Numerical simulation of fluid flow caused by buoyancy forces during vacuum arc remelting process

The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.     

Asymmetric deformation of near hemispherical diaphragm under uniform surface load

The asymmetric deformation and eccentricity problems of near hemispherical diaphragm under the uniform surface load are quantitatively characterized in the paper. The analysis is based on a 3D finite element analysis (FEA) model established according to elastic-plasticity and large displacement nonlinear finite element method. Besides, the deformation experiments are taken to validate the reliability of FEA model which shows that the simulation results are in good agreement with the experimental results. Then, three angle parameters, deflection angle β, circumvolving angle θ and distributing angle γ, are introduced and expressed to characterize the asymmetric deformation and eccentricity quantitatively. According to the angle parameters, the inversion processes of uniform thickness diaphragm and varying thickness diaphragm are calculated respectively. The inversion process of varying thickness diaphragm is much steadier than that of uniform thickness diaphragm. The present results show that the asymmetric deformation process can be characterized by curve of three angle parameters (β, θ, γ) exactly, the degrees of eccentricity can be indicated by the final value of deflection angle and the eccentricity position can be characterized by the final values of the three angle parameters.     

Effect of remelting current on molten pool profile of titanium alloy ingot during vacuum arc remelting process

The performance of vacuum arc remelting (VAR) ingot depends largely on ingot structure and chemical uniformity, which are strongly influenced by molten pool profile that is influenced by VAR process. To better understand the effect of remelting current on molten pool profile of titanium alloy ingot during VAR process, a 3D finite element model is developed by the ANSYS software. The results show that there are three remelting stages during VAR process when the remelting current is 2.0 kA. The molten pool depth increases gradually from 30 to 320 s, then the change of molten pool depth is very small during the steady state stage from 320 to 386 s, and lastly the molten pool depth becomes shallow after 386 s. The melting rate and temperature of superheat increase with the remelting current increasing, which leads to the augment of molten pool volume. In the end, the total remelting time and steady state molten pool time decrease with the melting current from 1.6 to 2.8 kA.     

恒磁场对内皮细胞分泌和表达细胞间黏附分子-1及与单核细胞黏附的抑制作用

目的　观察不同强度恒磁场对氧化修饰低密度脂蛋白 (OX LDL)作用下人脐静脉内皮细胞 (HUVEC)分泌和表达细胞间黏附分子 1(ICAM 1)及HUVEC与人单核细胞株THP 1黏附的影响。方法　采用体外培养第 3代的HUVEC ,实验分为 6组 ,即对照组、OX LDL(10 0mg·L-1)组及OX LDL +不同磁感应强度 (1、5、10、2 0Gs)的恒磁场组。各组细胞于培养及恒磁场作用 2 4h后收集标本 ,用酶联免疫吸附试验 (ELISA)检测HUVEC分泌ICAM 1的量 ,免疫细胞化学检测ICAM 1的表达 ,计数法观察HUVEC与THP 1的黏附率。结果　OX LDL 10 0mg·L-1刺激细胞 2 4h,ICAM 1的分泌和表达显著增高(P <0 .0 5vs.对照组 ) ;而 1、5、10和 2 0Gs恒磁场组细胞ICAM 1的分泌和表达显著低于OX LDL组 (P <0 .0 5 )。OX LDL10 0mg·L-1与HUVEC孵育 2 4h后 ,HUVEC与THP 1的黏附率显著增加 (P <0 .0 5vs.对照组 ) ;而 1、5、10和 2 0Gs恒磁场组HUVEC与THP 1的黏附率显著低于OX LDL组 (P <0 .0 5 )。结论　 1～ 2 0Gs的恒磁场可拮抗OX LDL的作用 ,抑制HUVEC分泌和表达ICAM 1及与单核细胞的黏附率