Multi-physical fields distribution in billet during helical electromagnetic stirring:A numerical simulation research

Electromagnetic stirring is one of the widely applied techniques to modify the quality of casting billets.Different from conventional rotate stirring,the helical stirring is more professional in assisting multi-dimensional flow of molten metal and eliminating solidification defects.In this study,the single-winding helical stirring(SWHS)was introduced,offering advantages such as smaller volume and lower electromagnetic shielding compared to traditional helical stirring methods.Following a comprehensive numerical simulation,the stirring parameters of SWHS were adjusted to yoke inclination angle of 43°and frequency of 12 Hz.The higher electromagnetic force and flow velocity in drawing direction,as well as the lower temperature gradient induced by the SWHS,are positive factors for homogeneous solidification of billet.The experimental results on Al-8%Si alloy and 0.4%C-1.1%Mn steel demonstrate that compared to rotate stirring,the SWHS process can induce better billet quality and is more effective in accelerating the equiaxed expansion and reducing element segregation.The SWHS process can enhance the equiaxed ratio of the billet by 58.3%and reduce segregation degree of carbon element by 10.97%.Consequently,SWHS holds great promise as a potential approach for improving the quality of continuous casting billets.

Numerical simulation of nozzle structure to improve eccentric mold electromagnetic stirring in a round bloom mold

A three-dimensional mathematical model coupling electromagnetic,flow,heat transfer,and solidification has been developed to investigate the effect of eccentric mold electromagnetic stirring(EM-EMS)on the flow and heat transfer of molten steel in round blooms with different cross sections.The uneven distribution of the flow field caused by EM-EMS was improved by changing the straight submerged entry nozzle(SEN)to a four-port SEN.The symmetry index was determined by the velocity distributions on the left and right sides of the center cross section of mold electromagnetic stirring(M-EMS),which quantitatively evaluated the symmetry of EM-EMS on the flow field.In the presence of EM-EMS,the maximum temperature difference ofϕ500 mm andϕ650 mm round blooms between the inner and outer curves amounted to 63 and 26 K,respectively.The maximum distinction between the solidified shells in the inner and outer curves was 11.5 and 5.3 mm,respectively.After using the four-port SEN,the temperature and the shell distribution on the inner and outer curves for theϕ500 mm round bloom were almost the same.The symmetry indices ofϕ500 mm andϕ650 mm round blooms were increased from 0.55 and 0.70 to 0.77 and 0.87,respectively.The four-port SEN can be used to mitigate the negative impact of EM-EMS on the steel flow field.

Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.

3D MERGE与3D SPACE STIR序列在腰椎间盘突出症检查中的应用比较

目的:对比三维多回波恢复梯度回波(3D MERGE)、三维可变反转角快速自旋回波(3D SPACE STIR)序列在腰椎间盘突出症(LDH)检查中的应用效果。方法:选择2020年1月~2022年11月收治的135例LDH患者,回顾性分析患者临床和磁共振成像(MRI)资料,所有患者均接受常规MRI扫描及3D MERGE、3D SPACE STIR序列扫描,对比3D MERGE、3D SPACE STIR序列测量神经根直径的一致性,评价两种序列的图像质量参数[信噪比(SNR)、对比噪声比(CNR)]、图像清晰度评分。结果:3D MERGE和3D SPACE STIR序列测量的L3~S1神经根直径比较差异无统计学意义(P>0.05),且两组序列测量的L3、L4、L5和S1直径均显示出较高相关性(r=0.957,0.986,0.975,0.972,P<0.05);3D MERGE序列的SNR及CNR均高于3D SPACE STIR序列,神经根显示分级、图像清晰度评分优于3D SPACE STIR序列,差异有统计学意义(P<0.05)。结论:3D MERGE、3D SPACE STIR序列在LDH神经根直径测量中具有极高一致性,3D MERGE序列较3D SPACE STIR序列能够更清晰显示神经跟的解剖形态,图像质量更好。

Development and Research of Non⁃Stirring Conveying Device for Waste Resin in Nuclear Power Plant

