Dynamic behavior of a rotating gliding arc plasma in nitrogen:effects of gas flow rate and operating current

The effects of feed gas flow rate and operating current on the electrical characteristics and dynamic behavior of a rotating gliding arc （RGA） plasma codriven by a magnetic field and tangential flow were investigated.The operating current has been shown to significantly affect the time-resolved voltage waveforms of the discharge,particularly at flow rate =21 min^-1.When the current was lower than 140 mA,sinusoidal waveforms with regular variation periods of 13.5-17.0 ms can be observed （flow rate =21 min^-1）.The restrike mode characterized by serial sudden drops of voltage appeared under all studied conditions.Increasing the flow rate from 8 to 121 min^-1 （at the same current） led to a shift of arc rotation mode which would then result in a significant drop of discharge voltage （around 120-200 V）.For a given flow rate,the reduction of current resulted in a nearly linear increase of voltage.

Influences of nitrogen flow rate on the structures and properties of Ti and N co-doped diamond-like carbon films deposited by arc ion plating

In this paper, Ti-C-N nanocomposite films are deposited under different nitrogen flow rates by pulsed bias arc ion plating using Ti and graphite targets in the Ar/N2 mixture gas. The surface morphologies, compositions, microstructures, and mechanical properties of the Ti-C-N films are investigated systematically by field emission scanning electron mi- croscopy （FE-SEM）, x-ray photoelectron spectroscopy （XPS）, grazing incident x-ray diffraction （GIXRD）, Raman spectra, and nano-indentation. The results show that the nanocrystalline Ti（C,N） phase precipitates in the film from GIXRD and XPS analysis, and Raman spectra prove the presence of diamond-like carbon, indicating the formation of nanocomposite film with microstructures comprising nanocrystalline Ti（C,N） phase embedded into a diamond-like matrix. The nitrogen flow rate has a significant effect on the composition, structure, and properties of the film. The nano-hardness and elastic modulus first increase and then decrease as nitrogen flow rate increases, reaching a maximum of 34.3 GPa and 383.2 GPa, at a nitrogen flow rate of 90 sccm, respectively.

ArcCheck的剂量学特性测量及其对VMAT计划的验证

目的:对ArcCheck的剂量学特性进行测量,分析ArcCheck的剂量学特性曲线,探讨ArcCheck能否满足临床使用的要求。方法:分别测量ArcCheck的重复性、能量响应、角度响应和剂量率响应。结果:归一后ArcCheck的重复性为0.9906±0.0090。能量响应分析表明经过直线回归后的常数项为-0.2575,标准差为0.1215;回归系数为1.4643,标准差为5.3687E-4。角度响应的曲线符合探测器表面的模体材料厚度变化。剂量率的变化对探头的测量结果影响很小。结论:ArcCheck模体探测器的剂量学特性满足临床使用的要求,可以对容积弧形调强计划进行验证。

利用加速量热仪(ARC)研究热分析动力学反应机理

从动力学基础方程推导出绝热条件下ARC热分析动力学方程,与传统的DTA动力学方程比较,ARC理论模型更接近于化学过程工业.以SM型和RM型含能材料为样品进行热分析测试,运用新的理论模型分别计算出了SM型和RM型两种样品的活化能ESM=247.55kJ.mol-1,ERM=138.46kJ.mol-1和指前因子ASM=4.26×1023S-1,ARM=4.20×1012S-1.

ArcCHECK摆位误差对直肠癌VMAT计划剂量验证通过率的影响

目的探讨ArcCHECK摆位误差对直肠癌VMAT计划剂量验证通过率的影响。方法选取10例直肠癌VMAT计划,利用ArcCHECK进行计划剂量验证测量,通过在TPS上移动计划等中心的位置分别模拟Arc CHECK模体X、Y、Z方向上3、4、5 mm的摆位误差,采用绝对剂量Gamma的3%/3 mm为评价指标,分别得到每个计划的通过率。结果原计划平均通过率达到99%以上。ArcCHECK引入三个方向的摆位误差后,对直肠癌VMAT计划的剂量验证通过率均有一定程度的下降,误差越大通过率越低。引入误差后的计划与原计划的通过率相比均具有统计学意义(P<0.05)。不同方向上对通过率的影响存在差别,Y方向上误差的影响更大。结论 ArcCHECK摆位误差对直肠癌VMAT计划的剂量验证通过率有较大影响,直肠癌临床放疗中尤其要严格控制Y方向的摆位误差。

