附加外场力对锌锅表层锌液流动和锌渣分布的影响

实测了热镀锌锌锅表层锌液的流速,并分析了锌锅浮渣的分布特点,提出了一种在锌锅锌液上方主动加载外场力作用以驱动锌液流动进而改变锌渣分布的新方法,称为锌渣流动管理方法(DFMS-Dross Flowing Management System)。通过源力加载的方式修正了流体动量守恒方程,建立了锌液流场数值计算模型,模拟了不同外场力加载布局下锌锅表层锌液的流场。结果表明,附加外场力作用可有效促进锌锅表层锌液的切向流动,最大切向流速可达0.8 m/s;表层锌液的切向流动可拖动锌渣跟随流动,进而改变锌渣分布,促进锌锅排渣,证实了DFMS的有效性。模拟结果还表明,锌锅表层锌液的切向流速受外场力加载时间的影响较小,而随加载外场力的增大而增大,但加载外场力的大小对100~200 mm深锌液的流速影响较小。最后,通过定义锌锅表层锌液的排渣时间因子讨论了不同外场力加载方式的排渣效率。     

Feedforward control of the transverse strip profile in hot-dip galvanizing lines

Hot-dip galvanizing is a standard technology to produce coated steel strips. The primary objective of the galvanizing process is to establish a homogeneous zinc layer with a defined thickness. One condition to achieve this objective is a uniform transverse distance between the strip and the gas wiping dies, which blow off excessive liquid zinc. Therefore, a flat strip profile at the gas wiping dies is required. However, strips processed in such plants often exhibit residual curvatures which entail unknown flatness defects of the strip. Such flatness defects cause non-uniform air gaps and hence an inhomogeneous zinc coating thickness. Modern hot-dip galvanizing lines often use electromagnets to control the transverse strip profile near the gas wiping dies. Typically, the control algorithms ensure a flat strip profile at the electromagnets because the sensors for the transverse strip displacement are also located at this position and it is unfeasible to mount displacement sensors directly at the gas wiping dies. This brings along that in general a flatness defect remains at the gas wiping dies, which in turn entails a suboptimal coating.In this paper, a model-based method for a feedforward control of the strip profile at the position of the gas wiping dies is developed. This method is based on a plate model of the axially moving strip that takes into account the flatness defects in the strip. First, an estimator of the flatness defects is developed and validated for various test strips and settings of the plant. Using the validated mathematical model, a simulation study is performed to compare the state-of-the-art control approach (flat strip profile at the electromagnets) with the optimization-based feedforward controller (flat strip profile at the gas wiping dies) proposed in this paper. Moreover, the influence of the distance between the gas wiping dies and the electromagnets is investigated in detail.     

热镀锌渣中浸渣硫酸浸出锌的工艺研究

以锌含量为17.22%的热镀锌渣中浸渣为原料,在水热反应釜中以硫酸为浸出剂浸出其中锌。结果表明,最佳浸出条件为: 硫酸体积浓度15%、浸出温度180 ℃、液固比6∶1、浸出时间8 h,此条件下锌浸出率可达到99.71%; 浸渣主要成分为硫酸铝盐和硫酸钙。     

镀锌层硅酸盐+虫胶复合转化膜的制备和表征

目的阻碍热镀锌板出现白锈,提高镀锌层的耐腐蚀性能。方法采用正交试验法优化出添加虫胶水溶液的有机无机复合钝化液。通过电化学Tafel极化曲线、交流阻抗(EIS)、乙酸铅点滴和中性盐雾试验,对比分析基体、硅酸盐+虫胶复合钝化膜与铬酸盐钝化膜的耐腐蚀性能。采用摩擦法测试对比分析基体和无铬钝化膜试样的附着性能,并通过扫描电子显微镜、X射线光电子能谱和红外光谱对形貌和结构进行分析。结果添加虫胶水溶液的复合钝化膜表面平整致密,72 h中性盐雾试验后的腐蚀面积小于10%。乙酸铅点滴试验和电化学测试显示,复合钝化膜的耐腐蚀性能较基体好。附着力试验测试显示,复合钝化膜具有良好的附着能力。结论因为复合钝化液中的虫胶与硅酸盐交织为O—Si—CH_2结构,与金属离子结合生成致密的膜层附着在镀锌层表面,使得复合钝化膜致密平整,且使腐蚀过程得到了强烈的抑制。     

热镀锌带钢表面色差缺陷形成机理及改进措施

为了消除热镀锌板卷的色差缺陷，从热轧、镀锌、冲压工艺对色差缺陷形成机理进行分析。导致热镀锌板卷色差缺陷的主要原因有原料表面粗糙度不均匀、锌层厚度不均、冲压导致锌层开裂。针对这3种不同原因，制定了相应措施在热轧工序冷却装置上进行边部遮蔽；提高沉没辊安装精度、调节镀后冷却段移动风箱上下表面的风量；冲压模具表面强化、润滑等，有效减少了色差缺陷的不合格率。     