Blockage in the storage and transportation of waste resin is a difficult problem in the radioactive waste treatment process of nuclear power plants.In this study,in order to solve the problems of unstable resin transport concentration and easy blockage of conveying equipment and pipelines in nuclear power plants in China,a set of non⁃stirring conveying devices is developed,and theoretical calculations,simulation analysis and experimental verification are carried out.By transporting resin using the no stirring conveying device developed in this paper,it is not only to eliminate the risk of blockage and ensure the safety of transportation,but also to adjust the concentration of conveying resin to change the transport efficiency according to the operating conditions.The effective bearing rate of waste resin storage tank can be improved,so that the comprehensive performance of waste resin storage and transportation in nuclear power plants can be greatly improved.

Microstructure characteristics and thermodynamic properties of A357-SiCp/A357 layered composites prepared by semi-solid vacuum stirring suction casting

A357-SiCp/A357 layered composites were prepared using a semi-solid vacuum stirring suction casting method.The microstructures,mechanical properties,and thermal conductivities of the composites fabricated under different suction casting processes were compared.Additionally,the microstructural evolution characteristics and performance enhancement mechanism of the A357-SiCp/A357 layered composites were discussed.The results demonstrate that suction casting at 610°C with a low solid phase ratio can significantly enhance the material density and reduce the agglomeration of SiCp.The A357-SiC_(p)/A357 interface is clear and straight with good bonding.With an increase in the suction casting temperature,the bending resistance and thermal conductivity of the A357-SiC_(p)/A357 layered composites exhibit a trend of significantly increase at first and then slowly decrease owing to casting defects,interface bonding,and SiCp distribution.Compared with SiCp/A357 composites,the bending strength,deflection,and thermal conductivity of the A357-SiCp/A357 layered composites increase from 257 MPa,1.07 mm,and 155.72 W·(m·K)^(-1) to 298 MPa,2.1 mm,and 169.86 W·(m·K)^(-1),respectively.This study provides a reference for improving the rheological casting of aluminum matrix layered composites.

搅拌子吸附-热脱附-气相色谱-质谱法分析北京大气中33种多氯联苯

用包覆聚二甲基硅氧烷(PDMS)吸附层的搅拌子作被动大气采样器,建立了搅拌子吸附-热脱附-气相色谱-质谱法(SBSE-TD-GC-MS)分析大气中多氯联苯(PCBs)的方法。优化后的热脱附温度为280℃,热脱附时间为6 min,聚焦冷阱的温度为-40℃,33种PCB单体的热脱附残留比例低于7%。验证了方法的线性、精密度和重复性。标准曲线5个点线性关系良好,33种PCB单体的相关系数r>0.998。方法精密度验证的相对标准偏差(RSD)为0.79%~20.2%(n=8),日内重复性实验的RSD为0.43%~29.8%(n=10),日间重复性实验的RSD为3.20%~29.6%(n=20),方法检出限(LOD)为0.01~2.51 pg,回收率为98%±18%。将建立的方法用于北京大气中PCBs的分析。检出8种PCB单体,质量为2.94~129 pg。在32 d的采样周期内PCB-52、PCB-123、PCB-155一直处于线性吸附阶段,而PCB-1和PCB-3经过了线性吸附阶段、曲线吸附阶段和平衡阶段。研究结果表明,SBSE-TD-GC-MS可以用于大气中PCBs的样品采集和快速分析。

双螺带式搅拌器的搅拌特性及关键结构参数研究

运用Fluent软件对双螺带搅拌器的混合过程进行模拟,利用多功能搅拌实验平台进行功耗测试,验证仿真模型的合理性。结合实例,分析了边界间隙、螺带直径以及螺距对搅拌特性的影响。针对混合效果和效率(经济功耗)的定量评价难点,提出用功耗因子与轴向功耗因子的数值,表征高黏度流体混合时的能量利用效果与整体混合效果,并以此为依据对螺带式搅拌器关键几何参数进行优化。实例的模拟结果表明:当螺带直径为1 200 mm时,即螺带直径达到罐体直径0.8倍时,轴向功耗因子最大为0.232 6 s,表明轴向流体宏观混合效果最好;螺距为1 350 mm时,即螺距与螺带直径之比为1(螺旋升角为45°)时,轴向功耗因子达到最大为0.180 6 s,表明轴向流体宏观混合效果最好;随着边界间隙的减小,罐壁总速度峰值增大,表明防附着效果增强,罐壁内侧的热边界层减薄。

