Experimental Study on Wire Melting Control Ability of Twin-Body Plasma Arc

The twin-body plasma arc has the decoupling control ability of heat transfer and mass transfer,which is beneficial to shape and property control in wire arc additive manufacturing.In this paper,with the wire feeding speed as a characteristic quantity,the wire melting control ability of twin-body plasma arc was studied by adjusting the current separation ratio(under the condition of a constant total current),the wire current/main current and the position of the wire in the arc axial direction.The results showed that under the premise that the total current remains unchanged(100 A),as the current separation ratio increased,the middle and minimum melting amounts increased approximately synchronously under the effect of anode effect power,the first melting mass range remained constant;the maximum melting amount increased twice as fast as the middle melting amount under the effect of the wire feeding speed,and the second melting mass range was expanded.When the wire current increased,the anode effect power and the plasma arc power were both factors causing the increase in the wire melting amount;however,when the main current increased,the plasma arc power was the only factor causing the increase in the wire melting amount.The average wire melting increment caused by the anode effect power was approximately 2.7 times that caused by the plasma arc power.The minimum melting amount was not affected by the wire-torch distance under any current separation ratio tested.When the current separation ratio increased and reached a threshold,the middle melting amount remained constant with increasing wire-torch distance.When the current separation ratio continued to increase and reached the next threshold,the maximum melting amount remained constant with the increasing wire-torch distance.The effect of the wire-torch distance on the wire melting amount reduced with the increase in the current separation ratio.Through this study,the decoupling mechanism and ability of this innovative arc heat source is more clearly.

DC Arc Plasma Furnace Melting of Waste Incinerator Fly Ash

Municipal solid waste incinerator （MSWI） fly ash was melted using a set of direct current （DC） arc plasma furnace system for the first time in China. At a feed-rate of flying ash of 80 kg/h, the temperature at the gas outlet was above 1300℃. Dioxins in the off-gas were recorded as 0.029 ng I-TEQ/Nma （international toxic equivalent, I-TEQ）, well below 0.5 ngTEQ/Nm^3（toxic equivalent, TEQ）, while those in the melted product （slag） were 0.00035 ng/g I-TEQ. Molten slag from the furnace showed excellent resistance against the leaching of heavy metals. These results prove that the plasma furnace is effective for the detoxification and stabilization of MSWI fly ash.

Oxidation resistance of Si-coated TZM alloy prepared through combined process of plasma spray and laser surface melting

Plasma thermal spraying ofSi coating layer ontitanium-zirconium-molybdenum （Ti-Zr-Mo）,TZM alloy,was conducted for the surface protection of the Mo substrate that is unstable in air at high temperatures. Although the plasma thermal spraying alone could protect the Mo alloy from oxidation at a high temperature for a short time, the post laser surface melting process further improved the oxidation resistance of Si-coated alloy. In the case of the post laser treated specimen,MoSi compounds, mainly MoSi2 phases, were formed during the additional annealing process, and the oxidation resistance could be even further enhanced. The corrosion behaviors of Si-coated specimens in 3.5%NaCl solution were also investigated;however,nosignificant variations with respect to the post treatment procedure were found.

Preparation of Ni60-WC Coating by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, the plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% tungsten carbide （WC） ceramic powder used as coating material to obtain different Nickel-based WC alloys coating. Micro-structure and micro-hardness analysis of the coating layer are conducted, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70%Ni60, 30%WC powder has the best properties with plasma spray welding, in which the micro-hardness can achieve 900HV, meanwhile it can improve the thermal property of hot-forging die dramatically.

Ni60-SiC Coating Prepared by Plasma Spraying, Plasma Re-melting and Plasma Spray Welding on Surface of Hot Forging Die

In order to produce the hear-resistant inner layer of hot-forging die, plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% SiC ceramic powder used as coating material to obtain different Ni-based SiC alloys coating. Micro-structure and micro-hardness analysis of the coating layer were followed, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70% Ni60, 30% SiC powder has best properties with plasma spray welding, in which the micro-hardness can achieve 1100 HV, meanwhile can improve the thermal property of hot-forging die dramatically.