Tri-Arc与Tandem双丝电弧焊焊接工艺特性的对比

通过焊接工艺试验,对比Tri-Arc双丝焊与Tandem双丝焊的焊接工艺特性。结果表明:Tri-Arc双丝焊不但可以达到与Tandem双丝焊相同的焊接效率,而且在相同的焊丝熔敷率(送丝速度)和焊接速度条件下,Tri-Arc双丝焊的焊接热输入低于Tandem双丝焊,结果显示焊缝熔合比和焊接变形量更低。因此,Tri-Arc双丝电弧焊不仅可以在高效焊接应用场合替代Tandem双丝电弧焊,达到相同甚至更高的焊丝熔敷率,而且具有比Tandem双丝焊更优越的焊接性能和更广泛的适用范围。

A study on consumable aided tungsten indirect arc welding

A consumable aided tungsten indirect arc welding method has been studied. This method is different from the traditional TIG welding because it introduces an MIG welding torch into the traditional TIG welding system. An indirect arc is generated between the consumable electrode of the MlG welding torch and the tungsten electrode of the TIG welding torch, but not generated between the tungsten electrode of the welding torch and the base metal. Welding current flows from the consumable electrode to the tungsten electrode in the free-burning indirect are. The consumable aided tungsten indirect arc welding not only rapidly melts the welding wire but also effectively restrains the excessive fusion of the base metal. The welding experiment and the theoretical analysis confirm that this method can obtain a high deposition rate and a low dilution ratio during the welding process.

Tri-Arc与Tandem双丝电弧焊的工作原理对比分析

目的介绍一种称为Tri-Arc的新型双丝电弧焊接方法。方法将Tri-Arc双丝电弧焊与应用较广的Tandem双丝电弧焊的系统构成和焊接电流波形进行对比分析。结果Tri-Arc和Tandem两种双丝电弧焊接方法所使用的双丝焊枪相近,双电源相位同步控制和U/I脉冲控制方式类似。Tri-Arc和Tandem两种双丝电弧焊接方法的差异在于:Tandem双丝电弧焊的2个电弧是相对独立的,而Tri-Arc双丝电弧焊的2个电弧是相互耦合的,因此Tri-Arc双丝电弧焊又具有旁路耦合电弧的某些特点。结论这种新型的Tri-Arc双丝电弧焊不仅具有与Tandem双丝电弧焊一样的高焊丝熔敷率,而且具有比Tandem双丝电弧焊更低的焊接热输入。

Characteristics of Atmospheric Pressure Rotating Gliding Arc Plasmas

In this work, a novel direct current （DC） atmospheric pressure rotating gliding arc （RGA） plasma reactor has been developed for plasma-assisted chemical reactions. The influence of the gas composition and the gas flow rate on the arc dynamic behaviour and the formation of reactive species in the N2 and air gliding arc plasmas has been investigated by means of electrical signals, high speed photography, and optical emission spectroscopic diagnostics. Compared to conventional gliding arc reactors with knife-shaped electrodes which generally require a high flow rate （e.g., 10-20 L/min） to maintain a long arc length and reasonable plasma discharge zone, in this RGA system, a lower gas flow rate （e.g., 2 L/min） can also generate a larger effective plasma reaction zone with a longer arc length for chemical reactions. Two different motion patterns can be clearly observed in the N2 and air RGA plasmas. The time-resolved arc voltage signals show that three different arc dynamic modes, the arc restrike mode, takeover mode, and combined modes, can be clearly identified in the RGA plasmas. The occurrence of different motion and arc dynamic modes is strongly dependent on the composition of the working gas and gas flow rate.

Numerical analysis of plasma arc behaviors

Completely understanding the physical mechanisms of the plasma arc is critical to its application in welding of medium thickness plates. In this study, a mathematical model is developed to analyze the temperature, fluid flow, electromagnetic fields and pressure distribution in plasma arc welding. The correlations between the torch structure （ nozzle diameter） and the plasma are properties are analyzed qualitatively. The influence of the plasma gas flow rate on the plasma arc behavior is also simulated numerically. The temperature distribution and current density of the plasma are change greatly with a little variation of the nozzle diameter and^or the plasma gas flow rate. Compared to the tungsten-inert-gas arc with almost same conditions, the heat intensity, fluid velocity and pressure at the anode suoCace rise by one order of magnitude for a plasma arc. The analysis results lay solid foundation for effective usage ofplnsma arc welding.