6061铝合金FSW接头组织与耐蚀性能的研究

对4 mm厚的6061-T6铝合金板进行了搅拌摩擦焊接,通过浸泡腐蚀试验和电化学腐蚀试验研究焊缝腐蚀性能,采用金相显微镜、透射电镜等观察接头的微观组织。结果表明:6061铝合金FSW焊核区晶粒显著细化,晶界第二相较少;焊核区的耐剥落腐蚀和晶间腐蚀性能优于热影响区的;焊核区比热影响区的腐蚀电位较高,腐蚀电流密度较小,焊核区表现出更好的耐腐蚀性能。

底吹搅拌技术在电弧炉中的应用与发展

发展电弧炉短流程炼钢是钢铁工业实现“双碳”目标的重要途径。近年来,现代电弧炉技术发展迅速,电弧炉底吹搅拌技术也在不断进步和推广,对电弧炉生产的高效化和节能化作出了重要贡献。针对电弧炉底吹搅拌技术的机理、工艺特点、系统组成、气体种类、底吹元件类型及工艺布置方式进行综述,并对底吹技术的应用情况进行总结分析。模拟计算得出,远离底吹装置的区域,钢液流速明显偏低。结合炉型特点布置底吹装置及优化底吹气量,可改善熔池动力学条件,促进钢液元素传质,实现降低能耗和原材料消耗、提高生产效率的效果。深度开展底吹技术研发,与吹炼、供电、喷粉等工艺技术耦合,并结合新炉型特点制定底吹工艺制度,实现智能化底吹是发展现代电弧炉短流程技术的重要方向。

固相搅拌摩擦沉积增材制造技术研究进展

搅拌摩擦沉积增材(Additive friction stir deposition,AFSD)是一种先进的固相增材制造(Additive manufacturing, AM)技术。与传统基于熔融的增材制造技术相比,它具有增材结构致密、材料低变形和过程高效节能等优势,在航空装备制造、交通运输、机械制造等领域拥有广阔的应用前景。本文综述了AFSD技术的原理、优势、组织演变特点和应用情况。重点介绍了AFSD过程中“工艺条件-微观组织-力学性能”相关性的研究现状,沉积材料力学性能受材料流动状态、界面连接机制、微观组织演变情况的综合影响。列举了AFSD技术在大型构件整体制造、高性能涂层、表面缺陷修复等领域的应用。最后,对AFSD技术进行了展望,指出该技术在工艺与组织变化耦合、原位变形条件模拟、工具头设计和新材料增材等方面需进一步研究和突破。

降低石墨微细鳞片含量的再磨工艺优化研究

对黑龙江某石墨粗精矿进行了立式搅拌磨机再磨试验。以陶瓷球为磨矿介质,研究了磨机转速、介质球直径、磨矿时间等工艺参数对石墨磨矿-浮选效果的影响。结果表明,石墨磨矿的优化工艺参数为:采用慢-快-慢交替的磨机转速,陶瓷介质球直径8~10 mm,磨矿时间5 min,在该优化条件下进行磨矿-浮选开路试验,获得了固定碳含量95.83%、-0.045 mm粒级含量24.51%、大鳞片(+0.15 mm)含量14.27%的石墨精矿。