Exercised blood plasma promotes hippocampal neurogenesis in the Alzheimer's disease rat brain

Background:Exercise training promotes brain plasticity and is associated with protection against cognitive impairment and Alzheimer’s disease(AD).These beneficial effects may be partly mediated by blood-borne factors.Here we used an in vitro model of AD to investigate effects of blood plasma from exercise-trained donors on neuronal viability,and an in vivo rat model of AD to test whether such plasma impacts cognitive function,amyloid pathology,and neurogenesis.Methods:Mouse hippocampal neuronal cells were exposed to AD-like stress using amyloid-βand treated with plasma collected from human male donors 3 h after a single bout of high-intensity exercise.For in vivo studies,blood was collected from exercise-trained young male Wistar rats(high-intensity intervals 5 days/week for 6 weeks).Transgenic AD rats(McGill-R-Thyl-APP)were inj ected 5 times/fortnight for 6 weeks at2 months or 5 months of age with either(a)plasma from the exercise-trained rats,(b)plasma from sedentary rats,or(c)saline.Cognitive function,amyloid plaque pathology,and neurogenesis were assessed.The plasma used for the treatment was analyzed for 23 cytokines.Results:Plasma from exercised donors enhanced cell viability by 44.1%(p=0.032)and reduced atrophy by 50.0%(p<0.001)in amyloid-β-treated cells.In vivo exercised plasma treatment did not alter cognitive function or amyloid plaque pathology but did increase hippocampal neurogenesis by~3 fold,regardless of pathological stage,when compared to saline-treated rats.Concentrations of 7 cytokines were significantly reduced in exercised plasma compared to sedentary plasma.Conclusion:Our proof-of-concept study demonstrates that plasma from exercise-trained donors can protect neuronal cells in culture and promote adult hippocampal neurogenesis in the AD rat brain.This effect may be partly due to reduced pro-inflammatory signaling molecules in exercised plasma.

Effect of Feed Forms on the Results of Melting of Fly Ash by a DC Plasma Arc Furnace

Fly ash from a municipal solid waste incinerator （MSWI） without preprocessing （original fly ash, OFA） was melted by a direct current （DC） plasma arc furnace to investigate how the feed forms governed the results. Dioxins in flue gas from stack and bag-filter ash （BFA） were detected. The distribution of heavy metals of Pb, Cd, As, and Cr along the flue gas process system was analyzed. Through a comparison of the results for dioxins and heavy metals in this study and previous work, carrying-over of fly ash particles with the flue gas stream can be deduced. Based on the magnetic induction equation and Navier-Stokes equations, a magnetohydrodynamic （MHD） model for the plasma arc was developed to describe the particle-carrying effect. The results indicate that, a. when melted, the feed forms of MSWI fly ash affect the results significantly; b. it is not preferable to melt MSWI fly ash directly, and efforts should be made to limit the mass transfer of OFA from the plasma furnace.

Volt-ampere characteristics of a nitrogen DC plasma arc with anode melting

The characteristics of a nitrogen arc using a graphite cathode and a melting anode in a pilot-scale plasma furnace are investigated. The voltage is examined as a function of current and apparent plasma length. The voltage increases non-linearly with the increase of apparent plasma length, with the current fixed. The experimental data so obtained are compared with the predictions of the Bowman model for the electric arc, and with numerical simulations as well. The level of agreement between the experimental data at the melting anode and the numerical predictions confirms the suitability of the proposed the Bowman model. These characteristics are relevant to the engineering design and evaluation of a DC plasma furnace and reactor for the treatment of hazardous fly ash waste.

Application of In-Flight Melting Technology by RF Induction Thermal Plasmas to Glass Production

An innovative in-flight glass melting technology with induced thermal plasmas was developed for the purpose of energy conservation and environmental protection. Two-dimensional modeling was used to simulate the thermofluid fields in the plasma torch. The in-flight melting behavior of glass raw material was investigated by various analysis methods. Results showed that the plasma temperature was up to 10000 K with a maximum velocity over 30 m/s, which made it possible to melt the granulated glass raw material within milliseconds. The carbonates in the raw material decomposed completely and the compounds in the raw material attainted 100% vitrification during the in-flight time from the nozzle exit to substrate. The particle melting process is similar to the unreacted-core shrinking model.

Effect of Injection Position on In-Flight Melting Behavior of Granular Alkali-Free Glass Raw Material in 12-Phase AC Arc Plasma

An innovative in-flight glass melting technology with a multi-phase AC arc plasma was developed to save energy and reduce emissions for the glass industry. The effect of the injection position on the in-flight melting behavior of granulated powders was investigated. Results show that the injection position has a strong effect on the melting behavior of alkali-free glass raw material. With the increase in injection distance, the vitrification, decomposition, and particle shrinkage of initial powders are improved. Longer injection distance causes much energy to transfer to particles due to a longer residence time of powder in the high temperature zone. The high vitrification and decomposition degrees indicate that the new in-flight melting technology with 12-phase AC arc can substantially reduce the melting and refining time for glass production.