The alternate wire-feed control in the automatic CO_2 arc welding

In the automatic CO_2 arc welding, the alteration of the vertical distance between the welding torch and the workpiece has a strong effect on the welding parameters such as welding current and voltage, with the result that the appearance and quality of weld are not steady. To weaken the influence of the distance alteration, a method is put forward in the paper. The method is that the alternate wire-feed control is used for compensating the welding current. On the basis of theoretical analysis, a static numerical model for alternate wire-feed control is established. The experiments show that the model-based regulation of the wire feed rate can compensate the welding current and ensure the appearance of weld. When the alteration of vertical distance between the torch and the workpiece is greater, not only is the wire feed rate regulated, but the output voltage of the power source is adjusted to ensure the appearance and quality of weld.

A DECAGONAL QUASICRYSTAL WITH AN ARC-SHAPED CRACK

A decagonal quasicrystal, which is weakened by an arc-shaped crackpenetrating through the solid in the period direction, and which is subjected to remote uniformphonon stresses, is investigated by applying the complex variable method which is just developed bythe authors. It is found that the phonon and phason stresses near the crack tips exhibit inversesquare root singularities. The four complex stress functions characterizing the phonon and phasonfields are derived. Explicit expressions for the phonon and phason stress intensity factors, crackopening displacements and energy release rate are also presented.

Structure and Tribological Properties of CrTiAlN Coatings Deposited by Multi-Arc Ion Plating

CrTiAIN coatings were prepared by using a home-made industrial scale multi-arc ion plating system. The coatings were found to be composites of face-center-cubic CrN and TiN. The surface roughness, microhardness, and tribological properties of the films were significantly affected by the nitrogen pressure and dc-pulsed bias voltage applied to the substrate. The CrTiA1N coatings with the smoothest surfaces were obtained at optimum conditions of nitrogen pressure of 5.0 Pa and bias voltage of -200 V. The samples were found to exhibit a hardness of 2900 HV0.05 with an average friction coefficient of 0.16 and wear rate of 1.5× 10^-16 m^3/N.m against cemented carbide.

超高功率电弧炉变压器和电抗器技术参数设计

电弧炉变压器主要作用是降低供电电压,产生大电流,在保证供电效率的情况下,适应电弧炉冶炼所需的电弧弧长,保证电弧炉冶炼过程的安全性。同时提供不同挡位的电压和电流,以满足冶炼过程需要。电抗器主要作用是增加线路的无功功率,降低短路电流和功率因数,稳定电弧燃烧。同时提供不同挡位的电抗,以满足冶炼过程不同工况的需要。变压器和电抗器技术参数的合理设计是保证电弧炉稳定冶炼的关键,依据电弧炉所需的冶炼效率及出钢量,系统分析电弧炉变压器和电抗器参数的设计原理。从分析可知,变压器的容量是基于电弧炉的通电时间及出钢量进行确定,而变压器的二次电压、额定电流及电抗器容量等参数是基于电弧冶炼稳定性的约束条件进行计算。计算结果与JB/T 9640-2014参考值进行对比分析,结果匹配度较好。

基于响应曲面法的双丝三弧堆焊工艺参数优化

为了优化双丝三弧焊堆焊工艺参数和预测堆焊稀释率和焊接电流,基于响应曲面法建立了双丝间电流(M弧电流)、主弧电压等焊接工艺参数与稀释率和焊接电流的数学模型。利用Design-Expert软件对稀释率和焊接电流响应进行方差分析、模型显著性检验及模型信噪分析,研究了堆焊工艺参数对稀释率和焊接电流的影响规律,并对堆焊工艺进行了优化设计,以及结果验证。结果表明,M弧电流对焊接电流和稀释率的影响比较显著;增加M弧电流,焊接电流减小,基材熔化量变小,稀释率越小;减小熔化母材过多的进入堆焊层,保证金属粉芯焊丝的有效成分,有利于堆焊合金材料组织和耐磨性的控制。经过优化设计获得最佳堆焊工艺参数主弧电压为35 V,M弧电流为260 A,送丝速度为10 m/min,频率为70 Hz,占空比50%。

