线材轧制中的表面裂纹

线材和棒材轧制中的表面缺陷是常见的，并且为轧钢工作者所皆知。当今，表面缺陷对于高合金钢线材而言是不能接受的。炼钢、烧注和轧制过程中会引起表面缺陷，线材及棒材的最终装卸也可能损坏其表面。在本文中对不同轧制孔型系统下纵向的人工V-型裂纹进行了研究。圆．椭圆系统被认为是用于优质钢的，而且通常要优于方-椭圆的系统。诸多试验证明，在圆．椭圆道次中，在槽孔底部的表面裂纹在轧制过程中在其深度变浅的同时可能会扩展，这是一种有利的情况。     

2200m3高炉冷却壁水管的冷弯

对安钢2200m3高炉冷却壁内铸循环水管冷态下弯曲缺陷进行分析，采用辅助芯棒的新方法，达到了通球率、椭圆度的进一步提高。     

喷涂分层与气泡区别的分析

根据美国酿造协会规定(U.S.B.A.),易拉罐涂喷气泡是一种可导致金属暴露的气泡。实际检测时,往往把外观圆形或椭圆的喷涂分层都判为气泡缺陷,并按外观严重缺陷处理。为了更准确判断产品缺陷、我们对所谓气泡进行了剖析。为了便于讨论,我们把直接在金属表面形成的小泡叫作气泡,     

基于计算机数值模拟技术的钢管矫直质量研究

矫直就是对金属塑性加工产品的形状缺陷进行的矫正,是重要的精整工序之一。主要是利用AN-SYS/LS-DYNA对六辊斜辊钢管矫直机矫直过程进行数值模拟,分析压下量与压扁量对于不同壁厚钢管的平直度与椭圆度的影响。     

低压OMVPE法GaAs外延层表面缺陷

日本研究人员用 SEM 与 TEM 详细研究了低压OMVPE 法 GaAs 外延层的表面缺陷。外延层生长以GaAs 为基底,方向(100)±0.5°,生长温度630～650℃,Ⅴ/Ⅲ约20～100,生长压力0.1～76Torr 文章用 SEM 与 TEM 详细观测了表面缺陷的形状和内部构造。研究发现,低压 OMVPE 法 GaAs 外延层表面分布着从表面凸起的椭圆锥形缺陷,与氯化物 VPE 法GaAs 外延层表面的小丘类似。而且,在每个缺陷中心附近存在一个位错。这一现象表明,具有旋转成分的位错终端的缧旋生长导致了椭圆锥形表面缺陷的形     

椭圆孔型张减过程模拟及横向壁厚分布预测

通过对宝钢钢管厂１５２．５ＢＯ椭圆孔型系统主变形机架生产不同壁厚管子的轧制过程进行三维弹塑性有限元模拟,得出经减径后管子沿圆周方向的壁厚分布不均,产生内多边形的缺陷,随着总减径率和壁厚的增加,引起内多边形的程度增大。根据模拟结果对１５２．５ＢＯ椭圆孔型系生产不同规格的管子引起管子在沿圆周方向的壁厚不均进行预测。     

浅谈随圆浮动加工组合刀具优化设计

针对棒材和管坯在工件表面出现轧痕和结疤缺陷,不能进行有效处理的问题,设计一种加工组合刀具,此组合刀具能随轧制棒材和轧制管坯内表面椭圆度和长度方向的弯曲度,对表面进行均匀加工。     

楔横轧小断面收缩率轴类件的椭圆度研究

利用有限元软件对楔横轧成形小断面收缩率轴类件的椭圆度进行数值模拟,通过对数值模拟结果进行正交回归分析,研究工艺参数对小断面收缩率轧件椭圆度的影响规律.结果表明:展宽角和断面收缩率对轧件椭圆度影响显著,展宽角越大或断面收缩率越小,则轧件椭圆度越大;当断面收缩率较小时,成形角对轧件椭圆度几乎没有影响.并解释了各工艺参数对轧件椭圆度影响的原因.通过轧制实验,验证了数值模拟结果的可靠性.      