Surface treatment of 0Cr19Ni9 stainless steel SMAW joint by plasma melting

Micro plasma arc surface melting of 0Cr19Ni9 shielded metal arc welding joint with a micro plasma arc welder produced a thin surface melted layer with a refined microstructure. The surface treatment changed the anodic polarization behavior in 0.5 mol/L H 2SO 4 solution. The polarization tests showed that for the as welded joint both the heat affected zone and the weld metal decreased in resistance to corrosion compared with the as received parent material while for the micro plasma arc surface melted joint the corrosion resistance increased significantly. This increase in corrosion resistance is attributed to the rapid solidification of the melted layer. Rapid solidification of the melted layer refines its microstructure, decreases its microsegregation, and inhibits the precipitation of chromium carbides at the grain boundaries.

Preparation of Ni60-Cr_3C_2 Coating by Plasma Spraying,Plasma Re-melting and Plasma Spray Welding on W6Mo5Cr4V2

In order to prepare heatresistant inner layer of hot-forging die, plasma spraying, plasma re- melting and plasma spray welding were adopted. Cr3C2 coatings of Ni-Based were prepared respectively with 10%, 20% and 30% Cr3C2 powder and W6Mo5Cr4V2 substrate. The coating microstructure analysis, the micro-hardness test, and the measurement of thermal parameters of coating were conducted. The experimental results show that the coating has the better thermo-physical property by using plasma spray welding method with the powder ratio of 90% Ni60 and 10% Cr3C2, and by this way the micro-hardness of coating can achieve 1100 HV.

Graft of Polybutylene Terephthalate Meltblown Nonwovens by Plasma Initiation and Their Surface Performance

Main factors affecting the low temperature plasma initia-tion and graft modification of acrylic acid onto polybuty-lene terephthalate(PBT)meltblown nonwovens are stud-ied.The relations between hydrophilic performance ofthe product and plasma power,treating time,andmonomer concentration are investigated.The surfaceperformances of grafted products are analyzed.It is ob-tained that hydrophilic performance of PBT nonwovens isgreatly improved due to the etching of the plasma andthe introduction of polar groups so as to meet the needsof leukocyte depleting materials.

Study on Carburizing and Temperature Rising of the Semi-Steel Melt with Plasma Heating

Experiments were carried out on carburizing and temperature rising of the semi steel melt in a plasma induction furnace.Influence of many factors, such as power supply mode,position of the plasma torch and bottom blown gas stirring,on heating efficiency and melt temperature distribution was studied. Melt temperature could be effectively controlled by plasma heating,and carbon content of semi steel melt increased from 1.92 % to 4.58 %, and the utilization rate of carbon reached up to 61.57 % during carburizing of the melt.

TiVNbTa高熵合金球形粉末制备及选区激光熔化成形

利用氢化脱氢、机械球磨、等离子体球化技术成功制备了TiVNbTa难熔高熵合金球形粉末,并采用选区激光熔化(SLM)技术将此球形粉末制备成TiVNbTa难熔高熵合金块体试样,研究不同SLM工艺参数对合金显微组织和力学性能的影响。结果表明:所制备的粉末球形度高、分散良好,平均粒度为48μm;SLM成形的TiVNbTa难熔高熵合金具有超细晶组织,其熔池心部为胞状晶区,熔池边缘为柱状晶区。随着激光功率的增加,合金的压缩屈服强度整体变化不大,但塑性应变呈下降趋势;然而,随着扫描速率的增加,合金的压缩屈服强度和塑性应变持续下降。当激光功率为175 W、扫描速率为400 mm/s时,沉积态合金具有最低的孔隙率,XOY面和YOZ面的孔隙率分别降低至0.26%和1.42%,压缩屈服强度σ_(0.2)为1001 MPa,最大抗压强度σ_(bc)为1741 MPa,塑性应变ε_(p)为10.0%。

球形粉体制备技术研究进展

【目的】球形粉体由于具有更好的流动性和均匀性被广泛应用于增强材料、涂料、陶瓷、3D打印等领域。为了满足不同行业对粉体材料的表面特性和物理性能要求,提升产品性能,降低工艺损失,促进绿色制造,对球形粉体制备技术的研究现状进行总结和思考。【研究现状】综述球形粉体常见制备技术,包括传统物理法(机械整形法和喷雾干燥法)、化学法(气相化学反应法、沉淀法、水热合成法、溶胶凝胶法及微乳液法)和高温熔融法(等离子体球化法、雾化法和气体燃烧火焰成球法),总结上述方法的优势及目前的局限性,重点阐述不同球形粉体材料制备技术的基本原理与应用领域的研究进展。【展望】对球形粉体制备技术的发展趋势进行分析与展望,认为高温熔融法是最具实现大规模工业化生产潜力的球形粉体制备技术,提出高纯超细、窄分布、粒径可控、高球化率、高效率工业智能化绿色生产是我国未来球形粉体制备技术的发展趋势。