基于工程应用的CW-GMAW熔滴过渡形态表征

综述了涉及工程应用的冷丝熔化极气体保护焊(Cold wire gas metal arc welding,CW-GMAW)熔滴过渡形态特征。结果表明,在大电流、强规范、富氩混合气体保护下,CW-GMAW工艺的熔滴过渡形态呈喷射过渡;当电流较小、电弧电压较低时,可能为滴状过渡,甚至在弧压很低时,呈现短路过渡形态。该工艺电弧发生偏向冷丝的位移,弧长变短甚至发生短路,与冷丝送进速率比增高及冷丝在电弧中产生大量金属蒸气时弧柱电阻下降有关。在具有富氩混合保护气体的相同工艺参数下,CWGMAW转变电流比GMAW降低了4%~7%。焊接工艺参数对CW-GMAW和GMAW工艺熔滴过渡形态的影响规律大致相近,但前者因涉及冷丝送进速率比和电极焊丝送进速度,以及它们的匹配等,使焊接电流的影响更为复杂。

微真空电弧推力器阴极斑点烧蚀特性数值计算研究

为了研究放电参数及阴极材料对微真空电弧推力器(μVAT)烧蚀与推力性能的影响规律,本文建立了μVAT阴极斑点烧蚀模型,完成了对推力器工作性能的数值计算研究,通过与实验数据对比验证了模型有效性。本文系统比较了几种典型阴极材料(Al,Ti,Cu)的烧蚀特性,并获得了微真空电弧推力器工作中离子电流、阴极烧蚀率、阴极斑点烧蚀半径、推力、比冲、推功比及效率等性能参数与电弧电流之间的定量关系。结果表明,工作过程中电弧电流的变化及阴极材料的选取都会对推力器的工作性能产生较为显著的影响。综合考虑各目标性能参数需求,当使用铜作为阴极材料时推力器综合性能最优。

TC4钛合金短电弧钻孔工艺性能研究

为了提高小孔钻削的加工效率和尺寸精度,文章提出了一种新颖高效的管电极短电弧钻孔方法。然而,由于电弧放电能量过大与进给速度不匹配,使得高效、高尺寸精度的小孔加工困难重重。文章揭示了基于脉冲电源的短电弧钻孔的工作原理,分析了SEAD的电压电流波形和截面形貌。此外,还研究了不同电极极性、电压、脉冲频率、占空比和电极进给速率对材料去除率(MRR)、电极相对磨损比(REWR)、平均直径和锥度的影响。最后,通过工艺参数优化实验,得到了小孔SEAD参数的最优组合,验证了小孔SEAD的加工性能。实验结果表明,在最佳加工参数下,小孔SEAD的材料去除率最高,为84.51μm/s,电极相对磨损比较低,为29.34%。加工小孔的最小平均直径和锥度分别为698.49μm和0.001 1°。

中低速磁浮列车受流状态在线检测技术研究

中低速磁浮列车的受流器通过接触轨获取电能,但该接触过程中出现了电弧现象。为了检测和定位中低速磁浮列车运行过程中产生的电弧情况,文章根据紫外传感器和测速检测原理建立电弧检测系统,并在线路中进行试验测试。测试结果表明,电弧的燃弧点主要集中在接触轨的接缝处,燃弧率在标准可控范围内。

基于蒙特卡洛方法的配电网线路雷击跳闸率计算

雷击是造成配电网线路跳闸的主要因素,现提出基于蒙特卡洛方法来计算雷击跳闸率。通过模拟线路遭受雷击并判断随机变量的值是否满足线路跳闸的条件,对模拟结果进行统计,并通过屏蔽因子进行修正得到雷击跳闸率。同时结合某地区的雷电流幅值概率分布拟合曲线,计算该地区配电网线路的雷击跳闸率,并与IEEE和国标推荐法计算出的雷击跳闸率进行了比较,得出基于蒙特卡洛方法的拟合曲线计算出的雷击跳闸率更接近实际进行统计值,表明所提出的方法相比IEEE和国标推荐法具有较高的准确性。