组织,并出现了多边形TiN夹杂物,屈服强度提高到489 MPa,韧性稍许下降;当TiO_(2)添加达到10%后,由于熔敷金属中过高Ti含量的影响,组织转变为粒状贝氏体,TiN夹杂物增多并发生粗化,此时屈服强度增高至615 MPa,但韧性急剧恶化,冲击断口放射区完全为河流花样,属于脆性断裂;更高的TiO_(2)含量(20%)对应的熔敷金属,组织仍为粒状贝氏体,因形成大量的晶界Ti_(4)C_(2)S_(2),强度及韧性均降低.

盾构自动驾驶性能评价体系设计和应用

针对当前自主驾驶盾构评价缺乏一套系统、客观、全面的评价标准和方法的问题,在分析当前盾构自主驾驶发展现状基础上,围绕隧道质量、环境安全、掘进效率、控制性能和用户体验5个维度建立了盾构自动驾驶性能评价体系。并以此为基础,以“智驭号”盾构自主掘进控制系统在南京和郑州的应用为例,对项目的自动驾驶性能进行评价和分析。评价结果表明:“智驭号”盾构自主掘进控制系统在各维度下控制效果好,对不同情况适应性强,但在高程下坡姿态控制、自立性差的土层中的沉降控制、砂性土中速度和转矩的控制方面有提升的空间,掘进效率方面也有改进的空间。该评价体系能够科学准确地识别盾构自动驾驶系统性能的特点、实现简洁清晰的评分。评价体系不仅有助于定量化地分析各个控制系统的特点,而且还可以帮助开发者和实施者发现盾构自动驾驶系统存在的问题,为盾构自动驾驶技术发展和工业化应用提供参考。

处理板状双重非均匀性系统的方法研究

针对弥散颗粒空间自屏效应产生的双重非均匀性,需对处理板状双重非均匀性系统的方法进行研究。本文通过对给定算例的计算,研究了DRAGON程序的Hebert和Sanchez-Pomraning双重非均匀性模型、环形RPT方法、IRPT方法和杂交RPT方法、基于颗粒直径的反应性等效物理转换(DRPT)方法处理板状双重非均匀性系统的能力,并与弥散模型参考值进行对比,结果表明:使用DRAGON程序的Hebert和Sanchez-Pomraning双重非均匀性模型可能会带来较大的计算误差,具有一定的局限性;IRPT方法和杂交RPT方法在燃耗计算过程中也存在一定的计算偏差;但是,本文提出的基于颗粒直径的反应性物理等效转换方法对于板状非均匀性系统的处理具有良好的计算精度,其操作简单、效果更好且适用范围广。