大跨度桥梁缆索用钢丝热浸镀层研究综述

综述了热浸镀Zn、Zn-Al和Zn-Al-Mg系合金镀层的性能特点和研究现状。在Zn-Al合金中添加Al元素可以减缓Zn的腐蚀氧化,同时可以在镀层表面形成致密的Al_2O_3薄膜起到屏蔽保护作用。在此基础上,采用Mg合金化,不仅可细化镀层组织,还可抑制疏松腐蚀产物的生成,进一步延长合金镀层的寿命。阐明了桥梁缆索用钢丝热浸镀工艺的特点和不足。采用中性盐雾试验评估了应力加载对桥梁缆索用热浸镀层组织和耐腐蚀性能的影响。应力加载会使镀层表面的腐蚀产物保护层破裂,加快腐蚀进程。同时指出了现有桥梁缆索用钢丝镀层评价标准尚存在一些争议,应结合现行的评价体系,重视讨论和探索新的更合适的评价标准。需要研究新一代(Zn-Al-Mg)合金镀层的制备技术和评价标准,推动具有高耐蚀性的多元合金镀层在桥梁缆索用钢丝上的推广应用。同时,桥梁缆索用钢丝热浸镀层的腐蚀性能应考虑应力加载下的腐蚀破坏和相关机理研究。     

热镀铝锌硅镀层凸点缺陷组织分析及生产工艺优化

热镀铝锌硅镀层板(Galvalum)因其优异的耐蚀性得到广泛的应用,其生产技术已较成熟,而其产品(尤其是厚规格产品)表面质量控制一直是生产中的技术难点.凸点缺陷是该产品的主要缺陷之一,采用扫描电子显微镜(SEM)及其配备的能谱仪(EDS),分别对凸点缺陷的表面、截面组织进行了分析,结果表明凸点缺陷是在热浸镀过程中形成,而沉没辊积渣是凸点缺陷形成的重要原因.通过工艺优化,在沉没辊上方增设积渣盘,可有效地减少产品凸点缺陷,提高镀层表面质量.     

观察裂纹路径及组织演变的SEM样品制备方法研究

本试验利用SEM和电阻炉研究一种SEM样品的制备方法,用于观察裂纹路径,并分析断裂后的显微组织变化。结果表明:通过浸镀焊锡,能够在不同断裂方式形成的裂纹轨迹上形成一条明显的"纯锡带",呈现出裂纹路径。同时该方法能够观察分析拉伸、冲击、断裂韧性及疲劳断裂等过程中产生的二次裂纹路径及断裂表层下的组织演变。     

Studies on the potential risk of liquid metal assisted cracking (LMAC) in normal‐temperature and high‐temperature hot‐dip galvanizing of high strength bolts of dimensions greater M24

Liquid metal assisted cracking (LMAC) mainly occurs due to an unfavorable interaction of three factors: a susceptible material condition, presence of a liquid metal and sufficient tensile stress. Hot‐dip galvanizing of high‐strength bolts induces high thermal loads in bolts made of tempered steel in the presence of a zinc melt and thus, provides the boundary conditions for the above mentioned critical factors to interact. The focus of this study is on investigating thermally‐induced stresses in large diameter bolts and their impact on the formation of liquid metal assisted cracking (LMAC). In order to calculate the thermal loads in hot‐dip galvanizing, simulations were carried out regarding the thermo‐mechanical behavior of bolts during the hot‐dip galvanizing process. The simulations illustrate that cracks are most likely to occur in the first thread turn. This prediction is confirmed by experimental observations.     

低碳铝镇静钢热镀锌表面粗晶缺陷形成原因及对策

低碳铝镇静钢热镀锌板表面易产生"指甲印"缺陷,缺陷主要分布在整卷带钢带中1/3长度位置、带钢表面中间位置。通过金相观察可以确认缺陷处因晶粒明显长大,形成粗晶,晶界处开裂表现为"指甲印"缺陷。低碳铝镇静钢在热轧工序生产时的卷取温度为730℃,这个温度恰好处于A_1温度以上,卷取后带钢仍处在奥氏体和铁素体两相区。在卷取后,带中1/3位置散热较慢,温度保持在A_1线以上,奥氏体晶粒在此温度下继续长大,形成粗大晶粒。在冷轧工序的生产过程中,带钢表面受压应力和切应力作用,粗大的晶粒沿边界开裂,表现为"指甲印"缺陷。通过降低热轧卷取温度,使带钢卷取后的温度处于A_1线以下,带钢组织由铁素体和渗碳体组成,使带钢晶粒在卷取后冷却的过程中不再长大形成粗晶,消除了低碳铝镇静钢热镀锌带钢表面"指甲印"缺陷。