基于虚拟样机技术的椭圆振动筛仿真分析

近年来,由于兼具圆振动筛和直线振动筛的优点,椭圆振动筛在筛分领域中引起了广泛关注。在椭圆振动筛椭圆运动轨迹形成机理的理论基础上,利用三维造型软件Pro／ENGINEER和多体系统动力学软件ADAMS,建立了双轴椭圆振动筛的虚拟样机模型,并对其运动轨迹进行了仿真,探讨了椭圆振动筛入口、质心以及出口处运动轨迹的影响因素,为椭圆振动筛的合理设计和使用提供了参考依据。     

张力减径机组孔型设计简介

张力减径机孔型设计最关键的两个因素是减径系列的分配和椭圆度的选取。一个减径系列可以生产多个规格的成品管,不同的成品管规格可以通过改变减径系列的总减径率来获得。孔型椭圆度的计算尤为重要,如果椭圆度过小,在轧制薄壁钢管时,钢管的外壁容易挤入辊缝,形成轧折缺陷;而椭圆度过大,钢管横向受力不均,形成内多边形。孔型设计时椭圆度选取一般根据宽展系数和实际轧制经验确定。     

A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils

For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B1 field. A simple theory was developed to create an optimized current distribution for elliptical birdcage coils. This optimized current pattern can create a perfectly homogeneous B1 field inside any elliptical shape. To verify the theory, a 16-element high-pass elliptical birdcage coil was built inside a circular RF shield. The current was optimized by using the inductance characteristics of the coil components to calculate the end-ring capacitances. The B1 field was theoretically calculated and experimentally mapped for the optimized elliptical bird-cage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B1 field is produced. This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross-sectional geometries in the human body.     

Effect of micro-pores on cracks formation in metallurgical coke

The relationships of micro-pores and cracks in metallurgical coke have been investigated by optical microscope and field emission scanning electron microscope, using surface section samples. The pores have circular, elliptical and irregular shapes with smooth outlines, formed during the thermoplastic stage of the coking process. They often associate with connecting cracks between neighbouring pores. In case of elliptical pores, the connecting cracks are usually oriented along the longer axis of the pore. The connecting cracks can be developed between the pores, depending on their size and the distance between them. The coke with a large number of small pores rather than with a small number of larger pores will have lower strength due to the increased amount of connecting cracks. When compared with circular pores, elliptical and flattened pores have a lower ability to resist load pressure. Nano-sized pores have polygonal outlines, indicating an ‘explosion’-type formation in the solidified matrix.     

Comparative Study of Magnetization Reversal Process Between Elliptical and Rectangular CoFe Nanomagnets

The magnetization reversal process for elliptical and rectangular permendur (CoFe) nanostructures were compared using micromagnetic simulations. Single domain states were observed in 10 nm thick elliptical and rectangular nanomagnets. The magnetization reversal along the major and minor axis in 60 nm thick elliptical nanomagnets occurred through the formation of double vortex states. In rectangular nanomagnets, it occurred through the formation of single vortex state along 225 nm and double vortex state along 335 nm.     

双轴椭圆振动筛系统动力学分析

近年来 ,由于兼有圆振动筛和直线振动筛的优点 ,椭圆振动筛在筛分领域中引起了广泛关注。根据动力学原理探讨了椭圆振动筛椭圆运动轨迹的形成及其影响因素 ,分析了附加扭矩对筛箱运动的影响。指出合理选择筛箱结构参数 ,可以减小附加扭矩 ,并利用椭圆长轴方向角的改变 ,实现理想的椭圆筛分     

Dean Equations Extended to a Rotating Helical Pipe Flow

In this paper, the fully developed laminar flow in a rotating helical elliptical pipe is examined theoretically. This study focuses on the combined effects of the rotation, the curvature, the torsion, and the shape of cross section. The secondary flow and the fluid particle trajectory are discussed for different elliptical cross sections in the range of ?2?σ?1, where σ represents the ratio of the Coriolis force to the centrifugal force.     

