基于Fluent的60 kg·m~(-1)重轨高压水除鳞过程钢轨表面温度分布研究

首先应用对流换热理论对钢轨除鳞前的初始温度场进行模拟,得出了应用均匀温度场代替差异温度场的方法,然后根据钢轨断面尺寸、除鳞设备参数和除鳞前钢轨断面温度分布结果,基于Fluent软件建立了钢轨异型坯高压水除鳞过程二维模型。考虑了钢轨不同部位喷嘴的布置方式以及除鳞时间的影响,得到了单喷嘴和双喷嘴条件下钢轨轨头、轨底及轨腰表面在不同除鳞时间的温度场分布图以及距离钢轨表面2 mm处的3个不同位置的温度变化曲线。结果显示,模拟结果与实际情况基本相符,异形坯表面温度的分布受断面形状和喷嘴布置影响比较明显。     

合金盘条高压磨料水射流除鳞系统实验研究

目的 对合金盘条高压磨料水射流除鳞系统进行优化.方法 建立一条合金盘条高压磨料水射流除鳞系统实验装置,研究材质、工作压力、喷嘴数量、移动速度、磨料浓度、靶距等参数对除鳞效果的影响;应用图像处理技术对除鳞效果量化为除净率并加以分析,采用MATLAB软件对系统压力、喷嘴数、移动速度、磨料浓度及靶距对除鳞效果进行拟合分析.结果 设计了年产5000吨合金盘条高压磨料水射流除鳞系统,参数为:额定压力45 MPa、额定流量10 m3/h、最大除鳞速度40 m/min、磨料质量分数35%、靶距20 mm、喷嘴12个.结论 高压磨料水射流除鳞系统能满足合金盘条除鳞的设计要求,应用前景广阔.     

除鳞喷嘴稳流器结构参数对喷嘴内流场特性的影响

在钢坯轧制过程中，需要及时去除高温钢坯表面形成的氧化铁皮，高压水除鳞技术较其它除鳞手段成本更低，除鳞率更高，优势明显，其中稳流器介于除鳞喷嘴前端过滤器与末端收缩段间，起到整流稳流的作用。建立不同结构的除鳞喷嘴稳流器模型，由稳流器两端平齐改为凸起、凹陷、平齐端面两两组合，建立全尺寸高压水除鳞喷嘴模型并进行CFD数值模拟。结果表明，稳流器叶片入口为凹陷结构、出口为平齐结构的稳流器整体湍动能较小，湍动能变化趋势更平稳，涡量变化较小且稳流器末端涡量趋于0。改变稳流器端面叶片形状可以对喷嘴出口动力学参数产生影响，部分结构稳流器出口速度较原结构提高至少2.126 m/s,最高3.817 m/s。     

高压水除鳞系统的设计及应用

在线热态除鳞系统用于清除精锻前工件表面鳞皮,以确保精锻质量。本文较详细地介绍了高压水除鳞的工作原理,阐述了用于热轧圆形钢坯的高压水除鳞系统的技术参数的设计计算,主要包括:射流压力、喷嘴参数及布置方式、工件表面打击力、射距的选择、水泵及除鳞管路参数等。经实际检测,工件表面鳞皮去除率几乎达到100%,温度下降幅度为2～5℃,符合精锻要求。     

射流压力对淹没水射流冲击与空蚀效果的影响

目的探究淹没水射流对铝合金及铜合金材料的冲击与空蚀作用。方法为获得关键射流工况参数对射流冲击和冲蚀效果的影响,对射流压力、冲击时间和靶距的作用进行了研究。在较低压力条件下对材料表面的残余应力进行测量与分析;在较高压力时对材料表面的破坏形貌进行观测。结果残余应力随射流压力的增加而增加,当冲击时间为20 min,射流压力为40 MPa时,残余应力达到最大值91 MPa;在空蚀作用初期,试样表面出现尺寸较小、呈离散分布的空蚀坑,其为离散空泡冲蚀所致。随着空蚀作用的增强,材料表面的空蚀坑增大,同时出现塑性变形,当冲击压力为300 MPa,靶距为7cm,冲击时间为15 min时,达到最显著冲击效果。结论当压力较小时,淹没水射流可以强化金属表面;当压力较大时,淹没水射流可以使金属表面产生空蚀坑和塑性变形。尽管淹没水射流具有连续的射流速度分布,但材料表面的破坏更多地取决于空化现象。     

水射流冲击压力最佳喷距数值仿真及试验研究

基于水射流冲击模型,应用Fluent流体分析软件对喷嘴射流冲击力进行数值仿真,得出不同喷距对射流冲击压力的影响。结果表明：在低压连续水射流条件下,出口直径为2 mm的喷嘴在喷距为50 mm时产生的射流冲击压力最大;并通过实验验证射流仿真模型的正确性和有效性。     

基于功率最小原理和遗传算法的钢轨万能轧制过程宽展预测

为得到钢轨万能轧制过程轨头和轨底的精确宽展,以轨头和轨底宽展为待定参数,在坯料断面尺寸、设备参数、轧制工艺参数已知的基础上,基于上限原理推导得出包含轨头和轨底宽展系数的钢轨万能轧制过程总功率表达式,并应用MATLAB软件遗传算法工具箱编写M文件对钢轨万能轧制总功率进行单目标优化,得到轧制功率最小时的轨头和轨底宽展系数。为验证理论模型,对18kg/m轻轨进行万能轧制实验,并用DEFORM软件模拟其万能轧制过程,将优化后宽展系数与实验结果进行对比,两者误差小于2%。     