土炒当归、油当归和当归炭的质量标准研究

目的:建立土炒当归、油当归和当归炭的质量标准。方法:参照2020年版《中华人民共和国药典》当归项下的技术要求,通过对甘肃产10批土炒当归、8批油当归和11批当归炭的性状比较,描述土炒当归、油当归和当归炭的性状特征,建立土炒当归、油当归和当归炭的粉末显微鉴别和薄层鉴别方法,并测定水分、总灰分、酸不溶性灰分、醇溶性浸出物和阿魏酸含量。结果:土炒当归、油当归和当归炭的性状特征基本相同,呈圆形、类圆形或不规则的条形薄片,但各具不同的颜色和细微特征;土炒当归和油当归均具有当归对照药材的粉末显微特征;土炒当归、油当归和当归炭均具有当归对照药材的薄层色谱行为,土炒当归、油当归中检出阿魏酸和藁本内酯。10批土炒当归中阿魏酸平均含量为0.067%,8批油当归中阿魏酸平均含量为0.062%。结论:研究所测得的各项指标,可为当归炮制品的地方标准制订提供依据。

HPLC多波长切换指纹图谱结合化学计量学研究白术土炒前后成分变化规律

目的 建立测定白术、土白术水溶性和脂溶性成分的高效液相色谱-二极管阵列检测器(HPLC-DAD)多波长切换指纹图谱,结合化学计量学研究白术土炒前后成分变化规律。方法 建立白术、土白术水溶性及脂溶性成分的HPLC-DAD多波长切换指纹图谱测定方法,测定17批白术和17批土白术的HPLC指纹图谱,采用相似度评价、聚类分析、OPLS-DA分析进行统计分析。结果 白术指纹图谱中共标定9个共有峰,土白术指纹图谱中共标定10个共有峰。指认了新绿原酸、绿原酸、白术内酯Ⅰ、白术内酯Ⅱ、白术内酯Ⅲ及苍术酮6个成分,土炒后1号峰、4号峰(白术内酯Ⅲ)、8号峰(白术内酯Ⅱ)峰面积增加,2号峰(新绿原酸)、3号峰(绿原酸)、5号峰、6号峰、7号峰、9号峰(白术内酯Ⅰ)、10号峰(苍术酮)土炒后峰面积均降低。结论 所建立指纹图谱方法能够系统地分析白术土炒前后化学成分的变化规律,可为进一步规范白术土炒工艺,制定土白术专属性质量标准,研究土白术炮制原理提供实验基础。

根部加强的镁合金搅拌摩擦焊分析

常规搅拌摩擦焊中,不同厚度的材料所适配的最佳搅拌针长度也不相同,搅拌针过长或过短都会对焊接效果产生不利影响.为了解决这一局限性,提出了一种在焊缝背面添加适当厚度同种材料垫板的新型焊接工艺,在该工艺中,搅拌针长度大于被焊板材厚度,将垫板与母材焊接在一起,一方面,降低了对搅拌针长度的要求;另一方面,可消除焊缝减薄产生的不利影响.结果表明,采用该方法分析1.5 mm厚AZ31B镁合金的对接焊,接头抗拉强度最大可达母材的91.19%,此外,分析了焊缝横截面微观组织和显微硬度分布,通过所建立的卷积神经网络模型,对接头抗拉强度随参数变化的分布情况进行了预测,获取了最佳工艺参数.

航空铝合金薄板搅拌摩擦焊内部缺陷的超声相控阵检测

针对3 mm厚度下航空铝合金薄板搅拌摩擦焊焊缝的检测需求,基于典型缺陷特征以及缺陷对焊接接头性能的影响规律分析,明确了搅拌摩擦焊无损检测应重点关注的缺陷类型;设计了不同深度和尺寸的隧道以及未焊透缺陷模拟样件,利用模拟缺陷样件验证了超声相控阵检测技术对铝合金搅拌摩擦焊中1 mm埋深0.2 mm孔径的隧道缺陷以及1.6 mm埋深2 mm长、0.2 mm深未焊透缺陷的检测能力,对3 mm厚度下搅拌摩擦焊实际样件的检测结果与X射线检测结果及断口观察结果吻合,超声相控阵检测技术可以用于3 mm以下航空铝合金薄板搅拌摩擦焊焊缝的检测。