冷却水管管形变化下的高炉冷却壁传热分析

建立了铸钢冷却壁的三维传热和热应力的数学模型,采用通用有限元软件ANSYS计算了冷却壁的温度场和应力场。计算结果表明：冷却水管由圆管改为椭圆管后,冷却壁热面最高温度和热应力升高不大,为冷却水管由圆形改成椭圆形提供了理论依据,由于椭圆水管截面积减少,就可以减少壁体厚度和大量节约冷却水量,从而达到降低炼铁成本的目的。     

Missed opportunities: teenagers and emergency contraception

Measurements of bone mineral density using dual-energy X-ray absorptiometry (DXA) gives area values (g cm-2) rather than true volumetric values (g cm-3). To calculate the vertebral volume using planar postero-anterior and lateral DXA values, several different geometrical approximations were used: cubic, cylindrical with a circular cross-section and cylindrical with an elliptical cross-section. The aim of this study was to compare these geometrical approximations with each other and with a reference standard, defined as the volume found on a computed tomographic (CT) scan. L2 and L3 were evaluated in a phantom study. Volume approximations by the cube or cylinder with circular cross-section geometry showed more than a 50% overestimation (range 54-74%). However, the elliptical cylinder approach showed very good agreement: 2.1% and 1.2% for L2 and L3, respectively, when compared to the CT volumes. In addition, we performed four patient studies with both CT and DXA to evaluate the elliptical cylinder estimate in a clinical setting. For L2 and L3, the mean relative difference was less than 2%. We conclude that the elliptical cylinder approach results in the most accurate bone volume estimates in both the phantom and patients.     

A Study on Elliptical Cross-Sectioned Spiral Equal-Channel Extrusion of AA7075: FE Simulation and RSM Approach

Elliptical cross-sectioned spiral equal-channel extrusion is newly developed sever plastic deformation technique that can be used for processing of cylindrical components. In the present study, numerical and experimental investigations were made to identify optimal setting of process parameters i.e. torsion angle, elliptical rotation transitional length and elliptical length ratio attaining minimum punch force and maximum effective strain. Firstly, the process was numerically simulated by using DEFORM software. Then, 15 series of simulation runs was implemented based on central composite design incorporating three-factors and three-levels. Response surface methodology was used here to correlate relationship between factors and responses. In order to find optimum solution regarding maximum strain and minimum punch force, desirability approach was used. The optimization results showed that for achieving maximum strain (that is most desirable during severe plastic deformation), settings of 120° torsion angle, 9 mm channel length and 1.45 elliptical length ratio was required. From the results obtained through experiments, it was found that performing three-passes ECSEE under optimal combination of factors resulted in about 30% enhancement in values of ultimate tensile strength and hardness.     

Changes in coronary risk profiles in employees after three years of multifactorial intervention

A mathematical model for computing stresses in sutured human skin wounds is presented. The model uses the incremental law of elasticity and elastic constants valid for in vivo orthotropic skin. The model is applied to compute the principal stress and displacements resulting from suturing small elliptical and circular wounds in a large flat sheet of skin, in order to determine the optimal suturing patterns. It is observed that the average stress index for a circular wound sutured toward the center is almost double that of a wound sutured transverse to the diameter. Thus, the latter type of suturing pattern is preferable. Similarly, suturing an elliptical wound transversely produces a lower average stress index than a circular wound of the same area. It is also found that the optimal ratio of semi-major to semi-minor axis of an elliptical wound is near 3 (for abdominal wounds), i.e., this ratio produces the most uniform stresses along the wound edges, where wound healing is slowest. Since high stresses have adverse effects on healing and blood flow, this work, depicting regions of high stresses, may be used along with other biological factors to help predict regions of slower healing in sutured wounds.