工艺参数对激光选区熔化316L零件电解质等离子抛光的影响

[目的]激光选区熔化技术(SLM)制备的316L不锈钢零件表面不易抛光。[方法]采用电解质等离子抛光技术对其进行抛光,研究了工艺参数对工件表面粗糙度(Ra)、微观形貌、元素含量、物相组成和耐蚀性的影响,并采用正交试验法进行工艺优化。[结果]各工艺参数对粗糙度的影响排序为:抛光电压>抛光时间>抛光液温度>下潜深度。最佳工艺参数为:抛光电压320 V,抛光时间300 s,抛光液温度80℃,下潜深度250 mm。抛光后的表面粗糙度可由2.1084μm降低至0.2127μm,表面Cr元素含量由初始的13.92%增大到17.28%,在3.5%NaCl溶液中的腐蚀电位正移,腐蚀电流密度降低。[结论]电解质等离子抛光可有效改善SLM制备的316L零件的表面形貌,降低其表面粗糙度,提高其耐蚀性。

碱熔-树脂分离-电感耦合等离子体质谱法测定黄铜矿单矿物中8种贵金属元素的含量

黄铜矿单矿物样品中常伴有金、银等贵金属元素,在冶炼铜时,还会综合回收贵金属等伴生元素,因此准确测定样品中各贵金属元素含量具有重要意义,但是相应方法未见报道。通过优化熔融、树脂分离条件以及校正共存元素干扰,提出了题示方法。取0.2000 g样品置于刚玉坩锅中,加入0.5 g氢氧化钠,于室温升温至700℃,熔融5 min。趁热加入1.5 g过氧化钠,于700℃熔融30 min,冷却后加入50 mL热水,于200℃煮沸3 min。用水洗涤坩埚,收集洗涤液并合并于样品溶液中,用体积比3∶1盐酸-硝酸溶液(王水)调节酸度至pH 1。加入由质量比2∶8的A21型阴离子交换树脂和R1S-82聚苯乙烯骨架硫脲螯合树脂混合制成的混合树脂1.0 g,于70℃吸附60 min。取出树脂,加入10 g·L^(-1)硫脲溶液20 mL和50%(体积分数)王水溶液20 mL,于90℃解吸60 min。用3%(体积分数)硝酸溶液将解吸溶液稀释至100 mL,分取1 mL,用3 mol·L^(-1)硝酸溶液稀释至10 mL,供电感耦合等离子体质谱仪分析。内标镥在线加入,用于补偿基体效应和灵敏度漂移;解吸溶液中含有微量铜、镍和铅,干扰低含量铑和钌测定,通过公式可校正相应干扰。结果显示:8种贵金属元素(铂、钯、铑、铱、钌、锇、金和银)的质量浓度均在一定范围内与质谱强度呈线性关系,7种元素的检出限(3s)为0.04~0.17 ng·g^(-1)(银的检出限为0.11μg·g^(-1))。对黄铜矿单矿物样品进行精密度和准确度考察,测定值的相对标准偏差(n=6)为0.47%~4.4%,加标回收率为97.2%~102%。

等离子体预处理对聚氨酯/涤纶复合织物贴合牢度的影响

为防止复合纺织品在生产过程中出现脱胶现象,文章采用低温空气等离子体技术对织物的贴合面进行预处理,以提高纤维的摩擦因数和比表面积,增加环保型水性聚氨酯热熔胶在复合织物间的贴合牢度。结果表明,等离子体预处理后,复合织物经向剥离强力提高了796%;纬向剥离强力提高了1050%;经30次水洗,复合织物的经向剥离强力为15.2 N,纬向剥离强力为9.4 N,仍符合国家标准。在电压25 kV、作用时间5.5 min、作用间距2 mm的等离子体预处理条件下,复合织物的经向剥离强力达到18.3 N,纬向剥离强力达到12.6 N,贴合牢度达到最佳。因此,等离子体预处理为解决聚氨酯/涤纶复合织物贴合牢度不佳的技术问题提供了一种可行性方法,能够同时满足市场对环保和高性能纺织品的需求。