高压水除鳞系统参数优化

通过对沙钢某热连轧机组高压水打击效果分析,认为其除鳞喷嘴个数、喷嘴间距和垂直射流高度需要优化。在对喷嘴个数和喷嘴间距优化基础上,结合现场实际和理论计算,进一步研究了垂直射流高度对高压水打击力、重叠度、喷射宽度和喷射厚度等的影响,优化出最佳的除鳞系统参数,从而为现场高压水除鳞系统参数设计和改进提供理论指导。     

万能轧制过程轧件相对立辊前滑的理论和实验研究

为便于钢轨万能轧制过程解析计算,将轧制轨头立辊合理简化为平辊,并且将钢轨断面形状等效为工字形断面。基于立辊的力矩平衡条件,推导出轨头、轨底变形区的中性角公式,并根据秒流量相等理论,推导出轨头和轨底相对于立辊的前滑系数公式。为验证理论模型,在燕山大学实验室的万能轧机上完成了18kg/m轻轨的万能热轧实验,用压痕法实测了不同轧制规程时轨头和轨底相对于立辊的前滑系数。通过对比,理论模型计算结果与实验结果比较接近,可以用于钢轨万能轧制过程前滑预测。     

3500mm炉卷轧机高压水除鳞系统射流参数设计

介绍了高压水除鳞机理,分析了各种参数对高压水除鳞效果的影响,提出了射流参数计算公式,并通过计算机软件进行模拟分析,验证了计算公式的正确性。在此基础上,确定了满足轧制工艺要求的3 500 mm炉卷轧机高压水除鳞系统的射流参数。     

Low pressure carburising and high pressure gas quenching

Abstract

The traditional technology of heat treatment for gear components is the combination of atmospheric gas carburising with oil quenching. This technology is proven to deliver reliable results. However, the need of modern production is to react fast according to changing processes and production volumes. The highest technical requirements in combination with economical production methods must be met to ensure the highest quality standards and to establish environmental friendly production. Low pressure carburising and high pressure gas quenching is a reliable method that is used more and more in Asia, Europe and North America. This technology is an answer to the above described needs. Major car and gear makers have proven this process and implemented it into the mass production of gears components. With low pressure carburising and high pressure gas quenching it is possible to have real high production volumes and to react very flexible to different production scenarios.     

压力加镁球化处理包工作压力的研究

本文以Ｃｌａｕｓｉｕｓ－Ｃｌａｐｅｙｒｏｎ方程为根据，提出了压力加镁包工作压力与待处理铁水温度之间的关系，同时以实测验证了理论计算的可靠性，对压力加镁包的设计有参考价值 。     

内压对薄壁管充液压弯时的影响

失稳起皱和截面畸变是薄壁管弯曲成形过程中的主要缺陷,通过数值模拟和实验的方法,研究了液压支承下管材的弯曲变形行为,进行了从无内压到内压为18MPa的管材充液弯曲成形,分析了充液弯曲成形过程中的内压值对成形的影响,给出了成形后的不圆度和典型点壁厚减薄率的变化规律,结果显示,随着充液压力的增加,管材的截面不圆度逐渐减小,管材内侧壁厚增厚趋势减小,外侧壁厚减薄趋势增大。并根据模拟结果给出了成形后的典型点的应力状态。     

Distinctions of dendritic behavior influenced by constant pressure and periodic pressure

The distinctions of dendritic morphology and sidebranching behavior when solidified under atmosphere pressure, constant pressure which is higher than atmosphere pressure (hereinafter referred to as constant pressure) and periodic pressure were investigated using 3-D phase field method. When growing at atmosphere pressure, side branches (secondary dendritic arms) are irregular. When solidified under constant pressure with a relatively high value, side branches are much more luxuriant, with more developed high-order side branches. When applied with periodic pressure, resonant sidebranching happens, leading to many more regular side branches and the smallest secondary dendritic arm spacing (SDAS) in the three cases. The significant difference in dendritic morphology is associated with tip velocity modulated by total undercooling including pressure and temperature undercooling. In the case of constant pressure, tip velocity increases linearly with total undercooling, and it varies periodically in periodic pressure case. The different variation trend in tip velocity is the reason for the distinct dendrite growth behavior in different cases. Unlike the phenomenon in constant pressure case where the dendrite grows faster with higher pressure, the dendrite grows slower under periodic pressure with higher amplitude, resulting in less developed primary dendrite and side branches. This is influenced by tip remelting due to low undercooling or even negative undercooling. It is revealed that the accelerated velocity of tip remelting increases with the decline of undercooling. The greater the amplitude of periodic pressure, the faster the tip remelting velocity during one period. This is the reason why the average tip velocity decreases with the rise of amplitude of periodic pressure.

     

Effect of blank holder pressure on viscous pressure forming aluminum alloy ladder parts

Viscous pressure forming (VPF), is suitable for forming difficult-to-form sheet metal parts. An investigation in the effect of blank holder pressure(BFIP) on VPF aluminum alloy ladder parts was conducted. Based on experimental and numerical simulation results of the effect of BFIP on dimensional accuracy, wall-thickness reduction, forming pressure, material flow and defects (such as wrinkling and fracture) of specimens, the effect patterns of BFIP load path on VPF ladder parts were explained. The limits of BFIP corresponding to specimens with no defect and with wrinkling or fracture defect were determined. In the limits of formable BFIP, the variable load path of BFIP was beneficial to drawing blank into the die and decreasing wall-thickness reduction of specimens. The experimental results show that the ladder parts of good surface fineness and high dimensional accuracy can be obtained by variable load paths of BHP.