下层桨叶结构对搅拌反应器内部流场的影响

搅拌反应器可以对物料进行均匀的搅拌及混合,极大提高了工艺物料的处理效率。利用CFD技术对搅拌反应器内的流场特性进行数值分析,研究下层桨叶结构对流体流速的影响。研究结果表明,桨叶数目增加时搅拌效率增大,搅拌核心区域的流速较大,旋转域内部的流速增大;桨叶角度增加时桨叶搅拌区域的流速增大,但在旋转域的下部流速反而减小。

振动搅拌对复掺预制梁混凝土性能的影响研究

文中测试了两种搅拌方式下混凝土的坍落度、坍落度经时损失、含气量、表观密度、抗压强度以及抗冻性,采用热重分析仪、扫描电镜和压汞仪分别测试混凝土的水化产物含量、微观形貌及孔径分布.结果表明:与强制搅拌相比,虽然振动搅拌对复掺胶凝体系预制梁混凝土的坍落度以及坍落度经时损失均产生不利影响,但对混凝土的含气量、表观密度、抗压强度、抗冻性均有显著的提升作用;振动搅拌使得复掺胶凝体系预制梁混凝土3d龄期的CH含量提高了22.4%,少害孔、有害孔、多害孔含量及总孔隙量分别减少16.1%、42.3%、37.9%、27.6%,界面过渡区无明显微裂缝且结构密实.振动搅拌通过增加复掺胶凝体系预制梁混凝土水化产物数量、改善界面过渡区微观形貌以及细化孔径分布,从而提高混凝土的致密性、抗冻性和抗压强度.

双机镜像搅拌摩擦焊顶锻力变化规律与影响因素研究

随着搅拌摩擦焊板厚增大,设备承载能力无法满足单侧搅拌摩擦焊的高顶锻力要求,因而难以形成质量良好的焊缝。为了降低设备所受顶锻力,本文提出了一种双机镜像搅拌摩擦焊工艺方法,研究了工艺过程中顶锻力的变化规律和影响因素,并验证了该工艺的可行性和优越性。首先,建立热力耦合的有限元仿真模型,得到顶锻力随板厚的变化规律,同时得到了双机镜像搅拌摩擦焊工艺能够减小顶锻力的结论;之后,建立顶锻力估计模型,并基于数据驱动对模型进行试验修正和验证,实现无传感器的顶锻力监测;最后,在搭建好的试验平台样机上开展了镜像焊接试验、3组工艺参数的多因素试验及单侧搅拌摩擦焊对比试验,得到顶锻力随时间的变化规律和工艺参数的影响,验证了双机镜像搅拌摩擦焊工艺可以减小搅拌头所受顶锻力、降低设备承载能力需求的作用。

7075–O铝合金搅拌摩擦焊接头微观组织与力学性能

时效硬化态7075铝合金搅拌摩擦焊接头塑性较低,给进一步变形加工带来困难。本文采用3 mm厚的7075–O铝合金板进行搅拌摩擦对接焊,研究焊接速度对接头组织和强塑性的影响,为获得高塑性的搅拌摩擦接头提供解决方案。结果表明,7075–O铝合金接头焊核区为细小的等轴晶粒,随焊接速度的增加,焊核区平均晶粒尺寸呈先减小后缓慢增加的趋势,当焊接速度为40 mm/min时,焊核区晶粒尺寸最小,约为1.96μm。不同焊接速度下接头横截面显微硬度呈“凸”形分布,接头区域发生明显硬化,其中焊核区硬度最高,约为145HV。7075–O铝合金搅拌摩擦焊工艺窗口较宽,焊接速度在20~80 mm/min范围内接头强度均高于母材强度,焊接件伸长率达母材的82%,采用7075–O铝合金不仅能够克服时效硬化态7075铝合金搅拌摩擦焊接头的软化问题,而且能够获得更高的伸长率。接头弯曲试验结果表明,7075–O铝合金搅拌摩擦焊接头能够承受更大的弯曲角度,极限弯曲角达105°,具备更加出色的塑性变形能力。